Sven Matthias

Field Shielded Anode (FSA) concept enabling higher temperature operation of fast recovery diodes

In this paper, we introduce the Field Shielded Anode (FSA) concept that enables higher temperature operation of fast recovery diodes with planar junction termination. Conventional diodes utilizing local lifetime control principles show excellent dynamic properties at the expense of a higher leakage current, which is generated during reverse blocking when the space charge region penetrates into the zone containing the radiation defects. In contrast to this, the FSA concept spatially separates the space charge region from the zone with the radiation defects. The ruggedness of conventional diodes can be exceeded with the new FSA concept, while the leakage current is reduced by a factor of ∼4. This was achieved using a special junction extension introduced between the active area and the guard-ring termination. The design parameters and their influence on the softness and the safe-operating area are presented.

Bipolar transistor gain influence on the high temperature thermal stability of HV-BiGTs

In this paper we present the detailed investigation of the influence of the internal bipolar PNP transistor gain on the thermal stability of high voltage IGBTs and BiGTs. The bipolar gain is controlled by means of anode and buffer design and by the introduction of anode shorts. The influence of the different buffer and anode doping profiles and the different layouts in the case of anode-shorted designs are analyzed. Temperature dependent leakage current measurements confirm that the lowering of the leakage current and its subsequent weak temperature dependency can be achieved by buffer and anode engineering albeit with certain design trade-off restrictions. Nevertheless, another effective approach for suppressing the leakage current and its dependency on temperature is achieved by the introduction of anode shorts as demonstrated in reverse conducting IGBT or BiGT structures. Such designs eliminate to a large extent the internal bipolar transistor action in the BiGT anode shorted designs while allowing different anode and buffer doping profiles for the design trade-offs. Despite the fact that the lifetime control in the BiGT drift region causes the leakage current to increase, the temperature coefficient remains unchanged, hence, making the hard switched BiGT suitable for high temperature operation.

Inherently soft free-wheeling diode for high temperature operation

Traditionally, the major driver in IGBT and diode development is to minimize the static and dynamic losses. A significant reduction of the n-base thickness would yield this, however it can also jeopardize the switching characteristic leading to high overshoot voltages during diode reverse recovery. In this paper, we present an improved Field-Charge Extraction (FCE) concept that is achieving a soft reverse recovery behavior inherently. The new design allows for a 10% reduction of the thickness of the diodes n-base, while still maintaining the blocking capability and the softness of the conventional diode. Therefore, the technology curve and the ruggedness are improved significantly.

1.7kV high-power IGBT fabrication by bonded-wafer-concept

Lower losses and higher performance levels at elevated junction temperatures require fabrication processes enabling full design-flexibility for the IGBT buffer and anode to meet application requirements for the ≤1.7kV voltage-range. Here we present the bonded wafer concept that is enabling high thermal stability and soft and high turn-off capability due to full design flexibility for the critical backside layers.