Flexible Magnetoreceptor with Tunable Intrinsic Logic for On-Skin Touchless Human-Machine Interfaces

Artificial magnetoception is a new and yet to be explored path for humans to interact with the surroundings. This technology is enabled by thin film magnetic field sensors embedded in a soft and flexible format to constitute magnetosensitive electronic skins (e-skins). Being limited by the sensitivity to in-plane magnetic fields, magnetosensitive e-skins are restricted to basic proximity and angle sensing and are not used as switches or logic elements of interactive wearable electronics. Here, a novel magnetoreceptive platform for on-skin touchless interactive electronics based on flexible spin valve switches with sensitivity to out-of-plane magnetic fields is demonstrated. The technology relies on all-metal Co/Pd-based spin valves with a synthetic antiferromagnet possessing perpendicular magnetic anisotropy. The flexible magnetoreceptors act as logic elements, namely momentary and permanent (latching) switches. The switches maintain their performance even upon bending to a radius of less than 3.5 mm and withstand repetitive bending for hundreds of cycles. Here, flexible switches are integrated in on-skin interactive electronics and their performance as touchless human-machine interfaces is demonstrated, which are intuitive to use, energy efficient, and insensitive to external magnetic disturbances. This technology offers qualitatively new functionalities for electronic skins and paves the way towards full-fledged on-skin touchless interactive electronics.     

Bio‐Inspired Stretchable,Adhesive, and Conductive Structural Color Film for Visually Flexible Electronics

The rapid progress in flexible electronic devices has attracted immense interest in many applications, such as health monitoring devices, sensory skins, and implantable apparatus. Here, inspired by the adhesion features of mussels and the color shift mechanism of chameleons, a novel stretchable, adhesive, and conductive structural color film is presented for visually flexible electronics. The film is generated by adding a conductive carbon nanotubes polydopamine (PDA) filler into an elastic polyurethane (PU) inverse opal scaffold. Owing to the brilliant flexibility and inverse opal structure of the PU layer, the film shows stable stretchability and brilliant structural color. Besides, the catechol groups on PDA impart the film with high tissue adhesiveness and self‐healing capability. Notably, because of its responsiveness, the resultant film is endowed with color‐changing ability that responds to motions, which can function as dual‐signal soft human‐motion sensors for real‐time color‐sensing and electrical signal monitoring. These features make the bio‐inspired hydrogel‐based electronics highly potential in the flexible electronics field.     

Block Copolymer-Based Supramolecular Ionogels for Accurate On-Skin Motion Monitoring

Interest in wearable and stretchable on-skin motion sensors has grown rapidly in recent years. To expand their applicability, the sensing element must accurately detect external stimuli; however, weak adhesiveness of the sensor to a target object has been a major challenge in developing such practical and versatile devices. In this study, freestanding, stretchable, and self-adhesive ionogel conductors are demonstrated which are composed of an associating polymer network and ionic liquid that enable conformal contact between the sensor and skin even during dynamic movement. The network of ionogel is formed by noncovalent association of two diblock copolymers, where phase-separated micellar clusters are interconnected via hydrogen bonds between corona blocks. The resulting ionogels exhibit superior adhesive characteristics, including a very high lift-off force of 93.3 N m⁻¹, as well as excellent elasticity (strain at break ≈ 720%), toughness ( ≈ 2479 kJ m⁻³), thermal stability ( ≈ 150  ° C), and high ionic conductivity ( ≈ 17.8 mS cm⁻¹ at 150  ° C). These adhesive ionogels are successfully applied to stretchable on-skin strain sensors as sensing elements. The resulting devices accurately monitor the movement of body parts such as the wrist, finger, ankle, and neck while maintaining intimate contact with the skin, which was not previously possible with conventional non-adhesive ionogels.     

Stretchable Self‐Powered Fiber‐Based Strain Sensor

The rapid development of electrical skin and wearable electronics raises the requirement of stretchable strain sensors. In this study, an active fiber‐based strain sensor (AFSS) is fabricated by coiling a fiber‐based generator around a stretchable silicone fiber. The AFSS shows the sensitive and stable performance and has the ability to detect the strain up to 25%, which is also demonstrated to detect finger motion states. It may play an essential role in future self‐powered sensor system.     

