Ultra-wide temperature electronic synapses based on self-rectifying ferroelectric memristors.

Memristors have been intensively studied in recent years as promising building blocks for next-generation nonvolatile memory, artificial neural networks and brain-inspired computing systems. However, most memristors cannot simultaneously function in extremely low and high temperatures, limiting their use for many harsh environment applications. Here, we demonstrate that the memristors based on high-Curie temperature ferroelectrics can resolve these issues. Excellent synaptic learning and memory functions can be achieved in BiFeO3 (BFO)-based ferroelectric memristors in an ultra-wide temperature range. Correlation between electronic transport and ferroelectric properties is established by the coincidence of resistance and ferroelectricity switch and the direct visualization of local current and domain distributions. The interfacial barrier modification by the reversal of ferroelectric polarization leads to a robust resistance switching behavior. Various synaptic functions including long-term potentiation/depression, consecutive potentiation/depression and spike-timing dependent plasticity have been realized in the BFO ferroelectric memristors over an extremely wide temperature range of -170 °C âˆ¼ 300 °C, which even can be extended to 500 °C due to the robust ferroelectricity of BFO at high temperatures. Our findings illustrate that the BFO ferroelectric memristors are promising candidates for ultra-wide temperature electronic synapse in extreme or harsh environments.

Mediation in the second-order synaptic emulator with conductive atomic force microscopy.

Memristors have been extensively studied for synaptic simulation and neuromorphic computation. Instead of focusing on implementing specific synaptic learning rules by carefully engineering external programming parameters, researchers recently have paid more attention to taking advantage of the second-order memristor that is more analogous to biologic synapses and modulated not only by external inputs but also by internal mechanisms. However, experimental evidence is still scarce. Here, we explore a BiMnO3 memristor by applying simple spike forms. The filament evolution dynamics, including processes of forming and spontaneous decay, were directly observed by the conductive atomic force microscopy (c-AFM) technique. We propose that the unique conductance state of the BMO memristor is regulated by the oxygen vacancy (VO) dynamic process. We believe this primary result is helpful to improve understanding of the internal mechanisms of the second-order oxide memristor, which exhibits promising application in building selectors, memories and neuromorphic-computing systems.

Space-charge Effect on Electroresistance in Metal-Ferroelectric-Metal capacitors.

Resistive switching through electroresistance (ER) effect in metal-ferroelectric-metal (MFM) capacitors has attracted increasing interest due to its potential applications as memories and logic devices. However, the detailed electronic mechanisms resulting in large ER when polarisation switching occurs in the ferroelectric barrier are still not well understood. Here, ER effect up to 1000% at room temperature is demonstrated in C-MOS compatible MFM nanocapacitors with a 8.8 nm-thick poly(vinylidene fluoride) (PVDF) homopolymer ferroelectric, which is very promising for silicon industry integration. Most remarkably, using theory developed for metal-semiconductor rectifying contacts, we derive an analytical expression for the variation of interfacial barrier heights due to space-charge effect that can interpret the observed ER response. We extend this space-charge model, related to the release of trapped charges by defects, to MFM structures made of ferroelectric oxides. This space-charge model provides a simple and straightforward tool to understand recent unusual reports. Finally, this work suggests that defect-engineering could be an original and efficient route for tuning the space-charge effect and thus the ER performances in future electronic devices.