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Discusses the development of an effective method for computing the double infinite integrals of an acoustic plane wave by a rectangular plate. Numerical results for far diffracted pattern; Division of subregions consisting of annular sectors with different radii; Calculation of the integral K(m.n,s,t); Scattering of acoustic plane waves.

A simulation tool based on a 3D kinetic Monte Carlo algorithm has been employed to analyse bipolar conductive bridge RAMs fabricated with Cu/HfOx/Pt stacks. Resistive switching mechanisms are described accounting for the electric field and temperature distributions within the dielectric. The formation and destruction of conductive filaments (CFs) are analysed taking into consideration redox reactions and the joint action of metal ion thermal diffusion and electric field induced drift. Filamentary conduction is considered when different percolation paths are formed in addition to other conventional transport mechanisms in dielectrics. The simulator was tuned by using the experimental data for Cu/HfOx/Pt bipolar devices that were fabricated. Our simulation tool allows for the study of different experimental results, in particular, the current variations due to the electric field changes between the filament tip and the electrode in the High Resistance State. In addition, the density of metallic atoms within the CF can also be characterized along with the corresponding CF resistance description. [ABSTRACT FROM AUTHOR]

A multivariate analysis of the parameters that characterize the reset process in Resistive Random Access Memory (RRAM) has been performed. The different correlations obtained can help to shed light on the current components that contribute in the Low Resistance State (LRS) of the technology considered. In addition, a screening method for the Quantum Point Contact (QPC) current component is presented. For this purpose, the second derivative of the current has been obtained using a novel numerical method which allows determining the QPC model parameters. Once the procedure is completed, a whole Resistive Switching (RS) series of thousands of curves is studied by means of a genetic algorithm. The extracted QPC parameter distributions are characterized in depth to get information about the filamentary pathways associated with LRS in the low voltage conduction regime. [ABSTRACT FROM AUTHOR]

Practical use of Resistive Random Access Memory (ReRAM) depends on thorough understanding of the resistive switching (RS) mechanism in transition metal oxides. Although most of ReRAM samples have polycrystalline structures, both experimental studies and theoretical calculations do not often consider the effects that grain boundaries have on the RS mechanism. This paper discusses what determines resistance values in a Pt/polycrystalline NiO/Pt ReRAM structures by using both experiments and first-principles calculations. Electrical measurements suggest that the RS is caused in the grain boundaries of NiO films. First-principles calculations indicate that slight displacements of atoms with a small energy change of 0.04 eV per atom on the surfaces exposed in the grain boundaries can drastically change conductivities. We propose the tiling model, in which grain surfaces are composed by insulating and conductive micro surface structures, and the surface resistances are determined by the tiling patterns. [ABSTRACT FROM AUTHOR]

We report the effect of multivalent Cr-ion doping on the structural, optical, magnetic, and resistive switching properties of BiFe1-xCrxO3 (BFCO) thin films (where, 0 ≤ x ≤ 0.15). BFCO thin films were deposited on Pt/TiO2/SiO2/Si (100) substrate using pulsed laser deposition technique. X-ray diffraction and micro-Raman analysis revealed the presence of a secondary phase in BFCO thin films, above 5% Cr doping concentrations. Enhanced magnetization was observed in BFCO films owing to ferromagnetic superexchange interaction between Fe and Cr-ions. X-ray photoelectron spectroscopy measurements revealed the multivalent states of Cr and Fe-ions, where suppression of oxygen vacancies due to Cr-ion doping in BFCO films was discussed based on the defect chemistry viewpoint. Moreover, current conduction and resistive switching properties were studied and the dominant switching mechanism was explained in the light of oxygen vacancies assisted filamentary conduction model. [ABSTRACT FROM AUTHOR]

We have studied the thickness-dependent change in the valence band offset (VBO) of the SiO2/Si(001) interface using synchrotron-radiation photoemission spectroscopy with soft and hard X-rays. The SiO2-film thickness (Tox) and X-ray irradiation time (tirrad) were systematically parameterized to distinguish between the "intrinsic" Tox effects in the VBOs and the "extrinsic" differential charging phenomena in SiO2 films on Si substrates. The results revealed that at a spontaneous time (tirrad ≈ 5 s) that suppresses the differential charging phenomena as much as possible, the experimental VBO abruptly increases as a function of Tox and gradually saturates to the traditional VBO value range determined by the internal photoemission and photoconduction measurements. This effect is not attributed to the differential charging phenomena, but rather it is attributed to the "intrinsic" Tox-dependent change in the VBO. The two possible physical behaviors include electronic polarization and image charge. We have derived the electronic polarization contribution from experimental data by carefully describing the effects of the long-range image charges based on the classical dielectric-screening model. [ABSTRACT FROM AUTHOR]

