CN108358157B - Metamaterial microbridge structure and preparation method thereof - Google Patents
Metamaterial microbridge structure and preparation method thereof Download PDFInfo
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Abstract
The invention provides a metamaterial microbridge structure, which relates to the technical field of terahertz detection array imaging at room temperature, and comprises a substrate and a driving circuit layer, wherein the driving circuit layer is provided with a circuit interface, and the metamaterial microbridge structure further comprises a bottom metal film, a middle medium layer, an electrode layer, a thermosensitive film layer, a passivation layer and a top metal film which are sequentially arranged from bottom to top; the middle medium layer comprises a bridge deck, bridge legs and bridge columns; one part of the bottom metal film is positioned below the bridge deck, the other part of the bottom metal film is positioned below the bridge column, and a cavity is formed between the metal film positioned below the bridge deck and the drive circuit layer; the electrode layer is connected with the circuit interface, and a concave part is formed in the center of the electrode layer; the bottom of the heat-sensitive film layer is in contact with the intermediate medium layer through the recessed portion. The invention solves the problems that the existing metamaterial microbridge structure is easy to deform and the preparation process is complex, and further improves the thermal response rate of the device.
Description
Technical Field
The invention relates to the technical field of terahertz detection array imaging at room temperature, in particular to a metamaterial microbridge structure and a preparation method thereof.
Background
The Terahertz (THz) wave refers to electromagnetic radiation with a frequency between 0.1 and 10THz (wavelength 3mm to 30 μm), and the electromagnetic spectrum thereof is located between microwave and infrared bands, therefore, the THz system combines the advantages of electronics and optical systems, long-term, due to the lack of an effective THz radiation generation and detection method, people have very limited knowledge on the nature of the electromagnetic radiation in the band, so that the band is called a THz gap in the electromagnetic spectrum, which is also the last frequency window to be comprehensively studied in the electromagnetic spectrum, compared with the electromagnetic waves in other bands, the THz electromagnetic waves have the unique properties of ① transient state with typical pulse width of THz pulses on the picosecond scale, ② broadband property that a THz pulse source usually contains only several cycles of electromagnetic oscillation, the frequency band of a single pulse can cover the range of GHz to tens of THz, ③ that the coherent measurement technology of the time domain spectroscopy technology can directly measure the amplitude and phase of electric fields, can conveniently extract the refractive index of samples, the absorption coefficient of THz, the low-energy property of a Terahertz (THz) wave, the low-energy-frequency band can cover the frequency band of GHz to tens of THz to-THz-induced electromagnetic waves, and the wide-induced electromagnetic radiation detection technology of the detection of the Terahertz radiation-induced electromagnetic radiation detection of the electromagnetic radiation, the Terahertz-induced electromagnetic radiation, the electromagnetic radiation of the Terahertz-induced electromagnetic radiation detection of the electromagnetic radiation, the electromagnetic radiation detection of the electromagnetic radiation, the electromagnetic radiation of the electromagnetic radiation, the electromagnetic.
According to the 1/4 wavelength theory, taking the radiation frequency 3THz as an example, in order to fully absorb the Terahertz radiation, the height of an optical resonator of a non-refrigerated infrared focal plane array should be 25 μ M (1/4 wavelength of incident radiation), but the height of such a resonant cavity is difficult to realize on the preparation of the device (the height of the resonant cavity of the conventional non-refrigerated infrared focal plane array is about 1.5-3 μ M), if the height of the resonant cavity is not changed, the absorption of the Terahertz radiation by the film system structure is extremely low, so that the difficulty of signal detection is large, the absorption of the Terahertz radiation is high, and the absorption of the Terahertz radiation by the film system structure is usually found in the literature (F.Simosens, the "Terahertz imaging with a quartz-silicon microphone array", the resolution of the Terahertz radiation is improved by using a Terahertz radiation-absorbing film-silicon-quartz-glass-quartz-glass array, the absorption of Terahertz radiation-infrared-quartz-glass-quartz-glass-quartz-film array is a non-quartz-glass-quartz-glass-quartz-glass-quartz-glass-quartz-glass-quartz-glass-quartz-glass-film-glass-quartz-glass-quartz-glass-quartz-glass-quartz-glass-quartz-glass-quartz.
