Applications In Stretchable Electronics Research Articles

Impact of Elongation Stress on Island-Bridge Shaped Oxide Thin-Film Transistors with Metal Interconnects for Stretchable Electronics Applications

Impact of Elongation Stress on Island-Bridge Shaped Oxide Thin-Film Transistors with Metal Interconnects for Stretchable Electronics Applications

Recyclable and Stable Strain Sensors Based on Semi‐Wrapped Structure of Silver Nanowires in Polyvinyl Alcohol for Human Motion Monitoring

AbstractHighly sensitive strain sensors have been widely used in human motion monitoring, medical treatment, soft robots, and human–computer interaction, and the recycling of functional materials is in a huge demand for eco‐friendly and sustainable electronics. However, the manufacturing of recyclable strain sensors still remains challenging. Here, a semi‐wrapped structure based on silver nanowires and polyvinyl alcohol is proposed to realize a recyclable and stable strain sensor. It has shown excellent sensitivity, fast response, high stretchability and good environmental stability, and is successfully applied for human motion monitoring. In addition, a simple strategy is developed to effectively recycle silver nanowires in an eco‐friendly manner. The recyclable and stable strain sensor demonstrates potential applications in wearable and stretchable electronics, and the recycling strategy can be extended to other noble metal nanomaterials.

Scalable Fabrication of Large-Scale, 3D, and Stretchable Circuits.

Stretchable electronics have demonstrated excellent potential in wearable healthcare and conformal integration. Achieving the scalable fabrication of stretchable devices with high functional density is the cornerstone to enable the practical applications of stretchable electronics. Here, a comprehensive methodology for realizing large-scale, 3D, and stretchable circuits (3D-LSC) is reported. The soft copper-clad laminate (S-CCL) based on the "cast and cure" process facilitates patterning the planar interconnects with the scale beyond 1 m. With the ability to form through, buried and blind VIAs in the multilayer stack of S-CCLs, high functional density can be achieved by further creating vertical interconnects in stacked S-CCLs. The application of temporary bonding substrate effectively minimizes the misalignments caused by residual strain and thermal strain. 3D-LSC enables the batch production of stretchable skin patches based on five-layer stretchablecircuits, which can serve as a miniaturized system for physiological signals monitoring with wireless power delivery. The fabrications of conformal antenna and stretchable light-emitting diode display further illustrate the potential of 3D-LSC in realizing large-scale stretchable devices.

Best-in-class modeling: A novel strategy to discover constitutive models for soft matter systems

The ability to automatically discover interpretable mathematical models from data could forever change how we model soft matter systems. For convex discovery problems with a unique global minimum, model discovery is well-established. It uses a classical top-down approach that first calculates a dense parameter vector, and then sparsifies the vector by gradually removing terms. For non-convex discovery problems with multiple local minima, this strategy is infeasible since the initial parameter vector is generally non-unique. Here we propose a novel bottom-up approach that starts with a sparse single-term vector, and then densifies the vector by systematically adding terms. Along the way, we discover models of gradually increasing complexity, a strategy that we call best-in-class modeling. To identify and select successful candidate terms, we reverse-engineer a library of sixteen functional building blocks that integrate a century of knowledge in material modeling with recent trends in machine learning and artificial intelligence. Yet, instead of solving the NP hard discrete combinatorial problem with 216=65,536 possible combinations of terms, best-in-class modeling starts with the best one-term model and iteratively repeats adding terms, until the objective function meets a user-defined convergence criterion. Strikingly, for most practical purposes, we achieve good convergence with only one or two terms. We illustrate the best-in-class one- and two-term models for a variety of soft matter systems including rubber, brain, artificial meat, skin, and arteries. Our discovered models display distinct and unexpected features for each family of materials, and suggest that best-in-class modeling is an efficient, robust, and easy-to-use strategy to discover the mechanical signatures of traditional and unconventional soft materials. We anticipate that our technology will generalize naturally to other classes of natural and man made soft matter with applications in artificial organs, stretchable electronics, soft robotics, and artificial meat.

