Self-Assembled On-Chip-Integrated Giant Magneto-Impedance Sensorics

Advances in Flexible Magnetosensitive Materials and Devices for Wearable Electronics

Emerging fields, such as wearable electronics, digital healthcare, the Internet of Things, and humanoid robots, highlight the need for flexible devices capable of recording signals on curved surfaces and soft objects. In particular, flexible magnetosensitive devices garner significant attention owing to their ability to combine the advantages of flexible electronics and magnetoelectronic devices, such as reshaping capability, conformability, contactless sensing, and navigation capability. Several key challenges must be addressed to develop well-functional flexible magnetic devices. These include determining how to make magnetic materials flexible and even elastic, understanding how the physical properties of magnetic films change under external strain and stress, and designing and constructing flexible magnetosensitive devices. In recent years, significant progress is made in addressing these challenges. This study aims to provide a timely and comprehensive overview of the most recent developments in flexible magnetosensitive devices. This includes discussions on the fabrications and mechanical regulations of flexible magnetic materials, the principles and performances of flexible magnetic sensors, and their applications for wearable electronics. In addition, future development trends and challenges in this field are discussed.

Miniaturized double-wing ∆E-effect magnetic field sensors

Magnetoelastic micro-electromechanical systems (MEMS) are integral elements of sensors, actuators, and other devices utilizing magnetostriction for their functionality. Their sensitivity typically scales with the saturation magnetostriction and inversely with magnetic anisotropy. However, large saturation magnetostriction and small magnetic anisotropy make the magnetoelastic layer highly susceptible to minuscule anisotropic stress. It is inevitably introduced during the release of the mechanical structure during fabrication and severely impairs the device's reproducibility, performance, and yield. To avoid the transfer of residual stress to the magnetic layer, we use a shadow mask deposition technology. It is combined with a free-free magnetoelectric microresonator design to minimize the influence of magnetic inhomogeneity on device performance. Magnetoelectric resonators are experimentally and theoretically analyzed regarding local stress anisotropy, magnetic anisotropy, and the ΔE-effect sensitivity in several resonance modes. The results demonstrate an exceptionally small device-to-device variation of the resonance frequency < 0.2% with large sensitivities comparable with macroscopic ΔE-effect magnetic field sensors. This development marks a promising step towards highly reproducible magnetoelastic devices and the feasibility of large-scale, integrated arrays.

A Photolithographable Electrolyte for Deeply Rechargeable Zn Microbatteries in On-Chip Devices

Zn batteries show promise for microscale applications due to their compatibility with air fabrication but face challenges like dendrite growth and chemical corrosion, especially at the microscale. Despite previous attempts in electrolyte engineering, achieving successful patterning of electrolyte microscale devices has remained challenging. Here, successful patterning using photolithography is enabled by incorporating caffeine into a UV-crosslinked polyacrylamide hydrogel electrolyte. Caffeine passivates the Zn anode, preventing chemical corrosion, while its coordination with Zn2+ ions forms a Zn2+-conducting complex that transforms into ZnCO3 and 2ZnCO3·3Zn(OH)2 over cycling. The resulting Zn-rich interphase product significantly enhances Zn reversibility. In on-chip microbatteries, the resulting solid-electrolyte interphase allows the Zn||MnO2 full cell to cycle for over 700 cycles with an 80% depth of discharge. Integrating the photolithographable electrolyte into multilayer microfabrication creates a microbattery with a 3D Swiss-roll structure that occupies a footprint of 0.136 mm2. This tiny microbattery retains 75% of its capacity (350 µAh cm-2) for 200 cycles at a remarkable 90% depth of discharge. The findings offer a promising solution for enhancing the performance of Zn microbatteries, particularly for on-chip microscale devices, and have significant implications for the advancement of autonomous microscale devices.

Self-assembly of Co/Pt stripes with current-induced domain wall motion towards 3D racetrack devices

Modification of the magnetic properties under the induced strain and curvature is a promising avenue to build three-dimensional magnetic devices, based on the domain wall motion. So far, most of the studies with 3D magnetic structures were performed in the helixes and nanowires, mainly with stationary domain walls. In this study, we demonstrate the impact of 3D geometry, strain and curvature on the current-induced domain wall motion and spin-orbital torque efficiency in the heterostructure, realized via a self-assembly rolling technique on a polymeric platform. We introduce a complete 3D memory unit with write, read and store functionality, all based on the field-free domain wall motion. Additionally, we conducted a comparative analysis between 2D and 3D structures, particularly addressing the influence of heat during the electric current pulse sequences. Finally, we demonstrated a remarkable increase of 30% in spin-torque efficiency in 3D configuration.

