Unravelling the mechanism of phase fraction modulation via process parameter tuning and first-principles study for enhanced TCR in VOx-based uncooled microbolometers

Abstract

Vanadium oxide (VO_x)-based bolometric membrane films with high temperature coefficient of resistance (TCR) and low 1/f noise were deposited by tuning the argon and oxygen flow rate inside a DC magnetron sputtering chamber. The process temperature was maintained below 300 °C so that the film was compatible with the readout integrated circuit (ROIC). Initially, the phase fraction was optimized at the elevated temperature of 550 °C, and later, the optimized argon and oxygen flow rate ratio was used to deposit the film at its deposition temperature, i.e., 250 °C. The TCR value of −3.4% K⁻¹ and sheet resistivity of 1.2 ohm sq⁻¹ were obtained for an optimized argon and oxygen flow rate ratio at 550 °C, while TCR > −2.2% K⁻¹ was obtained for films deposited at 250 °C. Additionally, a 1/f noise constant with the order of K = 10⁻¹² was obtained for the films. Qualitative and quantitative analyses of films were carried out using X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy. Finally, first-principles density functional theory (DFT) calculations were performed to analyse the influence of phases on the TCR of the films grown using the optimized parameters.