Efficient Switching Research Articles

Ta thickness effect on field-free switching and spin–orbit torque efficiency in a ferromagnetically coupled Co/Ta/CoFeB trilayer

Current induced spin–orbit torque (SOT) switching of magnetization is a promising technology for nonvolatile spintronic memory and logic applications. In this work, we systematically investigated the effect of Ta thickness on the magnetic properties, field-free switching and SOT efficiency in a ferromagnetically coupled Co/Ta/CoFeB trilayer with perpendicular magnetic anisotropy. We found that both the anisotropy field and coercivity increase with increasing Ta thickness from 0.15 nm to 0.4 nm. With further increase of Ta thickness to 0.5 nm, two-step switching is observed, indicating that the two magnetic layers are magnetically decoupled. Measurements of pulse-current induced magnetization switching and harmonic Hall voltages show that the critical switching current density increases while the field-free switching ratio and SOT efficiency decrease with increasing Ta thickness. Both the enhanced spin memory loss and reduced interlayer exchange coupling might be responsible for the β DL decrease as the Ta spacer thickness increases. The studied structure with the incorporation of a CoFeB layer is able to realize field-free switching in the strong ferromagnetic coupling region, which may contribute to the further development of magnetic tunnel junctions for better memory applications.

3T2M canted-type x SOT-MRAM: Field-free, high-energy-efficiency, and high-read-margin memory toward cache applications

We propose a novel cell structure of spin-orbit torque (SOT) magnetic random-access memory (MRAM), which consists of three transistors and two canted-type x SOT magnetic tunnel junctions (3T2M) with opposite canting angle (+ φ /- φ ) on a shared heavy-metal, enabling a self-referencing scheme. Owing to the canting-angle-dependent switching polarity, the 3T2M unit keeps switching to complementary states without any complex structure, corroborating an excellent application potential for practical CMOS integration. Moreover, upon tailoring the canting angle and the ratio of field-like over anti-damping torque in the free layer, the developed architecture demonstrates efficient and reliable field-free magnetization switching with a significantly improved read sensing margin (230 mV and 160 mV for reading “1” and “0”) and outstanding thermal stability (Δ∼70). The 3T2M cell exhibits 0.25 ns ultra-fast write speed, a 6× reduced write energy of 35.41 fJ, and 23.65 fJ for “1” and “0” than the state-of-the-art.

Electrochromic and energy storage properties of novel terpyridine-Fe(II) coordination polymers: Improving performance by molecular engineering of nonconjugated linkers from linear to three-arm star configuration

In this work, two novel terpyridine-Fe(II) coordination polymers ( DTP-Fe and TTP-Fe ) with nonconjugated linkers were developed for electrochromism and energy storage. Both coordination polymers exhibited efficient electrochromic switch between purple and pale yellow with optical contrast over 60%, short coloring time around 2 s, high coloration efficiency over 440 cm 2 C −1 , and good cycle stability. Moreover, the electrodes based on polymers DTP-Fe and TTP-Fe showed a specific capacitance of 21.42 and 35.84 mAh·g −1 at 1 A g −1 , respectively. More important, we demonstrated that the three-arm star configuration may be superior to the conventional linear configuration for efficient electrochemical process, which resulted in the improved performance of the coordination polymer TTP-Fe . An asymmetric electrochromic supercapacitor based on TTP-Fe thin film and Prussian blue thin film was fabricated and possessed potential application in energy saving smart windows. • Two terpyridine-Fe(II) coordination polymers were developed for electrochromism and supercapacitor. • TTP-Fe with a three-arm star configuration showed superior performance. • An asymmetric electrochromic supercapacitor based on TTP-Fe was fabricated.

Research Group Introduction: Eneclus Laboratory, Dept. of Computer and Information Sciences, Sojo University

Our research focuses on energy electronics including high efficiency switching converters for DC power supply systems, battery management system for recycling used EV batteries, and solar power generation systems for mobilities.

A MoS2 Hafnium Oxide Based Ferroelectric Encoder for Temporal-Efficient Spiking Neural Network.

