Yasuo Namikawa

Reflection Mode Polymer-Dispersed Liquid Crystal Light Valve

This paper describes the procedure for fabrication of a reflection-mode polymer-dispersed liquid crystal light valve (PDLCLV) consisting of a polymer-dispersed liquid crystal film, a diamondlike carbon film, a dielectric mirror, a Bi12SiO20 photoconductive crystal plate, and transparent electrode films. The many advantages of the PDLCLV include the lack of need for polarizers, high optical transmittance, high-speed response and ease of fabrication. The performance of the device as evaluated experimentally is as follows: optical transmittance 72%; extinction ratio 178/1; limiting resolution 34 lp/mm; and rise/decay times 14/15 ms. These values are suitable for the image converter of an optically addressed projection display. It has also been found that the resolution increases as the frequency of the AC voltage driving the PDLCLV decreases.

Polymer-dispersed liquid crystal light valves for projection display

We describe the polymer-dispersed liquid crystal light valve (PDLCLV) using a polymer-dispersed liquid crystal (PDLC) film and a Bi 12 SiO 20 (BSO) photoconductive crystal. The PDLCLV has many features suitable for large screen displays, such as no polarizer requirement, a high transmittance (72 to 78%) and high extinction ratio (146:1 to 178:1) in the entire visible wavelength, short rise/decay times (3/5 to 14/15 ms), and a high resolution (34 lp/mm). We discuss the light scattering and modulation characteristics of the PDLC film; photoconductive characteristics of the BSO crystal; and the design, fabrication method, and optical input/output characteristics of the PDLCLV. We also describe the configuration and image display characteristics of a monochrome projection-type display consisting of the PDLCLV as an image converter, an active matrix liquid crystal panel with thin film transistors as an image source, and a 1-kW xenon arc lamp as a reading light source.

Improvement of Interface State and Channel Mobility Using 4H-SiC (0-33-8) Face

In this paper, we characterized MOS devices fabricated on 4H-SiC (0-33-8) face. The interface state density of SiO2/4H-SiC(0-33-8) was significantly low compared to that of SiO2/4H-SiC(0001). The field-effect channel mobility obtained from lateral MOSFET (LMOSFET) was 80 cm2/Vs, in spite of a high p-well concentration of 5x1017 cm-3 (implantation). The double implanted MOSFET (DMOSFET) fabricated on 4H-SiC(0-33-8) showed a specific on-resistance of 4.0 mΩcm2 with a blocking voltage of 890 V.

CRYSTALLINITY OF YBA2CU3O7-X SINGLE CRYSTALS GROWN BY THE PULLING METHOD

Large YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} (Y123) single crystals (larger than 13 mm cubed) have been grown along the {ital c}-axis reproducibly by the modified pulling method. The crystallinity of {ital Y}123 single crystal was investigated by a x-ray diffraction and a x-ray topography. Crystals grown from an MgO single crystal seed had some low angle subgrain boundaries which tilted 0.1{endash}0.8{degree} from each other. These grain boundaries originated from the seed crystal, and the subgrains were extended along the growth direction from the seed crystal. Y123 single crystals with no marked subgrains in the whole area were obtained by using Y123 single subgrain crystal seeds. FWHM of the x-ray rocking curve for the crystal so produced was about 0.14{degree}, which was much better than the spectrum consisted of several separated peaks obtained from the previous crystals.{ital T}{sub {ital c}} onset of the annealed sample was about 93.6 K, the transition width was about 0.9 K. The low angle subgrain boundaries did not seem not to be effective pinning centers for the magnetic flux. {copyright} {ital 1996 Materials Research Society.}

High Channel Mobility of 4H-SiC MOSFET Fabricated on Macro-Stepped Surface

Improvement of the channel mobility is needed in 4H-SiC MOSFETs for the maximum utilization of the material potential for novel power devices. We have attempted to obtain smoother MOS interfaces as one of the ways to reduce the interface states which lead to decrease of the channel mobility. We formed a terrace on the macro-stepped surface by annealing in Si melt and found that it was atomically flat. We fabricated a lateral MOSFET on the macro-stepped surface and obtained a high MOS channel mobility of 102 cm2/Vs.

