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Multiferroic composites and heterostructures comprising ferroelectric and ferromagnetic materials exhibit room-temperature magnetoelectric (ME) effects greatly exceeding those of single-phase magnetoelectrics known to date. Since these effects are mediated by the interfacial coupling between ferroic constituents, the ME responses may be enhanced by increasing the density of interfaces and improving their quality. A promising material system providing these features is a ferroelectric-ferromagnetic multilayer with epitaxial interfaces. In this paper, we describe theoretically the strain-mediated direct ME effect exhibited by free-standing multilayers composed of single-crystalline ferroelectric nanolayers interleaved by conducting ferromagnetic slabs. Using a nonlinear thermodynamic approach allowing for specific mechanical boundary conditions of the problem, we first calculate the polarization states and dielectric properties of ferroelectric nanolayers in dependence on the lattice mismatch between ferroic constituents and their volume fractions. In these calculations, the ferromagnetic component is described by a model which combines linear elastic behavior with magnetic-field-dependent lattice parameters. Then the quasistatic ME polarization and voltage coefficients are evaluated using the theoretical strain sensitivity of ferroelectric polarization and measured effective piezomagnetic coefficients of ferromagnets. For Pb(Zr0.5Ti0.5)O3-FeGaB and BaTiO3-FeGaB multilayers, the ME coefficients are calculated numerically as a function of the FeGaB volume fraction and used to evaluate the output charge and voltage signals. It is shown that the multilayer geometry of a ferroelectric-ferromagnetic nanocomposite opens the way for a drastic enhancement of the output charge signal. This feature makes biferroic multilayers advantageous for the development of ultrasensitive magnetic-field sensors for technical and biomedical applications. [ABSTRACT FROM AUTHOR]

We report the electrical characteristics of metal-ferroelectric-insulator-semiconductor structures, where the ferroelectric layer is a Langmuir-Blodgett film of a copolymer of 70% vinylidene fluoride and 30% trifluoroethylene. The 36-nm thick copolymer films were deposited on thermally oxidized (10 nm SiO2) p-type silicon and covered with a gold gate electrode. Polarization-field hysteresis loops indicate polarization switching in the polymer film. The device capacitance shows hysteresis when cycling the applied voltage between ±3 V, exhibiting a zero-bias on/off capacitance ratio of over 3:1 and a symmetric memory window 1 V wide, with little evidence of bias that can arise from traps in the oxide. Model calculations are in good agreement with the data and show that film polarization was not saturated. The capacitance hysteresis vanishes above the ferroelectric-paraelectric transition temperature, showing that it is due to polarization hysteresis. The retention time of both the on and off states was approximately 15 min at room temperature, possibly limited by leakage or by polarization instability in the unsaturated film. These devices provide a basis for nonvolatile data storage devices with fast nondestructive readout. [ABSTRACT FROM AUTHOR]

Presents a study which examined the electric forming effect in lead/bismuth/indium-oxide-lead/bismuth tunnel junctions in terms of telegraph noise investigations before and after forming. Brief introduction to the forming process; Materials and methods used; Findings.

Recently, ferromagnetic tunnel junctions attracted much interest because they exhibit large magnetoresistance effects up to ΔR/R=40% at room temperature. In this paper, an alternative approach will be presented, i.e., exposing the aluminum film to ultraviolet light during oxidation. The underlying mechanism can be explained in the framework of the Cabrera–Mott theory of oxidation. With UV assisted oxidation, magnetoresistance ratios of up to 22.5% at room temperature have been obtained in Ni[sub 80]Fe[sub 20]–Al(ox)–Co junctions. The resistivities were in the 1 kΩ μm[sup 2] range for junctions of 25–400 μm[sup 2]. Barrier heights obtained by fitting to different theories will be discussed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Deals with a study which examined the role of surface roughness in the fabrication of stacked Nb/Al-AlO[subx]/Nb tunnel junctions. Methods and procedures; Results; Conclusions.

Presents a study that investigated the behavior of vertically stacked tunnel junctions in a circuit suitable for voltage standards using microwave irradiation. Types of microwave irradiated Josephson tunnel junction arrays fabricated in the study; Description of the current-voltage characteristic of the junction array in the absence of radio frequency bias; Advantage of three-dimensional integrated circuits in comparison with two-dimensional circuits with the same number of junctions.

