Potential Applications In Memory Devices Research Articles

Phase transition induced threshold resistive switching in two-dimensional VTe2 nanosheets for Boolean logic operations

Vanadium chalcogenides have been extensively studied owing to the diverse crystallographic structures with various stoichiometric ratios. The metal-to-insulator transition (MIT) widely reported in vanadium chalcogenides is a rapid reversible phase transition that requires small energy, demonstrating potential applications in memory devices. In this work, two-dimensional (2D) vanadium telluride (VTe2) nanosheets are prepared by the chemical vapor deposition method. The synthesized VTe2 nanosheets exhibit volatile threshold switching (TS) behaviors due to the MIT phase transition, which can be further confirmed by the temperature dependent TS behaviors. The TS memristor demonstrates good stability and high reliability with up to 1000 continuous and repeatable writing/erasing operations. Furthermore, based on the TS behaviors, the fabricated memristor can be utilized to implement basic Boolean logic operations of “OR,” “AND,” and “NOT.” This study not only demonstrates the TS behaviors in the 2D VTe2 nanosheets owing to the MIT phase transition but also shows the potential applications of the TS devices in Boolean logic operations.

Roadmap on ferroelectric hafnia- and zirconia-based materials and devices

Ferroelectric hafnium and zirconium oxides have undergone rapid scientific development over the last decade, pushing them to the forefront of ultralow-power electronic systems. Maximizing the potential application in memory devices or supercapacitors of these materials requires a combined effort by the scientific community to address technical limitations, which still hinder their application. Besides their favorable intrinsic material properties, HfO2–ZrO2 materials face challenges regarding their endurance, retention, wake-up effect, and high switching voltages. In this Roadmap, we intend to combine the expertise of chemistry, physics, material, and device engineers from leading experts in the ferroelectrics research community to set the direction of travel for these binary ferroelectric oxides. Here, we present a comprehensive overview of the current state of the art and offer readers an informed perspective of where this field is heading, what challenges need to be addressed, and possible applications and prospects for further development.

Magnetoelectric response in laminated BaFe12O19/Pb(Zr,Ti)O3 composites

The magnetoelectric (ME) response of laminated composites consisting of BaFe12O19 and Pb(Zr,Ti)O3 ceramics is systematically investigated. A butterfly-shaped curve of a magnetoelectric coefficient emerges in both three-layer and multilayer composites. We show that the appearance of a 7 ppm residual strain in the BaFe12O19 layer after magnetization is the main reason for this special curve. We also observe the self-biasing effect of the composites and a maximum ME response from 0.6 to 5 mV/(Oe cm) in laminated composites with magnetic and ferroelectric layers of different thicknesses that can be measured at a zero-bias magnetic field. The repeatable and stable maximum and minimum values of the magnetoelectric coefficient can be obtained under periodically applied biasing magnetic fields, which is important for a practical device application. An electric-field control of ferromagnetism, evidenced by a 17%–19% enhancement in the magnetization of the BaFe12O19 layer after Pb(Zr,Ti)O3 is polarized, is observed in the composites, implying potential applications in memory devices for the composites. Our work indicates that both magnetic field-controlled polarization and electric-field-controlled magnetization exist in BaFe12O19/Pb(Zr,Ti)O3 laminated composites.

Enhancement of coercivity, permeability, and dielectric properties of Co0.2Zn0.3Ni0.5EuxFe2–xO4 ferrites for memory and high frequency devices