The thin metal or metal composite film can absorb terahertz radiation, and the film thickness below 50nm has little influence on the heat capacity of the detector, which is beneficial to the manufacture of a high response rate Detection unit and is commonly used as an absorption layer of a terahertz microarray detector, N.Oda et al adopt 320 × and 640 × uncooled infrared focal plane arrays based on vanadium oxide thermal sensitive films to detect terahertz radiation, because the absorption rate of terahertz radiation of the original film system structure is only 2.6-4%, therefore, a metal film with proper sheet resistance is added on the top layer of the film system structure to be used as a terahertz radiation absorption layer, the noise equivalent power of incident radiation with the frequency of 3THz is reduced to 40pW (N.Oda, etc.' Detection of terahertz radiation, "Detection of terahertz radiation using vanadium oxide microwave atomic crystal plane arrays", Proceedings of IE, spcedenting, 020, spy-1-82Y-7634 ", and the terahertz radiation absorption layer is also used as a terahertz radiation absorption layer in the Martinez microarray detector-34 absorption layer.
The patent 201310124924.8 discloses a microbridge structure of an infrared-terahertz dual-band array detector and a preparation method thereof, wherein the top layer of the microbridge structure is a double-layer vanadium oxide layer, the lower vanadium oxide layer is a phase-change-free vanadium oxide layer with a high Temperature Coefficient of Resistance (TCR) and is used as a sensitive layer of infrared and terahertz wave bands, the upper vanadium oxide layer has a lower phase-change temperature and can generate reversible phase change of a semiconductor phase and a metal phase, the semiconductor phase and the lower vanadium oxide layer are used as an infrared absorption layer together, and the semiconductor phase and the lower vanadium oxide layer are used as terahertz radiation absorption layers after being changed into the metal phase; in patent 201110434601, a film structure for enhancing terahertz radiation absorption rate and a preparation method thereof are disclosed, wherein the film structure comprises a dielectric thin film and a terahertz absorption layer located thereon. The preparation method comprises the following steps: firstly, preparing a low-stress silicon nitride or silicon oxide film by adopting a PECVD (plasma enhanced chemical vapor deposition) mixing technology, etching the medium film into a micro-nano-scale rough surface by reactive ions, and then preparing a metal film on the medium film with the rough surface by a magnetron sputtering method to obtain a medium and metal film system structure with a high body surface ratio so as to enhance the terahertz absorption rate; patent 201210529449.8 discloses an ultra-thin metal film terahertz absorbing layer and a method for making the same, wherein the ultra-thin metal film is made by etching and thinning a metal film with a larger thickness, and the process parameters and the concentration distribution of an etchant are adjusted in the etching and thinning process to cause the difference of micro-area etching rates, so that a rough, porous and blackened ultra-thin metal film can be obtained. There are two etching methods: one is to etch the metal film into an ultrathin metal film by using a reactive ion etching method and a post-corrosion phenomenon of dry etching, and has the advantages of easily controlling the reaction process and the thickness of the ultrathin metal film and the like; the other method is to corrode the metal film into an ultrathin metal film by a wet chemical corrosion method, and has the advantages of easy control of the surface appearance and color of the ultrathin metal film and the like. The rough, porous and blackened metal film surface structure has the characteristics of high surface-to-volume ratio and low reflectivity, and can effectively enhance the absorption performance and efficiency of terahertz radiation. In the methods, a layer of metal film is used as the terahertz radiation absorption layer, however, the absorption rate of the metal film is limited, the highest terahertz radiation absorption rate of the unsupported metal film is only 50% under an ideal condition, and the absorption rate of the metal film integrated into the microbridge structure is lower due to the influence of the preparation process and the substrate state.