Highly elastic polymer substrates with local strain management for stretchable electronic applications

Stretchable electronic devices have been extensively investigated in healthcare and wearable electronics. The stretchable substrate with strain control is paramount to integrating rigid devices into stretchable electronic systems for high mechanical strain. The common approach utilizes rigid strain control islands integrated on the surface of the soft stretchable matrix, but strain concentration effect and poor adhesion at the interface between the rigid islands and the elastic substrate are challenges. In this work, a stretchable substrate is developed by embedding the bottom strain control islands into the interior of an elastic substrate and the top strain control islands on the substrate surface to minimize strain concentration and improve the adhesion of the interface. The simulation results show that the strain concentration at the interface of the top island is suppressed and the maximum strain on the substrate surface is reduced by more than 30%. The interface between strain control islands of PI film and elastic substrate of Ecoflex can maintain more than 3000 stretch cycles under repeated strain of 100%. A stretchable inverter is fabricated based on this stretchable substrate with stretchable conductive wire. It is shown that the voltage transfer characteristics of the stretchable inverter have no significant change under strain of 100% for more than 3000 stretch cycles, demonstrating the capability of this stretchable substrate to integrate rigid devices for reliable stretchable electronic systems.

Spider silk-inspired supramolecular polydimethylsiloxane network with prominent mechanical robustness for bifunctional flexible electronics

Self-healing and recyclable polymer elastomers are being developed to provide new prospects in building sustainable societies. Nevertheless, the synthesis of such materials still poses a significant difficulty because of the conflicting requirements between the self-healing ability and mechanical robustness for the dynamicity of crosslinks. Herein, a self-healing and recyclable supramolecular polydimethylsiloxane with outstanding tensile stress and ultrahigh mechanical toughness is constructed by synergistically incorporating dynamic disulfide bonds and multiple hydrogen bonds into a siloxane chain. The adipic dihydrazide (AD) bearing two hydrazide groups is appropriate introduced to provide multiple hydrogen bonding sites between polymer chains and improve the mechanical robustness of the crosslinked structure. The aromatic disulfide bonds contribute to shorter healing time due to the elevated dynamicity of the crosslinked network. The resulting elastomers exhibit high tensile strength (6.44 ± 0.24 MPa), distinguished toughness (37.00 ± 0.85 MJ m−3), superior elastic restorability, outstanding self-healing capability (∼86 %) and multiple recyclability. Furthermore, a bifunctional sensor based on this elastomer is constructed to monitor human motions and pressure changes, demonstrating the potential application in flexible stretchable electronics.

All-in-One fast response electrochromic devices based on PAAm/P2W18 hydrogel without additional electrolytes

All-in-one electrochromic devices (ECDs) have potential applications in wearable stretchable electronics. However, ECDs today are inflexible, slow to respond and at risk of electrolyte leakage. We have prepared a novel electrochromic hydrogel by introducing polyoxometalates [P2W18O62] 6− (P2W18) into polyacrylamide (PAAm) via ionic and covalent cross-linking. Negatively charged P2W18 have ionic conductive properties, thus the hydrogel is able to undergo electrochromic behavior without the addition of electrolytes. PAAm/P2W18 hydrogel has good flexibility and tensile properties, high transparency and a simple preparation process. The PAAm/P2W18 hydrogel is reversibly switchable between colorless and dark blue over a voltage range from 0 V to −2.8 V. The ECDs had a large transmittance contrast (53.7 %), fast response time (coloring/bleaching times of 6.9 s and 5.6 s) and satisfactory coloring efficiency (125.5 cm2/C). PAAm/P2W18 hydrogel has good open-circuit memory properties which maintains coloring state after 7 days of power off. The sandwich-structured (ITO/hydrogel/ITO) electrochromic device based on this hydrogel is simple to manufacture, low in cost and fast in response, which have potential applications in the fields of smart windows, energy-saving displays, and anti-glare mirrors.

