Brain-inspired neuromorphic computing can overcome the energy and throughput limitations of traditional von Neumann-type computing systems, which requires analog updates of their artificial synaptic strengths for the best recognition performance and low energy consumption. Here, we report synaptic devices made from highly insulating ferroelectric LiNbO₃ (LNO) thin films bonded to SiO₂/Si wafers. Through the creation/annihilation of periodically arrayed antiparallel domains within LNO nanocells, which are stimulated using positive/negative voltage pulses (synaptic plasticity), we can modulate the synaptic conductance linearly by controlling the number of the conducting domain walls. The multilevel conductance is nonvolatile and reproducible with negligible dispersion over 100 switching cycles, representing much better performance than that of random defect-based nonlinear memristors, which generally exhibit large-scale resistance dispersion. The simulation of a neuromorphic network using these LNO artificial synapses achieves 95.6% recognition accuracy for faces, thus approaching the theoretical yield of ideal neuromorphic computing devices.

Single LiNbO₃ (LNO) crystals are widely utilized in surface acoustic wave devices, optoelectronic devices, and novel ferroelectric memory devices due to their remarkable electro-optic and piezoelectric properties, and high saturation and remnant polarizations. However, challenges remain regarding their nanofabrication that hinder their applications. The prevailing etching techniques for LNO encompass dry etching, wet etching, and focused-ion-beam etching, each having distinct merits and demerits. Achieving higher etching rates and improved sidewall angles presents a challenge in LNO nanofabrication. Building upon the current etching researches, this study explores various etching methods using instruments capable of generating diverse plasma densities, such as dry etching in reactive ion etching (RIE) and inductively coupled plasma (ICP), proton exchange-enhanced etching, and wet chemical etching following high-temperature reduction treatment, as well as hybrid dry and wet etching. Ultimately, after employing RIE dry etching combined with wet etching, following a high-temperature reduction treatment, an etching rate of 10 nm/min and pretty 90° sidewall angles were achieved. Furthermore, high etching rates of 79 nm/min with steep sidewall angles of 83° were obtained using ICP dry etching. Additionally, using SiO₂ masks, a high etching rate of 108 nm/min and an etching selectivity ratio of 0.86:1 were achieved. Distinct etching conditions yielded diverse yet exceptional results, providing multiple processing paths of etching for the versatile application of LNO.

High-density domain wall memory based on crossbar architecture is a strong contender among next-generation high performance versatile memories due to its ultra-fast operation speed and excellent size scalability. Herein, we report 4 $\times $ 4 domain wall crossbar memory arrays fabricated on a LiNbO3 single crystal. Reversible creation and erasure of conducting domain walls between two antiparallel/parallel domains at bipolar write voltages enable the storage of digital “0” and “1” information. At the crosspoint of each word and bit lines, the memory cell can be accurately accessed, programmed and erased. The diode-like rectification of readout currents exhibited by all memory cells can inhibit read and write crosstalk. The electrical testing results in the crossbar memory array demonstrated the good stability of on/off currents and good uniformity of operating voltages, which can be reflected by the fact that the distribution of the coercive voltages is within 2.9 V and the “on”/ “off” current ratio is around 100 at a reading voltage of 3 V. Good data retention and fatigue resistance are also exhibited, making it possible to integrate domain wall random access memories in high density and reliability.