Understanding the coexistence of two bipolar resistive switching modes with opposite polarity in CuxO (1 ≤ x ≤ 2)-based two-terminal devices

In this work, we have fabricated and tested the resistive switching behavior of non-volatile nature in a number of devices with mainly two architectures: (1) W tip/Cu x O/Pt/Ti/SiO 2 /Si and (2) Cu contact pad/Cu x O/Pt/Ti/SiO 2 /Si. The device type (1) showed coexistence of two bipolar resistive switching modes, commonly known as eight-wise (8w) and counter-eight-wise (c8w), in their current–voltage ( I-V ) characteristics. We report considerably high ON/OFF ratio of 10 5 and stable retention time 15 × 10 3 s. The formation and annihilation of metallic Cu nanofilaments were argued as the plausible reason behind the observed resistive switching events. The onset of quantized conductance steps in the typical conductance plots (in units of quanta of conductance 2 e 2 /h, where e and h are electronic charge and Planck’s constant, respectively) – a phenomenon usually observed in narrow conductive channel – was exploited to provide an “indirect” proof for formation of metallic Cu-based filaments or channels during switching. On the contrary, in device type (2), we observed only “regular” bipolar switching. The operating voltage was less than 1 V in both the devices – suggesting its potential low-power applications. We assessed the underlying conduction mechanism in depth and also theoretically estimated the lateral size of the tiny conductive nanofilaments formed during the switching events. Copper being a cost-effective and widely available substance, our results indicate that Cu x O-based cells can be a feasible and useful route for non-volatile resistive memories.