EP0757372A1 - Herstellungsverfahren einer Feldemissionsanzeigevorrichtung - Google Patents

Herstellungsverfahren einer Feldemissionsanzeigevorrichtung Download PDF

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Publication number
EP0757372A1
EP0757372A1 EP96302725A EP96302725A EP0757372A1 EP 0757372 A1 EP0757372 A1 EP 0757372A1 EP 96302725 A EP96302725 A EP 96302725A EP 96302725 A EP96302725 A EP 96302725A EP 0757372 A1 EP0757372 A1 EP 0757372A1
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EP
European Patent Office
Prior art keywords
layer
emitters
display
displays
emission
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EP96302725A
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English (en)
French (fr)
Inventor
Guy Dubois
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STMicroelectronics lnc USA
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SGS Thomson Microelectronics Inc
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Publication of EP0757372A1 publication Critical patent/EP0757372A1/de
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
    • H01J9/02—Manufacture of electrodes or electrode systems
    • H01J9/022—Manufacture of electrodes or electrode systems of cold cathodes
    • H01J9/025—Manufacture of electrodes or electrode systems of cold cathodes of field emission cathodes

Definitions

  • the present application relates to vacuum microelectronic devices, and more particularly to field emission displays.
  • the present application discloses an improvement in fabricating Field Emission displays. Before the describing the claimed improvement, the technical context in the art of Field Emission displays (especially as developed by Micron Display Technologies) will be reviewed.
  • Vacuum tube technology which was the dominant technology for three-terminal gain devices from 1920 to about 1960, was almost entirely replaced by solid-state technology during the 1960s and 1970s. (Transistors did not begin to achieve real commercial impact until the late 1950s, although they were invented much earlier. Tubes survived in high-power-high-frequency and other specialty applications, but these applications were a relatively small dollar fraction of the market for semiconductor devices.)
  • AMLCD Active Matrix Liquid Crystal Displays
  • AMLCD Active Matrix Liquid Crystal Displays
  • laptop computers and portable hand-held color television sets have provided a means of employing displays in devices, locations and applications never before possible, such as laptop computers and portable hand-held color television sets.
  • AMLCD technology is the best high quality portable display technology in production; but AMLCDs still suffer from significant limitations in the area of cost, power consumption, angle of view, smearing of fast moving video images, temperature range of operation, ad the environmental concerns of employing mercury vapor in the AMLCD's backlight.
  • Field Emission Displays offer the possibility of circumventing the limitations of AMLCDs, particularly in the area of small, high-resolution displays (e.g . for use in camcorder viewfinders, HMDs, and virtual reality headware).
  • the display has characteristics which make it superior to the present LCDs which dominate the small color display market. The history of this display development, its advantages, and the display characteristics are discussed here.
  • FEDs move from prototypes into production, it becomes necessary to develop new technologies which enable production-level testing of these devices.
  • Typical camcorder viewfinders use displays that range from 0.55" to 0.7 in diagonal.
  • the color displays which are entirely AMLCDs, generally have from 96,000 to 180,000 dots, or 32,000 to 60,000 full-color pixels.
  • Commercial viewfinder displays usually emit around 15 ft-L. At 15 ft-L the typical 0.55" black and white CRT viewfinder draws around 0.9 W.
  • a FED display with 100,800 dots, or 33,600 full-color pixels, can operate with a power of only about 0.1 W. This is a major advantage in camcorders and HMDs, where power consumption can be crucial to battery lifetime.
  • AMLCDs do not respond fast enough in some video applications.
  • a particular example is in the panning of a camcorder during live imaging.
  • the slow response of the LCD causes a "smearing" effect in the video image.
  • the FED does not have this problem.
  • FIG. 1 shows a sectional view
  • Figure 2 shows a perspective view.
  • a faceplate having a cathodoluminescent phosphor coating similar to that of a cathode ray tube receives patterned electron bombardment which can be seen by a viewer.
  • the faceplate is separated from the baseplate by a vacuum gap, and outside atmospheric pressure is prevented from collapsing the two plates together by physical standoffs between them, often referred to as spacers.
  • Electrodes are typically sharp cones that produce electron emission in the presence of an intense electric field.
  • a positive voltage is applied to an extraction grid relative to the sharp emitters to provide the intense electric field required for generating cold cathode electron emission.
  • the Fowler-Nordheim equation is generally considered to accurately describe the emission process of Figure 1 when a field is applied to the emitter by generating a voltage differential between the extraction grid and the emitter tip.
  • the Fowler-Nordheim equation is thoroughly discussed in the literature, and one useful explanation of it as directly applied to vacuum microelectronics can be found in Spindt et al ., "Physical Properties of Thin Film Field Emission Cathodes with Molybdenum Cones," 47 J. APPLIED PHYSICS 5248 (1976), which is hereby incorporated by reference.
