Enhanced Resistive Switching in Dopant-Free BFO Devices via TiO2 Insertion

Abstract

This work reports the tailoring of resistive switching behavior in multilayer BiFeO₃/TiO₂ heterostructures through controlled oxygen vacancies. TiN/TiO₂/BFO/Pt devices are fabricated using a sputtering process and the effect of BFO thickness on grain size, oxygen vacancies and in turn, on the memory window is investigated. The grain size was observed to be dependent on thickness, influencing the density of grain boundaries and consequently altering the oxygen vacancies. Furthermore, the resistive cell's switching behavior and conduction mechanism are systematically investigated. This study reveals notable enhancements in resistive switching behavior, including an increased memory window and improved endurance, due to the insertion of the TiO₂ layer. The incorporation of TiO₂ improves the resistive switching performance of BFO-based thin films by reducing defects, as confirmed by XPS analysis, thus enhancing stability and reproducibility. TiO₂ modulates oxygen vacancies, regulating their distribution within the BFO layer and reducing their density, which directly improves switching behavior. It also enables more uniform electroforming and SET/RESET processes, boosting retention, endurance, and reliability. Furthermore, TiO₂ may alter the local electric field, potentially lowering the switching voltage and increasing energy efficiency. The devices demonstrate resistive switching behavior at nanoscale dimensions, as indicated by conductive atomic force microscopy measurements. Remarkably, devices with 80 nm thick BFO on 20 nm thick TiO₂ exhibit a high ON/OFF current ratio of 1850 at a read voltage of 0.5 V and stable endurance up to 5.8×10⁶ cycles at room temperature, which is highest so far reported in multilayer BFO rewritable resistive devices. The devices have shown data retention of 10 years with less variation. Our findings indicate that the manipulation of oxygen vacancies through TiO₂/BFO bilayer heterostructures holds significant potential as a promising switching layer in the development of advanced RRAM devices with significantly enhanced performance characteristics.