The phenomenon of ferromagnetic resonance (FMR) provides fundamental information on the physics of magnetic materials and lies at the heart of a variety of signal processing microwave devices. Here we demonstrate theoretically that substrate-induced lattice strains can change the FMR frequency of an epitaxial ferromagnetic film dramatically, leading to ultralow and ultrahigh resonance frequencies at room temperature. Remarkably, the FMR frequency varies with the epitaxial strain nonmonotonically, reaching minimum at a critical strain corresponding to the strain-induced spin reorientation transition. Furthermore, by coupling the ferromagnetic film to a ferroelectric substrate, it becomes possible to achieve an efficient voltage control of FMR parameters. In contrast to previous studies, we found that the tunability of FMR frequency varies with the applied electric field and strongly increases at critical field intensity. [ABSTRACT FROM AUTHOR]

We present a study on low-Tc superconductor-insulator-ferromagnet-superconductor (SIFS) Josephson junctions. SIFS junctions have gained considerable interest in recent years because they show a number of interesting properties for future classical and quantum computing devices. We optimized the fabrication process of these junctions to achieve a homogeneous current transport, ending up with high-quality samples. Depending on the thickness of the ferromagnetic layer and on temperature, the SIFS junctions are in the ground state with a phase drop of either 0 or π. By using a ferromagnetic layer with variable step-like thickness along the junction, we obtained a so-called 0–π Josephson junction, in which 0 and π ground states compete with each other. At a certain temperature the 0 and π parts of the junction are perfectly symmetric, i.e. the absolute critical current densities are equal. In this case the degenerate ground state corresponds to a vortex of supercurrent circulating clock- or counterclockwise and creating a magnetic flux which carries a fraction of the magnetic flux quantum Φ0. [ABSTRACT FROM AUTHOR]

Abstract: We report on the state-of-the art memory devices on the basis of ferroelectric materials. The paper starts with a short survey on competitive non-volatile memory technologies and focuses then on ferroelectric memories. This includes the ferroelectric random access memory (FeRAM) and the ferroelectric field effect transistor (FeFET). Cell layouts, material aspects and CMOS compatibility as well as fabrication issues will be discussed. Beside the current research on ferroelectric memory devices we present results on the superparaelectric limit of ferroelectric materials with respect to lateral and thickness scaling. Scanning probe techniques showed ferroelectric properties in dots as small as 20 nm. Ultra thin ferroelectric films as thin as a few unit cells can be achieved on lattice matched substrates. These investigations can be considered as a guideline for the maximum achievable packaging density of FeRAMs including low power consumption. The most challenging task to achieve storage above 128 Mb, is the conformal coverage of 3-D electrodes, e.g. by atomic layer deposition (ALD). Three dimensional capacitors are mandatory to achieve sufficient charge for clear signal sensing. In addition, we present a few new concepts based on ferroresistive films, strain induced enhanced ferroelectricity, and lead-free ferroelectrics which may be relevant for the future FeRAM technology. Finally, a new challenging concept of an entire organic ferroelectric field effect transistor (OFeFET) is briefly discussed. [Copyright &y& Elsevier]

Abstract: We have used high-pressure on-axis sputtering to deposit single crystalline epitaxial PbZr0.52Ti0.48O3 either on SrRuO3/SrTiO3 or on SrTiO3 substrates. The PbZr0.52Ti0.48O3 films possess a small mosaicity on both, on SrRuO3/SrTiO3 and on SrTiO3 substrates. PbZr0.52Ti0.48O3 thin films have a larger out-of-plane lattice parameter and a smaller in-plane lattice parameter when it is grown on SrRuO3/SrTiO3 substrates. Atomic force microscopy reveals very smooth surfaces. The stoichiometry has been verified by Rutherford backscattering spectrometry. Channeling measurements indicate that the crystalline quality of the PbZr0.52Ti0.48O3 films grown on SrRuO3/SrTiO3 substrate is significantly improved compared to its deposition on blank SrTiO3 substrates. This observation is discussed in the framework of lattice mismatch, thermal expansion coefficients, interdiffusion at the PbZr0.52Ti0.48O3/SrRuO3 interface, the depolarization field in the ferroelectrics and the surface layer termination of the substrate. [Copyright &y& Elsevier]

Abstract. Aluminum films with thicknesses ranging from 1 nm to 12 nm have been sputtered on 20 nm thick Co layers. The properties of the Co/Al bilayers were studied by X-ray photoemission spectroscopy (XPS) and spin-echo nuclear magnetic resonance (NMR). Both methods show independently that a 1 nm Al film covers the Co surface completely. XPS and NMR also showed that layers thicker than 1 nm Al are not oxidized completely in ambient air. Similarities to and deviations from niobium with Al overlayers (Nb/Al) are described. Prerequisites for the fabrication of tunneling magnetoresistance devices based on Co or NiFe ferromagnets and an aluminum oxide barrier are discussed. [ABSTRACT FROM AUTHOR]

Investigates the magnetic field dependence of current-voltage characteristics of 7-layer stacked Nb/Al-AlO.../Nb long Josephson junctions. Magnetic coupling between the junctions; What is shown by current-voltage characteristics; Information on the flux-flow behavior.

