Reliable and Low-Power Multilevel Resistive Switching in TiO₂ Nanorod Arrays Structured with a TiO_x Seed Layer

The electrical performance of TiO₂ nanorod array (NRA)-based resistive switching memory devices is examined in this paper. The formation of a seed layer on the fluorine-doped tin oxide (FTO) glass substrate after treatment in TiCl₄ solution, before the growth of TiO₂ NRAs on the FTO substrate via a hydrothermal process, is shown to significantly improve the resistive switching performance of the resulting TiO₂ NRA-based device. As fabricated, the Al/TiO₂ NRA/TiO_x layer/FTO device displayed electroforming-free bipolar resistive switching behavior while maintaining a stable ON/OFF ratio for more than 500 direct sweeping cycles over a retention period of 3 × 10⁴ s. Meanwhile, the programming current as low as ∼10^-8 A and 10^-10 A for low resistance state and high resistance state respectively makes the fabricated devices suitable for low-power memristor applications. The TiO_x precursor seed layer not only promotes the uniform and preferred growth of TiO₂ nanorods on the FTO substrate but also functions as an additional source layer of trap centers due to its oxygen-deficient composition. Our data suggest that the primary conduction mechanism in these devices arises from trap-mediated space-charge-limited current (SCLC). Multilevel memory performance in this new device is achieved by varying the SET voltage. The origin of this effect is also discussed.