U.S. patent application number 10/167422 was filed with the patent office on 2003-01-02 for liquid crystal display device.
This patent application is currently assigned to Hitachi, Ltd.. Invention is credited to Kawachi, Genshiro, Kondo, Katsumi, Mikami, Yoshiro, Miyazawa, Toshio, Sato, Hideo.
Application Number | 20030002002 10/167422 |
Document ID | / |
Family ID | 19033901 |
Filed Date | 2003-01-02 |
United States Patent
Application |
20030002002 |
Kind Code |
A1 |
Kawachi, Genshiro ; et
al. |
January 2, 2003 |
Liquid crystal display device
Abstract
A liquid crystal display device of low power consumption which
exhibits high image quality is realized. To each
liquid-crystal-side pixel region of one substrate out of respective
substrates which are arranged while sandwiching liquid crystal
therebetween, a first switching element and a second switching
element which are operated in response to a scanning signal from a
gate signal line, a pixel electrode to which a video signal is
supplied from the drain signal line through the first switching
element, and a counter electrode to which a reference voltage
signal is supplied from a reference voltage signal line through the
second switching element, and the pixel electrode and the counter
electrode are respectively formed of strip-like transparent
conductive layers and are substantially alternately arranged in the
inside of the pixel region.
Inventors: |
Kawachi, Genshiro; (Chiba,
JP) ; Sato, Hideo; (Hitachi, JP) ; Miyazawa,
Toshio; (Chiba, JP) ; Mikami, Yoshiro;
(Hitachiota, JP) ; Kondo, Katsumi; (Mito,
JP) |
Correspondence
Address: |
Stanley P. Fisher
Reed Smith LLP
3110 Fairview Park Drive, Suite 1400
Falls Church
VA
22042-4503
US
|
Assignee: |
Hitachi, Ltd.
|
Family ID: |
19033901 |
Appl. No.: |
10/167422 |
Filed: |
June 13, 2002 |
Current U.S.
Class: |
349/143 |
Current CPC
Class: |
G02F 1/134363
20130101 |
Class at
Publication: |
349/143 |
International
Class: |
G02F 001/1343 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 28, 2001 |
JP |
2001-196019 |
Claims
What is claimed is:
1. A liquid crystal display device being characterized in that: a
first switching element and a second switching element which are
operated in response to a scanning signal from a gate signal line,
a pixel electrode to which a video signal is supplied from a drain
signal line through the first switching element, and a counter
electrode to which a reference voltage signal is supplied from a
reference voltage signal line through the second switching element
are formed on each liquid-crystal-side pixel region of one
substrate out of respective substrates arranged by way of liquid
crystal, and the pixel electrode and the counter electrode are
respectively formed of strip-like light-transmitting conductive
layers and are substantially alternately arranged in the inside of
the pixel region.
2. A liquid crystal display device according to claim 1, wherein
the pixel electrode and the counter electrode are respectively
formed as same layers on a protective film which covers the first
switching element and the second switching element, and the pixel
electrode and the counter electrode are respectively electrically
connected with the first switching element and the second switching
element via a through hole formed in the protective film.
3. A liquid crystal display device according to claim 1, wherein
the protective film is formed of a sequential laminated body
constituted of a protective film made of inorganic material and a
protective film made of organic material.
4. A liquid crystal display device being characterized in that: a
first switching element and a second switching element which are
operated in response to a scanning signal from a gate signal line,
a pixel electrode to which a video signal is supplied from a drain
signal line through the first switching element, and a counter
electrode to which a reference voltage signal is supplied from a
reference voltage signal line through the second switching element
are formed on each liquid-crystal-side pixel region of one
substrate out of respective substrates arranged by way of liquid
crystal, the pixel electrode and the counter electrode are
respectively formed of strip-like light-transmitting conductive
layers which are arranged approximately parallel to the drain
signal line and are substantially alternately arranged in the
inside of the pixel region, and the reference voltage signal line
is arranged approximately parallel to the drain signal line.
5. A liquid crystal display device being characterized in that: a
first switching element and a second switching element which are
operated in response to a scanning signal from a gate signal line,
a pixel electrode to which a video signal is supplied from a drain
signal line through the first switching element, and a counter
electrode to which a reference voltage signal is supplied from a
reference voltage signal line through the second switching element
are formed on each liquid-crystal-side pixel region of one
substrate out of respective substrates arranged by way of liquid
crystal, the pixel electrode and the counter electrode are
respectively formed of strip-like light-transmitting conductive
layers which are arranged approximately parallel to the drain
signal line and are substantially alternately arranged in the
inside of the pixel region, and the reference voltage signal line
is arranged approximately parallel to the drain signal line and is
arranged to be superposed on one electrode out of the pixel
electrode and the counter electrode.
6. A liquid crystal display device being characterized in that: a
switching element which is operated in response to a scanning
signal from a gate signal line, a pixel electrode to which a video
signal is supplied from a drain signal line through the switching
element, and a counter electrode to which a reference voltage
signal is supplied from a reference voltage signal line are formed
on each liquid-crystal-side pixel region of one substrate out of
respective substrates arranged by way of liquid crystal, the pixel
electrode and the counter electrode are respectively formed of
strip-like light-transmitting conductive layers and are
substantially alternately arranged in the inside of the pixel
region.
7. A liquid crystal display device according to claim 6, wherein
the pixel electrode and the counter electrode are respectively
formed as same layers on a protective film which covers the
switching element, and pixel electrode and the counter electrode
are respectively electrically connected with the switching element
and the reference voltage signal line via a through hole formed in
the protective film.
8. A liquid crystal display device according to claim 6, wherein
the protective film is formed of a sequential laminated body
constituted of a protective film made of inorganic material and a
protective film made of organic material.
9. A liquid crystal display device according to claim 6, wherein
the switching element is a thin film transistor having a
semiconductor layer formed of polycrystalline silicon.
10. A liquid crystal display device being characterized in that: a
switching element which is operated in response to a scanning
signal from a gate signal line, a pixel electrode to which a video
signal is supplied from a drain signal line through the switching
element, and a counter electrode to which a reference voltage
signal is supplied from a reference voltage signal line are formed
on each liquid-crystal-side pixel region of one substrate out of
respective substrates arranged by way of liquid crystal, the pixel
electrode and the counter electrode are respectively formed of
strip-like light-transmitting conductive layers which are arranged
approximately parallel to the drain signal line and are
substantially alternately arranged in the inside of the pixel
region, and the reference voltage signal line is arranged
approximately parallel to the drain signal line.
11. A liquid crystal display device being characterized in that: a
switching element which is operated in response to a scanning
signal from a gate signal line, a pixel electrode to which a video
signal is supplied from a drain signal line through the switching
element, and a counter electrode to which a reference voltage
signal is supplied from a reference voltage signal line are formed
on each liquid-crystal-side pixel region of one substrate out of
respective substrates arranged by way of liquid crystal, the pixel
electrode and the counter electrode are respectively formed of
strip-like light-transmitting conductive layers which are arranged
approximately parallel to the drain signal line and are
substantially alternately arranged in the inside of the pixel
region, and the reference voltage signal line is arranged
approximately parallel to the drain signal line and is arranged to
be superposed on one electrode out of the pixel electrode and the
counter electrode.
12. A liquid crystal display device being characterized in that: a
first switching element and a second switching element which are
operated in response to a scanning signal from a gate signal line,
a pixel electrode to which a video signal is supplied from a drain
signal line through the first switching element, and a counter
electrode to which a reference voltage signal is supplied from a
reference voltage signal line through the second switching element
are formed on each liquid-crystal-side pixel region of one
substrate out of respective substrates arranged by way of liquid
crystal, the pixel electrode and the counter electrode are
respectively formed of strip-like light-transmitting conductive
layers on an upper surface of a protective film which is formed to
cover the first switching element and the second switching element
and are substantially alternately arranged in the inside of the
pixel region, and a reflection film which is held at a potential
equal to a potential of the counter electrode is formed on a lower
surface of the protective film over a whole region in the inside of
the pixel region.
13. A liquid crystal display device according to claim 12, wherein
the protective film is formed of a sequential laminated body
constituted of a protective film made of inorganic material and a
protective film made of organic material.
14. A liquid crystal display device being characterized in that: a
first switching element and a second switching element which are
operated in response to a scanning signal from a gate signal line,
a pixel electrode to which a video signal is supplied from a drain
signal line through the first switching element, and a counter
electrode to which a reference voltage signal is supplied from a
reference voltage signal line through the second switching element
are formed on each liquid-crystal-side pixel region of one
substrate out of respective substrates arranged by way of liquid
crystal, the pixel electrode and the counter electrode are
respectively formed of strip-like light-transmitting conductive
layers on an upper surface of a protective film which is formed to
cover the first switching element and the second switching element
and are substantially alternately arranged in the inside of the
pixel region, and a reflection film which is held at a potential
equal to a potential of the counter electrode is formed on a lower
surface of the protective film over a portion in the inside of the
pixel region.
15. A liquid crystal display device according to claim 14, wherein
the protective film is formed of a sequential laminated body
constituted of a protective film made of inorganic material and a
protective film made of organic material.
16. A liquid crystal display device being characterized in that: on
each liquid-crystal-side pixel region of one substrate out of
respective substrates which are arranged to face each other in an
opposed manner by way of liquid crystal, a reference voltage signal
line which is arranged to divide the pixel region in halves and
first and second gate signal lines which are respectively arranged
at one-side pixel region and the-other-side pixel region with
respect to the reference voltage signal line in parallel with the
reference voltage signal line are formed, a first thin film
transistor which is operated in response to a scanning signal from
the first gate signal line, a first pixel electrode to which a
video signal is supplied through the first thin film transistor,
and a first counter electrode to which a reference voltage signal
is supplied from the reference voltage signal line are provided to
the one-side pixel region, a second thin film transistor which is
operated in response to a scanning signal from the second gate
signal line, a second pixel electrode to which a video signal is
supplied through the second thin film transistor, and a second
counter electrode to which a reference voltage signal is supplied
from the reference voltage signal line are provided to the
the-other-side pixel region, and the first and the second pixel
electrodes and the first and the second counter electrodes are
respectively formed of strip-like light-transmitting conductive
layers on an upper surface of a protective film which is formed to
cover the first and the second thin film transistors and are
substantially alternately arranged in the inside of the pixel
region, and a reflection film is formed on a lower surface of the
protective film over either one of the one-side pixel region and
the the-other-side pixel region with respect to the reference
voltage signal line.
