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(a) Prototype SPCB consisting of a 32 Hz oscillator, frequency dividers, shift resisters, LEDs, and passive devices. (b-c) Optical images of the data shifting operation and (d-e) signal waveforms at (b, d) the initial state and (c, e) the 25% stretched state after 3 k-cycles under 25% biaxial strain.
Source publication
Reported herein is a stretchable strain-tolerant soft printed circuit board (SPCB) following optimized circuit design rules. Inkjet-printed interconnects with a wrinkled structure and rigid epoxy patterns allow the outstanding stretchability and strain distribution controllability of the SPCB, respectively. The prototype circuits show reliable oper...
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Context 1
... on the aforementioned results, a prototype of the SPCB was successfully implemented using printing techniques. The layout of the circuit consisting of an oscillator, frequency dividers, shift resistors, and LEDs is shown in Figure 5a and Supplementary Figure S5. Pulse wave signals with a 32 Hz frequency were changed to those with a 2 Hz frequency by the frequency dividers connected in series, and then the signal was inserted to the series of shift resisters. ...
Context 2
... on the aforementioned results, a prototype of the SPCB was successfully implemented using printing techniques. The layout of the circuit consisting of an oscillator, frequency dividers, shift resistors, and LEDs is shown in Figure 5a and Supplementary Figure S5. Pulse wave signals with a 32 Hz frequency were changed to those with a 2 Hz frequency by the frequency dividers connected in series, and then the signal was inserted to the series of shift resisters. ...
Context 3
... wave signals with a 32 Hz frequency were changed to those with a 2 Hz frequency by the frequency dividers connected in series, and then the signal was inserted to the series of shift resisters. After the 3 k-cycling test at a 25% biaxial strain, even when stretched (target ε = 25%, after 1 s), the SPCB showed reliable operation; when the clocks were accurately divided by the frequency dividers, the regularly shifted operation was synchronized to 2 Hz clock, and turned on the LEDs (Figure 5b-e). These behaviors can be shown only when all the components, including the interconnect, ICs, and epoxy layers, are strain-tolerant, without disconnection, fatigue, or delamination issues, under 25% tensile strain. ...
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Citations
... Due to the superior softness and elasticity compared to conventional rigid siliconbased semiconductor devices, flexible and stretchable electronics have received great attention in the past few decades [1,2], especially in the community of electrical and computer engineering [3,4], materials science [5,6], chemistry [7,8], biology and biomedical engineering [9][10][11]. Devices manufactured from flexible materials or structures have the mechanical capability to intrinsically bend, twist, stretch, and compress while maintaining excellent electrical properties and working performance, which has greatly expanded the applications and opened up new opportunities for various novel electronic devices [12,13]. ...
In recent years, the emergence of low-dimensional carbon-based materials, such as carbon dots, carbon nanotubes, and graphene, together with the advances in materials science, have greatly enriched the variety of flexible and stretchable electronic devices. Compared with conventional rigid devices, these soft robotic sensors and actuators exhibit remarkable advantages in terms of their biocompatibility, portability, power efficiency, and wearability, thus creating myriad possibilities of novel wearable and implantable tactile sensors, as well as micro-/nano-soft actuation systems. Interestingly, not only are carbon-based materials ideal constituents for photodetectors, gas, thermal, triboelectric sensors due to their geometry and extraordinary sensitivity to various external stimuli, but they also provide significantly more precise manipulation of the actuators than conventional centimeter-scale pneumatic and hydraulic robotic actuators, at a molecular level. In this review, we summarize recent progress on state-of-the-art flexible and stretchable carbon-based sensors and actuators that have creatively added to the development of biomedicine, nanoscience, materials science, as well as soft robotics. In the end, we propose the future potential of carbon-based materials for biomedical and soft robotic applications.
... Island-bridge structure devices with rigid electronic components and stretchable silver paste have been utilized in applications including LED lighting, ultrasonic probes, and Internet of Things edge devices. However, when an island bridge structure is stretched, a serious problem arises; the interconnection at the boundary between the island and the bridge of the wiring is prone to breakage 5,[15][16][17][18] . The modulus of elasticity of cloth and soft stretchable wiring is a few MPa, while the modulus of elasticity of plastic substrates and electronic components is several GPa to several hundred GPa. ...
