Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Including integrally formed optical element
Reexamination Certificate
2001-02-27
2002-10-15
Christianson, Keith (Department: 2813)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Including integrally formed optical element
C349S155000
Reexamination Certificate
active
06465268
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor display device using thin-film transistors. In particular, the invention relates to a semiconductor display device in which a pixel switching circuit and driver circuits are formed on the same substrate in an integral manner.
2. Description of the Related Art
In recent years, the techniques of forming semiconductor devices, such as thin-film transistors (TFTs), by using a semiconductor thin film formed on an inexpensive glass substrate have made rapid progress. This is because of increased demand for active matrix liquid crystal display devices.
In active matrix liquid crystal display devices, TFTs are provided for respective ones of hundreds of thousands to millions of pixel regions that are arranged in matrix and charge that enters or exits from each pixel electrode is controlled by the switching function of the associated TFT.
The basic configuration of an active matrix liquid crystal display device in which thin-film transistors are arranged will be described below with reference to
FIGS. 34A and 34B
.
FIG. 34A
is a sectional view obtained by cutting a liquid crystal display device by a plane perpendicular to a substrate, specifically taken along a chain line A-A′ in FIG.
34
B.
An insulating film (not shown) is formed on the surface of a transparent base substrate
1
. Reference numeral
2
denotes an active layer of a TFT;
3
, a gate electrode;
4
, a data line;
5
, a drain electrode;
6
, an interlayer insulating film;
7
, a black matrix;
8
, a transparent conductive film as a pixel electrode; and
9
, an alignment film.
In this specification, the structure including the base substrate
1
and the other members mentioned above (including the TFTs) is called an “TFT substrate.” Although
FIG. 34A
focuses on a single pixel, actually the TFT substrate is composed of a pixel area including hundreds of thousands to millions of pixel switching TFTs (called pixel TFTs) and peripheral driver circuit areas including a number of TFTs for driving the pixel TFTs.
On the other hand, reference numerals
10
-
12
denote a transparent substrate, a transparent conductive film as an opposed electrode, and an alignment film, respectively. The structure including these members, which is opposed to the TFT substrate, is called an “opposed substrate.”
As shown in
FIG. 35A
, the TFT substrate
20
and the opposed substrate
30
are subjected to an alignment treatment such as rubbing for giving proper alignment to a liquid crystal. Thereafter, to control a substrate interval (cell gap) between the TFT substrate
20
and the opposed substrate
30
, grainy spacers
41
are uniformly scattered over the entire surface of the TFT substrate
20
. Then, a sealing agent
42
is printed. The sealing agent
42
has a role of an adhesive for bonding the substrates
20
and
30
together as well as a role of a sealing material for sealing the space between the substrates
20
and
30
to prevent a liquid crystal material that will be injected there from leaking to the outside of the substrates.
FIG. 36
is a sectional view of the TFT substrate
20
. Since the grainy spacers
41
are uniformly scattered over the entire surface of the TFT substrate
20
to control the cell gap, the spacers
41
exist in not only the pixel area
22
but also the peripheral driver circuit regions
23
as shown in FIG.
36
. Usually, the pixel TFTs formed in the pixel area
22
are not much different in device size from the driver circuit TFTs formed in the driver circuit areas
23
. However, the black matrix for covering the pixel TFTs, the pixel electrodes that are transparent conductive films, and other members are formed in the pixel area
22
. Further, in reflection-type liquid crystal display devices, a reflective electrode is formed in the pixel area
22
. On the other hand, connection lines necessary to constitute CMOS circuits for driving the pixel TFTs are formed in the driver circuit areas
23
. Therefore, there are differences in the height (distance) from the surface of the base substrate
1
between the pixel area
22
and the driver circuit areas
23
.
A description will now be made of a case where the height as measured from the surface of the substrate
1
in the pixel area
11
is greater than in the driver circuit areas
23
. The grainy spacers
41
are scattered in not only the pixel area
22
but also the driver circuit areas
23
by a wet or dry method. If the grainy spacers
41
have approximately uniform sizes, they have differences in the height as measured from the substrate
1
depending on their positions. Now, the height of the top of each spacer
41
in the pixel area
22
and that of the top of each spacer
41
in the driver circuit areas
23
are represented by hp and hd, respectively. As seen from
FIG. 36
, a height difference &Dgr;h=hp−hd occurs due to the difference in height between the pixel area
22
and the driver circuit areas
23
.
Then, as shown in
FIG. 37A
, the TFT substrate
20
and the opposed substrate
30
are bonded together with the sealing agent
42
. Thereafter, the space between the TFT substrate
20
and the opposed substrate
30
are filled with a liquid crystal material
43
and a liquid crystal injection inlet
44
is sealed with a sealing material (see FIG.
37
B). In this manner, an active matrix liquid crystal display device having the configuration shown in
FIG. 34A
is obtained.
However, the liquid crystal display device having the above configuration has the following problems.
Because of the height difference &Dgr;h that is caused by the difference in height between the pixel area
22
and the driver circuit areas
23
, the cell gas cannot be made uniform, that is, a cell thickness variation occurs, when the TFT substrate
20
and the opposed substrate are bonded together. Further, as shown in
FIGS. 37A and 37B
, strain occurs in the opposed substrate
30
. Defects such as display unevenness and an interference fringe (on the top surface of the opposed substrate) may occur in a liquid crystal display device having a cell thickness variation and strain in the opposed substrate
30
.
Where the height as measured from the substrate
1
in the driver circuit areas
23
is greater than in the pixel area
22
, because of the above-described height difference &Dgr;h, unduly strong force is exerted on the spacers
41
that are scattered in the driver circuit areas
23
when the TFT substrate
20
and the opposed substrate
30
are bonded together. As a result, the driver circuit TFTs having a more complex structure than the pixel TFTs are damaged considerably, which adversely affects the yield of products.
Where grainy spacers
15
exist in the pixel area, disorder in image display (disclination) may be observed as shown in
FIG. 34B
because the alignment of the liquid crystal material is disordered in the vicinity of the spacers
15
.
As described above, where the cell gap is controlled by using conventional grainy spacers, satisfactory display may not be obtained due to various factors.
In liquid crystal display devices that are commonly manufactured or manufactured as trial products, the cell gap appears to be set at 4-6 &mgr;m irrespective of the pixel pitch. However, in the future, liquid crystal panels will be required to have higher resolution and hence the pixel pitch will be increasingly reduced.
For example, projection-type liquid crystal display devices are desired to be able to display images having as high resolution as possible in view of the fact that the images are projected onto a screen in an enlarged manner. Also from the viewpoint of the cost, the optical system needs to be miniaturized and the panel size needs to be reduced. For the above reasons, in the future, it will be necessary to manufacture liquid crystal display devices having a pixel pitch of 40 &mgr;m or less, preferably 30 &mgr;m or less.
In liquid crystal display devices for displaying such high resolution images, even grainy spacers of several micrometer
Hirakata Yoshiharu
Nishi Takeshi
Yamazaki Shunpei
Robinson Eric J.
Robinson Intellectual Property Law Office PC
Semiconductor Energy Laboratory Co,. Ltd.
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