U.S. patent application number 11/255425 was filed with the patent office on 2006-02-16 for reflective liquid crystal display device.
Invention is credited to Takayuki Iwasa, Toshihiko Nishihata.
Application Number | 20060033870 11/255425 |
Document ID | / |
Family ID | 32290250 |
Filed Date | 2006-02-16 |
United States Patent
Application |
20060033870 |
Kind Code |
A1 |
Iwasa; Takayuki ; et
al. |
February 16, 2006 |
Reflective liquid crystal display device
Abstract
A reflective liquid crystal display device has at least one
anti-reflection layer made of a metallic film and a silicon
oxynitride film that exhibits low reflectivity against light beams
which may otherwise be incident into pixel switching transistors.
At least one pair of pixel switching transistor and a capacitor are
formed on a semiconductor substrate. The transistor and the
capacitor are electrically isolated from each other. A first
interlayer insulating layer is formed on the transistor and the
capacitor. A wiring layer is formed on the first interlayer
insulating layer. A second interlayer insulating layer is formed
over the wiring layer. A light shielding layer is formed on the
second interlayer insulating layer. A third interlayer insulating
layer is formed over the light shielding layer. At least one pixel
electrode is formed on the third interlayer insulating layer. A
common electrode is formed over the pixel electrode. A
light-transmissive substrate is formed on the common electrode. A
liquid crystal layer is provided between the pixel electrode and
the common electrode. An anti-reflection layer is formed on, at
least, either the wiring layer or the light shielding layer. The
anti-reflection layer is a double layer of a metallic film and a
silicon oxynitride film that exhibits a refraction index different
from a refraction index of the third interlayer insulating
layer.
Inventors: |
Iwasa; Takayuki;
(Yamato-Shi, JP) ; Nishihata; Toshihiko;
(Yokohama-Shi, JP) |
Correspondence
Address: |
Renner, Kenner, Greive, Bobak, Taylor & Weber
Fourth Floor
First National Tower
Akron
OH
44308-1456
US
|
Family ID: |
32290250 |
Appl. No.: |
11/255425 |
Filed: |
October 20, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10712923 |
Nov 13, 2003 |
|
|
|
11255425 |
Oct 20, 2005 |
|
|
|
Current U.S.
Class: |
349/137 |
Current CPC
Class: |
G02F 1/136209 20130101;
G02F 1/133553 20130101; G02F 1/133502 20130101 |
Class at
Publication: |
349/137 |
International
Class: |
G02F 1/1335 20060101
G02F001/1335 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 18, 2002 |
JP |
2002-334310 |
Claims
1. A reflective liquid crystal display device comprising: a
semiconductor substrate; at least one pair of pixel switching
transistor and a capacitor formed on the semiconductor substrate
and electrically isolated from each other; a first interlayer
insulating layer formed on the pixel switching transistor and the
capacitor; a wiring layer formed on the first interlayer insulating
layer; a second interlayer insulating layer formed over the wiring
layer; a light shielding layer formed on the second interlayer
insulating layer, the light shielding layer being divided into a
plurality of layer portions by gaps; a third interlayer insulating
layer formed over the light shielding layer; at least one pixel
electrode formed on the third interlayer insulating layer; a common
electrode formed over the pixel electrode; a liquid crystal layer
provided between the pixel electrode and the common electrode; a
light-transmissive substrate formed on the common electrode; and at
least one anti-reflection layer formed on the light shielding
layer, the anti-reflection layer covering the gaps of the light
shielding layer.
2. The reflective liquid crystal display device according to claim
1, wherein the anti-reflection layer includes a film having Si.
3. The reflective liquid crystal display device according to claim
2, wherein the film having Si is a silicon oxynitride film.
4. The reflective liquid crystal display device according to claim
3, wherein the refraction index of the silicon oxynitride film is
in the range from 1.7 to 1.9.
5. The reflective liquid crystal display device according to claim
3, wherein a thickness of the silicon oxynitride film is in the
range from 400 to 600 .ANG..
6. A reflective liquid crystal display device comprising: a
semiconductor substrate; at least one pair of pixel switching
transistor and a capacitor formed on the semiconductor substrate
and electrically isolated from each other; a first interlayer
insulating layer formed on the pixel switching transistor and the
capacitor; a wiring layer formed on the first interlayer insulating
layer, the wiring layer being divided into a plurality of layer
portions by gaps; a second interlayer insulating layer formed over
the wiring layer; a light shielding layer formed on the second
interlayer insulating layer; a third interlayer insulating layer
formed over the light shielding layer; at least one pixel electrode
formed on the third interlayer insulating layer; a common electrode
formed over the pixel electrode; a liquid crystal layer provided
between the pixel electrode and the common electrode; a
light-transmissive substrate formed on the common electrode; and at
least one anti-reflection layer formed on the wiring layer, the
anti-reflection layer covering the gaps of the wiring layer.
