Measurement of the Channel Temperature of a GaN Microwave Power Transistor During Pulsed I.V Excitation

In this paper a thermoreflectance measurement technique is used to capture the channel temperature within a GaN-on-Si HEMT during pulsed I-V excitation. Using pulsed I-V measurements in combination with thermoreflectance measurements allows the direct assessment of the isothermal approximation that is often made during the characterization of the transistor for nonlinear model development. The thermoreflectance measurement has a temporal response of 50 ns, which is sufficiently fast to measure the temperature rise within the pulsed I-V excitation, across the I-V plane of the transistor. We first determine the minimum pulse duration needed to minimize the temperature rise as assessed from drain current measurements as a function of the excitation pulse width. The thermoreflectance measurements show that self-heating occurs during the pulse, revealing a maximum of 13.5°C change over all pulsed I-V measurements. Transient thermoreflectance measurements were then performed to determine that sub-200 ns pulses are required to eliminate the self-heating for this device.