Magnetic field dependence of current-voltage characteristics of 7-layer stacked Nb/Al-AlO/sub x//Nb long Josephson junctions are investigated experimentally. The magnetic coupling between the junctions is provided by their common superconducting electrodes of the thickness smaller than the London penetration depth. The current-voltage characteristics clearly display collective flux-flow behaviour of Josephson vortices (fluxons) which simultaneously move in up to 5 layers of the stack under the influence of the bias current. The flux-flow behaviour is modulated by a complicated structure of cavity-like resonances which show a broad range of characteristic frequencies. Our observations can be qualitatively explained as the interplay between the Fiske modes and the two-dimensional resonances in these stacks. For the intermediate magnetic field range, we find pronounced resonant modes with large voltage spacing which indicates mutually coherent operating junctions. [ABSTRACT FROM PUBLISHER]

The concept of a magnetic tunnel junction fabricated on a ferroelectric substrate is described theoretically. It is shown that the application of a moderate electric field to a substrate having strong piezoelectric response may induce an in-plane magnetization rotation in a ferromagnetic electrode made of a highly magnetostrictive cubic material with small magnetocrystalline anisotropy. Remarkably, an abrupt change of the junction’s electrical resistance can result from the substrate-induced magnetization reorientation in the free ferromagnetic layer. Hence the described hybrid multiferroic device may be employed as an electric-write nonvolatile magnetic memory cell with nondestructive readout. [ABSTRACT FROM AUTHOR]

To study ferroelectric size effects in heteroepitaxial SrRuO3/BaTiO3/SrRuO3 capacitors, ultrathin BaTiO3 layers were deposited in wedge form across SrTiO3 substrates. The wedgelike films were fabricated by using either an off-center substrate-target geometry or via a moveable shutter during high-pressure sputter deposition. The crystallinity, composition, and surface roughness along wedgelike BaTiO3 films were verified by x-ray diffraction, Rutherford backscattering spectrometry, and atomic force microscopy, respectively. The electrical measurements performed at 77 K showed that, despite progressive reduction in remanent polarization as the film thickness decreases even the 3.5-nm-thick BaTiO3 film retains a large remanent polarization of 28 μC/cm2. [ABSTRACT FROM AUTHOR]

We present investigations on the resistive switching effect in SrRuO3/PbZr0.2Ti0.8O3/Pt ferroelectric capacitors. Using a conductive atomic force microscope, the out-of-plane piezoelectric response and the capacitive and resistive current were simultaneously measured as a function of applied bias voltage. We observed two independent switching phenomena, one attributed to the ferroelectric switching process and the other to resistive switching.We show that I-V curves alone are not sufficient in ferroelectric materials to clarify the underlying switching mechanism and must be used with sufficient caution. [ABSTRACT FROM AUTHOR]

The aim of this work is to investigate the electron transport through metal–ferroelectric–metal (MFM) junctions with ultrathin barriers in order to determine its dependence on the polarization state of the barrier. To that end, heteroepitaxial Pt/Pb(Zr[sub 0.52]Ti[sub 0.48])O[sub 3]/SrRuO[sub 3] junctions have been fabricated on lattice-matched SrTiO[sub 3] substrates. The current–voltage (I–V) characteristics of the MFM junctions involving a few-nanometer-thick Pb(Zr[sub 0.52]Ti[sub 0.48])O[sub 3] barriers have been recorded at temperatures between 4.2 K and 300 K. Typical I–V curves exhibit reproducible switching events at well-defined electric fields. The mechanism of charge transport through ultrathin barriers and the origin of the observed resistive switching effect are discussed. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this letter, we report on the thickness dependence of the remanent polarization of Pt/PbZr[SUB0.52]Ti[SUB0.48]O[SUB3]/SrRuO[SUB3] capacitors. Two different patterning techniques were used to fabricate) the capacitors. For lift-off processed capacitors, the remanent polarization decreased with decreasing thickness. Ion-beam-etched capacitors, however, showed a constant remanent polarization for all PbZr[SUB0.52]Ti[SUB0.48]O[SUB3] film thicknesses down to 23 nm. Remarkably, this constant remanent polarization for ion-beam-etched capacitors corresponds to the spontaneous polarization expected for a stress-free bulk PbZr[SUB0.52]Ti[SUB0.48]O[SUB3] crystal. [ABSTRACT FROM AUTHOR]

A correction to the article "Electric forming and telegraph noise in tunnel junctions" that was published in a previous issue is presented.

Investigates the tunable phase locking oscillator of stacked Josephson junctions. Accounts on several kinds of mutually synchronized flux-flow states; Introduction of magnetic flux on the same polarity of both junctions; Effect of in-phase locking modes on radiation linewidth.

