Conduction mechanisms of TaN/HfOx/Ni memristors

The conduction mechanisms of TaN/HfOx/Ni memristors are investigated in the wide temperature range from 4.2 to 400 K. The hafnium oxide layer was deposited by ion-beam sputtering deposition (IBSD) at different partial oxygen pressures for various samples, for which resistive switching was possible. This range of partial oxygen pressures corresponded to the x range from 1.78 to 1.81 The analysis and fitting of the current-voltage (I-V) curves of low- and high-resistance states (LRS and HRS, respectively) at different temperatures revealed that, at temperatures above similar to 70 K, the conduction is governed by the thermal generation of free carriers and space-charge-limited current (SCLC). Specifically, it is shown that trap-free and trap-mediated SCLCs govern the conduction for the LRS and HRS, respectively. At lower temperatures, the conduction in both states was found to be practically temperature-independent. At the same time, the TaN/HfOx/Ni memristor functioned properly at temperatures as low as 4.2 K. The x value is shown to influence the slope of the HRS I-V curves, and it correlates with the change in the SCLC power-law exponent (m, I proportional to V-m). TaN/HfOx/Ni memristors with low values of x <= 1.79 demonstrated the current power-law dependence on voltage in the HRS with m > 2 (3.0-6.5) and for the memristors with higher x values in the HRS of m approximate to 2. Within the suggested model, a local trap-rich conducting region was presumed to be formed in the oxide layer between the metal electrodes after the memristor forming process. The I-V curves modeling indicates that the LRS and HRS differ from each other by the thickness of this active region and the trap distribution. The role of oxygen vacancies and polyvacancies in HfOx, which are considered to act as charge carrier traps, is discussed.