7. The reflective liquid crystal display device according to claim
6, wherein the anti-reflection layer includes a film having Si.
8. The reflective liquid crystal display device according to claim
7, wherein the film having Si is a silicon oxynitride film.
9. The reflective liquid crystal display device according to claim
8, wherein the refraction index of the silicon oxynitride film is
in the range from 1.7 to 1.9.
10. The reflective liquid crystal display device according to claim
8, wherein a thickness of the silicon oxynitride film is in the
range from 400 to 600 .ANG..
11. A reflective liquid crystal display device comprising: a
semiconductor substrate; at least one pair of pixel switching
transistor and a capacitor formed on the semiconductor substrate
and electrically isolated from each other; a first interlayer
insulating layer formed on the pixel switching transistor and the
capacitor; a wiring layer formed on the first interlayer insulating
layer, the wiring layer being divided into a plurality of layer
portions by gaps; a second interlayer insulating layer formed over
the wiring layer; a light shielding layer formed on the second
interlayer insulating layer, the light shielding layer being
divided into a plurality of layer portions by gaps; a third
interlayer insulating layer formed over the light shielding layer;
at least one pixel electrode formed on the third interlayer
insulating layer; a common electrode formed over the pixel
electrode; a liquid crystal layer provided between the pixel
electrode and the common electrode; a light-transmissive substrate
formed on the common electrode; a first anti-reflection layer
formed on the wiring layer, the first anti-reflection layer
covering the gaps of the wiring layer; and a second anti-reflection
layer formed on the light shielding layer, the second
anti-reflection layer including Si and covering the gaps of the
light shielding layer.
12. The reflective liquid crystal display device according to claim
11, wherein each anti-reflection layer includes a film having
Si.
13. The reflective liquid crystal display device according to claim
12, wherein each film having Si is a silicon oxynitride film.
14. The reflective liquid crystal display device according to claim
13, wherein the refraction index of the silicon oxynitride film is
in the range from 1.7 to 1.9.
15. The reflective liquid crystal display device according to claim
13, wherein a thickness of the silicon oxynitride film is in the
range from 400 to 600 .ANG..
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation application of U.S.
patent application Ser. No. 10/712,923 filed on Nov. 13, 2003.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a reflective liquid crystal
display device used for displaying images with reflection of read
light beams modulated in accordance with video signals.
[0003] There are strong demands for projection-type display
apparatus for displaying images on a large screen, such as,
apparatus for outdoor public use or those for use in airport
control towers, high-precision display apparatus for high vision
and projectors.
[0004] The projection-type display apparatus is classified into
transmission and reflective types, both using a liquid crystal
display device. In operation, a read light beam incident into a
liquid crystal display device is modulated per pixel in accordance
with a video signal, thus converted into a light beam to be
projected onto a screen.
[0005] Liquid crystal display devices are equipped with an
active-matrix substrate aligned on which are switching transistors
such as thin-film transistors and pixel electrodes to which
voltages are supplied while controlled by the switching
transistors. Formed over the active-matrix substrate is a common
electrode coated with a light-transmissive substrate (such as a
glass substrate). A liquid crystal layer is provided between the
active-matrix substrate and the common electrode.
[0006] A voltage across the common electrode and each pixel
electrode is varied in accordance with a video signal to control
orientation of a liquid crystal filled in the liquid crystal layer
for modulation of a read light beam.
[0007] The liquid crystal display device is also classified into
transmission and reflective types.
[0008] Transmission-type liquid crystal display devices are
equipped with liquid-crystal drive circuitry and wirings in a
liquid crystal panel with a width of about 10 .mu.m around pixel
electrodes.
[0009] This configuration causes a low ratio (aperture) of a pixel
area to the total displaying area in the liquid crystal panel. The
aperture is more or less 60% even for a transmission-type liquid
crystal display device having a highest aperture at present.
[0010] Display apparatus such as liquid crystal projectors equipped
with the transmission-type liquid crystal display device cannot
display images of high intensity because of decrease in aperture
due to increase in the number of pixels, thus increase in pixel
density, or resolution.
[0011] Accordingly, developed and put in practical use recently,
instead of transmission-type liquid crystal display devices, are
reflective liquid crystal display devices that give high intensity
and resolution.
[0012] Discussed next are problems caused for known reflective
liquid crystal display devices.
[0013] Illustrated in FIG. 1 is a cross section of a known
reflective liquid crystal display device for each pixel.
[0014] Provided on a semiconductor substrate 10 (a P-type silicon
substrate) are pixel switching transistor Tr and a capacitor C. The
transistor Tr and the capacitor C are electrically isolated by an
SiO2 field oxide film 12.
[0015] The pixel switching transistor Tr is formed on an N-type
well 14. It is an MOSFET constituted by a drain 16 and a source 18,
each a highly-dense impurity layer, and a gate electrode 20
situated therebetween via a gate oxide film.