The terahertz micro-bolometer based on the metamaterial and the preparation method thereof are disclosed in patent 201510023632.4, the terahertz micro-bolometer comprises a metamaterial terahertz absorber and a thermal detector, wherein the thermal detector comprises a microbridge supporting layer, a thermistor film, a metal electrode and a passivation layer, the terahertz absorber comprises a bottom layer metal film, a middle medium layer and a top layer metal film, the invention integrates the terahertz absorber and the thermal detector together, transfers heat generated by terahertz radiation absorbed by the metamaterial to the thermal detector, so that the electrical property of the thermistor film is changed, thus realizing terahertz room temperature detection imaging, the invention discloses a microbridge structure of a terahertz high-absorption terahertz wave and a preparation method thereof in patent 201510392320.0, which are used for overcoming the problem of low response rate of the terahertz high-absorption terahertz microbridge structure under a wide frequency band, the microbridge structure comprises a metal absorption film positioned in the middle layer, the terahertz absorption bridge structure is positioned between the terahertz absorption bridge, the terahertz absorption bridge structure is ensured to be matched with a terahertz absorption material, the terahertz absorption rate of a terahertz micro-absorption-bridge structure is increased, the terahertz micro-absorption-micro-bridge structure is prepared by a terahertz micro-absorption-micro-bridge structure, the terahertz micro-bridge structure, the terahertz absorption-micro-bridge structure is prepared by adopting a terahertz absorption-micro-absorption-micro-bridge structure, the terahertz absorption-micro-absorption-micro-absorption-bridge structure, the terahertz absorption-micro-terahertz absorption structure, the terahertz absorption structure can be prepared by adopting a terahertz absorption-micro-bridge structure, the terahertz absorption-micro-.
Disclosure of Invention
The invention aims to: the invention provides a metamaterial microbridge structure and a preparation method thereof, aiming at solving the problems that the existing metamaterial microbridge structure is easy to deform and the preparation process is complex and further improving the thermal response rate of devices.
The technical scheme of the invention is as follows:
on one hand, the invention provides a metamaterial microbridge structure which comprises a substrate, a driving circuit layer, a bottom metal film, a middle medium layer, an electrode layer, a heat-sensitive film layer, a passivation layer and a top metal film, wherein the driving circuit layer is provided with a circuit interface; the middle dielectric layer comprises a bridge deck, bridge legs and bridge columns, and the bridge leg parts of the middle dielectric layer are positioned above the driving circuit layer; one part of the bottom metal film is positioned below the bridge deck, the other part of the bottom metal film is positioned below the bridge column, a cavity is formed between the bottom metal film positioned below the bridge deck and the driving circuit layer, and the bottom metal film positioned below the bridge column is connected with the circuit interface; the electrode layer is connected with the circuit interface, and a concave part is formed in the center of the electrode layer; the bottom of the heat-sensitive film layer is in contact with the intermediate medium layer through the recessed portion.
Specifically, the top metal film is one or a mixture of several of periodic structures such as a rectangle, a circular ring, an open ring, a cross and the like.
Preferably, the height of the cavity is 1-3 μm.
Preferably, the bottom metal film, the electrode layer and the top metal film are made of one or more of aluminum, tungsten, titanium, platinum, nickel and chromium; the thickness of the bottom layer metal film is 100-300nm, the thickness of the electrode layer is 20-100n, and the thickness of the top layer metal film is 30-100 nm.
Specifically, the intermediate dielectric layer and the passivation layer are made of silicon dioxide, silicon nitride or composite films of silicon dioxide and silicon nitride, the thickness of the intermediate dielectric layer is 100-500nm, and the thickness of the passivation layer is 50-200 nm.
Specifically, the material of the heat-sensitive thin film layer is one of vanadium oxide, titanium oxide or amorphous silicon thin film.
On the other hand, the invention provides a preparation method of a metamaterial micro-bridge structure, which comprises the following steps:
step 1: a sacrificial layer is grown and patterned on a substrate with a drive circuit layer with a circuit interface.
Step 2: and preparing a bottom metal film on the sacrificial layer, wherein the bottom metal film covers part of the surface of the top of the sacrificial layer and the circuit interface.
And step 3: and preparing an intermediate dielectric layer on the bottom metal film to expose the circuit interface.
And 4, step 4: and preparing an electrode layer on the intermediate dielectric layer, patterning the electrode layer, electrically connecting the electrode layer with the circuit interface, and forming a concave part in the center of the electrode layer.
And 5: and preparing a heat-sensitive film layer on the electrode layer, and patterning the heat-sensitive film layer, wherein the bottom of the heat-sensitive film layer is in contact with the intermediate medium layer through the concave part.
Step 6: and preparing a passivation layer on the heat-sensitive film layer, and patterning the passivation layer, wherein the passivation layer completely covers the heat-sensitive film layer.
And 7: and preparing and patterning a top metal film on the passivation layer, wherein all the top metal films are positioned on the passivation layer.