  • the baseplate of a field emission display includes arrays of emission sites, and connections for addressing and activating the generation of electron beams from those sites. Many techniques are available for creating the emission from arrays, addressing the emission arrays, and activating the emission sites. Furthermore, a technique must be employed to achieve variations in display brightness (gray scales) when the sites are activated.
  • Varying the charge which is delivered to the phosphor in a given frame from an emission array will vary the light output of the pixel associated with it. Increasing the total electron charge delivered to the phosphor of an individual pixel within a frame results in increased brightness of that pixel. In many cases the brightness charge will be nearly proportional to the increase in the delivered charge.
  • Cathodoluminescent phosphors have a property known as persistence, i.e . the phosphors continue to emit photons even after electron bombardment excitation has ceased. The duration of the persistence is a materials property which can be varied and controlled by the selection and synthesis of the phosphor materials used.
  • the persistence of phosphors provides for a high degree of latitude in how charge variation may be implemented during frame updates of a display, and allows for production of a bright, high quality image without requiring pixel activation throughout the frame time, as is required by an AMLCD display.
  • Frae time is the duration between refreshes of a display's image, and is generally required to be no more than 1/60 second to avoid flicker of fast random image movements as perceived by a human viewer.
  • Two techniques for varying the charge delivered by an emission array in a given frame are to vary either the time period within the frame that the site is activated or alternatively to vary the emission current produced during activation.
  • the technique employs high resolution lithography and etching to create openings in a metal dielectric sandwich which are generally on the order of about one micron in diameter with the dielectric layer being of nearly equal thickness to the diameter.
  • a subsequent directional molylbdenum deposition of about one micron in thickness is then employed at an angle to the openings in the dielectric with thin film vacuum evaporation processing equipment. As the thickness of the deposition increases, the openings in the original metal-dielectric sandwich are reduced and finally closed off. This results in the formation of a pointed molybdenum cone which is self aligned to the openings in the original metal-dielectric sandwich.
  • This technique is commonly referred to as the “Spindt Technique” and the resultant structures as “Spindt emitters.”
  • Alignment of the extraction grid to the emission site is a key factor. If alignment is not achieved, emitted electrons which would ordinarily be accelerated towards and collected by the faceplate would be collected by the grid electrode. Collection of a large amount of emission current by the nearby grid electrode would result in power inefficiency, image degradation, and an increase in the probability of failures.
  • Another approach for forming self-aligned extraction grids utilizes the combination of deposition, polishing and wet etching.
  • a silicon dioxide dielectric layer is deposited over the emitter tips, with a thickness less than the emitter height.
  • a conductive layer for forming the extraction grid is then deposited over the silicon dioxide layer, with a thickness such that the sum of the conductive layers thickness with the previously deposited dielectric thickness was greater than the tip height.
  • the surface of the deposited conductive material is then removed by a wet polishing process with an aqueous based slurry and a conformal polishing pad. During polishing, the rate of material removal atop the emitter tips is much faster than that of material deposited to the sides of the emitter tips.
  • the difference in material removal rates can be attributed to the local pressure and contact difference between the polishing pad with the film stack on top of the emitter and that of the film stack on the topographical lower surface surrounding the emitters.
  • the conductive material above the emitters has been polished to nearly the same height as the surrounding local topology the removal reduces dramatically.
  • This self limiting effect of the material removal during processing provides the process margin required to scale to large area panels. Without this self limiting effect, the uniformity of a bulk removal process would be difficult to manage.
  • the self-aligned extraction grid is formed relative to the emitters. The tips remain buried and surrounded in silicon dioxide until a wet chemical etch is employed to remove the silicon dioxide surrounding the tip. The resulting void exposes the tip so that it will be capable of emitting electrons into the vacuum cavity of an assembled FED.
  • This polishing process has the advantages of: self alignment; wide process window; definition of grid diameter by deposition rather than lithography; avoids the need for thick angularly evaporated molybdenuml and capability of being scaled up for use with large area tip formation processes.
  • a further advantage of the polishing process is the ability to incorporate the use of a flowable dielectric between the silicon dioxide and conductive grid materials. The combination results in the fabrication of structures with a large standoff distance between the base of the emitters and the extraction grid for reducing parasitic capacitance. The combination simultaneously results in a small grid diameter which reduces the applied voltage required for emission. Finally, both of the dimensions are determined by a deposition thickness which enables large area dimensional control.
  • Emitters across the same substrate and even within the same array with the same applied voltage differential to their respective extraction grids can produce significantly different emission current as a result of small variations in tip diameter and surface morphology because of the effects to the electrical field imposed by the extraction grid.
