Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1996-08-21
2001-01-30
Nguyen, Chanh (Department: 2775)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C315S169300
Reexamination Certificate
active
06181308
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to field emission devices, and more particularly, to field emission displays having current-limiting resistors.
BACKGROUND OF THE INVENTION
A typical field emission display
8
is shown in FIG.
1
. The display
8
includes a substrate or base plate
10
having a conductive layer
12
formed thereon. A plurality of emitters
14
are formed on the layer
12
. Also formed on the layer
12
is an electrically insulating layer
16
having a conductive layer formed thereon. The conductive layer formed on the insulating layer
16
typically functions as an extraction grid
18
to control the emission of electrons from the emitters
14
, and is typically formed from metal. An anode
20
, which acts as a display screen and has a cathodoluminescent coating
22
formed on an inner surface thereof, is positioned a predetermined distance from the emitters
14
. Typically, a vacuum exists between the emitters
14
and the anode
20
. A power source
24
generates a voltage differential between the anode
20
and the substrate
10
, which acts as a cathode. Also, a voltage applied to the extraction grid
18
generates an electric field between the grid and the substrate
10
. An electrical path is provided to the emitters
14
via the conductive layer
12
such that in response to this electric field, the emitters
14
emit electrons. The emitted electrons strike the cathodoluminescent coating
22
, which emit light to form a video image on the display screen. Examples of such field emission displays are disclosed in the following U.S. patents, all of which are incorporated by reference:
U.S. Pat. No.
Issue Date
3,671,798
June 20, 1972
3,970,887
July 20, 1976
4,940,916
July 10, 1990
5,151,061
September 29, 1992
5,162,704
November 10, 1992
5,212,426
May 18, 1993
5,283,500
February 1, 1994
5,359,256
October 25, 1994
Field emission displays, such as the field emission display
8
of
FIG. 1
, often suffer from technical difficulties relating to the control of the current flowing through the emitters
14
. For example, due to the relatively small dimensions of the components involved, manufacturing defects are common in which an emitter
14
is shorted to the extraction grid
18
. Because the voltage difference between the substrate
10
and the anode
20
is typically on the order of 1000 volts or more and a high electric field exists between tip
14
and substrate
10
, the above defect can cause a current to flow through the emitter
14
that is sufficient to destroy not only the shorted emitter
14
itself, but other surrounding emitters
14
and circuitry as well. Thus, such a current draw will typically result in damage to, if not complete destruction of, the field emission display. Furthermore, if the current through the emitters
14
is unregulated, it is virtually impossible to control the emission level of the emitters
14
, and thus the brightness level of the field emission display
8
.
Efforts to solve the above limitations have focused on providing a resistance between the conductive layer
12
and the emitters
14
to limit the current flow through the emitters
14
. An example of such a resistance is disclosed in U.S. Pat. No. 4,940,916, was previously incorporated by reference. One limitation to this scheme, however, is that the resistivity (which is the inverse of the conductivity) of the resistive layer often fluctuates in response to conditions that vary during the operation of the field emission display, particularly the varying light intensity resulting from the emitted electrons striking the cathodoluminescent coating
22
or from ambient light.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, a semiconductor structure is provided for use in a field emission display. The structure includes a substrate that may be formed from a semiconductor material, Coming glass, soda lime glass, plastic, or silicon dioxide. A first layer of a conductive material is formed on the substrate. A second layer of microcrystalline silicon is formed on the conductive layer. One or more cold-cathode emitters are formed on the second layer. The second layer forms a current-limiting resistance between the conductive layer and the emitters.
In one aspect of the invention the second layer, while exposed to optical energy, exhibits a resistivity that differs less than approximately 10% from the resistivity of the second layer while it is unexposed to optical energy, or “in the dark.”
In further aspects of the invention, the second layer of microcrystalline silicon is doped with an impurity of either the p-type or the n-type.
An advantage provided by one aspect of the present invention is a current-limiting resistor that has a resistivity that remains relatively stable while the resistor is exposed to varying light intensities.
REFERENCES:
patent: 3814968 (1974-06-01), Nathanson et al.
patent: 4940916 (1990-07-01), Borel et al.
patent: 5396150 (1995-03-01), Wu et al.
patent: 5532177 (1996-07-01), Cathey
patent: 5572041 (1996-11-01), Betsui et al.
patent: 5585301 (1996-12-01), Lee et al.
patent: 5619097 (1997-04-01), Jones
patent: 5656886 (1997-08-01), Westphal et al.
patent: 5696389 (1997-12-01), Ishikawa et al.
patent: 5729094 (1998-03-01), Geis et al.
patent: 5734361 (1998-03-01), Suzuki et al.
patent: 5747918 (1998-05-01), Eom et al.
patent: 5760536 (1998-06-01), Susukida et al.
patent: 0 757 341 (1997-02-01), None
patent: WO 95/07543 (1995-03-01), None
Shigeo Itoh et al., “A New Structure of Field Emitter Arrays”Journal of Vacuum Science and Technology B 14(3):1977-1981, 1996.
McGruer, Nicol, “NU/Micron R.I.S. F.E.A. Project,”First Quarterly Report, Department of Electrical and Computer Engineering, Northeastern University, Boston, MA 02115, Oct. 15, 1996.
Madan, Arun, and Melvin P. Shaw,The Physics and Applications of Amorphous Semiconductors, Academic Press, Inc., California, 1988, pp. 97-106, 117-125.
Lee, Kon Jiun, “Current Limiting of Field Emitter Array Cathodes,” thesis, Georgia Institute of Technology, 1986, pp. iii-xii, 1-165, 185-188.
Alwan James J.
Cathey, Jr. David A.
Lee John K.
Moradi Behnam
Tjaden Kevin W.
Dorsey & Whitney LLP
Micro)n Technology, Inc.
Nguyen Chanh
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