Thermal Conductance of beta-Ga2O3/Metal Interfaces

H Aller and XX Yu and AJ Gellman and JA Malen and AJH McGaughey, PROCEEDINGS OF THE 17TH IEEE INTERSOCIETY CONFERENCE ON THERMAL AND THERMOMECHANICAL PHENOMENA IN ELECTRONIC SYSTEMS (ITHERM 2018), 567-571 (2018).

The wide-bandgap semiconductor beta-Ga2O3 is of growing interest for high power devices. Its thermal conductivity, however, is an order of magnitude lower than commonly used semiconductors such as Si, SiC, and GaN. Thermal management is thus a central issue in device design. Our objectives in this study are twofold. First, we measure the thermal conductance of the interfaces that beta-Ga2O3 forms with the metal layers that serve as source and drain. These interfaces may be barriers to effective heat removal and prevent optimal performance. Second, we use theoretical tools to investigate the bulk properties of the alpha, beta, and epsilon phases of Ga2O3. The thermal conductance of the Au/beta-Ga2O3 interface is measured using frequency-domain thermoreflectance to be 45 +/- 5 and 80 +/- 8 MW/m(2)-K for e-beam evaporated and sputtered Au layers. To increase the thermal conductance, an adhesion layer of Ti or Cr of thickness up to 10 nm is deposited between the beta-Ga2O3 and the Au. The relationship of thermal conductance vs. adhesion layer thickness is finely determined for Ti and Cr. Depending on the adhesion layer material and thickness, the thermal conductance can be increased by as much as 10 times. The results are interpreted by considering the phonon density of states overlap. We apply molecular dynamics simulations to predict the lattice parameters, bulk modulus, and thermal conductivity tensor of the three bulk phases of Ga2O3. Our predictions for the beta phase match experimental results with less than 10% error. The lattice parameters of both alpha and epsilon phases of Ga2O3 are within 5% error from experimental results (the other properties have not been measured). Despite the same chemical composition, we predict that the epsilon phase thermal conductivity is an order of magnitude lower than the alpha and beta phases.

Return to Publications page