  • Small variations in the final atomic make-up and structure of the outer most surface can also generate significant differences in emission current as a result of their influence on the work function of the surface.
  • Variations in emission current between tips result in a corresponding effect on image quality.
  • the variation at the image is partly reduced by employing large numbers of emitters operating electrically in parallel at each pixel site. Further improvements of imperfectly uniform emitters can be achieved electrically, by operating the emitters in the display with a grid voltage capable of producing higher than the desired electron emission current, while limiting the electron current supplied to the emitters.
  • a very wide selection of passive and active current limiting approaches are shown in the literature. This form of regulated emitter operation is also beneficial in preventing very high performance emitters in an array from generating very large currents and being physically destroyed. When high performance emitters in an array are allowed to emit high enough currents to cause thermal ablation or other dramatic deterioration, the charged and neutral particles from them can contribute to electrical arcs which further damage display components or cause shorts.
  • the faceplate of a field emission display operates on the principle of cathodoluminescent emission of light by the same qualitative principles of physics as that of a conventional CRT.
  • a color image can be obtained using a color sequential approach (sometimes referred to as frame sequential or temporal integration), or with a spatial color approach (sometimes referred to as spatial integration).
  • a color sequential approach sometimes referred to as frame sequential or temporal integration
  • a spatial color approach sometimes referred to as spatial integration
  • a common way to employ spatial integration is to provide red, green, and blue pixels which are addressed in the form of R/G/B triads.
  • the intensities of the color dots within each triad are adjusted relative to one another to produce a range of colors within the triangular boundary formed by the CIE color coordinates of the R, G, and B dots.
  • the human eye is then relied upon for integrating the spatially separated R/G/B dots into a perceived color image.
  • Spatial color displays generally employ a black region separating the red, green, and blue patterned dots.
  • One conventional major advantage to the black region referred to as the black matrix, is to improve the contrast of a display in ambient light. Some of the ambient light that falls on the face of a display is reflected back toward the viewer, mixed with the imaged color light pattern produced by the display. The reflected ambient light reduces the contrast performance of the display and tends to ''wash out' the image. When a black matrix is employed on the faceplate it will absorb ambient light falling upon it, thereby improving the contrast performance of the display.
  • field emission displays employ physical support spacers between the faceplate and the baseplate to prevent collapse from the forces of atmospheric pressure.
  • the spacers In the case of moderate and large FED displays, the spacers must be distributed across the viewable and active region of the display sot that thin light weight faceplates and baseplates can be used.
  • the black matrix regions of the display provide an excellent location in which to place support spacers so that they are invisible to the user.
  • FEDs are less tolerant to particle shedding from the faceplate than CRTs, and so excellent and repeatable adhesion and faceplate integrity are required.
  • the cathodes of the field emission display are in very close proximity to the faceplate and are sensitive to any electronegative chemicals arriving on the cold cathode emitter surfaces which could absorb and increase the value of the work function. Because of the sensitivity just mentioned, some phosphor materials which are suitable for use in CRTs, most notably sulfides of cadmium or zinc, are not recommended for use in FEDs. In fact, the release of sulfur and sulfur compounds from sulfide phosphors under electron bombardment has been shown to poison even the sub red emitter wires in vacuum florescent displays.
  • FEDs are operated at anode voltages well below those of conventional CRTs.
  • Spacer technology will be discussed later in the paper and is a major factor determining the maximum allowable anode voltage.
  • the maximum voltage between two nodes in a vacuum which can be maintained across a solid surface is generally lower than that which can be maintained across a vacuum gap of equal distance in high vacuum devices.
  • the material properties of the surface, distance along the surface, and changes in the orientation of the surface relative to a straight line between the two voltage nodes determine the voltage at which flash over will occur.
  • Another factor which tends to limit the anode operating voltage is the use of simple proximity focus single grid structures. Increasing the space between the faceplate and the baseplate results in greater lateral beam spread. Increasing anode voltage helps reduce the spot size of the beams by accelerating them more rapidly, however, it less than compensates for increased spreading of the beams from increased spacing.
  • the processes used to pattern phosphors on the faceplate bind the phosphors to the faceplate and prepare and treat the phosphor materials prior to application to the faceplate are critical in the fabrication of FEDs. With the important exceptions of storage tube CRTs, which have anode operating voltages of several hundred volts, and vacuum fluorescent displays, which operate well below that, conventional CRTs operate at anode voltages well above FEDs.
