Study of self-heating and mutual thermal coupling resistance in power HBTs with non-uniform finger spacing

The thermal resistance matrix of multi-finger power HBT including self-heating thermal resistance and mutual thermal coupling resistance is presented to describe the improvement mechanism of non-uniform finger spacing technology. It is shown in the thermal network of multi-finger power HBT that the finger temperature depends on the value of thermal resistance matrix. For HBT with non-uniform finger spacing, the values of mutual thermal resistance decreases markedly as center finger spacing increases, which could effectively lower the center finger temperature. At the same time, the outside finger spacing increases moderately to maintain the total finger spacing of the device constant. As a result, the mutual thermal coupling resistance of outside fingers increased, and results in a slight temperature rise of the outside fingers. Therefore, the non-uniformity of the finger temperature profile is also improved effectively.