Alloy electrode engineering in memristors for emulating the biological synapse.

The development of conductive bridging random access memory (CBRAM) as an artificial synaptic device is an important step in the realization of an efficient biomimetic neural morphology computing system. In fact, CBRAM devices with simple substance electrodes often form unstable and discrete conductive filaments, thereby resulting in poor device performance. In this work, the effects of different alloy electrode ratios on the performance of HfOx devices with dielectric layers were systematically investigated via electrode composition engineering. The devices (a kind of memristor) with an Ag-Cu ratio of 63 : 37 exhibited a lower formation voltage and set voltage, better set voltage distribution uniformity, faster response speed, and lower power consumption than other devices. Moreover, the device is capable of emulating the biosynapse functions, including paired-pulse facilitation (PPF), post-tetanic potentiation (PTP), spike-rate-dependent plasticity (SRDP), and spike-timing-dependent plasticity (STDP). Interestingly, the associative learning process of Pavlov's dog experiment and aversion therapy were also realized without the use of complex external circuits. The use of electrode component engineering provides a new path for boosting the memristor properties via CBRAM devices, thereby laying the foundation for further development of neural morphology computing systems.

Flexible Transparent Organic Artificial Synapse Based on the Tungsten/Egg Albumen/Indium Tin Oxide/Polyethylene Terephthalate Memristor.

As artificial synapses in biomimetics, memristors have received increasing attention because of their great potential in brain-inspired neuromorphic computing. The use of biocompatible and degradable materials as the active resistive layer is promising in memristor fabrication. In this work, we select egg albumen as the resistive layer to fabricate flexible tungsten/egg albumen/indium tin oxide/polyethylene terephthalate devices, which can operate normally under mechanical bending without significant performance degradation. This proposed memristor device exhibits a transparency of more than 90% under visible light with a wavelength range of 230-850 nm. Moreover, by changing amplitudes of pulse voltage instead of intervals, paired-pulse facilitation can be transmitted to paired-pulse depression, which can faithfully mimic dynamical balance of Ca2+ concentration shaped by voltage-sensitive calcium channels. The device resistance can be modulated gradually by applied pulse trains to mimic certain neural bionic behaviors, including excitatory postsynaptic current, short-term plasticity (STP) and long-term plasticity (LTP), and transitions between STP and LTP. The reasons behind these behaviors are analyzed through power consumption calculation. Excellent biosimulation characteristics have been demonstrated in this egg albumen-based memristor device, which is desirable in biocompatible and dissolvable electronics for flexible artificial neuromorphic systems.