Spinel cubic ferrites have huge applications in memory and high frequency devices. For the improvement of these modern devices, the magnetic coercivity, permeability, and dielectric properties of a ferrite are the important issues. This article focuses on improving the magnetic coercivity, magnetic permeability, and dielectric properties of Co0.2Zn0.3Ni0.5EuxFe2–xO4 ferrites, where x = 0.00, 0.06, and 0.10. The X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX), vibrating sample magnetometer (VSM), and an impedance analyzer were used to characterize the structural, magnetic, and dielectric properties of the samples. The XRD patterns indicate the formation of spinel cubic structure of the samples with a secondary peak (EuFeO3) for Eu doped samples. The densities and porosities of the samples follow an inverse trend, where the doped samples’ lattice parameters are increased with the increment of rare earth Eu concentration. The FTIR analysis also proves the spinel cubic phase of the samples. The average grain size of the ferrites is obtained via FESEM images, and it is increased from 121 to 198 nm. VSM analysis confirms that doping of the Eu content also changes other hysteresis loop properties of Co0.2Zn0.3-Ni0.5EuxFe2–xO4 ferrites. Particularly, the coercivity of the Eu doped samples is greater than that of the mother alloy (x = 0.00). The EDX study shows that there is no impurity contamination in the ferrites. The permeability and dielectric measurements show an improved quality factor of the Eu-doped samples with low magnetic and dielectric losses. Frequency dependent resistivity and impedance analysis also show the improved nature. From the observed properties of the samples, all the investigated ferrites might be strong candidates for potential applications in memory devices, magnetic sensors, and high frequency applications.

Pristine leaf based electrochemical resistive switching device

There has been increasing interest in two-terminal resistive switching devices due to their potential applications in memory devices. On the other hand, there is also growing interest in using biological materials for developing biodegradable electronics to help minimize the environmental footprint of electronics and also to explore ways to integrate electronics and living systems. Here, we present our study on resistive switching behavior observed on pristine unprocessed leaves. The resistance can reliably be switched between high and low resistance states for at least 375 cycles with ON/OFF ratio of ~ 73, demonstrating a high level of endurance and their potential for resistive random-access memory devices. We attribute this phenomenon to ionic transport within the leaf cells, the buildup of the electric double layer at the cell wall interfaces, and electron transfer assisted by redox reactions. The results presented here highlight the potential of constructing two-state resistive switching devices in living systems and using biological materials for the construction of biodegradable and biocompatible memory devices while also possibly serving as an inspiration for biomimetic resistive switching devices.

Structural, dielectric, ferroelectric and optical properties of Er doped BiFeO3 nanoparticles

In this work, an effort has been made to show the effect of Er doping on the dielectric, electrical, ferroelectric, and optical properties of BiFeO3 (BFO) nanoparticles prepared by the sol-gel route. XRD of Bi1-xErxFeO3 samples revealed that the rhombohedral (R3c) structure is stable for 0 ≤ x ≤ 0.08 with distortional changes, whereas a co-existence of two phases, rhombohedral (R3c) and orthorhombic (Pn21a) is present for x = 0.12. At room temperature, dielectric properties are slightly improved with the appearance of defects at a higher temperature. The ln σacvs. 1000/T plots revealed the presence of different Arrhenius-type thermally activated mechanisms and, for their analysis, were divided in five regions: the low temperature regions (I and II), followed by a small polaron hopping (intermediate region III) and a single and a double oxygen vacancies regions in the high temperature side (IV and V). Er doped BFO displays an improvement of the dielectric properties with respect to those of BFO, clearly reflected in better P-E loops. UV–Vis spectroscopy revealed the optical band energy lies in the 2.10 eV–1.70 eV interval, suggesting possible applications in the visible range of the spectrum. The multiferroic properties at room temperature make it a good candidate for future potential application in memory devices.

Synaptic learning and memory functions in SiO2:Ag/TiO2 based memristor devices

In this study, a TiO2 thin layer is deliberately inserted in the Pt–Ag/SiO2:Ag/p++-Si memristor to achieve enhanced resistive switching performance in terms of retention and cyclic endurance characteristics. The memristor device exhibits a bidirectional analog switching behavior corresponding to a wide dynamic range of synaptic weight modulation as potentiation and depression under the consecutive positive or negative DC bias sweeps and pulse trains. Moreover, the learning and memory functions, including paired-pulse facilitation and pulse repetition-induced short-term memory to long-term memory transition, are also demonstrated. The relation of the memory stability to the repeated input pulse stimulus and the device conductance with time have also been revealed by the stretched exponential relaxation model. It is shown that the conductance of our newly fabricated Pt–Ag/SiO2:Ag/TiO2/p++-Si memristor device can be modulated by successive Ag-filament growth and dissolution in the SiO2:Ag/TiO2 bilayer oxide structure, which is essential for potential applications in memory devices and artificial neural systems.

