Electronic Display Forum, 4/94, Yokohama Japan - Kahaner Report

[David Farber <farber () central cis upenn edu>]

Nntp-Posting-Host: optima.cs.arizona.edu
Apparently-To: farber () pcpond cis upenn edu


polyamide with large pretilt angle was adopted as the orientation film
to prevent the domain wall, which is detrimental to image quaility, to
intrude inside display electorde.


Concerning a Poly-Si TFT HDTV projetcor, Mr. Yojiro Matsueda in High
definition television Engineering Corp/SEIKO EPSON Corp explained as
follows.


Seiko developed a new TFT structure with integrated black matrix on the
TFT substrate, enabling us to eliminate the LC cell alignment process
and minimize the design margin of the black matrix. A metal layer which
has the same light shielding effect as the data line has been added
under the edge of the pixel electrode. Each pattern is divided into an
island, so that circuit does not occur by the additional metal pattern.
The capacitance between the data line and pixel electrode which causes
cross-talk is very small in this type. A high aperture ratio of 70% has
been achieved in 3.7-inch (9.4cm) diagonal HDTV TFT-LCD by using the new
TFT structure.


Seiko also developed high speed TFT analog data drivers which are
suitable not only for HDTV but also for data applications. The data
driver consists of 6 blocks operating at 10.5 MHZ, and each block drives
two data lines simultaneosly.  Seiko evaluated the delay time in the TFT
data driver and decided to offset the input of data by 40nsec in order
to compensate for the delay time of the TFT driver which operates at 15
volts. The horizontal resolution has been improved by this method and no
horizontal cross-talk between adjacent pixels is detected even when
one-dot data is written. The combination of the high speed TFT drivers
and non-interlaced double speed scanning method realizes full vertical
resolution and fast response time. It enables us to use the TFT-LCD not
only for HDTV video applications but also for data applications.  In
order to decrease the cost of HDTV-LCD's, the chip size must be
decreased. However, it is difficult to realize high aperture ratio in
such small TFT- LCD's. A low temperature process for poly-Si TFT-LCD
with integrated peripheral drivers is one of the candidates which
achieves both lower cost and high aperture ratio.


Mr.Nobusuke Konishi explained the development of poly-Si TFT and low
temperature fabrication process for TFT-LCD in Hitachi.  He stressed
that active liquid matrix liquid crystal will have a unique role in
poly-Si TFT because of its superior switching characteristics in the
"on" state. As for the low temperature process for poly-Si, there
remains unsolved the problem in the "off" state of switching
characteristics.  There are two methods in the film forming process. One
is low pressure chemical vapor deposition (LPCVD) in which film can be
formed by the decomposition of silicon hydride, and  another is plasma
enhanced CVD method (P-CVD). In the former process, cheap glass cannot
be used due to its non-heat resistance, and there occurs the bumping of
hydrogen during the time of poly-Si forming, so that preheating at 400C
and stepwise irrdation is required. As for the polycrystalization, heat
annealing and laser processing are applied.  Heat annealing results in
the homogeneous crystal structure and small damage by heating. Laser
processing brought about dramatic improvement of switching
characteristics because the distribution of crystal becomes
inhomogeneous. Also, Hitachi adopted XeCl eximer laser annealing for the
peripheral circuits.


Mr. Akira Otsuka of Fujitsu Ltd. explained about the development of
21-inch full color plasma display. Its unit features 640x480 pixels,
200cd/mm2 peak area luminance, 140 degrees of viewing angle, 248 levels
of gray scale, a thickness of 32mm, 4.8kg of weight and 100W of power
consumption. This is the most highly developed machine in this area in
the world at the present time. Also, Fujitsu developed an AC type panel
in which pulsed alternating current is applied between display electrode
on the same substrate. The discharge occurs in adjacent parts of
electrode plate of face side which is separated from the fluoroscence
material, thus preventing the materials from deteriorating. Fujitsu has
just develped long life, high luminance, high efficiency, high
resolution panels with three electrodes and reflection type surface
discharge structures plus full color driving techniques.


Fujitsu views the future prospects of flat display panels as follows. In
the TFT- LCD, 10-inch panel are in mass production at the present time,
and the 20 inch panel will be in production after 1995. In the PDPs,
although it is difficult to manufacture panels whose cell pitch is less
than 0.1mm, thick film printing technique is quite effective for making
large scale panels for monitor used in cars, airplanes and FA machine as
well as home television. For the planer type for direct seeing, PDP will
be used in large scale area and LCD will be limited in area of less than
20 inch panels. Concerning glass, Fujitsu commented that the development
of glass whose softening point is more than 600 degree in compliance
with the use of High Vision Television.


Mr.Jyunro Koike of NHK Science & Reserach Laboratories explained about
the development of plasma dispaly panels, especially a 40-inch high
vision panel.  After NHK established the technique of pulse drive system
having memory function in panel, planar pulse memory associated with the
thick film printing technique was made the target of development. Now,
40-inch high vision with thick film is at the stage of experimentation.
In these panels, the face plate is composed of anode and fluorescence
plate and back plate is composed of cathode and diaphram. The
specification of the 40 inch panel is as follows: screen size is
520x874mm, number of display cells 800x1344, average display cell pitch
is 0.65mm, panel thickness is 6mm, weigh is 8kg, driving method is pulse
memory driving, enclosed gas is He-Xe, fluorescence material is barium
aluminum oxide compound, Mn is used for upgrading the color quality. As
for the 26 inch panel that was developed with Matsusita Electronic
Conmapny, the brightness and life have been improved up to 10,000hrs and
150 cd/m2 respectively, NHK has a bright prospect for the production.
The life of PDP for personal computer is determined by the declination
of brightness caused by the contamination of electrode materials
sputtered by the discharge of gases in the cell. NHK has the opinion
that LCD is suitable for small size as regards precision and power
consumption, CRT is used for around 30 inch panels, and PDP is most
suitable for large scale and unrivaled in that area.


