Tuning local conductance to enable demonstrator ferroelectric domain wall diodes and logic gates

Fundamentally, lithium niobate is an extremely good electrical insulator. However, this can change dramatically when 180o domain walls are present, as they are often found to be strongly conducting. Absolute conductivities depend on the inclination angles of the walls with respect to the [001] polarisation axis and so, if these inclination angles can be altered, then electrical conduction can be tuned, or even toggled on and off. In ~500nm thick z-cut ion-sliced thin films, localised wall angle variations can be controlled by both the sense and magnitude of applied electrical bias. We show that this results in a diode-like charge transport response which is effective for half-wave rectification at modest frequencies. Importantly, we experimentally demonstrate that such domain wall diodes can be used to construct “AND” and inclusive “OR” logic gates, where “0” and “1” output states are clearly distinguishable. An extrapolation of experimental results for the operation of these domain wall diodes in more complex arrangements was done using realistic modelling and, although non-ideal, output states can still be distinguished even in two-level cascade logic. Our insights hence show that simple logic gates can be realised by localised manipulation of domain wall conductivity, resulting from changes in the magnitude of the polarisation discontinuity supported at the wall (changing the wall inclination angle with respect to the polar axis). Our insights complement those published very recently by Jie Sun et al. (Adv. Funct. Mater. 2207418 (2022)) where NOT, NOR and NAND gates were realised by moving conducting domain walls to make or break electrical contacts.