Kenji Sera

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>>

51.1: A DC-DC Converter Circuit Integrated into a Poly-Si TFT LCD Containing a 6-bit DAC

A DC-DC converter composed of charge pumps and regulators has been integrated into a poly-Si TFT LCD that also contains a 6-bit DAC. It has the ability to supply regulated voltages to the 6-bit DAC and to the LCDs gate driver circuit.

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>>

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.

L-3: Late-News Paper: A 0.9″ XGA Temperature Poly-Si TFT LCLV with Stacked Storage Capacitor

A 0.9” XGA liquid crystal light valve with low temperature Poly-Si TFT has been developed by using a stacked capacitor structure. The stacked capacitor structure could reduce storage capacitor area because most of the capacitor area is located above the pixel components, such as bus-lines and TFTs. Therefore, this structure could obtain the required storage capacitance without decreasing aperture ratio. A high aperture ratio of 65% and a high contrast ratio of over 500:1 have been achieved with the fabricated light valve.

Reliability improvement in low-temperature processed poly-Si TFTs for AMLCDs

Low-temperature processed polysilicon thin-film-transistors have shown negative threshold voltage shift under gate bias stress. This shift was produced as a result of the positive charge created by water penetration and by the subsequent field activated chemical reaction in the gate oxide. Thermal desorption mass spectrometry (TDS) measurements reveal that dissociation of Si-OH bonds with hydrogen-bonded water in the oxide may be a fundamental contributor to the creation of the positive charge. As a preventative measure, we used hydrogenation to dissociate the Si-OH bonds beforehand, and in this way we have been able to obtain stable TFTs that can be applied to drivers for AMLCDs.<<ETX>>

27.4: A Low Temperature Poly‐Si TFT Liquid Crystal Light Valve (LCLV) with a Novel Light‐Shielding Structure for High Performance Projection Displays

We have successfully achieved a very high contrast ratio of over 700:1 without attaching optical compensation films. This good contrast ratio is much higher than that for commercially available projection displays whose typical contrast ratios are about 400:1. A novel light-shielding structure has been employed in order to realize the excellent performance that has been brought by suppressing low photo leakage current in the TFTs for the LCLVs.