SUMMARY

Gallium Oxide (Ga2O3) is envisioned to fabricate high performance transistors for RF or power electronic applications. However, the low thermal conductivity of Ga2O3 will require innovative solutions for thermal management. In portable electronics, attaching heat spreaders made of materials with high in-plane thermal conductivity, such as hexagonal boron nitride (h-BN) and highly oriented pyrolytic graphite (HOPG), can be promising for hot spot mitigation. This dissertation aims to investigate the thermal performance of thin films of Ga2O3, h-BN and HOPG for emerging electronic applications.
The thermal conductivity of Ga2O3 grown on SiC was studied using Time Domain Thermoreflectance. The effect of atomic-scale defects on thermal conductivity were investigated by comparing measured results against first principle simulations. New experiments using Frequency Domain Thermoreflectance are planned for samples with different thicknesses and at different temperatures to estimate thermal conductivity and thermal boundary conductance. Next, the use of h-BN and HOPG as heat spreaders is analyzed. h-BN is typically grown on a metal substrate and need to be transferred to the substrate of electronic chip. The transfer process could affect the in-plane thermal conductivity. The initial experiments showed that h-BN can be contaminated if appropriate transfer practices are not followed. The thermoreflectance imaging techniques will be used to estimate the in-plane thermal conductivity of transferred h-BN. However,simulations showed that the thickness of h-BN might not be good enough to have significant heat spreading. Thus, HOPG has been investigated as heat spreading material. Different set of methods and materials (e.g., nanoporous copper) will be used to bind HOPG to a substrate. The thermal performance of the heat spreader/bonding method combination will be assessed using an in-house setup that simulates a hot spot, in combination with a thermal infrared microscope.