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Register a new userSubstrate effect on the resistive switching in BiFeO3 thin films
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BiFeO3 thin films have been deposited on Pt/sapphire and Pt/Ti/SiO2/Si substrates with pulsed laser deposition using the same growth conditions, respectively. Au was sputtered as the top electrode. The microscopic structure of the thin film varies by changing the underlying substrate. Thin films on Pt/sapphire are not resistively switchable due to the formation of Schottky contacts at both the top and the bottom interface. However, thin films on Pt/Ti/SiO2/Si exhibit an obvious resistive switching behavior under forward bias. The conduction mechanisms in BiFeO3 thin films on Pt/sapphire and Pt/Ti/SiO2/Si substrates are discussed to understand the different resistive switching behaviors.
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BiFeO3 thin films with various thicknesses were grown epitaxially on (001) LaSrAlO4 single crystal substrates using pulsed laser deposition. High resolution x-ray diffraction measurements revealed that a tetragonal-like phase with c-lattice constant ~4.65 {AA} is stabilized by a large misfit strain. Besides, a rhombohedral-like phase with c-lattice constant ~3.99 {AA} was also detected at film thickness of ~50 nm and above to relieve large misfit strains. In-plane piezoelectric force microscopy studies showed clear signals and self-assembled nanoscale stripe domain structure for the tetragonal-like regions. These findings suggest a complex picture of nanoscale domain patterns in BiFeO3 thin films subjected to large compressive strains.
We have investigated the nanoscale switching properties of strain-engineered BiFeO3 thin films deposited on LaAlO3 substrates using a combination of scanning probe techniques. Polarized Raman spectral analysis indicate that the nearly-tetragonal films have monoclinic (Cc) rather than P4mm tetragonal symmetry. Through local switching-spectroscopy measurements and piezoresponse force microscopy we provide clear evidence of ferroelectric switching of the tetragonal phase but the polarization direction, and therefore its switching, deviates strongly from the expected (001) tetragonal axis. We also demonstrate a large and reversible, electrically-driven structural phase transition from the tetragonal to the rhombohedral polymorph in this material which is promising for a plethora of applications.
Crystal and domain structures of tensile-strained BiFeO3 films grown on orthorhombic (110)o PrScO3 substrates were investigated. All films possess a MB-type monoclinic structure with 109o stripe domains oriented along the [=i10]o direction. For films thicknesses less than ~40 nm, presence of well-ordered domains is proved by the detection of satellite peaks in synchrotron x-ray diffraction studies. For thicker films, For thicker films, only the Bragg reflections from tilted domains were detected. This is attributed to the broader domain size distribution in thicker films.Using planar electrodes,the in-plane polarization of the MB phase is determined to be 85 uC/cm2, which is much larger than that of compressive strained BiFeO3 films. Our results further reveal that the substrate monoclinic distortion plays a major role in determining the stripe domain formation of the rhombohedral ferroic epitaxial thin films, which sheds light to the understanding of elastic domain structure evolution in many other functional oxide thin films as well.
We studied the resistive memory switching in pulsed laser deposited amorphous LaHoO3 (LHO) thin films for non-volatile resistive random access memory (RRAM) applications. Nonpolar resistive switching (RS) was achieved in PtLHOPt memory cells with all four possible RS modes ( positive unipolar, positive bipolar, negative unipolar, and negative bipolar) having high RON and ROFF ratios (in the range of 104 to 105) and non-overlapping switching voltages (set voltage, VON 3.6 to 4.2 V and reset voltage, VOFF 1.3 to 1.6 V) with a small variation of about 5 to 8 percent. X ray photoelectron spectroscopic studies together with temperature dependent switching characteristics revealed the formation of metallic holmium (Ho) and oxygen vacancies (VO) constituted conductive nanofilaments (CNFs) in the low resistance state (LRS). Detailed analysis of current versus voltage characteristics further corroborated the formation of CNFs based on metal like (Ohmic) conduction in LRS. Simmons Schottky emission was found to be the dominant charge transport mechanism in the high resistance state.
Films produced by assembling bare gold clusters well beyond the electrical percolation threshold show a resistive switching behavior whose investigation has started only recently. Here we address the challenge to charaterize the resistance of a nanogranular film starting from limited information on the structure at the microscopic scale by the means of Bruggemans approach to multicomponent media, within the framework of Effective Medium Approximations. The approach is used to build a model that proves that the observed resistive switching can be explained by thermally regulated local structural rearrangements.
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