Thermal and electrical modeling of power electronics devices with emphasis on heat generation

The thermal-electrical behaviors of power electronics devices have been investigated in this dissertation, with emphasis on the heat generation in the power devices. Non-uniformity of the distribution of heat generation in power BJT transistors is first investigated. Due to the emitter current crowding, Joule heating occurs mainly at the base-emitter contact rather than distributing uniformly within transistor devices. In this dissertation, a heat generation model induced by current crowding is proposed. This model, in turn, is applied to the thermal calculation of typical multi-finger emitter structures of BJTs. The internal temperature distribution obtained from this model provides clear indication of the existence of hot spots in base-emitter contact region. The characteristics of the location and the magnitude of hot spots are also presented. Various pertinent effects due to the non-uniform heat dissipation are discussed. The result serves to locate potential hot spots, which must be considered to prevent thermal breakdown of power BJTs as well as other types of power devices.; A two-dimensional numerical thermal-electrical model is then established on a typical power MOSFET device. The temperature and heat generation distributions within the device are obtained and their effects on the device I-V characteristics are examined. An abrupt temperature step-up occurring before the traditionally known onset of the avalanche breakdown of the drain-body p-n junction is observed. It is found that although the highest temperature does not occur in the channel region, the temperature gradient in the horizontal direction along the channel is the highest in the device domain. It is also found the maximum heat generation occurs in the channel region for all of the computation cases. The magnitude of the heat generation in the channel region is found to be two orders higher than that in the drift region, which must be considered in the optimal design of power MOSFET devices for high temperature applications.