Treating the case of incurable hysteresis in VO2

The resistivity ρ(T) of VO2 changes by 3–5 orders of magnitude in a spectacular semiconductor-tometal phase transition around 68 C. This transition is always hysteretic; in thin films, the hysteresis width is typically 10–20 C. For a variety of reasons, of the many proposals to use this transition in applications almost none have materialized. One serious commercial and military application in which the use of VO2 was initially envisioned is IR visualization (night vision) based on resistive microbolometers. However, technology eventually settled on a VO2's poor cousin, a non-transitioning mixed oxide VOX, mainly to avoid hysteresis, which greatly complicates bolometer operation. We found the way to obtain hysteresis-free operation of VO2 right in the midst of its hysteretic transition, while at the same time keeping the benefit of adjustable resistance. This new way of operation is based on a new phenomenon of interest in its own right. Here is how it works. In the hysteresis region, a backward round-trip temperature excursion taken from any point on the major loop will produce a minor loop, as can be seen in the figure on the left.