Coexistence of bipolar and unipolar resistive switching behaviors in the double-layer Ag/ZnS-Ag/CuAlO₂/Pt memory device

Graphical abstract: The schematic diagrams of the resistive switching (RS) mechanism with the different compliance current (CC). The formation and rupture of Ag-CFs in the CuAlO₂ layer should be accepted as the BRS behavior under the low CC of 1 mA, as shown in (a) and (b). A following transformation ("forming") process is necessary to realize the BRS-to-URS transformation, as shown in (c) and (d). Afterward, the formation and rupture of Cu-vacancy-CFs are responsible for the URS behavior in the case of high CC (10 mA), as shown in (e) and (f). - Highlights: • The coexistence of bipolar and unipolar resistive-switching (BRS and URS). • Increasing compliance current can realize the transformation from BRS to URS. • The CFs are composed of Ag atoms and Cu vacancies for BRS and URS, respectively. • The ZnS-Ag layer plays an important role in the RS localization. • The RS is located in the CuAlO₂ layer, realizing the uniform BRS and URS. - Abstract: The coexistence of uniform bipolar and unipolar resistive-switching (RS) characteristics was demonstrated in a double-layer Ag/ZnS-Ag/CuAlO₂/Pt memory device. By changing the compliance current (CC) from 1 mA to 10 mA, the RS behavior can be converted from the bipolar mode (BRS) to the unipolar mode (URS). The temperature dependence of low resistance states further indicates that the CFs are composed of the Ag atoms and Cu vacancies for the BRS mode and URS mode, respectively. For this double-layer structure device, the thicker conducting filaments (CFs) will be formed in the ZnS-Ag layer, and it can act as tip electrodes. Thus, the formation and rupture of these two different CFs are located in the CuAlO₂ layer, realizing the uniform and stable BRS and URS.