Coexistence of Bipolar and Unipolar Resistive Switching Behavior in Ag/ZnMn_2O_4/p^+-Si Device

ZnMn_2O_4 thin films were deposited by a sol-gel technique onto a p+-Si substrate, and a RRAM device with the Ag/ZnMn_2O_4/p^+-Si structure was fabricated. The microstructure of ZnMn_2O_4 films and the resistive switching behavior of Ag/ZnMn_2O_4/p^+-Si device were investigated. ZnMn_2O_4 thin films had a spinel structure after annealing at 650 °C for 1 h. The Ag/ZnMn_2O_4/p^+-Si device showed unipolar and/or bipolar resistive switching behavior, exhibiting different ION/IOFF ratio and switching endurance properties. In bipolar resistive switching, high-resistance-state(HRS) conduction was dominated by the space-charge-limited conduction mechanism, whereas the filament conduction mechanism dictated the low resistance state(LRS). For unipolar resistive switching, HRS and LRS were controlled by the filament conduction mechanism. For bipolar resistive switching, the conduction process can be explained by the space-charge region of the p-n junction.

Security enhancement of artificial neural network using physically transient form of heterogeneous memristors with tunable resistive switching behaviors

As a critical command center in organisms,the brain can execute multiple intelligent interactions through neural networks,including memory,learning and cognition.Recently,memristive-based neuromorphic devices have been widely developed as promising technologies to build artificial synapses and neurons for neural networks.However,multiple information interactions in artificial intelligence devices potentially pose threats to information security.Herein,a transient form of heterogeneous memristor with a stacked structure of Ag/MgO/SiN_(x)/W is proposed,in which both the reconfigurable resistive switching behavior and volatile threshold switching characteristics could be realized by adjusting the thickness of the SiN_(x)layer.The underlying resistive switching mechanism of the device was elucidated in terms of filamentary and interfacial effects.Representative neural functions,including short-term plasticity(STP),the transformation from STP to long-term plasticity,and integrate-and-fire neuron functions,have been successfully emulated in memristive devices.Moreover,the dissolution kinetics associated with underlying transient behaviors were explored,and the water-assisted transfer printing technique was exploited to build transient neuromorphic device arrays on the water-dissolvable poly(vinyl alcohol)substrate,which were able to formless disappear in deionized water after 10-s dissolution at room temperature.This transient form of memristive-based neuromorphic device provides an important step toward information security reinforcement for artificial neural network applications.

Effects of Electrode on Resistance Switching Properties of ZnMn_2O_4 Films Deposited by Magnetron Sputtering

ZnMn_2O_4 films for resistance random access memory（RRAM） were fabricated with different device structures by magnetron sputtering. The effects of electrode on I-V characteristics, resistance switching behavior, endurance and retention characteristics of ZnMn_2O_4 films were investigated. The ZnMn_2O_4 films, using p-Si and Pt as bottom electrode, exhibit bipolar resistive switching（BRS） behavior dominated by the space-charge-limited conduction（SCLC） mechanism in the high resistance state（HRS） and the filament conduction mechanism in the low resistance state（LRS）, but the ZnMn_2O_4 films using n-Si as bottom electrodes exhibit both bipolar and unipolar resistive switching behaviors controlled by the Poole-Frenkel（P-F） conduction mechanism in both HRS and LRS. Ag/ZnMn_2O_4/p-Si device possesses the best endurance and retention characteristics, in which the number of stable repetition switching cycle is over 1000 and the retention time is longer than 106 seconds. However, the highest RHRS/R_（LRS） ratio of 104 and the lowest V_（ON） and V_（OFF） of 3.0 V have been observed in Ag/ZnMn_2O_4/Pt device. Though the Ag/ZnMn_2O_4/n-Si device also possesses the highest RHRS/R_（LRS） ratio of 104, but the highest values of V_（ON）,V_（OFF）, RHRS and R_（LRS）, as well as the poor endurance and retention characteristics.