Thermal Analysis of AlGaN/GaN HEMTs Using Angular Fourier Series Expansion

Abstract

Thermal analysis of planar and nearsquare semiconductor device chips employing angular Fourierseries (AFS) expansion is presented for the first time. The determination of the device peak temperature using AFS requires only a single twodimensional computation, while full threedimensional temperature distribution can be obtained, if desired, by successively adding higherorder Fourier terms, each of which requires a separate 2D computation. The AFS method is used to compare the heat spreading characteristics of AlGaN/GaN highelectronmobility transistors (HEMTs) fabricated on silicon, silicon carbide, and synthetic diamond. We show that AlGaN/GaN HEMTs built using GaN/diamond technology can offer better than half the thermal resistance of GaN/SiC HEMTs under worstcase cooling conditions. Furthermore, we show that, if left unmanaged, an inherent and nonnegligible thermal boundary resistance due to the integration of semiconductor epilayers with nonnative substrates will dampen the benefits of highly conductive substrates such as SiC and diamond.