Electric lamp or space discharge component or device manufacturi – Process – Electrode making
Reexamination Certificate
2001-07-25
2002-10-29
Ramsey, Kenneth J. (Department: 2879)
Electric lamp or space discharge component or device manufacturi
Process
Electrode making
C445S058000
Reexamination Certificate
active
06471561
ABSTRACT:
TECHNICAL FIELD
This invention relates in general to visual displays for electronic devices and more particularly to improved emitters for field emission displays.
BACKGROUND OF THE INVENTION
FIG. 1
is a simplified side cross-sectional view of a portion of a field emission display
10
including a faceplate
20
and a baseplate
21
in accordance with the prior art.
FIG. 1
is not drawn to scale. The faceplate
20
includes a transparent viewing screen
22
, a transparent conductive layer
24
and a cathodoluminescent layer
26
. The transparent viewing screen
22
supports the layers
24
and
26
, acts as a viewing surface and as a wall for a hermetically sealed package formed between the viewing screen
22
and the baseplate
21
. The viewing screen
22
may be formed from glass. The transparent conductive layer
24
may be formed from indium tin oxide. The cathodoluminescent layer
26
may be segmented into pixels yielding different colors for color displays. Materials useful as cathodoluminescent materials in the cathodoluminescent layer
26
include Y
2
O
3
:Eu (red, phosphor P-56), Y
3
(Al, Ga)
5
O
12
:Tb (green, phosphor P-53) and Y
2
(SiO
5
):Ce (blue, phosphor P-47) available from Osram Sylvania of Towanda Pa. or from Nichia of Japan.
The baseplate
21
includes emitters
30
formed on a planar surface of a substrate
32
. The substrate
32
is coated with a dielectric layer
34
. In one embodiment, this is effected by deposition of silicon dioxide via a conventional TEOS process. The dielectric layer
34
is formed to have a thickness that is less than a height of the emitters
30
. This thickness is on the order of 0.4 microns, although greater or lesser thicknesses may be employed. A conductive extraction grid
38
is formed on the dielectric layer
34
. The extraction grid
38
may be formed, for example, as a thin layer of doped polysilicon. The radius of an opening
40
created in the extraction grid
38
, which is also approximately the separation of the extraction grid
38
from the tip of the emitter
30
, is about 0.4 microns, although larger or smaller openings
40
may also be employed.
The baseplate
21
also includes a field effect transistor (“FET”)
50
formed in the surface of the substrate
32
for controlling the supply of electrons to the emitter
30
. The FET
50
includes an n-tank
52
formed in the surface of the substrate
32
beneath the emitter
30
. The n-tank
52
serves as a drain for the FET
50
and may be formed via conventional masking and ion implantation processes. The FET
50
also includes a source
54
and a gate electrode
56
. The gate electrode
56
is separated from the substrate
32
by a gate oxide
57
and a field oxide layer
58
. The emitter
30
is typically about a micron tall, and several emitters
30
are generally included together with each n-tank
52
, although only one emitter
30
is illustrated.
The substrate
32
may be formed from p-type silicon material having an acceptor concentration N
A
ca. 1-5×10
15
/cm
3
, while the n-tank
52
may have a surface donor concentration N
D
ca. 1-2×10
16
/cm
3
.
In operation, the extraction grid
38
is biased to a voltage on the order of 40-80 volts, although higher or lower voltages may be used, while the substrate
32
is maintained at a voltage of about zero volts. Signals coupled to the gate
56
of the FET
50
turn the FET
50
on, allowing electrons to flow from the source
54
to the n-tank
52
and thus to the emitter
30
. Intense electrical fields between the emitter
30
and the extraction grid
38
then cause field emission of electrons from the emitter
30
. A larger positive voltage, ranging up to as much as 5,000 volts or more but often 2,500 volts or less, is applied to the faceplate
20
via the transparent conductive layer
24
. The electrons emitted from the emitter
30
are accelerated to the faceplate
20
by this voltage and strike the cathodoluminescent layer
26
. This causes light emission in selected areas, i.e., those areas adjacent to where the FETs
50
are conducting, and forms luminous images such as text, pictures and the like. Integrating the FETs
50
in the substrate
32
to provide an active display
10
(ie., a display
10
including active circuitry for addressing and providing control signals to specific emitters
30
, etc.) yields advantages in size, simplicity and ease of interconnection of the display
10
to other electronic componentry.
When the emitted electrons strike the cathodoluminescent layer
26
, compounds in the cathodoluminescent layer
26
dissociate. This causes outgassing of materials from the cathodoluminescent layer
26
. When the outgassed materials react with the emitters
30
, a barrier height of the emitters
30
may increase. When the emitter barrier height increases, the emitted current is reduced. This reduces the luminance of the display
10
.
Residual gas analysis indicates that the dominant materials outgassed from some display cathodoluminescent layers
26
include oxygen and hydroxyl radicals. This leads to oxidation of the emitters
30
and especially emitters
30
formed from silicon. Silicon emitters
30
are useful because they are readily formed and integrated with other electronic devices on silicon substrates. Electron emission is reduced when silicon emitters
30
oxidize. This degrades performance of the display
10
.
Therefore there is a need for a way to prevent degradation, and especially oxidation, of emitters
30
used in displays
10
.
SUMMARY OF THE INVENTION
In accordance with an aspect of the invention, a field emission display has a plurality of emitters including titanium silicide nitride. The plurality of emitters is formed on a substrate that is part of a baseplate. A dielectric layer is formed on the substrate, a semiconductor device formed in or on the substrate for controlling the flow of electrons to the emitters, and the plurality of emitters. The display includes an extraction grid formed in a plane defined by tips of the plurality of emitters. The extraction grid includes an opening surrounding and in close proximity to each tip of the plurality of emitters. Significantly, the tips include titanium silicide nitride.
As a result, the emitters are markedly more resistant to reaction with compounds released from the cathodoluminescent layer by electron bombardment than are silicon emitters. This results in a robust display that resists emitter degradation the emitters may also exhibit increased emissivity due to reduced work function provided by titanium silicide nitride compared to the work function of silicon.
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patent: 5666020 (1997-09-01), Takemura
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Michiaki Endo et al., “Fabrication of transition metal nitride field emitters,”Applied Surface Science, 94/95:113-116, 1996.
Chalamala, Babu R. and Bruce E. Gnade, “Fed Up With Fat Tubes,”IEEE Spectrum, Apr. 1998, pp. 42-51.
Eung Joon Chi et al., “Electrical Characteristics of Metal Silicide Field Emitters” 9thInternational Vacuum Microelectronics Conference, St. Petersburg, 1996, pp. 188-191.
Masayuki Nakamoto et al., “Low Operation Voltage Field Emitter Arrays Using Low Work Function Materials Fabricated by Transfer Mold Technique,”EEDM, pp. 297-300, 1996.
Yukihiro Morimoto et al., “Analysis of Gas Release From Vitreous Silica,”Journal of Non-Crystalline Solids, 139:35-46, 1992.
Lee John K.
Moradi Behnam
Zhang Tianhong
Dorsey & Whitney LLP
Micro)n Technology, Inc.
Ramsey Kenneth J.
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