Electric lamp or space discharge component or device manufacturi – Process – With assembly or disassembly
Reexamination Certificate
2001-11-02
2002-12-10
Ramsey, Kenneth J. (Department: 2879)
Electric lamp or space discharge component or device manufacturi
Process
With assembly or disassembly
Reexamination Certificate
active
06491561
ABSTRACT:
TECHNICAL FIELD
This invention relates in general to visual displays for electronic devices and in particular to improved spacers 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
18
and a baseplate
20
in accordance with the prior art.
FIG. 1
is not drawn to scale. The faceplate
18
includes a transparent viewing screen
22
, an antireflective layer
23
, a transparent conductive layer
24
and a cathodoluminescent layer
26
. The transparent viewing screen
22
supports the layers
23
,
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
20
. The viewing screen
22
may be formed from glass. The antireflective layer
23
may be formed from Si
3
N
4
having a thickness of 900 Angstroms. The transparent conductive layer
24
may be formed from indium tin oxide. The cathodoluminescent layer
26
may be segmented into localized portions that are separated from each other within openings in a grille
28
of light-absorbing, opaque material formed on the antireflective layer
23
. The light absorption and opacity of the grille
28
increases the contrast of the faceplate
18
. The grille
28
is formed by conventional patterning of a layer of material such as silicon, cobalt oxide, manganese oxide or chromium oxide.
In a conventional monochrome display
10
, each localized portion of the cathodoluminescent layer
26
forms one pixel of the display
10
. Also, in a conventional color display
10
, each localized portion of the cathodoluminescent layer
26
forms a primary color such as a green, red or blue sub-pixel of the display
10
. 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
20
includes emitters
30
formed on a planar surface of a substrate
32
, which may be formed from glass having a layer of silicon formed on it. The baseplate
20
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 approximately equal to or just 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 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.
In operation, the extraction grid
38
is biased to a voltage on the order of 100 volts, although higher or lower voltages may be used, while the baseplate
32
is maintained at a voltage of about zero volts. Signals coupled to the emitter
30
allow electrons to flow to the emitter
30
. Intense electrical fields between the emitter
30
and the extraction grid
38
cause field emission of electrons from the emitter
30
in response to the signals impressed on the emitter
30
.
An anode voltage V
A
, ranging up to as much as 5,000 volts or more but often 2,500 volts or less, is applied to the faceplate
18
via the transparent conductive layer
24
. The electrons emitted from the emitter
30
are accelerated to the faceplate
18
by the anode voltage V
A
and strike the cathodoluminescent layer
26
. The electron bombardment causes light emission in selected areas, i.e., those areas adjacent to where the emitters
30
are emitting, and forms luminous images such as text, pictures and the like.
A gap separating the faceplate
18
and the baseplate
20
of the conventional field emission display
10
is relatively small, on the order of one thousandth of an inch or twenty-five microns per 100 volts of anode voltage V
A
. Too large a gap leads to spreading of the emitted electrons and thus to defocusing or blurring of luminous images formed on the faceplate
18
. Too small a gap leads to catastrophic failure of the display
10
due to arcing between the faceplate
18
and the baseplate
20
. The gap must be evacuated in order for electrons to travel from the emitters
30
to the faceplate
18
. As a result, atmospheric pressure is exerted on the faceplate
18
and the baseplate
20
that forces the baseplate
20
and the faceplate
18
toward each other.
In relatively small displays
10
, such as those having a diagonal measurement of an inch or less, the pressure on the faceplate
18
does not cause significant bowing of the faceplate
18
. In larger displays
10
, however, the faceplate
18
tends to bow towards the baseplate
20
, and the baseplate
20
also bows towards the faceplate
18
. In a display
10
having a diagonal measurement of thirty inches, the force compressing the baseplate
20
and the faceplate
18
together is several tons. The bowing is exaggerated because of need to keep the faceplate
18
and the baseplate
20
light and thus to make them as thin as is practicable. Bowing leads to non-uniform spacing between the faceplate
18
and the baseplate
20
, causing focusing and intensity variations and thereby degrading images formed on the faceplate
18
. As a result, spacers
62
are incorporated between the faceplate
18
and the baseplate
20
.
The spacers
62
typically are formed from glass and have a width of 25 to 250 micrometers. The spacers
62
typically extend from the baseplate
20
to the faceplate
18
and thus have a height that is similar to the spacing separating the faceplate
18
from the baseplate
20
, in the range of 0.2 to 1 mm. In relatively small displays
10
, the transparent viewing screen
22
may be formed from glass having a thickness of about 1.1 mm. In such displays
10
, spacers
62
are needed about every fifteen mm. in order to provide adequate support for the faceplate
18
, but the spacers
62
may be separated by smaller distances. The spacers
62
typically are positioned to contact the faceplate
18
in areas that are opaque due to the grille
28
in order to avoid interfering with images formed on the display
10
.
Spacers
62
tend to be made from insulating materials because the large voltage applied to the transparent conductive layer
24
otherwise causes arcing between the baseplate
20
and the faceplate
18
. Additionally, other techniques that might be tried are either impractical or unworkable for a variety of reasons. For example, forming reverse-biased diodes (not illustrated) on the baseplate
32
and placing conductive spacers
32
on the reverse-biased diodes is impractical, because the materials requirements for such diodes are not compatible with other requirements for the baseplate
32
.
Typically, the spacers
62
are made from glass or ceramic. As described in U.S. Pat. No. 5,717,287, entitled “Spacers For A Flat Panel Display And Method,” issued to Amrine et al., the spacers
62
can cause problems in the display
10
. When the spacers
62
are affixed to the faceplate
18
using organic glue, the glue can chemically decompose, causing contamination of the evacuated interior of the display
10
. Alternatively, the glue can exhibit mechanical failure, causing the spacers
62
to become detached and misplaced in the interior of the display
10
. Affixation of glass spacers
62
to the faceplate
18
using glass frit results in a brittle bond that is subject to mechanical failure and that may cause particulate contamination within the display
10
. Additionally, use of a jig to facilitate correct placement of the spacers
62
on the faceplate
18
is laborious and may be unreliable.
What is needed is a way to simp
Dorsey & Whitney LLP
Haynes Mack
Micro)n Technology, Inc.
Ramsey Kenneth J.
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