Molecular Electronics: Creating and Bridging Molecular Junctions and Promoting Its Commercialization

Molecular electronics is driven by the dream of expanding Moore's law to the molecular level for next-generation electronics through incorporating individual or ensemble molecules into electronic circuits. For nearly 50 years, numerous efforts have been made to explore the intrinsic properties of molecules and develop diverse fascinating molecular electronic devices with the desired functionalities. The flourishing of molecular electronics is inseparable from the development of various elegant methodologies for creating nanogap electrodes and bridging the nanogap with molecules. This review first focuses on the techniques for making lateral and vertical nanogap electrodes by breaking, narrowing, and fixed modes, and highlights their capabilities, applications, merits, and shortcomings. After summarizing the approaches of growing single molecules or molecular layers on the electrodes, the methods of constructing a complete molecular circuit are comprehensively grouped into three categories: 1) directly bridging one-molecule-electrode component with another electrode, 2) physically bridging two-molecule-electrode components, and 3) chemically bridging two-molecule-electrode components. Finally, the current state of molecular circuit integration and commercialization is discussed and perspectives are provided, hoping to encourage the community to accelerate the realization of fully scalable molecular electronics for a new era of integrated microsystems and applications.

Proposing magnetoimpedance effect for neuromorphic computing

Oscillation of physical parameters in materials can result in a peak signal in the frequency spectrum of the voltage measured from the materials. This spectrum and its amplitude/frequency tunability, through the application of bias voltage or current, can be used to perform neuron-like cognitive tasks. Magnetic materials, after achieving broad distribution for data storage applications in classical Von Neumann computer architectures, are under intense investigation for their neuromorphic computing capabilities. A recent successful demonstration regards magnetisation oscillation in magnetic thin films by spin transfer or spin orbit torques accompanied by magnetoresistance (MR) effect that can give a voltage peak in the frequency spectrum of voltage with bias current dependence of both peak frequency and amplitude. Here we use classical magnetoimpedance (MI) effect in a magnetic wire to produce such a peak and manipulate its frequency and amplitude by means of the bias voltage. We applied a noise signal to a magnetic wire with high magnetic permeability and owing to the frequency dependence of the magnetic permeability we got frequency dependent impedance with a peak at the maximum permeability. Frequency dependence of the MI effect results in different changes in the voltage amplitude at each frequency when a bias voltage is applied and therefore a shift in the peak position and amplitude can be obtained. The presented method and material provide optimal features in structural simplicity, low-frequency operation (tens of MHz-order) and high robustness at different environmental conditions. Our universal approach can be applied to any system with frequency dependent bias responses.

Full-field, conformal epiretinal electrode array using hydrogel and polymer hybrid technology

Shape-morphable electrode arrays can form 3D surfaces to conform to complex neural anatomy and provide consistent positioning needed for next-generation neural interfaces. Retinal prostheses need a curved interface to match the spherical eye and a coverage of several cm to restore peripheral vision. We fabricated a full-field array that can (1) cover a visual field of 57° based on electrode position and of 113° based on the substrate size; (2) fold to form a compact shape for implantation; (3) self-deploy into a curvature fitting the eye after implantation. The full-field array consists of multiple polymer layers, specifically, a sandwich structure of elastomer/polyimide-based-electrode/elastomer, coated on one side with hydrogel. Electrodeposition of high-surface-area platinum/iridium alloy significantly improved the electrical properties of the electrodes. Hydrogel over-coating reduced electrode performance, but the electrodes retained better properties than those without platinum/iridium. The full-field array was rolled into a compact shape and, once implanted into ex vivo pig eyes, restored to a 3D curved surface. The full-field retinal array provides significant coverage of the retina while allowing surgical implantation through an incision 33% of the final device diameter. The shape-changing material platform can be used with other neural interfaces that require conformability to complex neuroanatomy.

Flexible Magnetic Sensors

With the merits of high sensitivity, high stability, high flexibility, low cost, and simple manufacturing, flexible magnetic field sensors have potential applications in various fields such as geomagnetosensitive E-Skins, magnetoelectric compass, and non-contact interactive platforms. Based on the principles of various magnetic field sensors, this paper introduces the research progress of flexible magnetic field sensors, including the preparation, performance, related applications, etc. In addition, the prospects of flexible magnetic field sensors and their challenges are presented.

Design of an Er-doped surface plasmon resonance-photonic crystal fiber to improve magnetic field sensitivity

In order to meet the demand for large-scale magnetic field testing, this paper proposes a D-shaped magneto-refractive photonic crystal fiber (MRPCF) based on surface plasmon resonance (SPR) by using the erbium-doped materials. The four different structures of Models A, B, C, and D are designed by changing the diameter, the position, and the number of layers of the air holes, and the corresponding magnetic field sensing characteristics are analyzed. The results show that in the magnetic field range of 5-405 mT, the magnetic field sensitivities of Models A, B, C, and D are 28 pm/mT, 48 pm/mT, 36 pm/mT, and 21 pm/mT, respectively. Meanwhile, the figure of merit (FOM) of the four MRPCF-SPR sensors is investigated, which have FOMs of 4.8 × 10^-4 mT^-1, 6.4 × 10^-4 mT^-1, 1.9 × 10^-4 mT^-1, 0.9 × 10^-4 mT^-1. Model B has higher sensitivity and larger FOM. In addition, the effect of the structural parameters of Model B on the sensing performance is also studied. By optimizing each parameter, the magnetic field sensitivity of the optimized Model B is increased to 53 pm/mT, and its magneto-refractive sensitivity and FOM are 2.27 × 10^-6 RIU/mT and 6.2 × 10^-4 mT^-1, respectively. It shows that the magneto-refractive effect of MRPCF can be effectively enhanced by optimizing the structural design of fiber. The proposed MRPCF is an all-solid-state fiber, which solves the instability problem of the magnetic fluid-filled fiber and reduces the complexity of the fabrication process. The all-solid-state MRPCF can be used in the development of quasi-distributed optical fiber magnetic field sensors and has broad applications in the fields of geological exploration, earthquake and tsunami monitoring, and military navigation.

