• Journal of Sensor Science and Technology
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• v.32 no.6
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• pp.386-390
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• 2023

Stiffness-engineered stretchable substrate technology has been widely used to produce stretchable displays, transistors, and integrated circuits because it is compatible with various flexible electronics technologies. However, the stiffness-engineering technology has never been applied to transistor-based stretchable strain sensors. In this study, we developed thin-film transistor-based strain sensors on stiffness-engineered stretchable substrates. We designed and fabricated strain-sensitive stretchable resistors capable of inducing changes in drain currents of transistors when subjected to stretching forces. The resistors and source electrodes of the transistors were connected in series to integrate the developed stretchable resistors with thin-film transistors on stretchable substrates by printing the resistors after fabricating transistors. The thin-film transistor-based stretchable strain sensors demonstrate feasibility as strain sensors operating under strains of 0%-5%. This strain range can be extended with further investigations. The proposed stiffness-engineering approach will expand the potential for the advancement and manufacturing of innovative stretchable strain sensors.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.05a
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• pp.707-708
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• 2010

• Journal of the Microelectronics and Packaging Society
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• v.24 no.3
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• pp.19-26
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• 2017

Stretchable deformation-resistance characteristics of Au, Pt, and Cu films were measured for the stretchable packaging structure where a parylene F was used as an intermediate layer between a PDMS substrate and a metal thin film. The 150 nm-thick Au and Pt films, sputtered on the parylene F-coated PDMS substrate, exhibited the initial resistances of $1.56{\Omega}$ and $5.53{\Omega}$, respectively. The resistance increase ratios at 30% tensile strain were measured as 7 and 18 for Au film and Pt film, respectively. The 150 nm-thick Cu film, sputtered on the parylene F-coated PDMS substrate, exhibited a very poor stretchability compared to Au and Pt films. Its resistance was initially $18.71{\Omega}$, rapidly increased with applying tensile deformation, and finally became open at 5% tensile strain.

• Journal of the Microelectronics and Packaging Society
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• v.24 no.3
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• pp.27-34
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• 2017

We investigated the feasibility of parylene F usage as an intermediate layer between a polydimethylsiloxane (PDMS) substrate and an Au thin-film interconnect as well as the swelling effect of PDMS substrate on the stretchable deformability of an Au thin film. The 150-nm-thick Au film, which was sputtered on a PDMS substrate without a parylene F layer, exhibited an initial resistance of $11.7{\Omega}$ and an overflow of its resistance at a tensile strain of 12.5%. On the other hand, the Au film, which was formed with a 150-nm-thick parylene F layer, revealed an much improved resistance characteristics: $1.21{\Omega}$ as its initial resistance and $246{\Omega}$ at its 30% elongation state. With swelling of PDMS substrate, the resistance of an Au film substantially decreased to $14.4{\Omega}$ at 30% tensile strain.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.4
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• pp.721-726
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• 2017

We fabricated stretchable thin-film transistors(TFTs) on a polydimethylsiloxane substrate with patterned polyimide island structures by using an amorphous InGaZnO semiconductor and parylene gate insulator. The TFTs exhibited a field- effect mobility of $5cm^2V^{-1}s^{-1}$ and a current on/off ratio of $10^5$ at a relatively low operating voltage. Furthermore, the fabricated transistors showed no noticeable changes in their electrical performance for large strains of up to 50 %.

• Journal of Power System Engineering
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• v.22 no.1
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• pp.64-71
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• 2018

Currently, functional patterns are formed by screen printing on stretchable films, and they are applied to wearable and stretchable devices. In this study, three types of silver paste were prepared using three polyester binders with different Tg and molecular weights in order to impart elasticity to the conductive pattern itself. Rheological properties and DSC measurements were performed for each silver paste. Then, each silver paste was screen printing and cured by an IR dryer to evaluate adhesive strength, pencil hardness, resistance and surface shape change according to strain. As a result, it was found that the silver paste using a binder with a low Tg and a high molecular weight has the smallest resistance change depending on the strain. Namely, it was found that it is most preferable to use a binder with a low Tg and a high molecular weight as the stretchable electrode.

