Multiple nano-filaments based efficient resistive switching in TiO ₂ nanotubes array influenced by thermally induced self-doping and anatase to rutile phase transformation

Abstract

In this paper, the impact of thermally induced self-doping and phase transformation in TiO₂ based resistive random-access memory (ReRAM) is discussed. Instead of a thin film, a vertically aligned one-dimensional TiO₂ nanotube array (TNTA) was used as a switching element. Anodic oxidation method was employed to synthesize TNTA, which was thermally treated in the air at 350 °C followed by further annealing from 350 °C to 650 °C in argon. Au/TiO₂ nanotube/Ti resistive switching devices were fabricated with porous gold (Au) top electrode. The x-ray diffraction results along with Raman spectra evidently demonstrate a change in phase of crystallinity from anatase to rutile, whereas photoluminescence spectra revealed the self-doping level in terms of oxygen vacancies (OV) and Ti interstitials (Ti_i) as the temperature of thermal treatment gets increased. The electrical characterizations establish the bipolar and electroforming free resistive switching in all the samples. Among those, the ReRAM sample S₃ thermally treated at 550 °C displayed the most effective resistive switching properties with R _OFF/R _ON of 10² at a read voltage of -0.6 V and a SET voltage of -2.0 V. Moreover, the S₃ sample showed excellent retention performance for over 10⁶ s, where stable R _OFF/R _ON ≈ 107 was maintained throughout the experiment.