Measurement and Modeling of Thermal Behavior in InGaP/GaAs HBTs

Thermal-impedance models of single-finger and multifinger InGaP/GaAs heterojunction bipolar transistors (HBTs) are extracted from low-frequency S-parameters that are measured on wafer and at room-temperature, and from temperature-controlled dc measurements. Low-frequency S-parameters at room temperature are accurate for extracting thermal corner frequencies. However, the dc value of the thermal impedance depends on the emitter resistance and the dc current definitions of the HBT model; hence, they need to be extracted together from temperature-dependent dc measurements. The resulting thermal-impedance model explains the low-frequency dispersion well at varying bias conditions, and it is suitable for nonlinear circuit analysis.