[0016] The capacitor C is constituted by a lower electrode
(highly-dense impurity layer) 22 and an upper electrode 24 formed
over the lower electrode 22 via an insulating film, for storing
charges.
[0017] Formed over the pixel switching transistor Tr and the
capacitor C is a first SiO2 interlayer insulating layer 26,
patterned on which is an A1 wiring layer 28. Formed on the wiring
layer 28 is a second SiO2 interlayer insulating layer 30.
[0018] Patterned on the second interlayer insulating layer 30 is an
A1 light shielding layer 32 for light shielding so that a reading
light beam is hardly be incident below the shielding layer 32.
Formed on the light shielding layer 32 is a third SiO2 interlayer
insulating layer 34.
[0019] Moreover, formed on the third interlayer insulating layer 34
is a quadrangular A1 pixel electrode 4 that is connected to the
source 18 of the pixel switching transistor Tr and the upper
electrode 24 of the capacitor C, via the light shielding layer
32.
[0020] Multiple pixel electrodes 4 are arranged into a matrix over
a liquid crystal panel, with a gap 36 between two adjacent pixel
electrodes, thus constituting an active matrix substrate.
[0021] Provided as facing the multiple pixel electrodes 4 is a
transparent common electrode 38 with a light-transmissive
(glass-like) substrate 40 formed thereon.
[0022] Formed between the multiple pixel electrodes 4 and the
transparent common electrode 38 is a liquid crystal layer LC filled
with a liquid crystal.
[0023] The common electrode 38 is provided as covering over
multiple pixels Px. In addition, alignment films (not shown) are
formed on the pixel electrodes 4 and the common electrode 38.
[0024] The width of each gap 36 between two adjacent pixel
electrodes 4, the area without serving light modulation in this
type of reflective liquid crystal display device, is about in the
range from 0.5 to 0.7 .mu.m. Therefore, reflective liquid crystal
display devices having a pixel-electrode pitch of, for example, 14
.mu.m can have aperture in the range from 90 to 93%.
[0025] In operation, a reading light beam LT is incident via the
light-transmissive substrate 40, as indicated by dot lines in FIG.
1.
[0026] It is inevitable that some light components of the light
beam LT are incident into the active-matrix substrate as intruding
beams LTi via the gaps 36.
[0027] Each intruding beams LTi propagates between the pixel
electrode 4 and the light-shielding layer 32 and also the shielding
layer 32 and the wiring layer 28 while reflected therebetween, as
indicated by dot lines.
[0028] The intruding beam LTi is finally incident into the drain 16
and/or the source 18 that constitute a PN-junction photo diode.
This generates photo carriers to cause a leak current, thus
resulting in variation in voltage at the pixel electrode 4, which
is a cause of flickering or burn-in.
[0029] Such light intrusion could be prevented by a long optical
path of each intruding beam LTi with a large pixel electrode 4.
Nevertheless, it goes against the trend of pixel miniaturization,
and hence cannot be employed.
[0030] In order to solve such a problem, for example, Japanese
Unexamined Patent Publication No. 2000-193994 discloses an
anti-reflection (reflection protective) layer 42 formed on the
light-shielding layer 32 before the third interlayer insulating
layer 34 formed thereon, as shown in FIG. 1, to attenuate the
intruding beams LTi.
[0031] The anti-reflection layer 42 is made of a single layer of
titanium nitride (TiN) or a double layer of silicon nitride (SiN)
and TiN, an SiN film being formed on a TiN film.
[0032] Reflective liquid crystal display devices with a single
liquid crystal panel use a read light beam within a visible-light
having wavelengths of 4000 to 7000 .ANG.. The titanium nitride of
the anti-reflection layer 42 can be adjusted as exhibiting a low
reflectivity against some wavelengths, but not all wavelengths in
the visible-light range, thus reflection blocking being not enough.
This is the same for the TiN/SiN anti-reflection layer.
[0033] Reflection of intruding light beams may be blocked on each
panel in reflective liquid crystal display devices with three
liquid crystal panels of red, blue and green. For instance, a
anti-reflection 42 used in a liquid crystal panel for red can be
adjusted as having a thickness to exhibit a low reflectivity
against light of wavelength in the range from 6000 to 7000 .ANG.
for red. Nevertheless, this results in difference in thickness for
anti-reflection layers in the liquid crystal panels for red, blue
and green. In other words, common liquid crystal panels cannot be
used for red, blue and green, which causes low productivity.
SUMMARY OF THE INVENTION
[0034] A purpose of the present invention is to provide a
reflective liquid crystal display device with no decrease in
performance of pixel transistors which may otherwise be caused by a
light beam incident into each transistor via a gap between pixel
electrodes.
