A Numerical Study on Comparing the Active and Passive Cooling of AlGaN/GaN HEMTs

In this paper, the power density capability of AlGaN/GaN high-electron mobility transistors (HEMTs) made on Si, SiC, and diamond substrates were compared with devices on Si and SiC with integrated microchannel cooling. A device temperature limit of 200 °C was used to define the power density. The numerical model accounts for heat transfer from channel of the AlGaN/GaN HEMTs to the heat sink, fluid flow rates, pressure drop, and pumping power required for liquid cooling. The diamond substrate was shown to be superior in reducing the junction temperatures in conventional passive cooling methods employing high thermal conductivity substrates. However, singlephase liquid cooling with microchannels integrated into a SiC substrate showed that it is possible to operate the devices at power densities higher than that on 200-μm-thick diamond substrates, considering a maximum operational temperature of 200 °C. Microchannels integrated into the Si substrate also showed a slight increase in the power density compared with passively cooled devices on SiC. Overall, this methodology shows a promising alternative to expensive high thermal conductivity substrates for cooling AlGaN/GaN HEMTs.