Study On Fabrication And Optical Property Of VO_x Thin Films With Phase Transition Characteristic

Vanadium Oxide (VO_x) thin films have excellent thermal-induced and photo-induced phase transition, and its metal-semiconductor phase transition could occur under thermal excitation or optical excitation with mutation in resistivity and optical transmission rate. VO_x thin films are the ideal semiconductor materials used in optical switches. At present, there is a research focus on fabrication of VO_x thin films with good phase transition performance, and corresponding optical and electrical test technology. By the methods of direct current facing targets magnetron sputtering and dual ion beam sputtering, combined with annealing process, the VO_x thin films which have phase transition were prepared. The phase transition properties of VO_x thin films were tested by Fourier transform infrared spectroscopy (FTIR) and THz time-domain spectroscopy system (THz-TDS).Using DC facing magnetron sputtering with rapid thermal annealing process, VO_x thin films with thermal-induced phase transition were prepared. The resistance of VO_x thin films changed up to three orders of magnitude, before and after phase transition. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis informed by the films of the monoclinic structure as the main component of VO₂. Rapid thermal annealing help improve film crystallinity, reducing the grain boundary and crystal defects, thus contributing the improvement of phase transition performance.By dual ion beam sputtering, VO_x thin films were deposited on Si3N4 substrates. After annealed in N2 atmosphere at 400℃for 3 hours, there was a clear electrical and optical phase transition with VO_x thin films. Near the phase transition point 45℃, the resistance of films had a mutation in three orders of magnitude. At the communication band 1550nm, the optical transmission of VO_x dropped from 32% to 1% before and after phase transition. When VO_x thin films under excitation by 980nm pump laser, it led to lower infrared transmission of VO_x thin films from 32% to 2%. These work laid the foundation for the optical switch.The optical switching characteristics of VO_x thin films were studied, by using THz-TDS. Under photo excitation, the indicators of VO_x optical switch were excellent, extinction ratio 7.96dB; insertion loss 3dB, and has a large bandwidth; the fastest switching speed up to 20ns. And the transmission properties of VO_x thin films in THz band had a significantly frequency characteristics. VO_x deposited on SiO₂ substrates after annealing in vacuum, photo-induced phase transition occurred. Before and after excitation, the THz transmission changed of 8%, which can be used in optical device.