An Invariable Temperature during the Phase Transition of W Doped VO2 Film

Abstract

The phase transition temperature of the functional VO2 films was adjusted to near room temperature by the W6+ doping. The V1−xW xO2 (0 ≤ x ≤ 0.04) films were deposited by the one‐step thermal decomposition process (30 min at 793 K) on a sapphire (0001) substrate under inert conditions. The electrical resistivity of the films showed that the ending point of the metal to insulator transition (TCE) of the pure VO2 phase transition, which appeared at ~310 K, was shifted down to ~265 K along with the increased doping level of W. The hysteresis gap between cooling and heating cycles in the plot of temperature vs. electrical resistivity for the films decreased from ~25 to ~2 K by the increased W level. The transition temperature shift and the hysteresis gap decrement were also observed in the measurement of infrared (IR) transmittance near the transition temperature. The degree of IR (1550 nm) transmittance of the VO2 film in the low‐temperature region was decreased from ~80 to ~40% by the W doping, but nearly the same transmittance in the high‐temperature region. Even though the characteristics of the transition in resistivity and transmittance measurements were greatly altered by the W doping, the starting point of the metal to insulator transition (TCS) was nearly constant, TCS ~338 K.