Memristive Electronic Synapses Made By Anodic Oxidation And On The Limits Of Conductive Atomic Force Microscopy Three-dimensional(3D) Characterization Of Nanomaterials

Since found in 2008 by Hewlett-Packard Laboratories,Memristors have recently gained growing interests due to their potential application in non-volatile information storage and neuromorphic computing systems.The conductance of memristive device could be tuned to multilevel states,which is capable to be used as electronic synapse for advancing neuromorphic computing and artificial intelligence systems.Despite the memristive devices made of atomic layer deposition and physical vapor deposition have been widely studied,here we present a new method(i.e.electrochemical anodic oxidation)to produce transition metal oxide film for memristive electronic synapses.The properties of anodic memristive synapses have been studied.The conductive atomic force microscopy(CAFM)is a very useful technique for studying the electrical properties of nanomaterials for memristive devices,recently the CAFM has been applied to etch the memristive devices to study memristive switching mechanism.Here by performing multi experiments we analyzed the reliability the CAFM etching technique.This thesis is divided into two parts.i)Anodic oxidation as means to fabricate electronic synapses.We present the first fabrication of memristive electronic synapses using transition metal oxide(TiO2-x)produced by electrochemical oxidation.We found that Pt/anodic TiO2-x/Ti memristive synapses show very low programming voltages,stable resistive switching behavior and fast switching times shorter than 100 ns.We are able to specifically tune the resistance values of anodic synapses by applying different current compliances and programming voltages,and by applying different amplitudes of pulsed voltage stresses the synaptic potentiation and depression rates could be controlled.Cross-sectional transmission electron microscopy reveals the switching of anodic synapses is governed by interface charge between TiO2-x and Ti layers under external electrical stimuli.It is concluded that anodic oxidation method may be a cheap and effective route to fabricate memristive electronic synapses.ii)Conductive atomic force microscopy has been widely used for electrical characterization of high-k dielectrics,CAFM uses a gentle contact force(Fc)to scan sample surface to obtain topographic and electrical information.Recently,the CAFM has been used to obtain 3D information of nanomaterials applying high contact force to scan sample surface.Specifically,it has been applied to study resistive switching devices and the conductive nanofilaments.However,the effect of the high contact forces/pressures on the change of materials during the etching has never been considered.In this study,by collecting cross-sectional transmission electron microscopy images at the CAFM etched areas,we found the CAFM etching process can modify the morphology of thin dielectric films(producing phase change,generation of defects)and thus affect their electrical properties.It is also observed that this technique severely damaged CAFM tips,as a result affect the reliability of collected topographic and electrical information of martials being studied.This work should contribute to understand the limitations of CAFM 3D characterization and disseminate it among other useful applications...