And 8: and removing the sacrificial layer to form a cavity between the metal film of the bottom layer below the bridge floor of the middle dielectric layer and the drive circuit layer.
Specifically, the material of the sacrificial layer is one of polyimide, silicon dioxide, oxidized porous silicon or phosphorosilicate glass.
Specifically, the top metal film is of one or a mixture of more of rectangular, circular, open-ring, cross-shaped and other periodic structures; the height of the cavity is 1-3 μm.
Specifically, the bottom metal film, the electrode layer and the top metal film are made of one or more of aluminum, tungsten, titanium, platinum, nickel and chromium; the thickness of the bottom layer metal film is 100-300nm, the thickness of the electrode layer is 20-100n, and the thickness of the top layer metal film is 30-100 nm;
the middle dielectric layer and the passivation layer are made of silicon dioxide, silicon nitride or composite films of silicon dioxide and silicon nitride, the thickness of the middle dielectric layer is 100-500nm, and the thickness of the passivation layer is 50-200 nm.
Compared with the prior art, the passivation layer is also a thin dielectric layer, the thermosensitive thin film layer can also be used as a dielectric layer, the two layers and the middle dielectric layer are jointly used as the dielectric layer positioned between the bottom metal film and the top metal film, so that the metamaterial thin film is formed by the two layers, the metal electrode can not be used as the medium, but as can be seen from the attached drawing, the designed electrode layer is only distributed at the edge of the bridge floor of the microbridge and does not influence the middle large-area metamaterial part, therefore, the layer structure in the invention is changed, but does not influence the working principle of the metamaterial microbridge structure, and the terahertz radiation absorption rate of the device can be effectively enhanced. And, still have following beneficial effect simultaneously:
(1) in the invention patent application with patent numbers 201510023632.4 and 201510392320.0 mentioned in the background art, a metamaterial structure is prepared on a microbridge supporting layer, the microbridge supporting layer is a layer of medium, a layer of medium is added in the metamaterial, and the two layers are thicker, so that the thickness of the suspended part of the microbridge is very large, the mechanical property is influenced, and the microbridge is easy to deform or even collapse only by supporting two slender bridge legs;
(2) the heat capacity is mainly related to the dielectric layer, compared with the prior art, the dielectric layer of the invention is reduced by about half, and the response time can be reduced by half under the condition of the same thermal conductivity (same bridge leg).
(3) The invention does not need to prepare the micro-bridge structure and the metamaterial structure respectively, reduces the layer structure, greatly reduces the preparation process steps compared with the prior art, and has simple preparation process and good compatibility.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts. The above and other objects, features and advantages of the present invention will become more apparent from the accompanying drawings. Like reference numerals refer to like parts throughout the drawings. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
In FIG. 1, a-i are the preparation process (cross-sectional view) of the metamaterial micro-bridge structure of the present invention;
in FIG. 2, a-i are the process flow (top view) for preparing the metamaterial micro-bridge structure of the present invention;
wherein, fig. 1-a and fig. 2-a are the substrate with the bottom driving circuit layer, fig. 1-b and fig. 2-b are the substrate with the prepared sacrificial layer pattern, fig. 1-c and fig. 2-c are the substrate with the prepared bottom metal film pattern, fig. 1-d and fig. 2-d are the substrate with the prepared middle dielectric layer pattern, fig. 1-e and fig. 2-e are the substrate with the prepared electrode layer pattern, fig. 1-f and fig. 2-f are the substrate with the prepared heat sensitive film pattern, fig. 1-g and fig. 2-g are the substrate with the prepared passivation layer pattern, fig. 1-h and fig. 2-h are the substrate with the prepared top metal film pattern, and fig. 1-i and fig. 2-i are the cross-sectional schematic diagrams of the device structure after the sacrificial layer is released. (Note: since it is a top view, part of the pattern in FIG. 2 is hidden, not shown.)
Reference numerals: 10-substrate, 20-drive circuit layer, 21-circuit interface, 30-sacrificial layer, 40-bottom metal film, 50-middle dielectric layer, 60-electrode layer, 70-heat-sensitive film layer, 80-passivation layer and 90-top metal film.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In order to solve the problems that the existing metamaterial microbridge structure is easy to deform and the preparation process is complex, and further improve the thermal response rate of a device, the invention provides a metamaterial microbridge structure and a preparation method thereof, which are respectively explained below.
