Koji Hotta

Mechanical stress dependence of power device electrical characteristics

This paper describes how mechanical stress affects the electrical characteristics of a power device, depending on the surface structure of the device or the device type. Experimental results show that devices in which the current flow direction is vertical to the substrate, such as trench structure devices, are affected the least by mechanical stress

Effects of uni-axial mechanical stress on IGBT characteristics

This paper describes the impacts of mechanical stress on vertical power devices. The stress dependence of the DC characteristics of trench insulated gate bipolar transistors (IGBTs) was measured. The experimental results could be reproduced by the device simulation, which included stress dependence models of the carrier mobility and the band gap. We found that the stress dependence of the on-state voltage mainly arose from the MOSFET portion of the IGBT. Using the device simulation, we estimated the effects of mechanical stress on the surge voltage and the saturation current, which give us the important information for designing a power module with higher ruggedness.

An abnormal turn-off surge suppression concept for PT-IGBTs at high voltage operation

In this paper, we investigate the turn-off surge behavior of PT-IGBTs, and in particular, abnormal increases in surge voltage appearing at high voltage conditions, which are required for a hybrid vehicle with a more powerful motor output. Simulation and experimental results showed that the abnormal surge voltage can be suppressed by increase of an extra-carrier at the interface between the n-drift and n+buffer layers, because the abnormal phenomenon resulted from depletion of the accumulated carrier during the turn-off period. This countermeasure is achieved by designing the PT-IGBT as the increase of the extra-carrier at the interface during the turn-off period. This allows reduction of the surge voltage, and thereby makes it possible to use the device for higher voltage operation over 600 V, such as in hybrid vehicle application, and consequently, to increase the motor power of the hybrid vehicle without sacrificing reliability and cost.