Papers by Author: Hiroki Niwa

Abstract: In this study, to demonstrate the potential of the SiC-IGBT for high voltage application, we fabricated 13 kV class SiC-IGBT, and evaluated static characteristics and the ruggedness. The on-state forward voltage of 5.2 V at a collector current density of 100 A/cm² was obtained, and the breakdown voltage of 13.7 kV was achieved. Successful evaluation of SCSOA was obtained under the collector voltage of 4.6 kV, and utilizing the optimized layout with low saturation current, we realized the increase of the short circuit time. RBSOA turn-off was successfully achieved without any breakdown by latch up mode under the collector voltage of 4.0 kV and current density of 900 A/cm².

Abstract: Ultrahigh-voltage SiC PiN diodes with an original junction termination extension (JTE) structure and improved forward characteristics are presented. A space-modulated JTE (SM-JTE) structure was designed by device simulation, and a high breakdown voltage of 26.9 kV was achieved by using a 270 μm-thick epilayer and 1050 μm-long JTE. In addition, lifetime enhancement process via thermal oxidation was performed to improve the forward characteristics. The on-resistance of the SiC PiN diodes was remarkably reduced by lifetime enhancement process. The temperature dependence of the on-resistance was also discussed.

Abstract: Impact ionization coefficients of 4H-SiC were measured at room temperature and at elevated temperatures up to 200°C. Photomultiplication measurement was done in two complementary photodiodes to measure the multiplication factors of holes (M_p) and electrons (M_n), and ionization coefficients were extracted. Calculated breakdown voltage using the obtained ionization coefficients showed good agreement with the measured values in this study, and also in other reported PiN diodes and MOSFETs. In high-temperature measurement, breakdown voltage exhibited a positive temperature coefficient and multiplication factors showed a negative temperature coefficient. Therefore, extracted ionization coefficient has decreased which can be explained by the increase of phonon scattering. The calculated temperature dependence of breakdown voltage agreed well with the measured values not only for the diodes in this study, but also in PiN diode in other literature.

Abstract: Breakdown characteristics of 4H-SiC PiN diodes with various JTE structures have been investigated. By combining two-zone JTE and Space-Modulated JTE (SM-JTE), a breakdown voltage over 15 kV, corresponding to about 93 % of the parallel-plane breakdown voltage, was realized. The window of optimum JTE dose to obtain high breakdown voltage was widened, which indicates the robustness to the deviation of JTE dose. By comparing the breakdown voltage obtained by simulation and experimental results, impacts of the charge near the SiO₂/SiC interface are discussed.