Examines a system of two vertically stacked niobium/Al-AlO[sub x]/Nb long Josephson junctions. Observation of magnetic coupling between junctions; Examination of current-voltage characteristics of the stack displaying resonant steps; Application of stacked long Josephson junctions as local oscillators for millimeter and submillimeter wave circuits.

Investigates the nanobridges of optimized Y-Ba[sub 2]Cu[sub 3]O[sub 7] thin films for superconducting devices. Use of ion beam milling for dry etching of the thin films; Superconducting features of long bridges; Details on the Shapiro steps and the critical current of the microwave field.

Fundamental aspects of ferroelectric HfO 2 , a fluorite-type oxide, are not understood yet. This is evident by different theories regarding, e.g., the wake-up effect or the antiferroelectric-like behavior of HfO 2 manufactured with different doping or deposition techniques. Therefore, we focus on sputtered and undoped HfO 2 to gain deeper understanding of the ferroelectric properties of pure HfO 2. A temperature gradient on a 10 × 10 mm 2 substrate during rapid thermal annealing led to different ferroelectric device performances in terms of remnant polarization and the wake-up effect. The results from the electrical characterization are compared to observations by transmission electron microscopy, performed on pristine and trained samples in plan-view as well as in cross section. We observed that different temperature treatments caused effects at the interfaces of the TiN electrodes and also affected the microstructure and defect concentration of the HfO 2 itself. Devices from the hot corner showed wake-up free ferroelectricity with a remnant polarization below 10 μ C / cm 2 , whereas devices from the cold corner showed a strong wake-up effect with remnant polarization starting from 0 to above 20 μ C / cm 2 after 10 6 cycles. After observing a small structural transformation in trained devices, we attributed this strong wake-up effect to gradual ferroelastic switching of pristine [110] oriented grains with in-plane polarization to partially out-of-plane polarization, while the predominantly ⟨ 111 ⟩ oriented grains in the hot corner can suppress the wake-up effect. [ABSTRACT FROM AUTHOR]

Ferroelectric lead-free thin films of 0.5(Ba0.7Ca0.3TiO3) - 0.5[Ba(Zr0.2Ti0.8)O3] (BCZT) were successfully deposited by pulsed laser deposition on Pt/TiO2/SiO2/Si substrates using a ceramic BCZT target prepared by conventional solid state reaction. The in (111) direction orientated 600 nm thick films shows a clamped piezoelectric response of approximately d33,f = 80 pm/V and a dielectric coefficient of about &eh;r = 1010; these are close to values obtained for lead zirconate titanate (PZT) films. [ABSTRACT FROM AUTHOR]

Among the ferroelectric thin films considered for use in nonvolatile memory devices, the ferroelectric copolymer of polyvinylidene fluoride, PVDF (C2H2F2), with trifluoroethylene, TrFE (C2HF3), has distinct advantages, including low dielectric constant, low processing temperature, relative low cost compared with epitaxial ferroelectric oxides, and compatibility with organic semiconductors. We report the operation and polarization retention properties of a metal–ferroelectric–insulator–semiconductor bistable capacitor memory element consisting of an aluminum gate, a P(VDF-TrFE) Langmuir–Blodgett film, a 30 nm cerium oxide buffer layer, and a moderately doped silicon wafer. The device exhibited a 1.9 V wide hysteresis window obtained with a ±7 V operating range with a state retention time of 10 min. The mechanisms contributing to loss of state retention are discussed. [ABSTRACT FROM AUTHOR]

High-quality BaTiO3 films with thicknesses ranging from 2.9 to 175 nm were grown epitaxially on SrRuO3-covered (001)-oriented SrTiO3 substrates by high-pressure sputtering. The crystal structure of these films was studied by conventional and synchrotron x-ray diffraction. The in-plane and out-of-plane lattice parameters were determined as a function of film thickness by x-ray reciprocal space mapping around the asymmetric (103) Bragg reflection. BaTiO3 films were found to be fully strained by the SrTiO3 substrate up to a thickness of about 30 nm. Ferroelectric capacitors were then fabricated by depositing SrRuO3 top electrodes, and the polarization-voltage hysteresis loops were recorded at the frequencies 1–30 kHz. The observed thickness effect on the lattice parameters and polarization in BaTiO3 films was analyzed in the light of strain and depolarizing-field effects using the nonlinear thermodynamics theory. The theoretical predictions are in reasonable agreement with the measured thickness dependences, although the maximum experimental values of the spontaneous polarization and the out-of-plane lattice parameter exceed the theoretical estimates (43 μC/cm2 vs 35 μC/cm2 and 4.166 Å vs 4.143 Å). Possible origins of the revealed discrepancy between theory and experiment are discussed. [ABSTRACT FROM AUTHOR]

