Fujio Okumura

High-performance TFTs fabricated by XeCl excimer laser annealing of hydrogenated amorphous-silicon film

High-performance staggered a-Si:H and poly-Si thin-film transistors (TFTs) fabricated by XeCl excimer laser annealing of a-Si:H films are discussed. The field-effect mobility of poly-Si TFT is 102 cm/sup 2//V-s, and that of a-Si:H TFT is 0.23 cm/sup 2//V-s. Their drain current on/off ratios are over 10/sup 6/. Except for the crystallization, the fabrication process was the same for both of them. This process appears extremely promising for the integration of matrix elements and peripheral drivers in a single substrate. >

Excimer-laser doping into Si thin films

The fabrication of n+ and p+ silicon thin film by using a combination of ‘‘spin‐on‐glass’’ and XeCl excimer‐laser doping is described. The doping can be achieved by rapid dopant atom diffusion into molten silicon from a spin‐coated film containing the dopant. This technology offers the advantages of process simplicity, low processing temperature, and ultrashallow high‐concentration doping. The obtained sheet resistances (2 kΩ/⧠ for n+ and 9 kΩ/⧠ for p+) are acceptable for thin‐film transistors (TFTs). The energy required for doping into a thin film was less than half of that for a silicon wafer. This is mainly due to the absorption rate difference between noncrystalline and crystalline silicon. This process appears extremely promising for TFT fabrication.

Self-referenced poly-Si TFT amplifier readout for a linear image sensor

A readout scheme with thin film transistor (TFT) amplifier is proposed for a linear image sensor. Each pixel is provided with a TFT amplifier and additional TFT circuits which allow self-calibration of the amplifier. Prototype sensors were successfully fabricated by the low-temperature poly-Si process utilizing excimer laser annealing.<<ETX>>

Ferroelectric liquid-crystal shutter array with poly-Si TFT driver

A novel ferroelectric liquid-crystal (FE-LC) shutter array with a poly-Si thin-film-transistor (TFT) driver has been fabricated which has 256 dots (300 dots/in. resolution) and is 21.7 mm long. The TFT driver is capable of driving the FE-LC in the static mode and reduces the number of outlet electrodes. This results in a device with the advantages of high contrast ratio (over 20 to 1), compact device size, and low cost.<<ETX>>

Ferroelectric Liquid Crystal Spatial Light Modulator with Gray-Scale Capability

Memorized gray-scale capability was demonstrated in a ferroelectric liquid crystal optically addressed spatial light modulator (OASLM) prepared by using polyimide Langmuir-Blodgett films for the orientation of the liquid crystal.

29.3: A 1450-ppi Field-Sequential System-on-Glass LCD Capable of Operating Over a Wide Temperature Range

We succeeded in developing a field-sequential color system-on-glass (SOG) LCD with a twisted-nematic mode using a novel material and novel driving method. We achieved a 4-ms response time and operation over a wide range of temperatures with a 2.1-μm cell gap. High optical efficiency was demonstrated with an aperture ratio of 59% and a 17.5-μm pixel pitch.

A poly-Si defect-tolerant scanner for large area AMLCDs

A poly-Si TFT (thin-film transistor) defect-tolerant scanner for large-area AMLCD (active-matrix liquid-crystal displays) is described. The scanner consists of regular and spare delay circuits, error correcting circuits, transfer switches, exchange switches, and output buffers. An 8-stage prototype scanning circuit on a quartz substrate uses a low-temperature (<or=600 degrees C) poly-Si CMOS process. The poly-Si active layer is recrystallized by XeCl excimer laser to improve the TFT characteristics. Different short/open defects intentionally introduced on each state by laser cutting demonstrate defect-tolerant operation. Operation of the proposed scanner is faster than that of conventional scanners, because of the driving method used.<<ETX>>

Amorphous Si:H Contact Linear Image Sensor

A contact linear image sensor using a-Si:H heterojunction photodiode array has been developed. The sensor is composed of a pair of LED array, a rod lens array and a document width linear image sensor in which a-Si:H photodiode array and driving ICs are mounted on the same glass The a-Si:H diode has ITO/p-a-SiC/a-Si:H/metal structure. It exhibits as high as 104 photo-to-dark current ratio and quick photoresponse because of excellent blocking characteristics and large built in potential of heterojunction. The contact sensor has been operated with 1 msec/line scanning speed. Performance tests show excellent results with 8 lines/mm resolution. Images have been satisfactorily recorded using a thermal printer. Moreover, thin film image sensor using a-Si:H TFT will be discussed as a lower cost linear image sensor.

Controlling the Amount of Si-OH Bonds for the Formation of High-Quality Low-Temperature Gate Oxides for Poly-Si TFTs

Lowering process temperatures for polysilicon Thin-Film-Transistors (TFTs) has given rise to new worries about the quality of TFT gate oxides. Specifically, the presence of large amounts of Si-OH bonds in gate oxides has become a matter of concern. We discuss methods for suppressing the formation of Si-OH bonds during Chemical Vapor Deposition (CVD) of Low-Temperature Processed (LTP) gate oxides. In various kinds of CVD techniques, the use of Remote-Plasma Enhanced CVD (RPCVD is shown to be efficacious for the suppression. The control of the reaction between the silicon source gas and the oxygen source gas is also shown to be effective. We also show that decreased amounts of Si-OH bonds in LTP-CVD gate oxides result in desirable decreases in both leakage current and fixed oxide charge densities, and that the amount of Si-OH bonds can be used as an index of gate oxide quality.

Compact imaging apparatus for a pen-shaped handheld scanner

A compact imaging system is proposed for electronic document input. In this configuration, a linear image sensor formed on a glass substrate is coupled with an optical fiber array plate. There are multiple apertures in each photodiode of this sensor. Light from a linear light emitting diode array is transmitted through the glass, the apertures and the fiber successively and illuminates a document. The scattered light comes back in the same fiber and is detected by the sensitive part of the photodiode. Experiment with a 200dpi sensor shows a good spatial resolution. With a white paper illuminated at 100(mu) W/cm2, a signal yield of 0.75 pC is obtained with 1msec storage time. The depth of field is 70 micrometers . A prototype hand-held scanner has been developed by housing this imaging system in a 10mm-wide pen-shaped speed of 12cm/sec.