Research On The Characteristics Of Non-volatile Memory Based On Hafnium-based Ferroelectric Materials

Non-volatile memory is in strong demand due to the need for miniaturized,high-speed storage and low power consumption memory to meet big data.On the one hand,memristors are regarded as outstanding candidates in new types of memory due to their high-speed,non-volatile data storage capabilities.But integrated materials in memristors often suffer from process compatibility issues.The study found that ferroelectric memristors have functional materials that are compatible with conventional semiconductor technologies,with easily manipulated and reproducible physical mechanisms.However,there is a high lattice mismatch problem between conventional ferroelectric thin films and Si substrates.Against this background,researchers have shown great interest in hafnium-based ferroelectric materials,which have strong ferroelectric properties,with the most notable advantages being silicon process compatibility,size advantages,and the possibility of preparing functional thin films.On the other hand,Metal-Ferroelectric-Semiconductor（MFS）is a basic non-volatile ferroelectric memory.Since the ferroelectric layer is in direct contact with silicon,chemical reactions and interdiffusion occur,resulting in device performance degradation.Based on this structure,Metal-Ferroelectric-Insulator-Semiconductor（MFIS）is to improve the interdiffusion between the ferroelectric layer and silicon by adding an insulating layer between them.This thesis mainly studies the characteristics of two ferroelectric hafnium-based materials in non-volatile memory:ferroelectric memristor and MFIS ferroelectric memory.Its main contents are as follows:Firstly,A ferroelectric memristor with Pd/HGO/La_0.67Sr_0.33MnO₃/SrTiO₃/Si structure was fabricated using Gd-doped hafnium oxide（HGO）.To a start,X-Ray Diffraction（XRD）,Piezoelectric Force Microscope（PFM）,and hysteresis loops were used to characterize the ferroelectricity of HGO thin-film devices.Secondly,in the electrical test,the device shows good positive and negative switching characteristics and repeatability,stable high and low resistance retention characteristics,its high and low resistance ratio can reach 10³,and then on and off voltages are 1.53 V and-1.67 V respectively.Finally,this paper uses pulsed square waves to explore the law of enhancement and inhibition of gradual changes in bidirectional conductance,and successfully simulate biological synaptic functions such as PPF（Paired-pulse facilitation,PPF）and STDP（Spiking-Timing-Dependent Plasticity,STDP）.Importantly,we propose that ferroelectric inversion and oxygen vacancies are responsible for the resistance-switching mechanism.Secondly,A ferroelectric memristor with Pd/HSO/La_0.67Sr_0.33MnO₃/SrTiO₃/Si structure was fabricated by using Sm-doped hafnium oxide（HSO）.In this work,the device exhibits excellent ferroelectricity after characterization tests such as XRD and PFM.After the electrical test,the device shows excellent electrical performance.Under the action of the scanning voltage,the I-V curve shows the characteristics of positive and negative switching.Compared with the HGO thin film ferroelectric memristor,it has excellent switching characteristics,higher repetition,and more Stable holdover characteristics with smaller turn-on voltage（1.04 V）and turn-off voltage（-1.46 V）.In addition,the bionic function of synapses was explored.By regulating electrical signal pulses,two-way regulation of device conductance was achieved,and long-term potentiation（LTP）,long-term depression（LTD）,and PPF were realized.and STDP function emulation.This has a milestone effect on the entry of hafnium-based ferroelectric memristor into artificial neuromorphic computing.Thirdly,The MFIS memory device with Pd/HGO/SiO₂/Si structure was fabricated by using Gd-doped hafnium oxide.The characterization test was carried out first,and the ferroelectricity of the device was characterized by XRD and AFM.Then,the device was electrically tested,and the clockwise CV characteristics showed that the device was ferroelectric,and the CV characteristics of the device increased with the increase of the scan voltage.Under the voltage excitation of±5 V,a storage window of 0.85 V,and Cycle durability greater than 10⁴.Finally,the positive and negative bias energy band diagrams of Pd/HGO/SiO₂/Si devices are analyzed and discussed.These findings provide a new development direction for the application of hafnium-based ferroelectric materials in non-volatile memory.