Study On Preparation And Neural Synaptic Characteristics Of Memristors Based On Hf_0.5Zr_0.5O₂ And SnO₂ Thin Films

With the development of artificial intelligence and cloud computing technologies,conventional computers based on the Von Neumann architecture are gradually failing to meet the increasing demand for data acquisition and storage,and there is an urgent need to develop new computing architectures in order to overcome these difficulties.Research has found that neuromorphic computing systems are considered to be a very promising candidate.Inspired by the biological brain,simulating artificial synaptic behavior is a key way to accomplish neuromorphic computing.As a typical representative of the next generation of non-volatile memories,memristors have received a lot of attention due to a series of advantages such as their simple structure,small size and the ability to mimic neurosynaptic behavior.Among them,Hf_0.5Zr_0.5O₂（HZO）ferroelectric memristors have shown great potential for neurosynaptic applications as their resistance depends on the polarization flip of ferroelectric domains.Sn O₂,an abundant,inexpensive and harmless oxide semiconductor material with good conductivity tunability,is a good candidate for the preparation of memristors to achieve synaptic plasticity behavior,and therefore this thesis addresses the above two materials to carry out research related to memristor properties,mainly as follows:Firstly,Pd/HZO/La_0.67Sr_0.33Mn O₃（LSMO）/Sr Ti O₃（STO）/Si devices were prepared by using pulsed laser deposition technique.At first,two laser energy densities were used to deposit the buffer layer STO film and the bottom electrode LSMO film,and the optimal experimental laser energy density conditions were selected.Then,by investigating the effects of different deposition temperatures,deposition oxygen pressure and laser sputtering frequency on the ferroelectricity,crystalline quality and roughness of HZO films,the deposition temperature of 750°C,deposition oxygen pressure of 20 Pa,laser sputtering frequency 2 Hz and laser energy density of 1.1 J/cm²were identified as the optimum preparation conditions,which laid a solid foundation for the study of the neurosynaptic bionic properties of HZO thin film ferroelectric memristor.Secondly,the Pd/HZO/LSMO/STO/Si device prepared under optimum conditions was tested.In terms of electrical performance,the device demonstrated good resistive switching characteristics,excellent repeatability and stable high and low resistance retention characteristics,with endurance tests up to 10⁸cycles in pulse mode.Pulse modulation tests have shown that the device has continuous conductance tunability and has achieved the simulation of a 3×3 memristor array with a memory letter“X”,and has successfully simulated paired pulse facilitation（PPF）,post-tetanic potentiation（PTP）and spike time dependent plasticity（STDP）were successfully simulated.Finally,the physical mechanism of resistive change was analyzed by I-V fitting,and the properties of the memristor were used to simulate Pavlovian conditioned reflex experiments.Thirdly,Pd/Sn O₂/Ti N/Si devices were prepared using magnetron sputtering technology,and a series of electrical performance tests on resistive switching were carried out.A retention time of 2×10⁴s and a continuous I-V scan of 50 cycles could be achieved in the voltage scan mode,showing the good resistive switching stability of the devices.Interestingly,continuously tunable conductance was achieved by pulse modulation,which simulated the pre-learning behavior and biological synaptic functions such as PPF,PTP,PPD and STDP during learning,and successfully implemented the four-rule operation.Finally,the I-V fit analysis indicates that the low resistance state（LRS）of the device is dominated by the ohmic conduction mechanism,and Schottky emission is the primary conduction mechanism in the high resistance state（HRS）of the device.