Yoshiharu Nagae

A new patterning process concept for large-area transistor circuit fabrication without using an optical mask aligner

A new concept to produce large thin film transistor liquid crystal displays (TFT-LCDs) without using an optical mask aligner is proposed which emphasizes patterning technology. Some experimental thin film transistors (TFTs) are fabricated according to the concept and operated like conventional transistors fabricated by using an optical mask aligner. The concept includes improvement of printing technology and development of a double-layer resist method. The latter method employs a printed ink pattern and a photoresist. This prevents contamination of thin films by metal impurities which affect electrical characteristics of the TFTs. A special gravure offset printing technology is proposed, composed of a large thixotropy valued UV ink, and a fine, precision etched glass intaglio. The experimental TFTs, with a designed minimum gate length of 10 /spl mu/m, have comparable electric characteristics to those of conventional poly-Si TFTs. >

A 10-s doping technology for the application of low-temperature polysilicon TFTs to giant microelectronics

A bucket-type high-density (0.25-1.2-mA/cm/sup 2/) low-energy (500-2000 V) ion source was utilized for high-speed phosphorus doping directly into a thin polysilicon layer without cap SiO/sub 2/. Doping gas with He dilution was selected to reduce etching of polysilicon film. Excimer laser (XeCl, 8 mm*8 mm) pulse annealing was introduced to activate effectively the doped impurity. The combination of these techniques provided a practically low sheet resistance for the TFT source, drain, and gate with a short time doping. The low-temperature polysilicon TFT fabricated with a doping time of 10 s had characteristics comparable to those of that fabricated by a longer time doping or conventional ion implantation, showing the practicality of this technology and its promise for giant microelectronics. >

Peripheral circuit integrated poly-Si TFT LCD with gray scale representation

A 3.3-in.-diagonal fully-integrated low-temperature-processed poly-Si TFT LCD (thin-film transistor liquid-crystal diode) with 4 gray scale (64 colours) representation was fabricated on a glass substrate. Good viewing characteristics, with a high contrast ratio more than 25 were obtained. Integrated data drive circuits consisted of divided matrix switches, line memories, and multilevel selectors. High-frequency drive capability was realized by using divided matrix switches with small line memory capacitance. Four-level gray-scale voltage was generated by the multilevel selectors. Integrated scan drive circuits consist of shift registers, level shifters, ratioless buffers, and multiplexers. Using a ratioless buffer, high-speed operation and low-power consumption was realized. By integrating peripheral drive circuits in a prototype display with (132*3)*133 dots, the number of external connections was reduced from 531 to 101. The maximum scan and data frequencies were 100 kHz and 10 MHz, respectively. These integrated peripheral circuits were capable of driving a display with (640*3)*400 dots at a frame frequency of 60 Hz.<<ETX>>

Consideration of feed-through voltage in amorphous-Si TFT's

Feedthrough voltage is an important factor in designing integrated data drive circuits and display area in thin-film-transistor liquid-crystal displays (TFT LCDs). With respect to feedthrough voltage, only the gate-source overlay capacitance has been considered in amorphous-Si (a-Si) TFTs, because of their staggered structure with overlap area. It is pointed out that, in a-Si TFTs designed as active elements, feedthrough voltage is mainly due to the carrier redistribution. The main reason is that, since the field-effect mobility is low (W/L>1), the leakage current must be kept low (L>or=10 mu m), and an active layer is inserted in the overlap area (unlike the case with MOS device structures), the area of the active layer is large. Taking the carrier redistribution into account, the maximum difference between the voltage obtained using the modified model and the experimental voltage is within 20%. By comparison, the results obtained using the previous model for TFTs are approximately three times smaller than the experimental results. >

A Monochromatic Black and White Supertwisted Nematic Liquid Crystal Display with a Single Cell and a Birefringent Film

To achieve a monochromatic black-and-white (B/W) STN-LCD with a single cell and a birefringent plastic film, the optimum conditions of optical properties in the birefringent film are analyzed theoretically and experimentally. By optimizing the film retardation to minimize the transmission of a STN-LCD at 550 nm, optical retardation in a STN cell is canceled and a B/W STN-LCD is obtained. By selecting the suitable conditions for compensating retardation of the STN cell, a B/W STN-LCD is achieved with the contrast ratio of 10:1.

Recent trends in wide-viewing-angle color TFT-LCDs

Many important innovations on LC display mode for wide- viewing angle color TFT-LCDs were reported within this several years, and recently the volume productions of LC monitors and LC TVs have been started using them. To realize good wide-viewing angle color TFT-LCDs, we have to design not only optical property of LC layer but also film polarizers and back lights. Typical wide-viewing angle LC display modes are classified into several categories and discuss their features.

Fine gate TFT circuits fabricated with a new printing technology

Fine-gate polysilicon thin-film transistors (TFTs) and TFT circuits for large-area electronics have been successfully fabricated with a new printing technology. Electric characteristics for an experimental 3- mu m-gate n-channel TFT are comparable to those for conventional TFTs. A 5- mu m design-rule NMOS shift register and 8*8 liquid crystal display (LCD) operations have also been achieved. The printing technology can delineate patterns fine enough to produce large-area high-resolution TFT-LCDs without using an optical mask aligner.<<ETX>>

Threshold Behavior of a Bistable Ferroelectric Liquid Crystal with a Large Tilt Angle in Thick Cells (4-14µm)

Threshold characteristics were measured of a cell consisting of a compound which shows a large tilt angle of 35° and possesses bistability in cells thicker than 4 µm. A value, which represents the sharpness of the threshold, Vsat(max)/Vth(min), of 2.5 was obtained at T-Tc=-20°C. The optical responses to two kinds of voltage waveform applications were also measured. The introduction of zero voltage periods improved the bistability and, consequently, made it possible to drive matrix displays.

Multi-colour laser-addressed liquid crystal projection display

Abstract A multi-colour, large-screen (2 m x 2 m, 2000 x 2000 pixels) laser-addressed liquid crystal (LC) projection display is constructed which has three LC cells corresponding to the three primary colours. Only one f-θ lens and one projection lens are used. To increase brightness, two dichroic mirrors and an off-axis projection lens are employed in the projection system.

Thermal Writing Displays

Thermally addressed displays, where the heat input is provided by a laser beam or a heat pulse current, have been established for several years.1–21 It is generally known that the thermal writing liquid-crystal display is the most promising because of its intrinsic memory effect. The display overcomes the inherent addressing limitation associated with liquid-crystal displays that use just an electro-optical effect because that effect lacks memory and has insufficient nonlinearity to keep a large number of lines separate.