Riteshkumar Bhojani

Dynamic self-clamping at short-circuit turn-off of high-voltage IGBTs

Measurements show that the IGBT is able to clamp the collector-emitter voltage to a certain value at short-circuit turn-off despite a very low gate turn-off resistor in combination with a high parasitic inductance is applied. The IGBT itself reduces the turn-off diC/dt by avalanche injection. However, device destructions during fast turn-off were observed which cannot be linked with an overvoltage failure mode. Measurements and semiconductor simulations of high-voltage IGBTs explain the self-clamping mechanism in detail. Possible failures which can be connected with filamentation processes are described. Options for improving the IGBT robustness during short-circuit turn-off are discussed.

Requirements in power cycling for precise lifetime estimation

Abstract This paper discusses power cycling as a method to evaluate the reliability of interconnections in power electronic devices. While the approach proved a reliable tool for investigating the potential of improvement for alternative interconnect technologies and rejecting design flaws, precise estimations about lifetime in the field are still challenging. Many questions are still in discussion, such as ultra-high cycle fatigue, applicability of Miners rule, or the influence of on-time and cross-effects with mechanical shocks or humidity. This leaves application engineers with a blurred safety margin. In the following basic considerations of power cycling are described. The introduction shows two applications with different load profiles. Section 2 explains methods of temperature measurement. In Section 3 theoretical requirements for measurement accuracy are given, the obstacle minimal measurement delay and possible workarounds are evaluated. Finally aging effects and their acceleration in different devices are discussed in Section 4. In the conclusion suggestions for power cycling methods and a revision of the end-of-life criteria are made.

Methods for virtual junction temperature measurement respecting internal semiconductor processes

This paper discusses the limitation in measurement accuracy of junction temperature measurements of bipolar devices. A limiting factor the measurement delay, caused by slow removal of charge carriers, was investigated by single pulse measurements and evaluated by simulations. A minimal measurement delay of 650μs was found for a 6.5 kV IGBT at high temperature.

Measurement of a complete HV IGBT I-V-characteristic up to the breakdown point

This paper describes how to measure the complete output characteristic of a high-voltage IGBT non-destructively up to the breakdown point and beyond. Hereby, a deep knowledge of the IGBT behaviour at high voltages and saturation currents is gained. To construct the complete characteristic, short-circuit and curve-tracer measurements are combined. The results are compared and recapitulated with semiconductor simulations of IGBT models fitted to experimental characteristics.

Unified view on energy and electrical failure of the short-circuit operation of IGBTs

Abstract This work investigates the relation of the two destruction modes, the so-called energy destruction and the electrical destruction, during short-circuit operation of an Insulated Gate Bipolar Transistor (IGBT). The critical energy as a function of the short circuit current reveals a kink indicating the transition between two different failure modes. The failure signatures show that energy destruction takes place at lower currents and electrical destruction at higher currents. This supports the hypothesis that there is a huge current range with non-destructive filaments at low dc-link voltages. For both destruction mechanisms, the final failure occurs locally. For the energy destruction, the current crowding happens very late during the runaway itself, whereas in the case of an electrical destruction, filaments are formed mainly by an electrical mechanism leading to a stronger local self-heating. Both mechanisms take place far above the safe operating area of the chip.

A novel Injection Enhanced Floating Emitter (IEFE) IGBT structure improving the ruggedness against short-circuit and thermal destruction

In this work, we introduce a new collector IGBT structure that shows a huge improvement of the short-circuit (SC) ruggedness without deteriorating the static and dynamic losses of the device. The Injection Enhanced Floating Emitter (IEFE) concept enhances the emitter efficiency at the collector side by means of higher hole current injection which increases the bipolar current gain of the IGBT device. The simulation results indicate that the proposed structure can suppress a SC turn-off failure due to an electrical current crowding to a considerable extent. The critical pulse width to avoid thermal runaway of the leakage current after the SC event can be increased.

Internal processes in power semiconductors at virtual junction temperature measurement

Abstract High measurement accuracy is the basis for a precise determination of the junction temperature T j . Temperature measurement can be performed by means of temperature sensitive parameters (TSP) using the V CE (T)-method, however, internal semiconductor processes like the removal of stored charge in bipolar devices have to be respected. The aim of this work is to determine the earliest time point of accurate measurement t MD after switching off, as well as dependencies on device voltage classes and applied battery voltage. Measurement results are confirmed by performing the simulation with Sentaurus TCAD. Dependencies of delay t MD on temperature, applied measurement current and battery voltage are demonstrated for IGBT and silicon diode.