A metamaterial microbridge structure comprises a substrate 10 and a driving circuit layer 20, wherein a circuit interface 21 is arranged on the driving circuit layer 20, and the metamaterial microbridge structure further comprises a bottom metal film 40, a middle dielectric layer 50, an electrode layer 60, a heat-sensitive film layer 70, a passivation layer 80 and a top metal film 90 which are sequentially arranged on the driving circuit layer 20 from bottom to top; the middle dielectric layer 50 comprises a bridge deck, bridge legs and bridge columns, and the bridge leg parts of the middle dielectric layer are positioned above the driving circuit layer 20; one part of the bottom metal film 40 is positioned below the bridge deck, the other part is positioned below the bridge column, a cavity is formed between the bottom metal film 40 positioned below the bridge deck and the driving circuit layer 20, and the bottom metal film 40 positioned below the bridge column is connected with the circuit interface 21; the bottom metal film 40 part under the bridge deck is used as a part of a metamaterial structure, the bottom metal film 40 part under the bridge column is equivalent to a metal step formed on a circuit interface and can be called a buffer layer, connection is facilitated, otherwise, the circuit interface is of a deep hole structure, the connection effect of a thin layer of electrode above and below the hole is possibly poor, and the connection effect is better when the step buffer is made by using the bottom metal film 40. The electrode layer 60 is connected with the circuit interface 21, and a concave part is formed in the center of the electrode layer 60; the bottom of the heat sensitive film layer 70 is in contact with the intermediate medium layer 50 through the concave portion. The middle dielectric layer 50 and the bottom metal film 40 are positioned between the upper part of the bridge column and the circuit interface 21 to form a ladder shape, and the electrode layer 60 is respectively contacted with the middle dielectric layer 50, the bottom metal film 40 and the electrode layer.
For the preparation method of the metamaterial micro-bridge structure, the preparation method specifically comprises the following steps:
step 1: growing a sacrificial layer on the substrate with the driving circuit layer 20 and patterning the sacrificial layer 30, wherein the driving circuit layer 20 is provided with a circuit interface 21; the material of the sacrificial layer 30 is one of polyimide, silicon dioxide, oxidized porous silicon or phosphorosilicate glass.
Step 2: an underlayer metal film 40 with a thickness of 100-300nm is prepared on the sacrificial layer 30, and the underlayer metal film 40 covers the top of the sacrificial layer 30 and a part of the surface of the circuit interface 21. The bottom metal film 40 is made of one or more of aluminum, tungsten, titanium, platinum, nickel and chromium.
And step 3: an intermediate dielectric layer 50 with a thickness of 100-500nm is prepared on the bottom metal film 40 to expose the circuit interface 21. The material of the middle dielectric layer 50 is silicon dioxide, silicon nitride or a composite film thereof.
And 4, step 4: an electrode layer 60 having a thickness of 20 to 100nmd is formed on the interlayer dielectric layer 50, and patterned, the electrode layer 60 is electrically connected to the circuit interface 21, and a recess is formed in the center of the electrode layer 60. The electrode layer 60 is made of one or more of aluminum, tungsten, titanium, platinum, nickel and chromium.
And 5: a heat-sensitive thin film layer 70 is prepared on the electrode layer 60, and the heat-sensitive thin film layer 70 is patterned, the bottom of the heat-sensitive thin film layer 70 being in contact with the intermediate medium layer 50 through the depressed portion. The material of the heat sensitive thin film layer 70 is one of vanadium oxide, titanium oxide or amorphous silicon thin film.
Step 6: a passivation layer 80 having a thickness of 50-200nm is prepared on the heat-sensitive thin film layer 70 and patterned, and the passivation layer 80 completely covers the heat-sensitive thin film layer 70. The passivation layer 80 is made of silicon dioxide, silicon nitride or a composite film thereof.
And 7: preparing a top metal film 90 with the thickness of 30-100nm on the passivation layer 80 and patterning the top metal film 90, wherein all the top metal films 90 are positioned on the passivation layer, and the top metal film 90 is in a mixed structure of one or more of rectangular, circular, open-ring, cross-shaped and other periodic structures. The top metal film 90 is made of one or more of aluminum, tungsten, titanium, platinum, nickel and chromium.