Ultrastretchable Helical Conductive Fibers Using Percolated Ag Nanoparticle Networks Encapsulated by Elastic Polymers with High Durability in Omnidirectional Deformations for Wearable Electronics

Stretchable interconnects with invariable conductivity and complete elasticity, which return to their original shape without morphological hysteresis, are attractive for the development of stretchable electronics. In this study, a polydimethylsiloxane‐coated multifilament polyurethane‐based helical conductive fiber is developed. The stretchable helical fibers exhibit remarkable electrical performance under stretching, negligible electrical and mechanical hysteresis, and high electrical reliability under repetitive deformation (10 000 cycles of stretching with 100% strain). The resistance of the helical fibers barely increases until the applied strain reaches the critical strain, which is based on the helical diameter of each fiber. According to finite element analysis, uniform stress distribution is maintained in the helical fibers even under full stretching, owing to the fibers' true helix structure. In addition, the stretchable helical fibers have the ability to completely return to their original shapes even after being fully compressed in the vertical direction. Cylinder‐shaped connecting pieces made using 3D printing are designed for stable connection between the helical fibers and commercial components. A deformable light‐emitting diode (LED) array and biaxially stretchable LED display are fabricated using helical fibers. A skin‐mountable band‐type oximeter with helical fiber‐based electrodes is also fabricated and used to demonstrate real‐time detection of cardiac activities and analysis of brain activities.     

Highly Adhesive Epidermal Sensors with Superior Water-Interference-Resistance for Aquatic Applications

Grand challenges exist in the fabrication of robust skin electronics that are resistant to water interference, which can play vital roles in healthcare and lifesaving in activities such as showering, surfing, and swift water rescue. Particularly, dynamic water impingement is very destructive to skin electronics by causing device–skin delamination and sensing malfunctions. Herein, an anemone-inspired self-adhesive epidermal sensor with superior ability to resist water interference in various aquatic environments is developed. The epidermal sensor consists of a strain sensing layer composed of interconnected graphene flakes wrapped in ultrathin Ecoflex and a self-adhesive layer composed of semi-crosslinked polydimethylsiloxane, which is named as an adhesive graphene encapsulated in Ecoflex (a-G@E) sensor. The a-G@E sensor can conformally and stably attach on the skin under the synergy effect of the ultrathin thickness and the self-adhesive layer. Remarkably, it can maintain a highly stable device–skin interface even under extreme aquatic conditions such as intense water impingement (up to 4 m s⁻¹). As examples, this study demonstrates its applications in transmitting information, controlling robotics underwater, and tracking swimming modes of a fish. It is believed that the a-G@E sensor can play a unique role in health-care, sports-monitoring, and human–machine interactions, especially for aquatic scenarios.     

Enabling the Unconstrained Epidermal Pulse Wave Monitoring via Finger-Touching

Unconstrained measurement of physiological signals including electrocardiograph, respiration, and temperature by sensors through incorporation into commonly used objects has sparked a notable revolution in healthcare monitoring. However, unconstrained precision epidermal pulse wave monitoring is rarely reported. Although the current flexible skin-mounted sensors can capture pulse waves, they lack the capability to perceive tiny pulse pressure in an unconstrained manner. Herein, utilizing thin-film materials and multilevel microstructure design, an ultrathin and flexible sensor (UFS) with the features of high flexibility, shape-adaptability, and ultra-broad-range high pressure sensitivity is proposed for unconstrained precision pulse wave sensing. Given these compelling features, the UFS is mounted to the surfaces of commonly used objects and successfully detects the fingertip pulse wave even under an ultra-broad-range finger-touching force. Key cardiovascular parameters are also extracted from the acquired fingertip pulse wave accurately. Furthermore, a proof-of-concept healthcare system, by combining the UFS and flexible devices (for example, flexible phones or E-newspapers) is demonstrated, offering a great advancement in developing an all-in-one system for IoT-based bio-health monitoring at all times and places.     

