Design, fabrication and testing of a micromachined thermo-optical light modulator based on a vanadium dioxide array

Abstract

In this paper, a thermal-optical light modulator was developed based on a surface micromachined vanadium dioxide (VO2) array. VO2 thin film undergoes a reversible semiconductor-to-metal phase transition at about 68 °C, which is accompanied by an abrupt transformation from a transparent semiconductor phase at low temperature to a reflective metallic state at high temperature. To exploit this phase-transition related thermo-optical switching, low-thermal-mass pixels with long and thin supporting legs were surface micromachined above a glass substrate to achieve good thermal isolation between pixels and ensure fast enough switching speed. The pixel design was optimized by thermal and optical simulations. Active VO2 thin film was fabricated by e-beam evaporation of vanadium metal film followed by oxidation. The deposited VO2 film exhibits a grain structure and undergoes a phase transition at 65 °C with about 15 °C hysteresis. A surface micromachining process was developed to realize a light modulator with 64 × 64 pixels. The light switching and modulation ability of the VO2 array was experimentally tested and demonstrated. Further study shows that the surface micromachining process has no degrading effect on the optical property of VO2 film.