Direct imaging of nanoscale field-driven domain wall oscillations in Landau structures

Linear oscillatory motion of domain walls (DWs) in the kHz and MHz regime is crucial when realizing precise magnetic field sensors such as giant magnetoimpedance devices. Numerous magnetically active defects lead to pinning of the DWs during their motion, affecting the overall behavior. Thus, the direct monitoring of the domain wall's oscillatory behavior is an important step to comprehend the underlying micromagnetic processes and to improve the magnetoresistive performance of these devices. Here, we report an imaging approach to investigate such DW dynamics with nanoscale spatial resolution employing conventional table-top microscopy techniques. Time-averaged magnetic force microscopy and Kerr imaging methods are applied to quantify the DW oscillations in Ni₈₁Fe₁₉ rectangular structures with Landau domain configuration and are complemented by numeric micromagnetic simulations. We study the oscillation amplitude as a function of external magnetic field strength, frequency, magnetic structure size, thickness and anisotropy and understand the excited DW behavior as a forced damped harmonic oscillator with restoring force being influenced by the geometry, thickness, and anisotropy of the Ni₈₁Fe₁₉ structure. This approach offers new possibilities for the analysis of DW motion at elevated frequencies and at a spatial resolution of well below 100 nm in various branches of nanomagnetism.

Fundamentals of Curvilinear Ferromagnetism: Statics and Dynamics of Geometrically Curved Wires and Narrow Ribbons

Low-dimensional magnetic architectures including wires and thin films are key enablers of prospective ultrafast and energy efficient memory, logic, and sensor devices relying on spin-orbitronic and magnonic concepts. Curvilinear magnetism emerged as a novel approach in material science, which allows tailoring of the fundamental anisotropic and chiral responses relying on the geometrical curvature of magnetic architectures. Much attention is dedicated to magnetic wires of Möbius, helical, or DNA-like double helical shapes, which act as prototypical objects for the exploration of the fundamentals of curvilinear magnetism. Although there is a bulk number of original publications covering fabrication, characterization, and theory of magnetic wires, there is no comprehensive review of the theoretical framework of how to describe these architectures. Here, theoretical activities on the topic of curvilinear magnetic wires and narrow nanoribbons are summarized, providing a systematic review of the emergent interactions and novel physical effects caused by the curvature. Prospective research directions of curvilinear spintronics and spin-orbitronics are discussed, the fundamental framework for curvilinear magnonics are outlined, and mechanically flexible curvilinear architectures for soft robotics are introduced.

New Dimension in Magnetism and Superconductivity: 3D and Curvilinear Nanoarchitectures

Traditionally, the primary field, where curvature has been at the heart of research, is the theory of general relativity. In recent studies, however, the impact of curvilinear geometry enters various disciplines, ranging from solid-state physics over soft-matter physics, chemistry, and biology to mathematics, giving rise to a plethora of emerging domains such as curvilinear nematics, curvilinear studies of cell biology, curvilinear semiconductors, superfluidity, optics, 2D van der Waals materials, plasmonics, magnetism, and superconductivity. Here, the state of the art is summarized and prospects for future research in curvilinear solid-state systems exhibiting such fundamental cooperative phenomena as ferromagnetism, antiferromagnetism, and superconductivity are outlined. Highlighting the recent developments and current challenges in theory, fabrication, and characterization of curvilinear micro- and nanostructures, special attention is paid to perspective research directions entailing new physics and to their strong application potential. Overall, the perspective is aimed at crossing the boundaries between the magnetism and superconductivity communities and drawing attention to the conceptual aspects of how extension of structures into the third dimension and curvilinear geometry can modify existing and aid launching novel functionalities. In addition, the perspective should stimulate the development and dissemination of research and development oriented techniques to facilitate rapid transitions from laboratory demonstrations to industry-ready prototypes and eventual products.

