Wafer-scale freestanding vanadium dioxide film

Sci Adv. 2021 Dec 10;7(50):eabk3438. doi: 10.1126/sciadv.abk3438. Epub 2021 Dec 8.

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.