Influence of rapid thermal annealing in vacuum on the resistive switching of Cu/ZnO/ITO devices

In this paper, we investigate the resistive switching (RS) behavior of Cu/ZnO/ITO devices subjected to various rapid thermal annealing (RTA) temperatures under vacuum. Current–voltage characteristics reveal that following the application of a positive electroforming voltage, both unannealed ZnO films and those annealed at 200 °C exhibit bipolar RS, consistent with the electrochemical metallization mechanism (ECM). However, films annealed at higher temperatures exhibit RS with both positive and negative electroforming threshold voltages and coexistence of switching in both polarities. Ultimately, these films display RS behavior aligned with the valence change mechanism (VCM), dominated by a negative electroforming voltage and RS on the negative bias side, while positive electroforming voltage and RS vanish for films annealed at 600 °C. Curve fitting analysis was conducted for Schottky emission (SE), space-charge limited current, and Poole–Frenkel (PF) emission mechanisms, with SE and PF emission providing better fits. These results demonstrate the tunability of ECM and VCM RS modes and the polarity of the forming bias, underscoring the potential of vacuum RTA in advancing ZnO-based memory device development.