Short pulse thermal response of HBTs

Transient thermal characterization by thermal imaging in our earlier work demonstrated its ability to extract key information about the thermal response of transistors under operating conditions. We investigate a non-equilibrium response to a short time pulse for very high frequency devices, e.g. hetero-junction bipolar transistors (HBTs). Characterizing high speed thermal signals from devices with very small thermal mass has been an ongoing challenge, especially for the microwave and communication industries. A collaboration with a high time-precision pulsed I-V equipment with further advanced high speed thermoreflectance imaging technology enables a measurement of temperature response down to a sub microsecond pulse. Due to the short time pulse, the thermal response wave-form in rise and decay times shows differences from that expected for a typical thermal response, which is more symmetric in rise and decay. Modeling of the thermal diffusion considering the thermal boundaries helps to explain this phenomenon.