Research On Performance Optimization And Mechanisms Of HfO_x Based Resistive Switching Devices By Using Plasma Technology

Memory is the most basic electron components in Micro/nano electromechanical systems(MEMS/NEMS).Novel resistive random access memory(RRAM)has been the most promising memory in the next generation of information field due to the great possibility of continuing Moore's Law and breaking the von Neumann bottleneck.Oxygen ions migration is the fundamental resistive switching(RS)mechanism in oxide-based RRAM.It has obtained more attention because of the higher migration energy of oxygen ions than metal ions,which causes that the conductive filaments based on oxygen vacancies are more stable and the performance of devices can be modulated more easily.However,it is faced with problems such as poor stability and endurance failure,which hinder its commercialization process significantly.Oxygen plasma treatment(OPT)is a micro-nano processing method based on oxygen plasma implantation,which is mainly used in surface modification processes such as material oxidation and doping.It is expected to solve the dilemma encountered by oxide-based RRAM.This paper embarks from the OPT technology,the microscopic mechanism of OPT-enhanced stability in HfO_xbased RRAM is studied from material level based on the scanning probe microscope(SPM)technology.At the same time,the mechanism of endurance failure in HfO_xbased RRAM is studied.Furthermore,oxygen ions are provided to the endurance failed HfO_xbased RRAM by OPT,which can participate in the RS processes.As a result,the RS characteristics of devices are restored.The specific research contents and results are as follows:1. Atomic force microscope(AFM)based techniques were used to study theinfluence of OPT on the microstructure of HfO_xRS layer.We found that the structural deformations in HfO_xnanofilm induced by migration of oxygen ions and interfacial electrochemical reactions can be recovered by OPT effectively.In addition,such structural deformations no longer occur after OPT,which directly illustrates the enhanced quantity of HfO_xnanofilm after OPT.In the end,X-ray photoelectron spectroscopic(XPS)was used to characterize the elements contents and chemical valence states of HfO_xfilm before and after OPT.Combined with electrical performance tests,the micro-mechanism of stability improvement in HfO_xbased RRAM by OPT was revealed.This work can provide certain experimental and theoretical guidance for performance optimization studies of oxide-based RRAM by OPT.2. By monitoring the current-voltage(I-V)curves and resistance states evolutionof HfO_xbased RRAM throughout the whole lifetime,the endurance failure mechanism of devices was studied:the loss of oxygen ions in normal RS cycles leads to the large reduction of oxygen ions'migration barrier in the active area of conductive filaments.Subsequently,a negative SET event was observed after consecutively normal RS cycles and the intermediate resistance state at the initial stage of negative SET cycle occured.The novel negative SET behavior finally triggers the devices'endurance failure.In the research of endurance failure in oxide-based RRAM,this work will play a guiding role in device design.3. Based on the physical mechanism of endurance failure in HfO_xbased RRAM,moderate OPT processes were used to provide oxygen ions that can participate in RS processes for the endurence failed HfO_xbased RRAM,and the RS characteristics of devices were recovered.In addition,the first recovered devices with endurance failure can be recovered again through OPT,which better proves the validity of the recovery method.This work can provide a new idea for solving the endurance failure problems in oxide-based RRAM.