Crack-insensitive fracture of elastomer-based soft network materials under monotonic and cyclic loads

In various applications of stretchable electronics and soft robots, soft materials are subjected to long-term load-bearing conditions, requiring them to possess good extreme mechanical properties such as highly stretchable, strong, fracture-resistant and anti-fatigue. Conventional soft materials with a single polymer network typically exhibit relatively low fracture resistance, while commonly employed toughening method involves introducing mechanical dissipation into original polymer networks often require complicated chemical synthesis and result in significant hysteresis under cyclic loads. Designing soft solid materials into soft network materials with periodic lattice structure paving another effective route to improve the fracture-resistant performance of soft materials, which has not been reported in the literature. This work provides a combined experimental and computational study on the mechanical properties and fracture behaviors of elastomer-based soft network materials with/without a precut crack under monotonic and cyclic loads, aiming to present a structural design strategy for fracture-resistant soft materials. The elastomer-based soft network materials are proven to be crack-insensitive, low-hysteresis and anti-fatigue. The nonlinear finite element analysis (FEA) is employed to reveal the underlying mechanism of crack-insensitivity in elastomer-based soft network materials. Both the mechanical properties and deformed configurations of soft network materials with/without a precut crack are accurately predicted by the FEA method. The effect of microstructure geometry and network topology on the mechanical properties of soft network materials is systematically studied. Under various amplitudes of cyclic applied strain, the elastomer-based soft network materials can survive even after individual microstructures ruptured, and the fatigue fracture process slows down as the applied strain amplitude decreases. In contrast to the behavior observed in monotonic loads where fracture initiates at the microstructure located ahead of the crack tip, fatigue fracture initiation in soft network materials with a precut crack exhibits a random distribution.

Polymerized-Small-Molecule Acceptors Featuring Siloxane-Terminated Side Chains for Mechanically Robust All-Polymer Solar Cells.

Flexible and stretchable organic solar cells (OSCs) show great promise in wearable and stretchable electronic applications. However, current high-performance OSCs consisting of polymer donors (PDs) and small-molecule acceptors (SMAs) face significant challenges in achieving both high power conversion efficiency (PCE) and excellent stretch-ability. In this study, we synthesized a new polymerized-small-molecule acceptor (P-SMA) PY-SiO featuring siloxane-terminated side chains and compared its photovoltaic and mechanical performance to that of the reference PY-EH with ethylhexyl-terminated side chains. We found that the incorporation of siloxane-terminated side chains in PY-SiO enhanced the molecular aggregation and charge transport, leading to an optimized film morphology. The resultant of all-polymer solar cells (all-PSCs) based on PBDB-T/PY-SiO showed a higher PCE of 12.04% than the PY-EH-based one (10.85%). Furthermore, the siloxane-terminated side chains also increased the interchain distance and provided a larger free volume for chain rotation and reconfiguration, resulting in a higher film crack-onset strain (COS: 18.32% for PBDB-T/PY-SiO vs 11.15% for PBDB-T/PY-EH). Additionally, the PY-SiO-based stretchable all-PSCs exhibited an impressive PCE of 9.8% and retained >70% of its original PCE even under a substantial 20% strain, exceeding the performance of the PY-EH-based stretchable all-PSCs. Our result suggests the great potential of the siloxane-terminated side chain for achieving high-performance and stretchable OSCs.