17. A liquid crystal display device being characterized in that: on
each liquid-crystal-side pixel region of one substrate out of
respective substrates which are arranged to face each other in an
opposed manner by way of liquid crystal, a reference voltage signal
line which is arranged to divide the pixel region in halves and
first and second gate signal lines which are respectively arranged
at one-side pixel region and the-other-side pixel region with
respect to the reference voltage signal line in parallel with the
reference voltage signal line are formed, a first thin film
transistor and a second thin film transistor which are operated in
response to a scanning signal from the first gate signal line, a
first pixel electrode to which a video signal is supplied through
the first thin film transistor, and a first counter electrode to
which a reference voltage signal is supplied from the reference
voltage signal line through the second thin film transistor are
provided to the one-side pixel region, a third thin film transistor
and a fourth thin film transistor which are operated in response to
a scanning signal from the second gate signal line, a second pixel
electrode to which a video signal is supplied through the third
thin film transistor, and a second counter electrode to which a
reference voltage signal is supplied from the reference voltage
signal line through the fourth thin film transistor are provided to
the the-other-side pixel region, and the first and the second pixel
electrodes and the first and the second counter electrodes are
respectively formed of strip-like light-transmitting conductive
layers on an upper surface of a protective film which is formed to
cover the first, the second, the third and the fourth thin film
transistors and are substantially alternately arranged in the
inside of the pixel region, and a reflection film is formed on a
lower surface of the protective film over either one of the
one-side pixel region and the the-other-side pixel region with
respect to the reference voltage signal line.
18. A liquid crystal display device according to claim 16, wherein
the protective film is formed of a sequential laminated body
constituted of a protective film made of inorganic material and a
protective film made of organic material.
19. A liquid crystal display device according to claim 16, wherein
the scanning signal from the first gate signal line and the
scanning signal from the second gate signal line are supplied at
different timings.
20. A liquid crystal display device being characterized in that: a
first switching element and a second switching element which are
operated in response to a scanning signal from a gate signal line,
a pixel electrode to which a video signal is supplied from a drain
signal line through the first switching element, and a counter
electrode to which a reference voltage signal is supplied from a
reference voltage signal line through the second switching element
are formed on each liquid-crystal-side pixel region of one
substrate out of respective substrates arranged by way of liquid
crystal, the reference voltage signal line is arranged
approximately parallel to the drain signal line and is not
connected with the pixel electrode of a neighboring pixel by way of
the first switching element.
21. A liquid crystal display device being characterized in that: a
first switching element and a second switching element which are
operated in response to a scanning signal from a scanning wiring
electrode, a first pixel electrode to which a voltage is supplied
from a first signal wiring electrode through the first switching
element, and a second pixel electrode to which a voltage is
supplied from a second signal wiring electrode through the second
switching element are formed on each liquid-crystal-side pixel
region of one substrate out of respective substrates arranged by
way of liquid crystal, the second signal wiring electrode is
arranged approximately parallel to the first signal wiring
electrode and is not connected with the first pixel electrode of a
neighboring pixel by way of the first switching element.
22. A liquid crystal display device according to claim 17, wherein
the protective film is formed of a sequential laminated body
constituted of a protective film made of inorganic material and a
protective film made of organic material.
23. A liquid crystal display device according to claim 17, wherein
the scanning signal from the first gate signal line and the
scanning signal from the second gate signal line are supplied at
different timings.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a liquid crystal display
device, and more particularly to a so-called active matrix type
liquid crystal display device.
[0002] Recently, a liquid crystal display device has been popularly
used as a display equipment of image information and character
information for an information equipment represented by a personal
computer, a portable information terminal, a portable telephone, or
a visual equipment such as digital camera or a VTR equipment with a
built-in camera or the like.
[0003] Recently, along with the spreading of large capacity media
brought about by the advent of DVDs and the rapid progress of
large-capacity magnetic drives and the starting of BS digital
broadcasting, the fusion of personal computers and video digital
media has been in progress and the demand for an image display
device of high image quality which can cope with these applications
has been increasing.
[0004] A liquid crystal display adopting an in-plane switching
(IPS) mode has been admitted as a display method which can satisfy
the demand for high image quality and various improvements have
been made to obtain the further enhancement of the image
quality.
[0005] Here, the IPS mode liquid crystal display is a display which
is constituted such that on each liquid-crystal-side pixel region
of one substrate out of a pair of substrates which are arranged to
face each other in an opposed manner by way of liquid crystal
therebetween, a pixel electrode and a counter electrode which
generates an electric field between the pixel electrode and the
counter electrode are mounted, and the light transmittance of
liquid crystal is controlled by a component of the electric field
which is parallel to the substrates.
[0006] On the other hand, along with the spreading of portable
telephones and portable information terminals, the demand for
intermediate-sized or miniaturized liquid crystal display devices
of extremely small power consumption has been also increasing.
[0007] With respect to the IPS mode liquid crystal display device,
as disclosed in Japanese Patent Laid-Open No. 36058/1995, for
example, a method which switches on or off liquid crystal based on
a lateral electric field which is generated between metal
electrodes constituting different layers byway of an insulation
film is most popularly adopted. This structure, however, has a
drawback that it is difficult to increase the pixel numerical
aperture and hence, the light utilization efficiency is low
compared to a usual TN type display device.
[0008] However, to compensate for this drawback, it is necessary to
increase the brightness of a backlight and hence, it is difficult
for such a structure to achieve the low power consumption required
by a notebook type personal computer or a portable terminal as a
whole LCD module (the structure being referred to as "first
conventional technique" hereinafter).
[0009] Further, although it is necessary to increase a distance
between respective electrodes to increase the numerical aperture in
the pixel constitution of the above-mentioned method, a driving
voltage is elevated when the distance between electrodes is widened
and hence, the power consumption of the driver LSI is increased.
Accordingly, it has been difficult for the conventional technique
to achieve the low power consumption of the IPS mode LCD.
[0010] To solve such a problem, Japanese Patent Laid-Open No.
316383/1999, for example, discloses a method in which the numerical
aperture of the pixel is enhanced by driving liquid crystal based
on a fringe electric field which is generated between a planar
transparent electrode and a comb-like electrode made of a
transparent electrode which is formed as a layer different from the
former transparent electrode and above the former transparent layer
(hereinafter referred to as "second conventional technique").
[0011] Further, as a method for reducing a driving voltage,
Japanese Patent Laid-Open No. 148596/1994, for example, discloses a
method in which the driving voltage is reduced by providing two
transistors which connect liquid crystal driving electrodes to
pixels and these transistors are subjected to differential driving
(hereinafter referred to as "third conventional technique").
[0012] In this third conventional technique, y pieces of gate
signal lines and x+1 pieces of drain signal lines are provided to
the pixels arranged in a matrix array of y rows and x columns.
Accordingly, the drain signal lines are commonly used by a group of
pixels which belong to two neighboring columns.
[0013] First of all, the drawback of the first conventional
technique lies, as mentioned previously, in that the increase of
the numerical aperture is difficult because of the use of metal
electrodes which form different layers by way of the insulation
film as the liquid crystal driving electrodes and hence, the low
power consumption cannot be achieved.
[0014] With respect to the drawback of the second conventional
technique, although the second prior art can definitely enhance the
numerical aperture, residual images are considerably generated
compared to the conventional method and hence, it is difficult to
achieve high quality images. Further, since it is necessary to form
transparent electrodes which constitute respective layers during
steps, the steps become complicated and hence, the reduction of
cost is difficult.
[0015] With respect to the drawback of the third conventional
technique, although the lowering of driving voltage can be achieved
at the liquid crystal driving part, it is necessary to perform the
conversion of image data in the former stage of the driver LSI such
that the differential voltage is supplied between two signal lines
and this makes a circuit for conversion complicated and pushes up a
manufacturing cost. Further, a dynamic range of voltage in the
inside of the conversion circuit is increased to the contrary
compared to the usual driving and hence, the power consumption of
the conversion circuit is increased whereby it is difficult to
achieve the reduction of power consumption of the module as a
whole.
[0016] As mentioned above, it has been difficult for the respective
conventional techniques or the combination of these conventional
techniques to apply the IPS mode liquid crystal to the equipment
which is required to satisfy the low power consumption.
[0017] The present invention has been made to solve these drawbacks
of the conventional techniques and it is an object of the present
invention to provide a liquid crystal display device having a wide
viewing angle which is suitably applicable to a notebook type
personal computer or a portable terminal.
SUMMARY OF INVENTION
[0018] To briefly explain the summary of the typical inventions out
of the inventions disclosed in the present application, they are as
follows.
[0019] Means 1.
[0020] A first switching element and a second switching element
which are operated in response to a scanning signal from a gate
signal line, a pixel electrode to which a video signal is supplied
from a drain signal line through the first switching element, and a
counter electrode to which a reference voltage signal is supplied
from a reference voltage signal line through the second switching
element are formed on each liquid-crystal-side pixel region of one
substrate out of respective substrates arranged by way of liquid
crystal, and
[0021] the pixel electrode and the counter electrode are
respectively formed of strip-like light-transmitting conductive
layers and are substantially alternately arranged in the inside of
the pixel region.
[0022] Means 2.
[0023] With respect to the means 1,
[0024] the pixel electrode and the counter electrode are
respectively formed as same layers on a protective film which
covers the first switching element and the second switching
element, and the pixel electrode and the counter electrode are
respectively electrically connected with the first switching
element and the second switching element via a through hole formed
in the protective film.
[0025] Means 3.
[0026] With respect to the means 1,
[0027] the protective film is formed of a sequential laminated body
constituted of a protective film made of inorganic material and a
protective film made of organic material.
[0028] Means 4.
[0029] A first switching element and a second switching element
which are operated in response to a scanning signal from a gate
signal line, a pixel electrode to which a video signal is supplied
from a drain signal line through the first switching element, and a
counter electrode to which a reference voltage signal is supplied
from a reference voltage signal line through the second switching
element are formed on each liquid-crystal-side pixel region of one
substrate out of respective substrates arranged by way of liquid
crystal,
[0030] the pixel electrode and the counter electrode are
respectively formed of strip-like light-transmitting conductive
layers which are arranged approximately parallel to the drain
signal line and are substantially alternately arranged in the
inside of the pixel region, and
[0031] the reference voltage signal line is arranged approximately
parallel to the drain signal line.
[0032] Means 5.
[0033] A first switching element and a second switching element
which are operated in response to a scanning signal from a gate
signal line, a pixel electrode to which a video signal is supplied
from a drain signal line through the first switching element, and a
counter electrode to which a reference voltage signal is supplied
from a reference voltage signal line through the second switching
element are formed on each liquid-crystal-side pixel region of one
substrate out of respective substrates arranged by way of liquid
crystal,
[0034] the pixel electrode and the counter electrode are
respectively formed of strip-like light-transmitting conductive
layers which are arranged approximately parallel to the drain
signal line and are substantially alternately arranged in the
inside of the pixel region, and
[0035] the reference voltage signal line is arranged approximately
parallel to the drain signal line and is arranged to be superposed
on one electrode out of the pixel electrode and the counter
electrode.
