Optical switching of vanadium dioxide thin films deposited by reactive pulsed laser deposition

The parameters of reactive pulsed laser deposition were successfully optimized for fabrication of vanadium dioxide thin films. It is observed that the O₂ concentration in Ar gas and the total deposition pressure are critical in stabilizing the single VO₂ phase. Thermochromic VO₂ and V_1-xW_xO₂ (x=0.014) thin films were synthesized on various substrates (silicon, quartz, and sapphire) at 5% of O₂/Ar ratio gas and total pressure of 90 mTorr. The structural properties of the deposited films were analyzed by x-ray diffraction, while their semiconductor-to-metal phase transitions were studied by electrical resistivity using the four-point technique and infrared transmittance from room temperature up to 100 °C. The observed transition temperature was about 36 °C for W-doped VO₂ compared to 68 °C for VO₂ films. This transition temperature was then lowered by about 22.85 °C per 1 at. % of W added. The temperature coefficient of resistance was about 1.78%/°C for VO₂ and about 1.90%/°C for W-doped VO₂. Using the pump-probe experiment, the application of these thermochromic films as optical switches was demonstrated at the wavelength of 1.55 μm. The transmission switching was about 25 dB for VO₂ and 28 dB for W-doped VO₂. In addition, application of VO₂ on optical fiber components was demonstra- - ted by direct VO₂ coating on the end faces of cleaved single mode optical fibers and optical fiber connectors. © 2004 American Vacuum Society.