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Full color liquid crystal television addressed by amorphous silicon TFTs
Journal of Non-CrystallineSolids 77 & 78 (1985) 1383-1388 North-Holland, Amsterdam
1383
FULL COLOR LIQUID CRYSTAL TELEVISION ADDRESSED BY AMORPHOUS SILICON TFTS
Masaru YAMANO and Hajime TAKESADA Sanyo Electric Co., Ltd.
1-18-!3 Hashiridani Hirakata Osaka 573, Japan
A five inch color LCD panel addressed by amorphous silicon thin film transistors (TFTs) has been developed for TV receivers. To increase productivity of the panel, optimum design parameters of the display such as number of pixels, TFT structure, etc were studied.
i. INTRODUCTION It has been long time since television was popularized.
On the other hand
people have been earnestly wishing to reduce volume and weight of TV receivers. To respond these demands, various kinds of displays have been developed such as LED -l , EL -2, Plasma -3, LCD 4 panels and so on. type display used practically for TV recievers.
Among them, LCD is the only flat In Japan, 2-3 inch size
portable LCD TV receivers are now commercially available.
Among the flat type
displays, LCD panel has such advantages as low power consumption, less weight, possibility for color display, lower driving voltages and currents, thin plate, etc and is expected to be the most promissing flat panel display for color TV receivers.
Taking these advantages and economics into account, we believe that
LCD panels will be superior than CRT displays in the application of smaller size or very large size.
To drive the LCD panel, there are two basic methods,
i. e. direct addressing and active matrix addressing methods. In terms of 5 econmics, direct addressing method is superior than active matrix method. However, to obtain better picture quality, active matrix addressing method •
using TFT is superlor
6
than direct addressing.
With the thought that active matrix by TFT would become a dominant method for image display application, we have been concentrating our development effort in the active matrix by amorphous silicon TFTs. In our organization, amorphous silocon photovoltaic cells have been mass-produced since 1980 by using consecutive deposition method 7.
At the
present, we have reached the annual production level of 3 mega watts.
Based on
our expertism and experience on physical properties of a-Si and in making large area a-Si film, we have been conducting various researches to find a possibility to develop LCD panels that are addressed by a-Si TFT matrix.
As a
result, we have been convinced that the LCD panel would be very promissing not only from economical stand points, but also in performances.
0022~093/85/$03.30 © Elsevier Science Publishe~ B.V. (No~h-Holland Phys~s Publishing Division)
In 1982, we
M. Yamano, H. Takesada/FuOco~rliquidcrysmlte&vmmn
1384
demonstrated "Japan
a m o n o c h r o m e LCD p a n e l
Display'8Y',
panel 9 and at sponsored will
we a n n o u n c e d
for
5 inch
2. LCD PANEL Figure i shows a equivalent circuit
8
receivers
of a 3 inch
Conference
b y IEEE we a n n o u n c e d a 5 i n c h a newly developed
television
the development
the "1984 International
introduce
portable
full
.
color
At t h e LCD
on Consumer Electronics"
full
color
LCD p a n e l 10.
full
color
LCD TV r e c e i v e r .
This
t i m e we
Drain electrodes Pixel electrodes Counter
for the panel. Fig.2 shows a cross section of the TFT and Fig.3 shows its plane view.
ro~e ~
~
~
~
In the reverse staggered
type TFT, gate insulater film and a-Si minimal contamination at the channel
565
area which is the most important part
~
~
~
of the TFT. The plasma CVD equipment
n-
"%-
-i-
-z-
T
n-
-r,
-r
can be deposited continuously with
o
w
=z=
o _
o
~
nF.
developed by us for a-Si deposition. One of the important characteristics of a-Si TFT is that it can be made by
Gate electrodes
a low temperature deposition method and sodarime glass can be used for its substrate. In addlton, lower
~-SiH TFTs
FIGURE 1 Single Matrix LCD Panel
off-current TFTs can be made because of its higher specific resistance.
Pixel electrode
/
Drain electrode Source Gate a-Sill /electrode electrode / / Pl%~ " ~ i n s i u l a ~
i\
\
\
\
\
\
........
