In this research, solution-processed NiO-based memristors have been demonstrated with three resistive switching modes, including analog resistive switching, volatile threshold resistive switching and nonvolatile digital resistive switching, where the specific behavior is determined by the applied bias voltage and compliance current. The analog resistive switching is achieved via local oxygen ion migration at the NiO/Ag interface under low voltage stress. Based on this resistive switching mode, several synaptic functions are mimicked. When the device is stressed using a high voltage and a low compliance current, the device behavior changes to volatile threshold resistive switching. This behavior allows spiking neuron functions to be simulated. Furthermore, under application of a high compliance current, the device behavior converts to nonvolatile digital resistive switching. Ag filament formation and rupture processes are considered to be the mechanism behind the volatile threshold and nonvolatile resistive switching behavior. This multifunctional NiO-based memristor will provide a basis for fabrication of memory devices, analog circuits and artificial neural networks.
In this work, the effects of O2 or N2 microwave plasma treatment on β-Ga2O3 surface prior to Schottky metal deposition are reported. The device uniformity of Schottky barrier diodes (SBDs) is improved significantly by the microwave plasma treatments without any degradation such as ideality factor (near 1.0), and on-state resistance (Ron ~3 mΩ∙cm2). The standard deviation of Schottky barrier height (SBH, ϕb) is as small as less than 10 m eV. Kelvin probe force microscope (KFM) analysis shows that the surface electrostatic potential after O2 microwave plasma treatment is lower than that of the N2 microwave plasma treatment, which is consistent with the change of SBH obtained by Capacitance-Voltage (C-V) andCurrent-Voltage (I-V) measurements. The relatively low SBH with O2 microwave-plasma treatment corresponds to the high reverse leakage current. The oxygen related adsorption at metal/Ga2O3interface by O2microwave plasma treatment confirmed by X-ray photoelectron spectroscopy (XPS) can be attributed to the SBH and surface potential lowing.
The memristor-based neural crossbar is considered a promising device for research on neuromorphic computing. Moreover, memcapacitors can address the limitations caused by the resistive nature of memristors. A device with coexisting memristive and memcapacitive effects can provide rich features for neuromorphic computing systems. In this study, a device with a Pt/NiOx/NiO/Pt structure was developed; it demonstrates coexisting analog memristive and memcapacitive effects. The metallic NiOx serves as the oxygen storage layer and part of the top electrode. Analog memristive and memcapacitive effects are asynchronous; the resistance increases with reduction in capacitance. The physical mechanism for the asynchronous switching behavior of the resistance and capacitance was attributed to the reversible migration of oxygen ions between the metallic NiOx and semiconductor NiO in an electric field. The device was applied to mimicking simple synaptic functions such as short-term potentiation and short-term depression with small nonlinearity (0.0079 for potentiation and 0.00298 for depression). Complex neural properties such as homeostatic plasticity and habituation/sensitization were successfully simulated. This multifunctional device presents new applications for tunable oscillators and artificial neural networks (ANNs).
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