Site: TOHOKU UNIVERSITY

Date Visited: October 2, 1991

Report Author: W.E. Glenn

ATTENDEES

JTEC:

Glenn
Credelle
Doane
Hoffman
Larimer
Thompson

HOST:

Dr. Tatsuo Uchida

Professor, Department of Electronics Engineering,
Faculty of Engineering, Tohoku University

Dr. Uchida's research at Tohoku University is primarily in the area of liquid crystals. He is very active in the SID. He recently held a conference on LCD technology with an attendance of about 500 people. He reported that in universities, 100-250 people are working in the field of liquid crystal research. Most of these people are chemists or physicists. His laboratory has about 15 graduate students working in the area (mostly MS candidates).

TECHNICAL COMMENTS ON FERROELECTRIC LIQUID CRYSTALS

Ferroelectric liquid crystals are relatively fast. The time constant is about 50 microns at <10V and hopefully will be under 10 ęs in the near future. They are not very stable, but the antiferroelectric materials are more stable. Ferroelectric materials normally have memory but do not have gray scale. He felt that gray scale might be possible if the memory property was not used. Ferroelectric materials can be obtained from Chiso and Merck. Fujitsu is also working on ferroelectric liquid crystals. Dr. Uchida felt that optical processing was a good application for these materials.

With respect to TN liquid crystals he commented that the response time between full on or full off or vice versa is much faster than the response time to switch between two midgray levels.

In his opinion, many people like PDLC for projectors because it does not require polarization and therefore can provide more light output. However, one must compromise between light output and contrast. High contrast and high brightness cannot be obtained at the same time. Hysteresis and lag are problems for displaying moving images. Asahi Glass and Dai Nippon Dye are working on displays using PDLC.

With respect to STN, Dr. Uchida felt that very sharp transfer characteristics are needed to get over 400-line resolution at high contrast. This makes it difficult to get good uniformity for color displays. He felt that STN is somewhat limited because the driver cost is as much as the panel cost. The response time of STN is slower than TN, but the response time, viewing angle, and contrast are about the same.

Dr. Uchida has worked on ECB (CSH) displays with Stanley. These displays have good gray scale but are brightness-limited, since they are only good up to about 50% modulation. Their response time is about three times slower than is needed for television display. The viewing angle is very good.

In his work on reflective color displays, Dr. Uchida has achieved a reflectivity of about 20% and a contrast ratio of 5:1. These devices can have a good viewing angle if the scattering angle from the reflecting layer is controlled. These devices use dichroic dyes.

DR. UCHIDA'S GENERAL COMMENTS

The most critical techniques in making LC displays involve the processing of the alignment layer. Surface studies are considered very important. The degree of alignment is controlled by the rubbing time, speed, and pressure.

In producing LC displays a mask must be used over the fringing field area.

The most difficult part of making a retardation film is the adhesive that bonds it to the polarizer. They are sold bonded together.

As a general rule, universities are doing basic research. Devices and materials are developed by companies. Materials are being developed primarily by Chiso, Dai Nippon Dye, and Merck. Dyes are being developed by three or four companies.

For very large direct-view panels, such as will be needed for HDTV, he felt that it will be very costly to make them of AMLCD panels. He felt that PDP would be less expensive since it could be made using a printing process. PDP panels get about one lumen per watt optical efficiency, about the same as AMLCD panels. The AC surface discharge technique has a long life since the phosphor does not have ion bombardment. The discharge electrodes are on one plate and the phosphor is on the opposite plate.


Published: June 1992; WTEC Hyper- Librarian