\\
\
FIGURE 2 Cross Section of a-SiH TFT
I
Drain electrode
~ H ~
-
......
~
FIGURE 3 Plane View of Pixel Pattern
M. Yamano, H. Takesada / Full color liquid crystal television
Vacut~n Chamber
S\LN~ Deposition Chamber
a-SiH Deposition Chamber
1385
Cooling Chamber
FIGURE 4 CVD P r o c e s s
o
In the production process, intrinsic amorphous silicon ]ayer of 1000A is deposited over the gate insulator film of SiN and then conventional photolithographic process is used to form TFT array.
Typical static
characteristics such as Vg-I d curve and Vd-I d curve are shown in Figs.5 and 6 respectively. the TFTs.
Dynamic charactoristics are also important characteristics for
To write TV signal's voltage to the incidental capacitors of about
0.7 pF of LCD plxels, the capacitors has to be charged and dischared by TFTs in one horizontal scanning time of 65 ps.
Figure 7 and 8 show that the
-4
1.0 f~
--
Vg= 10V
/ "
liI/
H
/
'd' /
A
-t2 ~ ~ ~ -15
.-
7.sv
o
0
35 Vg (V)
FIGURE 5 On-Off Characteristics of TFT
5v
0
i0 Vd-s (V)
FIGURE 6 On Current of TFT
M. Yamano, t£ Takesada / Full color liquid crystal television
1386
equlvalent capacitors of 1.5 pF can be charged and discharged within I/3 of 65
~
I
I
~s respectively by the TFTs and turn
T F T
out that actual incidental capacitors
w=ll6j~n
can be charged or discharged in even shorter time.
Stability of the TFTs
~ ~ w ~
under the application of gate voltage
#~
of -7.5 volts were measured.
~
After 240
20~sec/div
~
Load capacitmLnoe 1.5pF Vg-s i7.5V
hour operation, no degradation was found as shown in Fig.9.
As for the FIGURE 7
panel construction, Fig.10 shows a
TFT S w i t c h i n g C h a r a c t e r i s t i c s
cross section of the full color panel.
(Vd = -3 + +3V)
In conventional LCDs, polyimide is used as an aligning layer for liquid crystal. Since this polyimide requires
ij.l~sii
~
300-4000C for polymerization it can not be used with a-SiH TFTs.
20usec/div
l - i~2V/~vl2v/div
For this
reason, various organic polymer films
-
that could be formed at lower
~
temperature (~I00°C) were tested and
~
a new aligning film was found without
~
-
i
~
TFT i=8~ n w=ll6~n
~
Load ca1.5pF Vg-s ±7.5V
sacrificing perfomances of a-SiH TFTs and the color filter.
For obtaining FIGURE 8 TFT Switching Characteristics
better performances of the panel, several selected liquid crystal
(Vd = +3 ~ -3)
-4
-4
.. r--I
A
=
-1_152
r
0
35
_12_S1
~
0
Vg (V)
I
35
Vg (V)
[Initial]
[240Hrs] Vg=-7.5V
Vd-s=OV
FIGURE9 Stability of TFT Characteristics ( Vg vs Id Curves )
M, Yamano, H. Takesada / Full color liquid crystal television
materials were blended.
1387
The response
time is about 30 ms which is an
Polarizer Color f i l t e r / Glass substrate
acceptable level for color TV
~\\\\\\\'\\t/
v±~//~ansparent
receivers.
"\\\\\\\\\\
/electrode
Since tlle light
transmittance of the liquid crystal
<.. . . . . •..... <. . Alic~ling .....' " ' ' ' "' layer ". >.: '.' : , ./
changed linearly at 3 to 7 volts, the
~
panel can be driven by conventional
- ' r w' r4~ '~J /~/ ~_
CMOS LSIs.
~kk~v~K~...
The color range was still
_ .....
'Liquid
\crystal
~ ~ ~ \aligning ~
narrower than that of conventional
~/Lu~Ice'~
CRT (NTSC), but it has been reached
n|
\
\layer
a~si\Gl~ss substrate \ ! Insulator Polarizer
to the practically acceptable level. Table 1 shows specifications of the panel.
