High-speed mott-transition switches bases on VO2 layers
Résumé
We present the out-of-plane non-linear electrical properties of vanadium dioxide thin films integrated in metal-insulator-metal (MIM) resistive devices. Vanadium dioxide (VO2) is a metal-insulator phase transition (MIT or Mott-transition) material which shows a reversible, temperature-driven structural and electronic phase transition near tMIT=68°C from an insulating state to a metallic one. VO2 films have been deposited by reactive electron beam evaporation from a vanadium target under oxygen atmosphere on different substrates (sapphire, Si, SiO2). The obtained films exhibit sharp changes in electrical and optical properties across the phase transition. We investigated the influence of the deposition parameters (substrate temperature, oxygen pressure, substrate R.F. incident power, and deposition rate) on the films' main properties (roughness, structural, evolution of MIT and electrical and optical properties). The films properties were optimized through experimental plans. The current-voltage characteristics of the fabricated MIM devices show the presence of negative differential resistance regions, allowing the onset of current- controlled electrical self-oscillations across the device. The measured switching speed between the high-and low-resistance states of the VO2 devices is below 5 nanoseconds. We investigate the influence of the MIM designs (metal electrodes, layer thickness) on the switching time and we correlate them with the film properties and excitation conditions.