WO2002082452A2 - Microelectronic device, structure, and system, including a memory structure having a variable programmable property and method of forming the same - Google Patents
Microelectronic device, structure, and system, including a memory structure having a variable programmable property and method of forming the same Download PDFInfo
- Publication number
- WO2002082452A2 WO2002082452A2 PCT/US2002/011082 US0211082W WO02082452A2 WO 2002082452 A2 WO2002082452 A2 WO 2002082452A2 US 0211082 W US0211082 W US 0211082W WO 02082452 A2 WO02082452 A2 WO 02082452A2
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- programmable
- ion conductor
- structures
- electrode
- programmable memory
- Prior art date
Links
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Classifications
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- G11C13/0009—RRAM elements whose operation depends upon chemical change
- G11C13/0011—RRAM elements whose operation depends upon chemical change comprising conductive bridging RAM [CBRAM] or programming metallization cells [PMCs]
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- G11C11/21—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements
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- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
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- H10B63/80—Arrangements comprising multiple bistable or multi-stable switching components of the same type on a plane parallel to the substrate, e.g. cross-point arrays
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- H10B63/84—Arrangements comprising multiple bistable or multi-stable switching components of the same type on a plane parallel to the substrate, e.g. cross-point arrays arranged in a direction perpendicular to the substrate, e.g. 3D cell arrays
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- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
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- H10N70/20—Multistable switching devices, e.g. memristors
- H10N70/24—Multistable switching devices, e.g. memristors based on migration or redistribution of ionic species, e.g. anions, vacancies
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- H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
- H10N70/801—Constructional details of multistable switching devices
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
- H10N70/801—Constructional details of multistable switching devices
- H10N70/821—Device geometry
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
- H10N70/801—Constructional details of multistable switching devices
- H10N70/821—Device geometry
- H10N70/826—Device geometry adapted for essentially vertical current flow, e.g. sandwich or pillar type devices
- H10N70/8265—Device geometry adapted for essentially vertical current flow, e.g. sandwich or pillar type devices on sidewalls of dielectric structures, e.g. mesa or cup type devices
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
- H10N70/801—Constructional details of multistable switching devices
- H10N70/841—Electrodes
- H10N70/8416—Electrodes adapted for supplying ionic species
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
- H10N70/801—Constructional details of multistable switching devices
- H10N70/881—Switching materials
- H10N70/882—Compounds of sulfur, selenium or tellurium, e.g. chalcogenides
- H10N70/8822—Sulfides, e.g. CuS
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
- H10N70/801—Constructional details of multistable switching devices
- H10N70/881—Switching materials
- H10N70/882—Compounds of sulfur, selenium or tellurium, e.g. chalcogenides
- H10N70/8825—Selenides, e.g. GeSe
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
- H10N70/801—Constructional details of multistable switching devices
- H10N70/881—Switching materials
- H10N70/882—Compounds of sulfur, selenium or tellurium, e.g. chalcogenides
- H10N70/8828—Tellurides, e.g. GeSbTe
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- G11C2207/10—Aspects relating to interfaces of memory device to external buses
- G11C2207/104—Embedded memory devices, e.g. memories with a processing device on the same die or ASIC memory designs
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C2213/00—Indexing scheme relating to G11C13/00 for features not covered by this group
- G11C2213/10—Resistive cells; Technology aspects
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- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C2213/00—Indexing scheme relating to G11C13/00 for features not covered by this group
- G11C2213/50—Resistive cell structure aspects
- G11C2213/51—Structure including a barrier layer preventing or limiting migration, diffusion of ions or charges or formation of electrolytes near an electrode
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- G11—INFORMATION STORAGE
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- G11C2213/72—Array wherein the access device being a diode
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- G11C2213/70—Resistive array aspects
- G11C2213/79—Array wherein the access device being a transistor
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10B—ELECTRONIC MEMORY DEVICES
- H10B63/00—Resistance change memory devices, e.g. resistive RAM [ReRAM] devices
- H10B63/20—Resistance change memory devices, e.g. resistive RAM [ReRAM] devices comprising selection components having two electrodes, e.g. diodes
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10B—ELECTRONIC MEMORY DEVICES
- H10B63/00—Resistance change memory devices, e.g. resistive RAM [ReRAM] devices
- H10B63/30—Resistance change memory devices, e.g. resistive RAM [ReRAM] devices comprising selection components having three or more electrodes, e.g. transistors
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
- H10N70/011—Manufacture or treatment of multistable switching devices
- H10N70/021—Formation of the switching material, e.g. layer deposition
- H10N70/023—Formation of the switching material, e.g. layer deposition by chemical vapor deposition, e.g. MOCVD, ALD
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
- H10N70/011—Manufacture or treatment of multistable switching devices
- H10N70/021—Formation of the switching material, e.g. layer deposition
- H10N70/026—Formation of the switching material, e.g. layer deposition by physical vapor deposition, e.g. sputtering
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
- H10N70/011—Manufacture or treatment of multistable switching devices
- H10N70/041—Modification of the switching material, e.g. post-treatment, doping
- H10N70/046—Modification of the switching material, e.g. post-treatment, doping by diffusion, e.g. photo-dissolution
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
- H10N70/011—Manufacture or treatment of multistable switching devices
- H10N70/061—Patterning of the switching material
- H10N70/063—Patterning of the switching material by etching of pre-deposited switching material layers, e.g. lithography
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
- H10N70/011—Manufacture or treatment of multistable switching devices
- H10N70/061—Patterning of the switching material
- H10N70/066—Patterning of the switching material by filling of openings, e.g. damascene method
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
- H10N70/011—Manufacture or treatment of multistable switching devices
- H10N70/061—Patterning of the switching material
- H10N70/068—Patterning of the switching material by processes specially adapted for achieving sub-lithographic dimensions, e.g. using spacers
Definitions
- the present invention generally relates to microelectronic memory devices. More particularly, the invention relates to programmable microelectronic structures having an electrical property that can be variably programmed by manipulating an amount of energy supplied to the structure during a programming function.
- Memory devices are often used in electronic systems and computers to store information in the form of binary data. These memory devices may be characterized into various types, each type having associated with it various advantages and disadvantages.
- RAM random access memory
- DRAM Dynamic RAM
- SRAM Static RAM
- PROM programmable read-only memory
- WORM write-once read-many
- PROM devices include erasable PROM (“EPROM”) and electrically erasable PROM (EEPROM) devices, which are alterable after an initial programming.
- EPROM devices generally require an erase step involving exposure to ultra violet light prior to programming the device. Thus, such devices are generally not well suited for use in portable electronic devices.
- EEPROM devices are generally easier to program, but suffer from other deficiencies. In particular, EEPROM devices are relatively complex, are relatively difficult to manufacture, and are relatively large. Furthermore, a circuit including EEPROM devices must withstand the high voltages necessary to program the device. Consequently, EEPROM cost per bit of memory capacity is extremely high compared with other means of data storage.
- an appliance system may include nonvolatile memory such as PROM to store user-specific information, including system instructions and critical data such as unit codes, identification, and user-entered information and also include volatile memory such as SRAM and/or DRAM to store, for example, session-specific information such as web pages and downloaded content such as compressed audio and/or video information.
- nonvolatile memory such as PROM
- PROM to store user-specific information
- critical data such as unit codes, identification, and user-entered information
- volatile memory such as SRAM and/or DRAM to store, for example, session-specific information such as web pages and downloaded content such as compressed audio and/or video information.
- the different forms of memory are typically formed on separate substrates because of different technologies and processing employed to form the various forms of memory.
- the multiple forms of memory are coupled together, e.g., through use of another substrate such as a printed circuit board, to integrated the various forms of memory with a digital processor.
- Forming the various forms of memory on separate substrates may be undesirable for several reasons. For example, forming various types of memory on separate substrate may be relatively expensive to manufacture, may require relatively long transmission paths to communicate between the memory devices and any associated electronic device, and may take up a relatively large amount of room within a system. Accordingly, memory devices including both volatile and nonvolatile memory and methods of forming the memory devices are desired. Furthermore, this memory technology should meet the requirements ofthe new generation of portable and/or stationary computer devices by operating at a relatively low voltage while providing high speed memory with high storage density and a low manufacturing cost.
- the present invention provides improved microelectronic memory devices, structures, and systems and methods of forming the same. More particularly, the invention provides memory structures that can be variably programmed depending on an amount of energy used to program the device. Such structures can replace both traditional nonvolatile and volatile forms of memory.
- a programmable structure includes an ion conductor and at least two electrodes.
- the structure is configured such that when a bias is applied across two electrodes, one or more electrical properties of the structure change.
- a resistance across the structure changes when a bias is applied across the electrodes.
- a capacitance or other electrical property ofthe structure changes upon application of a bias across the electrodes.
- an amount of change in the programmable property is manipulated by altering (e.g., thermally or electrically) an amount of energy used to program the device.
- altering e.g., thermally or electrically
- an amount of energy used to program the device e.g., thermally or electrically
- One or more of these electrical changes and/or the amount of change may suitably be detected.
- stored information may be retrieved from a circuit including the structure.
- a programmable structure in accordance with another exemplary embodiment ofthe invention, includes an ion conductor, at least two electrodes, and a barrier interposed between at least a portion of one of the electrodes and the ion conductor.
- the barrier material includes a material configured to reduce diffusion of ions between the ion conductor and at least one electrode. The diffusion barrier may also serve to prevent undesired electrodeposit growth within a portion of the structure.
- the barrier material includes an insulating material. Inclusion of an insulating material increases the voltage required to reduce the resistance of the device.
- the barrier includes material that conducts ions, but which is relatively resistant to the conduction of electrons.
- a programmable microelectronic structure is formed on a surface of a substrate by forming a first electrode on the substrate, depositing a layer of ion conductor material over the first electrode, and depositing conductive material onto the ion conductor material.
- a solid solution including the ion conductor and excess conductive material is formed by dissolving (e.g., via thermal and/or photodissolution) a portion ofthe conductive material in the ion conductor.
- a portion of the conductive material is dissolved, such that a portion of the conductive material remains on a surface of the ion conductor to form an electrode on a surface of the ion conductor material.
- at least a portion of a programmable structure is formed within a through-hole or via in an insulating material.
- a first electrode feature is formed on a surface of a substrate, insulating material is deposited onto a surface ofthe electrode feature, a via is formed within the insulating material, and a portion ofthe programmable structure is formed within the via.
- a portion ofthe structure within the via is formed by depositing an ion conductive material onto the conductive material, depositing a second electrode material onto the ion conductive material, and, if desired, removing any excess electrode, ion conductor, and/or insulating material.
- only the ion conductor is formed within the via.
- a first electrode is formed below the insulating material and in contact with the ion conductor and the second electrode is formed above the insulating material and in contact with the ion conductor.
- the configuration ofthe via may be changed to alter (e.g., reduce) a contact area between one or more of the electrodes and the ion conductor.
- the via may extend through the lower electrode to reduce the interface area between the electrode and the ion conductor.
- a portion of the ion conductor may be removed from the via or the ion conductor material may be directionally deposited into only a portion of the via to further reduce an interface between an electrode and the ion conductor.
- a programmable device may be formed on a surface of a substrate.
- the substrate includes a microelectronic circuit.
- the memory device is formed overlying the microelectronic circuit and conductive lines between the microelectronic circuit and the memory are formed using conductive wiring schemes within the substrate and the memory device. This configuration allows transmission of more bits of information per bus line.
- a programmable structure includes a floating electrode interposed between two additional electrodes.
- multiple programmable devices are coupled together using a common electrode (e.g., a common anode or a common cathode).
- a capacitance of a programmable structure is altered by causing ions within an ion conductor of the structure to migrate.
- a volatility of a memory cell in accordance with the present invention is manipulated by altering an amount of energy used during a write process for the memory.
- higher energy is used to form nonvolatile memory, while lower energy is used to form volatile memory.
- a single memory device, formed on a single substrate may include both nonvolatile and volatile portions.
- the relative volatility of one or more portions of the memory may be altered at any time by changing an amount of energy supplied to a portion of the memory during a write process.
- an electronic system includes programmable memory including an ion conductor and at least two electrodes.
- the memory can be used for apphcations that would typically use non- volatile memory such as PROM and/or volatile memory such as RAM.
- Figure 1 is a cross-sectional illustration of a programmable structure formed on a surface of a substrate in accordance with the present invention
- Figure 2 is a cross-sectional illustration of a programmable structure in accordance with an alternative embodiment ofthe present invention
- Figure 3 is a current-voltage diagram illustrating current and voltage characteristics ofthe device illustrated in Figure 2 in an "on” and "off state;
- Figure 4 is a cross-sectional illustration of a programmable structure in accordance with yet another embodiment ofthe present invention.
- Figure 5 is a schematic illustration of a portion of a memory device in accordance with an exemplary embodiment ofthe present invention.
- Figure 6 is a schematic illustration of a portion of a memory device in accordance with an alternative embodiment ofthe present invention
- Figures 7 and 8 are cross-sectional illustrations of programmable structures having an ion conductor/electrode contact interface formed about a perimeter of the ion conductor in accordance with another embodiment ofthe present invention
- Figures 9 and 10 are cross-sectional illustrations of programmable structures having an ion conductor/electrode contact interface formed about a perimeter ofthe ion conductor in accordance with yet another embodiment ofthe present invention
- Figures 11 and 12 illustrate a programmable device having a horizontal configuration in accordance with the present invention
- FIG. 13-19 illustrate programmable device structures with reduced electrode/ion conductor interface surface area in accordance with the present invention
- Figure 20 illustrates a programmable device with a tapered ion conductor in accordance with the present invention
- Figures 21-24 illustrate a programmable device including a floating electrode in accordance with the present invention
- FIGS. 25-29 illustrate common electrode programmable device structures in accordance with the present invention
- Figure 30 illustrates an internet appliance system in accordance with the present invention.
- Figure 31 illustrates a portion ofthe internet appliance of Figure 30 in greater detail.
- the present invention generally relates to microelectronic memory devices and to systems including the devices. More particularly, the invention relates to programmable structures, devices, and systems including memory that can be variably programmed, which is suitable for volatile data storage, nonvolatile data storage, or both forms of data storage.
- Figures 1 and 2 illustrate programmable microelectronic structures 100 and 200 formed on a surface of a substrate 110 in accordance with an exemplary embodiment of the present invention.
- Structures 100 and 200 include electrodes 120 and 130, an ion conductor 140, and optionally include buffer or barrier layers 155 and/or 255.
- structures 100 and 200 are configured such that when a bias greater than a threshold voltage (V ⁇ ), discussed in more detail below, is applied across electrodes 120 and 130, the electrical properties of structure 100 change.
- V ⁇ threshold voltage
- conductive ions within ion conductor 140 begin to migrate and form an electrodeposit (e.g., electrodeposit 160) at or near the more negative of electrodes 120 and 130; such an electrodeposit, however, is not required to practice the present invention.
- electrodeposit means any area within the ion conductor that has an increased concentration of reduced metal or other conductive material compared to the concentration of such material in the bulk ion conductor material. As the electrodeposit forms, the resistance between electrodes 120 and 130 decreases, and other electrical properties may also change. In the absence of any insulating barriers, which are discussed in more detail below, the threshold voltage required to grow the electrodeposit from one electrode toward the other and thereby significantly reduce the resistance of the device is approximately the redox potential of the system, typically a few hundred millivolts. If the same voltage is applied in reverse, the electrodeposit will dissolve back into the ion conductor and the device will return to a high resistance state.
