Annealing effect on forming-free bipolar resistive switching characteristics of sol-gel WOx resistive memories with Al conductive bridges

Abstract

This paper studies the annealing-temperature dependent resistive switching (RS) behavior of forming-free Al/WOx/ITO memories, where the WOx active layers were prepared using a sol-gel process. The as-fabricated WOx resistive random-access memory (RRAM) is highly conductive and shows no RS characteristic. Bipolar RS behavior is obtained when the 200 °C-annealed WOx film was employed as the RS layer. The ratio of the resistance in the high-resistance state (HRS) to that in the low-resistance state (LRS) is 10. When the annealing temperature is increased to 300–400 °C, a significant increase in the resistance ratio to ~103 is obtained. A clear resistance window can be observed in the endurance test of the 300 °C-annealed RRAM, while a failure in set operation, switching from the HRS to LRS, is detected in that of the 400 °C-annealed RRAM. The performance change caused by the annealing process is attributed to the differences in the crystallinities, content of oxygen-vacancy defects and surface morphologies between the RRAMs. Aluminum conductive bridges are able to explain the RS mechanisms of the WOx RRAMs.