Near junction thermal management of GaN HEMTs via wafer bonding

Abstract

Gallium nitride (GaN)-based high electron mobility transistors (HEMTs) offer excellent performance in power conversion and high frequency power amplification. However, device self-heating limits reliable output power to 1/8th of reported maximums. Device-level thermal management is therefore critical for reliable high power operation. This thesis proposes and examines wafer bonded GaN-on-SiC HEMTs as a thermally efficient alternative to growth structures. This work first compares the thermal properties of this novel structure to the state-of-the-art. It then develops suitable wafer bonding techniques to fabricate this structure. In addition, the bonded interface thermal conductivity is measured via time domain thermoreflectance. The results of these measurements are analyzed to determine the thermal performance of the structure. In all, this thesis shows that the proposed bonded technology is a promising method for the fabrication of the next generation of GaN HEMTs. These devices are expected to perform at a level equivalent to GaN-on-diamond devices, although further process development is needed to achieve high bonding yields.