Study On The Resistance Switching Properties Of VO₂ And Its Application Of Simulated Neurons

In the era of big data explosion,the demand of data information processing is increasing rapidly.Neuromorphic computational structures with powerful processing power and high energy efficiency attracted worldwide research interests.Neuromorphic devices are one of the hot topics in the field of neuromorphic computing.According to different functions,neuromorphic devices can be roughly divided into synaptic devices and artificial neuron.Relatively speaking,synaptic devices have been extensively studied,while artificial neurons have larged behind.Artificial neurons based on phase change materials have been considered as one kind of the most promising artificial neurons due to their unique phase change characteristics,scalability and integration.Among Mott phase change materials,VO₂ is a good candidate material for the preparation of artificial neurons due to its phase transformation temperature that is close to room temperature and good phase transformation performance.This thesis focuses on the potential of VO₂ in the field of artificial neurons.The mechanism analysis of VO₂ oscillation characteristics is presented through exploring several aspects in particular,i.e.the resistance characteristics of VO₂ materials,the preparation method of VO₂ devices,resistance properties of VO₂ thin film devices,and the simulation and verification of the VO₂ oscillation circuit.The research of VO₂artificial neurons is based on the construction of VO₂ simulation model,analysis of VO₂oscillation circuit,and the design and validation of VO₂ neurons.The main body of this thesis includes the following three sections:1.VO₂ devices with good resistance switching properties were fabricated by a three-step process consisting of reactive sputtering,rapid annealing and electroforming.The results show that,as the precursor film of electroforming VO₂ devices,the composite phase vanadium oxide films prepared by rapid annealing in the three-step process are densier than the polycrystalline VO₂ films prepared by reactive sputtering,and the crystallinity phase in the electroforming films is better than that of polycrystalline VO₂ films prepared by reactive sputtering.The test results show that the switching ratio of the VO₂ device prepared by the three-step method is significantly higher than that of the device prepared by the polycrystalline VO₂ film prepared by reactive sputtering.2.By using LTSPICE software,a circuit simulation model with similar resistance switching properties characteristics to VO₂ device was built,and on this basis,a VO₂oscillation circuit was constructed.The simulation results show that the oscillation amplitude of the VO₂ oscillation circuit is only related to its resistance switching properties,and the circuit components and input signals can only affect the oscillation period of the VO₂ device.Then,the influence mechanism of temperature on the oscillation characteristics of VO₂ oscillation circuit is further tested and analyzed.Temperature will obviously affect the amplitude and period of the VO₂ oscillation circuit.At higher ambient temperatures,the oscillating circuit exhibits the phenomenon of double amplitude oscillation.This may provide a new idea for the application of VO₂in new circuits.3.Based on the above VO₂ oscillation circuit,a novel VO₂ artificial neuron circuit is designed and verified.The simulation and test results show that the VO₂ artificial neuron circuit is similar to the biological neuron circuit in many aspects,including the output waveform after stimulation and the trend of waveform change.The pulse period of VO₂ artificial neuron is stable near room temperature.But the pulse period will show an obvious downward trend when the ambient temperature reaches 29?.When the temperature reached 40?,the VO₂ artificial neuron was destroyed.It suggests that the VO₂ artificial neuron circuit is similar to biological neuron in temperature dependence.