Optimal Thermal Resistance Model of GaN HEMTs Considering Thickness-Dependent Thermal Conductivity

We propose a thermal resistance model for gallium nitride (GaN) high electron mobility transistor (HEMT) that considers the thickness-dependence and anisotropy of the thermal conductivity of GaN films to improve the calculation accuracy. In this study, the Debye-Callaway model is used to calculate the in-plane and cross-plane thermal conductivity of the GaN buffer layer as a function of layer thickness. An electrical model of heat generation profiles is established by using the technology computer-aided design (TCAD). The temperature distribution is predicted by the finite element methods (FEMs) simulations. We confirm that as the thickness of the GaN layer increases, the total thermal resistance on diamond, SiC, and Si substrates decreases first and then increases, reaching their minimum values at 3.6, 5, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$48~\mu $ </tex-math></inline-formula> m at a thermal boundary resistance (TBR) of 30 m<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{{2}}\cdot \text { K/GW}$ </tex-math></inline-formula>, respectively. Moreover, there is a lack of research on the optimal GaN thickness of devices with different substrates. Based on this model, we investigate the effects of TBR, power dissipation level, and gate pitch values on the optimal GaN thickness of devices with different substrates (Si, SiC, and diamond).