On the effective thermal conductivity of gallium-based liquid metal filled elastomers

Gallium based alloys are liquid at ambient temperature, combining both metal-like high thermal conductivity and fluidity characteristics, which contributes to their applications in thermal management, soft robotics, stretchable electronics and etc. A great number of experimental researches have been performed in preparing Ga-based liquid metal filled elastomers (LMFEs) with various constituent systems, processing techniques, droplet morphology and filler sizes in attempt to obtain the best thermal conductive efficiency. The thermal conductive mechanisms in these LMFEs are still lacking a comprehensive understanding up to date, and therefore the present work aimed to conduct a thorough analysis on this topic using both theoretical models and finite element method (FEM) simulations. The predictability of four classic micromechanics models was compared with the experiments and FEM simulations, and their relevant thermal conductive principles were identified from the simulated thermal flux evolution. Some deficiencies of these analytical models are identified and amended by reconsidering their special architectures. This work is favorable for establishing a general and quantitative relationship between the effective thermal conductivity and microstructures for most of the synthesized LMFEs available in the literatures.

Self-Healable and 4D Printable Hydrogel for Stretchable Electronics.

Materials with high stretchability and conductivity are used to fabricate stretchable electronics. Self-healing capability and four-dimensional (4D) printability are becoming increasingly important for these materials to facilitate their recovery from damage and endow them with stimuli-response properties. However, it remains challenging to design a single material that combines these four strengths. Here, a dually crosslinked hydrogel is developed by combining a covalently crosslinked acrylic acid (AAC) network and Fe3+ ions through dynamic and reversible ionically crosslinked coordination. The remarkable electrical sensitivity (a gauge factor of 3.93 under a strain of 1500%), superior stretchability (a fracture strain up to 1700%), self-healing ability (a healing efficiency of 88% and 97% for the mechanical and electrical properties, respectively), and 4D printability of the hydrogel are demonstrated by constructing a strain sensor, a two-dimensional touch panel, and shape-morphing structures with water-responsive behavior. The hydrogel demonstrates vast potential for applications in stretchable electronics.

Enhancing the stretchability of two-dimensional materials through kirigami: a molecular dynamics study on tungsten disulfide.

In recent years, the 'kirigami' technique has gained significant attention for creating meta-structures and meta-materials with exceptional characteristics, such as unprecedented stretchability. These properties, not typically inherent in the original materials or structures, present new opportunities for applications in stretchable and wearable electronics. However, despite its scientific and practical significance, the application of kirigami patterning on a monolayer of tungsten disulfide (WS2), an emerging two-dimensional (2D) material with exceptional mechanical, electronic, and optical properties, has remained unexplored. This study utilizes molecular dynamics (MD) simulations to investigate the mechanical properties of monolayer WS2 with rectangular kirigami cuts. We find that, under tensile loading, the WS2 based kirigami structure exhibits a notable increase in tensile strain and a decrease in tensile strength, thus demonstrating the effectiveness of the kirigami cutting technique in enhancing the stretchability of monolayer WS2. Additionally, increasing the overlap ratio enhances the stretchability of the structure, allowing for tailored high strength or high strain requirements. Furthermore, our observations reveal that increasing the density of cuts and reducing the length-to-width ratio of the kirigami nanosheet further improve the fracture strain, thereby enhancing the overall stretchability of the proposed kirigami patterned structure of WS2.

Transfer-printing of patterned PEDOT:PSS structures for bendable, stretchable and biodegradable electronics

A novel technique to transfer-print variously treated PEDOT:PSS films onto stretchable substrates, including a patterning strategy and electrical and morphological analyses is presented to pave the way for advancements in stretchable electronics.

