Shin Harada

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.

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.

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.

The Influence of In-Grown Stacking Faults on the Reverse Current-Voltage Characteristics of 4H-SiC Schottky Barrier Diodes

The area where 4H-SiC SBDs showed high reverse currents was extracted. After KOH etching, the in-grown SF on the basal plane, composed of a straight etch line with a pair of tilted oval pits and additional etch pits forming an isosceles triangle, was observed on some devices. All of the devices containing this SF structure showed large reverse leakage currents in spite of the good forward I-V characteristics. We speculate that this in-grown SF includes another planar fault on the {1-100} plane besides the basal plane which has a great influence on reverse currents of SBDs.

Development of SiC Power Module and Loss Evaluation in DC-DC Converter Circuit Application

The thermal management of power module is one of the key important issues for power conversion circuit design. SiC power module is expected to give less conduction and switching loss than conventional Si device, which enables to facilitate the thermal management of a power conversion circuit. This paper develops 2in1 Full-SiC power module and studies the applicability for 600V→300V, 15kW DC-DC buck converter. The feasible thermal design of SiC power module to serve rated operation of the converter circuit is discussed based on the elemental experiments. The developed full-SiC power module realized lower loss and smaller converter circuit than conventional-Si power module.

High Temperature Characteristics of 4H-SiC RESURF-Type JFET

400V/2.5A 4H-SiC JFETs having a reduced surface field (RESURF) structure were fabricated. Measurements on the on-resistance, blocking and switching characteristics at high temperature were carried out. It was confirmed that the JFET has smaller dependence of on-resistance on temperature than a Si-MOSFET and positive temperature dependence of the breakdown voltage. It was also confirmed that the JFET has fast switching characteristics, that is, the turn-on and turn-off times are about 15 ns and 10 ns, at 200 °C as well as at 25 °C. A demonstration of a DC-DC converter using a module consisting of the JFET was carried out at a junction temperature of 200 °C. Stable continuous switching operation of the JFET at a junction temperature of 200 °C was confirmed.

Fast Switching Characteristics of 4H-SiC RESURF-Type JFET

400V/2.5A 4H-SiC JFETs having a reduced surface field (RESURF) structure were fabricated. Measurements on the static and switching characteristics were carried out. The on-resistance was 0.86 W. The turn-on time (ton) and the turn-off time (toff) were 8ns and 10 ns, respectively. The fabricated JFETs showed low on-resistance and fast switching characteristics. 4H-SiC RESURF-type JFETs, which is a sort of lateral transistor, are preferable to a module configuration of switching devices. Moreover, they are promising for application to DC power supplies with higher efficiency and smaller size owing to their low on-resistance and fast switching characteristics.

Fabrication of a multi-chip module of 4H-SiC RESURF-type JFETs

We fabricated a multi-chip module of 4H-SiC reduced surface field (RESURF)-type lateral JFETs. A single chip consists of 4 unit devices of 2.0 mm × 0.5 mm in size, which were isolated electrically from each other. The multi-chip module consists of 8 chips mounted on an AMC substrate. The drain current and the breakdown voltage of the module are over 3 A and 771 V, respectively. The turn-on time and the turn-off time are 36ns and 166ns, respectively. The module resistance is proportional to the absolute temperature to the 1.05th power.