Nb/Al2O3/Ni0.6Cu0.4/Nb based superconductor-insulator-ferromagnet-superconductor Josephson tunnel junctions with a thickness step in the metallic ferromagnetic Ni0.6Cu0.4 interlayer were fabricated. The step was defined by optical lithography and controlled etching. The step height is on the scale of a few angstroms. Experimentally determined junction parameters by current-voltage characteristics and Fraunhofer pattern indicate uniform ferromagnetic layer thicknesses and the same interface transparencies for etched and nonetched F layers. This technique could be used to tailor low-Tc Josephson junctions having controlled critical current densities at defined parts of the junction area, as needed for tunable resonators, magnetic-field driven electronics, or phase modulated devices. [ABSTRACT FROM AUTHOR]

Spin-dependent tunnel junctions with Co[sub 75]Fe[sub 25] electrodes and a Fe[sub 50]Mn[sub 50] pinning layer were fabricated with tunneling magnetoresistance of about 20% at room temperature. The Al[sub 2]O[sub 3] barriers were formed by ultra-violet light assisted oxidation. The resistance × area (R × A) product was about 375 kΩ µm² in the parallel alignment of the magnetizations. The effect of barrier impurities has been investigated via tunneling conductance as a function of temperature and bias voltage for as-deposited and annealed samples. The spin wave parameter a was determined to be 3.06 × 10[sup -5] and 2.03 × 10[sup -5] K[sup -3/2] before and after annealing, respectively. The improved barrier properties after annealing are explained by inelastic hopping via several localized states and reduced magnon scattering. We propose a qualitative model of the barrier homogenization during annealing which supports former Rutherford backscattering and x-ray photoelectron spectroscopy studies. [ABSTRACT FROM AUTHOR]

The mean-field Landau-type theory is used to analyze the polarization properties of epitaxial ferroelectric thin films grown on dissimilar cubic substrates, which induce biaxial compressive stress in the film plane. The intrinsic effect of the film surfaces on the spontaneous polarization is taken into account via the concept of the extrapolation length. The theory simultaneously allows for the influence of the misfit strain imposed on the film lattice by a thick substrate. Numerical calculations are performed for PbTiO[sub 3] and BaTiO[sub 3] films under an assumption of the polarization reduction in surface layers. The film mean polarization is calculated as a function of film thickness, temperature, and misfit strain. It is shown that the negative intrinsic size effect is reduced in epitaxial films due to the in-plane compression of the film lattice. At room temperature, strong reduction of the mean polarization may take place only in ultrathin films (thickness ∼1 nm). Theoretical predictions are compared with the available experimental data on polarization properties of BaTiO[sub 3] films grown on SrRuO[sub 3] coated SrTiO[sub 3]. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The basic building blocks of every neural network are neurons and their inter-cellular connections, called synapses. In nature, synapses play a crucial role in learning and memory, since they are plastic, which means that they change their state depending on the neural activity of the respectively coupled neurons. In neuromorphic systems, the functionality of neurons and synapses is emulated in hardware systems by employing very-large-scale integration technology. In this context, it seems rather natural to use non-volatile memory technology to mimic synaptic functionality. In particular, memristive devices are promising candidates for neuromorphic computing, since they allow one to emulate synaptic functionalities in a detailed way with a significantly reduced power usage and a high packing density. This tutorial aims to provide insight on current investigations in the field to address the following fundamental questions: How can functionalities of synapses be emulated with memristive devices? What are the basic requirements to realize artificial inorganic neurons and synapses? Which material systems and device structures can be used for this purpose? And how can cellular synaptic functionality be used in networks for neuromorphic computing? Even if those questions are part of current research and not yet answered in detail, our aim is to present concepts that address those questions. Furthermore, this tutorial focuses on spiking neural models, which enables mimicking biological computing as realistically as possible. [ABSTRACT FROM AUTHOR]

Vanadium oxide thin films (VO2) were deposited on 0.72Pb(Mg1/3Nb2/3)-0.28PbTiO3 (PMN-PT) crystalline substrates using pulsed laser deposition method. Due to their huge piezoelectric coefficients in the order of 2500 pm/V, the PMN-PT substrates are used to impose additional amount of biaxial strain to the VO2 films by applying an external bias to the substrates. The influence of the biaxial strain on the transition temperature and on the conductive properties of the VO2 films is investigated in this work. Thus, a change in the biaxial strain of -0.8 x 10-3 applied in the (110) plane of the rutile cell of the VO2 lowered the metal-to-insulator transition temperature by 1.35 °C. [ABSTRACT FROM AUTHOR]

