Katsumi Satoh

A newly structured high voltage diode highlighting oscillation free function in recovery process

At present, switching devices with high performance such as GCT (Gate Commutated Turn-off) thyristor and IGBT which had higher operation voltage than about 4.5 kV have been realized. However, as a freewheeling diode which should realize the suitable recovery performance to the turn-on performance of those switching devices is not successful, they were restricted in the turn-on operation for inverter systems. Therefore, advanced diodes with high operation voltage and soft recovery performance are desired in order to improve the system performance.

New design approach for ultra high power GCT thyristor

Turn-off capability is a major concern when designing ultra high power, large size GCTs (gate commutated turn-off thyristors). Unlike small size GCTs, which have a high turn-off capability, conventional large size GCTs have a low turn-off capability that is not proportionate to its high power. With the help of computer simulation and test sample evaluation, we developed a new design approach for ultra high power GCTs with improved turn-off capability. Turn-off simulation suggested that the low turn-off capability of large size GCTs is related to the nonuniformity in the GCT chip design. Optimizing the GCT chip uniformity following our new design approach resulted in large size GCTs with higher turn-off capability when compared with the conventional approach.

The present state of the art in high-power semiconductor devices

Since the mid-1990s, thyristors and GTO capacities have been increased, resulting from the use of 6-in floating zone (FZ) Si wafers (which were developed in 1993) and the integration of new technologies for wafer processing and design (also developed in the 1990s). As devices have become more capable, the next step in moving forward is to take these self-turnoff devices and bring higher performance to power electronics, thereby widening the application field.

High power symmetrical GCT for current source inverter

GCT (gate commutated turn-off thyristor) is a new high power device with snubberless turn-off operation which was developed in the mid-1990s, and is growing up to be the main device instead of GTO (gate turn-off thyristor) for high power application. For PWM current source inverters used in AC drive, symmetrical GCT with reverse blocking characteristics are expected. However, the symmetrical structure generally gives smaller turn-off capability compared with asymmetrical GCT, which has already been developed. This paper presents new GCT technologies, characteristics of 6 kV/4 kA symmetrical GCT and comparison of loss between current source inverter and voltage source inverter by using GCT.

8 kV/3.6 kA light triggered thyristor

We have developed a light triggered thyristor with the blocking voltage of 8 kV and the average current of 3.6 kA by using a 6 inch FZ Si wafer and adopting new design techniques. The new multidynamic gate structure achieved a high di/dt capability at the rating voltage. The new arrangement of pilot thyristors made the dv/dt capability high. Additionally, optimizing the new local lifetime control technology by proton irradiation improved the trade-off relationship between the on-state voltage and the reverse-recovered charge.

6 kV/4 kA gate commutated turn-off thyristor with operation DC voltage of 3.6 kV

Recently, a 4.5 kV/4 kA gate commutated turn-off thyristor (GCT) has been successfully introduced to the market. The GCT is a new high power device which has not only the same high blocking capability and low on-state voltage as the GTO, but also the same high turn-off performance as the IGBT. In order to ascertain the possibility of GCT use in higher voltage areas, a 6 kV/4 kA GCT with a DC operating voltage of 3.6 kV (long term DC stability of 100 FIT) has been developed by the adoption of the PT structure and local lifetime control, and has been evaluated. The results achieved indicated that the GCT may become a main high power device for high power applications.

4.5 kV soft recovery diode with carrier stored structure

In terms of recovery performance, freewheeling high voltage diodes have two problems: low di/dt capability and the oscillation of both anode voltage and anode current. In order to prevent the oscillation, a soft recovery performance is required, but this alone is not sufficient. However, a carrier stored diode with comb-like N/sup +/ structure was thought to minimize the oscillation. This diode produced a recovery performance which was near the theoretically predicted level. Considerations for the triggering of the oscillation and the dynamic characteristics data of the comb-like N/sup +/ diode is presented.

12kV, 1kA thyristor

The u l t r a h i g h b l o c k i n g v o l t a g e t h y r i s t o r w i t h b l o c k i n g v o l t a g e s of 12kV and t h e a v e r a g e o n s t a t e c u r r e n L of 1kA w a s r e a l i z e d . I n o r d e r t o o b L a i n h i g h b l o c k i n g v o l l a g e s and t h e low on-sLaLe v o l t a g e , d i f f u s i o n p r o c e s s e s and t h e g a t e and c a t h o d e s L r u c L u r e were o p t i m i z e d and t h e f u l l p r e s s u r e c o n t a c l s t r u c l u r e w a s employed. T h i s p a p e r e x p l a i n s t h e s t r u c t u r e and t h e e l e c t r i c a l c h a r a c L e r i s t i c s o f t h i s d e v i c e .