Bird-Inspired Self-Navigating Artificial Synaptic Compass

Extrasensory neuromorphic devices that can recognize, memorize, and learn stimuli imperceptible to human beings are of considerable interest in interactive intelligent electronics research. This study presents an artificially intelligent magnetoreceptive synapse inspired by the magnetocognitive ability used by birds for navigation and orientation. The proposed synaptic platform is based on arrays of ferroelectric field-effect transistors with air-suspended magneto-interactive top-gates. A suspended gate of an elastomeric composite with superparamagnetic particles laminated with an electrically conductive polymer is mechanically deformed under a magnetic field, facilitating control of the magnetic-field-dependent contact area of the suspended gate with an underlying ferroelectric layer. The remanent polarization of the ferroelectric layer is electrically programmed with the deformed suspended gate, resulting in analog conductance modulation as a function of the magnitude, number, and time interval of the input magnetic pulses. The proposed extrasensory magnetoreceptive synapse may be used as an artificially intelligent synaptic compass that facilitates barrier-adaptable navigation and mapping of a moving object.

Electronically integrated microcatheters based on self-assembling polymer films

Existing electronically integrated catheters rely on the manual assembly of separate components to integrate sensing and actuation capabilities. This strongly impedes their miniaturization and further integration. Here, we report an electronically integrated self-assembled microcatheter. Electronic components for sensing and actuation are embedded into the catheter wall through the self-assembly of photolithographically processed polymer thin films. With a diameter of only about 0.1 mm, the catheter integrates actuated digits for manipulation and a magnetic sensor for navigation and is capable of targeted delivery of liquids. Fundamental functionalities are demonstrated and evaluated with artificial model environments and ex vivo tissue. Using the integrated magnetic sensor, we develop a strategy for the magnetic tracking of medical tools that facilitates basic navigation with a high resolution below 0.1 mm. These highly flexible and microsized integrated catheters might expand the boundary of minimally invasive surgery and lead to new biomedical applications.

A review on nanostructured thin films on flexible substrates: links between strains and magnetic properties

This paper provides a topical review of work on systems based on magnetic nanostructured thin films on polymer substrates. This topic has indeed experienced a significant growth in the last ten years. Several studies show a strong potential of these systems for a number of applications requiring functionalities on non-planar surfaces. However, the deformations necessary for this type of applications are likely to modify their magnetic properties, and the relationships between strain fields, potential damages and functional properties must be well understood. This review focuses both on the development of techniques dedicated to this research, on the synthesis of the experimental results obtained over the last ten years and on the perspectives related to stretchable or flexible magnetoelectric systems. In particular, the article focuses on the links between magnetic behavior and the strain field developing during the whole history of these systems (elaboration, reversible and irreversible loading).

3D motion tracking display enabled by magneto-interactive electroluminescence

Development of a human-interactive display enabling the simultaneous sensing, visualisation, and memorisation of a magnetic field remains a challenge. Here we report a skin-patchable magneto-interactive electroluminescent display, which is capable of sensing, visualising, and storing magnetic field information, thereby enabling 3D motion tracking. A magnetic field-dependent conductive gate is employed in an alternating current electroluminescent display, which is used to produce non-volatile and rewritable magnetic field-dependent display. By constructing mechanically flexible arrays of magneto-interactive displays, a spin-patchable and pixelated platform is realised. The magnetic field varying along the z-axis enables the 3D motion tracking (monitoring and memorisation) on 2D pixelated display. This 3D motion tracking display is successfully used as a non-destructive surgery-path guiding, wherein a pathway for a surgical robotic arm with a magnetic probe is visualised and recorded on a display patched on the abdominal skin of a rat, thereby helping the robotic arm to find an optimal pathway.

Designing human-interactive displays enabling the simultaneous sensing, visualization, and memorization of a magnetic field remains a challenge. Here, the authors present a skin-patchable magneto-interactive electroluminescent display by employing a magnetic field-dependent conductive gate, thereby enabling 3D motion tracking.

Reversible and Non-Reversible Transformation of Magnetic Structure in Amorphous Microwires

We provide an overview of the tools directed to reversible and irreversible transformations of the magnetic structure of glass-covered microwires. The irreversible tools are the selection of the chemical composition, geometric ratio, and the stress-annealing. For reversible tuning we use the combination of magnetic fields and mechanical stresses. The studies were focused on the giant magnetoimpedance effect and the velocity of the domain walls propagation important for the technological applications. The essential increase of the giant magnetoimpedance effect and the control of the domain wall velocity were achieved as a result of the use of two types of control tools. The performed simulations reflect the real transformation of the helical domain structures experimentally found.

Electron Irradiation Driven Nanohands for Sequential Origami

Sequence plays an important role in self-assembly of 3D complex structures, particularly for those with overlap, intersection, and asymmetry. However, it remains challenging to program the sequence of self-assembly, resulting in geometric and topological constrains. In this work, a nanoscale, programmable, self-assembly technique is reported, which uses electron irradiation as "hands" to manipulate the motion of nanostructures with the desired order. By assigning each single assembly step in a particular order, localized motion can be selectively triggered with perfect timing, making a component accurately integrate into the complex 3D structure without disturbing other parts of the assembly process. The features of localized motion, real-time monitoring, and surface patterning open the possibility for the further innovation of nanomachines, nanoscale test platforms, and advanced optical devices.