[0036] Means 6.
[0037] A switching element which is operated in response to a
scanning signal from a gate signal line, a pixel electrode to which
a video signal is supplied from a drain signal line through the
switching element, and a counter electrode to which a reference
voltage signal is supplied from a reference voltage signal line are
formed on each liquid-crystal-side pixel region of one substrate
out of respective substrates arranged by way of liquid crystal,
[0038] the pixel electrode and the counter electrode are
respectively formed of strip-like light-transmitting conductive
layers and are substantially alternately arranged in the inside of
the pixel region.
[0039] Means 7.
[0040] With respect to the means 6,
[0041] the pixel electrode and the counter electrode are
respectively formed as same layers on a protective film which
covers the switching element, and pixel electrode and the counter
electrode are respectively electrically connected with the
switching element and the reference voltage signal line via a
through hole formed in the protective film.
[0042] Means 8.
[0043] With respect to the means 6,
[0044] the protective film is formed of a sequential laminated body
constituted of a protective film made of inorganic material and a
protective film made of organic material.
[0045] Means 9.
[0046] With respect to the means 6,
[0047] the switching element is a thin film transistor having a
semiconductor layer formed of polycrystalline silicon.
[0048] Means 10.
[0049] A switching element which is operated in response to a
scanning signal from a gate signal line, a pixel electrode to which
a video signal is supplied from a drain signal line through the
switching element, and a counter electrode to which a reference
voltage signal is supplied from a reference voltage signal line are
formed on each liquid-crystal-side pixel region of one substrate
out of respective substrates arranged by way of liquid crystal,
[0050] the pixel electrode and the counter electrode are
respectively formed of strip-like light-transmitting conductive
layers which are arranged approximately parallel to the drain
signal line and are substantially alternately arranged in the
inside of the pixel region, and
[0051] the reference voltage signal line is arranged approximately
parallel to the drain signal line.
[0052] Means 11.
[0053] A switching element which is operated in response to a
scanning signal from a gate signal line, a pixel electrode to which
a video signal is supplied from a drain signal line through the
switching element, and a counter electrode to which a reference
voltage signal is supplied from a reference voltage signal line are
formed on each liquid-crystal-side pixel region of one substrate
out of respective substrates arranged by way of liquid crystal,
[0054] the pixel electrode and the counter electrode are
respectively formed of strip-like light-transmitting conductive
layers which are arranged approximately parallel to the drain
signal line and are substantially alternately arranged in the
inside of the pixel region, and
[0055] the reference voltage signal line is arranged approximately
parallel to the drain signal line and is arranged to be superposed
on one electrode out of the pixel electrode and the counter
electrode.
[0056] Means 12.
[0057] A first switching element and a second switching element
which are operated in response to a scanning signal from a gate
signal line, a pixel electrode to which a video signal is supplied
from a drain signal line through the first switching element, and a
counter electrode to which a reference voltage signal is supplied
from a reference voltage signal line through the second switching
element are formed on each liquid-crystal-side pixel region of one
substrate out of respective substrates arranged by way of liquid
crystal,
[0058] the pixel electrode and the counter electrode are
respectively formed of strip-like light-transmitting conductive
layers on an upper surface of a protective film which is formed to
cover the first switching element and the second switching element
and are substantially alternately arranged in the inside of the
pixel region, and
[0059] a reflection film which is held at a potential equal to a
potential of the counter electrode is formed on a lower surface of
the protective film over a whole region in the inside of the pixel
region.
[0060] Means 13.
[0061] With respect to the means 12,
[0062] the protective film is formed of a sequential laminated body
constituted of a protective film made of inorganic material and a
protective film made of organic material.
[0063] Means 14.
[0064] A first switching element and a second switching element
which are operated in response to a scanning signal from a gate
signal line, a pixel electrode to which a video signal is supplied
from a drain signal line through the first switching element, and a
counter electrode to which a reference voltage signal is supplied
from a reference voltage signal line through the second switching
element are formed on each liquid-crystal-side pixel region of one
substrate out of respective substrates arranged by way of liquid
crystal,
[0065] the pixel electrode and the counter electrode are
respectively formed of strip-like light-transmitting conductive
layers on an upper surface of a protective film which is formed to
cover the first switching element and the second switching element
and are substantially alternately arranged in the inside of the
pixel region, and
[0066] a reflection film which is held at a potential equal to a
potential of the counter electrode is formed on a lower surface of
the protective film over a portion in the inside of the pixel
region.
[0067] Means 15.
[0068] With respect to the means 14,
[0069] the protective film is formed of a sequential laminated body
constituted of a protective film made of inorganic material and a
protective film made of organic material.
[0070] Means 16.
[0071] On each liquid-crystal-side pixel region of one substrate
out of respective substrates which are arranged to face each other
in an opposed manner by way of liquid crystal, a reference voltage
signal line which is arranged to divide the pixel region in halves
and first and second gate signal lines which are respectively
arranged at one-side pixel region and the-other-side pixel region
with respect to the reference voltage signal line in parallel with
the reference voltage signal line are formed,
[0072] a first thin film transistor which is operated in response
to a scanning signal from the first gate signal line, a first pixel
electrode to which a video signal is supplied through the first
thin film transistor, and a first counter electrode to which a
reference voltage signal is supplied from the reference voltage
signal line are provided to the one-side pixel region,
[0073] a second thin film transistor which is operated in response
to a scanning signal from the second gate signal line, a second
pixel electrode to which a video signal is supplied through the
second thin film transistor, and a second counter electrode to
which a reference voltage signal is supplied from the reference
voltage signal line are provided to the the-other-side pixel
region, and
[0074] the first and the second pixel electrodes and the first and
the second counter electrodes are respectively formed of strip-like
light-transmitting conductive layers on an upper surface of a
protective film which is formed to cover the first and the second
thin film transistors and are substantially alternately arranged in
the inside of the pixel region, and
[0075] a reflection film is formed on a lower surface of the
protective film over either one of the one-side pixel region and
the the-other-side pixel region with respect to the reference
voltage signal line.
[0076] Means 17.
[0077] On each liquid-crystal-side pixel region of one substrate
out of respective substrates which are arranged to face each other
in an opposed manner by way of liquid crystal, a reference voltage
signal line which is arranged to divide the pixel region in halves
and first and second gate signal lines which are respectively
arranged at one-side pixel region and the-other-side pixel region
with respect to the reference voltage signal line in parallel with
the reference voltage signal line are formed,
[0078] a first thin film transistor and a second thin film
transistor which are operated in response to a scanning signal from
the first gate signal line, a first pixel electrode to which a
video signal is supplied through the first thin film transistor,
and a first counter electrode to which a reference voltage signal
is supplied from the reference voltage signal line through the
second thin film transistor are provided to the one-side pixel
region,
[0079] a third thin film transistor and a fourth thin film
transistor which are operated in response to a scanning signal from
the second gate signal line, a second pixel electrode to which a
video signal is supplied through the third thin film transistor,
and a second counter electrode to which a reference voltage signal
is supplied from the reference voltage signal line through the
fourth thin film transistor are provided to the the-other-side
pixel region, and
[0080] the first and the second pixel electrodes and the first and
the second counter electrodes are respectively formed of strip-like
light-transmitting conductive layers on an upper surface of a
protective film which is formed to cover the first, the second, the
third and the fourth thin film transistors and are substantially
alternately arranged in the inside of the pixel region, and
[0081] a reflection film is formed on a lower surface of the
protective film over either one of the one-side pixel region and
the the-other-side pixel region with respect to the reference
voltage signal line.
[0082] Means 18.
[0083] With respect to the means 16 or 17,
[0084] the protective film is formed of a sequential laminated body
constituted of a protective film made of inorganic material and a
protective film made of organic material.
[0085] Means 19.
[0086] With respect to the means 16 or 17,
[0087] the scanning signal from the first gate signal line and the
scanning signal from the second gate signal line are supplied at
different timings.
[0088] Means 20.
[0089] A first switching element and a second switching element
which are operated in response to a scanning signal from a gate
signal line, a pixel electrode to which a video signal is supplied
from a drain signal line through the first switching element, and a
counter electrode to which a reference voltage signal is supplied
from a reference voltage signal line through the second switching
element are formed on each liquid-crystal-side pixel region of one
substrate out of respective substrates arranged by way of liquid
crystal,
[0090] the reference voltage signal line is arranged approximately
parallel to the drain signal line and is not connected with the
pixel electrode of a neighboring pixel by way of the first
switching element.
[0091] Means 21.
[0092] A first switching element and a second switching element
which are operated in response to a scanning signal from a scanning
wiring electrode, a first pixel electrode to which a voltage is
supplied from a first signal wiring electrode through the first
switching element, and a second pixel electrode to which a voltage
is supplied from a second signal wiring electrode through the
second switching element are formed on each liquid-crystal-side
pixel region of one substrate out of respective substrates arranged
by way of liquid crystal,
[0093] the second signal wiring electrode is arranged approximately
parallel to the first signal wiring electrode and is not connected
with the first pixel electrode of a neighboring pixel by way of the
first switching element.
[0094] Other features of the present invention will be apparent
from embodiments described hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0095] FIG. 1 is a plan view showing one embodiment of a unit pixel
of a liquid crystal display device of the present invention.
[0096] FIG. 2 is a cross-sectional view taken along a line A-A',
B-B' and C-C' of FIG. 1.
[0097] FIG. 3 is an equivalent circuit diagram of a pixel array
part.
[0098] FIG. 4 is a plan view showing another embodiment of the unit
pixel of a liquid crystal display device of the present
invention.
[0099] FIG. 5 is a cross-sectional view taken along a line A-A',
B-B' and C-C' of FIG. 4.
[0100] FIG. 6 is an equivalent circuit diagram of a pixel array
part.
[0101] FIG. 7 is a plan view showing another embodiment of the unit
pixel of a liquid crystal display device of the present
invention.
[0102] FIG. 8 is a cross-sectional view taken along a line A-A',
B-B' and C-C' of FIG. 7.
[0103] FIG. 9 is an equivalent circuit diagram of a pixel array
part.
[0104] FIG. 10 is a plan view showing another embodiment of the
unit pixel of a liquid crystal display device of the present
invention.
[0105] FIG. 11 is a cross-sectional view taken along a line A-A',
B-B' and C-C' of FIG. 10.
[0106] FIG. 12 is an equivalent circuit diagram of a pixel array
part.
