Lithography-free fabrication of Vanadium Dioxide and its devices using direct laser writing

Vanadium Dioxide (VO2) changes reversibly from metal and insulator phase around the transition temperature (68 °C) causing resistance and reflectance switching. Conventional VO2 device fabrication technology involves VO2 deposition, lithography for film patterning/etching, and contact formation. The overall fabrication process is complex, time-consuming, costly, and requires harmful chemicals. This work demonstrates a lithography-free method to fabricate VO2 devices where the VO2 region synthesis, isolation, and contact formation are all done in continuity using direct laser writing (DLW) on Vanadium (V) thin films. The effect of the laser parameters on oxidation is examined and spots of phase pure VO2 and V2O5 are obtained on the same sample, with VO2 showing ∼ 2 orders of resistance switching. Lines of VO2 are synthesized using DLW on V film, resulting in a V-VO2-V structure which after laser isolation forms a completely laser-written VO2 device exhibiting resistance switching driven by either voltage or temperature. To display the suitability of the fabricated device for circuit applications, a relaxation oscillator circuit is demonstrated. The presented DLW based lithography free approach to synthesize VO2 structures and devices significantly simplifies fabrication compared to traditional semiconductor processing approaches. It can also enable single step fabrication of integrated circuits based on vanadium oxide active regions with V interconnects.