Perspective: Ferromagnetic Liquids

Mechanical jamming of nanoparticles at liquid-liquid interfaces has evolved into a versatile approach to structure liquids with solid-state properties. Ferromagnetic liquids obtain their physical and magnetic properties, including a remanent magnetization that distinguishes them from ferrofluids, from the jamming of magnetic nanoparticles assembled at the interface between two distinct liquids to minimize surface tension. This perspective provides an overview of recent progress and discusses future directions, challenges and potential applications of jamming magnetic nanoparticles with regard to 3D nano-magnetism. We address the formation and characterization of curved magnetic geometries, and spin frustration between dipole-coupled nanostructures, and advance our understanding of particle jamming at liquid-liquid interfaces.

3D Self-Assembled Microelectronic Devices: Concepts, Materials, Applications

Modern microelectronic systems and their components are essentially 3D devices that have become smaller and lighter in order to improve performance and reduce costs. To maintain this trend, novel materials and technologies are required that provide more structural freedom in 3D over conventional microelectronics, as well as easier parallel fabrication routes while maintaining compatability with existing manufacturing methods. Self-assembly of initially planar membranes into complex 3D architectures offers a wealth of opportunities to accommodate thin-film microelectronic functionalities in devices and systems possessing improved performance and higher integration density. Existing work in this field, with a focus on components constructed from 3D self-assembly, is reviewed, and an outlook on their application potential in tomorrow's microelectronics world is provided.

Self-assembly of highly sensitive 3D magnetic field vector angular encoders

Novel robotic, bioelectronic, and diagnostic systems require a variety of compact and high-performance sensors. Among them, compact three-dimensional (3D) vector angular encoders are required to determine spatial position and orientation in a 3D environment. However, fabrication of 3D vector sensors is a challenging task associated with time-consuming and expensive, sequential processing needed for the orientation of individual sensor elements in 3D space. In this work, we demonstrate the potential of 3D self-assembly to simultaneously reorient numerous giant magnetoresistive (GMR) spin valve sensors for smart fabrication of 3D magnetic angular encoders. During the self-assembly process, the GMR sensors are brought into their desired orthogonal positions within the three Cartesian planes in a simultaneous process that yields monolithic high-performance devices. We fabricated vector angular encoders with equivalent angular accuracy in all directions of 0.14°, as well as low noise and low power consumption during high-speed operation at frequencies up to 1 kHz.

Self-Assembled Flexible and Integratable 3D Microtubular Asymmetric Supercapacitors

The rapid development of microelectronics has equally rapidly increased the demand for miniaturized energy storage devices. On-chip microsupercapacitors (MSCs), as promising power candidates, possess great potential to complement or replace electrolytic capacitors and microbatteries in various applications. However, the areal capacities and energy densities of the planar MSCs are commonly limited by the low voltage window, the thin layer of the electrode materials and complex fabrication processes. Here, a new-type three-dimensional (3D) tubular asymmetric MSC with small footprint area, high potential window, ultrahigh areal energy density, and long-term cycling stability is fabricated with shapeable materials and photolithographic technologies, which are compatible with modern microelectronic fabrication procedures widely used in industry. Benefiting from the novel architecture, the 3D asymmetric MSC displays an ultrahigh areal capacitance of 88.6 mF cm-2 and areal energy density of 28.69 mW h cm-2, superior to most reported interdigitated MSCs. Furthermore, the 3D tubular MSCs demonstrate remarkable cycling stability and the capacitance retention is up to 91.8% over 12 000 cycles. It is believed that the efficient fabrication methodology can be used to construct various integratable microscale tubular energy storage devices with small footprint area and high performance for miniaturized electronics.

Engineering of Magnetic Softness and Domain Wall Dynamics of Fe-rich Amorphous Microwires by Stress- induced Magnetic Anisotropy

We observed a remarkable improvement of domain wall (DW) mobility, DW velocity, giant magnetoimpedance (GMI) effect and magnetic softening at appropriate stress-annealing conditions. Beneficial effect of stress-annealing on GMI effect and DW dynamics is associated with the induced transverse magnetic anisotropy. An improvement of the circumferential permeability in the nearly surface area of metallic nucleus is evidenced from observed magnetic softening and remarkable GMI effect rising. We assumed that the outer domain shell with transverse magnetic anisotropy associated to stress-annealing induced transverse magnetic anisotropy affects the travelling DW in a similar way as application of transversal bias magnetic field allowing enhancement the DW velocity. Observed decreasing of the half-width of the EMF peak in stress-annealed microwires can be associated to the decreasing of the characteristic DW width. Consequently, stress annealing enabled us to design the magnetic anisotropy distribution beneficial for optimization of either GMI effect or DW dynamics.

