Study On The Properties Of Artificial Synapses Based On Organic Ferroelectric Materials

The current emergence of the von Neumann bottleneck(the large developmental difference between CPU and memory)greatly limits the efficient processing of information in data-driven applications.The human biological brain is a multifunctional and energy-efficient system with strong cognitive ability and parallel computation-storage.It is the goal of most fields to build a perfect human brain computer.The existence of neurons and synapses is essential to the realization of brain function.One of the most fundamental features of an artificial synaptic device is that the signal output can be manipulated by either the intensity of the stimulus applied or the history of the excitation.As an artificial synaptic device,ferroelectric tunnel junction can effectively simulate synaptic function by controlling its electric polarization state.In this paper,we complete the simulation of synaptic responses in manufactured organic ferroelectric tunnel junctions(OFTJs)under optimized PVDF conditions,and verify the role of LTP,LTD and pulse training performance.In addition,our device can also achieve polymorphic storage function.The main contents are as follows:(1)Optimization of PVDF thin film preparation process.The preparation process was adjusted to prepare PVDF films with good properties.For example,in order to achieve the polarization reversal of PVDF layer under the condition of low voltage,it requires a certain limit on the thickness of the film.We control the thickness of polyvinylidene fluoride(PVDF)film after spinning by adjusting the concentration of DMF:PVDF solution.At the same time,important parameters such as rotational speed and time in the process of spinning and coating are adjusted.Change the heat treatment conditions of PVDF films after spinning coating,such as annealing environment,annealing temperature and annealing time.Then,the properties of PVDF films were characterized by phase structure analysis,surface morphology analysis,roughness and thickness analysis.The results show that the PVDF films obtained at 20 mg/ m L of DMF:PVDF solution by spinning coating at 3000 RPM for 60 s and heat treatment at 150?for 2 h have obvious diffraction peaks corresponding to ? phase,and the ferroelectric behavior is obvious.And the film surface has no obvious defects such as cracks,cavities,the film surface is smooth,continuous,compact,relatively smooth enough,better performance.(2)Preparation of ferroelectric tunnel junction based on indium tin oxide(ITO)/PVDF/Au structure.The ITO conductive layer with a thickness of 100 nm was used as the bottom layer of the organic ferroelectric tunnel junction.The ITO layer was exposed by ultraviolet exposure machine in the laboratory,and then developed and etched with hydrogen chloride solution.The long strip bottom electrode with a width of 200 ?m was obtained.According to the optimized process parameters,DMF:PVDF solution was spin-coated on ITO/ glass substrate.In order to improve the crystallinity of ferroelectric phase,it was heat-treated in the air at 150 ? for 2 h to complete the growth and preparation of organic ferroelectric thin film as the intermediate layer.Finally,the top electrode Au was sputtered on PVDF thin film by changing a specific mask and magnetron sputtering method.(3)The synaptic behavior of ITO/PVDF/Au samples was simulated.The ferroelectric polarization of the barrier layer is regulated by applying an electric field between the electrodes of the device using an electrical test platform,thereby regulating its resistance(synaptic weight).Experiments demonstrated LTP,LTD and pulse training performance of synaptic plasticity.It was found that the resistance of the device could be successfully enhanced by 20 positive pulses and reduced by 15 subsequent negative pulses.The resistance of the device increases monotonically with the increase of the number of pulses,and the device has the characteristics of resistance retention and reproducibility,which proves the reliability of the device prepared by us.In addition,our device can also achieve polymorphic storage function.