Unipolar Resistive Switching and Associated Photo Response in Multifunctional BiFeO3 (BFO) Thin Films in Planar Geometry Grown By RF Sputtering

We have studied the resistance switching phenomenon and associated photo response   in BiFeO₃ (BFO) thin films in planer electrode configuration. The films were grown by optimized RF sputtering process on SrRuO₃ (SRO) buffered Pt/TiO₂/SiO₂/Si substrates. X-ray diffraction pattern and Raman spectrum of as grown film showed formation of high quality BFO thin films. To fabricate device structure top electrodes of platinum of thickness ~50nm and diameter ~200μm were grown on BFO layer using DC sputtering.  The as grown film in planer geometry measurements showed high resistance of ~1MΩ and when voltage of ~ 4.0V was applied to the structure the resistance of the device switched to a low value of ~20Ω. It is noted that no forming process was required in this case.  The repeatable switching of resistance of the Pt/BFO/SRO structure between low and high resistances has been observed with resistance ratio of ~ 10⁵   and well defined switching voltages in the range of 1.75-2.5V and 3.0-4.0 V respectively in case of reset and set processes which is suitable for non volatile resistive random access memory applications. The precise control of the compliance current during the switching process from high to low resistance state revealed multiple resistances of low resistance state indicating possibility of multibit non volatile memory.  To our knowledge, this type of resistance switching in BFO in planer geometry has been reported for the first time. The current conduction mechanism in the low resistance states was found to be dominated by the Ohmic behavior whereas in case of high resistance it followed poole frenkel emission at higher voltages. The efficient short circuit photo-current density was observed which was ~2 order in magnitude higher in  case  of low resistance state compared to high resistance state  when  illuminated with white light having power density of ~ 1kW/m² .  Further works are underway to understand the results and establish the associated photo voltaic effect and will be discussed at the meeting.