Study On Resistive Behavior Of Ferroelectrics By Scanning Probe Microscopy

As a data storage unit,memory occupies an indispensable position and plays an important role in in integrated circuit?IC?.With the rapid development of science and the advent of the information age,people raise higher requirements for the information storage and processing of integrated circuits.However,traditional memories are limited by its physical limits,so the researchers are looking for the next generation of nonvolatile random switch memory?RAM?with greater information storage,faster processing speeds and smaller device sizes.In new memories,due to the advantages of fast reading and writing speed,low power consumption and high reliability,resistance random switch memory?RRAM?,has been widely concerned.Among which,ferroelectric random switch memory?FeRRAM?,which uses ferroelectric materials as the resistance switch layer,is different from RRAM based on defect mechanism by using ferroelectric materials as the resistance layer due to its working mechanism.As it works by utilizing the intrinsic ferroelectric properties of materials,it has significant advantages in low power consumption,fatigue resistance and controllability,and stands out from RRAMs.However,the behavior of resistance switch?RS?is complex and the relevant RS mechanism is still controversial.In this paper,two typical ferroelectric oxide films BiFeO₃?BFO?and Pb(Zr_0.52Ti_0.48)O₃?PZT?were selected,using multifunctional Scanning Probe Microscopy?SPM?for in-situ testing of metal/functional layer/metal structure devices,systematically characterized the ferroelectric polarization,surface potential and transport characteristics of the films,deeply analyzed the RS mechanism of the devices.Firstly,in chapter three,using Scanning Kelvin Probe Microscopy?SKPM?analyzed the surface charges of voltage written films,and found that the injected charges and the polarization charges are the origins of RS behavior and also the most important charges on the surface,the injected charges have a covering effect on the polarization charges,so that the SKPM cannot be used to characterize the polarization charges on the ferroelectric function layer.In the fourth chapter,through the joint characterization of Piezoelectric Force Microscopy?PFM?and SKPM,it was found that there are two optimized heat treatment processes:using a high temperature for a short time and using a low temperature for a long time can both achieve the relaxation of injected charges,the former fits for high Curie temperature materials such as BFO,and the latter can be applied to both high Curie temperature materials and low Curie temperature materials such as PZT.Subsequently,in combination with the in-situ test of Conducting Atomic Force Microscopy?CAFM?,the RS behavior before and after charge injection relaxation was characterized in situ,and the corresponding relationship between RS behavior and polarization is completely opposite:the former RS behavior was originated from the injected charges,the mechanism is the trapping/detrapping of the injected charges,and the latter was originated from the polarized charges,and the mechanism is the polarization charge regulates the interface potential barrier.This study provides a practical and effective method for analyzing the mechanism of RS behavior on the surface of ferroelectric materials,and successfully characterizes the diverse RS behavior in FeRRAM.The study will play an important role in the development of high-performance FeRRAM.In addition,we conducted a preliminary study on the ferroelectricity of the two-dimensional In₂Se₃ and the device using it as a resistive layer.We confirmed that In₂Se₃exhibits intrinsically intercorrelated out-of-plane and in-plane polarization,and the obvious odd even effect of initial polarization direction was observed.Finally,using the SPM conductive probe as the top electrode confirmed that the MIM structure with In₂Se₃ as the ferroelectric functional layer has RS behavior.