FREQUENCY DOMAIN DYNAMIC THERMAL ANALYSIS IN GAAS HBT FOR POWER AMPLIFIER APPLICATIONS

Dynamic temperature distributions in GaAs HBT are numerically analyzed in frequency domain as a function of power dissipation, frequency and space. Complete thermal characteristics, including frequency-dependent thermal impedance and phase lag behavior, are presented. The analysis is also extended for arbitrary periodic or aperiodic pulse heating operation to predict junction temperature of a Power Amplifler (PA) with non-constant envelope input signal. Dynamic junction temperatures of a single flnger 2"m£20"m GaAs HBT are predicted for square pulse envelope signal input with power levels varying with up to 10dB above a nominal average level of 40mW and with pulse widths ranging from 10ns to 100"s. With the input envelope signal amplitude of 10dB above the average, the analytical results show that junction temperature rises from room temperature of 27 - C to 39 - C when heated by 10ns pulse and increases to 63 - C by 100ns pulse, 105 - C by 1"s pulse and to 198 - C by 100"s pulse. A novel setup is developed for nano-second pulsed measurements, and the analysis is validated through time domain on wafer pulsed measurements at three difierent power levels: 0dB, 3dB, and 6dB above the average level. Results show that analytical results track well with measured junction temperature within the accuracy of §5 - C over the entire measurement set.