This specification has been
FIGURE I0 Cross Section of Color LCD
selected to have better productivity and performances vs cost.
Number of
pixels has been reduced to 216 x 384 from 250 x 666.
In spite of its less
Display Size
?5.8×99.8 mm
Panel Size
99.0xlZ3. gx2.0 mm
Number of Pixels
216×384
Pixel Size
350×260
Liquid Crystal
TN
Filter Color
RGB
enabled elimination of light shield II
Display Mode
Transmissive
for gates were slected to simplify
Cell Gap
~I0
tight design rule of 5pm, production of the panel requires various additional know-how to the LSI
~ m
production technique because of its large area LCD panel.
For example,
optimum deposition conditions that
the process.
~ m
With the reduction of
number of pixels, aperture ratio of
'FABLE 1
the panel has been improved to 74 %
Specifications of the LCD Panel
from 53 % and obtained better contrast, as well as improvement of production yield.
By selecting material of the
mosaic color filter, optical transparency has also been improved to 20% from 15%.
Another methods to improve the yield are driving of gate line from both
ends of the panel and adoption of by-pass circuits to prevent shorting problem between drain and gate lines.
Since amorphous silicon TFT LCD panel is
basically suitable for transparent type, an optical reflector is required when it is used in brighter ambience. light is required.
When being used in darker ambience, a back
For this backlight sourse, we have developed a high
efficiency 5 inch flat fluorescent lamp that utilizes combination of three phospors.
M. Yamano, H. Takesada / Full color liquid crystal television
1388
3. COLOR LCD TV RECEIVERS To take the advantage of low power
EffectiveDisplay 5 inches Size
performance of LCD, specially designed CMOS LSIs are used.
All circuits after
level amplifiers for R, G and B signals are composed of CMOS ICs to minimize power consumption.
Circuit Size Display Back light
L Weight
168x141x23m 1.00 1,,g
light 055
As a result, total
power consumption has became as low as
(w) (D) (Thic~mess) 188xlgOx25mm 168x138×I0m
DC 2.4 W Power consumption DC 4 9 W (WithBack light)
2.4 watts (DC) which is equivalent to 3
Frequencyrange
VHF.UHF
hour operation by 5 penlight alkaline
Responsetime
30 msec
batteries.
When the back light is
±45" (horizontal) Viewi~ ~ l e
used, another 2~3 watts are required.
+30" .-I0" (ve/-tical)
Table 2 shows specifications of the TV
Contrastratio
8 (WithP~ck light)
receiver.
Light source
Flat fluorescentla,~por Ambient light
4. CONCLUSIONS
~iv/ng volt~e
Gate:lbV [~ain:±6V
In sun.nary, it is important to select the optimum numbers of pixels to commercialize a-Si TFT LCD TV
TABLE 2 Specifications of the Color LCD TV
receivers based on the most advanced current technologies to form a-Sl film and a-SiH TFT array.
This type of LCD
panel is suitable not only for color TV receivers, but also for other displays such as personal computers, automabile displays, etc. because of its high performances vs cost.
This panel can also be used as a monochrome display
without the color filter.
REFERENCES i) T. Niina et al. IEEE Trans. Vol. ED-26 No. 8 (Aug., 1979) pp. 1182-1186 2) S. Mite et al. SlD (1974) pp. 86-87 3) H. Murakaml et al Inst. of TV Eng. Japan Vol. 38, No. 9 (Sept., 1984) pp. 836-842 4) E. Kaneko et al SID Vol. 23, No. I (1982) pp. 3-8 5) H. Watanabe et al SID (1985) pp. 86-87 6) M. Yamano et al Japan Display (1983) pp. 356-357 7) Y. Kuwano et al 14th IEEE PV Specialists Conf. (1980) pp. 1408-1411 8) Nikkei Electronics (Japan, Nov., 1982, No. 303) 95 9) M. Yamano et al Japan Display (1983) pp. 214-217 I0) M. Yamano et al IEEE ICCE (1984) pp. 74-75 Ii) M. Matsushita et al Inst. of TV Eng. Japan ED 885 IPD 96-28 pp. 79-84
1383
FULL COLOR LIQUID CRYSTAL TELEVISION ADDRESSED BY AMORPHOUS SILICON TFTS
Masaru YAMANO and Hajime TAKESADA Sanyo Electric Co., Ltd.
