• 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.26 no.4
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• pp.39-46
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• 2019

A stiffness-gradient soft PDMS/hard PDMS/FPCB stretchable package of the island-bridge structure was processed using the polydimethylsiloxane (PDMS) as the base substrate and the more stiff flexible printed circuit board (FPCB) as the island substrate, and its effective elastic modulus and stretchable deformation characteristics were analyzed. With the elastic moduli of the soft PDMS, hard PDMS, and FPCB to be 0.28 MPa, 1.74 MPa, and 1.85 GPa, respectively, the effective elastic modulus of the soft PDMS/hard PDMS/FPCB package was analyzed as 0.58 MPa. When the soft PDMS of the soft PDMS/hard PDMS/FPCB package was stretched to a tensile strain of 0.3, the strains occurring at hard PDMS and FPCB were found to be 0.1 and 0.003, respectively.

• Journal of the Microelectronics and Packaging Society
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• v.26 no.4
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• pp.55-62
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• 2019

Stiffness-gradient stretchable electronic packages of the soft PDMS/hard PDMS/FPCB structure were processed using the polydimethylsiloxane (PDMS) as the base substrate and the more stiff flexible printed circuit board (FPCB) as the island substrate. The elastic characteristics of the stretchable packages were estimated and their long-term reliabilities on stretching cycles and bending cycles were characterized. With 0.28 MPa, 1.74 MPa, and 1.85 GPa as the elastic moduli of the soft PDMS, hard PDMS, and FPCB, respectively, the effective elastic modulus of the soft PDMS/hard PDMS/FPCB package was estimated as 0.6 MPa. The resistance of the stretchable packages varied for 2.8~4.3% with stretching cycles ranging at 0~0.3 strain up to 15,000 cycles and for 0.9~1.5% with 15,000 bending cycles at a bending radius of 25 mm.

• Journal of the Microelectronics and Packaging Society
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• v.25 no.4
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• pp.155-161
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• 2018

A Si chip with the Cu/Au bumps of $100-{\mu}m$ diameter was flip-chip bonded using different anisotropic conductive adhesives (ACAs) onto the local stiffness-variant stretchable substrate consisting of polydimethylsiloxane (PDMS) and flexible printed circuit board (FPCB). The average contact resistances of the flip-chip joints processed with ACAs containing different conductive particles were evaluated and compared. The specimen, which was flip-chip bonded using the ACA with Au-coated polymer balls as conductive particles, exhibited a contact resistance of $43.2m{\Omega}$. The contact resistance of the Si chip, which was flip-chip processed with the ACA containing SnBi solder particles, was measured as $36.2m{\Omega}$, On the contrary, an electric open occurred for the sample bonded using the ACA with Ni particles, which was attributed to the formation of flip-chip joints without any entrapped Ni particles because of the least amount of Ni particles in the ACA.

• Electronics and Telecommunications Trends
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• v.34 no.5
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• pp.48-57
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• 2019

As the super-aged society approaches rapidly, the number of people suffering from post-stroke and other neurological disorders is significantly increasing, where prompt and intensive rehabilitation is essential for such people to resume their physical activities in normal daily lives. To overcome the inherent limitations of manual physical therapy, various types of exoskeleton robots are being employed. However, the need of the hour is softer, thinner, lighter, and even stretchable systems for precisely monitoring the motion of each joint without restricting the patients' movements in rehabilitation tasks. In this paper, we discuss the technological trends and current status of emerging stretchable rehabilitation systems, in which sensors, interconnects, and signal-processing circuits are monolithically integrated within a single stretchable substrate attachable to the skin. Such skin-like stretchable rehabilitation devices are expected to provide much more convenient, user-friendly, and motivating rehabilitation to patients with neurological impairments.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.10
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• pp.609-614
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• 2017

The proposed stretchable transparent electrodes based on silver nanowires (AgNWs) were prepared on a polyurethane (PU) substrate. In order toavoid the surface roughness caused by the silver nanowires, a titanium oxide ($TiO_2$) buffer layer was addedby coating and heating the organometallic sol-gel solution. The fabricated stretchable electrodes showedan electrical sheet resistance of $24{\Omega}sq^{-1}$, 78% transmittance at 550 nm, and an average surface roughness below 5 nm. Furthermore, the AgNW-based electrode maintained its initial electrical resistance under 130% strain testing conditions, without the assistance of additional conductive polymer layers. In this paper, the critical role of the $TiO_2$ buffer layer between the AgNW network and the PU substrate has been discussed.

• Journal of Industrial Convergence
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• v.20 no.12
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• pp.79-85
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• 2022

Recently, a smartphone manufactured on a flexible substrate has been released as an electronic device, and research on a stretchable electronic device is in progress. In this paper, a silicon-based stretchable material is made and used as a substrate to implement and evaluate an optical sensor device using oxide semiconductor. To this end, a substrate that stretches well at room temperature was made using a silicone-based solution rubber, and the elongation of 350% of the material was confirmed, and optical properties such as reflectivity, transmittance, and absorbance were measured. Next, since the surface of these materials is hydrophobic, oxygen-based plasma surface treatment was performed to clean the surface and change the surface to hydrophilicity. After depositing an AZO-based oxide film with vacuum equipment, an Ag electrode was formed using a cotton swab or a metal mast to complete the photosensor. The optoelectronic device analyzed the change in current according to the voltage when light was irradiated and when it was not, and the photocurrent caused by light was observed. In addition, the effect of the optical sensor according to the folding was additionally tested using a bending machine. In the future, we plan to intensively study folding (bending) and stretching optical devices by forming stretchable semiconductor materials and electrodes on stretchable substrates.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.363.2-363.2
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• 2016

Stretchable strain sensors are becoming essential in diverse future applications, such as human motion detection, soft robotics, and various biomedical devices. One of the well-known approaches for fabricating stretchable strain sensors is to embed conductive nanomaterials such as metal nanowires/nanoparticles, graphene, conducting polymer and carbon nanotubes (CNTs) within an elastomeric substrate. Among various conducting nanomaterials, CNTs have been considered as important and promising candidate materials for stretchable strain sensors owing to their high electrical conductivity and excellent mechanical properties. In the past decades, CNT-based strain sensors with high stretchability or sensitivity have been developed. However, CNT-based strain sensors which show both high stretchability and sensitivity have not been reported. Herein, highly stretchable and sensitive strain sensors were fabricated by integrating single-walled carbon nanotubes (SWNTs) and nylon textiles via vacuum-assisted spray-layer-by-layer process. Our strain sensors had high sensitivity with 100 % tensile strain (gauge factor ~ 100). Cyclic tests confirmed that our strain sensors showed very robust and reliable characteristic. Moreover, our SWNTs-based strain sensors were easily and successfully integrated on human finger and knee to detect bending and walking motion. Our approach presented here might be route to preparing highly stretchable and sensitive strain sensors with providing new opportunity to realize practical wearable devices.