Titanium oxide (TiOx) has attracted a lot of attention as an active material for resistive random access memory (RRAM), due to its versatility and variety of possible crystal phases. Although existing RRAM materials have demonstrated impressive characteristics, like ultra-fast switching and high cycling endurance, this technology still encounters challenges like low yields, large variability of switching characteristics, and ultimately device failure. Electroforming has been often considered responsible for introducing irreversible damage to devices, with high switching voltages contributing to device degradation. In this paper, we have employed Al doping for tuning the resistive switching characteristics of titanium oxide RRAM. The resistive switching threshold voltages of undoped and Al-doped TiOx thin films were first assessed by conductive atomic force microscopy. The thin films were then transferred in RRAM devices and tested with voltage pulse sweeping, demonstrating that the Al-doped devices could on average form at lower potentials compared to the undoped ones and could support both analog and binary switching at potentials as low as 0.9 V. This work demonstrates a potential pathway for implementing low-power RRAM systems. [ABSTRACT FROM AUTHOR]

In this paper, we propose a TaOx resistive switching random access memory (RRAM) device with operation-polarity-dependent self-selection effect by introducing highly doped silicon (Si) electrode, which is promising for large-scale integration. It is observed that with highly doped Si as the bottom electrode (BE), the RRAM devices show non-linear (>10³) I-V characteristic during negative Forming/Set operation and linear behavior during positive Forming/Set operation. The underling mechanisms for the linear and non-linear behaviors at low resistance states of the proposed device are extensively investigated by varying operation modes, different metal electrodes, and Si doping type. Experimental data and theoretical analysis demonstrate that the operation-polarity-dependent self-selection effect in our devices originates from the Schottky barrier between the TaOx layer and the interfacial SiOx formed by reaction between highly doped Si BE and immigrated oxygen ions in the conductive filament area. [ABSTRACT FROM AUTHOR]

The conduction characteristics of Pt/NiO/Pt resistive switching cells were investigated systematically through DC and AC conductance measurements in each of three resistance states: the initial state, the low resistance state (LRS), and the high resistance state (HRS). In the initial state, two different conduction processes are dominant, although this dominance is temperature-dependent. The activation energy (Ea) of the DC conductance was approximately 4.3 meV below 170 K. In addition to the low Ea, the frequency and temperature dependence of the AC conductance confirmed that the conduction originated from hopping between isolated sites. However, above 170 K, the Ea of the DC conductance was 330 meV, and this conductance was independent of frequency at low frequencies. The dominant conduction process above 170 K was found to be band conduction from analysis of the AC conductance. The resistance in the LRS varied linearly with temperature and was almost independent of frequency, thus representing the characteristics of metallic band conduction of conductive filaments. In the HRS, the DC conductance exhibited an Ea of 16 meV, which was higher than that in the initial state (4.3 meV), thus indicating that the dominant conduction mechanism in the HRS is different to the mechanism in the initial state. From discussions based on a filament model, it was concluded that filament conduction is dominant in the HRS. As a result, it is proposed that the resistive switching originates from changes in the conduction properties of the filaments themselves rather than from their rupture and formation. [ABSTRACT FROM AUTHOR]

This report investigates the phase evolution pathway of magnetite nanocrystal synthesis on oxide-supported substrates. A template-free phase separation approach, which exploits the thermodynamic instability of ternary perovskite BiFeO3 and inherent volatility of bismuth oxide in low oxygen pressure and high temperature is presented. The formation of an intermediate hematite nanocrystal phase is found as a key step that controls the eventual size and morphology of the magnetite nanocrystals. X-ray absorption spectra measurements and X-ray magnetic circular dichroism confirm that the spectral fingerprints of the magnetite nanocrystals match with that of bulk crystals. Magnetic measurements show that magnetic anisotropy is directly attributed to the nanocrystal morphology. [ABSTRACT FROM AUTHOR]

Superlattices composed of non-magnetic La0.5Sr0.5TiO3 and ferromagnetic La0.7Sr0.3MnO3 were grown by pulsed laser deposition on various substrates to impose different epitaxial strain states. Well-defined superlattice structures with sharp interfaces were observed using scanning transmission electron microscopy and confirmed by electron energy loss spectroscopy. Defects such as misfit dislocations, partial dislocations, and low-angle grain boundaries were found to partially or fully relax the epitaxial strain while dramatically increasing the magnetic coercive field. Conversely, a large tensile strain was seen to induce a tetragonal distortion in the film lattice and alter the magnetic and magneto-transport properties of the superlattices. [ABSTRACT FROM AUTHOR]