1-18-!3 Hashiridani Hirakata Osaka 573, Japan
A five inch color LCD panel addressed by amorphous silicon thin film transistors (TFTs) has been developed for TV receivers. To increase productivity of the panel, optimum design parameters of the display such as number of pixels, TFT structure, etc were studied.
i. INTRODUCTION It has been long time since television was popularized.
On the other hand
people have been earnestly wishing to reduce volume and weight of TV receivers. To respond these demands, various kinds of displays have been developed such as LED -l , EL -2, Plasma -3, LCD 4 panels and so on. type display used practically for TV recievers.
Among them, LCD is the only flat In Japan, 2-3 inch size
portable LCD TV receivers are now commercially available.
Among the flat type
displays, LCD panel has such advantages as low power consumption, less weight, possibility for color display, lower driving voltages and currents, thin plate, etc and is expected to be the most promissing flat panel display for color TV receivers.
Taking these advantages and economics into account, we believe that
LCD panels will be superior than CRT displays in the application of smaller size or very large size.
To drive the LCD panel, there are two basic methods,
i. e. direct addressing and active matrix addressing methods. In terms of 5 econmics, direct addressing method is superior than active matrix method. However, to obtain better picture quality, active matrix addressing method •
using TFT is superlor
6
than direct addressing.
With the thought that active matrix by TFT would become a dominant method for image display application, we have been concentrating our development effort in the active matrix by amorphous silicon TFTs. In our organization, amorphous silocon photovoltaic cells have been mass-produced since 1980 by using consecutive deposition method 7.
At the
present, we have reached the annual production level of 3 mega watts.
Based on
our expertism and experience on physical properties of a-Si and in making large area a-Si film, we have been conducting various researches to find a possibility to develop LCD panels that are addressed by a-Si TFT matrix.
As a
result, we have been convinced that the LCD panel would be very promissing not only from economical stand points, but also in performances.
0022~093/85/$03.30 © Elsevier Science Publishe~ B.V. (No~h-Holland Phys~s Publishing Division)
In 1982, we
M. Yamano, H. Takesada/FuOco~rliquidcrysmlte&vmmn
1384
demonstrated "Japan
a m o n o c h r o m e LCD p a n e l
Display'8Y',
panel 9 and at sponsored will
we a n n o u n c e d
for
5 inch
2. LCD PANEL Figure i shows a equivalent circuit
8
receivers
of a 3 inch
Conference
b y IEEE we a n n o u n c e d a 5 i n c h a newly developed
television
the development
the "1984 International
introduce
portable
full
.
color
At t h e LCD
on Consumer Electronics"
full
color
LCD p a n e l 10.
full
color
LCD TV r e c e i v e r .
This
t i m e we
Drain electrodes Pixel electrodes Counter
for the panel. Fig.2 shows a cross section of the TFT and Fig.3 shows its plane view.
ro~e ~
~
~
~
In the reverse staggered
type TFT, gate insulater film and a-Si minimal contamination at the channel
565
area which is the most important part
~
~
~
of the TFT. The plasma CVD equipment
n-
"%-
-i-
-z-
T
n-
-r,
-r
can be deposited continuously with
o
w
=z=
o _
o
~
nF.
developed by us for a-Si deposition. One of the important characteristics of a-Si TFT is that it can be made by
Gate electrodes
a low temperature deposition method and sodarime glass can be used for its substrate. In addlton, lower
~-SiH TFTs
FIGURE 1 Single Matrix LCD Panel
off-current TFTs can be made because of its higher specific resistance.
Pixel electrode
/
Drain electrode Source Gate a-Sill /electrode electrode / / Pl%~ " ~ i n s i u l a ~
i\
\
\
\
\
\
........
\\
\
FIGURE 2 Cross Section of a-SiH TFT
I
Drain electrode
~ H ~
-
......