[0035] The present invention provides a reflective liquid crystal
display device comprising: a semiconductor substrate; at least one
pair of pixel switching transistor and a capacitor formed on the
semiconductor substrate and electrically isolated from each other;
a first interlayer insulating layer formed on the pixel switching
transistor and the capacitor; a wiring layer formed on the first
interlayer insulating layer; a second interlayer insulating layer
formed over the wiring layer; a light shielding layer formed on the
second interlayer insulating layer; a third interlayer insulating
layer formed over the light shielding layer; at least one pixel
electrode formed on the third interlayer insulating layer; a common
electrode formed over the pixel electrode; a liquid crystal layer
provided between the pixel electrode and the common electrode; a
light-transmissive substrate formed on the common electrode; and at
least one anti-reflection layer formed on either the wiring layer
or the light shielding layer, the anti-reflection layer being a
double layer of a metallic film and a silicon oxynitride film that
exhibits a refraction index different from a refraction index of
the third interlayer insulating layer.
BRIEF DESCRIPTION OF DRAWINGS
[0036] FIG. 1 shows a cross section of a known reflective liquid
crystal display device for each pixel;
[0037] FIG. 2 shows a schematic block diagram of a liquid crystal
display apparatus;
[0038] FIG. 3 shows a circuit provided for each pixel in the liquid
crystal display apparatus shown in FIG. 2;
[0039] FIG. 4 shows a cross section of an embodiment of a liquid
crystal display device for each pixel according to the present
invention, installed in the liquid crystal display device apparatus
shown in FIG. 2;
[0040] FIG. 5 shows change in reflectivity of anti-reflection
layers in the present invention and the known liquid crystal
display device against change in wavelength;
[0041] FIG. 6 shows change in reflectivity of the anti-reflection
layer in the present invention against change in wavelength, with
change in thickness (in optimum range) for the SiON film, one
composition of the anti-reflection layer;
[0042] FIG. 7 shows change in reflectivity of the anti-reflection
layer in the present invention against change in wavelength, with
change in thickness (out of optimum range) for the SiON film;
[0043] FIG. 8 shows change in reflectivity of the anti-reflection
layer in the present invention against change in wavelength, with
change in thickness (out of optimum range) for the SiON film;
[0044] FIG. 9 shows change in reflectivity of the anti-reflection
layer in the present invention against change in wavelength, with
change in refraction index (in optimum range) for the SiON
film;
[0045] FIG. 10 shows change in reflectivity of the anti-reflection
layer in the present invention against change in wavelength, with
change in refraction index (out of optimum range) for the SiON
film;
[0046] FIG. 11 shows change in reflectivity of the anti-reflection
layer in the present invention against change in wavelength, with
change in refraction index (out of optimum range) for the SiON
film;
[0047] FIG. 12 shows a cross section of a modification to the
embodiment of the liquid crystal display device according to the
present invention shown in FIG. 4; and
[0048] FIG. 13 shows a cross section of another modification to the
embodiment of the liquid crystal display device according to the
present invention shown in FIG. 4.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
[0049] An embodiment according to the present invention will be
disclosed with reference to the attached drawings.
[0050] Explained first with reference to FIGS. 2 and 3 is a liquid
crystal display apparatus with drive circuitry in which an
embodiment of a reflective liquid crystal display device according
to the present invention can be installed.
[0051] In FIG. 2, column-signal electrodes D1, D2, D3, . . . , and
Di are aligned on a semiconductor substrate 2. Also aligned on the
substrate 2 are row-scanning electrodes G1, G2, G3, . . . , and Gj,
intersecting with the column-signal electrodes.
[0052] Provided at the intersection of each column-signal electrode
D (D1, D2, D3, . . . , or Di) and the corresponding row-scanning
electrode G (G1, G2, G3, . . . , or Gj) is a pixel Px1 having a
pixel-switching transistor Tr1, a capacitor C1, and a liquid
crystal layer LC1, as shown in FIG. 3. Multiple pixels Px1 are
arranged into a matrix.
[0053] A column-signal-electrode driver 100 is equipped with a
horizontal shift register 101 and several video switches S1, S2,
S3, . . . , and Si.
[0054] Input terminals of the video switches S1, S2, S3, . . . ,
and Si are connected to a video-signal supply line L through which
a video signal VIDEO is supplied. Output terminals of the switches
S1, S2, S3, . . . , and Si are connected to the column-signal
electrodes D1, D2, D3, . . . , and Di, respectively. A control
terminal of each switch S (S1, S2, S3, . . . , or Si) is connected
to the corresponding output of the horizontal shift register
101.
[0055] The horizontal shift register 101 is driven by a horizontal
start signal and a horizontal clock signal to output pulses. The
start and horizontal clock signals are supplied from a drive timing
pulse generator (not shown).
[0056] The pulses output from the horizontal shift register 101 are
supplied to the video switches S1, S2, S3, . . . , and Si, to
sequentially turn on these switches. The turn-on switches allow the
video signal VIDEO for one horizontal period to be sequentially
supplied to the column-signal electrodes D1, D2, D3, . . . , and
Di.