[0107] FIG. 13 is a plan view showing another embodiment of the
unit pixel of a liquid crystal display device of the present
invention.
[0108] FIG. 14 is a cross-sectional view taken along a line A-A',
B-B' and C-C' of FIG. 13.
[0109] FIG. 15 is a plan view showing another embodiment of the
unit pixel of a liquid crystal display device of the present
invention.
[0110] FIG. 16 is a cross-sectional view taken along a line A-A',
B-B' and C-C' of FIG. 15.
[0111] FIG. 17 is a plan view showing another embodiment of the
unit pixel of a liquid crystal display device of the present
invention.
[0112] FIG. 18 is a cross-sectional view taken along a line A-A' of
FIG. 17.
[0113] FIG. 19 is an equivalent circuit diagram of a pixel array
part.
[0114] FIG. 20 is a cross-sectional view showing one embodiment of
the constitution of the liquid crystal display device of the
present invention including liquid crystal and a counter substrate
and is also a schematic cross-sectional view of liquid crystal
cells of the transmission type liquid crystal display device
according to embodiments 1 to 4.
[0115] FIG. 21 is a graph showing the relationship between an
applied voltage and the transmittance in the constitution shown in
FIG. 20.
[0116] FIG. 22 is a cross-sectional view showing another embodiment
of the constitution of the liquid crystal display device of the
present invention including liquid crystal and a counter substrate
and is also a schematic cross-sectional view of liquid crystal
cells of the partial reflection/transmission type liquid crystal
display device according to embodiments 6 to 7.
[0117] FIG. 23 is a graph showing the relationship among an applied
voltage, the transmittance and the reflectance in the constitution
shown in FIG. 22.
[0118] FIG. 24 is an equivalent circuit diagram showing one
embodiment of the whole constitution of the liquid crystal display
device of the present invention.
[0119] FIG. 25 is an equivalent circuit diagram showing another
embodiment of the whole constitution of the liquid crystal display
device of the present invention.
[0120] FIG. 26 is a perspective view of the liquid crystal display
device shown in FIG. 24 or FIG. 25.
[0121] FIG. 27 is an equivalent circuit diagram showing another
embodiment of the whole constitution of the liquid crystal display
device of the present invention.
[0122] FIG. 28 is a perspective view of the liquid crystal display
device shown in FIG. 27.
[0123] FIG. 29 is a cross-sectional view showing one embodiment of
a manufacturing method of the liquid crystal display device
according to the present invention, wherein the first step of the
method is shown.
[0124] FIG. 30 is a cross-sectional view showing one embodiment of
the manufacturing method of the liquid crystal display device
according to the present invention, wherein the second step of the
method is shown.
[0125] FIG. 31 is a cross-sectional view showing one embodiment of
the manufacturing method of the liquid crystal display device
according to the present invention, wherein the third step of the
method is shown.
[0126] FIG. 32 is a cross-sectional view showing one embodiment of
the manufacturing method of the liquid crystal display device
according to the present invention, wherein the fourth step of the
method is shown.
[0127] FIG. 33 is a cross-sectional view showing one embodiment of
the manufacturing method of the liquid crystal display device
according to the present invention, wherein the fifth step of the
method is shown.
[0128] FIG. 34 is a cross-sectional view showing one embodiment of
the manufacturing method of the liquid crystal display device
according to the present invention, wherein the sixth step of the
method is shown.
[0129] FIG. 35 is a cross-sectional view showing one embodiment of
the manufacturing method of the liquid crystal display device
according to the present invention, wherein the seventh step of the
method is shown.
[0130] FIG. 36 is a cross-sectional view showing another embodiment
of the manufacturing method of the liquid crystal display device
according to the present invention, wherein the first step of the
method is shown.
[0131] FIG. 37 is a cross-sectional view showing another embodiment
of the manufacturing method of the liquid crystal display device
according to the present invention, wherein the second step of the
method is shown.
[0132] FIG. 38 is a cross-sectional view showing another embodiment
of the manufacturing method of the liquid crystal display device
according to the present invention, wherein the third step of the
method is shown.
[0133] FIG. 39 is a cross-sectional view showing another embodiment
of the manufacturing method of the liquid crystal display device
according to the present invention, wherein the fourth step of the
method is shown.
[0134] FIG. 40 is a cross-sectional view showing another embodiment
of the manufacturing method of the liquid crystal display device
according to the present invention, wherein the fifth step of the
method is shown.
[0135] FIG. 41 is a cross-sectional view showing another embodiment
of the manufacturing method of the liquid crystal display device
according to the present invention, wherein the sixth step of the
method is shown.
[0136] FIG. 42 is a cross-sectional view showing another embodiment
of the manufacturing method of the liquid crystal display device
according to the present invention, wherein the seventh step of the
method is shown.
[0137] FIG. 43 is a cross-sectional view showing another embodiment
of the manufacturing method of the liquid crystal display device
according to the present invention, wherein the eighth step of the
method is shown.
[0138] FIG. 44 is a cross-sectional view showing another embodiment
of the manufacturing method of the liquid crystal display device
according to the present invention, wherein the ninth step of the
method is shown.
[0139] FIG. 45 is a circuit diagram showing an embodiment of a
vertical scanning circuit of the liquid crystal display device
according to the present invention.
[0140] FIG. 46 is a view showing an example of a signal waveform of
a circuit shown in FIG. 45.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0141] Preferred embodiments the liquid crystal display device
according to the present invention are explained hereinafter in
conjunction with attached drawings.
[0142] <Constitution of Pixel>
[0143] Embodiment 1.
[0144] FIG. 1 is a plan view showing one embodiment of a unit pixel
of a liquid crystal display device according to the present
invention. A liquid crystal display part of the liquid crystal
display device is constituted of a large number of pixels which are
arranged in a matrix array and the unit pixel constitutes one of
these pixels. Accordingly, the unit pixels which are arranged above
and below as well as at left and at right of the unit pixel shown
in FIG. 1 also have the same constitution.
[0145] Then, respective right, middle and left views of FIG. 2
respectively show cross-sections taken along a line A-A', B-B' and
C-C' in FIG. 1. Further, FIG. 3 shows an equivalent circuit of a
pixel array portion.
[0146] The overall constitution of the pixel array portion is
formed on a buffer insulation film consisting of a Si.sub.3N.sub.4
film 200 having a film thickness of 50 nm and a SiO.sub.2 film 2
having a film thickness of 120 nm which is, in turn, formed on an
alkalifree glass substrate 1 having a strain point of 670 degree
centigrade. The buffer insulation film plays a role of preventing
the diffusion of impurities such as Na and the like from the glass
substrate 1.
[0147] On the SiO.sub.2 film 2, two polycrystalline Si (hereinafter
referred to as poly-Si) films 30 having a film thickness of 50 nm
which correspond to two thin film transistors Q1, Q2 are formed. On
respective poly-Si films 30, scanning wiring electrodes 10 made of
Mo are formed by way of a gate insulation film 20 made of
SiO.sub.2. Further, a second signal wiring electrode (reference
voltage signal line) 11 is formed using the same Mo as the scanning
wiring electrodes (gate signal lines) 10.
[0148] An interlayer insulation film 21 made of SiO.sub.2 is formed
such that the interlayer insulation film 21 covers the
above-mentioned all components. A first signal wiring electrode
(drain signal line) 12 formed of a three-layered metal film made of
Mo/Al/Mo and a source electrode 13 are connected to source and
drain layers formed on portions of one poly-Si layer via contact
through holes formed in the interlayer insulation film 21.
[0149] Further, a connection electrode 16 formed of a three-layered
metal film made of Mo/Al/Mo is connected to one source and drain
layers formed on portions of the other poly-Si layer and a second
signal wiring electrode 11 via contact through holes formed in the
interlayer insulation film 21. A second source electrode 13' formed
of a three-layered metal film made of Mo/Al/Mo is connected to the
other source and drain layers via contact through holes formed in
the interlayer insulation film 21.
[0150] Among the three-layered metal film made of Mo/Al/Mo, the Mo
film which constitutes a layer below the Al film is provided for
reducing the contact resistance between the poly-Si film 30 and Al,
while the Mo film which constitutes a layer above the Al film is
provided for reducing the contact resistance between the source
electrodes 13, 13' and the pixel electrodes 14, 15.
[0151] All of these elements are covered with a protective
insulation film 22 made of Si.sub.3N.sub.4 having a film thickness
of 400 nm and an organic insulation film (organic protective film)
23 containing acrylic resin as a major component and having a film
thickness of 2 .mu.m.
[0152] Further, a first pixel electrode 14 made of indium-tin-oxide
(ITO) is connected to the source electrode 13 of one thin film
transistor Q1 via a contact through hole formed in the protective
insulation film 22 and the organic insulation film 23. A second
pixel electrode (counter electrode) 15 made of ITO is connected to
the second source electrode 13' of the other thin film transistor
Q2 via contact through holes formed in the protective insulation
film 22 and the organic insulation film 23.
[0153] As shown in FIG. 1 which is a plan view, the first pixel
electrode 14 and the second pixel electrode 15 are constituted of
comb-shaped electrodes which are meshed with each other. In this
case, in a region which is surrounded by the scanning wiring
electrodes (gate signal lines) 10 and the first signal wiring
electrodes (drain signal lines) 12, a portion of the region which
functions substantially as the pixel region is formed of a portion
excluding a periphery of the region (corresponding to an opening
portion of a black matrix formed on a liquid-crystal-side surface
of the other substrate which faces one substrate in an opposed
manner by way of liquid crystal). Accordingly, in the pixel region,
the first pixel electrode 14 and the second pixel electrode 15 are
alternately arranged in their parallel directions.
[0154] Further, as shown in FIG. 3, out of two signal wiring
electrodes, the first signal wiring electrode 12 is formed such
that the electrode 12 crosses the scanning wiring electrode 10,
while the second signal wiring electrode 11 is arranged parallel to
the scanning wiring electrode 10. A voltage supplied to the first
signal wiring electrode 12 is applied to the first pixel electrode
14 through the first thin film transistor Q1 and a voltage supplied
to the second signal wiring electrode 11 is applied to the second
pixel electrode 15 through the second thin film transistor Q2. The
liquid crystal is driven by an electric field generated between two
pixel electrodes 14, 15.
[0155] In the liquid crystal display device having such a
constitution, by applying the differential voltages to the first
and second signal wiring electrodes 12, 11, the voltages applied to
respective pixel electrodes can be reduced to one half of the
voltages required in the usual case.
[0156] Further, since two pixel electrodes 14, 15 are constituted
of transparent electrodes made of ITO and are formed into
comb-shaped electrodes having a width of 4 .mu.m which are meshed
with each other, the driving voltage can be reduced.
