Resistive Switching Effect In Oxide Heterostructures

Recently, electric field and/or current induced resistive switching （RS） effectobserved in the metal-insulator-metal （MIM） structures has attracted much attention dueto its importance in both basic research and potential applications in resistance randomaccess memory （RRAM）, which is a strong contender for the nonvolatile random accessmemory （NVM） due to its high-density, fast operation, and low energy operation. Thereare many reports on the RS effect in the MIM structures composed of metal and oxide.Some mechanisms were proposed to explain the experimental results, including the trapcontrolled space charge limited conduction （SCLC）, formation and rupture ofconducting filament, variation of depletion thickness et al. However, there are someambiguity in these mechanisms, such as the characteristics of traps and the relativeaffection on the RS effect and electronic transport, and the detail composition andphysical properties of filaments. These messages are very important for wellunderstanding the mechanism of RS effect and also essential for optimizing memorydevices. Aim at these problems above, this thesis has researched the RS effect inmultiple oxide heterostructures, and the main work can be divided to two parts asfollows:LaAlO3（LAO） films were grown on0.7wt%Nb-doped SrTiO3（NSTO） singlecrystal substrates by pulsed laser deposition （PLD） to form oxide heterostructures.Measurements and data analysis in different representations of AC impedance techniquewere employed to study the RS effect. It was demonstrated that the bipolar RS effectoriginates from the LAO/NSTO interface and resistance and capacitance states are bothcontrolled by the filling status of traps. The relaxation of the low resistance statewas described in time-domain and frequency-domain, respectively. The resultsin two domains are the same and the relaxation index n increases exponentiallywith increasing temperature. We also investigated the mechanism of conductionof LAO/NSTO through the transport behavior of the low-and high-resistancestates in different historical processes. It was found that the electronic transportis determined by trap state, and strong dependent on historical process. Finally,a model based on the variation of trap state was proposed to explain the RS effect and the history dependent electronic transport behavior.In another aspect, we performed complex impedance measurements on thelow-and high-resistance states in Au/NiO/Pt, Ti/HfO₂/Pt and ITO/TiO₂/ITOheterostructures. We investigated the impedance characteristics of differentkinds of conducting filaments through comparison analysis and quantitativecalculation. It was demonstrated that the important information of conductingfilaments such as the position and degree of rupture and the electrical propertiescan be obtained by analysis of the complex impedance data, suggesting compleximpedance spectroscopy is a powerful tool to study RS effect. We employed thistool in the study of HfO₂based heterostructures fabricated by different methods,discussed the effect of conducting filaments with different originations on theswitching mechanisms of HfO₂, and revealed the reasons for the formation ofdiverse conducting filaments under different growth processes.