Spiking neural network (SNN), where the information is evaluated recurrently through spikes, has manifested significant promises to minimize the energy expenditure in data-intensive machine learning and artificial intelligence. Among these applications, the artificial neural encoders are essential to convert the external stimuli to a spiking format that can be subsequently fed to the neural network. Here, a molybdenum disulfide (MoS2 ) hafnium oxide-based ferroelectric encoder is demonstrated for temporal-efficient information processing in SNN. The fast domain switching attribute associated with the polycrystalline nature of hafnium oxide-based ferroelectric material is exploited for spike encoding, rendering it suitable for realizing biomimetic encoders. Accordingly, a high-performance ferroelectric encoder is achieved, featuring a superior switching efficiency, negligible charge trapping effect, and robust ferroelectric response, which successfully enable a broad dynamic range. Furthermore, an SNN is simulated to verify the precision of the encoded information, in which an average inference accuracy of 95.14% can be achieved, using the Modified National Insitute of Standards and Technology(MNIST) dataset for digit classification. Moreover, this ferroelectric encoder manifests prominent resilience against noise injection with an overall prediction accuracy of 94.73% under various Gaussian noise levels, showing practical promises to reduce the computational load for the neural network.

Electropneumatic Surfaces: Pairing Electrowetting and Air Pressure for Reversible Droplet Mobility Switching

AbstractDesigning surfaces with controllable wettability and exploring methodologies for manipulating liquid motion on solid surfaces is an important research challenge. The impact on various interdisciplinary applications, ranging from self‐cleaning technology to the handling of droplets on Lab‐on‐a‐Chip self‐diagnostic devices, is expected to be significant. In this work, it is studied how the combined action of electric fields and pneumatic actuation can be used to achieve wetting transitions from states where droplets stick to surfaces, to states where droplets slide easily with low friction. The manipulation of water droplets on air‐permeable porous surfaces using both electric fields (electrowetting) and air‐pressure is investigated. The control over droplet mobility is achieved by tuning the solid‐liquid adhesion upon voltage application, in order to pin the droplet; de‐pinning is achieved by air pressure application through surface pores. This way low energy consumption and efficient switching between extreme wetting states and droplet mobility are realized.

A novel co-production of cadaverine and succinic acid based on a thermal switch system in recombinant Escherichia coli

BackgroundPolyamide (nylon) is an important material, which has aroused plenty of attention from all aspects. PA 5.4 is one kind of nylon with excellent property, which consists of cadaverine and succinic acid. Due to the environmental pollution, bio-production of cadaverine and succinic acid has been more attractive due to the less pollution and environmental friendliness. Microbes, like Escherichia coli, has been employed as cell factory to produce cadaverine and succinic acid. However, the accumulation of cadaverine will cause severe damage on cells resulting in inhibition on cell growth and cadaverine production. Herein, a novel two stage co-production of succinic acid and cadaverine was designed based on an efficient thermos-regulated switch to avoid the inhibitory brought by cadaverine.ResultsThe fermentation process was divided into two phase, one for cell growth and lysine production and the other for cadaverine and succinic acid synthesis. The genes of ldhA and ackA were deleted to construct succinic acid pathway in cadaverine producer strain. Then, a thermal switch system based on pR/pL promoter and CI857 was established and optimized. The fermentation conditions were investigated that the optimal temperature for the first stage was determined as 33 ℃ and the optimal temperature for the second stage was 39 ℃. Additionally, the time to shifting temperature was identified as the fermentation anaphase. For further enhance cadaverine and succinic acid production, a scale-up fermentation in 5 L bioreactor was operated. As a result, the titer, yield and productivity of cadaverine was 55.58 g/L, 0.38 g/g glucose and 1.74 g/(L·h), respectively. 28.39 g/L of succinic acid was also obtained with yield of 0.19 g/g glucose.ConclusionThe succinic acid metabolic pathway was constructed into cadaverine producer strain to realize the co-production of succinic acid and cadaverine. This study provided a novel craft for industrial co-production of cadaverine and succinic acid.