An All-Stretchable,Ultraviolet Protective,and Electromagnetic-Interference-Free E-Textile

Flexible and skin-mountable electronics have drawn tremendous research attention with the booming of smart medical systems and wearing technologies, however, their environmental adaptability to electromagnetic and solar radiation has long been neglected. Herein, a novel health monitoring e-textile with robust ultraviolet (UV) protecting and strong electromagnetic interference (EMI) shielding performance is rationally developed on an ultraelastic and bilayered nonwoven textile. Via the respective incorporation of silver flake-modified liquid metal (AgLM) and silver nanoparticles (AgNPs) on each side of a permeable substrate, a Janus sensing layer with electrophysiological monitoring function, Joule heating ability, and excellent EMI shielding capability (up to 38.5 dB in X band) is first fabricated. Elastic microfibers embedded with sensitive photochromic microcapsules are then in situ assembled on the bioelectric-sensing layer, achieving a bilayered e-textile with a reversible UV-chromic property and an extraordinary UV protection factor (UPF) of 335.56. The developed all-stretchable and UV-EMI proof e-textile is utilized as a safe and comfortable on-skin electronic to provide point-of-care health regulation under complex UV/EMI radiative environments. Specifically, stable Joule heating performance and accurate monitoring of electrocardiogram (ECG) and surface electromyography (sEMG) are simultaneously obtained, demonstrating promising applications in multifunctional and robust wearing electronics.     

A Self-Powered,Rechargeable, and Wearable Hydrogel Patch for Wireless Gas Detection with Extraordinary Performance

Flexible gas sensors play an indispensable role in diverse applications spanning from environmental monitoring to portable medical electronics. Full wearable gas monitoring system requires the collaborative support of high-performance sensors and miniaturized circuit module, whereas the realization of low power consumption and sustainable measurement is challenging. Here, a self-powered and reusable all-in-one NO₂ sensor is proposed by structurally and functionally coupling the sensor to the battery, with ultrahigh sensitivity (1.92%/ppb), linearity (R² = 0.999), ultralow theoretical detection limit (0.1 ppb), and humidity immunity. This can be attributed to the regulation of the gas reaction route at the molecular level. The addition of amphiphilic zinc trifluoromethanesulfonate (Zn(OTf)₂) enables the H₂O-poor inner Helmholtz layer to be constructed at the electrode–gel interface, thereby facilitating the direct charge transfer process of NO₂ here. The device is then combined with a well-designed miniaturized low-power circuit module with signal conditioning, processing and wireless transmission functions, which can be used as wearable electronics to realize early and remote warning of gas leakage. This study demonstrates a promising way to design a self-powered, sustainable, and flexible gas sensor with high performance and its corresponding wireless sensing system, providing new insight into the all-in-one system of gas detection.     

Calcium‐Modified Silk as a Biocompatible and Strong Adhesive for Epidermal Electronics

With the increasing interest and demand for epidermal electronics, a strong interface between a sensor and a biological surface is essential, yet achieving such interface is still a challenge. Here, a calcium (Ca)‐modified biocompatible silk fibroin as a strong adhesive for epidermal electronics is proposed and the physical principles behind its interfacial and adhesive properties are reported. A strong adhesive characteristic (>800 N m^?1) is observed because of the increase in both viscoelastic property and mechanical interlocking through the incorporation of Ca ions. Furthermore, additional key characteristics of the Ca‐modified silk: reusability, stretchability, biocompatibility, and conductivity, are reported. These characteristics enable a wide range of applications as demonstrated in four epidermal electronic systems: capacitive touch sensor, resistive strain sensor, hydrogel‐based drug delivery, and electrocardiogram monitoring sensor. As a reusable, biocompatible, conductive, and strong adhesive with water‐degradability, the Ca‐modified silk adhesive is a promising candidate for the next‐generation adhesive for epidermal biomedical sensors.     

A Single Droplet‐Printed Double‐Side Universal Soft Electronic Platform for Highly Integrated Stretchable Hybrid Electronics

Soft features in electronic devices have provided an opportunity of gleaning a wide spectrum of intimate biosignals. Lack of data processing tools in a soft form, however, proclaims the need of bulky wires or low‐performance near‐field communication externally linked to a “rigid” processor board, thus tarnishing the true meaning of “soft” electronics. Furthermore, although of rising interest in stretchable hybrid electronics, lack of consideration in multilayer, miniaturized design and system‐level data computing limits their practical use. The results presented here form the basis of fully printable, system‐level soft electronics for practical data processing and computing with advanced capabilities of universal circuit design and multilayer device integration into a single platform. Single droplet printing‐based integration of rigid islands and core–shell vertical interconnect access (via) into a common soft matrix with a symmetric arrangement leads to a double‐side universal soft electronic platform that features site‐selective, simultaneous double‐side strain isolation, and vertical interconnection, respectively. Systematic studies of island‐morphology engineering, surface‐strain mapping, and electrical analysis of the platform propose optimized designs. Commensurate with the universal layout, a complete example of double‐side integrated, stretchable 1 MHz binary decoders comprised of 36 logic gates interacting with 9 vias is demonstrated by printing‐based, double‐side electronic functionalization.     