~
FIGURE 3 Plane View of Pixel Pattern
M. Yamano, H. Takesada / Full color liquid crystal television
Vacut~n Chamber
S\LN~ Deposition Chamber
a-SiH Deposition Chamber
1385
Cooling Chamber
FIGURE 4 CVD P r o c e s s
o
In the production process, intrinsic amorphous silicon ]ayer of 1000A is deposited over the gate insulator film of SiN and then conventional photolithographic process is used to form TFT array.
Typical static
characteristics such as Vg-I d curve and Vd-I d curve are shown in Figs.5 and 6 respectively. the TFTs.
Dynamic charactoristics are also important characteristics for
To write TV signal's voltage to the incidental capacitors of about
0.7 pF of LCD plxels, the capacitors has to be charged and dischared by TFTs in one horizontal scanning time of 65 ps.
Figure 7 and 8 show that the
-4
1.0 f~
--
Vg= 10V
/ "
liI/
H
/
'd' /
A
-t2 ~ ~ ~ -15
.-
7.sv
o
0
35 Vg (V)
FIGURE 5 On-Off Characteristics of TFT
5v
0
i0 Vd-s (V)
FIGURE 6 On Current of TFT
M. Yamano, t£ Takesada / Full color liquid crystal television
1386
equlvalent capacitors of 1.5 pF can be charged and discharged within I/3 of 65
~
I
I
~s respectively by the TFTs and turn
T F T
out that actual incidental capacitors
w=ll6j~n
can be charged or discharged in even shorter time.
Stability of the TFTs
~ ~ w ~
under the application of gate voltage
#~
of -7.5 volts were measured.
~
After 240
20~sec/div
~
Load capacitmLnoe 1.5pF Vg-s i7.5V
hour operation, no degradation was found as shown in Fig.9.
As for the FIGURE 7
panel construction, Fig.10 shows a
TFT S w i t c h i n g C h a r a c t e r i s t i c s
cross section of the full color panel.
(Vd = -3 + +3V)
In conventional LCDs, polyimide is used as an aligning layer for liquid crystal. Since this polyimide requires
ij.l~sii
~
300-4000C for polymerization it can not be used with a-SiH TFTs.
20usec/div
l - i~2V/~vl2v/div
For this
reason, various organic polymer films
-
that could be formed at lower
~
temperature (~I00°C) were tested and
~
a new aligning film was found without
~
-
i
~
TFT i=8~ n w=ll6~n
~
Load ca1.5pF Vg-s ±7.5V
sacrificing perfomances of a-SiH TFTs and the color filter.
For obtaining FIGURE 8 TFT Switching Characteristics
better performances of the panel, several selected liquid crystal
(Vd = +3 ~ -3)
-4
-4
.. r--I
A
=
-1_152
r
0
35
_12_S1
~
0
Vg (V)
I
35
Vg (V)
[Initial]
[240Hrs] Vg=-7.5V
Vd-s=OV
FIGURE9 Stability of TFT Characteristics ( Vg vs Id Curves )
M, Yamano, H. Takesada / Full color liquid crystal television
materials were blended.
1387
The response
time is about 30 ms which is an
Polarizer Color f i l t e r / Glass substrate
acceptable level for color TV
~\\\\\\\'\\t/
v±~//~ansparent
receivers.
"\\\\\\\\\\
/electrode
Since tlle light
transmittance of the liquid crystal
<.. . . . . •..... <. . Alic~ling .....' " ' ' ' "' layer ". >.: '.' : , ./
changed linearly at 3 to 7 volts, the
~
panel can be driven by conventional
- ' r w' r4~ '~J /~/ ~_
CMOS LSIs.
~kk~v~K~...
The color range was still
_ .....
'Liquid
\crystal
~ ~ ~ \aligning ~
narrower than that of conventional
~/Lu~Ice'~
CRT (NTSC), but it has been reached
n|
\
\layer
a~si\Gl~ss substrate \ ! Insulator Polarizer
to the practically acceptable level. Table 1 shows specifications of the panel.
