Study On The Working Mechanism Of Resistive Random Access Memory Based On MoS₂

With the development of science and technology,the demands on memory are increasing.Flash memory has the advantages of fast speed and good endurance,accounting for 90%of nonvolatile memory market.However,flash memory suffers from several obvious disadvantages such as miniaturization limitation and difficulty to improve performance.So new solutions are needed.Resistive Random Access Memory(RRAM)is one of the potential candidates as next generation memory devices because of its simple structure and high performance.Organic material can be used as storage medium to obtain flexibility,which can be widely applied in the field of biomedicine and wearable devices.But its performance is not satisfying due to its poor high temperature tolerance and low operating frequency.Two-dimentional layerd MoS2 has been considered as storage medium owing to its flexibility and excellent thermal stability.Nonetheless,the performance of the memory based on MoS2 is not able to meet the requirements up to now.Recent researches are studied from the macroscopic scale,such as material modification,in which are rarely associated electrical properties with microstructural changes.In consequence,the mechanisms of resistive switching are not fully understood.In this thesis,two types of Cu/MoS2/W sandwich structures are constructed in the transmission electron microscope(TEM).One is lateral structure in which the direction of electric field is parallel to the MoS2 interlayer direction and the other is vertical structure in which the direction of electric field is perpendicular to the MoS2 interlayer direction.Combing with electrical properties and microstructural changes,we not only analyze the growth and dissolution processes of conductive filaments and characterise the products,but also discuss the effects of electron beam irradiation,which providing theoretical and experimental foundations for optimization of the performance of memory based on MoS2.The main results are as follows:(1)The working process of lateral structure is studied.It is found that the resisitive switching mechanism is based on the growth and dissolution of conductive filaments made up of Cu,which can be interpreted by electrochemical metallization.The filament growth can be divided into two growth modes:?Conductive filaments nucleate initially near W electrode and then extend toward Cu electrode;?Conductive filaments nucleate initially near the middle region and then extend toward both electrodes.The difference between reduction rate and oxidation rate is the main reason for the two growth modes,which is affected by local temperature,local electric field and local concentration of cations.In addition,the filaments are found to dissolve from the thinnest part mainly because of electric field distribution and Joule heating.(2)The working process of vertical structure is studied.It is found that Cu electrode can react with MoS2 to form copper sulfide.The device starts to show a resistive switching behavior due to the formation of Cu2S.It is believed that the resisitive switching mechanism is also based on the growth and dissolution of conductive filaments made up of Cu.(3)The effects of electron beam irradiation on the two structures are studied.The experiments show that the effect of electron beam irradiation on lateral structure is negligible while that on vertical structure is great.Cu2S was also formed under electron beam irradiation,which made the structure had the ability of resistive switching.The vertical structure under the electric field and that under electron beam irradiation was compared and it is found that the electric field plays a key role on its resistive switching behavior.