Thermal behavior depending on emitter finger and substrate configurations in power heterojunction bipolar transistors

Analytical and experimental results are used to investigate thermal behavior depending on the emitter-finger area and substrate thickness in multifinger heterojunction bipolar transistors (HBT´s). The temperature distributions along the depth direction of the substrate are obtained from a three-dimensional (3-D) analysis. The calculated results show a 3-D effect which depends upon the emitter finger area. This effect weakens with increasing the emitter-finger area. As the effect weakens, thinning the substrate effectively reduces the junction temperature (thermal resistance). This is verified by the measured results obtained from a simple thermal-resistance measurement