We present a sensitive method to simultaneously acquire the C(V ) characteristics and piezoresponse of sub-micron size ferroelectric capacitors using an Atomic Force Microscope (AFM). Model Pt/(La0.5,Sr0.5)CoO3/PbZr0.4Ti0.6 O3/(La0.5,Sr0.5)CoO3/La:SrTiO3/Si nanocapacitors were fabricated by focused ion beam milling from 100 μm2 down to 0.04 μm2. With this AFM based capacitance measurement technique we show clear “double-humped” C(V ) for all sizes with no significant change in the peak value of the εr down to capacitors with the smallest area of 0.04 μm2. The smallest capacitance measured is only of the order a few femtofarads, demonstrating the high sensitivity of the technique. Simultaneously, the piezoelectric response is recorded for each measurement, thus the technique facilitates simultaneous piezoresponse and dielectric characterization of ferroelectric memory devices. [ABSTRACT FROM AUTHOR]

Abstract: We present ferromagnetic Nb/Al2O3/Ni60Cu40/Nb Josephson junctions (SIFS) with an ultrathin Al2O3 tunnel barrier. The junction fabrication was optimized regarding junction insulation and homogeneity of current transport. Using ion-beam-etching and anodic oxidation we defined and insulated the junction mesas. The additional 2nm thin Cu-layer below the ferromagnetic NiCu (SINFS) lowered interface roughness and ensured very homogeneous current transport. A high yield of junctional devices with j c spreads less than 2% was obtained. [Copyright &y& Elsevier]

We report on the soft x-ray absorption spectroscopy investigation of thin film capacitors using a modified total electron yield detection mode. This mode utilizes two ammeters instead of one as commonly employed in the classical total electron yield scheme to measure photocurrents of devices under soft x-ray irradiation. The advantage of this configuration over the surface sensitive classical total electron yield mode is that it can provide information from buried layers and interfaces up to a thickness equal to the penetration depth of soft x-rays. The method can be easily adapted to existing synchrotron end stations. We investigate dielectric capacitors with dissimilar electrodes to assess the feasibility of the modified total electron yield method. Furthermore, in operando soft x-ray absorption spectroscopy measurements are performed on ferroelectric capacitors under bias and using two ammeters. The experimental results are discussed in terms of the external and internal photoemission processes and their distribution in thin film capacitors under an external bias condition. The proposed detection method opens the way to perform electronic and chemical state analyses of the buried interfaces and layers in various devices like multiferroic tunnel junctions, memristive devices, etc., during operation under an applied bias. [ABSTRACT FROM AUTHOR]

We report on the low resistance state (LRS) stability analysis of Ge0.3Se0.7 based solid electrolyte nonvolatile memory cells under elevated temperature and bias current stress conditions. The activation energy was found to be about 1.02 eV, which is comparable to that of an electromigration-induced failure process. Experimental results also show that there is trade-off between the LRS stability and the thickness of Ge0.3Se0.7 layer. [ABSTRACT FROM AUTHOR]

We present a quantitative study of the thickness dependence of the polarization and piezoelectric properties in epitaxial (001) PbZr0.52Ti0.48O3 films grown on (001) SrRuO3-buffered (001) SrTiO3 substrates. High-resolution transmission electron microscopy reveals that even the thinnest films (∼8 nm) are fully relaxed with a dislocation density close to 1012 cm-2 and a spacing of approximately 12 nm. Quantitative piezoelectric and ferroelectric measurements show a drastic degradation in the out-of-plane piezoelectric constant (d33) and the switched polarization (ΔP) as a function of decreasing thickness. In contrast, lattice-matched ultrathin PbZr0.2Ti0.8O3 films that have a very low dislocation density show superior ferroelectric properties. Supporting theoretical calculations show that the variations in the strain field around the core of the dislocation leads to highly localized polarization gradients and hence strong depolarizing fields, which result in suppression of ferroelectricity in the vicinity of a dislocation. [ABSTRACT FROM AUTHOR]

We report on the comparison of the resistance switching properties and kinetic behavior of Cu doped Ge0.3Se0.7 solid electrolyte based dual layer memory devices integrated with asymmetrical (Pt and Cu) and symmetrical electrodes (only Cu). In spite of the fact that the observed resistance switching properties and its parameters are quite similar for both memory devices, the dependence of the SET-voltage on the voltage sweep rate suggests different microscopic rate limiting factors for the resistance switching behavior. Additionally, in order to alleviate the cross talk problem in passive crossbar arrays, a dual layer oxide stack (TiO2/Al2O3) is integrated with Ge0.3Se0.7 based dual layer memory devices to achieve a specific degree of non-linearity in the overall resistance of the low resistance state. [ABSTRACT FROM AUTHOR]