Anomalous sign inversion of spin-orbit torque in ferromagnetic/nonmagnetic bilayer systems due to self-induced spin-orbit torque

Self-induced spin-orbit torques (SI-SOTs) in ferromagnetic (FM) layers have been overlooked when estimating the spin Hall angle (SHA) of adjacent nonmagnetic (NM) layers. In this work, we observe anomalous sign inversion of the total SOT in the spin-torque ferromagnetic resonance due to the enhanced SI-SOT, and successfully rationalize the sign inversion through a theoretical calculation considering the SHE in both the NM and FM layers. The findings show that using an FM layer whose SHA sign is the same as that of the NM achieves efficient SOT-magnetization switching with the assistance of the SI-SOT. The contribution of the SI-SOT becomes salient for a weakly conductive NM layer, and conventional analyses that do not consider the SI-SOT can overestimate the SHA of the NM layer by a factor of more than 150.

Wafer-Scale Growth of Sb2Te3 Films via Low-Temperature Atomic Layer Deposition for Self-Powered Photodetectors.

In this work, we demonstrate the performance of a silicon-compatible, high-performance, and self-powered photodetector. A wide detection range from visible (405 nm) to near-infrared (1550 nm) light was enabled by the vertical p-n heterojunction between the p-type antimony telluride (Sb2Te3) thin film and the n-type silicon (Si) substrates. A Sb2Te3 film with a good crystal quality, low density of extended defects, proper stoichiometry, p-type nature, and excellent uniformity across a 4 in. wafer was achieved by atomic layer deposition at 80 °C using (Et3Si)2Te and SbCl3 as precursors. The processed photodetectors have a low dark current (∼20 pA), a high responsivity of (∼4.3 A/W at 405 nm and ∼150 mA/W at 1550 nm), a peak detectivity of ∼1.65 × 1014 Jones, and a quick rise time of ∼98 μs under zero bias voltage. Density functional theory calculations reveal a narrow, near-direct, type-II band gap at the heterointerface that supports a strong built-in electric field leading to efficient separation of the photogenerated carriers. The devices have long-term air stability and efficient switching behavior even at elevated temperatures. These high-performance and self-powered p-Sb2Te3/n-Si heterojunction photodetectors have immense potential to become reliable technological building blocks for a plethora of innovative applications in next-generation optoelectronics, silicon-photonics, chip-level sensing, and detection.

Thickness Dependence of Interface‐Generated Spin Currents in Ferromagnet/Ti/CoFeB Trilayers

AbstractInterface‐generated spin currents in ferromagnet (FM)/nonmagnet (NM) structures provide both in‐plane and out‐of‐plane spin–orbit torques (SOTs), enabling the field‐free switching of perpendicular magnetization of the other FM layer in magnetic trilayers. In this study, the NM thickness dependence of interface‐generated spin currents and associated SOTs in FM/Ti/CoFeB trilayers is investigated. In such magnetic trilayers, it is known that the in‐plane SOT results from the spin–orbit filtering of the interface‐generated spin current, while the out‐of‐plane SOT is due to the spin–orbit precession. These results show that the polarity of current‐induced magnetization switching under an in‐plane magnetic field reverses with increasing Ti thickness. This indicates that the sign of the in‐plane SOT depends on the current distribution between the bottom FM and Ti layers. On the other hand, field‐free switching occurs only for a Ti thickness of up to ≈4 nm, and the same polarity is retained, demonstrating that out‐of‐plane SOT is governed by the charge current flowing near the interface. These results suggest that field‐free switching efficiency can be enhanced by engineering the relative conductance of the FM/NM bilayers to constructively combine in‐plane and out‐of‐plane SOTs caused by interface‐generated spin currents.

Broadband plasmonic switches based on nanodisc-dimers with progressively increasing diameters on a plasmonic film with a VO2 spacer

