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

[Display omitted] • Detailed study of laser-induced oxidation of vanadium enables synthesis of laser-written VO2 spots and lines. • Reversible phase transition of VO 2 observed in power dependent Raman measurements. • Voltage & temperature induced resistance switching of laser written VO 2 is observed. • Complete two terminal V-VO 2 -V device along with isolation fabricated using laser. • Relaxation oscillator based on fabricated VO 2 device is demonstrated. Vanadium Dioxide (VO 2) changes reversibly from metal and insulator phase around the transition temperature (68 °C) causing resistance and reflectance switching. Conventional VO 2 device fabrication technology involves VO 2 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 VO 2 devices where the VO 2 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 VO 2 and V 2 O 5 are obtained on the same sample, with VO 2 showing ∼ 2 orders of resistance switching. Lines of VO 2 are synthesized using DLW on V film, resulting in a V-VO 2 -V structure which after laser isolation forms a completely laser-written VO 2 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 VO 2 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. [ABSTRACT FROM AUTHOR]