Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1998-12-22
2002-06-25
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
Reexamination Certificate
active
06411346
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal displaying apparatus, and more particularly, to an active matrix type liquid crystal displaying apparatus.
2. Discussion of the Background
The array substrate of the conventional active matrix type liquid crystal displaying apparatus has a plurality of scanning wirings (or lines) in a row direction, and a plurality of signal wirings (or lines) in a column direction formed on an insulating substrate, thin film transistors (hereinafter,referred to as TFT(s)) formed in the intersecting positions of the scanning wirings and the signal wirings, and each pixel including a of pixel electrode connected with the TFT, an alignment film being formed on the pixel. Another substrate (hereinafter referred to as counter substrate) for interposing the liquid crystal has a common electrode on the insulating substrate, and an alignment film being formed on the common electrode. The array substrate and the counter substrate are confronted with each other in the face where the aforementioned pixel electrode and the common electrode are formed to interpose the liquid crystal composition in the gap between the array substrate and the counter substrate. As the alignment film is subjected to alignment process in a direction deviated by 90 degrees on the array substrate side and the counter substrate side, a TN liquid crystal is used with the liquid crystal molecule being twisted by 90 degrees in a thickness direction.
In such a TN type liquid crystal displaying apparatus, to prevent the leaking light from coming from the gap by removing the gap between the pixel electrode, the scanning wiring and the signal wiring in the periphery, and at the same time, to prevent disclination caused by the level difference of the pixel electrode end from the scanning wiring and the signal wiring and by the horizontal direction electric field between the pixel electrode and the scanning wiring or the signal wiring, there is disclosed such an art of forming a transparent insulating film with a film of 1 &mgr;m or thicker and forming the pixel electrode on the scanning wiring and the signal wiring through the transparent insulating film. Thus, the disclination is prevented from being caused, and at the same time, the pixel electrodes can be superposed on the scanning wiring and the signal wiring so that the aperture ratio of one pixel can be made larger.
FIG. 33
is a plan view of one pixel of a liquid crystal displaying apparatus using an art to form, on the scanning wiring and the signal wiring through the transparent insulating film, the conventional pixel electrode described in, for example, Japanese Unexamined Patent Publication No. 258247/1997.
FIG. 34
is a sectional illustrating view taken along a line of A—A of FIG.
33
. Referring to
FIGS. 33 and 34
, reference numeral
1
is a transparent substrate, reference numeral
2
is a scanning wiring, reference numeral
3
is a storage capacitance line (hereinafter referred to as Cs line), reference numeral
4
is a gate insulating film, reference numeral
5
is a semiconductor layer, reference numeral
6
is a semiconductor layer with impurities being doped in it, reference numeral
6
a
is a source region for taking a signal wiring metal and an ohmic contact, reference numeral
6
b
is a region for taking a drain electrode metal and an ohmic contact, reference numeral
7
is a signal wiring, reference numeral
8
is a drain electrode, reference numeral
9
is a passivation film, reference numeral
10
is an organic transparent resin film, and reference numeral
11
is a contact hole (or contact via) for electrically connecting the drain electrode
8
with a pixel electrode. Reference numeral
12
is a pixel electrode where the position is shown with two-dot chain line. In the conventional liquid crystal displaying apparatus shown in
FIGS. 33 and 34
, these films normally form a resist pattern on the film by a process called a photolithography, and by removing the film of an unnecessary portion by etching of the resist pattern on the mask, the desired shape is obtained. To form the resist pattern by the photolithography process, an exposing machine is used. In the negative resist, the light is illuminated by shielding the light in the unnecessary portion of the film. In the positive type resist, the light is illuminated by shielding the light in the necessary portion of the film. Later, the resist of the unnecessary portion is removed by using a developing solution to form the desired resist pattern. In the exposing process in the photolithography, by using an exposing apparatus called a stepper, the displaying portion of the liquid crystal displaying apparatus is divided into some regions and the exposing is conducted for each region, whereby the whole displaying portion is exposed by several exposing operations. At this time, the exposing condition is changed in the step in the boundary of the adjacent exposing region by the results in the alignment accuracy of the exposing apparatus and the difference in uniformity of the exposing amount for each exposing region. Thus, the positional deviation between the patterns positioned in the different layers are changed in the step condition in the boundary of the adjacent exposing region. In the conventional liquid crystal displaying apparatus shown in
FIG. 33
, the drain electrode
8
also acts as an electrode for forming the storage capacitance. Accordingly, in the case of the conventional liquid crystal displaying apparatus shown in
FIG. 33
, when the pattern position of the scanning wiring
2
and the drain electrode
8
are deviated in the x axial direction of
FIG. 33
, the coupling capacitance Cgd formed by the superposition between the scanning wiring
2
and the drain electrode
8
in the TFT portion is changed and the relative position between the scanning wiring
2
and the drain electrode is changed, thereby changing the superposed area to change the value. The storage capacitance Cs is formed by the same photolithography process in the scanning wiring
2
and the Cs wiring
3
. If the position of the drain electrode
8
is deviated in the x axial direction shown in
FIG. 33
, the superposing area of the Cs wiring
3
and the drain electrode
8
does not change, thus making the Cs value constant.
Influences of the change in the Cgd upon the picture quality will be described.
FIG. 35
shows an equivalent circuit of one pixel of the liquid crystal displaying apparatus. For a simpler description, only the capacity composition of the present invention will be described. When an ON signal enters, the TFT
23
is turned on, whereby a prescribed electric charge is stored from the signal wiring
7
into the storage capacitance (Cs)
21
and the liquid crystal capacitance (Clc)
22
. When the selection signal of the scanning wiring
2
is changed to off, the TFT is turned Off (high resistance condition), and the charge stored from the signal wiring is retained. The effective voltage to be decided by difference the between the electric potential to be decided by the electric charge and that of the Cs wiring (that is, common electrode of the counter substrate) is applied upon the liquid crystal, whereby the transmission ratio proportional to the effective voltage is obtained and the desired display is obtained. When the selecting signal of the scanning wiring
2
is changed, the electric potential of the drain electrode is changed by the coupling capacitance (Cgd)
24
between the scanning wiring
2
and the drain electrode
8
. &Dgr;Vgd is as follows:
&Dgr;
Vgd
=(
Cgd×&Dgr;Vg
)/(
Cgd+Cs+Clc
) (1)
wherein the electric potential change of the drain electrode is &Dgr;Vgd.
The &Dgr;Vg is a change amount of the electric potential when the signal of the scanning wiring is changed from on to off. The center potential of the electric potential
25
(hereinafter referred to as Vcom) of the common electrode of the counter substrate and the center electric voltage of the voltage to be app
Kawamoto Satoru
Nakashima Ken
Numano Yoshinori
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Schechter Andrew
Ton Toan
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