The mechanism of electrical threshold switching in VO2crystals

I-V characteristics of doped VO 2 (0.8% Ti, 1.0% Al and 0.8% Cr) single crystals have been measured using a constant current source in the ambient temperature region 230 to 310K. The temperature of the crystal surface has also been measured. At switching the temperature of the crystal surface increases by only 3 to 6K above the ambient for different ambient temperatures. This suggests the formation of a current channel before switching. It is observed that the threshold voltage (V th ) increases but the current at switching (I th ) decreases with decreasing ambient temperature, giving a temperature-independent threshold power. The average critical power density at switching is 4.33*10 -3 W mm -3 for different doped and undoped VO 2 crystals. I-V measurements have also been made by placing electrodes on the crystal surface. It is observed that the threshold voltage increases with increasing electrode separation d but for d to 0 V th gives a finite value. The ideal thermal models fail to give even qualitative agreement with the observed I-V and switching characteristics.