Title: Phonon Bridges and Thermal Boundary Conductance Studies at Au/Ultrawide Bandgap Interfaces

Optimizing the thermal boundary conductance, h_BD, of metal contact/ultrawide bandgap (UWBG) interfaces offers a promising thermal management strategy at the device-level. The “phonon bridge,” a thin layer with intermediate vibrational properties inserted between the metal and UWBG, provides an opportunity for improving h_BD beyond the baseline interface. In this talk, we will highlight h_BD measurements on Au/diamond and Au/β-Ga₂O₃ interfaces that incorporate a phonon bridge to improve h_BD. For Au/diamond, an oxygen termination at the diamond surface, which is commonly used to improve adhesion, enhanced h_BD from 10 to 99 MW/m²K. At Au/β-Ga₂O₃ interfaces, a thin layer of Ti, already used in electrical contacts, improved h_BD from 30 to 150 MW/m²K, while a thin layer of Ni improved h_BD to 100 MW/m²K. Additionally, the observation of non-equilibrium cooling effects in the multi-metal stacks/β-Ga₂O₃ due to differences in the electron-phonon coupling constants will be discussed.