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LCD tech widens visibility angle

Posted: 16 Aug 2006 ?? ?Print Version ?Bookmark and Share

Keywords:Hiroki Takao? EE Times? Sanyo Epson Imaging Devices Corp.? Photo Fine Vistarich? LCD panels?

Large quantities of small and medium-sized LCD panels are being delivered for cellphones and digital cameras, a market that continues to expand as prices fall. As a result, many LCD panel manufacturers are making less profit despite larger sales volumes. LCD panel makers are developing new technologies in an effort to correct the situation and prevent prices from falling further. These new technologies involve the improvement of LCD panel response time, visibility angle and color reproduction.

Sanyo Epson Imaging Devices Corp. has developed Photo Fine Vistarich, a new technology for widening the viewing angle of LCD panels. Displays incorporating this technology offer contrasts of about 100:1 at 80 from the top, bottom, left or right. When viewed from directly in front, the contrast is at 500:1.

According to Kogo Endo, general manager of Sanyo Epson's technology development division, contrast drops to about 10:1 at an angle of visibility of 80.

Better LCD picture
Sanyo Epson said its technology was achieved through improvements on its structure and liquid crystal materials, although no details about these materials were revealed.

LCD panels normally incorporate twisted nematic (TN) material. These panels adopt a structure that sandwiches a layer of TN liquid crystal between two plates of glass, where the pixel electrode is formed on the lower glass plate and the common electrode is formed on the upper plate. The structure of Sanyo Epson's LCD panels is different in that both the pixel electrode and common electrode are formed on the lower glass plate.

More specifically, the common electrode is formed on the lower glass plate and coated with an insulation layer. A patterned electrode is produced to function as a pixel. Only the color filter and polarization plate are adhered to the upper glass plate.

When a positive voltage is applied to the pixel electrode and a negative voltage to the common electrode, the line of electric force from the pixel electrode enters and passes through the liquid crystal layer, soon reaching the common electrodes that surround the pixel electrodes. At this time, the tilt of the liquid crystal molecules within the liquid crystal layer changes according to the direction taken by the line of electric force. In addition, the line of electric force from the pixel electrode disperses by the same amount in every direction (360). As a result, the liquid crystal molecules can be pointed in the same direction, regardless of whether the screen is viewed from above, below, left or right, thus widening the angle of visibility for the LCD panel.

Sanyo Epson said it will apply this technology in panels measuring from 2.4inches to 10.1inches. Initially, the company plans to release five models, with sequential launches scheduled from October onwards.

Designed for cellphones, the 2.4-inch panel has a resolution of 480-by-640pixels (VGA) and comes with a built-in function for receiving one-segment broadcastsa new terrestrial digital broadcasting service in Japan. A built-in digital camera is being planned for the 2.5-inch panel, while the 2.8-inch panel is being targeted for smart-phone-type devices. The 7-inch panel with an LED backlight is designed for in-car devices. The 10.1-inch panelwhich also targets in-car deviceswill feature Sanyo Epson's Photo Fine Chromarich technology, achieving more than 100 percent coverage of the NTSC color gamut.

"Color reproduction is good, regardless of which angle you view the panel from," declared Endo.

According to Shuji Aruga, president of Sanyo Epson, the wider-angle technology uses the same number of photolithography processes as existing LCD panels.

"There is no increase in manufacturing costs," said Aruga. "I hope this technology will become the new de facto standard for wider-angle LCD panels."

- Hiroki Takao
EE Times

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