In this paper, we propose active broadband plasmonic switches based on a periodic array of metallic dimers of nanodiscs with progressively increasing diameters on a gold coated SiO 2 substrate with a VO2 thin film as a spacer between the nanodiscs and the underlying plasmonic substrate. Periodic arrays based on unit cells with plasmonic nanodisc dimers of varying diameters are employed to couple multiple wavelengths of the incident radiation into the plasmonic modes of the nanostructure, which results in a broadband plasmonic response. We employ a vanadium dioxide (VO2) thin film as a spacer between these periodic sets of plasmonic nanodisc-dimers and the underlying gold coated substrate to achieve broadband switching. On exposure to voltage, infrared light or heat, the VO2 spacer layer changes from its semiconducting state to its metallic state. This transformation leads to significant changes in its optical properties leading to changes in the reflectance spectra of the proposed nanostructure. This results in an efficient switching action over wide range of wavelengths spanning the C, L and U bands of optical communication. We demonstrate a broadband extinction ratio of 5 dB over an operating wavelength range of 650 nm spanning from 1460 nm to 2110 nm, and a broadband extinction ratio of 4 dB over an operating wavelength range of 702 nm spanning from 1432 nm to 2134 nm. In addition, we demonstrate the trade-off between the extinction ratio and the operating wavelength range of these switches. An exhaustive analysis of these switches has been carried out using finite difference time domain (FDTD) modelling to demonstrate that the spectral range over which switching can be achieved by employing these switches can be varied by varying the geometrical parameters of the proposed switches and thus these switches offer the flexibility of being employed for different wavelength regimes. These switches can be potentially employed in optical communication networks or as switching elements in plasmonic circuits.

All-optical switch with ultrahigh switching efficiency and ultralow threshold energy based on a one-dimensional PT-symmetric ring optical waveguide network

In this work, we propose an all-optical switch based on one-dimensional (1D) parity-time-symmetric (PT-symmetric) ring optical waveguide network (PTSROWN). By use of the resonant coupling effect of the PT-symmetric structure, the all-optical switch based on our designed 1D PTSROWN generates an ultrahigh transmissivity of 1.42×1018 at ON state, which breaks the bottleneck of the transmissivity of 1 at ON state produced by the all-optical switches made of dielectric optical waveguide networks, photonic crystals, microring resonators, and meanwhile, creates an ultralow transmissivity of 1.01×10−18 at OFF state. It causes our designing all-optical switch reproducing extraordinary large switch efficiency of 1.41×1036, which is 10 orders of magnitude greater than the optimal results reported yet. On the other hand, the super resonant coupling effects can also make the all-optical switch generate ultrastrong photonic localization at ON state, and then drastically reduce the threshold energy. In addition, we have deeply optimized the PT-symmetric optical waveguide network and obtain better extremum spontaneous PT-symmetric breaking points. On this condition, our designing all-optical switch can produce an ultralow threshold energy of 4.3×10−34 J, which is 12 orders of magnitude smaller than the best reported results. This not only provides a better choice for developing all-optical switching devices with better performance, but also possesses a broad application prospect in designing high-efficiency optical amplifiers, optical energy saver devices, etc.

Estimation of greenhouse gas mitigation potential from refrigerant switching and energy efficiency improvement in Thai air conditioners

Thailand is an important manufacturing and export center of Refrigeration and Air Conditioning (RAC), especially wall-typed air conditioners (ACs). Environmentally friendly refrigerant such as Hydrofluorocarbons (HFCs) have become the future substitute potential due to their zero-ozone depleting potential (ODP) with lower global warming potential (GWP). In this paper, we focus on country-wide GHG mitigation potential from refrigerant switching from R-32 to R-290 in Thai air conditioners. We found that there are GHG mitigation opportunities with overall 1.48 MtCO 2eq from the switching in the year 2020 from two concept as follows; (i) GHG mitigation from refrigerant leakage results at around 0.50 MtCO 2eq, (ii) GHG mitigation from energy efficiency improvement result at around 0.98 MtCO 2. However, there are some safety concerns of R-290 which is flammable refrigerants, hence, the relevance government agencies have to be seriously considered especially the installation and operation of R-290 in Thai air conditioners. The well-designed capacity building and awareness for manufacturers, technical service, provider, and user have to be set. Technology transfer from industrialized country to Thailand is essential. All activities have to be implemented along with the Kigali Amendment which will be aligned with the national NDC Roadmap.