  • the phosphor material treatments, and screening and binding of the phosphors to the faceplate result in the formation of thin, non-luminescent coatings on the phosphor referred to as the dead layer.
  • spacers for FEDs cannot outgas and contaminate the deployed sensitive high vacuum environment.
  • the spacer materials must also be designed to withstand some stray electron bombardment without suffering from flash over, degradation, or secondary electron generation.
  • Spacer architectures employing a series of individual posts provide the greatest protection against local pressure build up which can result in destructive arcing damage by providing an unencumbered interstices between the faceplate and baseplate. This type of structure, however, dictates the use of spacer materials with high compressive strengths.
  • spacers with curved sides Another advantage of spacers with curved sides is that because it does not provide a straight line path between the faceplate and the baseplate it will yield a higher voltage stand-off than an equivalent line of site path across the same material.
  • Low resolution FEDs can readily accommodate spheres as spacer supports because of the relatively large spacing between phosphor patterns in which to hide them.
  • High resolution FEDs will provide very little distance between phosphor patterns to accommodate spacers. This requirement can be met with small diameter spheres. These smaller spacers provide a challenge in providing a practical working distance between the faceplate and the baseplate. Phosphor powders are often times on the order of seven microns in diameter and are typically deposited at a minimum of two particles deep. Smaller particle sizes are readily achievable, but generally result in lower phosphor efficiencies. A 25 micron diameter sphere could be placed with some alignment tolerance between phosphor patterns on many high resolution displays and provide a surface leakage path of 39 microns. The resultant narrow gap between the faceplate and baseplate produced by the use of these small diameter spheres generates a challenge in the area of display evacuation, voltage stand-off, and relative tolerance to the size of the phosphor particles.
  • a key innovative point is that an unpatterned self-aligned dense pattern for field-emission devices (especially field-emission displays), is provided by applying charged particles to a pattern-transfer layer.
  • Coulombic repulsion provides some self-regulating control of spacing, to get some approximation to uniform density.
  • the particles Once the particles have thus been deposited, they can be used as the mask for an etching technique which will form the pointed cathode structures used for field emission displays.
  • the present invention provides maskless patterning of one key step, and a corresponding reduction in cost.
  • each individual cathode operates efficiently, but contributes only a very small increment of current. It is therefore desirable to pack the cathodes very tightly (consistent with fabrication requirements, and with the spacing required to avoid lateral breakdown), e.g. to a pitch on the order of microns. However, all or most of the other patterning steps require merely geometries comparable to the pixel pitch, e.g. with geometries on the order of hundreds of microns.
  • the present invention permits use of VLSI processing techniques for fabrication of the microstructures, while minimizing the use of expensive VLSI lithographic procedures.
  • coulombic repulsion provides self-regulating control of spacing.
  • Coulombic repulsion also reduces the likelihood of particles gluing together to form agglomerates (which would disrupt the process, since the size of the tips is regulated by the size of the balls).
  • the deposited particles can be used directly as a mask, or may be used as a counter mask for pattern transfer into a photoresist layer.
  • the surface onto which the particles are deposited may not itself be conductive, but the electrostatic potential can be controlled by making a connection to the underlying conductive silicon layer.
  • the first conductive layer may comprise silicon.
  • the particles may carry a net charge, with respect to said first conductive layer, during said step (c).
  • Step (c) may deposit said charged particles directly onto said second layer.
  • Step (c) may deposit said charged particles onto a photoresist layer which overlies said second layer.
  • matrix addressing circuitry and device implementations can be used to address individual emitters.
  • the matrix addressing structure uses a striped gate, in combination with an orthogonal array of striped emitter contacts.
  • spacer and phosphor structures can be used in combination with the specific emitter topologies of the presently preferred embodiment.
  • the presently preferred embodiment uses silicon emitters, metal or diamond or other materials can be used instead to make emitter structures according to the disclosed innovative teachings.
  • an unpatterned fabrication of the emitter lips as described above, can be combined with a lithographically patterned fabrication of spacers.
  • emitter resistors can optionally be introduced to equalize current across individual emitter tips, and to provide protection against emitter-gate shorts.
  • the disclosed innovative teachings. can also be applied to fabrication of tetrode or pentode structures, in which an additional (focussing) grid is added to reduce divergence of the current from each emitter.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Cathode-Ray Tubes And Fluorescent Screens For Display (AREA)
  • Micromachines (AREA)
  • Cold Cathode And The Manufacture (AREA)
EP96302725A 1995-07-31 1996-04-18 Herstellungsverfahren einer Feldemissionsanzeigevorrichtung Withdrawn EP0757372A1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US5475 1987-01-20
US547595P 1995-07-31 1995-07-31

