Antenna-coupled microbolometer based on VO₂'s non-linear properties across the metal–insulator transition region

This paper presents an antenna-coupled non-linear vanadium dioxide (VO₂) microbolometer operating in the non-linear metal–insulator transition (MIT) region with an ultra-high responsivity of 6.55 × 10⁴ V/W. Sputtered VO₂ films used in this device exhibit 10⁴ times change in resistivity between the dielectric and conductive states. The VO₂ microbolometer is coupled to a wideband dipole antenna operating at 31–55 GHz and a coplanar waveguide for probed measurement. To enhance the sensitivity, the sensor is suspended in air by micro-electro-mechanical systems process. The large thermal coefficient of resistance of VO₂ is utilized by DC biasing the device in the MIT region. Measurements for the fabricated sensor were performed, and a high responsivity was demonstrated, owing to non-linear conductivity change in the transition region. The measured sensitivity is >10² times higher than the state-of-the-art sensors. In addition, the concept of utilizing the proposed VO₂ sensor in a mmWave imager was demonstrated by the radiation pattern measurement of a 4 × 4 (16 elements) antenna-coupled VO₂ sensor array. The results presented in this work reveal the initial step to employ VO₂'s MIT for a hyper-sensitive sensor in future mmWave sensing and imaging applications.