Investigation Of The Charge Storage Mechanism Of Organic/Inorganic Resistive Switching Memory Cells In Micro-Nano Scale

As downscaling size of electron products and an improvement of the integration levels,a memory device,which with high storge density,high stability and low power consumption,is urgently demanded in the near future.Conventional memory devices,especially the flash memory device,which is widely applied in massive electron products,are facing with a bottleneck in the storge density,power consumption and stability,because the function layer of SiO₂ is reaching its physical limit thickness.Resistive switching?RS?memory as one of new memories,its resistance switched from a high state?HRS?to low state?LRS?can be used to relize the information storage.Not only the lower consumption,higher storage density,but also the simple fabrication of the RS memory has.Depended upon the meatrial development,structure design and integration with other electron device,such as nanogenerator,field effect transistor and oscillator,great progress and breakthrough were made for the RS memory in recent years.Therefore,the RS memory is believed to be one of the most promising candidates to replace the convention flash memory application in next negetration memory device.Despite that,the RS memory is also facing some challenges,such as the variation parameter,stability and mechanism.The RS mechanism as fundamental and important factor dominates the RS memory development,control and application.Researchers have made great efforts in investigation the RS memchansim for decades.The ion migration-induced?conductive path?and trap-related?space charge limited current?as main mechanisms dominated the RS behaviors are widely accepted by tremendous researchers.The?traps?model is through the charge traping/deprapping from the traps to realize the resistance switching from HRS to LRS,while?conductive path?is through the formation and rupture of migration of metallic ion to realize the change of resistance.Up today,the RS behavior in most of nanoscale devices can be explained by the two physical models,but the microscale or bulk material-based RS memories are paied little attention.In addition,the typical meterials such as TiO₂,NiO and ZnO,the influence of ambient on the RS behavior also is insufficiently studied.In this work,therefore,we devote ourselves to investigate the RS mechanism of the organic/inorganic device with micro-nano scale.The study will give an important sight into the RS memory behaviors in micro-and nano-scale device,the influence of ambient on RS mechanism is deeply investigated as well.The paper contents are deviced into four parts:Firstly,a self-assembly three-dimensional MoS₂ microsphere was synthesized through hydrothermal method.The MoS₂ microspheres were spin-coated on the surface of ITO substrate,and then the Ag electrodes were fabricated using the steel hole-mask.Therefore,the microscale RS memoy with a Ag/MoS₂/ITO structure was developed.Current-voltage?I-V?measurement implies that the device shows a bipolar RS memory behavior,which with a ratio of HRS/LRS of 10⁴ and the endurance for 200 cycles.The I-V fitting results imply that the space charge limited current?SCLC?dominates the HRS region,and Omic conduction mechanism dominates the LRS region.Analysis of the energy dispersive X-ray spectroscopy of the memory cell cross-section,some Ag elements have penetrated into the MoS₂ film during the device fabrication process,but not reached the ITO electrode.It imples that the Ag conduction path might form or rupture in nanoscale.In addition,the charge transfer in the grain boundaries generated by the connection of MoS₂ nanosheets might contribute to the RS memory behaviors as well.Therefore,the charge transfer along the grain boundaries,Ag metal conductive filament and charge trapping/detrapping form traps co-contributes into the RS memory of microscle MoS₂ microsphere device.Secondly,in order to avoid the nanoscale Ag metal contribution,MoSe₂-doped Se ultralong microwires with length of⁵00?m and diameter of²?m were synthesized using hydrothermal method.Au electrodes firstly were deposited on the SiO₂ substrate,and then,single microwire was selected using the probstaion,finally,Ag electrodes were fabiracted.Therefore,the device with the structure of Ag-Au/MoSe₂-doped Se/Au-Ag was develoed.I-V cureve measurements demonstrate the RS memory behavior with a soft SET/RESET process,and asymmetric loops in negative and positive voltage regin.Therefore,the memory belongs to the electron type RS memory?ERSM?.The fitting result of I-V illustrates that both the LRS and HRS are dominated by the SCLC mechanism.Therefore,we deduced that the microscale RS memoy device is dominated by the charge trapping and detrappign from traps.Then,the transition metal oxide of TiO_x as the typical material of RS is further investigated.The isopropanol,titanium isopropoxide,hydrochloric acid?HCl?were mixed to fabricate precursor.Thin films of titanium oxide were fabricated using transparent precursor spin-coated on FTO glass or Pt/Si substrate and then were annealed at 850 K in atmosphere for 3 hours.The Ag or Au electrodes are fabricated using stell hole-mask.Comparsion study the Ag/TiO_x/FTO,Au/TiO_x/FTO and Ag/TiO_x/FTO memory cells,competition between the Ag filament and oxygen vacancy cocontributes to the coexistence of RS and negtive differential resistance.Water molecules interplay with the oxygen vacancy of surface or subsurface result in the generation of OH^-.The migration of OH^-along the grain boundaries facilitates the two conduction paths.Finally,among the organic-based nanoscale RS memory device,the 10%H₂O₂and egg albumen mixted as precursor is spin-coated on the flexiable ITO substrate,then the Ag electrodes are fabricated using stell hole-mask.The fabricated device after bending for more than 10³ times shows typical bipolar RS memory behaviors,the ratio of HRS/LRS is more than 10⁴ and the cycle number is higher than 900.By the analysis of Fourier transform infrared spectrum,Breakage of massive protein chains occurs followed by the recombination of new protein chain networks due to the oxidation of amidogen and the synthesis of disulfide during the hydrogen peroxide modifying egg albumen.Ions such as Fe³⁺,Na⁺,K⁺,which are surrounded by protein chains,are exposed to the outside of protein chains to generate a series of traps during the eggalbumen degeneration process.Due to the generation of the traps,the RS memory effect of egg albumen is enhanced.In conclusion,the RS mechanism is systemically investigated in terms of the material,structure,size and ambivent.The results indicate that a micro-size RS device is mainly dominated by the charge trapping and deptrapping from traps,but the RS device in a nano-scale,the charge tunneling,hopping or trapping in the interfaces and the migration of anion/cation co-contribute the RS behaviors,simultaneously,the RS behaviors are influenced by the ambient as well.