And 8: and removing the sacrificial layer 30, so that a cavity is formed between the metal film 40 of the bottom layer and the driving circuit layer 20 under the bridge surface of the middle dielectric layer 50, and the height of the cavity is 1-3 mu m.
The invention is further illustrated by the following examples and figures:
example 1
As shown in fig. 1 and 2, a method for preparing a metamaterial micro-bridge structure, which is spread on a substrate 10 with a prepared bottom driving circuit 20, and the driving circuit 20 flows out of a circuit interface 21, as shown in fig. 1-a, and the following steps are:
step 1: cleaning the surface of the substrate 10, removing surface contamination, and baking the substrate 10 at 200 ℃ to remove surface water vapor and enhance the bonding performance; coating the sacrificial layer 30 by using an automatic glue coating rail, wherein the material of the sacrificial layer 20 is photosensitive polyimide; the thickness of the polyimide film is adjusted through the rotating speed, and the coated photosensitive polyimide is baked at 120 ℃ to remove part of the solvent in the glue, so that the uniformity of exposed lines is facilitated. And (3) carrying out an exposure process on the photosensitive polyimide by adopting an NIKON photoetching machine, and conveying the exposed substrate 10 to an automatic developing track for developing the photoresist, wherein the developing solution is standard positive photoresist developing solution TMAH. The developed photosensitive polyimide pattern exhibited a pier hole pattern as shown in fig. 1-b. And then putting the polyimide film in an annealing oven protected by inert gas for imidization treatment, wherein the imidization temperature is set to be increased in stages, the highest temperature is 250-400 ℃, the constant temperature time is 30-120min, and the thickness of the imidized polyimide is within the range of 1-3 mu m.
Step 2: an underlayer metal film 40 with a thickness of 100-300nm is prepared on the sacrificial layer 30, and the underlayer metal film 40 covers the top of the sacrificial layer 30 and a part of the surface of the circuit interface 21. Specifically, the AZ5214 photoresist is spin-coated on the surface of the substrate 10, then mask exposure is performed, after exposure is completed, a hot plate at 110 ℃ is used for baking for 1.5min, so that the exposed portion of the photoresist is changed, then a flood exposure process is performed, and then a pattern to be stripped is obtained by development. The metal aluminum film is prepared by adopting a magnetron sputtering method, and the thickness of the aluminum film is within the range of 100-300 nm. Then, the photoresist was stripped off with an acetone solution under ultrasonic conditions. The pattern of the underlying metal film 40 at the bridge pier partially covers the pattern of the circuit interface 21, leaving a pattern of the underlying metal film on the face of the sheet after peeling as shown in fig. 1-c.
And step 3: an intermediate dielectric layer 50 with a thickness of 100-500nm is prepared on the bottom metal film 40 to expose the circuit interface 21. Specifically, a PECVD device and a frequency mixing sputtering technology are adopted to manufacture low-stress silicon nitride to be used as the intermediate dielectric layer 50, and the thickness range of the prepared silicon nitride layer is within the range of 100-500 nm. The thin film is then etched to form the pattern of the interlayer dielectric layer 50. The patterned portion of the layer of silicon nitride at the bridge pier covers the underlying metal film 40 pattern as shown in fig. 1-d.
And 4, step 4: an electrode layer 60 having a thickness of 20 to 100nmd is formed on the interlayer dielectric layer 50, and patterned, the electrode layer 60 is electrically connected to the circuit interface 21, and a recess is formed in the center of the electrode layer 60. Specifically, an AZ5214 photoresist is adopted to prepare a NiCr electrode pattern; the method comprises the steps of firstly, spin-coating AZ5214 photoresist on the surface of a substrate with a prepared substrate supporting layer, then carrying out mask exposure, baking for 1.5min by using a hot plate at 110 ℃ after exposure is finished, changing the photoresist at the exposed part, carrying out a flood exposure process, and then developing to obtain a pattern to be stripped. The NiCr film is prepared by a magnetron sputtering method, and the thickness of the NiCr film is within the range of 20-100 nm. Then, the photoresist was stripped off with an acetone solution under ultrasonic conditions. The stripping leaves a NiCr electrode pattern on one side as shown in fig. 1-e, which is connected to the underlying circuit interface 21.