[0157] Further, since the electrodes are transparent, the liquid
crystal on the electrodes is driven by a fringe electric field
within an area extended from an end portion of the electrode to an
inner position disposed away from the end portion by 1.5 to 2 .mu.m
and hence, the liquid crystal functions in the same manner as the
opening portion. Accordingly, the effective numerical aperture can
be enhanced so that the light utilization efficiency is
enhanced.
[0158] Due to these advantageous effects, the power consumption of
the whole LCD module can be reduced.
[0159] Embodiment 2.
[0160] FIG. 4 is a plan view showing another embodiment of the unit
pixel of the liquid crystal display device according to the present
invention and corresponds to FIG. 1. Respective right, middle and
left views of FIG. 5 respectively show cross-sections taken along a
line A-A', B-B' and C-C' in FIG. 4. Further, FIG. 6 is an
equivalent circuit of the pixel array portion.
[0161] Various types of film materials and their laminated
structures used in this embodiment are similar to those of the
embodiment 1. Further, this embodiment is similar to the embodiment
1 also with respect to the constitution that the voltage supplied
to the first signal wiring electrode (drain signal line) 12 is
applied to the first pixel electrode 14 through the first thin film
transistor Q1 and the voltage supplied to the second signal wiring
electrode (reference voltage signal line) 11 is applied to the
second pixel electrode 15 through the second thin film transistor
Q2 and the constitution that pixel electrodes 14, 15 are
constituted of transparent electrodes made of ITO and are formed
into comb-shaped electrodes having a width of 4 .mu.m which are
meshed with each other.
[0162] As shown in FIG. 6, this embodiment differs from the
embodiment 1 in that the second signal wiring electrodes 11 are
arranged approximately parallel to the first signal wiring
electrodes 12.
[0163] To be more specific, a member which corresponds to the
connection electrode 16 in the embodiment 1 is used as the second
signal wiring electrode 11 and is extended in the direction
parallel to the first signal wiring electrode 12. Here, the second
signal wiring electrode 11 is arranged as a layer below one
electrode out of the comb-shaped second pixel electrodes 15.
[0164] Due to such an arrangement, out of the through holes for
connecting the second signal wiring electrode 11 and the connection
electrode 16 which are necessary in the embodiment 1, one through
hole can be eliminated so that the numerical aperture can be
enhanced. Further, by arranging the second signal wiring electrode
11 as the layer below one electrode out of the comb-shaped second
pixel electrodes 15, the lowering of the numerical aperture due to
the presence of the opaque second signals wiring electrode 11 can
be minimized.
[0165] When the second signal wiring electrode 11 is extended
parallel to the scanning wiring electrode 10, the capacitance of
the second signal wiring electrode 11 becomes a sum of charge
holding capacitance of all pixels connected to the second signal
wiring electrode 11 and the capacitance of the liquid crystal layer
and hence, the capacitance of the second signal wiring electrode 11
becomes an extremely large value. When the resistance value of the
second signal wiring electrode 11 is not sufficiently small, there
arises a possibility that shadow wing in the lateral direction is
generated due to the delay of signal thus giving rise to poor image
quality.
[0166] In view of the above, in the second embodiment, the second
signal wiring electrode 11 is arranged such that the second signal
wiring electrode 11 is extended in the direction parallel to the
first signal wiring electrode 12. In this case, the capacitance per
a single piece of second signal wiring electrode 11 becomes a sum
of a crossing capacitance between a common electrode (second signal
wiring electrode 11) and a scanning electrode (scanning wiring
electrode 10), a charge holding capacitance for selected one pixel
and a capacitance of the liquid crystal layer and hence, the
capacitance per a single piece of second signal wiring electrode 11
becomes a small value compared to the former value. Accordingly,
the above-mentioned drawback on the image quality derived from the
delay of signals is not generated.
[0167] Embodiment 3.
[0168] FIG. 7 is a plan view showing another embodiment of the unit
pixel of the liquid crystal display device according to the present
invention and corresponds to FIG. 1.
[0169] Respective right, middle and left views of FIG. 8
respectively show cross-sections taken along a line A-A', B-B' and
C-C' in FIG. 7. Further, FIG. 9 shows an equivalent circuit of a
pixel array portion.
[0170] Various types of film materials and their laminated
structures used in this embodiment are substantially similar to
those of the embodiment 1.
[0171] In this embodiment, the second signal wiring electrode 11
and the second pixel electrode 15 are directly connected to each
other and a thin film transistor Q2 is not inserted between them.
By using only one piece of thin film transistor which is formed in
the pixel, an area occupied by the thin film transistor can be
reduced so that the numerical aperture of pixels can be increased.
Further, even when such a constitution is adopted, by applying a
differential voltage between the second signal wiring electrode 11
and the first signal wiring electrode 12, it is possible to obtain
the driving voltage reduction effect in the same manner as the
embodiments 1 and 2.
[0172] As a driving method, it is possible to use either one of a
frame inversion driving which inverts the polarity of voltage every
1 frame period and a line inversion driving which inverts the
polarity of voltage every 1 scanning period.
[0173] Further, this embodiment is similar to the embodiment 1 with
respect to the constitution that two pixel electrodes 14, 15 are
constituted of transparent electrodes made of ITO and are formed
into comb-shaped electrodes having a width of 4 .mu.m which are
meshed with each other. Accordingly, this embodiment can realize
the enhancement of numerical aperture and the reduction of driving
voltage power source in the same manner as the embodiment 1.
[0174] By using the poly-Si thin film transistor having the large
driving ability as the thin film transistor for driving pixel as in
the case of this embodiment, the thin film transistor can be
miniaturized and hence, the numerical aperture of the pixel can be
enhanced.
[0175] Embodiment 4.
[0176] FIG. 10 is a plan view showing another embodiment of the
unit pixel of the liquid crystal display device according to the
present invention and corresponds to FIG. 1. Respective right,
middle and left views of FIG. 11 respectively show cross-sections
taken along a line A-A', B-B' and C-C' in FIG. 10. Further, FIG. 12
shows an equivalent circuit of a pixel array portion.
[0177] Various types of film materials and their laminated
structures used in this embodiment are substantially similar to
those of the embodiment 1.
[0178] In this embodiment, in the same manner as the embodiment 3,
the second signal wiring electrode (reference voltage signal line)
11 and the second pixel electrode (counter electrode) 15 are
directly connected to each other and a thin film transistor Q2 is
not inserted between them.
[0179] However, here, the second signal wiring electrode 11 is
arranged approximately parallel to the first signal wiring
electrode 12. Due to such an arrangement, out of through holes
which connect the second signal wiring electrode 11 and the
connection electrode 16, one through hole can be eliminated and
hence, the numerical aperture can be enhanced.
[0180] Further, by arranging the second signal wiring electrode 11
as the layer below one electrode out of the comb-shaped second
pixel electrodes 15, the lowering of the numerical aperture due to
the presence of the opaque second signal wiring electrode 11 can be
minimized. Still further, since the thin film transistor Q2 is not
present between the second signal wiring electrode 11 and the
second pixel electrode 15, the numerical aperture can be further
enhanced.
[0181] This embodiment can obtain the largest numerical aperture
among all of the embodiments described heretofore.
[0182] Further, this embodiment can obtain the driving voltage
reduction effect as that of the embodiment 3.
[0183] As a driving method, it is possible to use either one of a
frame inversion driving which inverts the polarity of voltage every
1 frame period and a column inversion driving which inverts the
polarity of voltage every 1 frame period but applies a voltage of
an inverse polarity to the neighboring first signal wiring
electrode 12.
[0184] Embodiment 5.
[0185] FIG. 13 is a plan view showing another embodiment of the
unit pixel of the liquid crystal display device according to the
present invention and corresponds to FIG. 1. Respective right,
middle and left views of FIG. 14 respectively show cross-sections
taken along a line A-A', B-B' and C-C' in FIG. 13.
[0186] Various types of film materials and their laminated
structures used in this embodiment are similar to those of the
embodiment 1. Further, this embodiment is similar to the embodiment
1 also with respect to the constitution that the voltage supplied
to the first signal wiring electrode (drain signal line) 12 is
applied to the first pixel electrode 14 through the first thin film
transistor Q1 and a voltage supplied to the second signal wiring
electrode (reference voltage signal line) 11 is applied to the
second pixel electrode (counter electrode) 15 through the second
thin film transistor Q2 and the constitution that pixel electrodes
14, 15 are constituted of transparent electrodes made of ITO and
are formed into comb-shaped electrodes having a width of 4 .mu.m
which are meshed with each other.
[0187] This embodiment is characterized in that the reflection
electrode 13' which reflects light is arranged as a layer below the
comb-shaped electrodes 14, 15 constituting the display region which
are meshed with each other.
[0188] The reflection electrode 13' is formed by extending the
second source electrode 13' in the embodiment 1 over the whole area
of the pixel region. Accordingly, the reflection electrode 13' can
have a potential equal to that of the second pixel electrode 15.
Further, with respect to the constitution on the surface of the
reflection portion, only the upper layer made of Mo is eliminated
from the second source electrode 13' constituted of a three-layered
film made of Mo/Al/Mo. Due to such a constitution, the light
reflectance on the surface of the reflection electrode 13' can be
largely increased from 40% to 90%.
[0189] In this embodiment, the image display is obtained by
reflecting the external light on the reflection electrode 13'.
[0190] Further, the liquid crystal is driven by the lateral
electric field formed between two pixel electrodes 14, 15 and the
fringe electric field formed between the first pixel electrode 14
and the reflection electrode 13'.
[0191] Also in the previously-mentioned second conventional
technique (Japanese Patent Laid-Open No. 316383/1999), there is
disclosed the lateral-electric-field type liquid crystal display
device which uses the planar transparent electrodes and the
comb-shaped electrodes made of transparent electrodes which are
formed as a layer different from and above the planar transparent
electrodes. However, in the conventional technique, an equal
potential is applied to all comb-shaped electrodes and only the
electric field which is generated between the planar electrodes and
the comb-shaped electrodes is utilized. This embodiment differs
from such conventional technique in that two comb-shaped electrodes
which are meshed with each other are used and the liquid crystal is
driven by both of the electric field generated between two opposing
comb-shaped electrodes and the fringe electric field generated
between one of the comb-shaped electrodes and the reflection
electrode.
[0192] Due to such a constitution, the more uniform electric field
can be applied between two comb-shaped electrodes and hence, it is
possible to obtain favorable display images.
[0193] Embodiment 6.
[0194] FIG. 15 is a plan view showing another embodiment of the
unit pixel of the liquid crystal display device according to the
present invention and corresponds to FIG. 1.
