Hiroo Fuma

Current-Voltage and Capacitance-Voltage Characteristics of Metal/Oxide/6H-Silicon Carbide Structure

Current-voltage ( I-V ) and capacitance-voltage ( C-V ) characteristics of metal/ SiO2/6H-SiC structure fabricated on the concave surface in (000)C-face 6H-SiC p/n double epitaxial wafers were studied. Breakdown field of thermally grown gate oxide and effective charge density at SiO2/6H-SiC interface on sloped surface of the metal/oxide/semiconductor (MOS) structure were measured for the first time to be 9.2 MV/cm and 2.2-2.5×1012 cm-2, respectively, for both p- and n-epilayers. Fabricated SiC CONCAVE-MOS field-effect-transistor (FET) including the concave MOS structure achieved FET operation with blocking voltage of 250 V. Temperature dependence of the threshold voltage was -27 mV/K, which is considerably larger than the ideal value of -1.6 mV/K, due to high interface state density.

High temperature operated enhancement-type β-SiC MOSFET

Enhancement-type β-SiC MOSFETs have been fabricated on a single crystalline β-SiC layer grown on a 3-inch Si(100) substrate by chemical vapor deposition. The MOSFETs fabricated by applying the reactive ion etching technique show reasonable I-V characteristics at room temperature. The saturation tendency of the drain currents has been observed at a drain voltage as high as 18 V. The MOSFETs operate even at 350°C.

Fabrication of MOSFETs on β-SiC Single Crystalline Layers Grown on Si(100) Substrates

High temperature semiconductor devices are desirable for electronic control systems in automobiles. Silicon carbide is a promising semiconductor material for this purpose, because of its wide bandgap and physical stability[l]. Many devices fabricated in silicon carbide material have been reported[2–6]. Recently, a depletion-mode MOSFET, operating at 650°C, was reported by Palmour et al.[7]; this report demonstrates the high temperature capabilities of SiC devices.

Direct Observations of the 500 MHz Q-Patterns from the 10 and 35 GHz SQUID's

The 500 MHz Quantum Interference patterns (Q-patterns) beyond 100 MHz previously reported have been directly observed for the first time from 10 and 35 GHz Superconducting Quantum Interference Devices (SQUIDs). The observation was made by improving the bandwidth of the detection circuits, which was supposed to be the cause of the previous limitation on Q-patterns from the 10 and 35 GHz SQUIDs. An improved system including a 10 or 35 GHz SQUID has possible applications to the measurement of signals due to even faster magnetic flux changes.

An Ultrafast Operation of Microwave SQUID's Biased at 35 GHz

A microwave SQUID biased at 35 GHz with a Nb point contact has been improved in its characteristic performance, by changing the configuration of a SQUID, from the 35 GHz size to the 9 GHz size which is oversize for the 35 GHz microwave. About a 10 times larger signal output and higher frequency response up to 100 MHz have been directly obtained. Further, it has been confirmed for the first time that the SQUID biased at 35 GHz does respond up to the 9 GHz input signal by using the Bessel function method.