Thermal dynamics of VO2 films within the metal-insulator transition: Evidence for chaos near percolation threshold

The thermal dynamics of thin vanadium dioxide films at the martensitic meta l-insulator phase transition has been evaluated experimentally by thermal e xcitation spectroscopy. Over the transition region, the device becomes high ly nonlinear, and its bolometric performance is affected. At low thermal cy cling rates for a temperature around the percolation threshold, the device stochastically switches into an unusual pattern. The originally smooth and monotonic shape of the R(T) curve for minor loops suddenly becomes unstable and unpredictable. By direct observation of at least two strange attractor s, the phenomenon clearly has been identified as chaotic. Bolometric perfor mance of VO2 based devices in the transition region may suffer strong degra dation for low thermal cycling rates. In this region, sensor responsivity f or periodic thermal excitation is significantly reduced. Resistance noise i s 1/f-type and self-generated oscillations were observed at frequency < 10( -2) Hz. (C) 2000 American Institute of Physics. [S0003- 6951(00)04752-5].