Yusuke Zushi

A novel gate assist circuit for quick and stable driving of SiC-JFETs in a 3-phase inverter

A novel gate drive circuit for an SiC-JFET in a bridge circuit that ensures a quick and stable switching has been proposed and demonstrated. The gate voltage of an off-state transistor tends to rise up due to a steep drain-source voltage change caused by turning-on of the transistor in the other side of the bridge circuit. Even though the gate terminal is kept in the off-state by a voltage source, the abovementioned steep voltage change induces a non-off-state voltage across the parasitic inductance in the gate wiring. As a result, the capability of an SiC transistor for high switching speed in a bridge circuit is limited. The novel gate assist circuit using a PNP transistor with additional capacitors can overcome this limit. It was verified experimentally that the new gate assist circuit improves the turn-on delay time by approximately six fold and the turn-off time by 72%.

A Compact 5-nH One-Phase-Leg SiC Power Module for a 600V-60A-40W/cc Inverter

We have developed a small-volume, high-power-output inverter with a high output power density using SiC power devices. To fully utilize the advantages of SiC power devices, it is necessary to reduce the inductance of the power module. This is done by using a double-layer ceramic substrate, attaining a low inductance of 5 nH. A double pulse test was carried out up to 60 A under a DC voltage of 600 V. The low inductance greatly reduced the surge voltage and the oscillation at the switching transient. The SiC inverter with a volume of 250 cc was assembled using three of the power modules. The cooling performance of the inverter was evaluated at a loss equivalent to an output power of 10 kW, and it was found that the inverter can output 10 kW at a junction temperature (Tj) of about 200°C.

Eutectic Zn-Al Die Attachment for Higher Tj SiC Power Applications: Fabrication Method and Die Shear Strength Reliability

This paper comprehensively describes the fabrication method and shear strength reliability of a eutectic Zn-Al (m.p. = 382°C) attachment system, built by soldering SiC dice (2 × 2 mm2) onto Cu foil active-metal-brazed with a SiN ceramic plate. Four essential soldering conditions are presented and discussed for the formation of a strong and reproducible attachment. Die shear strength reliability data at Tj = 250°C are reported here for the first time. Storage tests at 250°C revealed that, after an initial slight decline, the die shear strength stayed virtually constant at a sufficient level (∼110 MPa) for at least 3,000 h. Thermal cycle test results indicated that the attachments can withstand thermal cycle stress for 3,000 cycles between −40°C and 250°C. The average die shear strength after 3,000 cycles was 18.5 MPa, a value that is three times higher than the IEC standard of 6.2 MPa specified in Document 60749-19.

Common Metal Die Attachment for SiC Power Devices Operated in an Extended Junction Temperature Range

A new high-temperature die attachment system that is cost effective has been strongly desired for SiC power applications in electric vehicles and consumer electronics. This paper presents preliminary results for SiC/Zn-Al/Cu-SiN die attachments using eutectic Zn-Al solder (m.p. = 356°C), focusing on preparation and die-shear reliability. Superior wettability and reproducibility were achieved in the soldering process. It was found that the attachments were viable at least for short-term application in a temperature range up to 300°C. Reliability test results revealed that they could withstand storage for 1500 hours at 200°C and thermal cycle stress of 1500 cycles between –40°C and 200°C.