Intrinsically Stretchable Fiber‐Shaped Solar Cells with Polymer‐Based Active Layer

Fiber‐shaped organic solar cells (FOSCs) with intrinsic stretchability show great potential in stretchable and wearable electronics applications. However, limited by the poor stretchability of small molecule semiconductors, the stretchability of FOSCs is still not satisfied. Polymerized nonfullerene acceptors with excellent photovoltaic performance are a promising strategy for preparing stretchable semiconductors and photovoltaics. Herein, an efficient polymer‐based bulk‐heterojunction blend is adopted as the photoactive material of the stretchable all‐polymer FOSCs. The fabricated all‐polymer FOSCs show superior intrinsic stretchability that remains more than 90% of the initial efficiency under the stretch strain of 50% and maintains stable performance even when undergoing hundreds of stretching–releasing cycles. By adding the third component of polystyrene‐block‐poly(ethylene‐ran‐butylene)‐block‐polystyrene (SEBS) elastomer, the stretchable all‐polymer FOSCs can endure the ultrahigh stretch strains over 80%. This study demonstrates the superior mechanical properties of the all‐polymer FOSCs and the simple yet effective strategy of SEBS additive to enhance stretchability.

A Hierarchical Theory for the Tensile Stiffness of Non-Buckling Fractal-Inspired Interconnects.

The design of non-buckling interconnects with thick sections has gained important applications in stretchable inorganic electronics due to their simultaneous achievement of high stretchability, low resistance, and low heat generation. However, at the same time, such a design sharply increased the tensile stiffness, which is detrimental to the conformal fit and skin comfort. Introducing the fractal design into the non-buckling interconnects is a promising approach to greatly reduce the tensile stiffness while maintaining other excellent performances. Here, a hierarchical theory is proposed for the tensile stiffness of the non-buckling fractal-inspired interconnects with an arbitrary shape at each order, which is verified by the finite element analysis. The results show that the tensile stiffness of the non-buckling fractal-inspired interconnects decreases with the increase in either the height/span ratio or the number of fractal orders but is not highly correlated with the ratio of the two adjacent dimensions. When the ratio of the two adjacent dimensions and height/span ratio are fixed, the tensile stiffness of the serpentine fractal-inspired interconnect is smaller than that of sinusoidal and zigzag fractal-inspired interconnects. These findings are of great significance for the design of non-buckling fractal-inspired interconnects of stretchable inorganic electronics.

Functional heterophasic liquid metals

AbstractLiquid metals (LMs) have compelling applications in stretchable electronics, wearable devices, and soft robotics ascribing to the unique combination of room temperature fluidity and metallic electrical/thermal conductivity. Adding metallic elements in gallium‐based LMs can produce heterophasic (i.e., solid and liquid) LMs with altered properties including morphology, surface energy, rheology, electrical/thermal conductivity, and chemical reactivity. Importantly, heterophasic LMs can respond to external stimuli such as magnetic fields, temperature, and force. Thus, heterophasic LMs can broaden the potential applications of LMs. This report reviews the recent progress about heterophasic LMs through metallic elements in the periodic table and discusses their functionalities. The heterophasic LMs are systematically organized into four categories based on their features and applications including electrical/thermal conductivity, magnetic property, catalysis/energy management, and biomedical applications. This comprehensive review is aimed to help summarize the field and identify new opportunities for future studies.

Stretchable and Self‐Healable Semiconductive Composites Based on Hydrogen Bonding Cross‐linked Elastomeric Matrix

AbstractSemiconductors with both high stretchability and self‐healing capability are highly desirable for various wearable devices. Much progress has been achieved in designing highly stretchable semiconductive polymers or composites. The demonstration of self‐healable semiconductive composite is still rare. Here, an extremely soft, highly stretchable, and self‐healable hydrogen bonding cross‐linked elastomer, amide functionalized‐polyisobutylene (PIB‐amide) is developed, to enable a self‐healable semiconductive composite through compounding with a high‐performance conjugated diketopyrrolopyrrole (DPP‐T) polymer. The composite, consisting of 20% DPP‐T and 80% PIB‐amide, shows record high crack‐onset strain (COS ≈1500%), extremely low elastic modulus (E≈1.6 MPa), and unique ability to spontaneously self‐heal atroom temperature within 5 min. Unlike previous works, these unique composite materials also show strain‐independent charge mobility. An in‐depth morphological study based on multi‐model techniques indicate that all composites show blending ratio‐ and stretching‐independent fibril‐like aggregation due to the strong hydrogen bond in elastomer to enable the unique stable charge mobility. This study provides a new direction to develop highly healable and electronically stable semiconductive composite and will enable new applications of stretchable electronics.

