Yoshifumi Tomomatsu

A study on the short circuit destruction of IGBTs

The short-circuit destruction of class n-ch 600-V IGBTs (insulated-gate bipolar transistors) is investigated experimentally and analyzed with the help of device simulation, focusing on three major destruction modes (power constant, energy constant, and turn-off destruction). Measured power dissipation for power constant destruction is 2000 approximately 2400 kW/cm/sup 2/, which coincides with the simulation result. The energy constant destruction and turn-off destruction are found to depend on the thermal effect. The critical temperature for destruction is predicted to be 350 degrees C.<<ETX>>

A new generation high speed low loss IGBT module

By virtue of simulation and advanced process technologies the IGBT and the fast recovery diode chip structures have been modified to develop new generation low-loss power chips. These newly structured chips have been integrated into a moduler housing to form a 100A,600V dual type IGBT module that has exhibited superior characteristics, particularly in terms of reducing operational power loss over the conventional second generation counterpart. This paper will give details of this new generation IGBT module development and describe its characteristical superiority.

An analysis and improvement of destruction immunity during reverse recovery for high voltage planar diodes under high dIrr/dt condition

Computer simulation for reverse recovery characteristics of a planar diode revealed that local heating occurred at the corner of the anode even when a surge voltage across the diode was lower than its static breakdown voltage. Analysis for origin of local heating resulted in a design principle for improving destruction immunity of the diode. Diodes designed according to the present principle showed excellent destruction immunity under high dIrr/dt condition.

High voltage IGBT (HV-IGBT) having p/sup +//p/sup -/ collector region

For high voltage IGBTs (HV-IGBTs; rated collector voltage over 2.5 kV), it is very important that the thickness of the n/sup -/ layer (tn/sup -/) is thin to improve the trade-off relationship between collector-emitter saturation voltage (V/sub ce/(sat)) and turn-off switching loss (E/sub off/). A punch-through IGBT (PT-IGBT) with n/sup +/ buffer layer thus has a better trade-off than that of a nonpunch-through IGBT (NPT-IGBT) without the n/sup +/ buffer layer. However, the HV-IGBT with thin tn/sup -/ has much worse characteristics in that collector leakage current (I/sub CES/) is high and reverse bias safety operating area (RBSOA) is narrow. In order to solve these problems, we examined the collector region of a PT-IGBT. In this paper, we developed a HV-IGBT with a p/sup +//p/sup -/ collector region which has better characteristics in terms of the trade-off relationship between V/sub CE/(sat) and E/sub off/, and a wide RBSOA.

An analysis for transient characteristics of shorted collector IGBTs in free wheeling mode of operation

Computer simulation analysis predicts that shorted collector IGBT is heated locally in free wheeling mode of operation to such extent that excess temperature, depending on operating and circuit conditions, destroys itself and this is verified by experiment.

A novel buffer structure and lifetime control technique with Poly-Si for thin wafer diode

A novel buffer structure for improving the trade-off between forward voltage and reverse recovery loss across the whole range of current density and realizing the softness during reverse recovery was developed. The structure named a “Broad Buffers from Double Sides structure” (BBDS) is composed a broad p- anode layer and a broad n- buffer layer. A novel technique called “Local Lifetime control technique with Poly-Si layer” (LLP) was also developed. LLP controls the conductivity modulation level without introducing recombination centers in the n- layer. Combining these new techniques, namely, BBDS and LLP, made it possible, for the first time, to create a fast-recovery diode without the need to use conventional heavy-metal diffusion or irradiation methods.