Papers by Author: Takeo Yamamoto

Abstract: The impacts of threading dislocations, surface defects, donor concentration, and schottky Schottky barrier height on the reverse IV characteristic of silicon carbide (SiC) junction barrier schottky Schottky (JBS) diodes were investigated. The 100 A JBS diodes were fabricated on 4H-SiC 3-inch N-type wafers with two types of threading dislocation density. The typical densities are were 0.2×104 and 3.8×104 cm-2, respectively. The improvement of vIt was found that variations in the leakage current and the high yield of large area JBS diodes werecould be were obtained improved by using a wafer with a low threading dislocation density. In the range of low leakage current, the investigation shows showed a correlation between leakage current and threading dislocation density.

Abstract: A new method for the separation of threading screw dislocations (TSD) and threading edge dislocations (TED) in a 4H-SiC epitaxial layer is proposed by measurement of the etch pit angles. The etch pit angles of the TSDs and TEDs were 28±3 and 18±3°, respectively. In the case of etch pit depths within the epitaxial layer, the values were almost constant. Almost all of the TSDs were converted from basal plane dislocations (BPDs) at the epitaxial layer/substrate interface.

Abstract: 4H-SiC SBDs have been developed by many researchers and commercialized for power application devices in recent years. At present time, the issues of an SiC-SBD are lower on-state current and a relatively larger-leakage current at the reverse bias than Si-PN diodes. A JBS (Junction Barrier Schottky) diode was proposed as a structure to realize a lower leakage current. We simulated the electrical characteristics of JBS diodes, where the Schottky electrode was made of molybdenum in order to optimize its performance. We fabricated JBS diodes based on the simulation with a diameter of 3.9mm (11.9 mm2). The JBS diode has a lower threshold voltage of 0.45 V, a large forward current of 40 A at Vf = 2.5V and a high breakdown voltage of 1660 V. Furthermore, the leakage current at 1200 V was remarkably low (Ir = 20 nA).

Abstract: In this paper a novel approach to the design and fabrication of a high temperature inverter module for hybrid electrical vehicles is presented. Firstly, SiC power electronic devices are considered in place of the conventional Si devices. Use of SiC raises the maximum practical operating junction temperature to well over 200°C, giving much greater thermal headroom between the chips and the coolant. In the first fabrication, a SiC Schottky barrier diode (SBD) replaces the Si pin diode and is paired with a Si-IGBT. Secondly, doublesided cooling is employed, in which the semiconductor chips are sandwiched between two substrate tiles. The tiles provide electrical connections to the top and the bottom of the chips, thus replacing the conventional wire bonded interconnect. Each tile assembly supports two IGBTs and two SBDs in a half-bridge configuration. Both sides of the assembly are cooled directly using a high-performance liquid impingement system. Specific features of the design ensure that thermo-mechanical stresses are controlled so as to achieve long thermal cycling life. A prototype 10 kW inverter module is described incorporating three half-bridge sandwich assemblies, gate drives, dc-link capacitance and two heat-exchangers. This achieves a volumetric power density of 30W/cm3.