Light-Programmable Ferroelectric Domain Walls in Thin-Film Lithium Niobate: A Multiphysics Simulation Study

Conductive ferroelectric domain walls in lithium niobate combine nonvolatile, multilevel memristive conductance with the strong electro-optic response of the host crystal, which makes them attractive functional elements for reconfigurable photonic devices on the thin-film lithium niobate platform. Here we report a multiphysics simulation study of how the domain-wall conductance, and therefore the electro-optically transduced optical response, can be programmed by illumination and temperature. The screening-charge relaxation is modelled as a thermally activated dark process combined with a photo-induced contribution from above-band-gap illumination; the predicted relaxation time decreases with both increasing temperature and increasing illumination. We examine three alternative photoconductivity models and find that the qualitative behaviour—the existence of an optimum illumination window and the direction of the tuning trends—is independent of the assumed functional form, while the quantitative relaxation time depends on it. Within the model, three device-level capabilities are predicted: light-tuned fading memory with an optimum illumination window in which the one-step prediction error of a chaotic time series improves by a factor of 1.7; optical assistance that enables low-voltage multilevel nonvolatile programming; and thermal robustness of the memory capacity over an extended temperature range of 250–400 K. A parameter-sensitivity analysis shows that the memory capacity remains within 0.98–1.02 for all parameter variations examined, whereas the one-step prediction error varies by less than a factor of 1.6. We additionally quantify the system-level energy budget including illumination and thermal control, estimate the interferometer operating limits, and present the light-absorption and domain-switching considerations that define the experimental conditions. All results are model predictions and are intended to guide and be tested by experiments; experimental verification in a thin-film lithium niobate interferometer remains to be performed.