Self-Assembly of Integrated Tubular Microsupercapacitors with Improved Electrochemical Performance and Self-Protective Function

Inspired by origami art, we demonstrate a tubular microsupercapacitor (TMSC) by self-assembling two-dimensional (2D) films into a "swiss roll" structure with greatly reduced footprint area. A polymeric framework consisting of swelling hydrogel and polyimide layers ensures excellent ion transport between poly(3,4-ethylenedioxythiophene) (PEDOT)-based electrodes and provides efficient self-protection of the TMSC against external compression up to about 30 MPa. Such TMSCs exhibit an areal capacitance of 82.5 mF cm^-2 at 0.3 mA cm^-2 with a potential window of 0.8 V, an energy density and power density of 7.73 μWh cm^-2 and 17.8 mW cm^-2 (0.3 and 45 mA cm^-2), and an improved cycling stability with a capacitance retention up to 96.6% over 5000 cycles. Furthermore, as-fabricated TMSC arrays can be detached from their surface and transferred onto target substrates. The connection of devices in parallel/series greatly improves their capacity and voltage output. Overall, our prototype devices and fabrication methodology provide a promising route to create integratable microscale tubular energy storage devices with an efficient self-protection function and high performance for future miniaturized electronics.

Magnetic origami creates high performance micro devices

Self-assembly of two-dimensional patterned nanomembranes into three-dimensional micro-architectures has been considered a powerful approach for parallel and scalable manufacturing of the next generation of micro-electronic devices. However, the formation pathway towards the final geometry into which two-dimensional nanomembranes can transform depends on many available degrees of freedom and is plagued by structural inaccuracies. Especially for high-aspect-ratio nanomembranes, the potential energy landscape gives way to a manifold of complex pathways towards misassembly. Therefore, the self-assembly yield and device quality remain low and cannot compete with state-of-the art technologies. Here we present an alternative approach for the assembly of high-aspect-ratio nanomembranes into microelectronic devices with unprecedented control by remotely programming their assembly behavior under the influence of external magnetic fields. This form of magnetic Origami creates micro energy storage devices with excellent performance and high yield unleashing the full potential of magnetic field assisted assembly for on-chip manufacturing processes.

Despite the potential of self-assembly strategies for fabricating 3D micro-electronic devices, technological limitations prohibit widespread industrial adoption. Here, the authors report the magnetic field-assisted Origami-based assembly of high-performance devices with high yield.

Three-Dimensional Microtubular Devices for Lab-on-a-Chip Sensing Applications

The rapid advance of micro-/nanofabrication technologies opens up new opportunities for miniaturized sensing devices based on novel three-dimensional (3D) architectures. Notably, microtubular geometry exhibits natural advantages for sensing applications due to its unique properties including the hollow sensing channel, high surface-volume ratio, well-controlled shape parameters and compatibility to on-chip integration. Here the state-of-the-art sensing techniques based on microtubular devices are reviewed. The developed microtubular sensors cover microcapillaries, rolled-up nanomembranes, chemically synthesized tubular arrays, and photoresist-based tubular structures via 3D printing. Various types of microtubular sensors working in optical, electrical, and magnetic principles exhibit an extremely broad scope of sensing targets including liquids, biomolecules, micrometer-sized/nanosized objects, and gases. Moreover, they have also been applied for the detection of mechanical, acoustic, and magnetic fields as well as fluorescence signals in labeling-based analyses. At last, a comprehensive outlook of future research on microtubular sensors is discussed on pushing the detection limit, extending the functionality, and taking a step forward to a compact and integrable core module in a lab-on-a-chip analytical system for understanding fundamental biological events or performing accurate point-of-care diagnostics.

Highly Integrated MEMS Magnetic Sensor Based on GMI Effect of Amorphous Wire

In this paper, a highly integrated amorphous wire Giant magneto-impedance (GMI) magnetic sensor using micro electron mechanical system (MEMS) technology is designed, which is equipped with a signal conditioning circuit and uses a data acquisition card to convert the output signal of the circuit into a digital signal. The structure and package of the sensor are introduced. The sensor sensing principle and signal conditioning circuit are analyzed. The output of the sensor is tested, calibrated, and the relationship between the GMI effect of the amorphous wire and the excitation current frequency is explored. The sensor supplies voltage is ±5 V, and the excitation signal is a square wave signal with a frequency of 60 MHz and an amplitude of 1.2 V generated by the quartz crystal. The sensor has the largest GMI effect at 60 MHz with a sensitivity of 4.8 V/Oe and a resolution of 40 nT.

Magnetic Field Patterning of Nickel Nanowire Film Realized by Printed Precursor Inks

This paper demonstrates an easily prepared novel material and approach to producing aligned nickel (Ni) nanowires having unique and customizable structures on a variety of substrates for electronic and magnetic applications. This is a new approach to producing printed metallic Ni structures from precursor materials, and it provides a novel technique for nanowire formation during reduction. This homogeneous solution can be printed in ambient conditions, and it forms aligned elemental Ni nanowires over large areas upon heating in the presence of a magnetic field. The use of templates or subsequent purification are not required. This technique is very flexible, and allows the preparation of unique patterns of nanowires which provides opportunities to produce structures with enhanced anisotropic electrical and magnetic properties. An example of this is the unique fabrication of aligned nanowire grids by overlaying layers of nanowires oriented at different angles with respect to each other. The resistivity of printed and cured films was found to be as low as 560 µΩ∙cm. The saturation magnetization was measured to be 30 emu∙g⁻¹, which is comparable to bulk Ni. Magnetic anisotropy was induced with an axis along the direction of the applied magnetic field, giving soft magnetic properties.

