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A resistive switching ZnO n–n homojunction diode fabricated with a stack of two dissimilar ZnO thin films shows promising characteristics necessary to address the crosstalk problem in a crossbar memory array. The device has a characteristic I–V-hysteresis loop in forward bias, in conjunction with its n–n junction characteristics. In the ac frequency range of 10 Hz–15 kHz, the area inside the hysteresis loop initially increased, reaching a maximum at 1 kHz, and then decreased with increasing frequency. The maximum in the area of the hysteresis loop corresponds to the accumulation of space charge at the interface. The resistivity of the device was found to vary from 5 to 100 kΩ in the bias range of 0–10 V and in the range of 106 Ω when reverse biased; the ratio of high resistive state to low resistive state has its maximum (∼2.4) at 1 kHz ac signal at 3 V. [ABSTRACT FROM AUTHOR]

A signature of synaptic potentiation conductance has been observed in an α-Fe2O3/p-Si device fabricated using spin coating. The conductance of the device in dark conditions and illumination with a white light source was characterized as a function of the application of a periodic bias (voltage) with a triangular profile. The conductance of the device increases with the number of voltage cycles applied and plateaus to its maximum value of 0.70 μS under dark conditions and 12.00 μS under illumination, and this mimics the analog synaptic weight change with the action potential of a neuron. In the range of applied voltage from 0 V to 0.7 V, the conduction mechanism corresponds to trap-assisted tunneling (TAT) and in the range of 0.7–5 V it corresponds to the Poole–Frenkel emission (PFE). The conductance as a function of electrical pulses was fitted with a Hill function, which is a measure of cooperation in biological systems. In this case, it allows one to determine the turn-on threshold (K) of the device in terms of the number of voltage pulses, which are found to be 3 and 166 under dark and illumination conditions, respectively. The gradual conductance change and activation after a certain number of pulses perfectly mimics the synaptic potentiation of neurons. In addition, the threshold parameter extracted from the Hill equation fit, acting as the number of pulses for synaptic activation, is found to have programmability with the intensity of the light illumination. [ABSTRACT FROM AUTHOR]