Investigation of a Sic Module with a High Operating Temperature for Power Applications

A silicon carbide (SiC) module with a high operating temperature has been designed, fabricated and tested at a device temperature of 200degC. The module has a multi- layered structure consisting of a SiC chip, a direct bond copper (DBC) SiN ceramic substrate, a copper-based plate, and water-cooled heatsink. The module was designed to have a temperature distribution of 200degC at the chip joint, 150degC at the DBC substrate joint and 65degC at the heatsink. A lead-free high temperature solder made of Au-Sn alloy was chosen to connect the SiC chip/DBC substrate joint in order to withstand the device temperature of 200degC. The joint of the DBC substrate/copper based plate was completed with Sn-Ag-Cu lead-free solder. The module was assembled by using a two- step reflow process for the above joints. The reflow conditions were optimized to reduce the void-area ratio to less than 5% for both solder junctions. High temperature aging tests were carried out for 1000 h at 150degC and 200degC, and for 600 h at 250degC. No significant cracks were observed in the Au-Sn solder joint after the 250degC test. A crack appeared in the Sn-Ag-Cu solder joint after 600 h in the 200degC test. The module was operated by feeding a 100 A DC current into the SiC device to maintain the device temperature at 200degC. A high operating temperature test was performed on the module for 12 h to confirm its reliability, and no significant degradation was observed. The temperature distribution was also measured in this test and compared with simulation results. The two temperature distributions were in good agreement. The results confirmed the possibility of applying this mounting technology to a SiC module for use at a high operating temperature of 200degC.

Polymer-dispersed liquid-crystal light valves for projection display application

This paper describes the polymer-dispersed liquid crystal light valve (PDLCLV) using a polymer-dispersed liquid crystal (PDLC) film and a photoconductive crystal. Bi12SiO20 (BSO) and its application to projection displays. The PDLCLV has many features suitable for large screen displays, including no requirement of polarizers, high transmittance, and high-speed response. We discuss the light scattering and modulation characteristics of the PDLC film, photoconductive characteristics of the BSO crystal, and the design, fabrication and optical input/output characteristics of the PDLCLV. We also describe the configuration of a monochrome projection display consisting of the PDLCLV as an image converter and a liquid crystal panel with thin film transistors as an image source and its image display characteristics.

Structure Analysis of In-Grown Stacking Faults and Investigation of the Cause for High Reverse Current of 4H-SiC Schottky Barrier Diode

Two types of structures related to in-grown SF having a different influence on reverse currents of 4H-SiC SBDs were investigated. One type contained only a single SF formed by 1c of 8H poly-type and showed low reverse currents. The other type was accompanied with short SFs which consisted of 3C poly-type in addition to two SFs formed by 1c of 8H poly-type and showed high reverse currents. SF formed by 1c of 8H poly-type was not the cause of the high reverse current, and we speculate that the barrier height lowering at the short SF attributed to the high reverse currents of SBDs.

Expansion of Stacking Faults by Electron-Beam Irradiation in 4H-SiC Diode Structure

The influence of electron-beam irradiation on defects in 4H-SiC diode structures was investigated by cathodoluminescence (CL) microscopy and spectroscopy. In addition to threading edge and screw dislocations, two types of stacking faults (SFs) were characterized by their emission energy, geometric shape, and the sensitivity of electron-beam irradiation. The SFs at λ = 425 nm (2.92 eV) expand from the surface of basal plane dislocation with line direction [11-20] and change their geometric shape by electron-beam irradiation. The SFs at λ = 471 nm (2.63 eV) are only slightly influenced by electron-beam irradiation. The former corresponds to the Shockley-type SFs previously observed in the degraded p-i-n diodes, and the latter to in-grown SFs with 8H structure. The panchromatic CL images constructed by the sum of monochromatic CL images suggest that there are nonradiative recombination centers in the vicinity of Shockley-type SFs. The nucleation sites and the driving force for SF expansion are discussed.

Process and mechanism of growth of YBa 2 Cu 3 O 6+x single crystal by the pulling method

Continuous growth of YBa2Cu3O6+x(Y123) single crystals was achieved by the modified pulling method1 using BaO+CuO(3:5) solvent and Y2BaCuO5(Y211) solute. Y211 solid was placed at the bottom of the crucible. Temperature was set ten degrees higher at the bottom than on the surface of the solution. The crystal rotation speed was 120 rpm at first; but as the crystal radius increased, it was reduced to prevent increasing the interface temperature. The maximum crystal growth rate was about 0.2 mm/h. The crystal growth direction was controlled by the seed crystal direction.2 Two-dimensional numerical simulation was performed using a finite-difference method by a supercomputer to investigate the solution flow and temperature distribution.