Electric lamp and discharge devices – With luminescent solid or liquid material – Vacuum-type tube
Reexamination Certificate
1998-07-13
2001-01-30
Day, Michael H. (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Vacuum-type tube
C313S309000, C313S351000, C313S336000
Reexamination Certificate
active
06181060
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to field emission devices and, more particularly, to processes for sharpening the emission tip of field emission devices.
BACKGROUND OF THE INVENTION
Cathode ray tube (CRT) displays, such as those commonly used in desk-top computer screens, function as a result of a scanning electron beam from an electron gun impinging on phosphors on a relatively distant screen. The electrons increase the energy level of the phosphors. When the phosphors return to their normal energy level, they release the energy from the electrons as a photon of light which is transmitted through the glass screen of the display to the viewer. One disadvantage of a CRT is the depth of the display required to accommodate the raster scanner.
Flat panel displays have become increasingly important in appliances requiring lightweight portable screens. Currently, such screens use electroluminescent or liquid crystal technology. Another promising technology is the use of a matrix-addressable array of cold cathode emission devices to excite phosphor on a screen, often referred to as a field emission display. To produce the desired field emission, a potential source is provided with its positive terminal connected to the gate, or grid, and its negative terminal connected to the emission electrode (cathode conductor substrate). The potential source is variable for the purpose of controlling the electron emission current. Upon application of a potential between the electrodes, an electric field is established between the emission tips and the low potential anode grid, thus causing electrons to be emitted from the cathode tips through the holes in the grid electrode.
The clarity, or resolution, of a field emission display is a function of a number of factors, including emission tip sharpness, alignment and spacing of the gates, or grid openings, which surround the tips, pixel size, as well as cathode-to-gate and cathode-to-screen voltages. These factors are also interrelated. For example, the voltage required for electron emission from the emission tips is a function of both cathode-to-gate spacing and tip sharpness. A relatively sharper emission tip may both improve resolution and lower power consumption.
Existing techniques for sharpening the emission tip typically involve an oxidation process followed by an etch process. The surface of the semiconductor substrate, such as silicon, and the emission tip are first oxidized to produce an oxide layer of SiO
2
, which is then etched to sharpen the tip. The oxidation process is ordinarily either a wet or a dry process. In a dry oxidation process, the substrate and emission tip are exposed to an atmosphere containing a significant percentage of gaseous oxygen at temperatures of 800° C. or more. In a wet oxidation process the substrate and tip are exposed to steam at around 800° C.
In either existing oxidation technique, there is the risk that the oxidation process itself will induce flow of silicon and oxide, that is, cause the silicon and the forming oxide layer near the top of the emission tip to, in essence, flow down the sloping sides of the tip. This flowing action results in an undesirable rounding of the tip. In a dry process, oxidation typically does not appreciably occur below 800° C. However, at temperatures above 800° C., flow of silicon and oxide can readily occur. A wet process will usually grow a sufficient oxide layer at 800° C., however, the chemical nature of existing wet processes can nevertheless lead to significant flow of silicon and oxide.
SUMMARY OF THE INVENTION
In one aspect of the present invention, a method of sharpening the emission tip in a field emission device that has a semiconductor substrate is provided. The method includes the steps of forming an insulating layer on the semiconductor substrate and the emission tip by exposing the semiconductor substrate and the emission tip to a mixture of gases containing oxygen and ozone, and selectively removing a portion of the insulating layer to expose the emission tip.
In another aspect of the present invention, a method for manufacturing a field emission display having reduced surface leakage is provided. In the method at least one emission tip is formed on a substrate and a first insulator is disposed on the emission tip by exposing the substrate and the emission tip to a mixture of gases containing oxygen and ozone. A second insulator is disposed on the first insulator. The second insulator is selectively etchable to the first insulator. A third insulator is disposed on the second insulator. The second insulator is selectively etchable to the third insulator. A conductive layer is disposed on the insulators. The insulators and the conductive layer are planarized, and portions of the insulators are selectively removed to expose the emission tip.
In still another aspect of the present invention, a field emission display having reduced surface leakage is provided. The field emission display includes a semiconductor substrate and at least one emission tip. The at least one emission tip is sharpened by forming an insulating layer on the semiconductor substrate and the emission tip by exposing the semiconductor substrate and the emission tip to a mixture of gases containing oxygen and ozone and selectively removing a portion of the insulating layer to expose the emission tip to leave a dielectric region surrounding the emission tip. The field emission display also includes a conductive gate that is disposed on the dielectric region.
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Day Michael H.
Fletcher Yoder & Van Someren
Micro)n Technology, Inc.
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