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ANODE PLATE FOR FLAT PANEL DISPLAY with the small volume within the cavity severely reduces the
HAVING SILICON GETTER pumping effectiveness of the getter.
This application is related to copending application Ser. No. 08/535,506, entitled Anode Plate for Flat Panel Display Having Integrated Getter, filed Sep. 28, 1995, application Ser. No. 08/292,915, entitled Low Density, High Porosity Material as Gate Dielectric for Field Emission Device, filed Iq Aug. 19,1994, now U.S. Pat. No. 5,525,857, application Ser. No. 08/253,476, Flat Panel Display Anode Plate Having Isolation Grooves, filed Jun. 3, 1994, now U.S. Pat. No. 5,491,376, application Ser. No. 08/258,803, entitled Anode Plate for Flat Panel Display Having Integrated Getter, filed 15 Jun. 10, 1994, now U.S. Pat. No. 5,453,659, and copending application Ser. No. 08/247,951, entitled Opaque Insulator for Use on Anode Plate of Flat Panel Display, filed May 24, 1994, all applications of the same assignee.
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to flat panel displays and, more particularly, to a structure and method for providing improved gettering within a field emission flat ^ panel display.
BACKGROUND OF THE INVENTION
The advent of portable computers has created demand for display devices which are lightweight, compact, and power 30 efficient. Since the space available for the display of these devices precludes the use of a conventional cathode ray tube (CRT), there has been an effort to produce flat panel displays having comparable or even superior display characteristics.
Liquid crystal displays are commonly used for laptop and 35 notebook computers. These displays may suffer from poor contrast, a limited range of viewing angles, and power requirements which are incompatible with extended battery operation. In addition, color liquid crystal displays tend to be far more costly than CRTs of equal screen size. 40
As a result of these limitations of liquid crystal display technology, field emission display technology has received more attention in the industry. Field emission flat panel displays employ a matrix-addressable array of field emission 4g cathodes in combination with an anode comprising a luminescent screen. The manufacture of inexpensive, low-power, high-resolution, high-contrast, full-color flat panel displays using this technology appears promising.
In order for field emission displays to operate efficiently, 50 it is desirable to maintain a vacuum within the cavity of the display, typically less than 10-6 Torr. The cavity is pumped out and degassed before assembly, but over time the pressure in the display builds up due to outgassing of the components inside the display and to the finite leak rate of the atmo- 55 sphere into the cavity. Getters are employed as pumps that adsorb these undesirable gases in order to maintain a minimum pressure in the cavity.
In field emission flat panel displays, the cathode or emitter plate and the anode plate may be spaced from one another 60 at a relatively small distance. This spacing, typically on the order of two hundred microns, limits the total volume of the cavity enclosed within the display screen. Due to the limited volume within the cavity, the getter is normally placed in peripheral regions, such as in the pump-out tabulation at the 65 back of the display. The placement of the getter material outside of the active region of the display in combination
SUMMARY OF THE INVENTION
In accordance with the present invention, the disadvantages and problems associated with the use of a getter to maintain a vacuum within a field emission flat panel display have been substantially reduced or eliminated.
In accordance with one embodiment of the present invention, an anode plate for use in a display device comprises a substantially transparent substrate. A plurality of spacedapart, electrically conductive regions are located on the substrate. A luminescent material is adjacent to the conductive regions. Getter material is disposed on the substrate and between the conductive regions.
In accordance with another aspect of the present invention, a method for fabricating an anode plate for use in a display device comprises the steps of providing a substantially transparent substrate, forming a plurality of spacedapart, electrically conductive regions on the substrate, forming a getter material on the substrate and between the conductive regions, and forming a luminescent material on the conductive regions.
Important technical advantages of the present invention include maintaining the vacuum integrity of a field emission flat panel display over the life of the display. This is accomplished by placing the getter material in close proximity to the display elements which are subject to outgassing and to those elements of the display which are adversely effected by increases in gas pressure. In particular, a getter material is deposited on the substrate and between the conductive regions of the anode plate. This placement substantially increases the pumping effectiveness of the getter material over other systems that place getters in the periphery of the display.
Other important technical advantages of the present invention include providing an electrically nonconductive getter which can be deposited within the cavity of the display. In the preferred embodiment, this getter material comprises porous silicon. Porous silicon provides a voltage standoff between conductive regions on the anode plate. Furthermore, porous silicon may be deposited as an opaque material between phosphor stripes to improve display performance by improving the contrast ratio.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention, and for further features and advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:
FIG. 1 illustrates in cross section a portion of a field emission flat panel display device;
FIG. 2A illustrates in cross section a portion of an anode plate of a field emission flat panel display device corresponding to a first embodiment of the present invention;
FIG. 2B illustrates in cross section a portion of an anode plate of a field emission flat panel display device corresponding to a second embodiment of the present invention;
FIGS. 3A through 3G illustrate steps for fabricating the anode plate of FIG. 2A;
FIGS. 4A through 4H illustrate alternative steps for fabricating the anode plate of FIG. 2A; and
FIGS. 5A through 5F illustrate steps for fabricating the anode plate of FIG. 2B.
DETAILED DESCRIPTION OF THE
FIG. 1 illustrates, in cross-section, a display device 8 which comprises an anode plate 10 and an emitter (or cathode) plate 12. The cathode portion of emitter plate 12 includes conductors 13 formed on an insulating substrate 18, a resistive layer 16 also formed on substrate 18 and overlaying conductors 13, and a plurality of electrically conductive emitters 14 formed on resistive layer 16. When viewed from above, conductors 13 comprise a mesh structure, and 10 emitters 14 are configured as a matrix within the mesh spacings.
