Papers by Author: Hiroshi Kimura

Abstract: The SiO₂/SiC interface quality has a significant effect on the performance of 4H-SiC MOS devices. The introduction of nitrogen to the SiO₂/SiC interface is a well-known method for reducing the interface state density (D_it). In this study, we introduced nitrogen to the SiO₂/SiC interface by forming SiN_x films using atomic layer deposition (ALD) and thus improved the interface quality. O₂ annealing with a SiN_x interface layer of optimal thickness enhanced the field effect mobility.

Abstract: A critical issue with the SiC UMOSFET is the need to develop a shielding structure for the gate oxide at the trench bottom without any increase in the JFET resistance. This study describes our new UMOSFET named IE-UMOSFET, which we developed to cope with this trade-off. A simulation showed that a low on-resistance is accompanied by an extremely low gate oxide field even with a negative gate voltage. The low R_onA was sustained as V_th increases. The R_onA values at V_G=25 V (E_ox=3.2 MV/cm) and V_G=20V (E_ox=2.5 MV/cm), respectively, for the 3mm x 3mm device were 2.4 and 2.8 mWcm² with a lowest V_th of 2.4 V, and 3.1 and 4.4 mWcm² with a high V_th of 5.9 V.

Abstract: 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.

Abstract: 4H-SiC(000-1) C-face was oxidized in H₂O and H₂ mixture gas (H₂ rich wet ambient) for the first time. H₂ rich wet ambient was formed by the catalytic water vapor generator (WVG) system, where the catalytic action instantaneously enhances the reactivity between H₂ and O₂ to produce H₂O. The dependence of SiC oxidation rate on the H₂O partial pressure was investigated. We fabricated 4H-SiC C-face MOS capacitor and MOSFET by the H₂ rich wet re-oxidation following the dry O₂ oxidation. The density of interface traps was reduced and the channel mobility was improved in comparison with the conventional O₂ rich wet oxidation.

Abstract: In this paper, we demonstrate the fabrication of SBD utilizing SiC process line specially designed for mass production of SiC power device. In SiC power device process, ion implantation and activation annealing are key technologies. Details of ion implantation system and activation annealing system designed for SiC power device production are shown. Further, device characteristics of SBD fabricated using this production line is also shown briefly.

Abstract: SiC power module with low loss and high reliability was developed by utilizing IEMOSFET and SBD. The IEMOSFET is the SiC MOSFET with high channel mobility in which the channel region is the p-type carbon-face epitaxial layer with low acceptor concentration. Elemental technologies for the high channel mobility and the high reliability of the gate oxide have been developed to realize the excellent characteristics by the IEMOSFET. The SBD was designed so as to minimize the forward voltage drops and the reverse leakage current. For the fabrication of these SiC power devices, the mass production technology such as gate oxidation, ion implantation and following activation annealing have been also developed.

Abstract: The 1200V class silicon carbide Schottky barrier diodes were designed and fabricated. The drift layer resistance was reduced in order to realize low forward voltage drops. Since the low drift layer resistance led to the low breakdown voltage, the avalanche withstanding capability should be enhanced not to cause the destructive breakdown. By means of the optimized device design, we succeeded to realize the low forward voltage drop while maintaining the high avalanche withstanding capability. The forward voltage drops at 200A/cm² were 1.35V at 25°C and 1.63V at 175°C, respectively. The avalanche withstanding capability was more than 3500mJ/cm² at 25°C. By substituting SiC-SBDs for Si-pin diodes, the estimated total power loss of the module comprised by Si-IGBTs and the diodes was reduced by 35%. We could also confirm that no failures happened after long term reliability tests.