[0057] A row-scanning-electrode driver 102 is equipped with a
vertical shift register having several register stages
corresponding to the number of rows to be displayed.
[0058] The vertical shift register is driven by a vertical start
signal and a vertical shift clock signal synchronizing with one
horizontal period to output scanning pulses. The start and vertical
shift clock signals are supplied from a drive timing pulse
generator (not shown).
[0059] The scanning pulses output from the vertical shift register
are sequentially supplied to the row-scanning electrodes G1, G2,
G3, . . . , and Gj per horizontal period (per row).
[0060] The scanning pulses turn on, sequentially per row, the
pixel-switching transistors Tr1 connected to the row-scanning
electrodes G1, G2, G3, . . . , and Gj.
[0061] Each turned-on pixel-switching transistor Tr1 shown in FIG.
3 allows the video signal VIDEO, supplied to the corresponding
column-signal electrode D, to be stored as charge information in
the capacitor C1 of the corresponding pixel Px1.
[0062] The stored charge information is supplied to the liquid
crystal layer LC1 via a pixel electrode 41 for light modulation.
The light modulation provides images to be displayed corresponding
to the video signal VIDEO.
[0063] Disclosed now with reference to FIG. 4 is an embodiment of a
reflective liquid crystal display device according to the present
invention, which can be installed in the liquid crystal display
apparatus shown in FIG. 2.
[0064] One particular feature of the reflective liquid crystal
display device according to the present invention shown in FIG. 4
is an anti-reflection (reflection protective) layer made of a
double layer of metal nitride, such as, a TiN (titanium nitride)
film and an SiON (silicon oxynitride) film, different from single
layer of TiN or a double layer of SiN and TiN for the
anti-reflection layer 42 shown in FIG. 1.
[0065] Illustrated in FIG. 4 is a cross section of an embodiment of
a reflective liquid crystal display device for each pixel according
to the present invention.
[0066] Provided on a semiconductor substrate 101 (e.g., a P-type
silicon substrate) are pixel switching transistor Tr1 and a
capacitor C1 (FIG. 3). The transistor Tr1 and the capacitor C1 are
electrically isolated by a field oxide film 121 made of, for
example, SiO2.
[0067] The pixel switching transistor Tr1 is formed on a well 141
of N-type, for example. It is an MOSFET constituted by a drain 161
and a source 181, each a highly-dense impurity layer, and a gate
electrode 201 situated therebetween via a gate oxide film.
[0068] The capacitor C1 is constituted by a lower electrode
(highly-dense impurity layer) 221 and an upper electrode 241 formed
over the lower electrode 221 via an insulating film, for storing
charges.
[0069] Formed over the pixel switching transistor Tr1 and the
capacitor C1 is a first interlayer insulating layer 261 made of,
for example SiO2, patterned on which is a wiring layer 281 made of
aluminum, for example. Formed on the wiring layer 281 is a second
interlayer insulating layer 301 made of, for example, SiO2.
Patterned on the second interlayer insulating layer 301 is a
metallic light shielding layer 321 made of, for example aluminum,
for light shielding so that a read light beam is hardly be incident
below this shielding layer 321. Formed over the light shielding
layer 321 is a third interlayer insulating layer 341 made of, for
example, SiO2.
[0070] Moreover, formed on the third interlayer insulating layer
341 is a pixel electrode 41 made of aluminum shaped into a
quadrangular, for example, that is connected to the source 181 of
the pixel switching transistor Tr1 and the upper electrode 241 of
the capacitor C1, via the light shielding layer 321.
[0071] Multiple pixel electrodes 41 are arranged into a matrix over
a liquid crystal panel, with a gap 361 between two adjacent pixel
electrodes, thus constituting an active matrix substrate.
[0072] Provided as facing the multiple pixel electrodes 41 is a
transparent common electrode 381 with a light-transmissive
(glass-like) substrate 401 formed thereon.
[0073] Formed between the multiple pixel electrodes 41 and the
transparent common electrode 381 is a liquid crystal layer LC1
filled with a liquid crystal.
[0074] The common electrode 381 is provided as covering over
multiple pixels Px1. In addition, alignment films (not shown) are
formed on the pixel electrodes 41 and the common electrode 381.
[0075] Moreover, an anti-reflection layer 501 is formed directly on
the light shielding layer 321 before the third interlayer
insulating layer 341 is formed thereon. The anti-reflection layer
501 is one particular feature of the embodiment of the liquid
crystal display device shown in FIG. 4.
[0076] The anti-reflection layer 501 is made of a double layer of
metal nitride, such as, a TiN film 501A and an SiON film 501B
formed thereon. The thicknesses of the TiN film 501A and the SiON
film 501B are about 800 .ANG. and 500 .ANG., respectively.
[0077] The SiON film 501B is an insulator so that it is formed not
only on the TiN film 501A but also in the third interlayer
insulating layer 341.
