Wafer-scale freestanding vanadium dioxide film.

Abstract

Vanadium dioxide (VO₂), with well-known metal-to-insulator phase transition, has been used to realize intriguing smart functions in photodetectors, modulators, and actuators. Wafer-scale freestanding VO₂ (f-VO₂) films are desirable for integrating VO₂ with other materials into multifunctional devices. Unfortunately, their preparation has yet to be achieved because the wafer-scale etching needs ultralong time and damages amphoteric VO₂ whether in acid or alkaline etchants. Here, we achieved wafer-scale f-VO₂ films by a nano-pinhole permeation-etching strategy in 6 min, far less than that by side etching (thousands of minutes). The f-VO₂ films retain their pristine metal-to-insulator transition and intrinsic mechanical properties and can be conformably transferred to arbitrary substrates. Integration of f-VO₂ films into diverse large-scale smart devices, including terahertz modulators, camouflageable photoactuators, and temperature-indicating strips, shows advantages in low insertion loss, fast response, and low triggering power. These f-VO₂ films find more intriguing applications by heterogeneous integration with other functional materials.