Field-Free-Switching State Diagram of Perpendicular Magnetization Subjected to Conventional and Unconventional Spin-Orbit Torques

The lack of certain crystalline symmetries in strong spin-orbit-coupled nonmagnetic materials allows for the existence of unconventional spin Hall responses, with electrically generated transverse spin currents possessing collinear flow and spin directions. The injection of such spin currents into an adjacent ferromagnetic layer can excite magnetization dynamics via unconventional spin-orbit torques, leading to deterministic switching in ferromagnets with perpendicular magnetic anisotropy. We study the interplay between conventional and unconventional spin-orbit torques on the magnetization dynamics of a perpendicular ferromagnet in the small intrinsic damping limit, and identify a rich set of dynamical regimes that includes deterministic and probabilistic switching, precessional and pinning states. Contrary to common belief, we find that there exists a critical conventional spin Hall angle, beyond which deterministic magnetization switching transitions to a precessional or pinned state. Conversely, we show that larger unconventional spin Hall angle is generally beneficial for deterministic switching. We derive an approximate expression that qualitatively describes the state-diagram boundary between the full deterministic switching and precessional states and discuss a criterion for searching symmetry-broken spin Hall materials in order to maximize switching efficiency. Our work offers a roadmap towards energy-efficient spintronic devices, which might open the door for applications in advanced in-memory computing technologies.

Effects of Sputtering Pressure on Electrochromic Properties of NiO films Prepared by DC Magnetron Sputtering

In this paper, nickel oxide films were deposited on ITO-coated glass substrates by DC magnetron sputtering at different pressures(1.2 Pa ∼ 3.0 Pa). The effects of sputtering pressure on microstructure and electrochromic properties of nickel oxide films were investigated. The film thickness was measured by a surface profilometer. The crystal structure and surface morphology of the films were observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochromic properties of the films were studied by combining UV-visible spectrophotometer with electrochemical workstation. The results showed that the nickel oxide film obtained the best surface morphology (uniform grain size and the fewer surface cracks) and outstanding electrochromic performances, including large transmittance modulation (ΔT = 57.19%), high coloration efficiency (CE = 33.59 cm2·C−1) and fast switching speed (tc = 4.63 s, tb = 4.87 s) at a wavelength of 550 nm when the sputtering pressure was 2.4 Pa. And after 500 electrochemical cycles, the transmittance modulation could continue to increase to 61.49% and the coloration efficiency can still be maintained at about 28.21 cm2·C−1, which showed excellent cycling durability.

A hierarchical transcription factor cascade regulates enteroendocrine cell diversity and plasticity in Drosophila

Enteroendocrine cells (EEs) represent a heterogeneous cell population in intestine and exert endocrine functions by secreting a diverse array of neuropeptides. Although many transcription factors (TFs) required for specification of EEs have been identified in both mammals and Drosophila, it is not understood how these TFs work together to generate this considerable subtype diversity. Here we show that EE diversity in adult Drosophila is generated via an “additive hierarchical TF cascade”. Specifically, a combination of a master TF, a secondary-level TF and a tertiary-level TF constitute a “TF code” for generating EE diversity. We also discover a high degree of post-specification plasticity of EEs, as changes in the code—including as few as one distinct TF—allow efficient switching of subtype identities. Our study thus reveals a hierarchically-organized TF code that underlies EE diversity and plasticity in Drosophila, which can guide investigations of EEs in mammals and inform their application in medicine.

Tailoring the Switching Efficiency of Magnetic Tunnel Junctions by the Fieldlike Spin-Orbit Torque

Current-induced spin-orbit torques provide a versatile tool for switching magnetic devices. In perpendicular magnets, the dampinglike component of the torque is the main driver of magnetization reversal. The degree to which the fieldlike torque assists the switching is a matter of debate. Here we study the switching of magnetic tunnel junctions with a CoFeB free layer and either W or Ta underlayers, which have a ratio of fieldlike to dampinglike torque of 0.3 and 1, respectively. We show that the fieldlike torque can either assist or hinder the switching of CoFeB when the static in-plane magnetic field required to define the polarity of spin-orbit torque switching has a component transverse to the current. In particular, the non-collinear alignment of the field and current can be exploited to increase the switching efficiency and reliability compared to the standard collinear alignment. By probing individual switching events in real-time, we also show that the combination of transverse magnetic field and fieldlike torque can accelerate or decelerate the reversal onset. We validate our observations using micromagnetic simulations and extrapolate the results to materials with different torque ratios. Finally, we propose device geometries that leverage the fieldlike torque for density increase in memory applications and synaptic weight generation.