- application of an electric field between electrodes 120 and 130 may cause ions dissolved within conductor 140 to migrate and thus cause a change in the electrical properties of device 100, without the formation of an electrodeposit.
- Structures 100 and 200 may be used to store information and thus may be used in memory circuits.
- structure 100 or other programmable structures in accordance with the present invention may suitably be used in memory devices to replace DRAM, SRAM, PROM, EPROM, EEPROM devices, or any combination of such memory.
- programmable structures of the present invention may be used for other applications where programming or changing of electrical properties of a portion of an electrical circuit are desired.
- the volatility of programmable memory can be manipulated by altering an amount of energy (e.g., altering time, current, voltage, thermal energy, and/or the like) applied during a write process.
- an amount of energy e.g., altering time, current, voltage, thermal energy, and/or the like
- the greater the amount of energy (having a voltage greater than the threshold voltage for the write process) applied during the write process the greater the growth of electrodeposit 160 and hence the less volatile the memory.
- relatively volatile memory can be formed by supplying relatively little energy to the cell.
- relatively volatile memory can be formed using the same or similar structures used to form nonvolatile memory, and less energy can be used to form the volatile memory.
- the volatile and nonvolatile memory may be formed on the same substrate and partitioned or separated from each other such that each partition is dedicated to either volatile or nonvolatile memory; or, an array of memory cells may be configured as volatile or nonvolatile memory using programming techniques, such that the configuration (i.e., volatile or nonvolatile) ofthe memory can be altered by changing an amount of energy supplied during programming the respective portions ofthe memory array.
- substrate 110 may include any suitable material.
- substrate 110 may include semiconductive, conductive, semiinsulative, insulative material, or any combination of such materials.
- substrate 110 includes an insulating material 112 and a portion 114 including microelectronic devices formed on a semiconductor substrate. Layers 112 and 114 may be separated by additional layers (not shown) such as, for example, layers typically used to form integrated circuits. Because the programmable structures can be formed over insulating or other materials, the programmable structures of the present invention are particularly well suited for apphcations where substrate (e.g., semiconductor material) space is a premium.
- substrate e.g., semiconductor material
- forming a memory cell overlying a microelectronic device may be advantageous because such a configuration allows greater data transfer between an a ⁇ -ay of memory cells and the microelectronic device using, for example, conductive pugs formed within layers 112 and 150.
- Electrodes 120 and 130 may be formed of any suitable conductive material.
- electrodes 120 and 130 may be formed of doped polysilicon material or metal.
- one of electrodes one of electrodes
- electrode 120 and 130 is formed of a material including a metal that dissolves in ion conductor 140 when a sufficient bias (V > V T ) is applied across the electrodes (an oxidizable electrode) and the other electrode is relatively inert and does not dissolve during operation of the programmable device (an indifferent electrode).
- electrode 120 may be an anode during a write process and be comprised of a material including silver that dissolves in ion conductor 140 and electrode 130 may be a cathode during the write process and be comprised of an inert material such as tungsten, nickel, molybdenum, platinum, metal suicides, and the like.
- Having at least one electrode formed of a material including a metal which dissolves in ion conductor 140 facilitates maintaining a desired dissolved metal concentration within ion conductor 140, which in turn facilitates rapid and stable electrodeposit 160 formation within ion conductor 140 or other electrical property change during use of structure 100 and/or 200. Furthermore, use of an inert material for the other electrode (cathode during a write operation) facilitates electrodissolution of any electrodeposit that may have formed and/or return ofthe programmable device to an erased state after application of a sufficient voltage.
- dissolution of any electrodeposit that may have formed preferably begins at or near the oxidizable electrode/electrodeposit interface.
- Initial dissolution of the electrodeposit at the oxidizable electrode/electrodeposit interface may be facilitated by forming structure 100 such that the resistance at the oxidizable electrode/electrodeposit interface is greater than the resistance at any other point along the electrodeposit; particularly, the interface between the electrodeposit and the indifferent electrode.
- One way to achieve relatively low resistance at the indifferent electrode is to form the electrode of relatively inert, non-oxidizing material such as platinum.
- Use of such material reduces formation of oxides at the interface between ion conductor 140 and the indifferent electrode as well as the formation of compounds or mixtures of the electrode material and ion conductor 140 material, which typically have a higher resistance than ion conductor 140 or the electrode material.
- Relatively low resistance at the indifferent electrode may also be obtained by forming a barrier layer between the oxidizable electrode (anode during a write operation) and the ion conductor, wherein the barrier layer is formed of material having a relatively high resistance.
- Exemplary high resistance materials include layers (e.g., layer 155) of ion conducting material (e.g., Ag x O, Ag K S, Ag x Se, Ag x Te, where x > 2, Ag y I, where x > 1,
- the roughened surface may be formed by manipulating film deposition parameters and/or by etching a portion of one of the electrode of ion conductor surfaces.
- relatively high electrical fields form about the spikes or peaks of the roughened surface, and thus the electrodeposits are more likely to form about the spikes or peaks.
- more reliable and uniform changes in electrical properties for an applied voltage across electrodes 120 and 130 may be obtained by providing a roughed interface between the indifferent electrode (cathode during a write operation) and ion conductor 140.
- Oxidizable electrode material may have a tendency to thermally dissolve or diffuse into ion conductor 140, particularly during fabrication and/or operation of structure 100.
- the thermal diffusion is undesired because it may reduce the resistance of structure 100 and thus reduce the change of an electrical property during use of structure 100.
- the oxidizable electrode includes a metal intercalated in a transition metal sulfide or selenide material such as A ⁇ (MB 2 )i- ⁇ , where A is Ag or Cu, B is S or Se, M is a transition metal such as Ta, V, and Ti, and x ranges from about 0.1 to about 0.7.
- the intercalated material mitigates undesired thermal diffusion ofthe metal (Ag or Cu) into the ion conductor material, while allowing the metal to participate in the electrodeposit growth upon apphcation of a sufficient voltage across electrodes 120 and 130.
- the TaS 2 film can include up to about 67 atomic percent silver.
- the A x (MB 2 ) ⁇ - x material is preferably amorphous to prevent undesired diffusion of the metal though the material.
- the amorphous material may be formed by, for example, physical vapor deposition of a target material comprising A x (MB 2 ) ⁇ - ⁇ .
- ⁇ -Agl is another suitable material for the oxidizable electrode, as well as the indifferent electrode.
- -Agl can serve as a source of Ag during operation of structure 100 — e.g., upon apphcation of a sufficient bias, but the silver in the Agl material does not readily thermally diffuse into ion conductor 140.
- Agl has a relatively low activation energy for conduction of electricity and does not require doping to achieve relatively high conductivity.
- the oxidizable electrode is formed of Agl, depletion of silver in the Agl layer may arise during operation of structure 100, unless excess silver is provided to the electrode.
- One way to provide the excess silver is to form a silver layer adjacent the Agl layer as discussed above when Agl is used as a buffer layer.
- the Agl layer (e.g., layer 155 and/or 255) reduces thermal diffusion of Ag into ion conductor 140, but does not significantly affect conduction of Ag during operation of structure 100.
- use of Agl increases the operational efficiency of structure 100 because the Agl mitigates non-Faradaic conduction (conduction of electrons that do not participate in the electrochemical reaction).
- buffer layers 155 and/or 255 include GeO 2 and SiO x .
- Amorphous GeO 2 is relatively porous an will "soak up" silver during operation of device 100, but will retard the thermal diffusion of silver to ion conductor 140, compared to structures or devices that do not include a buffer layer.
- GeO 2 may be formed by exposing ion conductor 140 to an oxidizing environment at a temperature of about 300 °C to about 800 °C or by exposing ion conductor 140 to an oxidizing environment in the presence of radiation having an energy greater than the band gap ofthe ion conductor material.
- the GeO may also be deposited using physical vapor deposition (from a GeO 2 target) or chemical vapor deposition (from GelL and an O 2 ).
- Buffer layers can also be used to increase a "write voltage" by placing the buffer layer (e.g., GeO 2 or SiO x ) between ion conductor 140 and the indifferent electrode.
- the buffer layer e.g., GeO 2 or SiO x
- the buffer material allows metal such as silver to diffuse though the buffer and take part in the electrochemical reaction.
- At least one electrode 120 and 130 is formed of material suitable for use as an interconnect metal.
- electrode 130 may form part of an interconnect structure within a semiconductor integrated circuit.
- electrode 130 is formed of a material that is substantially insoluble in material comprising ion conductor 140.
- Exemplary materials suitable for both interconnect and electrode 130 material include metals and compounds such as tungsten, nickel, molybdenum, platinum, metal suicides, and the like.
- Layers 155 and/or 255 may also include a material that restricts migration of ions between conductor 140 and the electrodes.
- a barrier layer includes conducting material such as titanium nitride, titanium tungsten, a combination thereof, or the like.
- the barrier may be electrically indifferent, i.e., it allows conduction of electrons through structure 100 or 200, but it does not itself contribute ions to conduction through structure 200.
- An electrically indifferent barrier may reduce undesired dendrite growth during operation of the programmable device, and thus may facilitate an "erase” or dissolution of electrodeposit 160 when a bias is applied which is opposite to that used to grow the electrodeposit.
- use of a conducting barrier allows for the "indifferent" electrode to be formed of oxidizable material because the barrier prevents diffusion ofthe electrode material to the ion conductor.
- Ion conductor 140 is formed of material that conducts ions upon application of a sufficient voltage. Suitable materials for ion conductor 140 include glasses and semiconductor materials. In one exemplary embodiment ofthe invention, ion conductor 140 is formed of chalcogenide material.
- Ion conductor 140 may also suitably include dissolved conductive material.
- ion conductor 140 may comprise a solid solution that includes dissolved metals and/or metal ions.
- conductor 140 includes metal and/or metal ions dissolved in chalcogenide glass.
- An exemplary chalcogenide glass with dissolved metal in accordance with the present invention includes a solid solution of As x S ⁇ . x -Ag, Ge x Se ⁇ . x -Ag, Ge x S ⁇ - x -Ag, As x Si. x -Cu, Ge x Se ⁇ .
- conductor 140 may include network modifiers that affect mobility of ions through conductor 140.
- materials such as metals (e.g., silver), halogens, halides, or hydrogen may be added to conductor 140 to enhance ion mobility and thus increase erase/write speeds ofthe structure.
- a sohd solution suitable for use as ion conductor 140 may be formed in a variety of ways.
- the sohd solution may be formed by depositing a layer of conductive material such as metal over an ion conductive material such as chalcogenide glass and exposing the metal and glass to thermal and/or photo dissolution processing.
- a sohd solution of As 2 S 3 -Ag is formed by depositing As 2 S 3 onto a substrate, depositing a thin film of Ag onto the As2S 3j , and exposing the films to hght having energy greater than the optical gap ofthe As2S 3 ,--e.g., hght having a wavelength of less than about 500 nanometers.
- network modifiers may be added to conductor 140 during deposition of conductor 140 (e.g., the modifier is in the deposited material or present during conductor 140 material deposition) or after conductor 140 material is deposited (e.g., by exposing conductor 140 to an atmosphere including the network modifier).
- a sohd solution may be formed by depositing one of the constituents onto a substrate or another material layer and reacting the first constituent with a second constituent.
- germanium preferably amorphous
- germanium may be deposited onto a portion of a substrate and the germanium may be reacted with HzSe to form a Ge-Se glass.
- H 2 Se gas or arsenic or germanium can be deposited and reacted with H 2 S gas.
- Silver or other metal can then be added to the glass as described above.
- a sohd solution ion conductor 140 is formed by depositing sufficient metal onto an ion conductor material such that a portion of the metal can be dissolved within the ion conductor material and a portion of the metal remains on a surface of the ion conductor to form an electrode (e.g., electrode 120).
- an electrode e.g., electrode 120
- solid solutions containing dissolved metals may be directly deposited onto substrate 110 and the electrode then formed overlying the ion conductor.
- the sohd solution is formed by photodissolution to form a macrohomogeneous ternary compound and additional metal is added to the solution using thermal diffusion (e.g., in an inert environment at a temperature of about 85 °C to about 150 °C) to form a sohd solution containing, for example, about 30 to about 50, and preferably about 34 atomic percent silver.
- thermal diffusion e.g., in an inert environment at a temperature of about 85 °C to about 150 °C
- Ion conductors having a metal concentration above the photodissolution solubility level facilitates formation of electrodeposits that are thermally stable at operating temperatures (typically about 85 °C to about 150 °C) of devices 100 and 200.
- the solid solution may be formed by thermally dissolving the metal into the ion conductor at the temperature noted above; however, sohd solutions formed exclusively from photodissolution are thought to be less homogeneous than films having similar metal concentrations formed using photodissolution and thermal dissolution.
- Ion conductor 140 may also include a filler material, which fills interstices or voids.
- Suitable filler materials include non-oxidizable and non-silver based materials such as a non- conducting, immiscible silicon oxide and/or silicon nitride, having a cross-sectional dimension of less than about 1 nm, which do not contribute to the growth of an electrodeposit.
- the filler material is present in the ion conductor at a volume percent of up to about 5 percent to reduce a likelihood that an electrodeposit will spontaneously dissolve into the supporting ternary material as the device is exposed to elevated temperature, which leads to more stable device operation without compromising the performance ofthe device.
- Ion conductor 140 may also include filler material to reduce an effective cross-sectional area of the ion conductor.
- concentration of the filler material which may be the same filler material described above but having a cross- sectional dimension up to about 50 nm, is present in the ion conductor material at a concentration of up to about 50 percent by volume.
- the filler material may also include metal such as silver or copper to fill the voids in the ion conductor material.
- ion conductor 140 includes a germanium-selenide glass with silver diffused in the glass.
- Germanium selenide materials are typically formed from selenium and Ge(Se) / 2 tetrahedra that may combine in a variety of ways. In a Se-rich region, Ge is 4-fold coordinated and Se is 2-fold coordinated, which means that a glass composition near Geo.2oSe 0 . 8 o will have a mean coordination
- ion conductor 140 includes a glass having a composition of Ge 0 .i7Se 0 . 83 to Geo. 25 Seo. 75 .
- composition and structure of ion conductor 140 material often depends on the starting or target material used to form the conductor. Generally, it is desired to form a homogenous material layer for conductor 140 to facilitate rehable and repeatable device performance.
- At least a portion of structure 100 is formed within a via of an insulating material 150.
- Forming a portion of structure 100 within a via of an insulating material 150 may be desirable because, among other reasons, such formation allows relatively small structures, e.g., on the order of 10 nanometers, to be formed.
- insulating material 150 facilitates isolating various structures 100 from other electrical components.
- Insulating material 150 suitably includes material that prevents undesired diffusion of electrons and/or ions from structure 100.
- material 150 includes silicon nitride, silicon oxynitride, polymeric materials such as polyimide or parylene, or any combination thereof.
- a contact 165 may suitably be electrically coupled to one or more electrodes 120, 130 to facilitate forming electrical contact to the respective electrode.
- Contact 165 may be formed of any conductive material and is preferably formed of a metal, alloy, or composition including aluminum, tungsten, or copper.