Magneto-dielectric properties of in-situ oxidized magnesium-aluminium spinel thin films using electrodeposition

Thermally and chemically stable spinel ferrites are electrically nonconductive material. These are important for their magnetic and dielectric properties. Spinel thin films of magnesium aluminium oxide are prepared on copper substrate using electrodeposition technique. A series of seven samples are prepared by changing the deposition time from 30 min to 120 min with an interval of 15min. In-situ oxidation is carried out for each sample for a fixed time of 10 min. Thin films are magnetic field (MF) annealed at 300 °C with an externally applied magnetic field of 500 Oe. Structural, magnetic and dielectric properties of magnesium aluminium oxide thin films are investigated by X-ray diffractometer, vibrating sample magnetometer and impedance analyzer. X-ray diffraction reveals the formation of pure phase of spinel magnesium aluminium oxide thin film at deposition time of 90 min with 10 min oxidation time. These electrodeposited magnesium aluminium oxide thin films exhibit ferromagnetism at room temperature. Pure phase exhibits maximum exchange bias of 274 Oe and minimum value of anisotropy constant (i.e. 0.121 × 109 erg/cm3). Anomalous behavior of dielectric constant is observed for the magnesium aluminum oxide thin films prepared under all conditions. Pure phase of spinel thin films prepared with 90 min deposition time exhibit higher value of dielectric constant (45.24 at log f = 5) and lower value of tangent loss (0.01 at log f = 5). Magnetodielectric coupling (MDC) is observed for electrodeposited magnesium aluminum oxide thin films suggesting its potential application in memory devices.

Long‐Lasting and Rapid‐Responsive Media for Rewritable Information Storage Based on Low‐Cost N‐Substituted Maleimides Oligomers

AbstractControllable synthesis of high‐performance materials with low‐cost is critical for the development of functional devices. Herein, a series of sequence‐controlled low‐dispersity oligomers with acid–base chromotropic capability via simple copolymerization between N‐substituted maleimides (NMI) and methyldiallylamine (MDAA) are synthesized. The structure and molecular weight of the oligomers are characterized. Owing to the presence of strong electrophilic carbonyl oxygen and imine nitrogen, a rapid‐responsive color switching system is achieved. This change is attributed to the acid/base‐triggered isomerization between enolate state and the enol or keto tautomer via intramolecular proton transfer. More importantly, the color of P(MDAA/NMI) is regulated by the variation of the substituent group of the N‐substituted maleimide. A new type of rewritable paper based on the designed N‐substituted maleimide oligomers is fabricated by a simple spin‐coating process, on which images with high resolution can be acid‐printed and base‐erased for over ten cycles. The writing and erasure times can be as short as 10 s and the legible time can be more than 90 days under ambient conditions. The as‐formed rewritable paper with excellent rewriting performances is low‐cost and easy for large‐scale production and may find more advanced potential applications in memory devices, rewritable labels, an sensors.

Bragg coherent diffractive imaging of strain at the nanoscale

Strain engineering is a promising technology with potential application in memory devices, electronic elements, photoactive materials, etc. Nanoscale imaging of the strain is therefore important to better understand the operating condition of the device, growth processes, and influences of other factors. X-rays offer the advantage over electron-based techniques in that they offer high spatial resolution and access to volumetric information within nanostructured materials. This paper describes the basic physics behind strain at the nanoscale and provides a concise summary of the efforts in coherent diffractive imaging for the imaging of the displacement fields in nanocrystals. Although the approach is still under development, with instruments being continuously improved, a number of important results have already been demonstrated.

Synthesis, structure, magnetism and photocatalysis of α-Fe2O3 nanosnowflakes.

