Evolution of Non‐Volatile to Volatile Memory Behaviour in HfO₂/TiO₂ Bilayer Thin Film Based RRAM

Achieving an optimum memory window in a resistive random‐access memory (RRAM) necessitates a comprehensive understanding of defect‐induced and interface‐mediated transport mechanisms in oxide‐based bilayer devices. This study investigates the resistive switching (RS) behavior of HfO₂/TiO₂ bilayer thin films, demonstrating an enhanced switching window. The films are deposited on platinized silicon substrates using RF‐magnetron sputtering in an Ar/O₂ (40:1) plasma, followed by rapid thermal annealing at 300–600 °C in an N₂ atmosphere. Structural, morphological, and chemical analyses are performed using grazing incidence X‐ray diffraction, field‐emission scanning electron microscopy (FE‐SEM), atomic force microscopy (AFM), and X‐ray photoelectron spectroscopy (XPS). The HfO₂ (Hafnia) films remain amorphous for all the annealing temperatures, whereas the TiO₂ (Titania) films exhibit an anatase phase for annealing temperatures below 600 °C and a mixed anatase‐rutile phase at 600 °C. FE‐SEM and AFM reveal densely packed, crack‐free surfaces. Electrical characterization using a two‐probe method indicates that postdeposition annealing significantly influences the nonvolatile and volatile RS modes. The devices exhibit a large switching window (>10³) at an optimized read voltage (+1 V), high endurance (>200 cycles), and stable retention (>1500 s), demonstrating their potential for RRAM applications.