Mechanism of analog bipolar resistive switching and work function in Au/Na0.5Bi0.5TiO3/Pt heterostructure thin films

Abstract

We report on the room temperature work function value of Na0.5Bi0.5TiO3 (NBT) thin films and bias dependent analog bipolar resistive switching characteristics in Au/Na0.5Bi0.5TiO3/Pt thin film hetero-structure. Na0.5Bi0.5TiO3 thin films crystallize in rhombohedral (R3c) structure, confirmed from the Raman and X-ray diffraction studies. Scanning electron microscope images indicates that the surface morphology is smooth and films grown in rod-like structure vertically. Oxidation states of Na, Bi and Ti elements are confirmed from the X-ray photoelectron spectroscopy technique. The device retains its bipolar switching behavior in direct current (dc) sweeping mode by an applied voltage of ±3 V, without any deterioration suggests good retention characteristics. The ON/OFF resistance ratio (RON/ROFF) between high and low resistance states is of the order of 10. The role of oxygen vacancies and charge transport process in low resistance state (LRS) and high resistance states (HRS) are examined using Ohmic and space-charge-limited conduction mechanisms. The current-voltage (I–V) characteristics show space-charge-limited conduction dominates at high electric fields. The average work function value of the Na0.5Bi0.5TiO3thin film at room temperature is found to be 5.09 eV. The interface interactions of Au/NBT and NBT/Pt thin layers and their role in initiating resistive switching is discussed in detailed.