- structure 100 is formed by forming electrode 130 on substrate 110.
- Electrode 130 may be formed using any suitable method such as, for example, depositing a layer of electrode 130 material, patterning the electrode material, and etching the material to form electrode 130.
- Insulating layer 150 may be formed by depositing insulating material onto electrode 130 and substrate 110 and forming vias in the insulating material using appropriate patterning and etching processes.
- Ion conductor 140 and electrode 120 may then be formed within insulating layer 150 by depositing ion conductor 140 material and electrode 120 material within the via.
- Such ion conductor and electrode material deposition may be selective - i.e., the material is substantially deposited only within the via, or the deposition processes may be relatively non-selective.
- any excess material remaining on a surface of insulating layer 150 may be removed using, for example, chemical mechanical pohshing and/or etching techniques.
- Barrier layers 155 and/or 255 may similarly be formed using any suitable deposition and/or etch processes.
- Information may be stored using programmable structures ofthe present invention by manipulating one or more electrical properties ofthe structures. For example, a resistance of a structure may be changed from a "0" or off state to a "1" or on state during a suitable write operation. Similarly, the device may be changed from a "1" state to a "0" state during an erase operation.
- the structure may have multiple programmable states such that multiple bits of information are stored in a single structure.
- Figure 3 illustrates current- oltage characteristics of a programmable structure (e.g. structure 200) in accordance with the present invention.
- via diameter, D is about 4 microns
- conductor 140 is about 35 nanometers thick and formed of
- electrode 130 is indifferent and formed of nickel, electrode
- 120 is formed of silver, and barrier 255 is a native nickel oxide.
- current through structure 200 in an off state begins to rise upon application of a bias of over about one volt; however, once a write step has been performed (i.e., an electrodeposit has formed), the resistance through conductor 140 drops significantly (i.e., to about 200 ohms), illustrated by curve 320 in Figure 3.
- electrode 130 is coupled to a more negative end of a voltage supply, compared to electrode 120, an electrodeposit begins to form near electrode 130 and grow toward electrode 120.
- An effective threshold voltage (i.e., voltage required to cause growth ofthe electrodeposit and to break through barrier 255, thereby couphng electrodes 320, 330 together) is relatively high because of barrier 255.
- a voltage Y ⁇ Vj must be applied to structure 200 sufficient to cause electrons to tunnel through barrier 255 (when barrier 255 comprises an insulating layer) to form the electrodeposit and to overcome the barrier (e.g., by tunneling through or leakage) and conduct through conductor 140 and at least a portion of barrier 255.
- an initial "write" threshold voltage is relatively low because no insulative barrier is formed between, for example, ion conductor 140 and either of the electrodes 120, 130.
- the relative volatility of the memory structures of the present invention may be altered by applying different amounts of energy to the structures during a write process. For example, a relatively high current pulse of a few hundred microamperes for a period of about several hundred nanoseconds may be applied to the structures illustrated in Figures 1 and 2 to form a relatively nonvolatile memory cell. Alternatively, the same current may be supplied to the same or similar memory structure for a shorter amount of time, e.g., several nanoseconds to form a relatively volatile memory structure. In either case, the memory of the present invention can be programmed at relatively high speeds and even the "volatile" memory is relatively nonvolatile compared to traditional DRAM. For example, the volatile memory may operate at speed comparable to DRAM and only require refreshing every several hours.
- a state of a memory cell may be read, without significantly disturbing the state, by, for example, applying a forward or reverse bias of magnitude less than a voltage threshold (about 1.4 V for a structure illustrated in Figure 3) for electrodeposition or by using a current limit which is less than or equal to the minimum programming current (the current which will produce the highest ofthe on resistance values).
- a current limited (to about 1 milliamp) read operation is shown in Figure 3. In this case, the voltage is swept from 0 to about 2 V and the current rises up to the set limit (from 0 to 0.2 V), indicating a low resistance (ohmic/linear current- voltage) "on" state.
- Another way of performing a non- disturb read operation is to apply a pulse, with a relatively short duration, which may have a voltage higher than the electrochemical deposition threshold voltage such that no appreciable Faradaic current flows, i.e., nearly all the current goes to polarizing/charging the device and not into the electrodeposition process.
- a programmable structure (e.g., structure 200) may suitably be erased by reversing a bias apphed during a write operation, wherein a magnitude of the applied bias is equal to or greater than the threshold voltage for electrodeposition in the reverse direction.
- V>V ⁇ is applied to structure 200 for a period of time, which depends on energy supphed during the write operation, but is typically less than about 1 millisecond to return structure 200 to its "off' state having a resistance well in excess of a milhon ohms.
- a threshold voltage for erasing the structure is much lower than a threshold voltage for writing the structure because, unlike the write operation, the erase operation does not require electron tunneling through a barrier or barrier breakdown.
- the concentration of conductive material in the ion conductor can be controlled by applying a bias across the programmable device.
- metal such as silver may be taken out of solution by applying a negative voltage in excess of the reduction potential of the conductive material.
- conductive material may be added to the ion conductor (from one of the electrodes) by applying a bias in excess of the oxidation potential of the material.
- the concentration can be reduced by reverse biasing the device to reduce the concentration of the conductive material.
- metal may be added to the solution from the oxidizable electrode by applying a sufficient forward bias. Additionally, it is possible to remove excess metal build up at the indifferent electrode by applying a reverse bias for an extended time or an extended bias over that required to erase the device under normal operating conditions. Control of the conductive material may be accomplished automatically using a suitable microprocessor.
- This technique may also be used to form one of the electrodes from material within the ion conductor material.
- silver from the ion conductor may be plated out to form the oxidizable electrode. This allows the oxidizable electrode to be formed after the device is fully formed and thus mitigates problems associated with conductive material diffusing from the oxidizable electrode during manufacturing ofthe device.
- multiple bits of data may be stored within a single programmable structure by controlling an amount of electrodeposit which is formed during a write process.
- An amount of electrodeposit that forms during a write process depends on a number of coulombs or charge supplied to the structure during the write process, and may be controlled by using a current limit power source.
- a resistance of a programmable structure is governed by Equation 1, where R on is the "on" state resistance, Vr is the threshold voltage for electrodeposition , and I UM is the maximum current allowed to flow during the write operation.
- the limitation to the amount of information stored in each cell will depend on how stable each of the resistance states is with time. For example, if a structure with a programmed resistance range of about 3.5 k ⁇ and a resistance drift over a specified time for each state is about ⁇ 250 ⁇ , about 7 equally sized bands of resistance (7 states) could be formed, allowing 3 bits of data to be stored within a single structure. In the limit, for near zero drift in resistance in a specified time limit, information could be stored as a continuum of states, i.e., in analog form.
- structure 400 includes electrodes 420 and 430, an ion conductor 440, a contact 460, and an amorphous silicon diode 470, such as a Schottky or p-n junction diode, formed between contact 460 and electrode 420.
- Rows and columns of programmable structures 400 may be fabricated into a high density configuration to provide extremely large storage densities suitable for memory circuits. In general, the maximum storage density of memory devices is limited by the size and complexity of the column and row decoder circuitry.
- a programmable structure storage stack can be suitably fabricated overlying an integrated circuit with the entire semiconductor chip area dedicated to row/column decode, sense amplifiers, and data management circuitry (not shown) since structure 400 need not use any substrate real estate.
- storage densities of many gigabits per square centimeter can be attained using programmable structures of the present invention.
- the programmable structure is essentiaUy an additive technology that adds capability and functionality to existing semiconductor integrated circuit technology.
- Figure 5 schematically illustrates a portion of a memory device including structure 400 having an isolating p-n junction 470 at an intersection of a bit line 510 and a word line 520 of a memory circuit.
- Figure 6 illustrates an alternative isolation scheme employing a transistor 610 interposed between an electrode and a contact of a programmable structure located at an intersection of a bit hne 610 and a word line 620 of a memory device.
- Figures 7-10 illustrate programmable devices in accordance with another embodiment ofthe invention.
- the devices illustrated in Figures 7-10 have an electrode (e.g., the cathode during a write process) with a smaller cross sectional area in contact with the ion conductor compared to the devices illustrated in Figures 1-2 and 4.
- the smaller electrode interface area is thought to increase the efficiency and endurance of the device because an increased percentage of ions in the sohd solution are able to take part in the electrodeposit formation process. Thus any cathode plating from ions that do not participate in the electrodeposit process is reduced.
- Figures 7 and 8 illustrate a cross sectional and a top cut-away view of a programmable device 700 including an indifferent electrode 710, an oxidizable electrode 720, and an ion conductor 730 formed overlying an insulating layer 740 such as silicon oxide, silicon nitride, or the like.
- Structure 700 is formed by depositing an indifferent electrode material layer and an insulating layer 750 overlying insulating layer 740.
- a via is then formed through layer 750 and electrode material layer 710, using an anisotropic etch process (e.g., reactive ion etching or ion milling) such that the via extends to and or through a portion of layer 740.
- the via is then filled with ion conductor material and is suitably doped to form a sohd solution as described herein. Any excess ion conductor material is removed from the surface of layer 750 and electrode 730 is formed, for example using a deposition and etch process.
- the indifferent electrode (cathode during write process) area in contact with ion conductor 730 is the surface area of electrode 710 about the perimeter of conductor 730, rather than the area underlying the ion conductor, as illustrated in Figures 1-2 and 4.
- Figures 9 and 10 illustrate a programmable device 900 having an indifferent electrode 910, an oxidizable electrode 920, an ion conductor 930 and insulating layers 940 and 950 in accordance with yet another embodiment of the invention.
- Structure 900 is similar to structure 700, except that once a via is formed through layer 950, an isotropic etch process (e.g., chemical or plasma) is employed to form the via through electrode 910, such that a sloped intersection between an ion conductor 930 and electrode 910 is formed.
- an isotropic etch process e.g., chemical or plasma
- FIGS 11 and 12 illustrate another programmable device 1100, with a reduced electrode/ion conductor interface, in accordance with the present invention.
- Structure 1100 includes electrodes 1110 and 1120 and an ion conductor 1130, formed on a surface of an insulating material 1140, rather than within a via as discussed above.
- the programmable structure is formed by defining an ion conductor 1130 pattern on a surface of insulating material 1140 (e.g., using deposition and etch techniques) and forming electrodes 1110 and 1120, such that the electrodes each contact a portion of the ion conductor.
- the electrodes are formed overlying and in contact with both a portion of the ion conductor and the insulating material.
- the thickness of the layers may be varied in accordance with specific applications ofthe device, in a preferred embodiment ofthe invention, the thickness ofthe ion conductor and electrode films is about 1 nmto about 100 nm.
- Sub-lithographic lateral dimensions of portions ofthe device may be obtained by overexposing photoresist used to pattern the portions and/or over etching the film layer.
- Figure 13 illustrates a device 1300 in accordance with yet another embodiment ofthe invention.
- Structure 1300 is similar to the devices illustrated in Figures 7 and 8, except that the cross-sectional area ofthe ion conductor that is in contact with the electrodes is reduced by filling a portion of a via with non-ion conductor material, rather than etching through an electrode layer.
- Structure 1300 includes electrodes 1310 and 1320 and an ion conductor 1330 formed within an insulating layer 1340.
- ion conductor 1330 is formed by creating a trench within insulating layer 1340, the trench having a diameter indicated by D2.
- the trench is then filled using, for example, interference lithography techniques or conformally lining the via with insulating material and using an anisotropic etch process to remove some ofthe insulating material, leaving a via with a diameter of D3.
- Structure 1300 formed using this technique may have a ion conductor cross sectional area as small as about 10 nm in contact with electrodes 1310 and 1320.
- Figures 14-17 illustrate another embodiment of the invention, where the cross sectional area of the ion conductor/electrode interface is relatively small.
- Structure 1400 illustrated in Figure 14, includes electrodes 1410 and 1420 and an ion conductor 1430.
- Structure 1400 is formed in a manner similar to structure 700, except that the ion conductor material is deposited conformally, using, for example, chemical vapor deposition or physical vapor deposition, into a trench, and the trench is not filled with the ion conductor material.
- Structure 1500 is similar to structure 1400, except that an ion conductor 1530 is formed by etching a portion of ion conductor 1430, such that a via 1540 is formed through to electrode 1410.
- Structure 1600 is similar to structure 1500 and is formed by conformally depositing the ion conductor material as described above and then removing the ion conductor material from a surface of insulating material 1450 prior to depositing electrode 1420 material.
- structure 1700 may be formed by selectively deposing the ion conductor 1730 material into only a portion ofthe trench formed in insulating material 1450 (e.g., using angled deposition and/or shadowing techniques), removing any excess ion conductor material on the surface of insulator 1450, and forming an electrode 1720 overlying the insulator and in contact with ion conductor 1730.
- Figures 18 and 19 illustrate yet another embodiment of the invention, where a pillar or wall within a trench is used to reduce a cross-sectional area of the interface between the ion conductor and one or more electrodes.
- Structure 1800, illustrated in Figure 18, includes electrodes 1810 and 1820 and an ion conductor 1830 formed within an insulating layer 1840.
- structure 1800 includes a pillar 1850 of insulating material (e.g., insulating material used to form layer 1840), formed within a trench within layer 1840. Structure 1800 may be formed using the shadowed deposition technique discussed above. Structure 1900 is similar to structure 1800, except structure 1900 includes a partial pillar 1950 and an ion conductor 1930, which fills the remaining portion ofthe formed trench.
- Figure 20 illustrates yet another structure 2000 in accordance with the present invention.
- Structure 2000 includes electrodes 2010 and 2020 and an ion conductor 2030 formed within an insulating layer 2040. Structure 2000 is formed using an anisotropic or a combination of an anisotropic and an isotropic etch processes to form a tapered via. Ion conductor 2030 is then formed within the trench using techniques previously described.
- Figures 21-24 illustrate programmable devices in accordance with yet another embodiment of the invention. The structures illustrated in Figures 21-24 include a floating electrode, which allows multiple bits of information to be stored within a single programmable device.
- Structure 2100 includes a first electrode 2110, a second, floating electrode 2120, a third electrode 2130, ion conductor portions 2140 and 2150, which may all be formed on a substrate or wholly or partially formed within a via as described above. Although structure 2100 is illustrated in a vertical configuration, the structure may be formed in a horizontal configuration, similar to structure 1100.
- the first and third electrodes are formed of an indifferent electrode material and the second electrode is formed of an oxidizable electrode material.
- the first and third electrodes may be formed of oxidizable electrode material and the second, floating electrode may be formed of an indifferent electrode material.
- the structure includes two "half cells,” where each half cell functions as a programmable device described above in connection with Figure 1.
- Each half cell is preferably configured such that the resistance of one half cell differs from the resistance ofthe other half cell when both cells are in an erased state.
- bits of data may be stored as follows.
- the overall impedance of structure 2100 is approximately equal to the resistance of portions 2140 and 2150. When no electrodeposit is formed within either portion, this high resistance state may be represented by the state 00.
- a voltage is applied to structure 2100, such that electrode 2130 is positive relative to electrode 2110 and the applied bias is greater than the threshold voltage required to form an electrodeposit in portion 2140, an electrodeposit 2160 will form through conductor portion 2140 from electrode 2110 toward floating electrode 2120 as illustrated in Figure 22. Under this condition, an electrodeposit will not form within conductor portion 2150 because portion 2150 is under a reverse bias condition and thus will not support growth of an electrodeposit.
