Determination of the thermal resistance and current exponent of heterojunction bipolar transistors for reliability evaluation

The reliability of Heterojunction Bipolar Transistors (HBT's) depends on pa rameters such as junction temperature and current density. For the descript ion of the failure behaviour of HBT devices, an extended half-empirical Arr henius model is used introducing a current acceleration exponent. The therm al resistance (Rh) of the device has to be determined which is itself tempe rature dependent. The novel approach presented in this paper allows the acc urate determination of the device junction temperature and thermal resistan ce of the HBT under actual working conditions at high collector currents. T he current exponent is estimated to be in the range between 1... 2, based o n prior knowledge gained on laser diodes, which leaves a huge range of unce rtainty. In this paper, this current exponent is determined by direct measu rement using two independent approaches with good correlation of results. ( C) 2001 Elsevier Science Ltd. All rights reserved.