Experimental methods to inform thermal interface engineering in high power GaN devices

Abstract

Current limitations in high-power GaN technologies exist due to thermal resistances in the device structures which impact heat dissipation during operation. Often, the thermal boundary resistance (TBR) between the GaN and substrate can be a limiting factor in heat transfer away from the initial generation. Experimental methods are used to evaluate the TBR for a series of GaN-on-Si wafers with varying interlayers. A complete analysis of material strain, TBR, and finally thermal device impact is presented. Additionally, bulk CVD diamond samples are evaluated along with thin films. An in-depth study of the impact of the dielectric layer on the TBR for a GaN on diamond device is carried out with CVD diamond that is grown on GaN using either an AlN or SiN interlayer and the TBR is evaluated as compared to a material system with no interlayer. Finally, a study of thermal transport in vertical GaN-on-GaN PN diodes was undertaken by evaluating the impact of polyimide passivation on device characteristics and heating. This was followed by measurements of the thermal properties of the GaN due to doping effects and full field transient thermal imaging of the device as compared to a thermal and FEM model in order to provide insight into thermal time constants and proper duty cycle operation.