- the growth of the electrodeposit will change the impedance of portion 2140 fromZi to Zi', thus changing the overall impedance of structure 2100, which may be represented by the state 01.
- the current level used to form electrodeposit 2160 should be selected such that it is sufficiently low, allowing the electrodeposit to be dissolved upon application of a sufficient reverse bias.
- a third state may be formed by reversing the polarity ofthe applied bias across electrodes 2110 and 2130, such that most of the voltage drop occurs across the high resistance ion conductor portion 2150 and formation of an electrodeposit 2170 begins, as illustrated in Figure 23, without causing electrodeposit 2160 to dissolve.
- the impedance of portion 2150 changes fromZ 2 to Z 2 ', and the overall impedance of structure 2100 is Zi' plus Z 2 ', which may be represented by the state 11.
- electrodeposit 2160 and/or 2170 may be dissolved by applying a sufficient bias across one or both of the half cells.
- Electrodeposit 2170 can be erased, for example, by sufficiently negatively biasing electrode 2130 with respect to electrode 2110, which may be represented by a state 00.
- the four possible states, along with the current limit used to form the state, are represented in table 1 below.
- Table 1 Structure 2100 can be changed to 11 from state 10 by applying a low current limit bias to grow electrodeposit 2150 in portion 2140. Similarly, structure 2100 can be changed from state 11 to state 01 by dissolving electrodeposit 2170 by applying a relatively high current limit bias such that upper electrode 2130 is positive with respect to lower electrode 2110. Finally, structure 2100 can be returned to state 00 using a short current pulse to thermally dissolve electrodeposit 2160, using a current which is high enough to cause localized heating of the electrodeposit. This will increase the metal concentration in the half-cell but this excess metal can be removed electrically from the cell by plating it back onto the floating electrode. This sequence is summarized in table 2 below.
- FIGS 25-29 illustrate structures in accordance with another embodiment of the invention in which multiple programmable devices include a common electrode (e.g., the devices share a common anode or cathode). Forming structures in which multiple structures share a common electrode is advantageous because such structures allow a higher density of cells to be formed on a given substrate surface area.
- Figures 25 and 26 illustrate a structure 2500, having a horizontal configuration and a common electrode.
- Structure 2500 includes an electrical connector 2510 coupled to a common surface electrode 2520, electrodes 2530 and 2540, and ion conductor portions 2550 and 2560 overlying an insulating layer 2170.
- Structure 2500 may be used to form word and bit lines as described above by forming a row of electrodes (e.g., anodes) coupled to conductor 2510, and columns of oppositely bias electrodes (e.g., cathodes) running perpendicular to electrodes 2520.
- a conductive plug formed of any suitably conducting material, can be used to electrically couple electrode 2520 to conductor 2510.
- common electrode structures in accordance with this embodiment may be formed using structures having a vertical configuration as described herein.
- Figures 27 and 28 illustrate additional structures 2700 and 2800 having a common electrode shared between two or more devices
- Structures 2700 and 2800 include a common electrode, electrodes 2720 and 2725, ion conductors 2730, 2735 and 2830, 2835 respectively, and insulating layers 2740 and 2750.
- Structures 2700 and 2800 may be formed using techniques described above in connection with Figures 15 and 16 — e.g., by conformally depositing ion conductor material within a trench of an insulating layer.
- directional deposition may be used to form a structure similar to structure 1700.
- Structures 2700 and 2800 each include two programmable devices including common electrode 2710, an ion conductor (e.g., conductor 2735), and another electrode (e.g., electrode 2725).
- Dielectric material 2750 is an insulating material that does not interfere with surface electrodeposit growth, such as silicon oxides, silicon nitrides, and the like.
- Figure 29 illustrates a structure 2900 including multiple programmable devices 2902- 2916 formed about a common electrode 2920.
- Each of the devices 2902-2916 may be formed using the method described above in connection with Figure 21.
- each of electrodes 2930-2936 and 2938-2944 may be coupled together in a direction perpendicular to the direction of common electrode 2920, such that electrode 2920 forms a bit line and electrodes 2930-2936 and electrodes 2938-2944 form word lines.
- Structure 2900 may operate and be programmed in a manner similar to structure 2100 described above.
- a programmable structure or device stores information by storing a charge as opposed to growing an electrodeposit.
- a capacitance of a structure or device is altered by applying a bias across electrodes of the device such that positively charged ions migrate toward one of the electrodes. If the applied bias is less that a write threshold voltage, no short will form between the electrodes. Capacitance ofthe structure changes as a result ofthe ion migration. When the applied bias is removed, the metal ions tend to diffuse away from the electrode or a barrier proximate the electrode. However, an interface between an ion conductor and a barrier is generally imperfect and includes defects capable of trapping ions.
- a programmable structure in accordance with the present invention may be used in many applications which would otherwise utilize traditional technologies such as EEPROM, FLASH or DRAM. Advantages provided by the present invention over present memory techniques include, among other things, lower production cost and the ability to use flexible fabrication techniques which are easily adaptable to a variety of applications. The programmable structures ofthe present invention are especially advantageous in applications where cost is the primary concern, such as smart cards and electronic inventory tags. Also, an ability to form the memory directly on a plastic card is a major advantage in these applications as this is generally not possible with other forms of semiconductor memories.
- memory elements may be scaled to less than a few square microns in size, the active portion of the device being less than on micron. This provides a significant advantage over traditional semiconductor technologies in which each device and its associated interconnect can take up several tens of square microns.
- Figures 30 and 31 illustrate one application for which programmable structures in accordance with the present invention are particularly well suited.
- Figure 30 illustrates an internet appliance 3000, which may be in the form of a computer, a personal digital assistant, a portable telephone, or the hke.
- system 3000 includes an internet connection 3002, a physical interface and logic portion 3004, a data processing and control portion 3006, a user interface 3008, a data buffer portion 3010, and data storage portion 3012.
- Portions 3002-3004 and 3008-3010 of system 3000 may include portions of an internet appliance as now known and therefore further description of these portions is not provided herein.
- Systems such as system 3000 in accordance with the present invention may either be portable or stationary appliances.
- Figure 31 illustrates a portion of system 3000 in greater detail.
- data storage portion 3012 is formed using the programmable structures as described herein.
- Storage portion 3012 may suitably include a first memory portion 3106, including relatively volatile memory (to replace e.g., RAM type memory that would otherwise be used in such a system), and a second portion 3104 including relatively nonvolatile memory (to replace ROM type memory that would otherwise be used in such a system).
- portions 3104 and 3106 may be formed on a single substrate and formed using the same or similar programmable structures.
- portion 3104 and portion 3106 are formed on separate portions on a substrate and are dedicated to storing relatively nonvolatile and volatile information, respectively.
- portion 3104 may suitably include larger scale drivers and/or conductive traces to supply the greater amount of energy, and need not include any erase circuitry.
- portions 3104 and 3106 may form part of an integrated array of programmable structures and the relative volatility of information stored in portions 3104 and 3106 may be governed by software capable of manipulating an amount of energy supplied to various programmable structures. In this case, the relative volatility of the memory may be altered during operation of system 3000, depending on such factors as the specific apphcation performed by the appliance.
- long- term storage e.g., portion 3104
- long- term storage e.g., portion 3104
- information such as user specific information, including certain system instructions that are intended to be upgradeable and therefore not typically within ROM portion 3102, and other information such as unit codes and identification as well as user-entered information.
- short term information storage is used to store information that is more session specific such as stored web pages and downloaded content.
- programmable structures as described herein may be used to form ROM memory 3102.
- the memory may be monohthically formed on the same substrate used to form data processing and control portion 3006, either directly or on the same substrate or formed overlying the integrated circuit comprising portion 3006, or may be formed on another substrate and integrated with portion 3006.
- programming energy of less than about one picojoule is used to store or write information within portion 3106.
- a 2.5 Volt, 1 ampere battery could support 10 million write and erase operations of a one gigabit memory device.
- Programmable structures and devices and system including the programmable structures described herein are advantageous because the programmable structures require relatively little internal voltage to perform write and erase functions, require relatively little current to perform the write and erase functions, are relatively fast (both write and read operations), require little to no refresh (even for "volatile" memory applications), can be formed in high-density arrays, are relatively inexpensive to manufacture, are robust and shock resistant, and do not require a monocrystalline starting material and can therefore be added to other electronic circuitry.
Abstract
A microelectronic programmable structure suitable for storing information and a method of forming and programming the structure are disclosed. The programmable structure generally includes an ion conductor and a plurality of electrodes. Electrical properties of the structure may be altered by applying energy to the structure, and thus information may be stored using the structure.
Description
MICROELECTRONIC DEVICE, STRUCTURE, AND SYSTEM, INCLUDING
A MEMORY STRUCTURE HAVING A VARIABLE PROGRAMMABLE
PROPERTY AND METHOD OF FORMING THE SAME
FIELD OF THE INVENTION
The present invention generally relates to microelectronic memory devices. More particularly, the invention relates to programmable microelectronic structures having an electrical property that can be variably programmed by manipulating an amount of energy supplied to the structure during a programming function.
BACKGROUND OF THE INVENTION
Memory devices are often used in electronic systems and computers to store information in the form of binary data. These memory devices may be characterized into various types, each type having associated with it various advantages and disadvantages.
For example, random access memory ("RAM") which may be found in personal computers is typically volatile semiconductor memory; in other words, the stored data is lost if the power source is disconnected or removed. Dynamic RAM ("DRAM") is particularly volatile in that it must be "refreshed" (i.e., recharged) every few microseconds in order to maintain the stored data. Static RAM ("SRAM") will hold the data after one writing so long as the power source is maintained; once the power source is disconnected, however, the data is lost. Thus, in these volatile memory configurations, information is only retained so long as the power to the system is not turned off. In general, these RAM devices can take up significant chip, area and therefore may be expensive to manufacture and consume relatively large amounts of energy for data storage. Accordingly, improved memory devices suitable for use in personal computers and the like are desirable.
Other storage devices such as magnetic storage devices (e.g., floppy disks, hard disks and magnetic tape) as well as other systems, such as optical disks, CD-RW and DVD-RW are non-volatile, have extremely high capacity, and can be rewritten many times. Unfortunately, these memory devices are physically large, are shock/vibration-sensitive, require expensive mechanical drives, and may consume relatively large amounts of power. These negative aspects make such memory devices non-ideal for low power portable
applications such as lap-top and palm-top computers, personal digital assistants ("PDAs"), and the like.
Due, at least in part, to a rapidly growing numbers of compact, low-power portable computer systems and hand-held appliances in which stored information changes regularly, low energy read/write semiconductor memories have become increasingly desirable and widespread. Furthermore, because these portable systems often require data storage when the power is turned off, non- volatile storage device are desired for use in such systems.
One type of programmable semiconductor non- volatile memory device suitable for use in such systems is a programmable read-only memory ("PROM") device. One type of PROM, a write-once read-many ("WORM") device, uses an array of fusible links. Once programmed, the WORM device cannot be reprogrammed.
Other forms of PROM devices include erasable PROM ("EPROM") and electrically erasable PROM (EEPROM) devices, which are alterable after an initial programming. EPROM devices generally require an erase step involving exposure to ultra violet light prior to programming the device. Thus, such devices are generally not well suited for use in portable electronic devices. EEPROM devices are generally easier to program, but suffer from other deficiencies. In particular, EEPROM devices are relatively complex, are relatively difficult to manufacture, and are relatively large. Furthermore, a circuit including EEPROM devices must withstand the high voltages necessary to program the device. Consequently, EEPROM cost per bit of memory capacity is extremely high compared with other means of data storage. Another disadvantage of EEPROM devices is that, although they can retain data without having the power source connected, they require relatively large amounts of power to program. This power drain can be considerable in a compact portable system powered by a battery. Various hand-held appliances such as PDA, portable phones, and the like as well as other electronic systems may desirably include multiple forms of memory. For example, an appliance system may include nonvolatile memory such as PROM to store user-specific information, including system instructions and critical data such as unit codes, identification, and user-entered information and also include volatile memory such as SRAM and/or DRAM to store, for example, session-specific information such as web pages and downloaded content such as compressed audio and/or video information. The different forms of memory are typically formed on separate substrates because of different technologies and processing employed to form the various forms of memory. The multiple
forms of memory are coupled together, e.g., through use of another substrate such as a printed circuit board, to integrated the various forms of memory with a digital processor.
Forming the various forms of memory on separate substrates may be undesirable for several reasons. For example, forming various types of memory on separate substrate may be relatively expensive to manufacture, may require relatively long transmission paths to communicate between the memory devices and any associated electronic device, and may take up a relatively large amount of room within a system. Accordingly, memory devices including both volatile and nonvolatile memory and methods of forming the memory devices are desired. Furthermore, this memory technology should meet the requirements ofthe new generation of portable and/or stationary computer devices by operating at a relatively low voltage while providing high speed memory with high storage density and a low manufacturing cost.
SUMMARY OF THE INVENTION
The present invention provides improved microelectronic memory devices, structures, and systems and methods of forming the same. More particularly, the invention provides memory structures that can be variably programmed depending on an amount of energy used to program the device. Such structures can replace both traditional nonvolatile and volatile forms of memory.
The ways in which the present invention addresses various drawbacks of now-known programmable devices are discussed in greater detail below. However, in general, the present invention provides a programmable device that is relatively easy and inexpensive to manufacture, which is relatively easy to program, and which be variably programmed. In accordance with one exemplary embodiment of the present invention, a programmable structure includes an ion conductor and at least two electrodes. The structure is configured such that when a bias is applied across two electrodes, one or more electrical properties of the structure change. In accordance with one aspect of this embodiment, a resistance across the structure changes when a bias is applied across the electrodes. In accordance with other aspects of this embodiment, a capacitance or other electrical property ofthe structure changes upon application of a bias across the electrodes. In accordance with a further aspect of this embodiment, an amount of change in the programmable property is manipulated by altering (e.g., thermally or electrically) an amount of energy used to program
the device. One or more of these electrical changes and/or the amount of change may suitably be detected. Thus, stored information may be retrieved from a circuit including the structure.