Novel information processing techniques are being actively explored to overcome fundamental limitations associated with CMOS scaling. A new paradigm of adaptive electronic devices is emerging that may reshape the frontiers of electronics and enable new modalities. Creating systems that can learn and adapt to various inputs has generally been a complex algorithm problem in information science, albeit with wide-ranging and powerful applications from medical diagnosis to control systems. Recent work in oxide electronics suggests that it may be plausible to implement such systems at the device level, thereby drastically increasing computational density and power efficiency and expanding the potential for electronics beyond Boolean computation. Intriguing possibilities of adaptive electronics include fabrication of devices that mimic human brain functionality: the strengthening and weakening of synapses emulated by electrically, magnetically, thermally, or optically tunable properties of materials.In this review, we detail materials and device physics studies on functional metal oxides that may be utilized for adaptive electronics. It has been shown that properties, such as resistivity, polarization, and magnetization, of many oxides can be modified electrically in a non-volatile manner, suggesting that these materials respond to electrical stimulus similarly as a neural synapse. We discuss what device characteristics will likely be relevant for integration into adaptive platforms and then survey a variety of oxides with respect to these properties, such as, but not limited to, TaOx, SrTiO3, and Bi4-xLaxTi3O12. The physical mechanisms in each case are detailed and analyzed within the framework of adaptive electronics. We then review theoretically formulated and current experimentally realized adaptive devices with functional oxides, such as self-programmable logic and neuromorphic circuits. Finally, we speculate on what advances in materials physics and engineering may be needed to realize the full potential of adaptive oxide electronics. [ABSTRACT FROM AUTHOR]

We report on multilevel bipolar resistance switching in Cu/amorphous-TaOx/Pt structures controlled by a coupled mechanism. The devices could be reproducibly programmed into three nonvolatile resistance states, and the on/off ratios between all neighboring states are >20. It is speculated that the switching between the high resistance state and the intermediate resistance state originates from a phase transformation between Ta2O5 and TaO2, while the low resistance state is induced by the formation of Cu filaments. This structure might be promising for developing multilevel logic and memory devices with high reliability. It may also serve as a model system for investigating the coupling effect between different switching mechanisms. [ABSTRACT FROM AUTHOR]

An electrical stress-induced resistance change in an Fe–O film was studied in detail. Under constant voltage stress (CVS) and constant current injection, the resistance of the Fe–O film abruptly increased. The observed time-to-resistance increase (tr) was found to depend on the applied voltage as well as on the injected current density. The total input energy until tr also depended on the applied voltage. From these observations, the mechanisms of resistance change are considered to obey a field-enhanced reaction, and this resistance increase is attributed to a high-resistive Fe–O layer formation at the interface between the anode electrode and the low-resistive Fe–O layer. We proposed a simplified two-step model for the time evolution of the current under CVS [ICVS(t)]. The predicted ICVS(t) showed a good agreement with experimental results. The model also explained the field dependence of tr. [ABSTRACT FROM AUTHOR]

Presents a study which examined the photoinduced surface deposition of metallic silver in silver-arsenic-sulfur glasses. Experimental methods; Results; Discussion.

A novel patterning technique that creates magnetization patterns in a continuous magnetostrictive film with surface acoustic waves is demonstrated. Patterns of 10 lm wide stripes of alternating magnetization and a 3 lm dot of reversed magnetization are written using standing and focusing acoustic waves, respectively. The magnetization pattern is size-tunable, erasable, and rewritable by changing the magnetic field and acoustic power. This versatility, along with its solid-state implementation (no moving parts) and electronic control, renders it as a promising technique for application in magnetic recording, magnonic signal processing, magnetic particle manipulation, and spatial magneto-optical modulation. [ABSTRACT FROM AUTHOR]

We report on multiphase thin film growth of the Bi-Mn-O system on SrTiO3 (100) substrates. By varying the deposition oxygen partial pressure, the dominant phase formed in the film can be continuously changed from single phase epitaxal multiferroic BiMnO3 to epitaxally grown ferromagnetic Mn3O4. X-ray diffraction and transmission electron microscopy revealed that epitaxial multiferroic nanocomposites consisting of BiMnO3 and Mn3O4 form when the deposition pressure is ≈10 mTorr. The magnetic properties of the films were found to change as a function deposition pressure in a manner consistent with the variation in the nanocomposite microstructure. [ABSTRACT FROM AUTHOR]

