The Coexistence Behavior of Bipolar and Unipolar Switching in AlN-Based Memristors

In this study, a memristor with an Al/aluminum nitride (AlN)/Pt structure was fabricated, and the coexistence of bipolar resistance switches (BRS) and unipolar resistance switches (URS) was observed. The device exhibits a high resistance state (HRS) with a resistance value exceeding$10^{{5}} \Omega $for both switching modes. Remarkably, the device demonstrates excellent retention characteristics, maintaining stability for up to$10^{{4}}$s. Endurance testing revealed that the device can sustain over$10^{{3}}$DC switching cycles, with resistance switching ratios greater than$10^{{2}}$in BRS mode and exceeding$10^{{3}}$in URS mode. To investigate the underlying conduction mechanisms, we performed conductive atomic force microscopy (C-AFM) measurements coupled with current-voltage (${I}$-${V}$) curve fitting analysis. Our findings reveal that the low-resistance state (LRS) conduction is governed by the formation of conductive filaments (CFs), while the forming process exhibits carrier transport characteristics consistent with Schottky emission. Both BRS and URS modes in the HRS regime demonstrate space-charge-limited current (SCLC) conduction behavior. Furthermore, temperature-dependent resistance measurements of the LRS suggest that the CFs are predominantly composed of Al atoms, providing crucial insights into the atomic-scale switching mechanisms in this memristive system.