In accordance with another exemplary embodiment ofthe invention, a programmable structure includes an ion conductor, at least two electrodes, and a barrier interposed between at least a portion of one of the electrodes and the ion conductor. In accordance with one aspect of this embodiment, the barrier material includes a material configured to reduce diffusion of ions between the ion conductor and at least one electrode. The diffusion barrier may also serve to prevent undesired electrodeposit growth within a portion of the structure. In accordance with another aspect, the barrier material includes an insulating material. Inclusion of an insulating material increases the voltage required to reduce the resistance of the device. In accordance with yet another aspect of this embodiment, the barrier includes material that conducts ions, but which is relatively resistant to the conduction of electrons. Use of such material may reduce undesired plating at an electrode. In accordance with another exemplary embodiment of the invention, a programmable microelectronic structure is formed on a surface of a substrate by forming a first electrode on the substrate, depositing a layer of ion conductor material over the first electrode, and depositing conductive material onto the ion conductor material. In accordance with one aspect of this embodiment, a solid solution including the ion conductor and excess conductive material is formed by dissolving (e.g., via thermal and/or photodissolution) a portion ofthe conductive material in the ion conductor. In accordance with a further aspect, only a portion of the conductive material is dissolved, such that a portion of the conductive material remains on a surface of the ion conductor to form an electrode on a surface of the ion conductor material. In accordance with another embodiment ofthe present invention, at least a portion of a programmable structure is formed within a through-hole or via in an insulating material. In accordance with one aspect of this embodiment, a first electrode feature is formed on a surface of a substrate, insulating material is deposited onto a surface ofthe electrode feature, a via is formed within the insulating material, and a portion ofthe programmable structure is formed within the via. After the via is formed within the insulating material, a portion ofthe structure within the via is formed by depositing an ion conductive material onto the conductive material, depositing a second electrode material onto the ion conductive material, and, if desired, removing any excess electrode, ion conductor, and/or insulating material. In
accordance with another aspect of this embodiment, only the ion conductor is formed within the via. In this case, a first electrode is formed below the insulating material and in contact with the ion conductor and the second electrode is formed above the insulating material and in contact with the ion conductor. The configuration ofthe via may be changed to alter (e.g., reduce) a contact area between one or more of the electrodes and the ion conductor. Reducing the cross-sectional area of the interface between the ion conductor and the electrode increases the efficiency of the device (change in electrical property per amount of power supplied to the device). In accordance with another aspect of this embodiment, the via may extend through the lower electrode to reduce the interface area between the electrode and the ion conductor. In accordance with yet another aspect of this embodiment, a portion of the ion conductor may be removed from the via or the ion conductor material may be directionally deposited into only a portion of the via to further reduce an interface between an electrode and the ion conductor.
In accordance with another embodiment of the invention, a programmable device may be formed on a surface of a substrate. In accordance with one aspect of this embodiment, the substrate includes a microelectronic circuit. In accordance with a further aspect of this embodiment, the memory device is formed overlying the microelectronic circuit and conductive lines between the microelectronic circuit and the memory are formed using conductive wiring schemes within the substrate and the memory device. This configuration allows transmission of more bits of information per bus line.
In accordance with a further exemplary embodiment ofthe invention, multiple bits of information are stored in a single programmable structure. In accordance with one aspect of this embodiment, a programmable structure includes a floating electrode interposed between two additional electrodes. In accordance with yet another embodiment ofthe invention, multiple programmable devices are coupled together using a common electrode (e.g., a common anode or a common cathode).
In accordance with yet a further exemplary embodiment of the present invention, a capacitance of a programmable structure is altered by causing ions within an ion conductor of the structure to migrate.
In accordance with yet another embodiment of the invention, a volatility of a memory cell in accordance with the present invention is manipulated by altering an amount of energy used during a write process for the memory. In accordance with this embodiment
of the invention, higher energy is used to form nonvolatile memory, while lower energy is used to form volatile memory. Thus, a single memory device, formed on a single substrate, may include both nonvolatile and volatile portions. In accordance with a further aspect of this embodiment, the relative volatility of one or more portions of the memory may be altered at any time by changing an amount of energy supplied to a portion of the memory during a write process.
In accordance with a further embodiment of the present invention, an electronic system includes programmable memory including an ion conductor and at least two electrodes. In accordance with one aspect of this embodiment, the memory can be used for apphcations that would typically use non- volatile memory such as PROM and/or volatile memory such as RAM.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete understanding ofthe present invention may be derived by referring to the detailed description and claims, considered in connection with the figures, wherein like reference numbers refer to similar elements throughout the figures, and:
Figure 1 is a cross-sectional illustration of a programmable structure formed on a surface of a substrate in accordance with the present invention; Figure 2 is a cross-sectional illustration of a programmable structure in accordance with an alternative embodiment ofthe present invention;
Figure 3 is a current-voltage diagram illustrating current and voltage characteristics ofthe device illustrated in Figure 2 in an "on" and "off state;
Figure 4 is a cross-sectional illustration of a programmable structure in accordance with yet another embodiment ofthe present invention;
Figure 5 is a schematic illustration of a portion of a memory device in accordance with an exemplary embodiment ofthe present invention;
Figure 6 is a schematic illustration of a portion of a memory device in accordance with an alternative embodiment ofthe present invention; Figures 7 and 8 are cross-sectional illustrations of programmable structures having an ion conductor/electrode contact interface formed about a perimeter of the ion conductor in accordance with another embodiment ofthe present invention;
Figures 9 and 10 are cross-sectional illustrations of programmable structures having an ion conductor/electrode contact interface formed about a perimeter ofthe ion conductor in accordance with yet another embodiment ofthe present invention;
Figures 11 and 12 illustrate a programmable device having a horizontal configuration in accordance with the present invention;
Figures 13-19 illustrate programmable device structures with reduced electrode/ion conductor interface surface area in accordance with the present invention;
Figure 20 illustrates a programmable device with a tapered ion conductor in accordance with the present invention; Figures 21-24 illustrate a programmable device including a floating electrode in accordance with the present invention;
Figures 25-29 illustrate common electrode programmable device structures in accordance with the present invention;
Figure 30 illustrates an internet appliance system in accordance with the present invention; and
Figure 31 illustrates a portion ofthe internet appliance of Figure 30 in greater detail.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments ofthe present invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
The present invention generally relates to microelectronic memory devices and to systems including the devices. More particularly, the invention relates to programmable structures, devices, and systems including memory that can be variably programmed, which is suitable for volatile data storage, nonvolatile data storage, or both forms of data storage.
Figures 1 and 2 illustrate programmable microelectronic structures 100 and 200 formed on a surface of a substrate 110 in accordance with an exemplary embodiment of the present invention. Structures 100 and 200 include electrodes 120 and 130, an ion conductor 140, and optionally include buffer or barrier layers 155 and/or 255.
Generally, structures 100 and 200 are configured such that when a bias greater than a threshold voltage (Vτ), discussed in more detail below, is applied across electrodes 120 and
130, the electrical properties of structure 100 change. For example, in accordance with one embodiment ofthe invention, as a voltage V > VT is applied across electrodes 120 and 130, conductive ions within ion conductor 140 begin to migrate and form an electrodeposit (e.g., electrodeposit 160) at or near the more negative of electrodes 120 and 130; such an electrodeposit, however, is not required to practice the present invention. The term "electrodeposit" as used herein means any area within the ion conductor that has an increased concentration of reduced metal or other conductive material compared to the concentration of such material in the bulk ion conductor material. As the electrodeposit forms, the resistance between electrodes 120 and 130 decreases, and other electrical properties may also change. In the absence of any insulating barriers, which are discussed in more detail below, the threshold voltage required to grow the electrodeposit from one electrode toward the other and thereby significantly reduce the resistance of the device is approximately the redox potential of the system, typically a few hundred millivolts. If the same voltage is applied in reverse, the electrodeposit will dissolve back into the ion conductor and the device will return to a high resistance state. In accordance with other embodiments of the invention, application of an electric field between electrodes 120 and 130 may cause ions dissolved within conductor 140 to migrate and thus cause a change in the electrical properties of device 100, without the formation of an electrodeposit. Structures 100 and 200 may be used to store information and thus may be used in memory circuits. For example, structure 100 or other programmable structures in accordance with the present invention may suitably be used in memory devices to replace DRAM, SRAM, PROM, EPROM, EEPROM devices, or any combination of such memory. In addition, programmable structures of the present invention may be used for other applications where programming or changing of electrical properties of a portion of an electrical circuit are desired.
In accordance with various embodiments of the invention, the volatility of programmable memory (e.g., cell 100 or 200) can be manipulated by altering an amount of energy (e.g., altering time, current, voltage, thermal energy, and/or the like) applied during a write process. In the case where electrodeposit 160 forms during a write process, the greater the amount of energy (having a voltage greater than the threshold voltage for the write process) applied during the write process, the greater the growth of electrodeposit 160 and hence the less volatile the memory. Conversely, relatively volatile memory can be formed by supplying relatively little energy to the cell. Thus, relatively volatile memory can be
formed using the same or similar structures used to form nonvolatile memory, and less energy can be used to form the volatile memory. Use of less energy is particularly desirable in portable electronic devices that depend on stored energy for operation. As discussed in greater detail below, the volatile and nonvolatile memory may be formed on the same substrate and partitioned or separated from each other such that each partition is dedicated to either volatile or nonvolatile memory; or, an array of memory cells may be configured as volatile or nonvolatile memory using programming techniques, such that the configuration (i.e., volatile or nonvolatile) ofthe memory can be altered by changing an amount of energy supplied during programming the respective portions ofthe memory array. Referring again to Figures 1 and 2, substrate 110 may include any suitable material.
For example, substrate 110 may include semiconductive, conductive, semiinsulative, insulative material, or any combination of such materials. In accordance with one embodiment ofthe invention, substrate 110 includes an insulating material 112 and a portion 114 including microelectronic devices formed on a semiconductor substrate. Layers 112 and 114 may be separated by additional layers (not shown) such as, for example, layers typically used to form integrated circuits. Because the programmable structures can be formed over insulating or other materials, the programmable structures of the present invention are particularly well suited for apphcations where substrate (e.g., semiconductor material) space is a premium. In addition, forming a memory cell overlying a microelectronic device may be advantageous because such a configuration allows greater data transfer between an aπ-ay of memory cells and the microelectronic device using, for example, conductive pugs formed within layers 112 and 150.
Electrodes 120 and 130 may be formed of any suitable conductive material. For example, electrodes 120 and 130 may be formed of doped polysilicon material or metal. In accordance with one exemplary embodiment of the invention, one of electrodes
120 and 130 is formed of a material including a metal that dissolves in ion conductor 140 when a sufficient bias (V > VT) is applied across the electrodes (an oxidizable electrode) and the other electrode is relatively inert and does not dissolve during operation of the programmable device (an indifferent electrode). For example, electrode 120 may be an anode during a write process and be comprised of a material including silver that dissolves in ion conductor 140 and electrode 130 may be a cathode during the write process and be comprised of an inert material such as tungsten, nickel, molybdenum, platinum, metal suicides, and the like. Having at least one electrode formed of a material including a metal
which dissolves in ion conductor 140 facilitates maintaining a desired dissolved metal concentration within ion conductor 140, which in turn facilitates rapid and stable electrodeposit 160 formation within ion conductor 140 or other electrical property change during use of structure 100 and/or 200. Furthermore, use of an inert material for the other electrode (cathode during a write operation) facilitates electrodissolution of any electrodeposit that may have formed and/or return ofthe programmable device to an erased state after application of a sufficient voltage.
During an erase operation, dissolution of any electrodeposit that may have formed preferably begins at or near the oxidizable electrode/electrodeposit interface. Initial dissolution of the electrodeposit at the oxidizable electrode/electrodeposit interface may be facilitated by forming structure 100 such that the resistance at the oxidizable electrode/electrodeposit interface is greater than the resistance at any other point along the electrodeposit; particularly, the interface between the electrodeposit and the indifferent electrode. One way to achieve relatively low resistance at the indifferent electrode is to form the electrode of relatively inert, non-oxidizing material such as platinum. Use of such material reduces formation of oxides at the interface between ion conductor 140 and the indifferent electrode as well as the formation of compounds or mixtures of the electrode material and ion conductor 140 material, which typically have a higher resistance than ion conductor 140 or the electrode material.
Relatively low resistance at the indifferent electrode may also be obtained by forming a barrier layer between the oxidizable electrode (anode during a write operation) and the ion conductor, wherein the barrier layer is formed of material having a relatively high resistance. Exemplary high resistance materials include layers (e.g., layer 155) of ion conducting material (e.g., AgxO, AgKS, AgxSe, AgxTe, where x > 2, AgyI, where x > 1,
Cul2, CuO, CuS, CuSe, CuTe, GeO2, GezS].-z, GezSe].-z,
where z is greater than or equal to about 0.33, SiO2, and combinations of these materials) interposed between ion conductor 140 and a metal layer such as silver. Such material layers may also be used as barrier layer 255, as discussed in more detail below. Reliable growth and dissolution of an electrodeposit can also be facilitated by providing a roughened indifferent electrode surface (e.g., a root mean square roughness of greater than about 1 nm) at the electrode/ion conductor interface. The roughened surface may be formed by manipulating film deposition parameters and/or by etching a portion of
one of the electrode of ion conductor surfaces. During a write operation, relatively high electrical fields form about the spikes or peaks of the roughened surface, and thus the electrodeposits are more likely to form about the spikes or peaks. As a result, more reliable and uniform changes in electrical properties for an applied voltage across electrodes 120 and 130 may be obtained by providing a roughed interface between the indifferent electrode (cathode during a write operation) and ion conductor 140.
Oxidizable electrode material may have a tendency to thermally dissolve or diffuse into ion conductor 140, particularly during fabrication and/or operation of structure 100. The thermal diffusion is undesired because it may reduce the resistance of structure 100 and thus reduce the change of an electrical property during use of structure 100.
To reduce undesired diffusion of oxidizable electrode material into ion conductor 140 and in accordance with another embodiment of the invention, the oxidizable electrode includes a metal intercalated in a transition metal sulfide or selenide material such as Aχ(MB2)i-χ, where A is Ag or Cu, B is S or Se, M is a transition metal such as Ta, V, and Ti, and x ranges from about 0.1 to about 0.7. The intercalated material mitigates undesired thermal diffusion ofthe metal (Ag or Cu) into the ion conductor material, while allowing the metal to participate in the electrodeposit growth upon apphcation of a sufficient voltage across electrodes 120 and 130. For example, when silver is intercalated into a TaS2 film, the TaS2 film can include up to about 67 atomic percent silver. The Ax(MB2)ι-x material is preferably amorphous to prevent undesired diffusion of the metal though the material. The amorphous material may be formed by, for example, physical vapor deposition of a target material comprising Ax(MB2)ι-χ. α-Agl is another suitable material for the oxidizable electrode, as well as the indifferent electrode. Similar to the Ax(MB2)ι_χ material discussed above, -Agl can serve as a source of Ag during operation of structure 100 — e.g., upon apphcation of a sufficient bias, but the silver in the Agl material does not readily thermally diffuse into ion conductor 140. Agl has a relatively low activation energy for conduction of electricity and does not require doping to achieve relatively high conductivity. When the oxidizable electrode is formed of Agl, depletion of silver in the Agl layer may arise during operation of structure 100, unless excess silver is provided to the electrode. One way to provide the excess silver is to form a silver layer adjacent the Agl layer as discussed above when Agl is used as a buffer layer. The Agl layer (e.g., layer 155 and/or 255) reduces thermal diffusion of Ag into ion conductor 140, but does not significantly affect conduction of Ag during operation of
structure 100. In addition, use of Agl increases the operational efficiency of structure 100 because the Agl mitigates non-Faradaic conduction (conduction of electrons that do not participate in the electrochemical reaction).
Other materials suitable for buffer layers 155 and/or 255 include GeO2 and SiOx. Amorphous GeO2 is relatively porous an will "soak up" silver during operation of device 100, but will retard the thermal diffusion of silver to ion conductor 140, compared to structures or devices that do not include a buffer layer. When ion conductor 140 includes germanium, GeO2 may be formed by exposing ion conductor 140 to an oxidizing environment at a temperature of about 300 °C to about 800 °C or by exposing ion conductor 140 to an oxidizing environment in the presence of radiation having an energy greater than the band gap ofthe ion conductor material. The GeO may also be deposited using physical vapor deposition (from a GeO2 target) or chemical vapor deposition (from GelL and an O2).
