Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2003-01-14
2004-10-19
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S114000
Reexamination Certificate
active
06806927
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to reflective electrooptic devices and electronic apparatuses using the same. More particularly, the present invention relates to a pixel structure of a reflective electrooptic device.
2. Description of Related Art
Related art electrooptic devices, such as liquid crystal devices, can be used as direct viewing type display devices for various apparatuses. Among the electrooptic devices described above, for example, in an active matrix liquid crystal device using TFTs as a non-linear element to provide pixel switching, as shown in
FIGS. 25 and 26
, pixel switching TFTs (thin film transistors)
30
and pixel electrodes
9
a
, each electrode being composed of a transparent conductive film, such as an ITO film, and being connected to the corresponding TFT
30
, are formed on a TFT array substrate
10
, and in addition, liquid crystal
50
used as an electrooptic material is held between the TFT array substrate
10
and a counter substrate
20
.
In addition, in a reflective liquid crystal device, a light reflection film
8
a
to reflect outside light incident from the counter substrate
20
side is formed at a lower layer side of a pixel electrode
9
a
so that the incident light is reflected from the TFT array substrate
10
side to the counter substrate
20
side, thereby displaying an image using light emitted from the counter substrate
20
side (reflection mode).
However, in a reflective liquid crystal device, when the directionality of light reflected from the light reflection film
8
a
is strong, apparent viewing angle dependence occurs in which brightness of image varies depending on a viewing angle or the like. Accordingly, when liquid crystal devices are manufactured, a photosensitive resin, such as an acrylic resin, is applied to an interlayer insulating film
4
or a surface protection film
14
formed thereon, and on the surface thereof, an irregularity-forming layer
13
a
is formed by a photolithographic technique, thereby forming an irregular pattern
8
g
for light scattering on a surface of the light reflection film
8
a.
In the following example, as shown in
FIG. 27
, after half exposure is performed for a photosensitive resin
13
using an exposure mask
200
so that the photosensitive resin
13
is partly exposed in the thickness direction thereof, the photosensitive resin
13
is melted by heating following the development, thereby forming the irregularity-forming layer
13
a
having irregularities thereon in conformity with gentle changes in film thickness. Accordingly, the light reflection film
8
a
is formed directly on the upper layer of the irregularity-forming layer
13
a.
That is, when half exposure is performed for the photosensitive resin
13
, since the photosensitive resin
13
are only partly exposed in the thickness direction thereof, after being developed, concave portions
13
b
are formed at positions which were exposed, and at the same time, the original thickness is maintained at positions which were not exposed. Accordingly, when the photosensitive resin
13
is melted by performing heat treatment following the development, the thickness of the photosensitive resin
13
changes gently, thereby forming the irregularity-forming layer
13
a
having gentle irregularities thereon in conformity with the changes in film thickness described above. As a result, even when the light reflection film
8
a
is formed directly on the upper layer of the irregularity-forming layer
13
a
, the gentle irregular pattern
8
g
having no edges is formed on the surface of the light reflection film
8
a.
However, in a related art liquid crystal device, since conductive films forming various wires and the TFT
30
, such as a scanning line
3
a
, a capacitance line
3
b
, a data line
6
a
, and a drain electrode
6
b
, are formed at the lower layer side of the irregularity-forming layer
13
a
, a height difference is formed in accordance with the presence of the conductive films described above. That is, in a pixel region, the following are provided: a first region
10
a
in which an extending portion
1
f
of a semiconductor film
1
a
, the capacitance line
3
b
, and the drain electrode
6
b
are provided so as to form a multilayer structure; a second region
10
b
in which the drain electrode
6
b
is formed, but the extending portion
1
f
of the semiconductor film
1
a
and the capacitance line
3
b
are not formed; and a third region
10
c
in which the extending portion
1
f
of the semiconductor film
1
a
, the capacitance line
3
b
, and the drain electrode
6
b
are not formed. As a result, among the regions described above, the height differences are present in accordance with the difference in the number of conductive films formed in the region. Hence, as shown in
FIG. 27
, when exposure is performed for the photosensitive resin
13
, since the distance from a light source to a higher position of the step thus formed is different from that to a lower position thereof, focus blurring occurs, resulting in occurrence of uneven exposure.
In addition, when exposure is performed for the photosensitive resin
13
, between a region (the first region
10
a
, and the second region
10
b
) in which the conductive films are provided at the lower layer side and a region (the third region
10
c
) in which the conductive film is not provided at the lower layer side, a problem of uneven exposure, which is caused by the presence and non-presence of reflected light from the conductive film and the variation in intensity thereof, occurs.
When the uneven exposure described above occurs, for example, since the concave portion
13
b
of the irregularity-forming layer
13
may become shallower at a lower position, the irregularity-forming layer
13
a
cannot be formed as designed. Accordingly, it is not preferable since a desired irregular pattern cannot be formed on the surface of the light reflection film
8
a.
In addition, there is the case in which the irregularity-forming layer
13
a
is entirely exposed so as to form a predetermined pattern, and the irregular pattern
8
g
is formed on the surface of the light reflection film
8
a
in accordance with the presence and non-presence of the irregularity-forming layer
13
a
. In the case described above, since edges are formed on the irregularity-forming layer
13
a
, after a photosensitive resin having high fluidity is applied onto the upper layer of the irregularity-forming layer
13
a
to additionally form an upper insulating film, on the upper layer side thereof, the light reflection film
8
a
is formed. However, even in this case, when there is a height difference at the lower layer side of the irregularity-forming layer
13
a
, uneven exposure occurs.
In addition, when a photosensitive resin is applied onto a region in which a height difference is present, due to the planation as shown in
FIG. 27
, a thin film of the photosensitive resin is formed in a higher region, and on the other side, a thick film thereof is formed in a lower region. As a result, after exposure and development, when the photosensitive resin
13
is melted by heating to form a irregularity-forming layer
13
a
having gentle irregularities thereon, since the thin film of the photosensitive resin is formed in the higher region, the sag of the resin is small, thereby forming relatively large irregularities. On the other hand, since the thick film of the photosensitive resin is formed in the lower region, the sag of the resin becomes large, and hence the irregularities become small, resulting in a disadvantageous increase in variation of the irregularities.
SUMMARY OF THE INVENTION
The present invention addresses or solves the above and/or other problems, and provides a reflective electrooptic device and an electronic apparatus using the same. In the reflective electrooptic device described above, when the irregularity-forming layer is formed by a photolithographic technique, the conditions at the lower layer side of the irregularity-forming layer are maintained un
Kim Robert H.
Schechter Andrew
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