Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-01-23
2001-05-08
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S087000, C345S090000, C349S042000, C349S038000, C359S016000
Reexamination Certificate
active
06229511
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an active matrix substrate used in a liquid crystal display device or the like, and a method for fabricating the same.
2. Description of the Related Art
In recent years, the development of a thin-film transistor (hereinafter, referred to as a “TFT”) has been conducted in order to apply the TFT to image display devices such as flat panel displays including a liquid crystal display device. In particular, the development of a driver monolithic type liquid crystal display panel in which polycrystalline silicon TFTs are used so as to form a display unit and a driving circuit unit on the same substrate has been vigorously conducted.
FIG. 3
is a plan view illustrating such a driver monolithic type active matrix substrate. In
FIG. 3
, the reference numeral
20
denotes a display unit. The reference numerals
21
and
22
denote a driving circuit unit for data signals and a driving circuit unit for scanning signals, respectively. Each of the driving circuit units
21
and
22
is provided in the periphery of the display unit
20
. Data signal lines
23
and scanning signal lines
24
are connected to the driving circuit unit
21
for data signals and the driving circuit unit
22
for scanning signals, respectively.
As shown in
FIG. 4
, a pixel TFT
25
as an active element and a pixel electrode
26
are connected to the vicinity of the intersection between the data signal line
23
and the scanning signal line
24
in the display unit
20
. A scanning signal from the driving circuit unit
22
for scanning signals drives the pixel TFT
25
, and a data signal voltage from the driving circuit unit
21
for data signals is applied to the pixel electrode
26
.
FIG. 5
is a cross-sectional view illustrating the structure of a TFT in this active matrix substrate. In
FIG. 5
, the reference numeral
27
denotes a transparent insulating substrate. The reference numeral
28
denotes a semiconductor layer having a channel region
29
and low resistance regions
30
. The reference numerals
31
and
32
represent a gate insulating film and a gate electrode, respectively. The reference numerals
33
and
34
represent an interlayer insulating film and source and drain electrodes, respectively. The active matrix substrate includes stagger type TFTs in which the semiconductor layer
28
of the TFT is composed of polycrystalline silicon.
The above-described driving circuit unit
21
for data signals or the driving circuit unit
22
for scanning signals shown in
FIG. 3
generally employs a clocked inverter shown in
FIG. 6
as an element in an output unit provided therein or the like. The clocked inverter includes: N-channel type TFTs
35
; P-channel type TFTs
36
; clock signal lines
37
for driving the TFTs
35
and
36
; and constant voltage lines
38
for supplying voltage. Such a complementary type clocked inverter where the N-channel type TFTs
35
and the P-channel type TFTs
36
are combined realizes a higher processing speed of the circuit and lower power consumption as compared to the case where the clocked inverter is composed of the N-channel type TFTs alone.
FIG. 7
is a plan view illustrating a pattern of the clocked inverter shown in the left side of FIG.
6
.
Hereinafter, a method for fabricating the conventional active matrix substrate will be described with reference to
FIGS. 8A and 8B
illustrating portions of the clocked inverter.
First, as shown in
FIG. 8A
, polycrystalline silicon thin films
39
are formed as semiconductor layers on a transparent insulating substrate. Then, a SiO
2
film is formed so as to form a gate insulating film (not shown). Next, an Al alloy thin film is used to form gate electrodes
40
and a line
41
for a crossing portion in a pattern as shown in FIG.
8
A.
Subsequently, as shown in
FIG. 8B
, an n-type low resistance region
42
and a p-type low resistance region
43
are formed in a pattern as shown by hatching using an ion doping method or the like. Then, a SiO
2
film is formed so as to form an interlayer insulating film, and contact holes
44
are formed in the interlayer insulating film. Next, clock signal lines
37
and constant voltage lines
38
are formed by the patterning of the same type of thin metal film, i.e., a thin metal film for data signal lines. In this manner, the clocked inverter portion as shown in
FIG. 7
is fabricated.
In such an active matrix substrate, defects in the driving circuit units
21
and
22
having the clocked inverter and the like, immediately leads to defects in the display unit
20
. As a result, it is extremely important to improve yield of the driving circuit units
21
and
22
. In the conventional driving circuit units shown in
FIG. 7
, however, due to a large number of the contact holes, these driving circuit units are susceptible to connection failure and the influence of static electricity. Moreover, due to their long line length and a large number of intersections between the lines, breakage of lines is more likely to occur.
As a result, the rate of connection failure at the contact holes and the number of line breakage increase, resulting in an unsatisfactory yield of the active matrix substrate as a product. In order to prevent such line breakage, Japanese Laid-open Publication No. 2-285678 suggests a technique for making a portion of the clock signal line and/or the constant voltage line a double line. However, since such a technique is more likely to be affected by static electricity, the rate of dielectric breakdown at the TFT is high. Thus, with such a technique, an increase in the yield has not been accomplished yet.
Accordingly, there is a need for an active matrix substrate having the reduced number of contact holes and excellent yield.
SUMMARY OF THE INVENTION
According to one aspect of this invention, an active matrix substrate includes: pixel electrodes for display which are disposed in a matrix; active elements for controlling input and output of signals to the pixel electrodes; a driving circuit unit for scanning signals for controlling ON and OFF operation of the active elements in a sequential manner; and a driving circuit unit for data signals for inputting and outputting data to the pixel electrodes via the active elements. A clock signal line in at least one of the driving circuit unit for scanning signals and the driving circuit unit for data signals is formed from a thin metal film for scanning signal lines, and a constant voltage line is formed from a thin metal film for data signal lines.
In one embodiment of the present invention, the at least one of the driving circuit units comprises a clocked inverter; and clock signal lines each supplying a clock signal in a phase opposite to each other to the clocked inverter are disposed with the clocked inverter interposed therebetween.
In another embodiment of the present invention, the active element for controlling input and output of a signal to the pixel electrode is a thin-film transistor and the at least one of the driving circuit units comprises a thin-film transistor. A gate electrode of the thin-film transistor for controlling input and output of a signal to the pixel electrode and a gate electrode of the thin-film transistor in the driving circuit unit are formed from a same thin metal film. Source and drain electrodes of the thin-film transistor for controlling input and output of a signal to the pixel electrode and source and drain electrodes of the thin-film transistor in the driving circuit unit are formed from a same thin metal film.
In still another embodiment of the present invention, the active element for controlling input and output of a signal to the pixel electrode is a thin-film transistor and the at least one of the driving circuit units comprises a thin-film transistor. A gate electrode of the thin-film transistor for controlling input and output of a signal to the pixel electrode and a gate electrode of the thin-film transistor in the driving circuit unit are formed from a same thin metal film. Source and drain electro
Nguyen Jimmy H.
Nixon & Vanderhye P.C.
Shalwala Bipin
Sharp Kabushiki Kaisha
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