Study On The Micro-structure Regulation Of Amorphous Carbon And Its Application To ReRAM

Resistive switching memory(ReRAM),has a tremendous potential to be the next generation non-volatile memory owing to its superior performance including simple structure,good scaling capacity,fast programming speed and low power consumption.ReRAM has a sandwich structure of metal/insulator/metal,in which the material property of switching insulator and the interface characteristic between electrode and insulator are the key factor to the switching performance of ReRAM devices.Therefore,the choice for insulating layer and optimization of the interface characteristic are the core topic.Generally,the migration of metal cations in electrochemical metallization devices and oxygen ions in valence change devices,which will result in the formation and rupture of conductive filaments,is the physical origin of resistance switch.However,the randomness of the formation location,diameter and micro morphology of the conductive filament is still far from resolution.Our works mainly aim at the key issues of ReRAM devices,making some regulations for switching behavior and investigating the switching mechanism,and make some exploration on function expansion.1.On the controlliabity of the geometrical morphology of conductive filament through annealing a-C:N.(i)Firstly,we have investigated the main cause of large switching fluctuation of the conventional amorphous carbon based ReRAM devices(cycle-to-cycle,device-to-device).The result shows that the operating state of memory devices has something to do with the particular case of forming operation.(ii)The pore diameter of amorphous carbon film could be continuously adjusted through annealing a-C:N film.And we have investigated the relationship between the switching performance and the diameter of conductive filament.(iii)A dual-layer nanoporous structure was proposed to regulate the micro-morphology of the preformed conductive filament.The resulting device showed super performance,forming-free characteristic,uniform switching parameter and excellent endurance capacity(>10~5 cycles).2.On the regulation of sp~2 cluster size to improve the switching uniformity of amorphous carbon based ReRAM and some application on anti-interference domain.The previous reported methods for improve the switching uniformity of ReRAM devices almost concentrated on the electrode morphology and the embedding of metal nanoparticles,and few reports carry out the adjustment on the switching insulator layer itself.This work had regulated the diameter of sp~2 culsters to improve the switching uniformity using the method of annealing amorphous carbon film(<400°C).And we have made some exploration on anti-interference domain.The write-once-read-many(WORM)devices with large operation voltage(8.9 V average voltage)and compliance current had been prepared.3.On the study of low temperature graphitization of amorphous carbon for adjusting the local electric field intensity to improve the resistive switching performance.(i)The mountain-like surface-graphited carbon(MSGC)layer had been realized through executing annealing operation under 500°C.And the realization of low temperature graphitization of amorphous carbon with high sp~2 concentration ratio had been validated with AFM images,XRD,XPS and Raman spectrum.(ii)The MSGC structure,as the interlayer between a-C and Pt electrode,was applied for building the Cu/a-C/MSGC interlayer/Pt memory devices,which showed outstanding RS reliability.For revealing the universal characteristic of MSGC interlayer,we had also made an attempt on oxide based ReRAM devices.In addition,the CFs switching region can be localized near the MSGC tips and the MSGC layer can also serve as good oxygen reservoir,which enables the complete CFs formation and rupture processes.As a result,good cycling endurance with low degradation rate can be realized.Therefore,the current work demonstrates that introducing the MSGC layer can be an effective,large-area-fabricate capable and universal approach to improve ReRAM performance.4.On the regulation of the oxygenated carbon bonds using oxygen plasma treatment for realizing self-power-read ReRAM.The oxygen plasma treatment on amorphous carbon would introduce many oxygenated carbon bonds,such as O-C-O and O-C=O.The structure of self-power-read memory device had been verified by XPS and cross-sectional TEM analysis.The introduction of oxygenated carbon bonds results in spontaneous ionizing of oxygen-containing functional groups,which leading to the longitudinal diffusion of the generated H~+.The induced open-voltage and short-current could be utilized to self-power-read function.