Analyzing the activation energy drift in quenched a-VO_x films

The conductivity drift (Δσ) in a-VO_x films were studied by studying temperature dependent conductivity when the films are subjected to thermal stress. This study includes temperature dependent conductivity and activation energy measurements. The experimental results indicate that the VO_x films exhibit a Δσ and reduction in activation energy after quenching. The origin of the Δσ is attributed to metastable defect formation in the film at high temperatures, that are subsequently frozen into the film during a rapid cooling in liquid nitrogen (quenching). The newly formed metastable defects must overcome a barrier energy to relax back into their normal state. The energy provided by room temperature is not enough to overcome this barrier. We present results to show that isothermal annealing of these quenched films (at 150^oC, 200^oC, and 220^oC) expedites the recovery of the Δσ back to its baseline value. The Δσ vs time data for the isothermal anneals exhibits a stretched exponential trend. In response to the accelerated recovery time when heated after quenching, an anneal before quenching was done on the VO_x films. This study found that a VO_x film, when slow annealed 100^oC in oxygen ambient and then quenched, had a lower Δσ immediately after quenching and an accelerated recovery when compared to an unannealed quenched film.