And 5: a heat-sensitive thin film layer 70 is prepared on the electrode layer 60, and the heat-sensitive thin film layer 70 is patterned, the bottom of the heat-sensitive thin film layer 70 being in contact with the intermediate medium layer 50 through the depressed portion. After the electrode lead is prepared, a vanadium oxide film is prepared by a sputtering apparatus to be used as the heat-sensitive film layer 70. The sputtering power is controlled to be 500 ℃ plus 100W during sputtering, the oxygen partial pressure is 0.5-10%, the sputtering time is 5-60min, and the annealing temperature is controlled to be 600 ℃ plus 200 ℃. The prepared vanadium oxide film has a resistance temperature coefficient of-2%/K to-6%/K and a thickness of 30-200 nm. And photoetching and etching the layer of vanadium oxide film to etch a vanadium oxide film pattern shown in figure 1-f.
Step 6: a passivation layer 80 having a thickness of 50-200nm is prepared on the heat-sensitive thin film layer 70 and patterned, and the passivation layer 80 completely covers the heat-sensitive thin film layer 70. The thickness range of the prepared silicon nitride layer is within 50-200 nm. The film is then subjected to photolithography and etching to etch the pattern of the passivation layer 80. This layer of silicon nitride passivation 80 completely covers the heat sensitive membrane layer 70 as shown in fig. 1-g.
And 7: preparing a top metal film 90 with the thickness of 30-100nm on the passivation layer 80 and patterning the top metal film 90, wherein all the top metal films 90 are positioned on the passivation layer, and the top metal film 90 is in a mixed structure of one or more of rectangular, circular, open-ring, cross-shaped and other periodic structures. The top metal film 90 pattern with a rectangular periodic structure was prepared using AZ5214 photoresist. The method comprises the steps of firstly, rotationally coating AZ5214 photoresist on the surface of a substrate with a prepared passivation layer, then carrying out mask exposure, baking the photoresist at a 110 ℃ hot plate for 1.5min after exposure is finished to change the photoresist at the exposed part, then carrying out a flood exposure process, and then developing to obtain a pattern to be stripped. The NiCr film is prepared by a magnetron sputtering method, and the thickness of the NiCr film is within the range of 30-100 nm. Then, the photoresist was stripped off with an acetone solution under ultrasonic conditions. The NiCr top metal film pattern was left on the one side after lift-off as shown in FIG. 1-h, with all top metal film patterns distributed over the passivation layer.
And 8: and removing the sacrificial layer 30, so that a cavity is formed between the metal film 40 of the bottom layer and the driving circuit layer 20 under the bridge surface of the middle dielectric layer 50, and the height of the cavity is 1-3 mu m. And bombarding the device with the top metal film pattern by using oxygen plasma, and removing the imidized sacrificial layer 30 to form a suspended metamaterial microbridge structure detection unit, wherein the schematic cross-sectional view of the detection unit is shown in fig. 1-i.
In the invention, the passivation layer 80 is also a thin dielectric layer, the heat-sensitive thin film layer 70 can also be used as a dielectric layer, and the two layers together with the intermediate dielectric layer 50 are used as a dielectric layer between the bottom metal film 40 and the top metal film 90, so that the layers together constitute an intermediate dielectric of the metamaterial, and the metal electrode can not be used as a dielectric, but as can be seen from the drawing, the designed electrode layer 60 is only distributed at the edge of the bridge floor of the microbridge and does not affect the middle large-area metamaterial part, therefore, although the layer structure in the invention is changed, the working principle of the metamaterial microbridge structure can not be affected, and the terahertz radiation absorption rate of the device can also be effectively enhanced.
The above description is only an embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Claims (10)
1. A metamaterial microbridge structure comprises a substrate (10) and a driving circuit layer (20), wherein a circuit interface (21) is arranged on the driving circuit layer (20),
the circuit board is characterized by further comprising a bottom metal film (40), an intermediate dielectric layer (50), an electrode layer (60), a heat-sensitive film layer (70), a passivation layer (80) and a top metal film (90) which are sequentially arranged on the driving circuit layer (20) from bottom to top;
the middle dielectric layer (50) comprises a bridge deck, bridge legs and bridge columns, and the bridge leg parts of the middle dielectric layer are positioned above the driving circuit layer (20);
one part of the bottom metal film (40) is positioned below the bridge deck, the other part of the bottom metal film is positioned below the bridge column, a cavity is formed between the bottom metal film (40) positioned below the bridge deck and the driving circuit layer (20), and the bottom metal film (40) positioned below the bridge column is connected with the circuit interface (21);
the electrode layer (60) is connected with the circuit interface (21), and a concave part is formed in the center of the electrode layer (60); the bottom of the heat-sensitive film layer (70) is in contact with the intermediate medium layer (50) through the recessed portion.
