Shuroku Sakurada

Ultrahigh-voltage high-current gate turn-off thyristors

High-power GTOs with ratings of 2500 V . 2000 A have been developed, and a 4500 V . 2000 A GTO was trial fabricated and performance tested, for use in traction motor control equipment. Their low ON-state voltage was attained by applying a unique anode emitter shorting structure which does not require doping of a lifetime killer such as gold to obtain suitable GTO characteristics. Their high interrupt current was obtained by introducing a ring-shaped gate structure which has uniform operation between many segments in the devices during turn-off process.

A new buried-gate GTO structure having a large safe operating area

A novel structure of a buried-gate GTO (gate turn-off thyristor) was proposed for expanding the safe operating area (SOA) of unit-GTOs. The SOA of unit-GTOs in a test sample GTO and the spike voltage at the limit of turn-off of the test sample were investigated experimentally. The SOA was calculated by means of a simple model in order to study the mechanism of the expansion of SOA in the structure. The SOA was expanded due to the reduction of the sheet resistance of the p-base layer by the fine mesh pattern of the buried layer. Corresponding to the increased size of the SOA, the spike voltage increased to 1000 V. >

Investigation of Low Loss and High Reliability Encapsulation Technology in Large-Area, High-Power Semiconductor Devices

In order to realize uniform and low contact resistance in the low mounting force region for large-area, high-power semiconductor devices, the effects of hardness and surface cleanliness of metal sheets inserted between an Al cathode and Mo internal electrode on the contact resistance were investigated as a function of mounting force. Contact resistance was lowered with increasing cleanliness and decreasing hardness of the inserted sheet for all values of the mounting force. A new process was developed in which an Ag-plated Mo sheet is heat-treated at 573 K for 15 min in air. It was confirmed that devices with the new Ag-plated Mo sheet have efficient long form reliability. The contact resistance and its dependence on the mounting force of the devices using this sheet are of the same level as those of an Ag-sputtered Mo sheet and an Ag sheet.