This specification has been
FIGURE I0 Cross Section of Color LCD
selected to have better productivity and performances vs cost.
Number of
pixels has been reduced to 216 x 384 from 250 x 666.
In spite of its less
Display Size
?5.8×99.8 mm
Panel Size
99.0xlZ3. gx2.0 mm
Number of Pixels
216×384
Pixel Size
350×260
Liquid Crystal
TN
Filter Color
RGB
enabled elimination of light shield II
Display Mode
Transmissive
for gates were slected to simplify
Cell Gap
~I0
tight design rule of 5pm, production of the panel requires various additional know-how to the LSI
~ m
production technique because of its large area LCD panel.
For example,
optimum deposition conditions that
the process.
~ m
With the reduction of
number of pixels, aperture ratio of
'FABLE 1
the panel has been improved to 74 %
Specifications of the LCD Panel
from 53 % and obtained better contrast, as well as improvement of production yield.
By selecting material of the
mosaic color filter, optical transparency has also been improved to 20% from 15%.
Another methods to improve the yield are driving of gate line from both
ends of the panel and adoption of by-pass circuits to prevent shorting problem between drain and gate lines.
Since amorphous silicon TFT LCD panel is
basically suitable for transparent type, an optical reflector is required when it is used in brighter ambience. light is required.
When being used in darker ambience, a back
For this backlight sourse, we have developed a high
efficiency 5 inch flat fluorescent lamp that utilizes combination of three phospors.
M. Yamano, H. Takesada / Full color liquid crystal television
1388
3. COLOR LCD TV RECEIVERS To take the advantage of low power
EffectiveDisplay 5 inches Size
performance of LCD, specially designed CMOS LSIs are used.
All circuits after
level amplifiers for R, G and B signals are composed of CMOS ICs to minimize power consumption.
Circuit Size Display Back light
L Weight
168x141x23m 1.00 1,,g
light 055
As a result, total
power consumption has became as low as
(w) (D) (Thic~mess) 188xlgOx25mm 168x138×I0m
DC 2.4 W Power consumption DC 4 9 W (WithBack light)
2.4 watts (DC) which is equivalent to 3
Frequencyrange
VHF.UHF
hour operation by 5 penlight alkaline
Responsetime
30 msec
batteries.
When the back light is
±45" (horizontal) Viewi~ ~ l e
used, another 2~3 watts are required.
+30" .-I0" (ve/-tical)
Table 2 shows specifications of the TV
Contrastratio
8 (WithP~ck light)
receiver.
Light source
Flat fluorescentla,~por Ambient light
4. CONCLUSIONS
~iv/ng volt~e
Gate:lbV [~ain:±6V
In sun.nary, it is important to select the optimum numbers of pixels to commercialize a-Si TFT LCD TV
TABLE 2 Specifications of the Color LCD TV
receivers based on the most advanced current technologies to form a-Sl film and a-SiH TFT array.
This type of LCD
panel is suitable not only for color TV receivers, but also for other displays such as personal computers, automabile displays, etc. because of its high performances vs cost.
This panel can also be used as a monochrome display
without the color filter.
REFERENCES i) T. Niina et al. IEEE Trans. Vol. ED-26 No. 8 (Aug., 1979) pp. 1182-1186 2) S. Mite et al. SlD (1974) pp. 86-87 3) H. Murakaml et al Inst. of TV Eng. Japan Vol. 38, No. 9 (Sept., 1984) pp. 836-842 4) E. Kaneko et al SID Vol. 23, No. I (1982) pp. 3-8 5) H. Watanabe et al SID (1985) pp. 86-87 6) M. Yamano et al Japan Display (1983) pp. 356-357 7) Y. Kuwano et al 14th IEEE PV Specialists Conf. (1980) pp. 1408-1411 8) Nikkei Electronics (Japan, Nov., 1982, No. 303) 95 9) M. Yamano et al Japan Display (1983) pp. 214-217 I0) M. Yamano et al IEEE ICCE (1984) pp. 74-75 Ii) M. Matsushita et al Inst. of TV Eng. Japan ED 885 IPD 96-28 pp. 79-84