GEOMETRY CONSIDERATIONS FOR THERMAL DESIGN OF MICROWAVE HETEROJUNCTION BIPOLAR-TRANSISTORS

An efficient general algorithm for three-dimensional thermal simulatio n of semiconductor chips and its exemplary application to AlGaAs/GaAs heterojunction bipolar transistols (HBT) is presented. Firstly, the as sumption of stationary heat sources as a boundary condition is validat ed by pulsed scattering parameter measurements. Secondly, the simulati on method based on the fast Fourier transform is introduced. The model is verified by liquid crystal thermography, infrared thermography and comparison to another simulation method. In the third part of the pap er, the model is applied to the self-heating problem in multifinger HB Ts. Geometrical design rules for minimization of the maximum temperatu re and temperature gradients between the individual emitters are deduc ed. A tradeoff between the emitter size, the number of emitters, the p ower level and cooling measures such as substrate thinning must be car ried out in order to control the thermal properties with respect to sa fe operation and reliability.