[0078] The SiON film 501B protects the pixel switching transistor
Tr1 from an intruding light beam LTi which may otherwise be
incident between two adjacent pixel electrodes 41, propagate
between each pixel electrode 41 and TiN film 501A while being
reflected therebetween, and finally reach the transistor Tr1.
[0079] The SiON film 501B is adjusted as exhibiting a reflectivity
of about 1.80 whereas the third interlayer insulating layer 341
made of SiO2 is adjusted as exhibiting a reflectivity of about
1.45. In other words, the SiON film 501B and the SiO2-made third
interlayer insulating layer 341 are adjusted as exhibiting
different reflectivities.
[0080] The SiON film 501B is also formed in each gap 521 between
two adjacent light shielding layers 321, the TiN film 501A being
not formed therein, for further effective blocking of intrusion of
the light beams LTi.
[0081] The anti-reflection layer 501 is formed, for example, as
follows:
[0082] An aluminum film and a TiN film are formed in this order by
sputtering, for forming the light shielding layer 321. The two
films are etched by pattern etching simultaneously, thus the
patterned light shielding layer 321 and also the TiN film 501 being
formed.
[0083] The SiON film 501B is then formed by plasma CVD, followed by
an SiO2 film formed thereon, as the third interlayer insulating
layer 341.
[0084] The SiON film 501B is an insulating film so that it exhibits
almost the same etching rate as the SiO2-made third interlayer
insulating layer 341 formed thereon.
[0085] Therefore, the SiON film 501B (one composition of the
anti-reflection layer 321) and the SiO2 film (the third interlayer
insulating layer 341) can be etched simultaneously in oxide-film
etching to provide a via hole 541 (a through hole).
[0086] In other words, the via hole 541, the SiON film 501B and the
third interlayer insulating layer 341 can be formed in a single
process, with no necessity to have two etching processes, or any
special etching process for the SiON film 501B.
[0087] Disclosed next is an operation of the reflective liquid
crystal display device shown in FIG. 4 when installed in the liquid
crystal display apparatus shown in FIG. 2. A video signal VIDEO is
supplied to the source 181 of the pixel switching transistor Tr1
via the video-signal supply line L and the column-signal electrodes
D. Scanning pulses are then supplied to the gate electrode 221 of
the capacitor C1 via the row-scanning electrodes G.
[0088] The pixel switching transistor Tr1 is thus turned on so that
charges carried by the video signal VIDEO are stored in the
capacitor C1 and also across the pixel electrode 41 and the
transparent common electrode 381. This makes the video signal VIDEO
being written in the liquid crystal layer LC1.
[0089] A read light beam LT is then incident into the liquid
crystal layer LC1 via the light-transmissive substrate 401. The
light beam LT is subjected to light modulation in accordance with
the video signal VIDEO while passing through the liquid crystal
layer LC1. The modulated light beam LT is reflected by the pixel
electrode 41 and again subjected to light modulation while passing
through the liquid crystal layer LC1. The re-modulated light beam
LT is emitted from the light-transmissive substrate 401, as an
image-information carrying light beam.
[0090] The image-information carrying light beam is projected onto
a screen (not shown), thus an image being displayed thereon.
[0091] It is inevitable that some light components of the light
beam LT are incident into the active-matrix substrate as intruding
beams LTi via the gaps 361 each between two adjacent pixel
electrodes 41.
[0092] Each intruding beam LTi is, however, absorbed by the
anti-reflection layer 501 while repeatedly reflected between the
pixel electrode 41 and this protective layer 501 made of the TiN
film 501A and the SiON film 501B formed on the light shielding
layer 321, as indicated by dot lines in FIG. 4.
[0093] Therefore, the intruding beam LTi is not incident below the
anti-reflection layer 501. In other words, the anti-reflection
layer 501 protects the pixel switching transistor Tr1 from the
intruding beam LTi which may otherwise be incident therein.
[0094] As disclosed above, the present invention achieves high
performance for the pixel switching transistor Tr1.
[0095] Discussed next is reflectively of the anti-reflection layer
against wavelength in a visible-light range, evaluated with
measurements with a reflectivity measuring instrument V-550 made by
JASOCO, CO., and simulations.
[0096] Measurements and simulations were performed for the
anti-reflection layer 501 (FIG. 4) in the embodiment of the
reflective liquid crystal display device according to the present
invention and also the counterpart layer 42 (FIG. 1) in the known
display device.
[0097] Reflectivities of the anti-reflection layer 501 (FIG. 4) and
the counterpart layer 42 (FIG. 1) were measured with thickness of
TiN and/or SiON films and refraction index of the SiON film as
parameters.
[0098] Measured as reflectivities were ratios of light beams
reflected by the anti-reflection layer 501 (FIG. 4) to read light
beams LT, visible light beams having wavelengths in the range from
4000 to 7000 .ANG., incident via the light-transmissive substrate
401. The same measurements were performed for the counterpart layer
42 (FIG. 1).
