Initiation of switching in VO2coplanar devices

Thin films of VO2have been formed at 400°C by reactive RF sputtering in an argon-oxygen atmosphere. Their resistivity changes by a factor of more than 100 at 68°C. Fabrication of coplanar devices has allowed measurements of the prebreakdown region and the breakdown parameters. When a voltage is applied between the electrodes, the internal temperature rises and the device switches to the "on" state. Threshold voltage and current are investigated versus ambient temperature. Below about 10°C, switching is a pure thermistor effect; above this point, application of voltage causes the device temperature to rise to the phase transition temperature, when the conductivity increases sharply. The IV characteristic in the prebreakdown region and the two different thermal breakdown phenomena are analyzed theoretically.