Improving the Electrical Contact Performance for Amorphous Wire Magnetic Sensor by Employing MEMS Process

This paper presents a novel fabrication method for amorphous alloy wire giant magneto-impedance (GMI) magnetic sensor based on micro electro mechanical systems (MEMS) technology. In this process, negative SU-8 thick photoresist was proposed as the solder mask due to its excellent properties, such as good stability, mechanical properties, etc. The low melting temperature solder paste was used for the electrical connections with the amorphous alloy wire and the electrode pads. Compared with the conventional welding fabrication methods, the proposed micro electro mechanical systems (MEMS) process in this paper showed the advantages of good impedance consistency, and can be fabricated at a low temperature of 150 °C. The amorphous alloy wire magnetic sensor made by the conventional method and by the micro electro mechanical systems (MEMS) process were tested and compared, respectively. The minimum resistance value of the magnetic sensor made by the conventional welding method is 19.8 Ω and the maximum is 28.1 Ω. The variance of the resistance is 7.559 Ω². The minimum resistance value of the magnetic sensor made by micro electro mechanical systems (MEMS) process is 20.1 Ω and the maximum is 20.5 Ω. The variance of the resistance is 0.029 Ω². The test results show that the impedance consistency by micro electro mechanical systems (MEMS) process is better than that of the conventional method. The sensor sensitivity is around 150 mV/Oe and the nonlinearity is less than 0.92% F.S.

Assembly and Self-Assembly of Nanomembrane Materials-From 2D to 3D

Nanoscience and nanotechnology offer great opportunities and challenges in both fundamental research and practical applications, which require precise control of building blocks with micro/nanoscale resolution in both individual and mass-production ways. The recent and intensive nanotechnology development gives birth to a new focus on nanomembrane materials, which are defined as structures with thickness limited to about one to several hundred nanometers and with much larger (typically at least two orders of magnitude larger, or even macroscopic scale) lateral dimensions. Nanomembranes can be readily processed in an accurate manner and integrated into functional devices and systems. In this Review, a nanotechnology perspective of nanomembranes is provided, with examples of science and applications in semiconductor, metal, insulator, polymer, and composite materials. Assisted assembly of nanomembranes leads to wrinkled/buckled geometries for flexible electronics and stacked structures for applications in photonics and thermoelectrics. Inspired by kirigami/origami, self-assembled 3D structures are constructed via strain engineering. Many advanced materials have begun to be explored in the format of nanomembranes and extend to biomimetic and 2D materials for various applications. Nanomembranes, as a new type of nanomaterials, allow nanotechnology in a controllable and precise way for practical applications and promise great potential for future nanorelated products.

Design and Fabrication of a Miniaturized GMI Magnetic Sensor Based on Amorphous Wire by MEMS Technology

A miniaturized Co-based amorphous wire GMI (Giant magneto-impedance) magnetic sensor was designed and fabricated in this paper. The Co-based amorphous wire was used as the sense element due to its high sensitivity to the magnetic field. A three-dimensional micro coil surrounding the Co-based amorphous wire was fabricated by MEMS (Micro-Electro-Mechanical System) technology, which was used to extract the electrical signal. The three-dimensional micro pick-up coil was designed and simulated with HFSS (High Frequency Structure Simulator) software to determine the key parameters. Surface micro machining MEMS (Micro-Electro-Mechanical System) technology was employed to fabricate the three-dimensional coil. The size of the developed amorphous wire magnetic sensor is 5.6 × 1.5 × 1.1 mm³. Helmholtz coil was used to characterize the performance of the device. The test results of the sensor sample show that the voltage change is 130 mV/Oe and the linearity error is 4.83% in the range of 0~45,000 nT. The results indicate that the developed miniaturized magnetic sensor has high sensitivity. By testing the electrical resistance of the samples, the results also showed high uniformity of each device.

A magnetoelectric flux gate: new approach for weak DC magnetic field detection

The magnetic flux gate sensors based on Faraday’s Law of Induction are widely used for DC or extremely low frequency magnetic field detection. Recently, as the fast development of multiferroics and magnetoelectric (ME) composite materials, a new technology based on ME coupling effect is emerging for potential devices application. Here, we report a magnetoelectric flux gate sensor (MEFGS) for weak DC magnetic field detection for the first time, which works on a similar magnetic flux gate principle, but based on ME coupling effect. The proposed MEFGS has a shuttle-shaped configuration made of amorphous FeBSi alloy (Metglas) serving as both magnetic and magnetostrictive cores for producing a closed-loop high-frequency magnetic flux and also a longitudinal vibration, and one pair of embedded piezoelectric PMN-PT fibers ([011]-oriented Pb(Mg,Nb)O₃-PbTiO₃ single crystal) serving as ME flux gate in a differential mode for detecting magnetic anomaly. In this way, the relative change in output signal of the MEFGS under an applied DC magnetic anomaly of 1 nT was greatly enhanced by a factor of 4 to 5 in comparison with the previous reports. The proposed ME flux gate shows a great potential for magnetic anomaly detections, such as magnetic navigation, magnetic based medical diagnosis, etc.

