Room Temperature Phase Transition of W-Doped VO2 by Atomic Layer Deposition on 200 mm Si Wafers and Flexible Substrates

Abstract

The unique structural transition of VO2 between dielectric and metallic phases has significant potential in optical and electrical applications ranging from volatile switches and neuromorphic computing to smart devices for thermochromic control and radiative cooling. Critical condition for their widespread implementation is scalable deposition method and reduction of the phase transition to near room temperature. Here, a W:VO2 process based on atomic layer deposition (ALD) is presented that enables precise control of W-doping at the few percent level, resulting in a viable controllable process with sufficient W incorporation into VO2 to reduce the phase transition to room temperature. It is demonstrated that the incorporation of 1.63 at.% W through ALD growth leads to a state-of-the-art phase transition at 32 °C with emissivity contrast between the low-temperature and high-temperature phase exceeding 40% in a metasurface-based radiative cooling device configuration. The process is shown to be viable on 200 mm silicon substrates as well as flexible polyimide films. The full and self-consistent temperature-dependent characterization of the W-doped VO2 using spectroscopic ellipsometry, electrical conductivity, mid-wave infrared camera, and Fourier transform infrared emissivity, allows for a fully validated material model for the theoretical design of various smart and switchable device applications.