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Breaking The Current

Posted on:2020-12-10Degree:DoctorType:Dissertation
Country:ChinaCandidate:X L ZhaoFull Text:PDF
GTID:1368330590453960Subject:Materials Physics and Chemistry
Abstract/Summary:PDF Full Text Request
Cation-based resistive switching?RS?devices based on electrochemical and thermoelectrical mechanism have provided a subversive technology for nonvolatile memory,volatile selector,nonvolatile logic and neuromorphic computing applications.The cation-based RS device is generally based on the typical two-terminal sandwich structure,including an active electrode?AE?,the RS insulator layer and another inert electrode?IE?.Dominated by the electrochemical reaction and electromigration of AE element under external bias,the formation/rupture of the conductive filaments?CFs?modulates the switch of the device between high resistive state?HRS?and low resistance state?LRS?.In consideration of the CF stability/retention property,cation-based RS behavior can be divided into volatile threshold switching?TS?and nonvolatile memory switching?MS?.TS behavior loses its LRS and returns back to HRS immediately after removal of external stimulus,while MS behavior maintains its LRS quite well.The MS device can be utilized as the resistor?memory?,while the TS device as the selector in the crossbar array of resistive switching random access memory?RRAM?,to configure the one selector-one resistor?1S1R?unit,which depresses the crosstalk issue for high-density integration of RRAM.To ensure the validity of the RESET operation for the MS memory in the 1S1R unit,the TS selector must provide higher driving current than the working current of the MS memory.Owing to the typical current-retention relationship that the CF stability deteriorates greatly with the decrease of SET compliance current(ICC),it still remains a challenge to obtain nonvolatile MS memory with low operating current and volatile TS selector with high ON-state current.This is the typical current-retention dilemma in resistive switching devices.In this work,we mainly focus on the above general current-retention dilemma in resistive switching devices.The mainly contents of this thesis were listed as follow:?1?Detailed investigation and summary of the factors that influence the CF stability and previous achievements on CF stability modulation were reviewed?Chapter 2?.The CF stability generally correlates to the following factors,namely diffusion barrier of CF component in the RS dielectric layer,electrochemical environment around the CF,the CF morphology and so on.Large amount researches were performed corresponding to the above factors to modulate the CF stability,however,in aforementioned studies,MS memory device with low operating current or TS selectors with high ON-state current is reported individually in different material systems by unilaterally enhancing or deteriorating the CF stability.However,breaking the typical current-retention dilemma to achieve nonvolatile MS memory with low operating current and volatile TS selector with high ON-state current simultaneously in the same material system remains a great challenge in this field.?2?Based on conventional device structure,the feasibility of volatile cation-based TS device for nonvolatile information storage was successfully demonstrated by innovation of device programing methods?Chapter 3?.The CF rupture degree?gap?which dominates the threshold voltage(VTH)of the device,can be modulated by an effective RESET operation.Therefore,we proposed to storage information by the concept of CF rupture degree of the TS device.Since the retention performance of this TS memory?TSM?depends rarely on the SET ICC,the TSM device evades the current-retention dilemma and deserves ultra-low power dissipation by decreasing the ICC.Owing to its high nonlinearity,self-selective TSM device can be utilized for high-density integration of RRAM 3D crossbar array.Emulated by HSPICE,a sufficient read margin?10%?can be obtained in 10 Tbit self-selective TSM array in the ideal case.Based on the transmission electron microscope?TEM?and energy dispersive spectrometry?EDS?results,the relationships between the CF states and various switching stages were clarified.With self-selective,low-cost,low-energy,and potential high-density integration characteristics,this proposed TSM device has a great potential in the field of high-density storage.?3?Based on the innovative method of confining cation migration,we proposed to centralize/decentralize the CF distribution?changing CF morphology?by barrier layer with engineered ion paths to bidirectionally modulate the CF stability of cation-based RS devices,thus breaking the typical current-retention dilemma.?Chapter 4 and 5?.Confirmed by conductive atomic force microscope?C-AFM?and high-resolution transmission electron microscope?HRTEM?characterization,cation migration and CF formation can be allocated at the designed locations of the engineered barrier layer?graphene?.Centralizing/decentralizing the CF distribution by graphene defect engineering,the CF stability can be modulated bidirectionally,leading to the achievement of low operating current?1?A?memory and a high driving current?1 mA?selector in the same material system.Therefore,this method breaks the typical current-retention dilemma in resistive switching devices.This general method for various cation-based RS devices paves the way for ultimate high-density 3D 1S1R integration application of RRAM.This modulation method is with the following advantages:1),universality for almost all RS device structure;2)compatibility with other modulation methods of CF stability;3)transmissibility to ion batteries,ion sensors and so on.
Keywords/Search Tags:resistive switching random access memory(RRAM), conductive filament, threshold switching, ion barrier, graphene
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