Conducting Ferroelectric Domain Walls in Neuromorphic and Conventional Logic Device Demonstrators

The electrical conductivity of lithium niobate thin film capacitor structures depends on the density of conducting 180 degree domain walls, that traverse the interelectrode gap, and on their inclination angles with respect to the polarization axis. Both microstructural characteristics can be altered by applying electric fields, but changes are time-dependent and relax, upon field removal, into a diverse range of remanent states. As a result, the measured conductance is a complex history-dependent function of electric field and time. Here, we discuss how the complexity in the kinetics of microstructural change, in this ferroelectric system, can generate transport behavior that is strongly reminiscent of that seen in key neurological building blocks, such as synapses and neurons. We show that potentiation-depression, spike-rate-dependent plasticity (SRDP) and spike-timing-dependent-plasticity (STDP) typically seen in synapses can also be seen in domain wall-based memristors. Even Ebbinghaus forgetting (a response more typical of an entire brain) can be replicated.<br/>Not only do such capacitor structures allow for neuromorphic responses, but the strong diode-like behaviours found can also be used to construct “AND” and inclusive “OR” logic gates, where “0” and “1” output states are clearly distinguishable. Realistic device modelling allows an extrapolation of results in more complex arrangements and, although non-ideal, output states can still be distinguished even in two-level cascade logic. Thus domain wall based devices allow for new kinds of processing in which both neuromorphic and conventional notions of computation sit side-by-side.