The quantum point contact (QPC) model for dielectric breakdown is used to explain the electron transport mechanism in HfO2-based resistive random access memories (ReRAM) with TiN(30 nm)\HfO2(5 nm)\Hf(10 nm)\TiN(30 nm) stacks. Based on experimental I-V characteristics of bipolar HfO2-based ReRAM, we extracted QPC model parameters related to the conduction mechanism in several devices in order to make a statistical study. In addition, we investigated the temperature effect on the conduction mechanism and compared it with the QPC model. Based on these experimental results, we show that the QPC model agrees well with the conduction behavior of HfO2-based ReRAM memory cells. [ABSTRACT FROM AUTHOR]

Oxides-based resistive switching memory induced by oxygen ions migration is attractive for future nonvolatile memories. Numerous works had focused their attentions on the sandwiched oxide materials for depressing the characteristic variations, but the comprehensive studies of the dependence of electrodes on the migration behavior of oxygen ions are overshadowed. Here, we investigated the interaction of various metals (Ni, Co, Al, Ti, Zr, and Hf) with oxygen atoms at the metal/Ta2O5 interface under electric stress and explored the effect of top electrode on the characteristic variations of Ta2O5-based memory device. It is demonstrated that chemically inert electrodes (Ni and Co) lead to the scattering switching characteristics and destructive gas bubbles, while the highly chemically active metals (Hf and Zr) formed a thick and dense interfacial intermediate oxide layer at the metal/Ta2O5 interface, which also degraded the resistive switching behavior. The relatively chemically active metals (Al and Ti) can absorb oxygen ions from the Ta2O5 film and avoid forming the problematic interfacial layer, which is benefit to the formation of oxygen vacancies composed conduction filaments in Ta2O5 film thus exhibit the minimum variations of switching characteristics. The clarification of oxygen ions migration behavior at the interface can lead further optimization of resistive switching performance in Ta2O5-based memory device and guide the rule of electrode selection for other oxide-based resistive switching memories. [ABSTRACT FROM AUTHOR]

High throughput (combinatorial) materials science methodology is a relatively new research paradigm that offers the promise of rapid and efficient materials screening, optimization, and discovery. The paradigm started in the pharmaceutical industry but was rapidly adopted to accelerate materials research in a wide variety of areas. High throughput experiments are characterized by synthesis of a 'library' sample that contains the materials variation of interest (typically composition), and rapid and localized measurement schemes that result in massive data sets. Because the data are collected at the same time on the same 'library' sample, they can be highly uniform with respect to fixed processing parameters. This article critically reviews the literature pertaining to applications of combinatorial materials science for electronic, magnetic, optical, and energy-related materials. It is expected that high throughput methodologies will facilitate commercialization of novel materials for these critically important applications. Despite the overwhelming evidence presented in this paper that high throughput studies can effectively inform commercial practice, in our perception, it remains an underutilized research and development tool. Part of this perception may be due to the inaccessibility of proprietary industrial research and development practices, but clearly the initial cost and availability of high throughput laboratory equipment plays a role. Combinatorial materials science has traditionally been focused on materials discovery, screening, and optimization to combat the extremely high cost and long development times for new materials and their introduction into commerce. Going forward, combinatorial materials science will also be driven by other needs such as materials substitution and experimental verification of materials properties predicted by modeling and simulation, which have recently received much attention with the advent of the Materials Genome Initiative. Thus, the challenge for combinatorial methodology will be the effective coupling of synthesis, characterization and theory, and the ability to rapidly manage large amounts of data in a variety of formats. [ABSTRACT FROM AUTHOR]

As a next-generation memory, we have developed a rare-metal-free memory using Al oxide with a high-density of oxygen vacancies (Vos). The electronic structure has been simulated using first-principles calculations. In this paper, we report the electronic structure of the band gap, analyzed using thermally stimulated current measurements, to evaluate the simulated results. We observed electronic states corresponding to resistance changes for the first time. These results show that Vo+2 (electron empty Vo) changes to Vo+1 by electron injection; the overlapped Vo+1 electron changes into a 'Vo conduction band' (VoCB), and the changed structure is stabilized by structural relaxation of Al ions around Vo. VoCB is considered as a kind of mid-gap impurity band. The origin of the on/off switching is considered to be generation/degeneration of the VoCB caused by increasing/decreasing numbers of Vo electrons. Based on knowledge of the electronic mechanism, we have changed metal/insulator/metal structure to a metal/insulator/semiconductor structure and decreased the reset-current to 7 μA. The Vos of Al oxide are considered to be useful for electronic memory storage. [ABSTRACT FROM AUTHOR]