Fabricating 1D stretchable fiber-shaped electronics based on inkjet printing technology for wearable applications

Advanced microfabrication on small and curved fiber surfaces remains a critical challenge and an urgent need to develop high-performance fiber-shaped electronics and advance the next generation of wearable electronics technology. In this study, we propose the preparation of 1D stretchable fiber-shaped electronics via inkjet printing technology for wearable applications. Utilizing self-built precision rotary inkjet printing equipment and a surface chemical modification process, we achieve high-precision and customizable microfabrication onto ultra-low diameter fiber surfaces (minimum printing line width of 133 µm and a printable fiber diameter as low as 500 µm with a large curvature of 4000 m−1). More importantly, this fabricating method is non-destructive and can prepare 1D stretchable conductors by printing conductive inks with stretchable structures and optimizing various synthetic fibers, which exhibit remarkable conductivity, mechanical stability, and strain-insensitive properties in practical applications. Furthermore, we demonstrate the performance of several 1D stretchable electronics applications, including a fiber-shaped electrothermal device, triboelectric strain sensor, and supercapacitor. Our work will greatly promote the development of 1D fiber-shaped electronics and smart textiles with wearability, high performance, functional diversification, and low cost.

An Overstretch Strategy to Double the Designed Elastic Stretchability of Stretchable Electronics.

Achieving or enhancing the elastic stretchability of inorganic stretchable electronics is critically significant. However, only two types of fundamental strategies-using the prestrained elastic substrate and designing the geometric layouts-are exploited thus far. This study proposes a third strategy, an overstretch strategy, applied beyond the designed elastic range of stretchable structures after transfer printing and bonding to a soft substrate. The theoretical, numerical, and experimental results collectively prove that the overstretch strategy can double the designed elastic stretchability of fabricated stretchable electronics and is valid for various geometrical interconnects with both thick and thin cross-sections. The underlying mechanism is that the elastic range of the critical part of the stretchable structure is doubled, owing to the evolution of the elastoplastic constitutive relation during overstretching. The overstretch strategy can be easily executed and combined with the other two strategies to enhance elastic stretchability, which has profound implications for the design, fabrication, and applications of inorganic stretchable electronics.

All-in-One plasticized Ionogel-based stretchable electrochromic devices

While all-in-one electrochromic devices (ECDs) have attracted attention for application in wearable stretchable electronics, electrochromic materials today are unstretchable, water-vulnerable, and prone to electrolyte leakage. To address this issue, water-resistive, leakage-free, transparent, and stretchable all-in-one plasticized electrochromic ionogels (pECIonogels) are prepared. The optimized pECIonogels are used to build flexible and stretchable ECDs. The fabricated ECDs exhibit high transmittance contrast (96.8% ΔT), rapid switching time (tc,90% = 7 s, tb,90% = 19 s), and high effective coloration efficiency (285.56 cm2 C−1) at 607 nm under an applied bias voltage of −1.0 V. Moreover, the flexible ECDs show good stability even upon compressive and tensile bending. A stretchable ECD was also fabricated by directly coating Ag nanowires on the pECIonogel through a water-assisted pre-strain method. The stretchable ECD at 50% tensile strain shows lower transmittance contrast (36.0% ΔT), slower coloration/bleaching switching (tc,90% = 222 s, tb,90% = 178 s), and reduced effective coloration efficiency (226.67 cm2 C−1) than the unstretched ECD. Nevertheless, the stretchable ECDs are stable in the relaxed and colored states after being stretched, twisted, and folded. Therefore, the proposed all-in-one pECIonogel-based ECDs are promising for the development of next-generation stretchable, wearable, and implantable electronics.