Improved VO2 microbolometers for infrared imaging: operation on the semiconducting-metallic phase transition with negative electrothermal feedback

We have investigated the performance of VO2 microbolometers biased on the semiconducting-metal phase transition with negative electrothermal feedback. We deposited crystalline thin films of phase-pure VO2, patterned these films into useful test structures, and evaluated the electrical and optical properties relevant to improved uncooled bolometric sensors. A novel ac-biasing method allows for biasing of the devices on the hysteretic semiconducting-metallic phase transition near 70 degrees C. Two important advantages result from biasing in the phase transition: high sensitivity, and negative electrothermal feedback. Under these conditions improvements in speed and noise equivalent power are expected. Modest improvements in noise performance and responsivity consistent with simulations were experimentally verified. Our result suggest a large potential performance advantage over current uncooled vanadium oxide sensor which can be realized as either increased bandwidth or higher sensitivity.