Thermal Transport in Atomic Layer Deposition-Grown Beryllium Oxide Thin Films and Implications on Device Cooling.

Thin film beryllium oxide (BeO) is an emerging material that can potentially be used as a high thermal conductivity gate dielectric and/or passivation layer for high power electronic devices. This study presents the measurement of the thermal conductivity and thermal boundary conductance associated with plasma-enhanced atomic layer deposition (PEALD)-grown polycrystalline BeO films on Si substrates with thicknesses ranging from 25 to 250 nm. The measured out-of-plane thermal conductivities of the 250, 113, 53, and 26 nm-thick BeO films are 13.45 ± 1.45, 8.7 ± 1.35, 7.2 ± 2.1, and 5 ± 2.2 W m-1 K-1, respectively, representing an order-of-magnitude improvement over conventional dielectric materials such as SiN and SiO2. The measured thermal boundary conductance across the BeO/Si interface is ∼200 MW m-2 K-1 at room temperature, which approaches the intrinsic interface limit and suggests that interfacial heat transport is predominantly governed by elastic phonon transmission. The growth of a ∼200 nm-thick polycrystalline diamond film on an AlGaN/GaN-on-Si epitaxial wafer using a 5 nm-thick BeO diamond-seeding is demonstrated, where the structural integrity of the underlying AlGaN/GaN heterostructure is fully preserved. Thermal simulations of AlGaN/GaN high electron mobility transistors (HEMTs) integrated with a top-side polycrystalline diamond heat spreader predict that replacing the conventional SiO2 passivation and nucleation layers with BeO helps reduce the channel temperature rise by an additional 5.2%.