Memristive devices are promising candidates to emulate biological computing. However, the typical switching voltages (0.2-2 V) in previously described devices are much higher than the amplitude in biological counterparts. Here we demonstrate a type of diffusive memristor, fabricated from the protein nanowires harvested from the bacterium Geobacter sulfurreducens, that functions at the biological voltages of 40-100 mV. Memristive function at biological voltages is possible because the protein nanowires catalyze metallization. Artificial neurons built from these memristors not only function at biological action potentials (e.g., 100 mV, 1 ms) but also exhibit temporal integration close to that in biological neurons. The potential of using the memristor to directly process biosensing signals is also demonstrated.

Metal halide perovskite materials have shown versatile functionality for a variety of optoelectronic devices. Remarkable progress in device performance has been achieved for last few years. Their high performance in combination with low production cost puts the perovskite optoelectronics under serious consideration for possible commercialization. A fundamental question that remains unanswered is whether these materials can sustain their optoelectronic properties during harsh and prolonged operational conditions of the devices. A major concern stems from an unprecedented and unique feature of perovskite materials, which is migration of ionic species (or charged defects). Recent studies have indicated that the ion migration might be a limit factor for long-term operational stability of the devices. In this regard, herein we have reviewed important studies on discovery, quantification, and mitigation of the ion migration process in metal halide perovskite materials. A possible emerging application using the ion migration is also briefly introduced.

Recently, organic-inorganic halide perovskite (OHP) has been suggested as an alternative to oxides or chalcogenides in resistive switching memory devices due to low operating voltage, high ON/OFF ratio, and flexibility. The most studied OHP is 3-dimensional (3D) MAPbI. However, MAPbI often exhibits less reliable switching behavior probably due to the uncontrollable random formation of conducting filaments. Here, we report the resistive switching property of 2-dimensional (2D) OHP and compare switching characteristics depending on structural dimensionality. The dimensionality is controlled by changing the composition of BAMAPbI (BA = butylammonium, MA = methylammonium), where 2D is formed from n = 1, and 3D is formed from n = ∞. Quasi 2D compositions with n = 2 and 3 are also compared. Transition from a high resistance state (HRS) to a low resistance state (LRS) occurs at 0.25 × 10 V m for 2D BAPbI film, which is lower than those for quasi 2D and 3D. Upon reducing the dimensionality from 3D to 2D, the ON/OFF ratio significantly increases from 10 to 10, which is mainly due to the decreased HRS current. A higher Schottky barrier and thermal activation energy are responsible for the low HRS current. We demonstrate for the first time reliable resistive switching from 4 inch wafer-scale BAPbI thin film working at both room temperature and a high temperature of 87 °C, which strongly suggests that 2D OHP is a promising candidate for resistive switching memory.

Perovskite-related (CH3NH3)3Sb2Br9 exhibits forming free properties in memristor devices and low energy consuming artificial synaptic behavior for neuromorphic computing.

As silicon-based metal oxide semiconductor field effect transistors get closer to their scaling limit, the importance of resistive random-access memory devices increases due to their low power consumption, high endurance and retention performance, scalability, and fast switching speed. In the last couple of years, organic-inorganic lead halide perovskites have been used for resistive switching applications, where they outperformed conventional metal oxides in terms of large on/off ratio and low power consumption. However, there were scarce reports on lead-free perovskites for such applications. In this report, we prepared lead-free Au/ABiI/Pt/Ti/SiO/Si (A is either Cs or Rb) devices and tested their resistive switching characteristics. They showed a forming step prior to repeating switching, low operating voltage (0.09 V for RbBiI and 0.1 V for CsBiI), large on/off ratio (>10), relatively high endurance (200 cycles for RbBiI and 400 cycles for CsBiI cycles), and high retention (1000 s). Such low voltage could be explained by grain boundary-modulated ion drift. Difference in endurance was speculated to be due to the difference in the surface roughness of films because CsBiI films are smoother. To get rid of the forming step, 10% of the Bi cations were substituted with Na cations. However, this method only worked on Rb-based structures. This phenomenon was explained by the defect formation energy, which can only be negative in a corner-sharing RbBiI structure compared to a face-sharing octahedral CsBiI structure. As a result, the forming step was removed, and 100 cycles endurance and 1000 s retention performance were obtained. Similarly, the lower endurance is suspected to be due to the poor surface quality of the film.