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.