Study On Fabrication,properties And Mechanism Of Resistive Random Access Memories Based On ZnO Films And Nanowires

With the size of device is reduced,the leakage current becomes worse which hiders its development.Resistive switching random access memory(RRAM)is one of the promising candidates for the next generation nonvolatile memory application,due to its merits of simple structure,high density,high operation speed,low power consumption and compatibility with standard CMOS process.Among these materials,ZnO is found to be a promising material for RRAM,as for its low cost,simple structure and easy processing.In this paper,we study on fabrication,properties and mechanism of resistive random access memories based on ZnO films and nanowires.This work includes the following three parts.1.Study on resistive switching memory based on Zn O film.There exist two fundamentally different types of switching mechanisms in the Cu/ZnO/Pt devices,the electrode metal in the case of electrochemical metallization memristors(ECMs)and the oxide layer in the case of valence change memristors(VCMs).In this study,by carefully checking the temperature dependence of the ON state resistance,it is found that a Zn filament should be formed in ZnO VCMs,a Cu filament should be formed in ZnO ECMs.The resistive switching can be operated in different modes by two types of switching mechanisms on the Cu/ZnO/Pt devices.At the last,we find that the operation mode of Cu/ZnO/Pt can be reversibly switched between ECM and VCM modes.2.Study on resistive switching memory based on single ZnO nanowire.As the size of the device is reduced,the nanowire RRAM device have attracted much attention owing to their fascinating functional properties.In this work,An individual ZnO nanowire resistive switch is making by fibre elongation method.Bipolar resistive switching(RS)behaviors were observed by Ag/ZnO single nanoowire/Ag memristors.The FORM voltage is more than 10V(From initial state into a low resistance state),the RESET voltages(from a low resistance state into a high resistance state)and the SET voltages(from a high resistance state into a lowresistance state)are very closely,all of them were less than 1V.The resistance ratios of high-resistance state(HRS)to low-resistance state(LRS)reached 109,but there are only steady within 15 cycles,the device(reversible switch between high and low resistance state)feature is poorer.3.Study on resistive switching memory based on Ag modified the single ZnO nanowire devices.In order to improve the resistive switching ability in single ZnO nanowire memristors,we use that Ag modified the ZnO nanowire by chemical deposition in this paper.It can improve electrical performance of the single ZnO nanowire devices.After this method,the devices exhibit outstanding performances with free FORM(<3V),steady cycles(>50),higher on/off ratio(109),furthermore,the device exists multilevel resistive switching.In the end,when the Ag atom modified the ZnO nanowire,the ZnO nanowire conductive ability rises highly.