Enhancement of Thermal Transfer From β-Ga2O3 Nano-Membrane Field-Effect Transistors to High Thermal Conductivity Substrate by Inserting an Interlayer

The role of a HfO2 or ZrO2 interlayer as a thermal bridge between a beta-Ga2O3 channel and a sapphire substrate was investigated using a beta-Ga2O3 nano-membrane FET as a test vehicle. A 35% less channel temperature increase was observed when a thin HfO2 or ZrO2 interlayer was inserted between the beta-Ga2O3 channel and the sapphire substrate compared to devices without interlayers. Phonon density of states (PDOS) mismatch can explain the improvement of the thermal boundary conductance (TBC). In the acoustic region, the PDOS of HfO2 or ZrO2 has about a 700% larger overlap area with the PDOS of beta-Ga2O3 compared to the PDOS of sapphire. This suggests that the insertion of a thermal bridge interlayer can provide a potential solution to the low thermal conductivity of beta-Ga2O3 and the self-heating effect of beta-Ga2O3-based FETs.