  Two-dimensional (2D) materials are popular candidates for emerging nanoscale
devices, including memristors. Resistive switching (RS) in such 2D material
memristors has been attributed to the formation and dissolution of conductive
filaments created by the diffusion of metal ions between the electrodes.
However, the area-scalable fabrication of patterned devices involves polymers
that are difficult to remove from the 2D material interfaces without damage.
Remaining polymer residues are often overlooked when interpreting the RS
characteristics of 2D material memristors. Here, we demonstrate that the
parasitic residues themselves can be the origin of RS. We emphasize the
necessity to fabricate appropriate reference structures and employ atomic-scale
material characterization techniques to properly evaluate the potential of 2D
materials as the switching layer in vertical memristors. Our
polymer-residue-based memristors exhibit RS typical for a filamentary mechanism
with metal ion migration, and their performance parameters are strikingly
similar to commonly reported 2D material memristors. This reveals that the
exclusive consideration of electrical data without a thorough verification of
material interfaces can easily lead to misinterpretations about the potential
of 2D materials for memristor applications.