Currently, there is great interest in using solid electrolytes to develop resistive switching based nonvolatile memories (RRAM) and logic devices. Despite recent progress, our understanding of the microscopic origin of the switching process and its stochastic behavior is still limited. In order to understand this behavior, we present a statistical 'breakdown' analysis performed on Cu doped Ge0.3Se0.7 based memory devices under elevated temperature and constant voltage stress conditions. Following the approach of electrochemical phase formation, the precursor of the 'ON resistance switching' is considered to be nucleation - the emergence of small clusters of atoms carrying the basic properties of the new phase which forms the conducting filament. Within the framework of nucleation theory, the observed fluctuations in the time required for 'ON resistance switching' are found to be consistent with the stochastic nature of critical nucleus formation. [ABSTRACT FROM AUTHOR]

We report electrical characterization of memory elements consisting of a p-type silicon field-effect transistor incorporating a ferroelectric polymer Langmuir–Blodgett film into the gate insulator to produce bistability through polarization hysteresis. The thin gate insulator, consisting of a 10 nm thick silicon oxide layer and a 35 nm thick ferroelectric polymer film, enabled bistable operation at 4 V. Device hysteresis as a function of gate voltage was evident both in the device capacitance, which was measured between the gate and drain, and in the source-drain conductance. The ferroelectric film polarization was not saturated, even up to operating voltages of 10 V. This is likely the reason for the short state retention of less than 10 s at room temperature. The hysteresis vanished as the sample was heated toward the ferroelectric-paraelectric phase transition temperature, showing that the bistability was due to ferroelectric polarization reversal. [ABSTRACT FROM AUTHOR]

The ultimate sensitivity of any solid state device is limited by fluctuations. Fluctuations are manifestations of the thermal motion of matter and the discreteness of its structure which are also inherent ingredients during the resistive switching process of resistance random access memory (RRAM) devices. In quest for the role of fluctuations in different memory states and to develop resistive switching based nonvolatile memory devices, here we present our study on random telegraph noise (RTN) resistance fluctuations in Cu doped Ge0.3Se0.7 based RRAM cells. The influence of temperature and electric field on the RTN fluctuations is studied on different resistance states of the memory cells to reveal the dynamics of the underlying fluctuators. Our analysis indicates that the observed fluctuations could arise from thermally activated transpositions of Cu ions inside ionic or redox “double-site traps” triggering fluctuations in the current transport through a filamentary conducting path. Giant RTN fluctuations characterized by relative resistance variations of up to 50% in almost macroscopic samples clearly point to the existence of weak links with small effective cross-sectional areas along the conducting paths. Such large resistance fluctuations can be an important issue for the industrial applications of RRAM devices because they might lead to huge bit-error rates during reading cycles. [ABSTRACT FROM AUTHOR]

An overview of the state of art in ferroelectric thin films is presented. First, we review applications: microsystems’ applications, applications in high frequency electronics, and memories based on ferroelectric materials. The second section deals with materials, structure (domains, in particular), and size effects. Properties of thin films that are important for applications are then addressed: polarization reversal and properties related to the reliability of ferroelectric memories, piezoelectric nonlinearity of ferroelectric films which is relevant to microsystems’ applications, and permittivity and loss in ferroelectric films—important in all applications and essential in high frequency devices. In the context of properties we also discuss nanoscale probing of ferroelectrics. Finally, we comment on two important emerging topics: multiferroic materials and ferroelectric one-dimensional nanostructures. [ABSTRACT FROM AUTHOR]

The SrTiO3 /Si interface was investigated by transmission electron microscopy for SrTiO3 films grown on s001d Si by molecular-beam epitaxy with different native oxide (SiO2) removal treatments, and Sr/Ti flux ratios. The interface and film microstructure were independent of the process used to remove the native oxide, but the interface reactivity was dependent on the Sr/Ti flux ratio. A low Sr/Ti flux ratio (~0.8) resulted not only in a layer of amorphous material at the film/substrate interface but also in the formation of crystalline C49 TiSi2 precipitates at that interface. These results are consistent with thermodynamic expectations in which it is paramount to maintain separation between TiO2 and the underlying silicon. [ABSTRACT FROM AUTHOR]

In SrRuO[sub 3]/PbZr[sub 0.52]Ti[sub 0.48]O[sub 3]/SrRuO[sub 3] multilayer thin films on SrTiO[sub 3] substrates the different lattice distortion behavior of the top and the bottom SrRuO[sub 3] film layer is found and characterized by means of transmission electron microscopy. The bottom SrRuO[sub 3] layer is compressively strained in the film plane by a constraint of the SrTiO[sub 3] substrate. In contrast, in the interface area of the top SrRuO[sub 3] layer, a lattice dilatation is measured not only in the film plane but also parallel to the film normal. The misfit strain, the lead interdiffusion and the oxygen concentration in this area are investigated and discussed as possible reasons for the unexpected lattice dilatation along the film normal direction. [ABSTRACT FROM AUTHOR]

