Hybrid memory characteristics of NbO_x threshold switching devices

By exploiting NbO_x, we demonstrate its hybrid memory characteristics, indicating that resistive switching is unified with selector behavior. First, we identify that the 50-nm-thick amorphous NbO_x inherently shows volatile threshold switching (TS). To enable memory switching (MS) in NbO_x, device environments are configured that can supply oxygen vacancies or cations constituting a conductive filament (CF). In the Al/NbO_x/TiN stack, oxygen vacancies can be internally generated from an interfacial oxide layer formed by the chemical reaction between a highly reactive Al electrode and NbO_x, which is confirmed via multiple physical analyses. When the effect of the extrinsic vacancies becomes comparable to the intrinsic properties of the NbO_x, the hybrid memory characteristics are observed. While the TS prevents leakage current, the MS is driven by oxygen vacancy CF, allowing multilevel cell operation. Furthermore, hybrid switching can be obtained using the Cu/NbO_x/TiN stack. However, the effect of a Cu CF is dominant, because the Cu electrode can externally provide ions infinitely in this case; therefore, hybrid memory behavior is achieved after MS is performed.