Electronic textile (e-textile) devices require mechanically reliable packaging that can bear up to 30% stretch induced by textile crimp stretch, because the boundary between the rigid electronic components and the soft fabric circuit in the e-textile is prone to rupture due to mismatch of their mechanical properties. Here, we describe a thin stress-concentration-relocating interposer that can sustain a textile stretch of up to 36%, which is greater than the 16% stretch of conventional packaging. The stress-concentration-relocating interposer consists of thin soft thermoplastic polyurethane film with soft via holes and is inserted between the electronic components and fabric circuit in order to move the area of stress concentration from the wiring area of the fabric circuit to the film. A finite element method (FEM) simulation showed that when the fabric is stretched by 30%, the boundary between the electrical components and the insulation layer is subjected to 90% strain and 2.5 MPa stress, whereas, at 30% strain, the boundary between the devices and the wiring is subjected to only 1.5 MPa stress, indicating that the concentration of stress in the wiring is reduced. Furthermore, it is shown that an optimal interposer structure that can bear a 30% stretch needs insulating polyurethane film in excess of 100 μm thick. Our thin soft interposer structure will enable LEDs and MEMS sensors to withstand stretching in several types of fabric.
... The presence of the rigid components on top of a deformable substrate plays a crucial role in the electromechanical behaviour of these systems, and often there is the need to minimize the dimensions of these 'rigid islands' in order to reduce strain concentration happening upon deformation of the system [28][29][30][31][32][33] . Recent application of this type of strategy, for example, feature the combination of multiple phenomena, such as prestretching the substrate to induce microbuckling or serpentine structures, together with the use of microislands with specific shapes to enhance the system electrical behaviour under cyclic loading 34,35 . However, substrate designs that lead to improvement of the electromechanical behaviour of stretchable systems are also dependent on the complexity on the device itself and on the arrangement of its components, which may strongly influence the local stiffness of the device and its behaviour at high levels of deformation. ...
Stretchable electronics promise to extend the application range of conventional electronics by enabling them to keep their electrical functionalities under system deformation. Within this framework, development of printable silver-polymer composite inks is making possible to realize several of the expected applications for stretchable electronics, which range from seamless sensors for human body measurement (e.g. health patches) to conformable injection moulded structural electronics. However, small rigid electric components are often incorporated in these devices to ensure functionality. Under mechanical loading, these rigid elements cause strain concentrations and a general deterioration of the system’s electrical performance. This work focuses on different strategies to improve electromechanical performance by investigating the deformation behaviour of soft electronic systems comprising rigid devices through Finite Element analyses. Based on the deformation behaviour of a simple stretchable device under tensile loading, three general strategies were proposed: local component encapsulation, direct component shielding, and strain dispersion. The FE behaviour achieved using these strategies was then compared with the experimental results obtained for each design, highlighting the reasons for their different resistance build-up. Furthermore, crack formation in the conductive tracks was analysed under loading to highlight its link with the evolution of the system electrical performance.
Elastomers, known for their high stretchability and flexibility, are widely used in high-tech applications. However, traditional manufacturing methods for elastomeric part production have limitations. 3D printing, particularly fused deposition modeling (FDM), offers a promising alternative by allowing the fabrication of customized elastomers with desired shapes and properties. Conventional filament-based FDM techniques struggle to print elastomers. This article presents a novel approach for 3D printing polyolefin elastomer (POE) using a direct pellet printing technique. A customized pellet printer with a pneumatic pressure feeding system was used that eliminates filament buckling issues commonly associated with conventional filament-based 3D printing methods. The mechanical properties and microstructure of the printed parts were analyzed to evaluate the suitability of the technique for producing high-quality elastomeric components. SEM images indicated a high-quality and accurate printing method; however, there are micro-holes between the raster due to the high shrinkage rate of POE and increasing the nozzle temperature improves the print quality. The mechanical properties of the printed samples exhibited remarkable formability, with elongation reaching up to 1965%. It is also found that as the nozzle temperature increased, the strength, elongation, and bonding between layers improved significantly. This innovative 3D printing technique has the potential for various applications such as soft robotics and wearable electronics.
A stretchable display would be the ultimate form factor for the next generation of displays beyond the curved and foldable configurations that have enabled the commercialization of deformable electronic applications. However, because conventional active devices are very brittle and vulnerable to mechanical deformation, appropriate strategies must be developed from the material and structural points of view to achieve the desired mechanical stretchability without compromising electrical properties. In this regard, remarkable findings and achievements in stretchable active materials, geometrical designs, and integration enabling technologies for various types of stretchable electronic elements have been actively reported. This review covers the recent developments in advanced materials and feasible strategies for the realization of stretchable electronic devices for stretchable displays. In particular, representative strain‐engineering technologies for stretchable substrates, electrodes, and active devices are introduced. Various state‐of‐the‐art stretchable active devices such as thin‐film transistors and electroluminescent devices that consist of stretchable matrix displays are also presented. Finally, the future perspectives and challenges for stretchable active displays are discussed.