Three-dimensional nanomagnetism

Magnetic nanostructures are being developed for use in many aspects of our daily life, spanning areas such as data storage, sensing and biomedicine. Whereas patterned nanomagnets are traditionally two-dimensional planar structures, recent work is expanding nanomagnetism into three dimensions; a move triggered by the advance of unconventional synthesis methods and the discovery of new magnetic effects. In three-dimensional nanomagnets more complex magnetic configurations become possible, many with unprecedented properties. Here we review the creation of these structures and their implications for the emergence of new physics, the development of instrumentation and computational methods, and exploitation in numerous applications.

Nanoscale magnetic devices play a key role in modern technologies but current applications involve only 2D structures like magnetic discs. Here the authors review recent progress in the fabrication and understanding of 3D magnetic nanostructures, enabling more diverse functionalities.

Deterministic Self-Rolling of Ultrathin Nanocrystalline Diamond Nanomembranes for 3D Tubular/Helical Architecture

Nanocrystalline diamond nanomembranes with thinning-reduced flexural rigidities can be shaped into various 3D mesostructures, such as tubes, jagged ribbons, nested tubes, helices, and nested rings. Microscale helical diamond architectures are formed by controlled debonding in agreement with finite-element simulation results. Rolled-up diamond tubular microcavities exhibit pronounced defect-related photoluminescence with whispering-gallery-mode resonance.

Highly Sensitive Flexible Magnetic Sensor Based on Anisotropic Magnetoresistance Effect

A highly sensitive flexible magnetic sensor based on the anisotropic magnetoresistance effect is fabricated. A limit of detection of 150 nT is observed and excellent deformation stability is achieved after wrapping of the flexible sensor, with bending radii down to 5 mm. The flexible AMR sensor is used to read a magnetic pattern with a thickness of 10 μm that is formed by ferrite magnetic inks.

Magnetically Patterned Rolled-Up Exchange Bias Tubes: A Paternoster for Superparamagnetic Beads

We realized a deterministic transport system for superparamagnetic microbeads through micrometer-sized tubes acting as channels. Beads are moved stepwise in a paternoster-like manner through the tube and back on top of it by weak magnetic field pulses without changing the field pulse polarity and taking advantage of the magnetic stray field emerging from the tubular structures. The microtubes are engineered by rolling up exchange bias layer systems, magnetically patterned into parallel stripe magnetic domains. In this way, the tubes possess distinct azimuthally aligned magnetic domain patterns. This transport mechanism features high step velocities and remote control of not only the direction and trajectory but also the velocity of the transport without the need of fuel or catalytic material. Therefore, this approach has the potential to impact several fields of 3D applications in biotechnology, including particle transport related phenomena in lab-on-a-chip and lab-in-a-tube devices.

Rashba Torque Driven Domain Wall Motion in Magnetic Helices

Manipulation of the domain wall propagation in magnetic wires is a key practical task for a number of devices including racetrack memory and magnetic logic. Recently, curvilinear effects emerged as an efficient mean to impact substantially the statics and dynamics of magnetic textures. Here, we demonstrate that the curvilinear form of the exchange interaction of a magnetic helix results in an effective anisotropy term and Dzyaloshinskii–Moriya interaction with a complete set of Lifshitz invariants for a one-dimensional system. In contrast to their planar counterparts, the geometrically induced modifications of the static magnetic texture of the domain walls in magnetic helices offer unconventional means to control the wall dynamics relying on spin-orbit Rashba torque. The chiral symmetry breaking due to the Dzyaloshinskii–Moriya interaction leads to the opposite directions of the domain wall motion in left- or right-handed helices. Furthermore, for the magnetic helices, the emergent effective anisotropy term and Dzyaloshinskii–Moriya interaction can be attributed to the clear geometrical parameters like curvature and torsion offering intuitive understanding of the complex curvilinear effects in magnetism.

Transformation of epitaxial NiMnGa/InGaAs nanomembranes grown on GaAs substrates into freestanding microtubes

NiMnGa/InGaAs nanomembranes grown by epitaxy on semiconductor substrates are transformed into freestanding microtubes using self assembly techniques and are investigated.

Biomimetic Microelectronics for Regenerative Neuronal Cuff Implants

Smart biomimetics, a unique class of devices combining the mechanical adaptivity of soft actuators with the imperceptibility of microelectronics, is introduced. Due to their inherent ability to self-assemble, biomimetic microelectronics can firmly yet gently attach to an inorganic or biological tissue enabling enclosure of, for example, nervous fibers, or guide the growth of neuronal cells during regeneration.