Electrothermal modeling of multi-emitter heterojunction-bipolar-transistors (HBTs)

A large signal equivalent circuit model for multi-emitter HBTs is proposed. The model is based on the description of a single-emitter-finger HBT which includes the intrinsic transistor temperature as a variable simulation parameter. This single-emitter device is described by a four node representation using the additional fourth node to calculate the transistor's pseudotemperature rise. The thermal coupling of the transistor elements is performed by thermal impedances. The model allows simulation of the thermally triggered collapse of the collector current at power densities greater than 10/sup 5/ W//sub cm/2. The use of emitter ballasting resistors improves the homogeneous temperature distribution of the power device and leads to an increase of the collector current of about 30%.