Layer-by-Layer Resistive Switching: Multistate Functionality due to Electric-Field-Induced Healing of Dead Layers

Materials exhibiting reversible resistive switching in electrical fields are highly demanded for functional elements in oxide electronics. In particular, multilevel switching effects allow for advanced applications like neuromorphic circuits. Here, we report a structurally driven switching mechanism involving the so-called “dead” layers of perovskite manganite surfaces. Forming a tunnel barrier whose thickness can be changed in monolayer steps by electrical fields, the switching effect exhibits well-defined and robust resistive states.

Figure 1

Metallic regions created by electric pulses at the initially insulating surface. (a) Current map recorded at 0.1 V showing the spatial distribution of conductance at the surface. (b) Distribution of current values with respect to their $x$ and $y$ position, visualizing regions of homogeneous conductance as horizontal lines.

Figure 2

Conductance and topography regions switched from LRS to HRS. (a) Current map recorded at $U=0.1\mathrm{V}$. After switching to LRS (red environment), negative voltage pulses have been applied at the locations indicated by circles. (b) Corresponding topography image. The correlation between contact resistance (red) and height (blue) is illustrated by profiles along the indicated path (d). (c) Distribution of current values occurring in dependence of the x and y locations as intensity map. Identified logarithmically spaced current values are shown in orange, missing levels are indicated in green. (e) Current in dependence of the ascribed tunnel barrier thickness with fit curve according to MIM model.

Figure 3

Schematic band picture of the intrinsic tunnel barrier and geometrical contact model of the regions switched in CAFM. (a) The bulk of the LSMO and the Pt-coated AFM tip are separated by an insulating tunnel barrier. (b) Switching to LRS creates metallic regions at the surface, which act as broadened electrode to the underlying barrier. (c) Applying negative voltage pulses at a fully LRS-switched sample creates insulating layers of integer monolayer thicknesses at the surface, giving rise of the logarithmically stepwise scaling of the current values.