[0195] Respective right, middle and left views of FIG. 16
respectively show cross-sections taken along a line A-A', B-B' and
C-C' in FIG. 15.
[0196] In this embodiment, various types of film materials and
their laminated structures used in this embodiment are similar to
those of the embodiment 1. Further, this embodiment is similar to
the embodiment 1 also with respect to the constitution that the
voltage supplied to the first signal wiring electrode (drain signal
line) 12 is applied to the first pixel electrode 14 through the
first thin film transistor Q1 and a voltage supplied to the second
signal wiring electrode (reference voltage signal line) 11 is
applied to a second pixel electrode (counter electrode) 15 through
the second thin film transistor Q2 and the constitution that two
pixel electrodes 14, 15 are constituted of transparent electrodes
made of ITO and are formed into comb-shaped electrodes having a
width of 4 .mu.m which are meshed with each other.
[0197] In this embodiment, the reflection electrode 13' which
partially reflects light is arranged as a layer below the
comb-shaped electrodes 14, 15 which constitute the display region
and are meshed with each other thus constituting the partial
reflection/transmission type display device. The reflection
electrode 13' has the same layer structure as that of the
embodiment 5 and only differs from the embodiment with respect to
the constitution that the reflection electrode 13' is formed
extending over approximately half of the pixel region. That is, the
reflection display region and the transmission display region are
constituted by the region where the reflection electrode 13' is
formed and the other remaining region.
[0198] The image display is performed by reflecting the external
light by the reflection electrode 13' in the reflection display
mode and by utilizing light from the backlight in the transmission
display mode. The transmission and reflection display principles
are those which have been described heretofore.
[0199] The partial reflection/transmission type display device is
suitable for a miniaturized equipment such as a portable telephone,
a portable terminal or the like which is popularly used outdoors.
With the use of the pixel structure of the present invention, the
driving voltage can be reduced so that the equipment of low power
consumption can be realized. Further, since the equipment can
obtain the wide viewing angle which is the feature of the lateral
electric field driving method, it is possible to obtain the
favorable image display.
[0200] Embodiment 7.
[0201] FIG. 17 is a plan view showing another embodiment of the
unit pixel of the liquid crystal display device according to the
present invention and corresponds to FIG. 1. FIG. 18 shows a cross
section of a part taken along a line A-A' of FIG. 17. FIG. 19 shows
an equivalent circuit of a pixel array portion.
[0202] In this embodiment, various types of film materials and
their laminated structures used in this embodiment are similar to
those of the embodiment 1.
[0203] In this embodiment, first of all, the first voltage supplied
to the first signal wiring electrode (drain signal line) 12 is
applied to the first pixel electrode 14 through the first thin film
transistor Q1 and the second voltage supplied to the second signal
wiring electrode (reference voltage signal line) 11 is applied to
the second pixel electrode (counter voltage) 15 through the second
thin film transistor Q2.
[0204] Further, a third voltage supplied to the first signal wiring
electrode 12 is applied to a third pixel electrode 140 through a
third thin film transistor Q3 and a fourth voltage supplied to the
second signal wiring electrode 11 is applied to a fourth pixel
electrode 150 through a fourth thin film transistor Q4. All of the
first to the fourth pixel electrodes 14, 15, 140, 150 are
constituted as comb-shaped electrodes which have a width of 4 .mu.m
and are meshed with each other.
[0205] Then, the reflection electrodes 130' are formed as layers
below the third and the fourth pixel electrodes 140, 150 and are
operated in the reflection display mode. On the other hand, the
display region constituted of the first and the second pixel
electrodes 14, 15 is operated in the transmission display mode and
is operated as a partial reflection/transmission display device as
a whole.
[0206] This embodiment is characterized in that a pair of thin film
transistors Q1 to Q4 are formed on each one of the reflection
display region and the transmission display region and these thin
film transistors Q1 to Q4 are driven with the voltages which are
different from each other.
[0207] The gate electrodes of the first and the second thin film
transistors Q1, Q2 are connected to the first scanning wiring
electrode 10, and the gate electrodes of the third and the fourth
thin film transistors Q3, Q4 are connected to the second scanning
wiring electrode 100. The selection gate pulse voltages are applied
at respectively different timing and the image signals are applied
to the first signal wiring electrode 12 and the second signal
wiring electrode 11 in synchronism with such an operation whereby
it is possible to apply different voltages to respective reflection
and transmission pixel electrodes.
[0208] Although such a constitution is disadvantageous in view of
the numerical aperture since the number of thin film transistors Q1
to Q4 in the inside of the pixel becomes four, when the voltage
value which generates the peak brightness differs between the
reflection mode and the transmission mode, the constitution is
advantageous to obtain the favorable images.
[0209] Although this embodiment is constituted such that the thin
film transistors Q2, Q4 are interposed between the second signal
wiring electrode (reference voltage signal line) 11 and the second
or the fourth pixel electrode (counter voltage) 15, 150, it is
needless to say that these thin film transistors Q2, Q4 are
eliminated.
[0210] <<One Embodiment of Constitution Including Liquid
Crystal and Counter Substrate>>
[0211] FIG. 20 is a schematic cross-sectional view of liquid
crystal cells of the transmission type liquid crystal display
device according to the embodiments 1 to 4 of the present
invention.
[0212] As mentioned previously, with respect to a liquid crystal
layer 506, on a glass substrate 1 which is disposed below the
liquid crystal layer 506, the scanning wiring electrodes (not shown
in the drawing) and the signal wiring electrodes (not shown in the
drawing) are formed in a matrix array and the first pixel
electrodes 14 and the second pixel electrodes 15 made of ITO are
driven through the thin film transistors (not shown in the drawing)
formed in the vicinity of crossing points of the wiring
electrodes.
[0213] On a counter glass substrate 508 which faces the glass
substrate 1 in an opposed manner while sandwiching the liquid
crystal layer 506 therebetween, color filters 507 and a color
filter protective film OC are formed.
[0214] Polarizers 505 are respectively formed on outer surfaces of
a pair of glass substrates 1, 508 and their polarization
transmitting axes are arranged to cross each other at a right
angle.
[0215] The liquid crystal layer 506 is filled between a lower
orientation film ORI1 and an upper orientation film ORI2 which
determine the direction of liquid crystal molecules and is sealed
by a sealing member 520 (not shown in the drawing) which is served
for fixing the glass substrate 1 and the counter glass substrate
508. The lower orientation film ORI1 is formed over an organic
insulation film 23 at the glass substrate 1 side.
[0216] The liquid crystal display device is assembled in such a
manner that the layers at the glass substrate 1 side and the layers
at the counter glass substrate 508 side are separately formed and,
thereafter, the upper and the lower glass substrates 1, 508 are
superposed on each other, and the liquid crystal 506 is filled
between the upper and lower glass substrate 1, 508.
[0217] By adjusting the transmission of light from the backlight BL
using the pixel electrodes 14 and 15, a color liquid crystal
display device of thin film transistor driving type can be
realized.
[0218] By driving the liquid crystal layer using the electric field
which is extended approximately along the surface of the substrate,
there is no possibility that the liquid crystal molecules rise with
respect to the surface of the substrate when the electric field is
applied and the liquid crystal molecules are rotated within the
surface of the substrate so that the image display can be performed
by controlling the polarization direction of the transmitting
light.
[0219] Accordingly, it is possible to substantially eliminate the
viewing angle dependency of the contrast caused by the
birefringence of the liquid crystal molecules so that the liquid
crystal display device of high image quality with a wide viewing
angle can be obtained.
[0220] FIG. 21 shows voltage/brightness (B-V) characteristics of
the liquid crystal display element shown in FIG. 20. "a" in the
drawing indicates the B-V characteristics of the display device of
the present invention and "b" in the drawing indicates the B-V
characteristics of a conventional so-called lateral electric field
type liquid crystal display element which uses metal electrodes
with a distance of 14 .mu.m between electrodes.
[0221] With the use of the display element of the present
invention, the voltage at which the transmittance becomes the peak
value can be reduced from the conventional approximately 7V to
3.5V. Further, it is also understood that the peak value of the
transmittance is also largely enhanced.
[0222] These advantageous effects can be obtained by constituting
two pixel electrodes using the transparent electrodes made of ITO
and by forming these pixel electrodes into the comb-shaped
electrodes having the width of 4 .mu.m which are meshed with each
other.
[0223] <<Another Embodiment of Constitution Including Liquid
Crystal and Counter Substrate>>
[0224] FIG. 22 is a schematic cross-sectional view of liquid
crystal cells of the partial reflection/transmission type liquid
crystal display device according to the embodiment 6 or 7 of the
present invention.
[0225] Although the cross-sectional constitution of the cells is
substantially similar to that of the cells shown in the
above-mentioned FIG. 20, the reflection electrodes 13' are provided
as layers below portions of the comb-shaped electrodes for
realizing the partial reflection/transmission display.
[0226] FIG. 23 shows the voltage/brightness characteristics of the
liquid crystal display element shown in FIG. 22. In the drawing,
"c" indicates the voltage dependency of the transmittance of the
transmission display region and "d" indicates the voltage
dependency of the reflectance of the reflection display region. The
voltage which generates the maximum reflectance or the maximum
transmittance differs between the reflection display and the
transmission display.
[0227] In such a case, by adopting the constitutions shown in FIG.
17 and FIG. 18, by connecting the thin film transistors to a pair
of respective pixel electrodes of the reflection part and the
transmission part and by applying the optimal voltages to these
pixel electrodes respectively, it is possible to obtain the
favorable display characteristics.
[0228] <<One Embodiment of Constitution of Whole Display
Device>>
[0229] FIG. 24 shows an equivalent circuit of the whole display
device which integrates peripheral driving circuits on the same
substrate together with thin film transistor active matrix. For
example, the display device includes the pixels having the
constitution shown in FIG. 1 and FIG. 2, a thin film transistor
active matrix 50 consisting of the scanning wiring electrodes 10
indicated by Y1-Yend, the first signal wiring electrodes 12
indicated by X1R, X1G, X1B-XendB and the second signal wiring
electrodes 11 indicated by C1-Cend, a vertical scanning circuit 51
for driving the thin film transistor active matrix 50, the first
signal-side driving circuit 53, the second signal-side driving
circuit 52 which supplies signals to the second signal wiring
electrodes 11, and a level shifter LS.
[0230] In this embodiment, the number of scanning lines is 600, the
number of signal lines is 2400 and the diagonal size of the display
part is approximately 5 inches.
