Abstract
A new theory is developed in this paper to explain the collapse of current gain in multifinger power AlGaAs/GaAs Heterojunction Bipolar Transistors (HBT's). The reasons behind this unwanted phenomenon are fully clarified using a simple model to investigate the thermoelectrical interaction between the fingers. The existence of multivalue equilibrium points in model's constitutive equations is shown to be the necessary condition for the collapse of current gain to appear. For a N finger device,Y different patterns of collapse exist. The criterion to select the global stable pattern is given. The method has been used to predict the collapse in AlGaAs/GaAs HBT's and the agreement is excellent. The method also predicts that the collapse can happen far earlier than is normally expected in multifinger highpower devices. The influence of ballasting resistance and thermal resistance is also investigated. © 1996 IEEE Publisher Item Identifier S 00189383(96)07709X.