[0099] Examined first was the anti-reflection layer 42 (FIG. 1)
made of an 800 .ANG.-thick TiN film and a 500 .ANG.-thick SiN film,
in the known reflective liquid crystal display device.
[0100] Examined next was the anti-reflection layer 501 (FIG. 4)
made of an 800 .ANG.-thick TiN film and a 500 .ANG.-thick SiON
film, in the embodiment of the reflective liquid crystal display
device according to the present invention.
[0101] Reflectivities (100%=1) of these anti-reflection layers
against wavelengths in a visible-light range are shown in FIG.
5.
[0102] Two curves in FIG. 5 represent change in reflectivity of the
anti-reflection layer 501 (RPL 501 in the present invention) and
the anti-reflection layer 42 (RPL 42 in the known liquid crystal
display device) against change in wavelength.
[0103] These curves were given under the conditions: 800 .ANG.
(fixed) in thickness of the TiN film for both RPL 42 and 501; 500
.ANG. (fixed) in thickness of both SiN and SiON films for RPL 42
and 501; and 2.0 and 1.8 in refraction index N for the SiN and SiON
films, respectively.
[0104] FIG. 5 teaches that the RPL 501 (in the present invention)
having SiON (500 .ANG.)/TiN (800 .ANG.) double-layer configuration
exhibits lower reflectivity than the RPL 42 (in the known liquid
crystal display device) having SiN(500 .ANG.)/TiN(800 .ANG.)
double-layer configuration, over the wavelength in the range from
4000 to 7000 .ANG..
[0105] Moreover, the reflectivity is almost zero for the RPL 501 in
the present invention against the wavelength from 4700 to 6000
.ANG..
[0106] It is evident from FIG. 5 that the SiON(500 .ANG.)/TiN(800
.ANG.) double-layer configuration in the present invention exhibits
higher protection capability against reflection than the SiN(500
.ANG.)/TiN(800 .ANG.) double-layer configuration in the known
liquid crystal display device.
[0107] Also shown in FIG. 5 is that the SiON(500 .ANG.)/TiN(800
.ANG.) double-layer configuration in the present invention exhibits
reflectivity of 5% or less against the wavelength from 4000 to 6000
.ANG. (visible-light range).
[0108] Discussed next with reference to FIG. 6 is reflectivity of
the anti-reflection layer 501 having SiON/TiN double-layer
configuration in the present invention against wavelength of
visible-light range, with change in thickness for the SiON
film.
[0109] Curves shown in FIG. 6 were given under the conditions: 800
.ANG. (fixed) in thickness of the TiN film and 400 .ANG., 500 .ANG.
and 600 .ANG. in thickness of the SiON film, with 1.8 in refraction
index N for the SiON film.
[0110] FIG. 6 shows reflectivity (100%=1) of 10% or less over the
wavelength in the range from 4000 to 7000 .ANG. at 400 .ANG., 500
.ANG. and 600 .ANG. in thickness of the SiON film. The lowest
reflectivity was given at 500 .ANG. among the three thicknesses for
the SiON film, with almost 0% at 500 .ANG. in SiON thickness
against the wavelength from 4700 to 6000 .ANG..
[0111] It is evident from FIG. 6 that the SiON/TiN double-layer
configuration in the present invention exhibits higher protection
capability against reflection, with thickness of 800 .ANG. for the
TiN film and thickness in the range from 400 to 600 .ANG. for the
SiON film.
[0112] In other words, the SiON/TiN double-layer configuration in
the present invention under the conditions defined as above
protects pixel switching transistors from intruding light beams
incident between pixel electrodes. The intruding light beams may
otherwise be reflected by the double-layer configuration and
finally reach the transistors to decrease the performance
thereof.
[0113] Curves shown in FIGS. 7 and 8 were also given for comparison
of reflectivities under change in SiON-film thickness.
[0114] Curves shown in FIG. 7 were given under the conditions: 800
.ANG. (fixed) in thickness of the TiN film and 250 .ANG., 300
.ANG.and 350 .ANG. in thickness of the SiON film, with 1.8 in
refraction index N for the SiON film.
[0115] Curves shown in FIG. 8 were given under the conditions: 800
.ANG. (fixed) in thickness of the TiN film and 650 .ANG., 700 .ANG.
and 750 .ANG. in thickness of the SiON film, with 1.8 in refraction
index N for the SiON film.
[0116] FIGS. 7 and 8 teach that the SiON film having thickness out
of the range from 400 to 6000 .ANG. cannot exhibit reflectivity of
10% or less over the wavelength from 4000 to 7000 .ANG.
(visible-light range).
[0117] Discussed next with reference to FIG. 9 is reflectivity of
the anti-reflection layer 501 having SiON/TiN double-layer
configuration in the present invention against wavelength of
visible-light range, with change in refraction index for the SiON
film.