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EP0757372A1 true EP0757372A1 (de) 1997-02-05

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JP (1) JPH09106774A (de)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE69841945D1 (de) 1997-08-08 2010-11-25 Dainippon Printing Co Ltd Struktur zur Musterbildung, Verfahren zur Musterbildung und deren Anwendung
JP3019041B2 (ja) * 1997-09-26 2000-03-13 日本電気株式会社 電界放出型陰極及びその製造方法

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1991019023A2 (en) * 1990-05-25 1991-12-12 Savin Corporation Electrophoretically deposited particle coatings and structures made therefrom
US5312514A (en) * 1991-11-07 1994-05-17 Microelectronics And Computer Technology Corporation Method of making a field emitter device using randomly located nuclei as an etch mask

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1991019023A2 (en) * 1990-05-25 1991-12-12 Savin Corporation Electrophoretically deposited particle coatings and structures made therefrom
US5312514A (en) * 1991-11-07 1994-05-17 Microelectronics And Computer Technology Corporation Method of making a field emitter device using randomly located nuclei as an etch mask

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
HUANG Z ET AL: "200-NM GATED FIELD EMITTERS", IEEE ELECTRON DEVICE LETTERS, vol. 14, no. 3, 1 March 1993 (1993-03-01), pages 121/122, XP000424038 *

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Publication number Publication date
JPH09106774A (ja) 1997-04-22

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