Substrate-bias driven sputter deposited β-phase dominated tungsten film for spintronic applications

Abstract

$\beta$-Tungsten ($\beta$-W), an A15 cubic phase of tungsten, exhibits a giant spin Hall angle compared to its bcc-phase $\alpha$-Tungsten ($\alpha$-W), making high-quality $\beta$-W films desirable for spintronic applications. We report the controlled growth of $\beta$-W films on SiO₂/Si substrates via DC sputtering, where substrate bias serves as a critical factor in stabilizing the $\beta$ phase by regulating the energy of deposited atoms. This approach enables the formation of $\beta$-W films over a wide thickness range. Power spectral density analysis of the atomic force microscopy images revealed that the $\beta$-W film grown at a positive substrate bias of +50 V exhibits low surface roughness along with small grain size. Additionally, we studied the spin pumping phenomena in different tungsten phases achieved through substrate bias. Ferromagnetic resonance measurements reveal an enhancement in the magnetic damping for $\beta$-W/Py compared to $\alpha$-W/Py dominated film. Importantly, the use of substrate bias does not deteriorate the interface quality, underscoring its effectiveness. These findings highlight the potential of substrate bias in thin-film engineering, paving the way for its advanced utilization in spintronic applications.