Electric lamp or space discharge component or device manufacturi – Process – With assembly or disassembly
Reexamination Certificate
2000-04-13
2001-08-28
Ramsey, Kenneth J. (Department: 2879)
Electric lamp or space discharge component or device manufacturi
Process
With assembly or disassembly
Reexamination Certificate
active
06280273
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to the structure and preparation of an organic electroluminescent display device (abbreviated as organic EL display device, hereinafter) for use as a display device or light source.
2. Background Art
Display devices which use organic EL elements have the following sorts of advantages over the liquid-crystal displays that currently represent the mainstream in flat panel displays.
1) They are self-emissive, so the viewing angle is wider.
2) Displays only 2-3 mm thick can easily be manufactured.
3) A polarizing plate is not used, so the color of the emitted light is natural.
4) The broad dynamic range in brightness results in a crisp, vibrant display.
5) They operate over a broad range in temperature.
6) The response rate is at least three orders of magnitude faster than liquid-crystal displays, easily enabling the display of moving images.
Despite such superiority, the appearance of organic EL display devices in the market was retarded for the following reason.
In general, organic EL elements include a stack of three thin films having different functions, an electrode in the form of a “transparent conductive film,” an “organic layer including a light emitting layer,” and another electrode made of a “metal or alloy having a low work function.” Difficult problems arose in the manufacture of EL elements, since the “organic layer including a light emitting layer” and “metal or alloy having a low work function” are susceptible to degradation by moisture and oxygen, and the “organic layer including a light emitting layer” is readily soluble in solvents and less resistant to heat. Differently stated, in methods using water, organic solvents and heat, once the “organic layer including a light emitting layer” and a layer of “metal or alloy having a low work function” were formed, it was difficult to isolate and divide the elements. This means that when it is desired to manufacture an organic EL display device of an equivalent class to the currently available display devices realized with liquid crystal, the full-grown semiconductor manufacturing technology and liquid crystal display manufacturing technology cannot be applied without modification.
Under the circumstances, several techniques capable of separating second electrode elements without exposure to the ambient air were devised. With these techniques, it became possible to manufacture highly reliable organic EL displays.
One exemplary method is disclosed in JP-A 275172/1993, JP-A 258859/1993, U.S. Pat. No. 5,276,380, and U.S. Pat. No. 5,294,869. This method utilizes the phenomenon that as shown in
FIG. 30
, when walls
43
of a height exceeding the thickness of a film
44
constructing the organic EL medium are positioned between display line electrodes to be separated, and a material
41
for organic EL elements is vacuum evaporated from a direction not orthogonal to a surface of a substrate
33
, the material
41
is not deposited in the areas shadowed by the walls
43
.
However, in order to form light emitting lines of an equal width in satisfactory yields, insulators
42
having a greater width than the walls
43
, called electrically insulative strips or pedestals
42
, must be formed below the walls
43
as shown in FIG.
30
. The reason is that since in the vacuum deposition process, the presence of the walls
43
obstructs the adhesion of an organic film in proximity to the walls
43
, a structure without the insulative strips
42
permits short-circuiting to occur between the first and second electrodes in the proximity of the walls
43
where the organic film becomes thin. Then the manufacturing yield becomes extremely low with large sized substrates which make it difficult to improve the thickness uniformity of the organic film.
Inversely, when the insulative strips
42
are formed for the purpose of increasing the manufacturing yield, the width of light emitting lines is restricted by the region where the insulative strips
42
are formed. The width of the insulative strips
42
is designed in accordance with the angle between a metal evaporation source
31
and the substrate
33
and the size of the substrate
33
itself, as shown in
FIG. 31
, for example. More particularly, as shown in
FIG. 31
, for example, if the width of the insulative strip
42
is narrow, there arises the problem that the width of light emitting lines varies with the position on the substrate
33
because at position A where the angle between metal atoms traveling from the metal evaporation source
31
to the substrate
33
and the wall
43
is small, as shown in
FIG. 32
, a film is deposited without problems, but at position B where the angle between metal atoms traveling from the metal evaporation source
31
to the substrate
33
and the wall
43
is large, as shown in
FIG. 33
, the region shadowed by the wall
43
becomes wider so that the light emitting region becomes narrower. Accordingly, in order to produce light emitting lines of equal width over the entire area of the substrate, the insulative strips must be given a greater width including a margin. Also a margin of at least 3 &mgr;m to 5 &mgr;m is necessary for the alignment between the insulative strips and the walls when display devices are fabricated on a large sized substrate using an aligner of the full exposure type. However, widening the insulative strips directly incurs a reduction of the light emitting region, which is disadvantageous in achieving a bright display.
Alternative methods are methods of providing isolation between light emitting elements by furnishing cavity structures, trench structures or well structures, and forming light emitting elements in the respective structures, as disclosed in JP-A 262998/1996 and 264828/1996. Apparently, these methods give rise to a similar inconvenient problem.
Further, in methods of forming on an electrode insulative walls having inversely tapered structures, overhang structures or undercut structures as disclosed in JP-A 315981/1996, 283280/1997, and 161969/1997, insulative strips become necessary in actual practice from considerations to form light emitting lines of an equal width in good yields.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an organic EL display device having a greater proportion of light emitting region and high reliability, and enabling use of a large size substrate, fabrication of a number of elements within a substrate, and reduction of manufacturing cost, and a method for preparing the same.
While several structures for isolating elements (which are designated element-isolating structures, hereinafter), including wall structures, cavity structures, trench structures, well structures, inversely tapered structures, overhang structures and undercut structures were proposed in the art, the element-isolating structures are always located closer to a depositing material source than the light emitting elements. On this account, when a display device is manufactured in high yields, insulative strips must be given a margin having a width approximately equal to the height of the element-isolating structures. However, the provision of a greater margin leads to narrowing of the light emitting region, affecting the quality of display. Lowering the height of the element-isolating structures increases the possibility for the “metal electrode having a low work function” to cover the element-isolating structures, which means that the isolation of elements becomes difficult and hence, the manufacturing yield lowers.
For example, when walls of 4 &mgr;m high and 5 &mgr;m wide are formed, the situation is as follows. Since the error of alignment between walls and insulative strips is approximately 5 &mgr;m when a common aligner of the full exposure type is used, the insulative strips must also have a width of 5 &mgr;m in consideration of a margin. Also, where the “organic layer including a light emitting layer” is incident on the substrate from a maximum inclination angle of 45° relative to a direction orthogonal to the substr
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ramsey Kenneth J.
TDK Corporation
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