Low Temperature p-Si (LTPS)

The LTPS LCD panel is expected to be the next-generation of LCD panel. Toshiba Mobile Display Co., Ltd. (TMD) was the first manufacturer and supplier in the world to realize a large screen-size LTPS LCD panel. A LTPS LCD panel answers a variety of needs, such as higher resolution, lower profile design, reduced weight and lower power consumption and allows for mobile devices that are more comfortable and convenient to use.

This section introduces the LTPS LCD panel, which constitutes TMD's core technology, in layman’s terms.

• LCD (Liquid Crystal Display) description
• High-speed switch "TFT"
• About LTPS (Low Temperature Poly Silicon)
• Major characteristics of LTPS

LCD (Liquid Crystal Display) description

High-speed switch "TFT"

Forming an image requires the control of liquid crystals for each picture element, by the unit called a "pixel." The number of pixels amounts to over two million in a display. A voltage is applied to the intersections of wires laid in a grid pattern to energize only the liquid crystals in the vicinity. n actuality, however, it is difficult to drive only the liquid crystals near one pixel and then, the liquid crystals in neighboring pixels also become energized, which causes failure of displaying clear pictures. As a solution to these problems, "TFT" was developed.

"TFT" is an acronym for "Thin Film Transistor." A "transistor" is a semiconductor element, acting as a switch to turn ON/OFF the voltage at a high speed.

About LTPS (Low Temperature Poly Silicon)

The TFT is made from of silicon, the same silicon as used to create semiconductors. It is very difficult to form a TFT on the glass substrate, and only the non-crystal, known as "amorphous silicon (a-Si)", has been formed. The drawbacks of the "amorphous silicon TFT" are its larger electrical resistance due to its random-aligned structure of amorphous silicon, which hinders electron flow and electron mobility. Thus, the "low-temperature poly-silicon TFT" was developed, utilizing low-temperature poly-silicon (LTPS) as poly-crystal silicon material.

Poly-silicon means polycrystalline silicon. In the polycrystalline substance, the electrons can move at a significantly higher speed (about 100 times) than possible in the a-Si (non-crystalline Si) substance, thus the volume of information handled by the silicon on the glass of a LTPS LCD would be increased to a greater extent.

In addition, the driver IC chips, which conventionally have been externally connected to the a-Si glass substrate, can be directly mounted onto the glass substrate, thereby allowing downsizing of the TFT section. Based on these characteristics, advanced features have been integrated to develop SOG (System on Glass) for LTPS LCDs. For information on SOG, refer to "SOG".

Major characteristics of LTPS

Beautiful, ultra high-definition image

The drive circuit, which conventionally has been designed onto the substrate outside the glass substrate, is mounted onto the glass surface in LTPS. This eliminates physical restrictions on wiring and allows for finer pitch between pixels.
In addition, the reduced size of the TFT section helps to achieve a higher aperture ratio, which contributes to achieving finer pitch, and beautiful, clear and crisp screen images.

Enhanced durability

Since the drive circuit is integrated directly onto the glass surface, the number of connecting pins is significantly decreased, and a thereby a vibration- and impact-resistant, highly-robust LCD is created.

Low profile and lightweight for increased convenience and mobility

The integration of drive circuits directly onto the glass surface also contributes to reducing the number of component parts designed on the outside substrate, as in conventional displays. This integration helps to make the peripheral edges of the display screen even smaller, and when assembled into a device, the displays are well-suited for mobile equipment thanks to the reduced thickness and weight of the panels.

Low power consumption contributes to an extended period of time for mobile use

The reduced size of the TFT section facilitates the transmission of light through the display from the backlight, increasing the efficiency of light utilization. This helps to reduce power consumption and thereby extends the duration of battery-powered operation.

TMD is the first manufacturer in the world to develop large screen-size LTPS LCDs, and continues to lead the industry in production of such large-size LTPS LCDs. TMD has received various industry awards, including the "SID Display of the Year in 1999" a well-known U.S. award in the field of display panels. TMD has been highly regarded by industry insiders and also rated high throughout the world for our advancements in display technology. In 2006, TMD started operation of the world's largest and most technically advanced LTPS LCD panel production line in TMD’s Ishikawa Plant. TMD will continue further developments with LTPS technology at its core.