[0118] Curves shown in FIG. 9 were given under the conditions: 800
.ANG. (fixed) in thickness of the TiN film and 500 .ANG. (fixed) in
thickness of the SiON film, with 1.7, 1.8 and 1.9 in refraction
index N for the SiON film.
[0119] FIG. 9 shows reflectivity (100%=1) of 10% or less over the
wavelength in the range from 4000 to 7000 .ANG. at 1.7, 1.8 and 1.9
in refraction index N of the SiON film. The lowest reflectivity was
given at 1.8 among the three refraction indices N, with almost 0%
at 1.8 against the wavelength from 4700 to 6000 .ANG..
[0120] It is evident from FIG. 9 that the SiON/TiN double-layer
configuration in the present invention exhibits higher protection
capability against reflection, with refraction index N in the range
from 1.7 to 1.9 for the SiON film.
[0121] In other words, the SiON/TiN double-layer configuration in
the present invention under the conditions defined as above
protects pixel switching transistors from intruding light beams
incident between pixel electrodes, even for 8.0 .mu.m-pitch pixels.
The intruding light beams may otherwise be reflected by the
double-layer configuration and finally reach the transistors to
decrease the performance thereof, as discussed above.
[0122] Curves shown in FIGS. 10 and 11 were also given for
comparison of reflectivities under change in SiON-film refraction
index N.
[0123] Curves shown in FIG. 10 were given under the conditions: 800
.ANG. (fixed) in thickness of the TiN film and 500 .ANG. (fixed) in
thickness of the SiON film, with 1.4, 1.5 and 1.6 in refraction
index N for the SiON film.
[0124] Curves shown in FIG. 11 were given under the conditions: 800
.ANG. (fixed) in thickness of the TiN film and 500 .ANG. (fixed) in
thickness of the SiON film, with 2.0, 2.1 and 2.2 in refraction
index N for the SiON film.
[0125] FIGS. 10 and 11 teach that the SiON film having refraction
index N out of the range from 1.7 to 1.9 cannot exhibit
reflectivity of 10% or less over the wavelength from 4000 to 7000
.ANG. (visible-light range).
[0126] The evaluations discussed above give the following optimum
requirements:
[0127] (1) the anti-reflection layer 501 having the double-layer
configuration of the TiN film with 800 .ANG. in thickness and the
SiON film with 500 .ANG. in thickness and 1.8 in refraction index
N; and
[0128] (2) the anti-reflection layer 501 having the double-layer
configuration of the TiN film with 800 .ANG. in thickness and the
SiON film with thickness in the range from 400 to 600 .ANG. and
refraction index N in the range from 1.7 to 1.9.
[0129] The refraction indices N for the SiON film in the
requirements (1) and (2) are adjusted as different from N at about
1.45 for the third interlayer insulating layer 341.
[0130] The requirements (1) and (2) offer reflectivity of 5% or
less and 10% or less, respectively, against read light beams over
the wavelength from 4000 to 7000 .ANG. (visible-light range).
[0131] Disclosed next are modifications to the reflective liquid
crystal display device shown in FIG. 4.
[0132] FIGS. 12 and 13 show cross sections of modification to the
embodiment of the liquid crystal display device according to the
present invention.
[0133] Elements in FIGS. 12 and 13 the same as or analogous to
those shown in FIG. 4 are given the same reference numerals and not
explained.
[0134] A modification shown in FIG. 12 has the anti-reflection
layer 501 formed on the wiring layer 281 but under the light
shielding layer 321, different from the counterpart 501 formed on
the light shielding layer 321 in the embodiment of FIG. 4.
[0135] Another modification shown in FIG. 13 has two
anti-reflection layers 501, one formed on the wiring layer 281 and
the other on the light shielding layer 321. This modification is
advantageous over the embodiment and the former modification on the
protection capability against reflection, thus serving further
pixel miniaturization.
[0136] As disclosed above in detail, the present invention protects
pixel switching transistors from intruding light beams, which may
otherwise be incident between pixel electrodes, reflected and
finally reach the transistors to decrease the performance thereof,
thus achieving further pixel miniaturization.
[0137] The present invention also achieves reflectivity of 10% or
less against read light beams over the wavelength from 4000 to 7000
.ANG. (visible-light range) in reflective liquid crystal display
devices with three liquid crystal panels of red, blue and green.
This allows common liquid crystal panels be used for red, blue and
green, which yields high productivity.
[0138] The embodiment and modifications employ a metallic nitride
film, or the TiN film 501A, as one of the compositions of the
anti-reflection layer 501. Not only that, however, other materials,
such as, titanium can be used.
[0139] The reflective liquid crystal display device according to
the present invention has at least one anti-reflection layer made
of a metallic film and a silicon oxynitride film that exhibits a
refraction index different from the interlayer insulating layer
formed over the protective layer and low reflectivity against light
beams which may otherwise be incident into pixel switching
transistors to decrease the performance thereof, thus achieving
further pixel miniaturization.
* * * * *