Exploring phase transition dynamics in VO2 films: The role of substrate temperature

We investigated the effect of substrate temperature (T_S) on the phase transition characteristics of RF sputtered VO₂ films deposited on hexagonal ALO (0001) and cubic YSZ (001) substrates at ∼500°C–800 °C under Ar ambient only, in correlation with structure and morphology. High-Resolution X-ray Diffraction (HRXRD) and Raman spectroscopy confirmed the formation of the polycrystalline VO₂ (M1) phase with traces of secondary phases. Atomic Force Microscopy (AFM) and Field Emission Electron Microscopy (FESEM) reveal distinct surface roughness and grain morphology. Surface roughness increases significantly with large and non-uniform grains on c-plane Sapphire (ALO), whereas on Yttria-stabilized zirconia (YSZ), grains are small and uniform, having minimal surface roughness variation with increasing temperature. Above 600 °C, VO₂ films on both substrates exhibit reversible insulator-metal transitions (IMT/MIT) with ∼ (3–4) order resistivity change and pronounced thermal hysteresis close to ∼340K. The transition temperature (T_C) decreases with minima at ∼700 °C and again increases with temperature. Hysteresis width increases on ALO (∼1K–∼10K), whereas it decreases on YSZ (∼14K–∼7K) with increasing temperature. Films on both substrates above ∼600 °C exhibit room temperature average Temperature Coefficient of Resistance (TCR) of ∼ (1.61–3.18 %K⁻¹) and warming peak TCR of ∼(54.30–85.39 %K⁻¹ on ALO) and ∼(85.31–98.02 %K⁻¹ on YSZ). Distinct Activation Energy (E_A) dependence on substrate type and temperature has been observed in metallic and insulating phases. The observed phase transition characteristics of VO₂ films have been explained based on variation in distinct structure and morphology, which strongly depends on substrate type and temperature. These findings anticipate that substrate type and temperature play a decisive role in tailoring the structural and phase transition characteristics of VO₂ films for potential applications.