SUBJECT: M.S. Thesis Presentation
BY: Xiuping Chen
TIME: Monday, March 31, 2014, 3:00 p.m.
PLACE: Love Building, 109
TITLE: Embedded Active and Passive Methods to Reduce the Junction Temperature of Power and RF Electronics
COMMITTEE: Dr. Samuel Graham, Co-Chair (ME)
Dr. Satish Kumar, Co-Chair (ME)
Dr. Yogendra Joshi (ME)


AlGaN/GaN high electron mobility transistors (HEMTs) have been widely used for high power and high frequency RF communications due to their fast switching and large current handling capabilities. The reliability of such devices is strongly affected by the junction temperature where the highest magnitude occurs in a local region on the drain side edge of the gate called the hotspot. Thus, thermal management of these devices remains a major concern in the design and reliability of systems employing AlGaN/GaN HEMTs. Due to the large power densities induced in these devices locally near the drain side edge of the gate, it is clear that moving thermal management solutions closer to the heat generation region is critical in order to reduce the overall junction temperature of the device. In this work, we explore the use of embedded microchannel cooling in the substrate of AlGaN/GaN HEMTs made on Si and SiC substrates and compare them to passive cooling techniques using Si, SiC, and diamond substrates. In addition, the impact of cooling fluids and harsh environmental conditions were considered. The study was performed using a combination of CFD and finite element analysis on packaged AlGaN/GaN HEMTs. Active cooling using embedded microchannels were shown to have a significant impact on the heat dissipation over the passive cooling methods, approaching or exceeding that of diamond cooled devices. For vertical power devices (IGBT), embedded microchannels in the power electronics substrates were explored. In both the power devices and lateral AlGaN/GaN HEMTs, the use of embedded microchannels with nonlinear channel geometries was shown to be the most effective in terms of reducing the device junction temperature while minimizing the pumping power required.