Demodulation of interferometric sensors using a fiber-optic passive quadrature demodulator

The passive quadrature demodulator (PQD) eliminates the phase stretcher and feedback electronics frequently used in fiber interferometric sensors by passively extracting the desired signal using two distinct interferometers which differ in phase bypi/2. A fusion technique is described to fabricate a fiber PQD which is sufficiently stable with respect to temperature, polarization, and wavelength to maintain the sensitivity of interferometric sensors constant to 0.25 dB.     

Conductive PEDOT:PSS on surface-functionalized chitosan biopolymers for stretchable skin-like electronics

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a promising alternative transparent electrode to replace conventional indium tix oxide (ITO) for flexible and stretchable electronics. For their applications in optoelectronic devices, realizing both high conductivity and transmittance for the films is of great necessity as a suitable high performance transparent electrode. Here, we demonstrate simultaneously enhanced electrical and optical properties of PEDOT:PSS films prepared on chitosan bio-substrates by using an organic surface modifier, 11-aminoundecanoic acid (11-AA). The sheet resistance of PEDOT:PSS films decreases from 1120.8 to 292.8 Ω/sq with an increase in a transmittance from 75.9 to 80.4% by 11-AA treatment on the chitosan films. The functional groups of 11-AA effectively enhance the adhesion property at the interface between the chitosan substrate and PEDOT:PSS by forming strong interfacial bondings and decrease insulating PSS from PEDOT:PSS films. The wearable heater devices and on-skin sensors based on the 11-AA-treated PEDOT:PSS on the chitosan bio-substrates are successfully fabricated, showing the excellent thermal and sensing performances. The 11-AA surface-modification approach for highly conductive PEDOT:PSS on chitosan bio-substrates presents a great potential for applications toward transparent, flexible and stretchable electronics.     

Electro-thermal resistance of GaAs interconnects

This paper describes the effect of steady-state heating on the electrical and thermal resistance of interconnects on GaAs. Examined is a typical dual-layer metal interconnect system, common to GaAs processing. The interconnect system is considered in three parts, the interconnect metals, the Si₃N₄ dielectric surrounding the metal, and the Al _x Ga_1−xAs epitaxial substrate. Using a mean-dering line as a test structure, measurements show how the direct current (DC) resistance increases with both temperature and dissipated power. Thermal resistors are proposed to account for self-heating and thermal coupling.     

以钯作扩散阻挡层——一种多功能线路板表面处理方法

电子工业不断的小型化,数种不同互联技术于线路板上电子零件连接及电接点被应用范畴不断增加。基于此用途,线路板组装垫位需被一层最后表面处理保护,如这最后表面处理层可用于不同互联技术,可被称为多功能表面层。钯是一个艮好的镍扩散阻挡层,故此层膜能抵受如焊接及键接之严酷老化测试条件。其两大优点为具有良好热超声波键接性及于无铅焊料之非常优艮焊接性。从预镀导线架过往多年经验已知即使很薄贵金属钯层及金层已可有保证可靠的金线键接性。从这一知识,沉镍浸钯浸金层膜系统（ENIPIG）被研发出来。此崭新表面处理ENIPIG三种金属镀液需互相配合才能于线路板工艺上达成理想多功能层膜。因着其薄贵金属层膜,相对于其他表面处理,可节省颇大的成本。     

Self-Healing Titanium Dioxide Nanocapsules-Graphene/Multi-Branched Polyurethane Hybrid Flexible Film with Multifunctional Properties toward Wearable Electronics

