Nonhysteretic Phenomena in the Metal–Semiconductor Phase-Transition Loop of $\hbox {VO}_{2}$ Films for Bolometric Sensor Applications

Hysteresis observed in the resistive semiconductor-to-metal phase transition in VO₂ causes problems in bolometric readout, and thus is an obstacle in utilizing this strong phase transition in bolometric sensor applications. It is possible to avoid the unwanted hysteresis when operating in limited temperature ranges within the hysteresis loop of VO₂. Nonhysteretic branches (NHB-s) traced in such limited temperature intervals turned out to have much higher temperature coefficient of resistance (TCR) than VO₂ at room temperature: while TCR at 25° C in VO₂ is close to 3%, peak TCR values in NHB-s reach 6% in VO₂ films on Si/SiO₂ substrates and 21% in films on crystalline sapphire substrates. At the same time, the nanoscopic-scale mixture of semiconducting and metallic phases in VO₂ within its hysteresis loop provides for partially shunted low resistivity, thus creating an unprecedented combination of record high semiconducting TCR and metal-like low resistance. This combination may benefit the uncooled focal plane array microbolometer IR visualization technology.