Multilevel non-volatile memory based on Al2O3/ZnO bilayer device

This Letter reports the multilevel resistive switching characteristics of bipolar bi-layer nanodevice made of Ag/Al2O3(10 nm)/ZnO (5 nm)/fluorine-doped tin oxide for the first time, exhibiting five distinguishable resistive states including both high resistance state (HRS) and low resistance state (LRS). Among five distinct memory states, three resistive states are attained with RESET voltages and two are attained with SET voltages. The distinguishable resistive levels obtained with RESET voltages 2.3, 3.0 and 3.8 V are 1300, 2700 and 4320 Omega, respectively, whereas two stable resistive levels attained with SET voltages 0.8 and 1.70 V are 3000 and 100 Omega, respectively. Moreover, the proposed device excels in its R-off/R-on ratio of 354 obtained with HRS/LRS at -1.4 V as well as the ratio of intermediate states IRS1, IRS2, IRS3 to HRS becomes 15, 04 and 27, respectively. Further, the conduction mechanism as well as the switching mechanism are demonstrated. Finally, the cycle-to-cycle as well as device-to-device variability in device characteristics and statistical distribution of their resistance levels are also analysed and report that devices in the sample are also exhibiting stable multilevel capability.