Buffer layers can also be used to increase a "write voltage" by placing the buffer layer (e.g., GeO2 or SiOx) between ion conductor 140 and the indifferent electrode. In this case, the buffer material allows metal such as silver to diffuse though the buffer and take part in the electrochemical reaction.
In accordance with one embodiment of the invention, at least one electrode 120 and 130 is formed of material suitable for use as an interconnect metal. For example, electrode 130 may form part of an interconnect structure within a semiconductor integrated circuit. In accordance with one aspect of this embodiment, electrode 130 is formed of a material that is substantially insoluble in material comprising ion conductor 140. Exemplary materials suitable for both interconnect and electrode 130 material include metals and compounds such as tungsten, nickel, molybdenum, platinum, metal suicides, and the like.
Layers 155 and/or 255 may also include a material that restricts migration of ions between conductor 140 and the electrodes. In accordance with exemplary embodiments of the invention, a barrier layer includes conducting material such as titanium nitride, titanium tungsten, a combination thereof, or the like. The barrier may be electrically indifferent, i.e., it allows conduction of electrons through structure 100 or 200, but it does not itself contribute ions to conduction through structure 200. An electrically indifferent barrier may reduce undesired dendrite growth during operation of the programmable device, and thus may facilitate an "erase" or dissolution of electrodeposit 160 when a bias is applied which is opposite to that used to grow the electrodeposit. In addition, use of a conducting barrier
allows for the "indifferent" electrode to be formed of oxidizable material because the barrier prevents diffusion ofthe electrode material to the ion conductor.
Ion conductor 140 is formed of material that conducts ions upon application of a sufficient voltage. Suitable materials for ion conductor 140 include glasses and semiconductor materials. In one exemplary embodiment ofthe invention, ion conductor 140 is formed of chalcogenide material.
Ion conductor 140 may also suitably include dissolved conductive material. For example, ion conductor 140 may comprise a solid solution that includes dissolved metals and/or metal ions. In accordance with one exemplary embodiment of the invention, conductor 140 includes metal and/or metal ions dissolved in chalcogenide glass. An exemplary chalcogenide glass with dissolved metal in accordance with the present invention includes a solid solution of AsxSι.x-Ag, GexSeι.x-Ag, GexSι-x-Ag, AsxSi.x-Cu, GexSeι.x-Cu, GexSι-x-Cu, GexTeι_x-Ag where x ranges from about 0.1 to about 0.5, other chalcogenide materials including silver, copper, zinc, combinations of these materials, and the like. In addition, conductor 140 may include network modifiers that affect mobility of ions through conductor 140. For example, materials such as metals (e.g., silver), halogens, halides, or hydrogen may be added to conductor 140 to enhance ion mobility and thus increase erase/write speeds ofthe structure.
A sohd solution suitable for use as ion conductor 140 may be formed in a variety of ways. For example, the sohd solution may be formed by depositing a layer of conductive material such as metal over an ion conductive material such as chalcogenide glass and exposing the metal and glass to thermal and/or photo dissolution processing. In accordance with one exemplary embodiment ofthe invention, a sohd solution of As2S3-Ag is formed by depositing As2S3 onto a substrate, depositing a thin film of Ag onto the As2S3j, and exposing the films to hght having energy greater than the optical gap ofthe As2S3,--e.g., hght having a wavelength of less than about 500 nanometers. If desired, network modifiers may be added to conductor 140 during deposition of conductor 140 (e.g., the modifier is in the deposited material or present during conductor 140 material deposition) or after conductor 140 material is deposited (e.g., by exposing conductor 140 to an atmosphere including the network modifier).
In accordance with another embodiment of the invention, a sohd solution may be formed by depositing one of the constituents onto a substrate or another material layer and reacting the first constituent with a second constituent. For example, germanium (preferably
amorphous) may be deposited onto a portion of a substrate and the germanium may be reacted with HzSe to form a Ge-Se glass. Similarly, As can be deposited and reacted with the H2Se gas, or arsenic or germanium can be deposited and reacted with H2S gas. Silver or other metal can then be added to the glass as described above. In accordance with one aspect of this embodiment, a sohd solution ion conductor 140 is formed by depositing sufficient metal onto an ion conductor material such that a portion of the metal can be dissolved within the ion conductor material and a portion of the metal remains on a surface of the ion conductor to form an electrode (e.g., electrode 120). In accordance with alternative embodiments of the invention, solid solutions containing dissolved metals may be directly deposited onto substrate 110 and the electrode then formed overlying the ion conductor.
An amount of conductive material such as metal dissolved in an ion conducting material such as chalcogenide may depend on several factors such as an amount of metal available for dissolution and an amount of energy applied during the dissolution process. However, when a sufficient amount of metal and energy are available for dissolution in chalcogenide material using photodissolution, the dissolution process is thought to be self limiting, substantially halting when the metal cations have been reduced to their lowest oxidation state. In the case of As2S3-Ag, this occurs at Ag4As2S3 = 2Ag2S + AS2S, having a silver concentration of about 44 atomic percent. If, on the other hand, the metal is dissolved in the chalcogenide material using thermal dissolution, a higher atomic percentage of metal in the solid solution may be obtained, provided a sufficient amount of metal is available for dissolution.
In accordance with a further embodiment of the invention, the sohd solution is formed by photodissolution to form a macrohomogeneous ternary compound and additional metal is added to the solution using thermal diffusion (e.g., in an inert environment at a temperature of about 85 °C to about 150 °C) to form a sohd solution containing, for example, about 30 to about 50, and preferably about 34 atomic percent silver. Ion conductors having a metal concentration above the photodissolution solubility level facilitates formation of electrodeposits that are thermally stable at operating temperatures (typically about 85 °C to about 150 °C) of devices 100 and 200. Alternatively, the solid solution may be formed by thermally dissolving the metal into the ion conductor at the temperature noted above; however, sohd solutions formed exclusively from photodissolution
are thought to be less homogeneous than films having similar metal concentrations formed using photodissolution and thermal dissolution.
Ion conductor 140 may also include a filler material, which fills interstices or voids. Suitable filler materials include non-oxidizable and non-silver based materials such as a non- conducting, immiscible silicon oxide and/or silicon nitride, having a cross-sectional dimension of less than about 1 nm, which do not contribute to the growth of an electrodeposit. In this case, the filler material is present in the ion conductor at a volume percent of up to about 5 percent to reduce a likelihood that an electrodeposit will spontaneously dissolve into the supporting ternary material as the device is exposed to elevated temperature, which leads to more stable device operation without compromising the performance ofthe device. Ion conductor 140 may also include filler material to reduce an effective cross-sectional area of the ion conductor. In this case, the concentration of the filler material, which may be the same filler material described above but having a cross- sectional dimension up to about 50 nm, is present in the ion conductor material at a concentration of up to about 50 percent by volume. The filler material may also include metal such as silver or copper to fill the voids in the ion conductor material.
In accordance with one exemplary embodiment of the invention, ion conductor 140 includes a germanium-selenide glass with silver diffused in the glass. Germanium selenide materials are typically formed from selenium and Ge(Se) /2 tetrahedra that may combine in a variety of ways. In a Se-rich region, Ge is 4-fold coordinated and Se is 2-fold coordinated, which means that a glass composition near Geo.2oSe0.8o will have a mean coordination
. number of about 2.4. Glass with this coordination number is considered by constraint counting theory to be optimally constrained and hence very stable with respect to
, devitrification. The network in such a glass is known to self-organize and become stress- free, making it easy for any additive, e.g., silver, to finely disperse and form a mixed-glass sohd solution. Accordingly, in accordance with one embodiment of the invention, ion conductor 140 includes a glass having a composition of Ge0.i7Se0.83 to Geo.25Seo.75.
The composition and structure of ion conductor 140 material often depends on the starting or target material used to form the conductor. Generally, it is desired to form a homogenous material layer for conductor 140 to facilitate rehable and repeatable device performance.
In accordance with one exemplary embodiment ofthe invention, at least a portion of structure 100 is formed within a via of an insulating material 150. Forming a portion of
structure 100 within a via of an insulating material 150 may be desirable because, among other reasons, such formation allows relatively small structures, e.g., on the order of 10 nanometers, to be formed. In addition, insulating material 150 facilitates isolating various structures 100 from other electrical components. Insulating material 150 suitably includes material that prevents undesired diffusion of electrons and/or ions from structure 100. In accordance with one embodiment of the invention, material 150 includes silicon nitride, silicon oxynitride, polymeric materials such as polyimide or parylene, or any combination thereof.
A contact 165 may suitably be electrically coupled to one or more electrodes 120, 130 to facilitate forming electrical contact to the respective electrode. Contact 165 may be formed of any conductive material and is preferably formed of a metal, alloy, or composition including aluminum, tungsten, or copper.
In accordance with one embodiment of the invention, structure 100 is formed by forming electrode 130 on substrate 110. Electrode 130 may be formed using any suitable method such as, for example, depositing a layer of electrode 130 material, patterning the electrode material, and etching the material to form electrode 130. Insulating layer 150 may be formed by depositing insulating material onto electrode 130 and substrate 110 and forming vias in the insulating material using appropriate patterning and etching processes. Ion conductor 140 and electrode 120 may then be formed within insulating layer 150 by depositing ion conductor 140 material and electrode 120 material within the via. Such ion conductor and electrode material deposition may be selective - i.e., the material is substantially deposited only within the via, or the deposition processes may be relatively non-selective. If one or more non-selective deposition methods are used, any excess material remaining on a surface of insulating layer 150 may be removed using, for example, chemical mechanical pohshing and/or etching techniques. Barrier layers 155 and/or 255 may similarly be formed using any suitable deposition and/or etch processes.
Information may be stored using programmable structures ofthe present invention by manipulating one or more electrical properties ofthe structures. For example, a resistance of a structure may be changed from a "0" or off state to a "1" or on state during a suitable write operation. Similarly, the device may be changed from a "1" state to a "0" state during an erase operation. In addition, as discussed in more detail below, the structure may have multiple programmable states such that multiple bits of information are stored in a single structure.
WRITE OPERATION
Figure 3 illustrates current- oltage characteristics of a programmable structure (e.g. structure 200) in accordance with the present invention. In the illustrated embodiment, via diameter, D, is about 4 microns, conductor 140 is about 35 nanometers thick and formed of
Ge3Se7-Ag (near Ag8Ge3Se7), electrode 130 is indifferent and formed of nickel, electrode
120 is formed of silver, and barrier 255 is a native nickel oxide. As illustrated in Figure 3, current through structure 200 in an off state (curve 310) begins to rise upon application of a bias of over about one volt; however, once a write step has been performed (i.e., an electrodeposit has formed), the resistance through conductor 140 drops significantly (i.e., to about 200 ohms), illustrated by curve 320 in Figure 3. As noted above, when electrode 130 is coupled to a more negative end of a voltage supply, compared to electrode 120, an electrodeposit begins to form near electrode 130 and grow toward electrode 120. An effective threshold voltage (i.e., voltage required to cause growth ofthe electrodeposit and to break through barrier 255, thereby couphng electrodes 320, 330 together) is relatively high because of barrier 255. In particular, a voltage Y≥Vj must be applied to structure 200 sufficient to cause electrons to tunnel through barrier 255 (when barrier 255 comprises an insulating layer) to form the electrodeposit and to overcome the barrier (e.g., by tunneling through or leakage) and conduct through conductor 140 and at least a portion of barrier 255. In accordance with alternate embodiments of the invention, where no insolating barrier layer is present, an initial "write" threshold voltage is relatively low because no insulative barrier is formed between, for example, ion conductor 140 and either of the electrodes 120, 130.
As noted above, the relative volatility of the memory structures of the present invention may be altered by applying different amounts of energy to the structures during a write process. For example, a relatively high current pulse of a few hundred microamperes for a period of about several hundred nanoseconds may be applied to the structures illustrated in Figures 1 and 2 to form a relatively nonvolatile memory cell. Alternatively, the same current may be supplied to the same or similar memory structure for a shorter amount of time, e.g., several nanoseconds to form a relatively volatile memory structure. In either case, the memory of the present invention can be programmed at relatively high speeds and even the "volatile" memory is relatively nonvolatile compared to traditional DRAM. For
example, the volatile memory may operate at speed comparable to DRAM and only require refreshing every several hours.
READ OPERATION A state of a memory cell (e.g., 1 or 0) may be read, without significantly disturbing the state, by, for example, applying a forward or reverse bias of magnitude less than a voltage threshold (about 1.4 V for a structure illustrated in Figure 3) for electrodeposition or by using a current limit which is less than or equal to the minimum programming current (the current which will produce the highest ofthe on resistance values). A current limited (to about 1 milliamp) read operation is shown in Figure 3. In this case, the voltage is swept from 0 to about 2 V and the current rises up to the set limit (from 0 to 0.2 V), indicating a low resistance (ohmic/linear current- voltage) "on" state. Another way of performing a non- disturb read operation is to apply a pulse, with a relatively short duration, which may have a voltage higher than the electrochemical deposition threshold voltage such that no appreciable Faradaic current flows, i.e., nearly all the current goes to polarizing/charging the device and not into the electrodeposition process.
ERASE OPERATION
A programmable structure (e.g., structure 200) may suitably be erased by reversing a bias apphed during a write operation, wherein a magnitude of the applied bias is equal to or greater than the threshold voltage for electrodeposition in the reverse direction. In accordance with an exemplary embodiment of the invention, a sufficient erase voltage
(V>Vτ) is applied to structure 200 for a period of time, which depends on energy supphed during the write operation, but is typically less than about 1 millisecond to return structure 200 to its "off' state having a resistance well in excess of a milhon ohms. In cases where the programmable structure does not include a barrier between conductor 140 and electrode 120, a threshold voltage for erasing the structure is much lower than a threshold voltage for writing the structure because, unlike the write operation, the erase operation does not require electron tunneling through a barrier or barrier breakdown.
CONTROL OF OPERATIONAL PARAMETERS The concentration of conductive material in the ion conductor can be controlled by applying a bias across the programmable device. For example, metal such as silver may be
taken out of solution by applying a negative voltage in excess of the reduction potential of the conductive material. Conversely, conductive material may be added to the ion conductor (from one of the electrodes) by applying a bias in excess of the oxidation potential of the material. Thus, for example, if the conductive material concentration is above that desired for a particular device apphcation, the concentration can be reduced by reverse biasing the device to reduce the concentration of the conductive material. Similarly, metal may be added to the solution from the oxidizable electrode by applying a sufficient forward bias. Additionally, it is possible to remove excess metal build up at the indifferent electrode by applying a reverse bias for an extended time or an extended bias over that required to erase the device under normal operating conditions. Control of the conductive material may be accomplished automatically using a suitable microprocessor.
This technique may also be used to form one of the electrodes from material within the ion conductor material. For example, silver from the ion conductor may be plated out to form the oxidizable electrode. This allows the oxidizable electrode to be formed after the device is fully formed and thus mitigates problems associated with conductive material diffusing from the oxidizable electrode during manufacturing ofthe device.
