Experiments and simulation of multilevel resistive switching in forming free Ti/TiO2−x RRAM devices

We report high multilevel resistive switching in forming free resistive random access memory (RRAM) using Ti (4 nm) as top electrode. We demonstrate that at least six-level resistance states could be obtained by modifying the amplitude of the voltage pulse applied on the memory cell or the compliance current, exhibiting excellent resistance uniformity and retention capability. The resistive switching mechanism is believed to be associated with the generation/dissolution of conducting filaments (CFs) that mainly consist of oxygen vacancies, while the gradual transitions indicate the manifestation of trap-assisted conduction model. During DC scan low power resistive switching was recorded for both SET (about 50 mW) and RESET (about 50 μW) processes, while for pulse voltages even lower power was achieved (0.4 mW and 30 nW respectively) for 100 ns switching duration. A numerical approach is also presented in order to elaborate on the origins of the switching effect. The self-rectification characteristics in conjunction with the room temperature fabrication process render our device attractive for future high-density crossbar memory arrays applications.