Multiphysics simulation of hypersensitive microbolometer sensor using vanadium dioxide and air suspension for millimeter wave imaging

Abstract

A highly sensitive uncooled antenna-coupled microbolometer for millimeter wave (mmW) imaging is reported in this paper. Vanadium dioxide (VO2) phase-change material is utilized in our design to exploit its non-linear change in electrical resistivity. The proposed microbolometer takes advantage of the large thermal coefficient of resistance (TCR) of VO2 at the non-linear region. The thermal resistance of the device is significantly improved by micro-electro-mechanical systems (MEMS) techniques to suspend the device above the substrate, compared with non-suspended microbolometers. Unlike semiconductor-based sensors that are characterized by capacitive roll-off limitations, the proposed antenna-coupled sensor has an inherently high operating frequency and wide bandwidth suitable for mmW imagers. The finite element method is employed to analyze the electrothermal and electromagnetic performance of the device. The frequency range of operation is 65–85 GHz, and the realized gain at broadside is > 1.0 dB. Simulation results indicate a high responsivity of 1.72 × 103 V/W and a low noise equivalent power (NEP) of 33 pW/√Hz. The enhanced device sensitivity is primarily the result of the sharp change in VO2′s electrical resistivity and is assisted by air suspension using MEMS microfabrication processes. In this work, for the first time, using multiphysics modeling we demonstrate exploitation of VO2′s non-linear behavior in enhancing the sensitivity of a conventional microbolometer. Based on the findings of this study, a pixilated array of the proposed sensors will enable the realization of a highly sensitive mmW camera for a variety of sensing applications.