• Journal of Magnetics
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• v.20 no.1
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• pp.11-20
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• 2015

In this work, Monte Carlo simulation was employed to model the stretchable Ising monolayer film to investigate the effect of the spatial distance variation among magnetic atoms on magnetic behavior of the film. The exchange interaction was considered as functions of initial interatomic distance and the stretched distance (or the strain). Following Bethe-Slater picture, the magnetic exchange interaction took the Lennard-Jones potential-like function. Monte Carlo simulations via the Wolff and Metropolis algorithms were used to update the spin systems, where equilibrium and dynamic magnetic profiles were collected. From the results, the strain was found to have strong influences on magnetic behavior, especially the critical behavior. Specifically, the phase transition point was found to either increase or decrease depending on how the exchange interaction shifts (i.e. towards or away from the maximum value). In addition, empirical functions which predict how the critical temperatures scale with initial interatomic distance and the strain were proposed, which provides qualitatively view how to fine tune the magnetic critical point in monolayer film using the substrate modification induced strain.

• ETRI Journal
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• v.44 no.1
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• pp.147-154
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• 2022

We demonstrate a new double-layer structure for stretchable interconnects, where the top surface of a serpentine polyimide support is coated with a thin eutectic gallium-indium liquid metal layer. Because the liquid metal layer is constantly fixed on the solid serpentine body in this liquid-on-solid structure, the overall stretching is accomplished by widening the solid frame itself, with little variation in the total length and cross-sectional area of the current path. Therefore, we can achieve both invariant resistance and infinite fatigue life by combining the stretchable configuration of the underlying body with the freely deformable nature of the top liquid conductor. Further, we fabricated various types of double-layer interconnects as narrow as 10 ㎛ using the roll-painting and lift-off patterning technique based on conventional photolithography and quantitatively validated their beneficial properties. The new interconnecting structure is expected to be widely used in applications requiring high-performance and high-density stretchable circuits owing to its superior reliability and capability to be monolithically integrated with thin-film devices.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.389.2-389.2
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• 2014

Polydimethylsiloxane (PDMS) based electronic devices are widely used for various applications in large area electronics, biomedical wearable interfaces and implantable circuitry where flexibility and/or stretchability are required. A few fabrication methods of electronic devices directly on PDMS substrate have been reported. However, it is well known that micro-cracks appear in the metal layer and in the lithography pattern on a PDMS substrate. To solve the above problems, a few studies for fabrication of stiff platform on PDMS substrate have been reported. Thin-film islands of a stiff region are fabricated on an elastomeric substrate, and electronic devices are fabricated on these stiff islands. When the substrate is stretched, the deformation is mainly accommodated by the substrate, and the stiff islands and electronic devices experience relatively small strains. Here, we report a new method to achieve stiff islands structures on an elastomeric substrate at a various thickness, as the platform for stretchable electronic devices. The stiff islands were defined by conventional photolithography on a stress-free elastomeric substrate. This technique can provide a practical strategy for realizing large-area stretchable electronic circuits, for various applications such as stretchable display or wearable electronic systems.

• Journal of Sensor Science and Technology
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• v.32 no.6
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• pp.335-339
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• 2023

Skin-compatible electronics have evolved to achieve both conformality and stretchability for stable contact with deformable biological skin. While existing research has largely concentrated on alternative materials, the potential of Parylene-based thin-film electrodes for stretchable on-skin applications remains relatively untapped. This study proposes an engineering strategy to achieve stretchability using the Parylene thin-film electrode. Unlike the conventional Parylene thin-film electrode, we introduce morphological adaptability via controlled microscale slits in the Parylene electrode structure. The slits-containing device enables unprecedented stretchability while maintaining critical electrical insulation properties during mechanical deformation. Finally, the demonstration on human skin shows the mechanical adaptability of these Parylene-based bioelectrodes while their electrical characteristics remain stable during various stretching conditions. Owing to the ultra-thinness of the Parylene coating, the wearable bioelectrode not only achieves stretchability but also conforms to the skin. Our findings broaden the practical use of Parylene thin-film bioelectrodes.