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Abstract Emerging non-volatile memristor-based devices with resistive switching (RS) materials are being widely researched as promising contenders for the next generation of data storage and neuromorphic technologies. Titanium nitride (TiN_x) is a common industry-friendly electrode system for RS; however, the precise TiN_xproperties required for optimum RS performance is still lacking. Herein, using ion-assisted DC magnetron sputtering, we demonstrate the key importance not only of engineering the TiN_xbottom electrodes to be dense, smooth, and conductive, but also understoichiometric in N. With these properties, RS in HfO₂-based memristive devices is shown to be optimised for TiN_0.96. These devices have switching voltages ≤ ±1 V with promising device-to-device uniformity, endurance, memory window of ~40, and multiple non-volatile intermediate conductance levels. This study highlights the importance of precise tuning of TiN_xbottom electrodes to achieve robust performance of oxide resistive switching materials. 

Tuning spin and charge degrees of freedom of complex oxide materials can enable significant advancements in future spintronics. In this study, by three dimensional strain engineering, we demonstrate room temperature ferroelectricity and magnetoelectricity in a vertically aligned nanocomposite thin film structure, composed of vertical nanopillars of SmFeO3 (SFO) embedded within the NiFeO4 (NFO) matrix. A three-dimensional tensile strain is induced in the SFO as a result of the unique film architecture. The tensile strain in SFO produces strong room temperature ferroelectric response instead of the normally very weak ferroelectricity of unstrained SFO, which is an improper ferroelectric. The induced ferroelectricity in SFO enables self-biased magnetoelectric coupling to be achieved between the two phases (magnetoelectric coupling coefficient ∼4 × 10−11 sm−1 at room temperature). The magnetoelectric coupling is facilitated by strain transfer across the vertical interfaces of the two phases. We additionally observe an exchange bias of ∼200 Oe (at 2 K) surviving up to the room temperature, indicating strongly coupled interfaces of SFO and NFO. These findings represent a step forward in future magnetoelectric RAM devices. 

Resistive switching devices are promising candidates for the next generation of nonvolatile memory and neuromorphic computing applications. Despite the advantages in retention and on/off ratio, filamentary-based memristors still suffer from challenges, particularly endurance (flash being a benchmark system showing 10⁴to 10⁶ cycles) and uniformity. Here, we use WO₃as a complementary metal-oxide semiconductor–compatible switching oxide and demonstrate a proof-of-concept materials design approach to enhance endurance and device-to-device uniformity in WO₃-based memristive devices while preserving other performance metrics. These devices show stable resistive switching behavior with >10⁶ cycles, >10⁵-second retention, >10 on/off ratio, and good device-to-device uniformity, without using current compliance. All these metrics are achieved using a one-step pulsed laser deposition process to create self-assembled nanocomposite thin films that have regular guided filaments of ≈100-nanometer pitch, preformed between WO₃grains and interspersed smaller Ce₂O₃grains. 

Highly promising performance for future computing applications is achieved based on a new materials design. 

Abstract Transition metal oxides are promising candidates for the next generation of spintronic devices due to their fascinating properties that can be effectively engineered by strain, defects, and microstructure. An excellent example can be found in ferroelastic LaCoO 3 with paramagnetism in bulk. In contrast, unexpected ferromagnetism is observed in tensile-strained LaCoO 3 films, however, its origin remains controversial. Here we simultaneously reveal the formation of ordered oxygen vacancies and previously unreported long-range suppression of CoO 6 octahedral rotations throughout LaCoO 3 films. Supported by density functional theory calculations, we find that the strong modification of Co 3 d -O 2 p hybridization associated with the increase of both Co-O-Co bond angle and Co-O bond length weakens the crystal-field splitting and facilitates an ordered high-spin state of Co ions, inducing an emergent ferromagnetic-insulating state. Our work provides unique insights into underlying mechanisms driving the ferromagnetic-insulating state in tensile-strained ferroelastic LaCoO 3 films while suggesting potential applications toward low-power spintronic devices. 

We report the dielectric Properties of HfO 2 -based films in the optical–high frequency range. The demonstrated tunability of the optical dielectric constant of HfO 2 -based compounds is of great relevance for optoelectronic applications, e.g., high-refractive index dielectrics for nanoantenna and optical coatings for electronic displays. Since the optical dielectric constant of HfO 2 is determined by the electronic structure and its crystal environment, we tune the physical properties of HfO 2 films on MgO by adding different dopants. In this work, we aim to determine the influence of doping together with the resulting crystal structure on the optical dielectric constant. Hence, we studied 20 mol. % Y-doped HfO 2 (HYO), Hf 0.5 Zr 0.5 O 2 (HZO), and Hf 0.5 Ce 0.5 O 2 (HCO). Among the dopants, Y 2 O 3 has the lowest, ZrO 2 an intermediate, and CeO 2 the highest real part of the optical dielectric constant. The optical dielectric constant is found to be lowest in the cubic HYO films. An intermediate dielectric constant is found in HZO films that is predominantly in the monoclinic phase, but additionally hosts the cubic phase. The highest dielectric constant is observed in HCO films that are predominantly in the cubic phase with inclusions of the monoclinic phase. The observed trend is in good agreement with the dominant role of the dopant type in setting the optical dielectric constant. 

δ-Bi 2 O 3 has long been touted as a potential material for use in solid oxide fuel cells (SOFC) due to its intrinsically high ionic conductivity. However, its limited operational temperature has led to stabilising the phase from >725 °C to room temperature either by doping, albeit with a compromise in conductivity, or by growing the phase confined within superlattice thin films. Superlattice architectures are challenging to implement in functional μSOFC devices owing to their ionic conducting channels being in the plane of the film. Vertically aligned nanocomposites (VANs) have the potential to overcome these limitations, as their nanocolumnar structures are perpendicular to the plane of the film, hence connecting the electrodes at top and bottom. Here, we demonstrate for the first time the growth of epitaxially stabilised δ-Bi 2 O 3 in VAN films, stabilised independently of substrate strain. The phase is doped with Dy and is formed in a VAN film which incorporates DyMnO 3 as a vertically epitaxially stabilising matrix phase. Our VAN films exhibit very high ionic conductivity, reaching 10 −3 S cm −1 at 500 °C. This work opens up the possibility to incorporate thin film δ-Bi 2 O 3 based VANs into functional μSOFC devices, either as cathodes (by pairing δ-Bi 2 O 3 with a catalytically active electronic conductor) and/or electrolytes (by incorporating δ-Bi 2 O 3 with an insulator).