Strongly enhanced THz generation enabled by a graphene hot-carrier fast lane

Semiconductor photoconductive switches are useful and versatile emitters of terahertz (THz) radiation with a broad range of applications in THz imaging and time-domain spectroscopy. One fundamental challenge for achieving efficient ultrafast switching, however, is the relatively long carrier lifetime in most common semiconductors. To obtain picosecond ultrafast pulses, especially when coupled with waveguides/transmission lines, semiconductors are typically engineered with high defect density to reduce the carrier lifetimes, which in turn lowers the overall power output of the photoconductive switches. To overcome this fundamental trade-off, here we present a new hybrid photoconductive switch design by engineering a hot-carrier fast lane using graphene on silicon. While photoexcited carriers are generated in the silicon layer, similar to a conventional switch, the hot carriers are transferred to the graphene layer for efficient collection at the contacts. As a result, the graphene-silicon hybrid photoconductive switch emits THz fields with up to 80 times amplitude enhancement compared to its graphene-free counterpart. These results both further the understanding of ultrafast hot carrier transport in such hybrid systems and lay the groundwork toward intrinsically more powerful THz devices based on 2D-3D hybrid heterostructures.

The giant orbital Hall effect in Cr/Au/Co/Ti multilayers

The spin–orbit torques originating from the spin Hall effect of heavy metals are of vital importance for applications in spintronics due to its low consumption of energy. Theoretical calculations have predicted that 3d and 4d light metals can produce a similar amount of torques to heavy metals via the strong orbital Hall effect (OHE). However, few experiments have been conducted since it is technically challenging to directly detect the orbital current from the OHE. Here, we report an effective approach to demonstrate the strong orbital torques in the light metal Cr with the aid of a conversion process from the orbital current to the spin current by introducing an Au interfacial layer in the Cr/ferromagnet structures. A rather large orbital torque efficiency and an increase with the increasing thickness of the Cr-layer are attained in the perpendicularly magnetized Cr/Au/Co/Ti multilayers. Moreover, an energy efficient magnetization switching and the domain wall motion in Cr/Au/Co/Ti multilayers induced by the OHE have also been observed. Our findings confirm the existence of the orbital Hall torques in Cr and provide an effective way to investigate the OHE.

Integrity analysis of wellbores in the bedded salt cavern for energy storage

Salt cavern used for energy (natural gas, hydrogen) storage has a significant advantage in peak shaving of gas supply due to their high injection-production efficiency and fast gas injection-delivery switching speed. As the only channel for gas injection and delivery, the wellbore is easily damaged by the alternating gas pressure and is a weak component. For salt cavern underground gas storages (UGSs) in bedded rock salt, the roof collapse can also cause tensile damage to the wellbore. Long-running UGSs may suffer leakage accidents due to wellbore failures, and wellbore safety issues need to be fully considered. This paper proposes a coupled analysis of cement sheath fatigue damage and rock salt creep, and its applicability is proved by mechanical tests. A three-dimensional numerical model was established that includes a wellbore, open well section (cavern neck), and bedded salt cavern. The creep and damage constitutive equations were used to calculate rock salt creep and cement sheath damage. The results show that the creep ability of bedded rock salt is lower than that of high-purity rock salt, confirmed by the creep test results and can be described by the creep constitutive equation in this paper. The cavity shrinkage of the bedded UGSs is generally lower than expected, resulting in better wellbore integrity. The low creep capacity of the impurity-containing rock salt will reduce the cavity shrinkage and protect the airtightness of the wellbore. Based on the integrity of the wellbore, the working gas volume of the UGSs in the bedded formation can be increased. Taking the Jintan gas storage as an example, under the operating pressure of 7–17 MPa, the damaged area of the cement sheath is limited to within 0.5 m of the lower end of the wellbore. When the lower limit pressure is reduced to 6 MPa, the damaged area is limited to within 2 m of the lower end of the wellbore, and the wellbore still maintains sufficient airtightness.