The need for oral health monitoring Point of Care (PoC) systems is ever growing. We have recently reported a novel, aptamer-based flexible biosensor for detection of a high impact hormone – cortisol – in saliva samples using organic electrolyte gated FET (OEGFET) technology. In this work, we are reporting a system-on-board level integration of an improved flexible OEGFET aptasensor which was previously reliant on a bench-top measurement set-up. The reported flexible OEGFET aptasensor has integrated soft microfluidics and a low power (< 300mW) customized printed circuit board. The interfacing of flexible aptasensor to the circuit board was achieved using a low-temperature extrusion printing technique. The system was assessed using spiked saliva supernatants which established comparable detection threshold for the miniaturized, board-based configuration. In this expanded paper, we furthermore demonstrate improvements to device structure and the integration process which improves signal to noise resolution. By implementing 3D printing technology, the interconnects between the flexible sensor and conventional PCB are more durable and possess better conductivity. The optimized transistor pattern allows for multiple analytes to be tested concurrently. Side-by-side analysis of a device that is specific to cortisol biomolecules and a non-specific device shows the system-on-board is capable of distinguishing between binding and non-binding device behavior. The portable oral biosensor has the potential to be transformed into a multianalyte sensing platform and is therefore a promising prototype for future clinical validation.
Strain-engineered elastic platforms that can efficiently distribute mechanical stress under deformation offer adjustable mechanical compliance for stretchable electronic systems. By fully exploiting strain-free regions that are favourable for fabricating thin-film devices and interconnecting with reliably stretchable conductors, various electronic systems can be integrated onto stretchable platforms with the assistance of strain engineering strategies. Over the last decade, applications of multifunctional stretchable thin-film devices simultaneously exhibiting superior electrical and mechanical performance have been demonstrated, shedding light on the realization of further reliable human-machine interfaces. This review highlights recent developments in enabling technologies for strain-engineered elastic platforms. In particular, representative approaches to realize strain-engineered substrates and stretchable interconnects in island-bridge configurations are introduced from the perspective of the material homogeneity and structural design of the substrate. State-of-the-art achievements in sophisticated stretchable electronic devices on strain-engineered elastic platforms are also presented, such as stretchable sensors, energy devices, thin-film transistors, and displays, and then, the challenges and outlook are discussed.
Stretchable hybrid electronics (SHE) that combine high-performance rigid electronic devices with stretchable interconnects offer a facile route for accessing and processing bio-signals and human interactions. Incorporated with sensors and wireless communications, SHE achieves novel applications such as biomedical diagnosis, skin prosthetics, and robotic skin. The implementation of reliable SHE requires the comprehensive development of stretchable electrodes, bonding techniques, and strain-engineered integration schemes. This review covers the recent development of enabling technologies for SHE in terms of materials, structures, and system engineering. We introduce various strategies for stretchable interconnects based on novel materials and structural designs. In particular, we classify SHE into three groups based on strain-relief configurations: thin-film devices on rigid islands, rigid devices with stretchable bridges, and flexible circuits with stretchable bridges. Appropriate methods for substrates, stretchable interconnects, and bonding between rigid and soft components and their pros and cons are extensively discussed. We also explore state-of-the-art SHE in advanced human-machine interfaces and discuss the challenges and prospects for future directions.
Mechanical metamaterials possess unusual mechanical properties that cannot be found in nature. Auxetic metamaterials have negative Poisson's ratios and tend to expand in a direction perpendicular to the axial extension direction. When the Poisson's ratio of a display circuit board is forced to be −1 by adopting an auxetic metamaterial, a display can be stretchable without image distortion, and this display is called a meta‐display in this study. The critical obstacles to implementing a stretchable display are large stretchability, high deformation uniformity, and low image distortion. The meta‐display overcomes these obstacles by incorporating micro‐LEDs and a kirigami‐based auxetic circuit board. An auxetic meta‐display with a stretchability of 24.5%, Poisson's ratio of −1, and no image distortion under uniaxial stretching is demonstrated. Finally, the roll transfer process enabled the scaling‐up of a 3‐inch meta‐display attachable to surfaces with non‐zero Gaussian curvatures. This conformity to the non‐zero Gaussian curvature helps realize biomedical applications such as wearable display, phototherapy, and skincare.