Stacked Josephson junction arrays located at the rf current antinodes of a superconducting microstripline resonator were investigated. The circuits were designed to obtain highly accurate voltages at cm-waveband microwave driving and low rf-power level. Nb-Al/AlO/sub x/-Nb Josephson junctions with tunneling area of 60 /spl mu/m/spl times/300 /spl mu/m and critical current density up to 7 A/cm/sup 2/ were used. We compared the average voltages of the rf induced maximal current steps in arrays with up to three junctions per stack. Quantized current steps up to 300 mV were observed under microwave irradiation at frequency of 19.20 GHz in circuits with 384 three-junction stacks. The dynamics of stacked tunnel junctions in the presence of rf-currents will be discussed with respect to application as voltage standards. [ABSTRACT FROM PUBLISHER]

Studies the properties of discrete Josephson multi-junction transmission lines (DMJTLs) based on double-barrier stacked junctions. Description of the fabrication technology of double-barrier DMJTLs; Distinct features of DMJTL; Possibility of multi-fluxon transfer through DMJTL.

Deals with a study that observed radiation measurements with double-junction stacked Josephson flux-flow oscillator on-chip coupled to a superconductor-insulator-superconductor detector. Induction of radiation from flux-flow oscillators; Determination of inductive coupling between adjacent junctions; Design of the detecting cell.

To obtain reliable magnetic tunnel junctions (MTJs) for sensor and memory applications, the quality of the Al[SUB2]O[SUB3] tunnel barrier is extremely important. Here, we studied the reliability of MTJs with a 1.6 nm Al[SUB2]O[SUB3] tunnel barrier formed by ultraviolet light assisted oxidation. In the stress measurements, prebreakdown current jumps and, finally, breakdown are observed. We show, by using statistics, that both the current jumps and the final breakdown can be attributed to single trap generation. Moreover, we can relate the current jump height to the trap location. In this way, we reveal the breakdown mechanism in MTJs and illustrate the importance of reliability studies. [ABSTRACT FROM AUTHOR]

We demonstrate an integration of tunneling magnetoresistance and the Josephson effects within one tunneling junction. Several sets of Nb-Fe-Al-Al2O3-Fe-Nb wafers with varying Al and Fe layers thickness were prepared to systematically explore the competition of TMR and Josephson effects. A coexistence of the critical current IC(dFe) and the tunneling magnetoresistance ratio T M R(dFe) is observed for iron layer dFe thickness range 1.9 and 2.9 nm. Further optimization such as thinner Al2O3 layer leads to an enhancement of the critical current and thus to an extension of the coexistence regime up to dFe ≃ 3.9 nm Fe. [ABSTRACT FROM AUTHOR]

The objective of this letter is to convey two essential principles of biological computing—synchronization and memory—in an electronic circuit with two van der Pol (vdP) oscillators coupled via a memristive device. The coupling was mediated by connecting the gate terminals of two programmable unijunction transistors through a resistance-capacitance network comprising an Ag-TiOx-Al memristive device. In the high resistance state the memristance was in the order of MΩ, which leads to two independent self-sustained oscillators characterized by the different frequencies f1 and f2 and no phase relation between the oscillations. Depending on the mediated pulse amplitude, the memristive device switched to the low resistance state after a few cycles and a frequency adaptation and phase locking were observed. The experimental results are underlined by theoretically considering a system of two coupled vdP equations. This experiment may pave the way to larger neuromorphic networks in which the coupling parameters (through memristive devices) can vary in time and strength and are able to remember the history of applied electrical potentials. [ABSTRACT FROM AUTHOR]

Dynamics of domain boundaries is expected to change drastically at low absolute temperatures but direct experimental information for this temperature range is still lacking. To clarify the mechanism of low-temperature domain dynamics, we studied the growth of ferroelectric domains in the temperature range 4.2-295K using the out-of-plane piezoresponse mode of a cryogenic atomic force microscope (AFM). Nanoscale 180° domains were created in epitaxial PbZr0.3Ti0.7O3 films by applying short voltage pulses between the conductive AFM tip brought into contact with the bare film surface and the bottom LaSr0.7Mn0.3O3 electrode. A quantitative analysis of acquired piezoresponse images enabled us to determine the in-plane domain size as a function of the writing voltage and pulse duration. It is found that at all studied temperatures the dependence of this size on the pulse duration can be fitted by a logarithmic function, which indicates that the domain-wall velocity exponentially depends on the driving electric field. The theoretical analysis of experimental data shows that the observed low-temperature domain dynamics is consistent with the creep of domain boundaries occurring in the presence of defects and structural nanoheterogeneities. [ABSTRACT FROM AUTHOR]