Study On Preparation And Performance Of Vanadium Dioxide Electric-phase Change Induced Oscillator

Since vanadium was discovered,the phase transition characteristics of its oxides have been studied extensively.Among them,VO₂ has attracted more attention with its phase transition temperature closest to room temperature.The phase transition of VO₂can be triggered by thermal,electrical,optical,pressure and other excitation modes,among which the triggering mode of the electric phase transition provides convenience for the device application of VO₂.In recent years,neuromorphic computing provides a new strategy to solve Von Neumann’s bottleneck,and new devices for neuromorphic computing have become a hot research topic.The phase transformation characteristics of VO₂ provide a new opportunity for the development of high performance Mott memristor neurons.VO₂ thin films with high switching ratio and Negative Differential Resistance（NDR）are the basis for the development of Mott memristor neurons.At present,most of the VO₂ films that meet the requirements are prepared by high temperature epitaxy process,which makes the preparation of VO₂ Mott memrisor difficult to be compatible with the traditional CMOS process.In this thesis,a VO₂ memristor with large switching ratio and NDR characteristics was fabricated by rapid thermal annealing process,and a VO₂ VCO with good oscillation characteristics was fabricated by 1T1R structure.On this basis,the effects of film thickness and ambient temperature on the stability of the oscillator and the decoding function of the oscillator as a neuron are explored.The main research of this thesis is as follows:（1）The VO₂ memristor obtained by magnetron sputtering after deposition of amorphous vanadium oxide films is studied.The VO₂ memristor prepared by in situ annealing process has low switching ratio and no NDR region,so it cannot meet the demand.In the second way,rapid thermal annealing is carried out first,and VO₂ thin films are formed at both ends of the electrode by electroforming process.The VO₂memristor prepared by rapid thermal annealing process has two orders of magnitude switch ratio and distinct NDR region,which lays a foundation for the preparation of subsequent oscillators.（2）The working principle and frequency performance of VO₂ VCO with 1T1R structure are studied.In the VO₂ oscillator unit with 1T1R structure,the VO₂ Mott memristor is used as the resistor R,and the field effect transistor is used as the transistor T.In the oscillating circuit,the VO₂ memristor provides negative feedback function in the negative differential region,and the field effect transistor plays the role of current limiting and pressure dividing.Compared with other VO₂ oscillators,this structure has the advantages of wide operating voltage,stable amplitude,adjustable crest and so on.The VO₂ VCO with a 400nm film thickness has a center frequency of 1.372MHz and an adjustable ratio of±44%.（3）The influence of film thickness and ambient temperature on the stability of VO₂oscillator is studied,and the application of the oscillator in neural morphology calculation is explored.Appropriate reduction of film thickness can effectively improve the oscillator center frequency,adjustable ratio basically unchanged.The VO₂ oscillator decodes the encoded space-time information and presents it as a clear waveform.The bionic properties of the oscillator are further explained.