Frank Pfirsch

Cosmic radiation as a cause for power device failure and possible countermeasures

DC stress tests on high power semiconductor devices at nominal device ratings yielded unexpected device failures. Without prior indication the devices were destroyed spontaneously anywhere in the bulk. The failure rate depends exponentially on the applied voltage. By transferring the test setup into a salt mine 130 m below ground we were able to prove that cosmic radiation is the cause for these failures. So far the only means to reduce the failure rate is to reduce the maximum field within the device by appropriate design.

1200 V-trench-IGBT study with square short circuit SOA

In this paper, the authors discuss the design of a new 1200 V trench IGBT structure. The combination of well-designed trench cell geometry and a favourably adjusted vertical carrier concentration profile leads to a trench IGBT chip with both low static and dynamic losses and a degree of ruggedness similar to state-of-the-art planar cell nonpunch-through (NPT) IGBTs, especially excellent gate oxide properties, high turn-off capability and a square short circuit safe operating area up to 1200 V.

A novel 8 KV light-triggered thyristor with overvoltage self protection

We have fabricated a novel 8 kV light-triggered power thyristor with integrated overvoltage self-protection. The light-sensitivity was improved by a special groove structure. Four amplifying gate-stages together with an integrated currentlimiting resistor guarantee a safe and homogeneous turn-on behavior. An improvement of the dynamic and static power losses could be obtained by a local lifetime reduction and by a decrease of the penetration depths of the blocking pn-junctions.

Theory of abnormal thyristor forward voltage behavior

The on-state current-voltage characteristic of thyristors is investigated by numerical simulation. For sufficiently high p-base concentration-as already known-an abrupt increase in on-state voltage is observed above a critical current density. Driving the device to higher currents results in a reduction of on-state voltage. Similar results are obtained for thyristor profiles with very shallow emitters. An analytic model that explains the described phenomena from first principles and leads to a simple criterion for current limiting in terms of Gummel numbers and carrier mobilities is presented. >