Akira Ishizu

Metal‐oxide‐semiconductor field‐effect transistors and a ring oscillator fabricated in laser‐recrystallized polycrystalline silicon islands

Directions of grain boundaries in laser‐recrystallized polycrystalline silicon (polysilicon) islands are found to be arranged along with the laser scan direction, and are connected to the electrical characteristics of metal‐oxide‐semiconductor field‐effect transistors (MOSFET’s) fabricated in polysilicon islands. When the laser scan is parallel to the channel direction, grain boundaries work as fast‐diffusion paths of arsenic from source and drain into the channel and a decrease of effective channel length of the MOSFET results. But when the laser scan is perpendicular to the channel direction, few grain boundaries are contributed to diffusion paths of arsenic. A maximum electron mobility of 590 cm2/V s approaching that of a single crystalline silicon can be obtained in devices with a channel length of 3 μm, though grain boundaries work as additional potential barriers for carriers. A nine‐stage ring oscillator is fabricated by applying these results. A minimum propagation delay of 38 ns is obtained.

Ge-Si n-n Heterojunctions

Ge-Si n-n heterojunctions have been fabricated by epitaxial vapour growth process of hydrogen reduction of germanium tetrachloride. They have a good rectification property and a short switching time less than a few nano-seconds. In the junction there exists a double Schottky barrier due to interface states, which capture electrons more than 1.5×1013 cm-2 as acceptor-like states. The voltage-current characteristics have been measured at temperatures between 77°K and 300°K. In the low voltage region of easy flow direction (Germanium positively biased), d(log I)/dV is independent of temperature, but in the higher voltage region it is proportional to q/kT. The reverse characteristics (Germanium negatively biased) are divided into three separate regions, which are I∝V0.7~0.8, I∝V3/2 and I∝exp (BV) in the order of magnitude of reverse bias voltage, where B is a constant depending on temperature and donor concentration of silicon. The conduction mechanisms of this heterojunction have been discussed qualitatively.

Evaluation and Control of Grain Boundaries in Laser-Recrystallized Polysilicon Islands for Device Fabrication

Directions of grain boundaries in laser-recrystallized polycrystalline silicon (polysilicon) islands are found to be arranged along with the laser scan direction, and are connected to the electrical characteristics of MOSFETs fabricated in polysilicon islands. In the case of the laser scan parallel to the channel direction, grain boundaries work as fast-diffusion paths of arsenic from source and drain into the channel, and results in a decrease of effective channel length of MOSFET. But in the case of the laser scan perpendicular to the channel direction, there are few grain boundaries contributing to diffusion paths of arsenic. The maximum electron mobility of 590 cm2/V sec approaching to that on a single crystalline silicon can be obtained in devices with a channel length of 3 µm, though grain boundaries work as an additional potential barriers for carriers. A nine stage ring oscillator is fabricated by applying these results. The minimum propagation delay of 38 nsec is obtained.

An analysis of source bus-line to common-electrode coupling effect in large-area TFT-LCDs

— The source (or data) bus-line to common (or backplane) electrode coupling effect in TFT-LCDs has been investigated through experiment and simulation using a new model. The important feature of this simulated model is that the common electrode consists of a network of discrete resistors. The horizontal crosstalk is caused by this coupling effect, and the mechanism of the crosstalk has become clear by the simulation of 5-in. TFT-LCDs. By adopting this simulation, useful information for large-area TFT-LCD designs can be obtained. As an example, this simulation has been performed for 10- and 15-in. TFT-LCDs and the requirement for a common resistance has been illustrated.

Formation of a Positive Photoresist Thin Film by Spin Coating: Influence of Atmospheric Temperature

Experimental formation of a positive photoresist film by spin coating at various atmospheric temperatures was investigated. The weight of the photoresist solution on a wafer during spinning decreases sharply during the first stage of spinning and gradually during the later stages. At a high temperature, the rate of outflow increases and that of solvent evaporation decreases in the initial stage of spinning, but the former decreases and the latter increases in the intermediate stages. In the later stages, both of them decrease. The baked film spun at a high temperature is thin up to the intermediate stages of spinning due to the higher rates of outflow in the initial stage and evaporation in the intermediate stages more than that at a low one. However, it becomes thick in the later stages due to the lower rates of outflow and evaporation.

Method For Evaluating The Interface Of Semiconductor Heterojunctions Using A Free Electron Laser

The method for evaluating the interface of semiconductor heterojunctions using the free electron laser internal photoemission (FEL-IPE) technique is presented. The nature of the interface in semiconductor heterojunctions plays an important role for determining the behavior and performances of an entire class of nanosemiconductor devices. It is indicated that the measurement using FEL-IPE makes it possible to determine the band discontinuities of semiconductor heterojunctions more precisely.

ITO thin film fabrication assisted by the infrared free-electron laser

We fabricated the ITO (In-Sn-O) thin film assisted by the infrared free electron laser (12.1 micron-meter-FEL). The novel method can in principle excite the vibration mode of the deposited molecules with matching the FEL energy and the molecular vibration-energy. The method thus is independent of the substrate temperature and has the advantage of fabrication on the low-temperature substrate. The ITO thin- film fabricated by the novel method preliminarily indicates similar transparency to one fabricated by the conventional method.

Novel thin-film deposition method and system with IR-FEL

We propose a novel method for thin film deposition with an IR-FEL using the IR-FEL wavelength tunability in infrared region. This is an unique method in which only the vapor deposition molecule is activated by applying laser of vibrational excitation wavelength of the vapor deposition molecule on the substrate surface, when the thin film intends to deposit on the substrate. We developed two equipments in order to realize and evaluate the new method. One is IR-FEL assisted RF sputter deposition chamber system, the other is IR-FEL assisted laser ablation chamber system. Moreover using the former equipment, we carry out the preliminary experiment on the preparation of ITO (In-Sn-O) thin film.

FEL research at FEL Research Institute in Osaka

Free Electron Laser Research Institute (FELI) had been established by the Key Technology Center project in Japan. Now it is operated under the collaboration of several organization after the end of the project. The FEL with wide tunable wave range from 0.27 to more than 50 micrometer installed in FELI has being used for applications of various fields. Beside the application of FEL as a users facility at FELI, an effort to extend the wavelength toward shorter region has being performed. SASE FEL with micro-wiggler and seed X-ray is proposed and preliminary investigation is under way. The basic development of micro-wiggler is almost finished. For seed X- ray, we will use Laser-produced Plasma X-ray. The 3D computer simulation results shows the feasibility of SASE in the range of up to 0.01 micrometer with FELI accelerator. This article describe the status and investigation of FELI update.