[0231] With respect to the configuration of the thin film
transistor active matrix 50, as shown in FIG. 25, the pixels having
the constitution shown in FIG. 4 and FIG. 5 may be used. In this
case, the thin film transistor active matrix 50 is constituted of
the scanning wiring electrodes 10 indicated by Y1-Yend, the first
signal wiring electrode 12 indicated by X1R, X1G, X1B-XendB and the
second signal wiring electrode 11 indicated by C1R-C1end. Further,
the vertical scanning circuit 51 for driving the matrix 50, the
first signal-side driving circuit 53, the second signal-side
driving circuit 52 which supplies signals to the second signal
wiring electrodes 11, and the level shifter LS are arranged in the
periphery of the matrix 50. This configuration differs from the
configuration of FIG. 24 in that the second signal-side driving
circuit 52 is arranged at the lower side of the display part.
[0232] The vertical scanning circuit 51 is constituted of a shift
register circuit driven by a vertical clock signal and the level
shifter to which the row selection voltage is supplied and outputs
the row selection pulse to the scanning wiring electrodes 10.
[0233] The horizontal scanning circuit (first signal-side driving
circuit) 53 includes a shift register circuit SRH which is driven
by a horizontal clock signal, a latch circuit L1 which latches
image data DATA (not shown in the drawing) which is digitized into
6 bits, a digital-analogue converter circuit DAC which decodes the
latched digital data to analogue data, a line memory LM (not shown
in the drawing) which temporarily stores an output from the
digital-analogue converter circuit DAC for 1 row, and an analogue
switch SW which is served for supplying the image data stored in
the line-memory LM to the first signal wiring electrodes 12. Here,
the reference voltage signals which are weighted corresponding to
respective bits are supplied to the digital-analogue converter
circuit DAC.
[0234] These driving circuits are constituted of the complementary
type (CMOS) poly-Si thin film transistors or N type poly-Si thin
film transistors.
[0235] FIG. 26 is an overall constitutional view of the liquid
crystal display element shown in FIG. 24 or FIG. 25. The glass
substrate 1 on which the thin film transistor active matrix, the
peripheral driving circuits and the like are formed and the counter
glass substrate 508 which forms color filters on the inner surface
thereof are laminated to each other by means of the sealing member
520 and the liquid crystal composition is filled in a space defined
by the glass substrate 1, the counter glass substrate 508 and the
sealing member 520. The polarization films (polarizers) 505 are
arranged on the respective outer surfaces of the glass substrate 1
and the counter glass substrate 508 in such a manner that their
polarization transmission axes cross each other at a right angle.
Connection terminals 521 are formed at one side on the TFT
substrate (glass substrate) 1 and display data, control signals,
power source voltages and the like are supplied to the TFT
substrate (glass substrate) 1 through FPCs 522 which are connected
to the connection terminals 521.
[0236] Since the driving circuits such as the digital analogue
converters and the like are integrated on the substrate using the
poly-Si thin film transistors, the number of external connection
terminals and the number of external parts can be largely reduced.
Further, with the use of the pixels of the present invention, the
liquid crystal driving voltage can be decreased so that the output
voltage of the signal-side driving circuit can be reduced whereby
the power consumption of such a circuit can be also reduced.
[0237] Accordingly, the adoption of the IPS mode driving method to
the miniaturized LCD which has been difficult conventionally now
becomes possible.
[0238] <<Another Embodiment of Constitution of the Whole
Display Device>>
[0239] FIG. 27 shows an equivalent circuit of the whole display
device which integrates a portion of the peripheral driving
circuits on the same substrate together with the thin film
transistor active matrix. For example, the display device includes
the thin film transistor active matrix 50 consisting of the pixels
having the constitution shown in FIG. 1 and FIG. 2, the scanning
wiring electrodes 10 indicated by Y1-Yend, the first signal wiring
electrodes 12 indicated by X1R, X1G, X1B-XendB, and the second
signal wiring electrodes 11 indicated by C1-Cend, the vertical
scanning circuit 51 for driving the matrix 50, the second
signal-side driving circuit 52 for supplying signals to the second
signal wiring electrodes 11, horizontal-side drivers LSIs
DRV1-DRV3, a switching circuit SW for dividing outputs of the
horizontal-side driver LSIs DRV1-DRV3 and supplying them into a
plurality of first signal wiring electrodes 12, and a level-shifter
LS. In this embodiment, the number of scanning lines is 480, the
number of signal lines is 1980, and the diagonal size of the
display part 1 is approximately 7 inches. Further, in this
embodiment, all of the driving circuits formed of poly-Si thin film
transistors are constituted by using only the N-type thin film
transistors.
[0240] FIG. 45 shows a vertical scanning circuit which is
constituted by using only the N-type thin film transistors and FIG.
46 shows an example of waveforms of operational signals. The
circuit is a dynamic circuit which is constituted of the N-type
thin film transistors and bootstrap capacitance Cb and is driven
based on a reference potential Vss, a start signal Vin, a clock
pulse voltage V1 and a clock pulse voltage V2 which is
complementary with the clock pulse voltage V1. The circuit is not
provided with a power source voltage supply wiring which is usually
necessary for the CMOS circuit and hence, the circuit is operated
using the charge supplied from the complementary clock voltages of
V1, V2. Accordingly, there exists no penetration current from the
power source wiring to the grand wiring which causes a problem in a
shift register circuit using an inverter circuit which is
constituted of the N-type transistors and a load. Accordingly, the
power consumption of the driving circuits can be reduced. Further,
since the circuit is constituted of only the N-type thin film
transistors, the manufacturing process is simplified compared to
the manufacturing process of the circuit constituted of CMOS so
that the circuit can be manufactured at a low cost.
[0241] FIG. 28 is an overall perspective constitutional view of the
liquid crystal display element shown in FIG. 27. The glass
substrate 1 on which the thin film transistor active matrix, the
peripheral driving circuits and the like are formed and the counter
glass substrate 508 which forms color filters on the inner surface
thereof are laminated to each other by means of the sealing member
520 and the liquid crystal composition is filled in a space defined
by the glass substrate 1, the counter glass substrate 508 and the
sealing member 520. The polarization films (polarizers) 505 are
arranged on the respective outer surfaces of the glass substrate 1
and the counter glass substrate 508 in such a manner that their
polarization transmission axes cross each other at a right angle.
Horizontal-side-driver LSIs DRV1-DRV3 are directly mounted on one
side of the TFT substrate (glass substrate) 1 and display data,
control signals, power source voltages and the like are supplied to
the driver LSIs through connection terminals 521 and FPCs 522 which
are connected to the connection terminals 521.
[0242] In this embodiment, the conversion of digital display data
into the analogue data is performed in the inside of the
horizontal-side driver LSIs DRV1-DRV3. The peripheral driving
circuits which are constituted of poly-Si thin film transistors are
only constituted of the vertical-side scanning circuit (vertical
scanning circuit 51) and the switching circuit SW which divides and
supplies analogue data outputted from the driver LSIs
(horizontal-side driver LSIs DRV1-DRV3) to a plurality of signal
wiring (first signal wiring electrodes 12). Since the output of one
driver LSI is divided into a plurality of signal wirings due to the
horizontal-circuit-side switching circuit SW, the number of output
pins of the driver LSI can be reduced. Due to such a constitution,
the power consumption of the driver LSI can be reduced.
[0243] <One Embodiment of Manufacturing Method>
[0244] Subsequently, taking a TFT active matrix substrate which is
used in a liquid crystal display element-constituted of only the N
type thin film transistors as shown in FIG. 28 as an example, the
manufacturing steps thereof are explained in conjunction with FIG.
29 to FIG. 35.
[0245] After cleaning an upper surface of an alkalifree glass
substrate 1 having a thickness of 500 .mu.m, width 750 mm, a length
950 mm and a strain point of 670 degree centigrade, a
Si.sub.3N.sub.4 film 200 having a film thickness of 50 nm is formed
on the substrate 1 by a plasma CVD method using a mixed gas of
SiH.sub.4, NH.sub.3 and N.sub.2. Subsequently, by a plasma CVD
method using a mixed gas of tetraethoxysilane and O.sub.2, a
SiO.sub.2 film 2 having a film thickness of 120 nm is formed. The
formation temperature of both of Si.sub.3N.sub.4 and SiO.sub.2 is
400 degree centigrade.
[0246] Then, by a plasma CVD method using a mixed gas of SiH.sub.4
and Ar, an intrinsic hydrogenerated amorphous silicon film 300
having a film thickness of 50 nm is formed on the SiO.sub.2 film 2.
The film formation temperature is 400 degree centigrade and a
hydrogen quantity immediately after the formation of film is
approximately 5 at %. Then, the substrate is subjected to annealing
for approximately 30 minutes at 450 degree centigrade so as to
discharge hydrogen in the inside of the hydrogenerated amorphous
silicon film 300. The hydrogen quantity after annealing is
approximately 1 at %.
[0247] Subsequently, excimer laser light LASER having a wavelength
of 308 nm is irradiated to the amorphous silicon film with the
fluence of 400 mJ/cm.sup.2 so as to obtain the approximately
intrinsic poly-crystalline silicon film 30 by fusing and
recrystallizing the amorphous silicon film. Here, the laser beam is
formed in a thin line having a width of 0.3 mm and a length of 200
mm and is irradiated to the substrate while moving the substrate in
the direction substantially perpendicular to the longitudinal
direction of the beam at a pitch of 10 .mu.m. The irradiation is
performed in the nitrogen atmosphere (FIG. 29).
[0248] A given resist pattern is formed on the poly-silicon film 30
by a usual photolithography method and the poly-silicon film 30 is
machined into a given shape by a reactive ion etching using a mixed
gas of CF.sub.4 and O.sub.2.
[0249] Then, a SiO.sub.2 film having a film thickness of 100 nm is
formed by a plasma CVD method using a mixed gas made of
tetraethoxysilane and oxygen so as to obtain a gate insulation film
20. The mixing ratio between the tetraethoxysilane and O.sub.2 at
this stage of operation is set to 1:50 and the formation
temperature is 400 degree centigrade.
[0250] Subsequently, a Mo film having a film thickness of 200 nm is
formed using a sputtering method and, thereafter, a given resist
pattern PR is formed on the Mo film using a usual photolithography
method. Then, the Mo film is machined in a given shape by a wet
etching process using a mixed acid so that the scanning wiring
electrodes 10 and the second signal wiring electrodes 11 are
obtained.
[0251] While leaving the resist pattern PR used for etching as it
is, P ions are implanted by an ion implantation method with an
acceleration voltage of 60 KeV and a dose quantity of 1E15
(cm.sup.-2) thus forming the source and drain regions 31 of the N
type thin film transistors (FIG. 30).