In this work, a simple one-step hydrothermal method was developed to synthesize high-quality α-Fe2O3 nanoparticles with a snowflake-like microstructure. First, a series of binary supramolecular aggregates were prepared by a non-covalent combination between a polymer such as polyvinylpyrrolidone (PVP) and a complex such as potassium ferrocyanide (PF). Then, the aggregates were used as the precursors of the one-step hydrothermal reactions. The snowflake-like nanostructure has six-fold symmetry as a whole, and each petal is symmetric. This synthesis method has the characteristics of simplicity, rapidity, reliance, and high yield, and can be used for creating high-quality α-Fe2O3 nanoparticles. Moreover, our results show that the molar ratio of PVP to PF, reaction time and temperature play important roles in the generation of a complete snowflake structure from different angles. Also, the snowflake-like α-Fe2O3 nanostructure exhibits a much higher coercivity (2997 Oe) compared to those reported by others, suggesting a strong hysteresis behaviour, which promises potential applications in memory devices, and other fields. Further, the α-Fe2O3 nanosnowflakes show a much higher photocatalytic degradation activity for cationic organic dyes such as crystal violet, rhodamine 6G than for anionic dyes such as methyl orange. A possible photocatalytic mechanism was proposed for explaining the selectivity of the photocatalytic oxidation reaction of organic dyes. We believe that this study provides a direct link among coordination compounds of transition metals, their supramolecular aggregates with polymers, and controlled hydrothermal synthesis of high-quality inorganic metal oxide nanomaterials.

Structural, dielectric and ferroelectric properties of rare earth substituted lead zirconate titanate

Rare-earth (RE) metal (Pr, Yb, Sm) ions doped lead zirconate titanate (PZT) ceramics were synthesized by the sol–gel auto-combustion technique and characterized for their structural, morphological and ferroelectric properties. The results from X-ray diffraction analysis of all these samples confirmed the tetragonal phase and only in the case of Sm doped PZT, there is pyrochlore phase. The surface morphology revealed a decrease in grain size with the RE doping with the lowest value for Yb–PZT. From the dielectric studies, a high value of dielectric constant of 2 × 105 was observed for Yb–PZT and drop in Curie temperature was observed for Pr and Sm doped PZT. The low dielectric loss and an increase in coercivity were found for Pr doped PZT which may have potential applications in memory devices.

Structure and Magnetic Property Control of Copper Hydroxide Acetate by Non-Classical Crystallization.

Copper hydroxide acetate (CHA), one layered hydroxide compound with tunable magnetism, attracts great interest because of its potential applications in memory devices. However, ferromagnetism for CHA is only demonstrated by means of GPa pressure. Herein, a new method is reported, involving the combination of different crystallization pathways to control crystallization of amorphous CHA toward the formation of CHA/polymer composites with tunable magnetic properties and even a tunability that can be tested at room temperature. By using poly[(ethylene glycol)6 methyl ether methacrylate]-block-poly[2-(acetoacetoxy) ethyl methacrylate] (PEGMA-b-PAEMA) diblock copolymers as additives in combination with a post-treatment process by ultracentrifugation, it is demonstrated that CHA and PEGMA-b-PAEMA form composites exhibiting different magnetic properties, depending on CHA in-plane nanostructures. Analytical characterization reveals that crystallization of CHA is induced by ultracentrifugation, during which CHA nanostructures can be well controlled by changing the degrees of polymerization of the PEGMA and PAEMA blocks and their block length ratios. These findings not only present the first example of using crystallization from polymer stabilized amorphous precursors toward the generation of magnetic nanomaterials with tunable magnetism but also pave the way for the future design of functional composite materials.

ChemInform Abstract: A Review of the Influential Factors on the Ferroelectric Domain Structure in BiFeO3 Thin Films

AbstractReview: 23 refs.

Spin–orbit torques in action

The spin–orbit interaction can generate torques that act on the magnetization of a ferromagnet. Here we examine recent experimental insights into spin–orbit torques, which have generated competing explanations and differing opinions over their potential application in memory devices.

