A Hybrid Multi-gate Model of a Gallium Nitride (GaN) High Electron Mobility Transistor (HEMT) Device Incorporating GaN-substrate Thermal Boundary Resistance

Abstract

Abstract : This report describes a pseudo-analytical thermal model of gallium nitride (GaN) high electron mobility transistors (HEMTs), which combines analytical heat spreading models with spreading width boundary conditions derived from two-dimensional finite element thermal simulations. We successfully produced an accurate GaN HEMT hybrid model capable of evaluating the impact of thermally important device parameters on junction and individual layer temperatures. A parameter space investigation, covering GaN-substrate thermal boundary resistance (TBR), gate pitch, substrate thickness, substrate thermal conductivity, and GaN thickness validated the hybrid model against full finite element numerical analysis and provided insight into device thermal behavior. This modeling showed near junction thermal resistance contributions from the GaN and interface TBR stay relatively constant with gate number and pitch down to 5 m. Alternatively, the thermal profiles in the substrate layers and below show strong interaction between gates; the magnitude of those components scale directly with gate number and increase significantly with decreasing gate pitch. Also finite substrate and GaN thicknesses produce a minimum temperature rise dependent on downstream thermal resistance. Finally, increasing substrate thermal conductivity, by replacing a silicon carbide (SiC) substrate with higher thermal conductivity diamond, appears to only be advantageous if the TBR does not increase substantially beyond the SiC range.