Impact of the current pulse width on the speed of metal-insulator transition in VO2 nanobeams

Physical electronics

VO2 undergoes an insulator-metal transition at ~ 68 °C, making it an attractive material for the development of tunable metasurfaces, steep-switching transistors, neuristors and other devices. Applications such as wireless communications call for ultrashort transition times, which are believed to be typically limited by heat dissipation. We consider the negative role of heat accumulation in the substrate, which slows down recovery after long heating pulses. Thermal simulations of VO2 nanobeam gratings show that they can display two different behaviors: single-nanobeam-like in the short-pulse regime and film-like in the long-pulse regime. In the long-pulse regime, the recovery time depends linearly on the pulse duration and approximately quadratically on the hysteresis width, in agreement with analytical expressions. In the short-pulse regime, the dependence is much weaker. To achieve nanosecond recovery times, either the short-pulse regime must be used (pulse duration less than the time constant of heat diffusion between adjacent nanobeams), or hysteresis must be eliminated (e. g., by doping). Our results quantify the impact of the pulse duration and hysteresis on the switching time of VO2 devices, clarify the conditions under which these factors are important, and therefore can guide the development of fast electronic/optoelectronic devices based on phase-change materials.