Mr.Kinzo Nonomura of Matsusita Electric Company described
flat displays using electron beams as follows.


Matsushita has had a 14 inch color television, named FLAT VISION since
autumn 1993, and Nonomura noted that presentations and patents relating
to cold cathode display have been increasing in number recently. The
problems relating to the electron source are stability, homogeneity,
life, and consumption of electric power.  Mo, W, LaB_6 are being
examined as emitters.  It is reported that electron can be emmitted with
10volt. CRT using cold cathode is expected to be commercialized in the
small scale panel.


Mr.Hiroyuki Kawano of Canon Inc. introduced 15-inch ferroelectric liquid
crystal display, which was shipped in 1993 for the Japanese-language
desktop publishing system "CANON".  With the new works being built,
Canon is planning to ship versatile type color flat panel displays.
Canon gave the development of stand alone FPD precedence, aiming at
replacement CRT displays in OA, personal computers and versatile
displays of workstations.  The specification of 15 inch color flat panel
color display is as follows: screen size is 15 inches, 128Ox1024 pixels,
16 display colors, 0.23mm pixel pitch, 40.1 contrast ratio, viewing
angle for both horizontal and vertical is 45degrees and response speed
is 75 seconds/line.  Canon intends to develop a video-interface next, to
interface both personal computers and workstation.  Also, Canon is
expanding for electronic publishing and electronic newspapers as well as
monochrome paperless viewers with high vision.


As for the liquid crystal polymer  composite  (LPCP),  Tsuneo
Wakabayasi of Asahi Glass Co Ltd explaned about its features and
applications.


In TN (Twisted Nematics), the efficiency of incident light is at most
40-50%.  Therefore LCPC is regarded as one of the most promising
dispersion types because of high transmissivity.  In this system,
microdroplet liquid crystals are dispersed in a polymer matrix.  When
the voltage is on, it becomes transparent, and when it is off, it
becomes cloudy. In the dispersed type liquid crystal, most of the
incident light passes through, resulting in high transmittance.  In
order to achieve a high contrast ratio and high operation ratio by
voltage, it is necessary to provide appropriate particle size and narrow
distribution of particle size.  Therefore, photo-polymerization induced
phase separation method (PIPS method) was developed.  In the PIPS,
spinodal decomposition could control the size of liquid crystal down to
the micron level.  The technology of TFT combined with LCPC led to the
development of large scale and high brightness display system.  Laser
annealed low temperature poly-Si TFT was manufactured as trial product.
With 53% aperture ratio, the efficiency of display amouted to 21m/W.


The lecture by Professor Tatsu Uchida of Tohoku University addressed the
general trend of the technology of flat panel display.  It gave us very
good summary of present technical development of flat panel display.


1. LCD:
The cost of driver IC is now low because of low driving voltage and low
driving current.  There has been many improvements in the direct matrix
since the SBE mode was proposed by Sceffer in 1984.  The active matrix
has superior characteristics, except for the large scale and cost of
production.  However, color display with backlight shows only 2 lm/w of
practical luminous efficiency, resulting in considerably low power
consumption.


2. FD (fluorescence display):
Good image and high brightness gave priority in the area of AV
instruments and cars.  Large capacity display shows dark image.  High
driving voltage and vacuum are necessry for obtaining a bright image.
However, "light" and "large scale" are not consistent with each other in
this area.


3. EL:
It features a high resistance to mechanical shock.  Yellow type matrix
display using ZnS films doped with manganese are in practical use.  The
development of materials generating blue color is necessary for high
resolution.  It shows the same performance as the plasma display because
of high voltage (150-20OV), though it is a disadvantage with respect to
cost.  Vacuum equipment is needed as in the active matreix LCD-TFT and
the process is relatively simple.  Summing up the above points, it is
situated in the position between palsma display and active matrix LCD.


4. Flat CRT;
The thick film printing has a large advantage in both production of
large scale panels and in cost of production.  Although the luminance
efficiency has recently gone up, high resolution has not yet been
attained and the cost of driving is still too hlgh. To attain low cost
production, the following two consideration are required.  One is that
wide range of sizs, shape, power and quality can be selected by using
standard equipment.  Two, the development of flat panel displays should
be harmonized with that of electronics under the presumption that these
can be driven at low voltage.


As for the marketing, TFT-LCD cover the area of view-finder, portable
television, general television, personal computer, and workstations
which satisfy NTSC standards.  It will not cover more than 17-inch
television and workstation satisfying NTSC standards.  However,
projection type allows us to expand the image size optionally.  For the
CRT, a view-finder and large scale machine will not available, and small
size plasma display will not be realized, and small size plasma display
with many pixels will not be realized because of low resolution.
However, plasma display will capture a large market for direct viewing
and large scale display.   Driving costs down by mass production is
necessary in order to expand the market.  Professor Uchida's opinion is
that plasma display is the most promising display for direct seeing and
large scale dispaly.  Though brightness is not as important when LDP is
used in information display, good display, good contrast, gray scale,
and brightness is quite necessary when used in information display.


In the TN, viewing angle dependance of transmission rate in intermediate
color is so severe that inversion occurs in a region more than 30
degree.  To solve this problem, several methods are being considered.


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