Tailored nanoplateau and nanochannel structures using solution-processed rutile TiO₂ thin films for complementary and bipolar switching characteristics

We synthesized two different nanostructures of rutile TiO₂ (r-TiO₂) thin films on a fluorine-doped tin oxide (FTO) substrate at the lowest temperature reported until now and fabricated resistive random access memory (RRAM) devices with these r-TiO₂ thin films having the stacking sequence of Ag/r-TiO₂/FTO. Complementary resistive switching (CRS) and bipolar resistive switching (BRS) were observed in different thicknesses of r-TiO₂ based devices. Benefiting from the in situ growth of the solution processed thin films and modulating the reaction growth rates, we successfully attained two different morphologies of r-TiO₂ with a nanoplateau at a controlled deposition rate and pre-defined nanochannels at a higher deposition rate. The RRAM devices with nano-plateaus of r-TiO₂ showed excellent CRS as well as unprecedented simultaneous observations of BRS. These CRS and BRS characteristics were reversible and reproducible. On the other hand, the tailored pre-defined nanochannels in r-TiO₂ led to forming-free BRS with a pulse endurance higher than 10⁷ without any degradation in the high and low resistance states. We propose a plausible switching mechanism of these unprecedented events using various physical and electrical characterization studies of low-temperature processed r-TiO₂ RRAM devices. This work suggests the importance of solution-processed thin film engineering for RRAM switching with reliable and reproducible characteristics.