Electric-pulse-controlled Schottky-like/Ohmic contact for Ag/Nb-doped SrTiO3 junctions

Applying conductive silver paint to the surface of a 0.1wt% Nb-doped SrTiO3 (STON) substrate resulted in an Ag/STON junction device. By applying electric current pulses to the junction, multiple resistance states ranging from high resistance (R≈75kΩ) to low resistance (R≈2kΩ) were observed. By alternating the electric pulses, the Ag/STON junctions oscillated between the two resistance states, which has potential applications in memory devices. Current–voltage (I–V) measurements were performed to study the interface between the Ag and STON substrate. The interface characteristics were dependent on the resistance state and could be easily controlled by the electric pulse. When the high-resistance state transitioned to the low-resistance state, a change from a Schottky-like to Ohmic contact was detected. These electric-pulse-induced variations in the I–V relationship may be interesting for applications such as multi-channel I–V transformers.

A Review of the Influential Factors on the Ferroelectric Domain Structure in BiFeO<sub>3</sub> Thin Films

BiFeO3 is a very promising multiferroic materials, which can present ferroelectric and antiferromagnetic properties at room temperature (Tn=643 K, Tc= 1103 K). Ferroelectric domains in BiFeO3 thin films have attracted much attention due to their potential applications in memory devices. The aim of this paper is to review the main factors which can influence the ferroelectric domain structure in BiFeO3 thin films, including substrate, doping and film thickness.

Effect of Electrons Trapping/De-Trapping at Si-SiO2 Interface on Two-State Current in MOS(p) Structure with Ultra-Thin SiO2 by Anodization

The phenomenon of two-state inversion gate current of metal-oxide-semiconductor device with p-type substrate (Al/SiO2/p-Si structure using an anodized SiO2 layer) at VG>0 was investigated. Different amounts of electrons are trapped/de-trapped at Si-SiO2 interface after exerting different set/reset stressing voltages over different set/reset time. And the electron trapping/de-trapping at the Si-SiO2 interface near the conduction band is thus proposed to rationalize the decreased/revertible gate current (Iset /Ireset) at VG>0. In particular, the Iset increases with the decreasing amount of trapped electrons. Furthermore, a specific voltage of sustainable voltage is proposed to investigate the filling condition of the Si-SiO2 interface traps in this paper. This simple and fully complementary metal-oxide-semiconductor compatible structure might have the potential application in memory devices.

PHASE FIELD STUDY OF POLARIZATION VORTEX IN FERROELECTRIC NANOSTRUCTURES

Ferroelectric nanostructures are attracting considerable attention due to their unusual physical properties and potential applications in memory devices and nanoelectromechanical systems. It has been found that low-dimensional ferroelectrics, such as ferroelectric nanodots, ferroelectric nanotubes and ferroelectric thin films, exhibit polarization vortices or vortex-like domain structures due to the strong depolarization field and the size effect. The polarization vortex is regarded as a new toroidal order in ferroelectrics which is different from the rectilinear order of polarization. The vortex states of polarization are bistable and can be switched from one state to the other, which holds the potential application in next generation ferroelectric memories. This paper briefly reviews the recent work on the phase field studies of polarization vortex in ferroelectric nanostructures. The homogeneous bulk thermodynamics of ferroelectrics is first introduced based on the Landau–Devonshire theory. To describe the inhomogeneous polarization distribution in ferroelectrics, the phase field model including interface thermodynamics is then presented in the form of time-dependent Ginzburg–Landau equations.

Carbon nanotube dispersed liquid crystal: A nano electromechanical system

Electric field induced director orientation of a nematic liquid crystal (LC)+carbon nanotube (CNT) system reveals insights on switching behavior for this anisotropic composite. Once the field goes off, the LC+CNT system relaxes back to the original orientation through a mechanical rotation, revealing the intrinsic dynamics. LC molecules and CNTs cooperatively form local pseudonematic domains in the isotropic phase due to strong LC-CNT interactions. These field-responsive anisotropic domains do not relax back to the original orientation on switching of the field off, which could find potential applications in memory devices.