2. A metamaterial microbridge structure as claimed in claim 1, wherein the top metal film (90) is one or more of a rectangular, circular, open-ring, cross-shaped periodic structure.
3. A metamaterial microbridge structure as claimed in claim 1, wherein the height of the cavity is 1-3 μm.
4. The metamaterial microbridge structure of claim 1, wherein the bottom metal film (40), the electrode layer (60) and the top metal film (90) are made of one or more of aluminum, tungsten, titanium, platinum, nickel and chromium; the thickness of the bottom metal film (40) is 100-300nm, the thickness of the electrode layer (60) is 20-100nm, and the thickness of the top metal film (90) is 30-100 nm.
5. The metamaterial microbridge structure as claimed in claim 1, wherein the materials of the intermediate dielectric layer (50) and the passivation layer (80) are silicon dioxide, silicon nitride or composite films thereof, the thickness of the intermediate dielectric layer (50) is 100-500nm, and the thickness of the passivation layer (80) is 50-200 nm.
6. A metamaterial microbridge structure as claimed in claim 1, wherein the material of the thermosensitive thin film layer (70) is one of vanadium oxide, titanium oxide or amorphous silicon thin film.
7. A preparation method of a metamaterial micro-bridge structure is characterized by comprising the following steps:
step 1: growing a sacrificial layer on a substrate (10) with a driving circuit layer (20), and patterning the sacrificial layer (30), wherein the driving circuit layer (20) is provided with a circuit interface (21);
step 2: preparing a bottom metal film (40) on the sacrificial layer (30), wherein the bottom metal film (40) covers the top of the sacrificial layer (30) and part of the surface of the circuit interface (21);
and step 3: preparing an intermediate dielectric layer (50) on the bottom metal film (40) to expose the circuit interface (21);
and 4, step 4: preparing an electrode layer (60) on the intermediate dielectric layer (50), patterning the electrode layer, electrically connecting the electrode layer (60) with the circuit interface (21), and forming a concave part in the center of the electrode layer (60);
and 5: preparing a heat-sensitive film layer (70) on the electrode layer (60), and patterning the heat-sensitive film layer (70), wherein the bottom of the heat-sensitive film layer (70) is in contact with the intermediate medium layer (50) through the concave part;
step 6: preparing a passivation layer (80) on the heat-sensitive thin film layer (70), and patterning the passivation layer (80), wherein the passivation layer (80) completely covers the heat-sensitive thin film layer (70);
and 7: preparing and patterning a top metal film (90) on the passivation layer (80), wherein all the top metal films (90) are positioned on the passivation layer;
and 8: and removing the sacrificial layer (30) to form a cavity between the metal film (40) of the bottom layer positioned below the bridge surface of the middle dielectric layer (50) and the drive circuit layer (20).
8. The method for preparing a metamaterial microbridge structure as claimed in claim 7, wherein the material of the sacrificial layer (30) is one of polyimide, silica, oxidized porous silicon or phosphorosilicate glass.
9. The method for preparing the metamaterial microbridge structure as claimed in claim 7, wherein the top metal film (90) is one or a mixture of several of a rectangular, circular, open-ring, and cross-shaped periodic structure; the height of the cavity is 1-3 μm.
10. The method for preparing the metamaterial microbridge structure as claimed in claim 7, wherein the bottom metal film (40), the electrode layer (60) and the top metal film (90) are made of one or more of aluminum, tungsten, titanium, platinum, nickel and chromium; the thickness of the bottom layer metal film (40) is 100-300nm, the thickness of the electrode layer (60) is 20-100nm, and the thickness of the top layer metal film (90) is 30-100 nm;
the intermediate dielectric layer (50) and the passivation layer (80) are made of silicon dioxide, silicon nitride or composite films of silicon dioxide and silicon nitride, the thickness of the intermediate dielectric layer (50) is 100-500nm, and the thickness of the passivation layer (80) is 50-200 nm.
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