As noted above, in accordance with yet another embodiment of the invention, multiple bits of data may be stored within a single programmable structure by controlling an amount of electrodeposit which is formed during a write process. An amount of electrodeposit that forms during a write process depends on a number of coulombs or charge supplied to the structure during the write process, and may be controlled by using a current limit power source. In this case, a resistance of a programmable structure is governed by Equation 1, where Ron is the "on" state resistance, Vr is the threshold voltage for electrodeposition , and IUM is the maximum current allowed to flow during the write operation.
Vτ
Ron —
ILIM
Equation 1
In practice, the limitation to the amount of information stored in each cell will depend on how stable each of the resistance states is with time. For example, if a structure
with a programmed resistance range of about 3.5 kΩ and a resistance drift over a specified time for each state is about ±250 Ω, about 7 equally sized bands of resistance (7 states) could be formed, allowing 3 bits of data to be stored within a single structure. In the limit, for near zero drift in resistance in a specified time limit, information could be stored as a continuum of states, i.e., in analog form.
A portion of an integrated circuit 402, including a programmable structure 400, configured to provide additional isolation from electronic components is illustrated in Figure 4. In accordance with an exemplary embodiment of the present invention, structure 400 includes electrodes 420 and 430, an ion conductor 440, a contact 460, and an amorphous silicon diode 470, such as a Schottky or p-n junction diode, formed between contact 460 and electrode 420. Rows and columns of programmable structures 400 may be fabricated into a high density configuration to provide extremely large storage densities suitable for memory circuits. In general, the maximum storage density of memory devices is limited by the size and complexity of the column and row decoder circuitry. However, a programmable structure storage stack can be suitably fabricated overlying an integrated circuit with the entire semiconductor chip area dedicated to row/column decode, sense amplifiers, and data management circuitry (not shown) since structure 400 need not use any substrate real estate. In this manner, storage densities of many gigabits per square centimeter can be attained using programmable structures of the present invention. Utilized in this manner, the programmable structure is essentiaUy an additive technology that adds capability and functionality to existing semiconductor integrated circuit technology.
Figure 5 schematically illustrates a portion of a memory device including structure 400 having an isolating p-n junction 470 at an intersection of a bit line 510 and a word line 520 of a memory circuit. Figure 6 illustrates an alternative isolation scheme employing a transistor 610 interposed between an electrode and a contact of a programmable structure located at an intersection of a bit hne 610 and a word line 620 of a memory device.
Figures 7-10 illustrate programmable devices in accordance with another embodiment ofthe invention. The devices illustrated in Figures 7-10 have an electrode (e.g., the cathode during a write process) with a smaller cross sectional area in contact with the ion conductor compared to the devices illustrated in Figures 1-2 and 4. The smaller electrode interface area is thought to increase the efficiency and endurance of the device because an increased percentage of ions in the sohd solution are able to take part in the electrodeposit
formation process. Thus any cathode plating from ions that do not participate in the electrodeposit process is reduced.
Figures 7 and 8 illustrate a cross sectional and a top cut-away view of a programmable device 700 including an indifferent electrode 710, an oxidizable electrode 720, and an ion conductor 730 formed overlying an insulating layer 740 such as silicon oxide, silicon nitride, or the like.
Structure 700 is formed by depositing an indifferent electrode material layer and an insulating layer 750 overlying insulating layer 740. A via is then formed through layer 750 and electrode material layer 710, using an anisotropic etch process (e.g., reactive ion etching or ion milling) such that the via extends to and or through a portion of layer 740. The via is then filled with ion conductor material and is suitably doped to form a sohd solution as described herein. Any excess ion conductor material is removed from the surface of layer 750 and electrode 730 is formed, for example using a deposition and etch process. In this case, the indifferent electrode (cathode during write process) area in contact with ion conductor 730 is the surface area of electrode 710 about the perimeter of conductor 730, rather than the area underlying the ion conductor, as illustrated in Figures 1-2 and 4.
Figures 9 and 10 illustrate a programmable device 900 having an indifferent electrode 910, an oxidizable electrode 920, an ion conductor 930 and insulating layers 940 and 950 in accordance with yet another embodiment of the invention. Structure 900 is similar to structure 700, except that once a via is formed through layer 950, an isotropic etch process (e.g., chemical or plasma) is employed to form the via through electrode 910, such that a sloped intersection between an ion conductor 930 and electrode 910 is formed.
Figures 11 and 12 illustrate another programmable device 1100, with a reduced electrode/ion conductor interface, in accordance with the present invention. Structure 1100 includes electrodes 1110 and 1120 and an ion conductor 1130, formed on a surface of an insulating material 1140, rather than within a via as discussed above. In this case, the programmable structure is formed by defining an ion conductor 1130 pattern on a surface of insulating material 1140 (e.g., using deposition and etch techniques) and forming electrodes 1110 and 1120, such that the electrodes each contact a portion of the ion conductor. In the case of the illustrated embodiment, the electrodes are formed overlying and in contact with both a portion of the ion conductor and the insulating material. Although the thickness of the layers may be varied in accordance with specific applications ofthe device, in a preferred embodiment ofthe invention, the thickness ofthe ion conductor and electrode films is about
1 nmto about 100 nm. Sub-lithographic lateral dimensions of portions ofthe device may be obtained by overexposing photoresist used to pattern the portions and/or over etching the film layer.
Figure 13 illustrates a device 1300 in accordance with yet another embodiment ofthe invention. Structure 1300 is similar to the devices illustrated in Figures 7 and 8, except that the cross-sectional area ofthe ion conductor that is in contact with the electrodes is reduced by filling a portion of a via with non-ion conductor material, rather than etching through an electrode layer.
Structure 1300 includes electrodes 1310 and 1320 and an ion conductor 1330 formed within an insulating layer 1340. In this case, ion conductor 1330 is formed by creating a trench within insulating layer 1340, the trench having a diameter indicated by D2. The trench is then filled using, for example, interference lithography techniques or conformally lining the via with insulating material and using an anisotropic etch process to remove some ofthe insulating material, leaving a via with a diameter of D3. Structure 1300 formed using this technique may have a ion conductor cross sectional area as small as about 10 nm in contact with electrodes 1310 and 1320.
Figures 14-17 illustrate another embodiment of the invention, where the cross sectional area of the ion conductor/electrode interface is relatively small. Structure 1400, illustrated in Figure 14, includes electrodes 1410 and 1420 and an ion conductor 1430. Structure 1400 is formed in a manner similar to structure 700, except that the ion conductor material is deposited conformally, using, for example, chemical vapor deposition or physical vapor deposition, into a trench, and the trench is not filled with the ion conductor material.
Structure 1500 is similar to structure 1400, except that an ion conductor 1530 is formed by etching a portion of ion conductor 1430, such that a via 1540 is formed through to electrode 1410. Structure 1600 is similar to structure 1500 and is formed by conformally depositing the ion conductor material as described above and then removing the ion conductor material from a surface of insulating material 1450 prior to depositing electrode 1420 material. Finally, structure 1700 may be formed by selectively deposing the ion conductor 1730 material into only a portion ofthe trench formed in insulating material 1450 (e.g., using angled deposition and/or shadowing techniques), removing any excess ion conductor material on the surface of insulator 1450, and forming an electrode 1720 overlying the insulator and in contact with ion conductor 1730.
Figures 18 and 19 illustrate yet another embodiment of the invention, where a pillar or wall within a trench is used to reduce a cross-sectional area of the interface between the ion conductor and one or more electrodes. Structure 1800, illustrated in Figure 18, includes electrodes 1810 and 1820 and an ion conductor 1830 formed within an insulating layer 1840. In addition, structure 1800 includes a pillar 1850 of insulating material (e.g., insulating material used to form layer 1840), formed within a trench within layer 1840. Structure 1800 may be formed using the shadowed deposition technique discussed above. Structure 1900 is similar to structure 1800, except structure 1900 includes a partial pillar 1950 and an ion conductor 1930, which fills the remaining portion ofthe formed trench. Figure 20 illustrates yet another structure 2000 in accordance with the present invention. Structure 2000 includes electrodes 2010 and 2020 and an ion conductor 2030 formed within an insulating layer 2040. Structure 2000 is formed using an anisotropic or a combination of an anisotropic and an isotropic etch processes to form a tapered via. Ion conductor 2030 is then formed within the trench using techniques previously described. Figures 21-24 illustrate programmable devices in accordance with yet another embodiment of the invention. The structures illustrated in Figures 21-24 include a floating electrode, which allows multiple bits of information to be stored within a single programmable device.
Structure 2100 includes a first electrode 2110, a second, floating electrode 2120, a third electrode 2130, ion conductor portions 2140 and 2150, which may all be formed on a substrate or wholly or partially formed within a via as described above. Although structure 2100 is illustrated in a vertical configuration, the structure may be formed in a horizontal configuration, similar to structure 1100. In accordance with one aspect of this embodiment, the first and third electrodes are formed of an indifferent electrode material and the second electrode is formed of an oxidizable electrode material. Alternatively, the first and third electrodes may be formed of oxidizable electrode material and the second, floating electrode may be formed of an indifferent electrode material. In either case, the structure includes two "half cells," where each half cell functions as a programmable device described above in connection with Figure 1. Each half cell is preferably configured such that the resistance of one half cell differs from the resistance ofthe other half cell when both cells are in an erased state.
In the case when floating electrode 2120 is formed of oxidizable electrode material, bits of data may be stored as follows. The overall impedance of structure 2100 is
approximately equal to the resistance of portions 2140 and 2150. When no electrodeposit is formed within either portion, this high resistance state may be represented by the state 00. When a voltage is applied to structure 2100, such that electrode 2130 is positive relative to electrode 2110 and the applied bias is greater than the threshold voltage required to form an electrodeposit in portion 2140, an electrodeposit 2160 will form through conductor portion 2140 from electrode 2110 toward floating electrode 2120 as illustrated in Figure 22. Under this condition, an electrodeposit will not form within conductor portion 2150 because portion 2150 is under a reverse bias condition and thus will not support growth of an electrodeposit. The growth of the electrodeposit will change the impedance of portion 2140 fromZi to Zi', thus changing the overall impedance of structure 2100, which may be represented by the state 01. The current level used to form electrodeposit 2160 should be selected such that it is sufficiently low, allowing the electrodeposit to be dissolved upon application of a sufficient reverse bias. A third state may be formed by reversing the polarity ofthe applied bias across electrodes 2110 and 2130, such that most of the voltage drop occurs across the high resistance ion conductor portion 2150 and formation of an electrodeposit 2170 begins, as illustrated in Figure 23, without causing electrodeposit 2160 to dissolve. The impedance of portion 2150 changes fromZ2 to Z2', and the overall impedance of structure 2100 is Zi' plus Z2', which may be represented by the state 11. Once both half cells are in the write state, electrodeposit 2160 and/or 2170 may be dissolved by applying a sufficient bias across one or both of the half cells. Electrodeposit 2170 can be erased, for example, by sufficiently negatively biasing electrode 2130 with respect to electrode 2110, which may be represented by a state 00. The four possible states, along with the current limit used to form the state, are represented in table 1 below.
Table 1
Structure 2100 can be changed to 11 from state 10 by applying a low current limit bias to grow electrodeposit 2150 in portion 2140. Similarly, structure 2100 can be changed from state 11 to state 01 by dissolving electrodeposit 2170 by applying a relatively high current limit bias such that upper electrode 2130 is positive with respect to lower electrode 2110. Finally, structure 2100 can be returned to state 00 using a short current pulse to thermally dissolve electrodeposit 2160, using a current which is high enough to cause localized heating of the electrodeposit. This will increase the metal concentration in the half-cell but this excess metal can be removed electrically from the cell by plating it back onto the floating electrode. This sequence is summarized in table 2 below.
Table 2 Other write and erase sequences are also possible (as are other definitions of the various states represented by the half-cell impedances). For example, it is possible to go from state 00 to either state 01 or state 10, depending on the write polarity chosen. Similarly, it is possible to go from state 11 to either state 10 or state 01. It is also possible to go from state 11 to state 00 by the application of a current pulse (in either direction) which is high and short enough to thermally dissolve the electrodeposits in both half-cells simultaneously. In addition to storing information in digital form, structure 2100 can also be used as a noise-tolerant, low energy anti-fuse element for use in field programmable gate arrays (FPGAs) and field configurable circuits and systems. Most physical anti-fuse technologies require large currents and voltages to make a permanent connection. The need for such high energy state-switching stimuli is generally considered to be somewhat beneficial as this reduces the likelihood ofthe anti-fuse accidentally forming a connection in electrically noisy situations. However, the use of high voltages and large currents on chip represent a significant problem as all components in the programming circuits are typically sized accordingly and the high energy consumption reduces battery life in portable systems.
Figures 25-29 illustrate structures in accordance with another embodiment of the invention in which multiple programmable devices include a common electrode (e.g., the devices share a common anode or cathode). Forming structures in which multiple structures share a common electrode is advantageous because such structures allow a higher density of cells to be formed on a given substrate surface area.
Figures 25 and 26 illustrate a structure 2500, having a horizontal configuration and a common electrode. Structure 2500 includes an electrical connector 2510 coupled to a common surface electrode 2520, electrodes 2530 and 2540, and ion conductor portions 2550 and 2560 overlying an insulating layer 2170. Structure 2500 may be used to form word and bit lines as described above by forming a row of electrodes (e.g., anodes) coupled to conductor 2510, and columns of oppositely bias electrodes (e.g., cathodes) running perpendicular to electrodes 2520. A conductive plug, formed of any suitably conducting material, can be used to electrically couple electrode 2520 to conductor 2510. Although illustrated with a horizontal configuration, common electrode structures in accordance with this embodiment may be formed using structures having a vertical configuration as described herein.
Figures 27 and 28 illustrate additional structures 2700 and 2800 having a common electrode shared between two or more devices Structures 2700 and 2800 include a common electrode, electrodes 2720 and 2725, ion conductors 2730, 2735 and 2830, 2835 respectively, and insulating layers 2740 and 2750. Structures 2700 and 2800 may be formed using techniques described above in connection with Figures 15 and 16 — e.g., by conformally depositing ion conductor material within a trench of an insulating layer. In accordance with another embodiment ofthe invention, directional deposition may be used to form a structure similar to structure 1700. Structures 2700 and 2800 each include two programmable devices including common electrode 2710, an ion conductor (e.g., conductor 2735), and another electrode (e.g., electrode 2725). Dielectric material 2750 is an insulating material that does not interfere with surface electrodeposit growth, such as silicon oxides, silicon nitrides, and the like.
Figure 29 illustrates a structure 2900 including multiple programmable devices 2902- 2916 formed about a common electrode 2920. Each of the devices 2902-2916 may be formed using the method described above in connection with Figure 21. In the embodiment illustrated in Figure 29, each of electrodes 2930-2936 and 2938-2944 may be coupled together in a direction perpendicular to the direction of common electrode 2920, such that
electrode 2920 forms a bit line and electrodes 2930-2936 and electrodes 2938-2944 form word lines. Structure 2900 may operate and be programmed in a manner similar to structure 2100 described above.