In one embodiment, display device 8 may be a field emission display device that benefits from removal of all ambient species between anode plate 10 and emitter plate 15 12. Display device 8 may also be a plasma display, in which the space between anode plate 10 and emitter plate 12 contains a plasma. A getter material for a plasma display may be chosen to react with undesirable species without substantially degrading the plasma. 20
Gate electrode 22 comprises a layer of an electrically conductive material deposited on an insulating layer 20 which overlays resistive layer 16. Emitters 14 are in the shape of cones which are formed within apertures 23 through gate electrode 22 and insulating layer 20. The 25 thickness of the conductive layer forming gate electrode 22 and the thickness of insulating layer 20 are chosen in conjunction with the size of apertures 23 so that the apex of each emitter 14 is substantially level with gate electrode 22. Gate electrode 22 is arranged as rows of conductive bands 30 across the surface of substrate 18, and the mesh structure of conductors 13 is arranged as columns of conductive bands across the surface of substrate 18. Emitters 14 are activated by energizing a row of gate electrode 22 and a column of conductors 13, which correspond to a pixel of display device 35 8.
Anode plate 10 comprises a substantially transparent substrate 26 with a plurality of electrically conductive regions 28 formed on substrate 26. In one embodiment, conductive regions 28 are spaced-apart to form parallel stripes on anode plate 10. Conductive regions 28 may also be continuous, such as the structure found in a cathode ray tube (CRT). Conductive regions 28 are formed on the surface of substrate 26, or on an optional thin insulating layer of silicon dioxide (Si02) 34 (FIGS. 2A and 2B). In display device 8, conductive regions 28 of anode plate 10 are positioned opposite gate electrode 22 of emitter plate 12.
In this example, conductive regions 28, which comprise the anode electrode, are in the form of electrically isolated 5Q stripes forming parallel conductive bands across the surface of substrate 26. Luminescent material 24 is formed over conductive regions 28 so as to be directly facing and immediately adjacent gate electrode 22. No true scaling information is intended to be conveyed by the relative sizes 55 and positioning of the elements of anode plate 10 and the elements of emitter plate 12 as depicted in FIG. 1.
Getter material 29 is disposed on substrate 26 and between conductive regions 28. Getter material 29, when activated and sealed in display device 8, acts as a pump to 60 adsorb undesirable elements caused by outgassing of surfaces and films inside display device 8 and finite leak rates from the outside atmosphere.
The placement of getter material 29 on anode plate 10 provides several advantages. Getter material 29 is placed in 65 close proximity to those components of display device 8 which are subject to outgassing, such as luminescent mate
rial 24 and gate electrode 22, and in close proximity to those components of display device 8 which are adversely affected by increases in gas pressure, such as emitters 14. This placement substantially increases the pumping effectiveness of the getter material from approximately one milliliter per second when getters are placed in the periphery of the display to as much as 1,000 liters per second. By virtue of its electrical insulating quality, getter material 29 increases the electrical isolation between conductive regions 28, which permits higher anode potentials without the risk of breakdown due to increased leakage current. Moreover, getter material 29 may be opaque to improve picture contrast of display device 8.
Emitters 14 are activated by applying a negative potential to conductors 13, functioning as the cathode electrode relative to the gate electrode 22, via voltage supply 30. The induced electric field draws electrons from the apexes of emitters 14. The emitted electrons are accelerated towards anode plate 10, which is positively biased by the application of a larger positive voltage from voltage supply 32 coupled between gate electrode 22 and conductive regions 28 functioning as the anode electrode. Energy from the electrons attracted to conductive regions 28 is transferred to luminescent material 24, resulting in luminescence. The luminescence is observed through conductive regions 28 and substrate 26. The electron charge is transferred from luminescent material 24 to conductive regions 28, completing the electrical circuit to voltage supply 32.
FIG. 2A illustrates, in cross-section, an anode plate 10 for use in display device 8 fabricated using the process steps described below with reference to FIGS. 3A through 3G. Anode plate 10 comprises a transparent substrate 26, which may include a thin layer 34 of an insulating material, such as silicon dioxide (Si02). A plurality of spaced-apart, electrically conductive regions 28 are patterned on insulating layer 34. Conductive regions 28 collectively comprise the anode electrode of display device 8. Luminescent material 24R, 24G, and 24B, referred to collectively as luminescent material 24, is positioned adjacent to conductive regions 28. Getter material 29 is disposed on substrate 26 and between conductive regions 28.
In the present example, substrate 26 preferably comprises glass. For the case where ultraviolet emission is important, substrate 26 may comprise quartz. Also in this example, conductive regions 28 comprise a plurality of parallel stripe conductors which extend normal to the plane of the drawing sheet. A suitable material for conductive regions 28 may be indium tin oxide (ITO), which is sufficiently optically transparent and electrically conductive. By way of illustration, parallel stripes of conductive regions 28 may be eighty microns in width, and spaced from one another by thirty microns. In this example, luminescent material 24 comprises a particulate phosphor coating which luminesces in one of the three primary colors, red (24s), green (24G), and blue (24B). Luminescent material 24 may also comprise a thinfilm phosphorescent material or any other suitable material that luminesces when subjected to electron bombardment or impingement. The thickness of conductive regions 28 may be approximately one hundred and fifty nanometers, and the thickness of luminescent material 24 may be approximately fifteen microns. Luminescent material 24 may be applied to conductive regions 28 using electrophoretic deposition.
A getter, such as getter material 29, has surfaces that can be rendered chemically active so as to promote the adsorption of ambient species. To be highly effective, the getter should have a high surface area to volume ratio. Also the getter should be chosen to specifically react with substances