Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
1998-04-06
2001-06-05
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169100, C313S496000, C313S497000
Reexamination Certificate
active
06242865
ABSTRACT:
TECHNICAL FIELD
The present invention relates in general to field emission display devices, and in particular to field emission display devices with focusing electrodes.
BACKGROUND OF THE INVENTION
Conventional field emission flat panel display devices are convenient for use in applications which require display devices having less bulk, weight and power consumption than venerable cathode ray tube (CRT) display devices. As shown in
FIG. 1
, a conventional field emission display device
10
includes a baseplate
12
having a plurality of field-induced electron emitters
14
carried by a supporting substrate
16
. The emitters
14
are disposed within respective apertures in an insulating layer
18
deposited on the surface of the supporting substrate
16
. Also, a conductive layer forming an extraction grid
20
is deposited on the insulating layer
18
peripherally about the respective apertures of the emitters
14
.
The conventional field emission display device
10
shown in
FIG. 1
also includes a faceplate
22
having a transparent viewing layer
24
separated from the baseplate
12
by spacers (not shown) between the faceplate
22
and the baseplate
12
. An anode
26
such as an indium tin oxide layer is deposited on a surface of the viewing layer
24
facing the baseplate
12
. Also, localized portions of a luminescent layer
28
are deposited on the anode
26
. The luminescent layer
28
typically comprises a phosphorescent material, such as a cathodophosphorescent material, which emits light when bombarded by electrons. A black matrix
30
is deposited on the anode
26
between the localized portions of the luminescent layer
28
to improve the contrast of the field emission display device
10
by absorbing ambient light.
In operation, a conductive voltage V
c
such as 40 volts applied to the extraction grid
20
and a source voltage V
s
such as 0 volts applied to the emitters
14
creates an intense electric field around the emitters
14
. This electric field causes an electron emission to occur from each of the emitters
14
in accordance with the well-known Fowler-Nordheim equation. An anode voltage V
a
such as 1,000 volts applied to the anode
26
draws these electron emissions toward the faceplate
22
. Some of these electron emissions impact on the localized portions of the luminescent layer
28
and cause the luminescent layer
28
to emit light. In this manner, the field emission display device
10
provides a display. Although the field emission display device
10
is shown in
FIG. 1
having only two emitters
14
associated with each localized portion of the luminescent layer
28
for ease of understanding, those with skill in the field of this invention will understand that hundreds of emitters
14
may be associated with each localized portion of the luminescent layer
28
in order to average out individual differences in the electron emissions from different emitters
14
.
In a conventional field emission display device configured as a monochrome display, each localized portion of the luminescent layer of the display device comprises one pixel of the monochrome display. Also, in a conventional field emission display device configured as a color display, each localized portion of the luminescent layer comprises a green, red or blue sub-pixel of the color display, and a green, a red and a blue sub-pixel together comprise one pixel of the color display. As a result, each pixel in a monochrome display and each sub-pixel in a color display is uniquely associated with one of the localized portions of the luminescent layer and hence is uniquely associated with a set of emitters.
If the electron emission from an emitter associated with a first localized portion of the luminescent layer of a conventional field emission display device also impacts on a second localized portion of the luminescent layer, then it causes both localized portions to emit light. As a result, a first pixel or sub-pixel uniquely associated with the first localized portion correctly turns on, and a second pixel or sub-pixel uniquely associated with the second localized portion incorrectly turns on. In a color display this can cause, for example, a purple light to be emitted from a blue sub-pixel and a red sub-pixel together when only a red light from the red sub-pixel was desired. This is obviously problematic because it provides a poor display.
This problem can be referred to as bleedover, and it can occur because the electron emission from each emitter in a conventional field emission display device tends to spread out from the baseplate of the display device. If the electron emission is allowed to spread out too far, it will impact on more than one localized portion of the luminescent layer of the display device. The likelihood that bleedover will occur is exacerbated by any misalignment between each localized portion of the luminescent layer and its associated set of emitters.
In conventional field emission display devices, bleedover is alleviated in three ways. First, the anode voltage V
a
applied to the anode of the conventional display device is a relatively high voltage such as 1,000 volts so the electron emissions from the emitters of the display device are rapidly accelerated toward the anode. As a result, the electron emissions have less time to spread out. Second, the gap between the baseplate and the faceplate of the conventional display device is relatively small, again giving the electron emissions less time to spread out. Third, the localized portions of the luminescent layer of the conventional display device are spaced relatively far from one another because of the relatively low display resolution provided by the conventional field emission display device. As a result, the electron emissions impact on the correct localized portion of the luminescent layer before they have a chance to impact on an incorrect localized portion.
However, as display designers attempt to increase the display resolution of the conventional field emission display device to provide a superior display, they necessarily crowd the localized portions of the luminescent layer of the display device closer together. As a result, bleedover begins to occur.
One solution to this problem might seem to be to decrease the distance between the faceplate and the baseplate of the conventional field emission display device. If this distance is decreased, the electron emissions from the emitters of the display device have less time to spread out and cause bleedover. However, it has been found that this is an impractical solution because the anode voltage V
a
applied to the anode of the display device needs to be as much as 1,000 volts or more in practice in order to adequately accelerate the electron emissions toward the anode. If the distance between the faceplate and the baseplate is decreased, arcing begins to occur between the faceplate and the baseplate because of this relatively high voltage. If, instead, the anode voltage V
a
is increased in order to accelerate the electron emissions toward the anode more rapidly and thereby prevent bleedover, arcing also begins to occur between the faceplate and the baseplate. Thus, there seems to be no practical way to both increase the display resolution of the conventional field emission display device and successfully prevent bleedover.
Therefore, there is a need in the art for a high display resolution field emission display device which successfully prevents bleedover.
SUMMARY OF THE INVENTION
In a preferred embodiment the present invention provides an electronic system including a display device having a baseplate and a faceplate. The baseplate includes an insulating layer having a plurality of apertures therein positioned on the surface of a supporting substrate. The baseplate also includes a plurality of field-induced electron emitters each carried by the supporting substrate and disposed within a respective aperture in the insulating layer. The baseplate further includes a conductive layer positioned on the insulating layer peripherally about the apertures
Alemu Ephrem
Dorsey & Whitney LLP
Micro)n Technology, Inc.
Wong Don
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