A Geometry Scalable Model for Nonlinear Thermal Impedance of Trench Isolated HBTs

This letter presents a geometry scalable approach for the calculation of temperature dependent thermal impedance (Z_TH) in trench-isolated heterojunction bipolar transistors. The model is capable of predicting the Z_TH at any desired temperature and bias points. The temperature dependency is derived by discretizing the heat flow region into n number of elementary slices depending on the thermal gradient. Temperature dependent thermal resistances R_ths and capacitances C_ths for each of the slices are calculated in a self-consistent manner. Finally, the proposed model is validated with low-frequency measurements at different ambient temperatures (T_amb) for different transistor geometries and found to be in good agreement.