In accordance with other embodiments of the present invention, a programmable structure or device stores information by storing a charge as opposed to growing an electrodeposit. A capacitance of a structure or device is altered by applying a bias across electrodes of the device such that positively charged ions migrate toward one of the electrodes. If the applied bias is less that a write threshold voltage, no short will form between the electrodes. Capacitance ofthe structure changes as a result ofthe ion migration. When the applied bias is removed, the metal ions tend to diffuse away from the electrode or a barrier proximate the electrode. However, an interface between an ion conductor and a barrier is generally imperfect and includes defects capable of trapping ions. Thus, at least a portion of ions remain at or proximate an interface between a barrier and an ion conductor. If a write voltage is reversed, the ions may suitably be dispersed away from the interface. A programmable structure in accordance with the present invention may be used in many applications which would otherwise utilize traditional technologies such as EEPROM, FLASH or DRAM. Advantages provided by the present invention over present memory techniques include, among other things, lower production cost and the ability to use flexible fabrication techniques which are easily adaptable to a variety of applications. The programmable structures ofthe present invention are especially advantageous in applications where cost is the primary concern, such as smart cards and electronic inventory tags. Also, an ability to form the memory directly on a plastic card is a major advantage in these applications as this is generally not possible with other forms of semiconductor memories.
Further, in accordance with the programmable structures of the present invention, memory elements may be scaled to less than a few square microns in size, the active portion of the device being less than on micron. This provides a significant advantage over traditional semiconductor technologies in which each device and its associated interconnect can take up several tens of square microns.
Figures 30 and 31 illustrate one application for which programmable structures in accordance with the present invention are particularly well suited. Figure 30 illustrates an internet appliance 3000, which may be in the form of a computer, a personal digital assistant, a portable telephone, or the hke. As illustrated, system 3000 includes an internet connection 3002, a physical interface and logic portion 3004, a data processing and control portion
3006, a user interface 3008, a data buffer portion 3010, and data storage portion 3012. Portions 3002-3004 and 3008-3010 of system 3000 may include portions of an internet appliance as now known and therefore further description of these portions is not provided herein. Systems such as system 3000 in accordance with the present invention may either be portable or stationary appliances.
Figure 31 illustrates a portion of system 3000 in greater detail. As illustrated in Figure 31 and in accordance with one embodiment of the invention, data storage portion 3012 is formed using the programmable structures as described herein. Storage portion 3012 may suitably include a first memory portion 3106, including relatively volatile memory (to replace e.g., RAM type memory that would otherwise be used in such a system), and a second portion 3104 including relatively nonvolatile memory (to replace ROM type memory that would otherwise be used in such a system). In accordance with the illustrated embodiment, portions 3104 and 3106 may be formed on a single substrate and formed using the same or similar programmable structures. In accordance with one aspect of this embodiment, portion 3104 and portion 3106 are formed on separate portions on a substrate and are dedicated to storing relatively nonvolatile and volatile information, respectively. In this case, portion 3104 may suitably include larger scale drivers and/or conductive traces to supply the greater amount of energy, and need not include any erase circuitry. In accordance with another embodiment of the invention, portions 3104 and 3106 may form part of an integrated array of programmable structures and the relative volatility of information stored in portions 3104 and 3106 may be governed by software capable of manipulating an amount of energy supplied to various programmable structures. In this case, the relative volatility of the memory may be altered during operation of system 3000, depending on such factors as the specific apphcation performed by the appliance. Storage for various forms of information may be selected as desired and allocated using appropriate programming. In accordance with one embodiment ofthe invention, long- term storage, e.g., portion 3104, is used to store information such as user specific information, including certain system instructions that are intended to be upgradeable and therefore not typically within ROM portion 3102, and other information such as unit codes and identification as well as user-entered information. In this case, short term information storage is used to store information that is more session specific such as stored web pages and downloaded content.
In addition, programmable structures as described herein may be used to form ROM memory 3102. In this case, the memory may be monohthically formed on the same substrate used to form data processing and control portion 3006, either directly or on the same substrate or formed overlying the integrated circuit comprising portion 3006, or may be formed on another substrate and integrated with portion 3006.
In accordance with one particular aspect of this embodiment, programming energy of less than about one picojoule is used to store or write information within portion 3106. In this case, a 2.5 Volt, 1 ampere battery could support 10 million write and erase operations of a one gigabit memory device. Programmable structures and devices and system including the programmable structures described herein are advantageous because the programmable structures require relatively little internal voltage to perform write and erase functions, require relatively little current to perform the write and erase functions, are relatively fast (both write and read operations), require little to no refresh (even for "volatile" memory applications), can be formed in high-density arrays, are relatively inexpensive to manufacture, are robust and shock resistant, and do not require a monocrystalline starting material and can therefore be added to other electronic circuitry.
Although the present invention is set forth herein in the context of the appended drawing figures, it should be appreciated that the invention is not limited to the specific form shown. For example, while the programmable structure is conveniently described above in connection with programmable memory devices, the invention is not so limited; the structure of the present invention may additionally or alternatively be employed as programmable active or passive devices within a microelectronic circuit. Furthermore, although only some of the devices are illustrated as including buffer, barrier, or transistor components, any of these components may be added to the devices of the present invention. Various other modifications, variations, and enhancements in the design and arrangement of the method and apparatus set forth herein, may be made without departing from the spirit and scope of the present invention as set forth in the appended claims.
Claims
1. An array of programmable memory structures comprising: a plurality of first programmable structures suitable for storing information, wherein each first programmable structure comprises a first ion conductor formed of an ion conductive material and conductive ions, a first oxidizable electrode proximate the ion conductor, and a first indifferent electrode proximate the ion conductor; and a plurality of second programmable structures suitable for storing information, wherein each second programmable structure comprises a second ion conductor formed of an ion conductive material and conductive ions, a second oxidizable electrode proximate the ion conductor, and a second indifferent electrode proximate the ion conductor.
2. The array of programmable memory structures of claim 1, further comprising a buffer layer between the first oxidizable electrode and the first ion conductor.
3. The array of programmable memory structures of claim 2, wherein the buffer layer comprises a material selected from the group consisting of AgxO, AgxS, AgxSe, AgxTe, where x > 2, Agyl, where y > 1, Cul2, CuO, CuS, CuSe, CuTe, GeO2,SiO2, GezSi.z, GtezSei. z, GezTe1.z, where z is greater than or equal to about 0.33, and combinations thereof.
4. The array of programmable memory structures of claim 1, further comprising a buffer layer between the second oxidizable electrode and the second ion conductor.
5. The array of programmable memory structures of claim 4, wherein the buffer layer comprises a material selected from the group consisting of AgxO, AgxS, AgxSe, AgxTe, where x > 2, Agyl, where y > 1, Cul2, CuO, CuS, CuSe, CuTe, GeO2, SiO2, GezSi.z,
GezSei.z, GezTe^, where z is greater than or equal to about 0.33, and combinations thereof.
6. The array of programmable memory structures of claim 1, wherein the first indifferent electrode and the second indifferent electrode comprise platinum.
7. The array of programmable memory structures of claim 1, wherein the first oxidizable electrode and the second oxidizable electrode comprise excess silver.
8. The array of programmable memory structures of claim 1, wherein the first ion conductor comprises a sohd solution selected from the group consisting of AsxSi.x-Ag, GexSeι.x-Ag, GexSi.x-Ag, AsxSι.x-Cu, 
GeχSi-χ-Cu, GexTeι.x-Ag and combinations thereof, where x ranges from about 0.1 to about 0.5.
9. The array of programmable memory structures of claim 1, wherein the second ion conductor comprises a solid solution selected from the group consisting of AsxS^x-Ag, GexSei.x-Ag, GexSi.χ-Ag, AsxSι.χ-Cu, GexSeι.x-Cu, GexSι.χ-Cu, GexTeι.x-Ag and combinations thereof, where x ranges from about 0.1 to about 0.5.
10. The array of programmable memory structures of claim 1, wherein the first ion conductor comprises a glass having a composition of Ge0.ι7Seo.83 to Geo.2sSeo.75.
11. The aπ-ay of programmable memory structures of claim 1 , wherein the second ion conductor comprises a glass having a composition of Ge0.ι7Seo.83 to Geo.25Seo.75.
12. The array of programmable memory structures of claim 11, wherein the first ion conductor and the second ion conductor further comprise up to about 67 atomic percent silver.
13. The aιτay of programmable memory structures of claim 1, further comprising a transistor in contact with one ofthe first oxidizable or the first indifferent electrodes.
14. The array of programmable memory structures of claim 1, further comprising a transistor in contact with one ofthe second oxidizable or the second indifferent electrodes.
15. The array of programmable memory structures of claim 1, further comprising a diode in contact with one ofthe first oxidizable or the first indifferent electrodes.
16. The array of programmable memory structures of claim 1, further comprising a diode in contact with one ofthe second oxidizable or the second indifferent electrodes.
17. The array of programmable memory structures of claim 1, further comprising a baπier layer between the first indifferent electrode and the first ion conductor.
18. The aπay of programmable memory structures of claim 17, wherein the barrier layer comprises a material selected from the group consisting of AgxO, AgxS, AgxSe,
AgxTe, where x > 2, Agyl, where y > 1, Cul2, CuO, CuS, CuSe, CuTe, GeO2, SiO2, GezSi.z, GezSeι.z, GβzTei.z, where z is greater than or equal to about 0.33, and combinations thereof.
19. The array of programmable memory structures of claim 17, wherein the baπier layer comprises a conductive material.
20. The aπay of programmable memory structures of claim 17, wherein the baπier layer comprises an insulating material.
21. The aπay of programmable memory structures of claim 1, further comprising a baπier layer between the second indifferent electrode and the second ion conductor.
22. The array of programmable memory structures of claim 21, wherein the baπier layer comprises a material selected from the group consisting of AgxO, AgxS, AgxSe,
AgxTe, where x > 2, AgyI, where y > 1, Cul2) CuO, CuS, CuSe, CuTe, GeO2, SiO2, Ge^,
GezSeι.z, GezTβi-z, where z is greater than or equal to about 0.33, and combinations thereof.
23. The aπay of programmable memory structures of claim 21, wherein the barrier layer comprises a conductive material.
24. The aπay of programmable memory structures of claim 21, wherein the barrier layer comprises an insulating material.
25. The array of programmable memory structures of claim 1, wherein the first programmable structures and the second programmable structures are formed on the same substrate.
26. The array of programmable memory structures of claim 1, wherein the first programmable structures and the second programmable structures are formed using the same processing techniques.
27. The aπ-ay of programmable memory structures of claim 1, wherein the volatility of the first programmable structures can be altered by manipulating an amount of energy applied during a write process.
28. The aπ-ay of programmable memory structures of claim 1, wherein the volatility of the second programmable structures can be altered by manipulating an amount of energy applied during a write process.
29. An electronic system formed using the aπay of programmable structures of claim 1.
30. The electronic system of claim 1, wherein the plurahty of first programmable structures are physically separated from the plurahty of second programmable structures.
31. A microelectronic structure comprising: a substrate; a microelectronic device formed using the substrate; a plurality of programmable structures suitable for storing information monolithically formed overlying the microelectronic device.
32. The microelectronic structure of claim 31, further comprising electrical interconnects formed within the structure to electrically couple the microelectronic device and at least one ofthe plurahty of programmable structures.
33. The microelectronic structure of claim 31, wherein the plurality of programmable structures are configured to alter an electrical property based on an amount of energy supplied during the programming process.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AU2002311808A AU2002311808A1 (en) | 2001-04-06 | 2002-04-08 | Microelectronic device, structure, and system, including a memory structure having a variable programmable property and method of forming the same |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US28205701P | 2001-04-06 | 2001-04-06 | |
| US60/282,057 | 2001-04-06 | ||
| US09/951,882 US6635914B2 (en) | 2000-09-08 | 2001-09-10 | Microelectronic programmable device and methods of forming and programming the same |
| US09/951,882 | 2001-09-10 |
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| Publication Number | Publication Date |
|---|---|
| WO2002082452A2 true WO2002082452A2 (en) | 2002-10-17 |
| WO2002082452A3 WO2002082452A3 (en) | 2003-11-27 |
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| PCT/US2002/011082 WO2002082452A2 (en) | 2001-04-06 | 2002-04-08 | Microelectronic device, structure, and system, including a memory structure having a variable programmable property and method of forming the same |
Country Status (2)
| Country | Link |
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| AU (1) | AU2002311808A1 (en) |
| WO (1) | WO2002082452A2 (en) |
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| DE102005003025A1 (en) * | 2005-01-22 | 2006-08-03 | Infineon Technologies Ag | Programmable metallization cell circuit memory for storing data, has data retaining unit applying memory voltage to programmable metallization cell component that stores related states in upper and lower current branches, respectively |
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| US10466969B2 (en) | 2017-05-08 | 2019-11-05 | Arizona Board Of Regents On Behalf Of Arizona State University | Tunable true random number generator using programmable metallization cell(s) |
| US10710070B2 (en) | 2015-11-24 | 2020-07-14 | Arizona Board Of Regents On Behalf Of Arizona State University | Low-voltage microfluidic valve device and system for regulating the flow of fluid |
| US11127694B2 (en) | 2017-03-23 | 2021-09-21 | Arizona Board Of Regents On Behalf Of Arizona State University | Physical unclonable functions with copper-silicon oxide programmable metallization cells |
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| US6985378B2 (en) | 1998-12-04 | 2006-01-10 | Axon Technologies Corporation | Programmable microelectronic device, structure, and system and method of forming the same |
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| DE102004018859B3 (en) * | 2004-04-19 | 2005-09-15 | Infineon Technologies Ag | Memory storage circuit e.g. for flip flop circuit for making available video or audio data for given length of time in terminal, has memory cell with PMC resistor having solid electrolyte material with write circuit |
| DE102005003025B4 (en) * | 2005-01-22 | 2013-10-31 | Adesto Technologies Corporation | PMC memory circuit and method for storing a date in a PMC memory circuit |
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| US10710070B2 (en) | 2015-11-24 | 2020-07-14 | Arizona Board Of Regents On Behalf Of Arizona State University | Low-voltage microfluidic valve device and system for regulating the flow of fluid |
| US11592016B2 (en) | 2015-11-24 | 2023-02-28 | Arizona Board Of Regents On Behalf Of Arizona State University | Low-voltage microfluidic valve device and system for regulating the flow of fluid |
| US11127694B2 (en) | 2017-03-23 | 2021-09-21 | Arizona Board Of Regents On Behalf Of Arizona State University | Physical unclonable functions with copper-silicon oxide programmable metallization cells |
| US11869852B2 (en) | 2017-03-23 | 2024-01-09 | Arizona Board Of Regents On Behalf Of Arizona State University | Physical unclonable functions with copper-silicon oxide programmable metallization cells |
| US10466969B2 (en) | 2017-05-08 | 2019-11-05 | Arizona Board Of Regents On Behalf Of Arizona State University | Tunable true random number generator using programmable metallization cell(s) |
| US11244722B2 (en) | 2019-09-20 | 2022-02-08 | Arizona Board Of Regents On Behalf Of Arizona State University | Programmable interposers for electrically connecting integrated circuits |
| US11935843B2 (en) | 2019-12-09 | 2024-03-19 | Arizona Board Of Regents On Behalf Of Arizona State University | Physical unclonable functions with silicon-rich dielectric devices |
Also Published As
| Publication number | Publication date |
|---|---|
| WO2002082452A3 (en) | 2003-11-27 |
| AU2002311808A1 (en) | 2002-10-21 |
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