Tsutomu Yatsuo

Design considerations for large-current GTOs

The current crowding of a GTO during turn-off operation and the limits to operating without breakdown were investigated by a newly developed measurement method of current distribution and by computer simulation. Design considerations for large-current GTOs were clarified as follows: to increase the maximum turnoff current, current crowding is suppressed by a gate structure optimized for the distribution of a steady on-state current, and the maximum current flowing into a unit GTO is reduced in a safe operating area by optimizing the number of unit GTOs. The characteristics of a 4000-A GTO trial-fabricated under these design considerations are shown to confirm the validity of the design assumptions. >

Low leakage current Schottky barrier diode

low forward voltage drop 0) compared to that of a pn junction diode, but has a serious problem of a large leakage current. No solution to the problem has been found which does not cause fatal increase in the FVD. We have examined a structure, in which the parallelly arranged Schottky junctions are put between the pn junctions. The device parameters to improve the trade-off between FVD and leakage current density were found through calculations. The effectiveness of the parameten was coniirmed by the experiments using the new structure. A Schottky barrier diode (SBD) has an advantage of

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 snubber-less GTO

Measurements of gate turn-off performance of GTOs have been made in terms of the safe operating area. The feasibility of the snubber-less GTO capable of 60 amperes controlling and 600 volts blocking has been demonstrated.

High speed, high current capacity LIGBT and diode for output stage of high voltage monolithic three-phase inverter IC

Structure of a high speed, high current capacity Latelal Insulated Gate Bipolar Transistor (LIGBT) and a diode for a 250V1A monolithic three-phase inverter IC are studied. A hybrid structure between Schottky junctions and pn junctions is effective for the diode, but not for the LIGBT. Characteristics of the IC using the LIGBT and diode are also presented.

Diode-integrated high speed thyristor

A diode-integrated high speed thyristor formed into one body by using a separation region for preventing interference between a thyristor and a diode.

A high power IGBT module for traction motor drive

A 2000-V, 300-A insulated-gate bipolar transistor (IGBT) module consisting of six IGBT chips and two soft-and-fast recovery diode (SFD) chips has been fabricated for the inverter of a traction motor. The module structure and chip layout were designed to provide sufficient reliability and uniform operation among chips. The main electrical characteristics which were obtained from the tradeoff relations between on-state voltages and switching losses of 2000-V chips, namely, a saturation voltage of 3.5 V, a forward voltage of 2.7 V, and a typical turn-off time of 5 mu s, are well suited to driving a motor at a high frequency.<<ETX>>

Design consideration for large current GTO

Current crowding of a GTO (gate-turn-off) during turn-off operation and operating limits without breakdown were investigated by a current-distribution-measurement method and by computer simulation. It was found that to increase the maximum turn-off current, current crowding is suppressed by a gate structure optimized for the distribution of a steady on-state current. Also, current flowing into a unit GTO is reduced by optimizing the number of unit GTOs so that they are operating in a safe operating area. The characteristics of a 4000 A trial GTO fabricated on the basis of these considerations are reported.<<ETX>>

Over 2000 V FLR termination technologies for SiC high voltage devices

The Field Limiting Ring (FLR) termination structures are examined in order to confirm the high voltage technology of SiC diodes and FETs. Elemental devices with planar FLR terminations are fabricated and their reverse I-V characteristics are determined using 4H n-type SiC. First demonstrations of breakdown voltages higher than 2000 V are succeeded by using FLR terminations. Optimal FLR spacing of the boron termination is wider than that of the aluminum case. This difference is considered to show that the lateral diffusion is remarkable for the process using boron implantation.

A high-voltage light-activated thyristor with a novel over-voltage self-protection structure

A new type of high voltage self-protected thyristor with a well structure formed in its p-base layer is described. The device structure is simple and easy to fabricate compared to past devices. Numerical analyses and experiments demonstrate that the breakover voltage of this thyristor can be controlled by varying the well diameter and its depth. The breakdown voltage fluctuation of the device is 10% when the junction temperature is varied from 23°C to 100°C. This device is turned on safely at 7300 V. Fabricated devices show no degrading in important thyristor features.