Enhanced Thermal Management in GaN Superlattice Castellated Field Effect Transistors

AlGaN/GaN multi-channel Super Lattice Castellated Field Effect Transistors (SLCFETs) have shown great potential for next generation RF applications. We demonstrate a 2.44× reduction in thermal resistance reduction in AlGaN/GaN multi-channel SLCFETs by replacing the standard AlGaN buffer with a high thermal conductivity AlN buffer layer and adding a poly-crystalline diamond overcoat layer. The thermal conductivity of each material in the device stack was measured using time-domain and frequency-domain thermoreflectance techniques, including 223+21−18W/m·K for 2.2 μm-thick AlN buffer versus 38+5.5−5W/m·K for the reference 1.8 μm AlGaN buffer. Device thermal resistance was reduced from 29 mm°C/W to 11.9 mm°C/W by combining the AlN buffer and poly-crystalline diamond overcoat layer, determined using Raman thermography together with 3-D thermal simulation. The corresponding 2.44× increase RF power density capability enabled by improved thermal management can unlock the next-generation ultra-high-power RF devices.