The integration of self-healing capabilities into flexible electronics arouses extensive attention. The application of self-healing electronics with multifunctional properties in a variety of exceptional environments has been identified to be significantly challenging and not yet proven to be fully viable thus far. In the present study, the self-healing octadecane loaded titanium dioxide nanocapsules (OTNs)-graphene/multi-branched polyurethane (PU) hybrid flexible multifunctional film is successfully prepared. The prepared film exhibits a novel self-repair capability that consists of disulfide bonds in the leading chains for efficient self-healing of PU damage, as well as multiple amino groups in the branches for damage between OTNs-graphene and PU. Impacted by the constructed self-healing system and well-dispersed OTNs-graphene, the prepared flexible film demonstrates a prominent performance in piezoresistive sensing and a desirable outcome of ultraviolet protection properties, which can effectively prolong its service life, especially when used outdoors. Moreover, the film exhibits thermal insulating properties, capable of offering a suitable route for thermal protection of bio-integrated wearable electronic devices system. Thus, this self-healing multifunctional film is promising in wearable electronics, human–machine interaction, artificial intelligence devices, etc.     

Low-Molecular-Weight Supramolecular-Polymer Double-Network Eutectogels for Self-Adhesive and Bidirectional Sensors

Ionic conducting eutectogels have attracted enormous attention as an alternative to the conventional temperature-intolerant hydrogels and costly ionic liquid gels in constructing flexible electronic devices. However, current eutectogels prepared via cross-linked polymer or low-molecular-weight gelators suffer from limited stretchability and insufficient surface-adaptive adhesion. Herein, a low-molecular-weight supramolecular network is introduced into a covalent polymer network in a eutectogel architecture, and a novel supramolecular-polymer double-network (SP-DN) strategy is demonstrated to fabricate conductive SP-DN eutectogels with high stretchability (>4000% elongation) and toughness (≈800 J m⁻²), as well as self-healing, self-adhesive and anti-freezing/anti-drying characteristics. These unique features lead to the successful realization of SP-DN eutectogels in wearable self-adhesive strain sensors, which can conformally deform with the skin and dynamically monitor body movements with high sensitivity and long-term stability over a wide temperature range (−40 to 60 °C). Furthermore, the strain sensors can accurately detect body movements along two opposite directions (bend up or bend down), which are rarely reported in the literature. Distinct from the widely explored polymer double-network (P-DN) hydrogels, the developed SP-DN eutectogel platform is capable of well-regulating molecular-scale noncovalent and covalent interactions, providing a paradigm for the creation of smart soft materials with versatile performance and high environmental adaptability.     

An effective lateral fiber-optic electronic coupling and packaging technique suitable for VHSIC applications

As part of a project to develop a high speed (500 MHz) monolithic silicon fiber-optic digital receiver IC, we have produced a novel and practical lateral fiber-detector coupling scheme employing a 45° mirror fabricated on the end of the fiber. Coupling losses of 1.1 dB have been achieved. The technique shows its greatest promise at very high speeds where the IC interconnect issue is emerging as one of utmost relevance. In the work described here, the laterally coupled IC's were packaged in high speed metal flat packs. This technique rendered a fiber-optic digital receiver compatible with two-dimensional layout techniques common in high speed electronics. However, the lateral coupler concept itself is not dependent on the use of metal flat packs. In fact, it is likely to find its greatest utility in the optical coupling of many fibers to a single IC. In this paper, system design considerations, fabrication techniques, and measured results for the lateral coupler concept are discussed.     

Gallium-Based Liquid–Solid Biphasic Conductors for Soft Electronics

Soft and stretchable electronics have diverse applications in the fields of compliant bioelectronics, textile-integrated wearables, novel forms of mechanical sensors, electronics skins, and soft robotics. In recent years, multiple material architectures have been proposed for highly deformable circuits that can undergo large tensile strains without losing electronic functionality. Among them, gallium-based liquid metals benefit from fluidic deformability, high electrical conductivity, and self-healing property. However, their deposition and patterning is challenging. Biphasic material architectures are recently proposed as a method to address this problem, by combining advantages of solid-phase materials and composites, with liquid deformability and self-healing of liquid phase conductors, thus moving toward scalable fabrication of reliable stretchable circuits. This article reviews recent biphasic conductor architectures that combine gallium-based liquid-phase conductors, with solid-phase particles and polymers, and their application in fabrication of soft electronic systems. In particular, various material combinations for the solid and liquid phases in the biphasic conductor, as well as methods used to print and pattern biphasic conductive compounds, are discussed. Finally, some applications that benefit from biphasic architectures are reviewed.