Multilevel characteristics for bipolar resistive random access memory based on hafnium doped SiO₂ switching layer

We fabricated TiN/Hf:SiO₂/Pt memory cell with the small size of 1×1 um² by lithography and sputtering technology, which demonstrated excellent bipolar resistive switching (RS) characteristics. The device presents good endurance and outstanding uniformity. The coefficient of variation of V_set, V_reset, R_on and R_off were found to be 5.05%, 4.78%, 4.18%, and 15.78%, respectively. For the device with hafnium doped SiO₂ switching layer, multilevel storage capability can be successfully obtained by varying either the stop voltage or the compliance current in the SET process. In addition, the impact of forming current on the RS properties was studied. We found that the ratio of On/Off current for the device increased with the decrease of the forming current, which would be beneficial for the design of low power device. Possible RS mechanisms aiming to explain the impact of forming current on the RS characteristics and multilevel storage were also deduced.