[0252] Subsequently, after removing the resist pattern PR used for
etching, P ions are implanted again by an ion implantation method
with an acceleration voltage of 65 KeV and a dose quantity of 2E13
(cm.sup.-2) thus forming the LDD regions 32 of the N type thin film
transistors (FIG. 31).
[0253] The length of the LDD region 32 is determined based on a
side etching quantity of Mo when Mo is subjected to wet etching. In
an example according to this embodiment, the length is
approximately 0.8 .mu.m. This length can be controlled by changing
the over-etching time of Mo. The irregularities of the length of
LDD in the inside of the substrate is approximately 0.1 .mu.m and
hence, the irregularities can be suppressed favorably. By adopting
such a step, a mask pattern forming step for forming the LDD can be
omitted and hence, the steps can be simplified.
[0254] Subsequently, the implanted impurities are activated by a
rapid thermal annealing (RTA) method which irradiates light of an
excimer lamp or a metal halide lamp to the substrate. By performing
the annealing using the light of the excimer lamp or the metal
halide lamp which contains a large quantity of ultraviolet rays UV,
only the poly-Si layers can be selectively heated so that damages
caused by heating the glass substrate 1 can be obviated. The
activation of the impurities can be performed by the heat treatment
at a temperature of equal to or more than 450 degree centigrade
provided that the heat treatment does not generate problems such as
the shrinkage or deformation by bending of the substrate (FIG.
32).
[0255] Subsequently, a SiO.sub.2 film having a film thickness of
500 nm is formed by a plasma CVD method using a mixed gas of
tetraethoxysilane and oxygen thus obtaining an interlayer
insulation film 21. Here, the mixture ratio of tetraethoxysilane
and oxygen is 1:5 and the formation temperature is 350 degree
centigrade.
[0256] Then, after forming a given resist pattern, a contact
through hole is formed in the interlayer insulation film 21 by a
wet etching process using a mixed acid. Subsequently, a Ti film
having a film thickness of 50 nm, an Al-Nd alloy film having a film
thickness of 500 nm and a Ti film having a film thickness of 50 nm
are formed sequentially in a laminated manner by a sputtering
method and, thereafter, a given resist pattern is formed.
Thereafter, these films are etched altogether by a reactive ion
etching process using a mixed gas of BCl.sub.3 and Cl.sub.2 thus
obtaining the first signal wiring electrodes 12, the source
electrodes 13, 13' and the connection electrodes 16 (FIG. 33).
[0257] A Si.sub.3N.sub.4 film (protective insulation film) 22
having a film thickness of 400 nm is formed by a plasma CVD method
using a mixed gas of SiH.sub.4, NH.sub.3 and N.sub.2. Further,
acrylic photosensitive resin having a film thickness of
approximately 3.5 .mu.m is coated on the Si.sub.3N.sub.4 film 22 by
a spin coating method and, thereafter, the exposure and the
development are performed using a given mask to form a through hole
in the acrylic resin. Subsequently, by performing the baking for 20
minutes at 230 degree centigrade so as to bake the acrylic resin
thus obtaining an organic protective film (organic insulation film)
23 having a film thickness of 2.3 .mu.m. Subsequently, using a
through hole pattern provided to the organic protective film 23 as
a mask, the Si.sub.3N.sub.4 film which constitutes a lower layer is
machined by a reactive ion etching process using CF.sub.4 thus
forming a through hole in the Si.sub.3N.sub.4 film (FIG. 34).
[0258] In this manner, by machining the insulation film (protective
insulation film) 22 which constitutes the lower layer using the
organic protective film 23 as a mask, the films in two layers can
be patterned with one photolithography step so that the steps can
be simplified.
[0259] Finally, an ITO film having a film thickness of 70 nm is
formed by a sputtering method and, thereafter, the ITO film is
machined in a given shape by a wet etching process using a mixed
acid thus forming the first and second pixel electrodes 14, 15
whereby the active matrix substrate is completed (FIG. 35).
[0260] <Another Embodiment of Manufacturing Method>
[0261] Subsequently, the manufacturing steps of the TFT active
matrix substrate used in the liquid crystal display element having
built-in driving circuits constituted of CMOS thin film transistors
shown in FIG. 26 are explained in conjunction with FIG. 36 to FIG.
44.
[0262] After cleaning an upper surface of an alkalifree glass
substrate 1 having a thickness of 500 .mu.m, a width of 750 mm, a
length of 950 mm and a strain point of 670 degree centigrade, a
Si.sub.3NO.sub.4 film 200 having a film thickness of 50 nm is
formed by a plasma CVD method using a mixed gas of SiH.sub.4,
NH.sub.3 and N.sub.2. Subsequently, by a plasma CVD method using a
mixed gas of tetraethoxysilane and O.sub.2, a SiO.sub.2 film 2
having a film thickness of 120 nm is formed. The formation
temperature of both of Si.sub.3N.sub.4 and SiO.sub.2 is 400 degree
centigrade.
[0263] Then, by a plasma CVD method using a mixed gas of SiH.sub.4
and Ar, an intrinsic hydrogenerated amorphous silicon film 300
having a film thickness of 50 nm is formed on the SiO.sub.2 film 2.
The film formation temperature is 400 degree centigrade and a
hydrogen quantity immediately after the formation of film is
approximately 5 at %. Then, the substrate is subjected to annealing
for approximately 30 minutes at 450 degree centigrade so as to
discharge hydrogen in the inside of the hydrogenerated amorphous
silicon film 300.
[0264] Then, a SiO.sub.2 film 201 having a film thickness of 100 nm
is formed by a plasma CVD method using a mixed gas made of
tetraethoxysilane and O.sub.2. Then, boron (B+) is implanted by an
ion implantation method with an acceleration voltage of 40 KeV and
a dose quantity of 5E12 (cm.sup.-2). Boron is used for adjusting a
threshold voltage of the thin film transistors (FIG. 36).
[0265] Subsequently, the SiO.sub.2 film 201 is removed using a
buffer hydrofluoric acid and, thereafter, excimer laser beams LASER
having a wavelength of 308 nm are irradiated to the amorphous
silicon film with the fluence of 400 mJ/cm.sup.2 so as to fuse and
re-crystallize the amorphous silicon film thus obtaining a P type
polycrystalline silicon film 30 (FIG. 37).
[0266] Subsequently, a Mo film having a film thickness of 200 nm is
formed using a sputtering method and, thereafter, a given resist
pattern is formed on the Mo film using a usual photolithography
method. Then, the Mo film is machined in a given shape by a
reactive ion etching process using CF.sub.4 so that the gate
electrodes 10N of the N type thin film transistors are
obtained.
[0267] While leaving the resist pattern PR used for etching as it
is, phosphorous (P) ions are implanted by an ion implantation
method with an acceleration voltage of 60 KeV and a dose quantity
of 1E15 (cm.sup.-2) thus forming the source and drain regions 31
(not shown in the drawing) of the N type thin film transistors.
Here, the P type thin film transistor (left side in FIG. 38) has
the whole element protected by the pattern of the Mo film and the
photo resist film PR so that the phosphorous ions are not implanted
(FIG. 38).
[0268] Subsequently, while leaving the resist pattern PR as it is,
the substrate is processed with a mixed acid and the machined Mo
electrodes are subjected to side etching so as to slim the pattern.
Then, after removing the resist, P ions are implanted by an ion
implantation method with an acceleration voltage of 65 KeV and a
dose quantity of 2E13 (cm.sup.-2) thus forming the LDD region 32
(not shown in the drawing) of the N type thin film transistor (FIG.
39).
[0269] In the same manner as the previously mentioned example, the
length of the LDD region 32 is controlled based on the side etching
time using a mixed acid.
[0270] Subsequently, a given resist pattern PR is formed on the Mo
film and the gate electrodes 10P of the P type thin film
transistors and wiring patterns other than the thin film
transistors are obtained by a reactive ion etching using CF.sub.4.
Here, the whole N type thin film transistor is protected by the
photo resist pattern PR so that the transistor is protected from an
etching gas (FIG. 40).
[0271] Subsequently, the implanted impurities are activated by a
rapid thermal annealing (RTA) method which irradiates light UV of
an excimer lamp or a metal halide lamp to the substrate (FIG.
41).
[0272] Subsequently, a SiO.sub.2 film having a film thickness of
500 nm is formed by a plasma CVD method using a mixed gas of
tetraethoxysilane and oxygen thus obtaining an interlayer
insulation film 21.
[0273] Then, after forming a given resist pattern, a contact
through hole is formed in the interlayer insulation film 21 by a
wet etching process using a mixed acid. Subsequently, a Ti film
having a film thickness of 50 nm, an Al--Nd alloy film having a
film thickness of 500 nm and a Ti film having a film thickness of
50 nm are formed sequentially in a laminated manner by a sputtering
and, thereafter, a given resist pattern is formed. Subsequently,
these films are etched altogether by a reactive ion etching process
using a mixed gas of BCl.sub.3and Cl.sub.2 thus obtaining the first
signal wiring electrodes 12, the source electrodes 13, 13' (not
shown in the drawing) and the connection electrodes 16 (not shown
in the drawing) (FIG. 42).
[0274] A Si.sub.3N.sub.4 film (protective insulation film) 22
having a film thickness of 400 nm is formed by a plasma CVD method
using a mixed gas of SiH.sub.4, NH.sub.3 and N.sub.2. Further,
acrylic photosensitive resin having a film thickness of
approximately 3.5 .mu.m is coated on the Si.sub.3N.sub.4 film 22 by
a spin coating method and, thereafter, the exposure and the
development are performed using a given mask to form a through hole
in the acrylic resin. Subsequently, by performing the baking for 20
minutes at 230 degree centigrade so as to bake the acrylic resin,
an organic protective film 23 having a film thickness of 2.3 .mu.m
is obtained. Subsequently, using a through hole pattern provided to
the organic protective film (organic insulation film) 23 as a mask,
the Si.sub.3N.sub.4 film which constitutes a lower layer is
machined by a reactive ion etching process using CF.sub.4 thus
forming a through hole in the Si.sub.3N.sub.4 film (FIG. 43).
[0275] Finally, an ITO film having a film thickness of 70 nm is
formed by a sputtering method and, thereafter, the ITO film is
machined in a given shape by a wet etching process using a mixed
acid thus forming the first and second pixel electrodes 14, 15
whereby the active matrix substrate is completed (FIG. 44).
[0276] According to the manufacturing method of this embodiment,
compared to the previous embodiment, it is possible to manufacture
the TFT active matrix substrate having the CMOS circuit by merely
increasing one sheet of mask.
[0277] As has been described heretofore, according to the present
invention, the liquid crystal display device which exhibits the low
power consumption, the wide viewing angle and the sufficient
brightness can be realized at a low cost.
* * * * *