The Study Of Mechanisms Of The Couplings Between Resistive Switchings And Photoinje Ction/Ferroelectric Polarization/Superconductivity

Owing to the high-density storage,fast data transfer rate,multilevel memory and simple structure,Resistive Random Access Memory?RRAM?has become one of the potential new types of memory devices which can be used commercially instead flash devices.Oxide resistive switching?RS?device is an ideal alternative to multifunctional electronics materials by the attention of the researchers worldwide.The different oxide RS models were built based on variety of materials so far.However,the mechanism behind of different material systems is not clear.It limits optimizations and applications of the devices.Therefore,it is very important to study and reveal the physics mechanism of the oxide RS and improve the properties of the devices by experiments.NiO,YMnO₃?YMO?and PrBa₂Cu₃O₇?PBCO?are representative two-spot,three-spot and four spot oxides,respectively.Their RS behaviors can be coupled with many interesting physics phenomena presenting a series of characteristics which is worthy of in-depth study.In this dissertation,the NiO,YMO and PBCO films devices were prepared by Pulsed Laser Deposition?PLD?technique.Through the investigation of the RS behaviors coupled with the photo injection,ferroelectric polarization and superconductivity,we revealed the mechanisms behind different materials and provide a reference for studies and applications in multifunction field of RS devices.The main results are as follows:1.The study on the coupling behaviors between the photo injection and electronic-type RS effects in NiO/NSTO deviceThe n-type and p-type NiO films were prepared on SrTi03:Nb?NSTO?by controlling oxygen pressures during the process of PLD.The results of I-V characteristics and the photocurrent investigation indicate that the junction shows a typical bipolar RS behavior and the optical injection can add some new resistance states.Photocurrents can be obviously modulated by different resistance states of NiO/NSTO junction.The linear fitting results of I-V curves revealed that the low resistance state?LRS?follows Ohmic behavior and the high resistance state?HRS?follows Schottky-emission mechanism.The depletion widths under the forward and reverse bias in the dark and with the illumination were estimated respectively.Combined with the energy band structure,the mechanism of RS and photoresponse in NiO/NSTO junction could be attributed to the variance of the width of the interfacial barrier during the electrical and optical injection.2.The study on the properties and mechanisms of RS in Pt/YMO/Pt devicesThe Pt/YMO/Pt device with a step was prepared by PLD technique exhibiting nonpolar RS behaviors.The RS behaviors of the YMO device and YMO film were synchronously measured by V source?Vs?-2 wires and?Is?-4 wires methods,respectively.It was found that the resistance of YMO film changed accompanying with the RS of whole Pt/YMO/Pt device.I-V curves fitting results exhibit the HRS and LRS according with the Schottky emission and Ohm's law,respectively.R-T curves show that the natures of HRS of device and film are on insulator states,but the LRS are on metallic states.The filament mechanism was further made clear through synchronously investigating by CAFM in the YMO/Pt interface.The RS behaviors were explained by the forming or rupture of conductive filaments in association with the local Joule-heat-induced redox of Mn vacancies.We suggest that such a phenomenon could be exploited to pattern conducting filaments within an insulating sandwich-shaped device,and so provide a route for fabricating micrometre-or nanometre-scale RS memory devices.3.The study on the coupling behaviors between the ferroelectricity and RS effects in YMO/NSTO devicesYMO/NSTO ferroelectric heterostructure with a step is fabricated by PLD.The multi-level RS properties in YMO layer and YMO/NSTO interface were distinguished and studied by impedance spectroscopy and 4 wires measurement.The results show a large RHRS/RLRs ratio?>1000 times?,high endurance?>100 cycles?,long retention?>14 h at 100??and four level operations.Piezoresponse force microscopy?PFM?images exhibit effective ferroelectric switchings which were corresponding to the I-V characteristics.Combined with the energy band structure,the RS behavior in YMO/NSTO heterostructure can be explained on the basis of polarization reversal induced modification of the width of depletion region at the p-n interface.These results could pave a way to control the multi-level RS behaviors of the ferroelectric layer and interface in RS devices.4.The study on the coupling behaviors between the superconductivity and RS effects in PBCO/NSTO devices?1?By a nonconventional approach,we study the coupling question for the RS effect and the superconductivity in the PBCO/NSTO device.Before the RS occur,the resistances of the PBCO/NSTO and PBCO film step increased with the temperature lowering.After the RS occur in low temperature,the resistances decreased with the temperature lowering.When the temperature reach to a special value,the resistance of PBCO film reduced to zero suddenly.That is to say the PBCO film has realized the transition of the nonsuperconducting state to the superconducting state.The superconductive critical temperature increased with the value of applied currents?I=10 mA,T_c=26 K;I=50 mA,T_c=70 K?.Additionally,after RS occur,there is a built-in electric field in the PBCO film.The bias of the built-in electric field is also having relations with applied currents?I=10 mA,V=0.13V;I=50 mA,V=0.1 mV?.?2?Using Vs-2 wires method,we measured the nonpolar RS behaviors in Pt/PBCO/Pt.The linear fitting results and analysis indicate that the position of nonploar RS is in the interface between the top electrode and the PBCO film.The RS were due to the forming and rupture of the filaments in the Schottky barrier.