Charge storage and transport in metal oxide resistive switching devices

Abstract

Metal oxide resistive switching devices are designed and prepared using atomic layer deposition (ALD) and spin coating methods. The electrical and optical characteristics are studied for their applications in memory, photo-detection, and chemical sensing. Two electrically dissimilar ZnO thin film layers produced by using two different ALD recipes on a Si substrate as a bilayer is studied and found to have characteristics (rectification, hysteresis, and threshold voltage) needed to solve the crosstalk problem in crossbar memory array. ZnO bilayer device has fingerprint of a memristive device with AC frequency. The ratio of high to low resistive states (HRS/LRS) increases, reaches its maximum and starts to decrease with increasing frequency of applied AC voltage which is attributed to the diffusion dominating low frequency transport and charge freeze at high frequency. The maximum HRS/LRS achieved at 1 kHz is 2.3. Next part of the study deals with the α-Fe₂O₃ thin films on p-Si and glass substrates. α-Fe₂O₃ /p-Si samples show excellent ultra-fast visible light photo-detection property of response times under 10 µs with large zero bias photocurrent of >16 nA. The study of resistive switching properties of the α-Fe₂O₃ /p-Si samples reveals that it has synaptic potentiation property of neurons. The device's conductance increases with increasing voltage pulse applied to it and saturates at its maximum after some pulses. The mathematical hill function fit to the conductance data shows that activation of the device is programmable with the intensity of white light illumination. α-Fe₂O₃ /glass sample shows the coexistence of resistive switching and negative differential resistance phenomena in the presence of humid air with the transport analysis, it is attributed to the formation of the space charge at the material electrode interface. The same sample is used to quantify the relative humidity in air by using a novel sweeping I-V method.