• 한국전기전자재료학회논문지
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• 제37권4호
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• pp.420-426
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• 2024

This study proposes an innovative methodology for developing flexible printed circuit boards (FPCBs) capable of conforming to three-dimensional shapes, meeting the increasing demand for electronic circuits in diverse and complex product designs. By integrating a traditional flat plate-based fabrication process with a subsequent three-dimensional thermal deformation technique, we have successfully demonstrated an FPCB that maintains stable electrical characteristics despite significant shape deformations. Using a modified polyimide substrate along with Ag flake-based conductive ink, we identified optimized process variables that enable substrate thermal deformation at lower temperatures (~130℃) and enhance the stretchability of the conductive ink (ε ~30%). The application of this novel FPCB in a prototype 3D-shaped sensor device, incorporating photosensors and temperature sensors, illustrates its potential for creating multifunctional, shape-adaptable electronic devices. The sensor can detect external light sources and measure ambient temperature, demonstrating stable operation even after transitioning from a planar to a three-dimensional configuration. This research lays the foundation for next-generation FPCBs that can be seamlessly integrated into various products, ushering in a new era of electronic device design and functionality.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.76-76
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• 2012

Surface engineering of polymers has a broad array of scientific and technological applications that range from tissue engineering, regenerative medicine, microfluidics and novel lab on chip devices to building mechanical memories, stretchable electronics, and devising tunable surface adhesion for robotics. Recent advancements in the field of nanotechnology have provided robust techniques for controlled surface modification of polymers and creation of structural features on the polymeric surface at submicron scale. We have recently demonstrated techniques for controlled surfaces of soft and relatively hard polymers using ion beam irradiation and plasma treatment, which allows the fabrication of nanoscale surface features such as wrinkles, ripples, holes, and hairs with respect to its polymers. In this talk, we discuss the underlying mechanisms of formation of these structural features. This includes the change in the chemical composition of the surface layer of the polymers due to ion beam irradiation or plasma treatment and the instability and mechanics of the skin-substrate system. Using ion beam or plasma irradiation on polymers, we introduce a simple method for fabrication of one-dimensional, two-dimensional and nested hierarchical structural patterns on polymeric surfaces on various polymers such as polypropylene (PP), polyethylene (PE), poly (methyl methacrylate) PMMA, and polydimethylsiloxane (PDMS).

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.198-198
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• 2012

Graphene has been the subject of intense study in recent years owing to its good optoelectronic properties, possibility for stretchable electronics, and so on. Especially, many research groups have studied about graphene nanostructures with various sizes and shapes. Graphene needs to be fabricated into useful devices with controllable electrical properties for its successful device applications. However, this been far from satisfaction owing to a lack of reliable pattern transfer techniques. Photolithography, nanowire etching, and electron beam lithography methods are commonly used for construction of graphene patterns, but those techniques have limitations for getting controllable GNRs. We have developed a novel nanoscale pattern transfer technique based on an electro-hydrodynamic lithography providing highly scalable versatile pattern transfer technique viable for industrial applications. This technique was exploited to fabricate nanoscale patterned graphene structures in a predetermined shape on a substrate. FE-SEM, AFM, and Raman microscopy were used to characterize the patterned graphene structures. This technique may present a very reliable high resolution pattern transfer technique suitable for graphene device applications and can be extended to other inorganic materials.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.500-500
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• 2011

With recent advances in flexible and stretchable electronics, the development of physically responsive field-effect transistors (physi-FETs) that are easily integrated with transformable substrates may enable the omnipresence of physical sensing devices in electronic gadgets. However, physical stimuli typically induce whole sensing physi-FET devices under global influences that also cause changes in the parameters of FET transducers, such as channel mobility and dielectric capacitance that prevent proper interpretations of response in sensing materials. Extended-gate structures with isolated stimuli have been used recently in physi-FETs to demonstrate performances of sensing materials only. However, such approaches are limited to prototype researches since isolated stimuli rarely occur in real-life applications. In this report, we theoretically and experimentally demonstrated that integrating piezoelectric nanocomposites directly into flexible organic FETs (OFETs) as gate dielectrics provides a general research direction to physi-FETs with a simple device structure and the capability of precisely investigating functional materials. Measurements with static stimulations, which cannot be performed in conventional systems, exhibited giant-positive d33 values of nanocomposites of barium titanate (BT) NPs and poly (vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)).

• 한국수소및신에너지학회논문집
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• 제27권2호
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• pp.176-181
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• 2016

Recent years, supercapacitors have been attracting a growing attention as an efficient energy storage, due to their long-lifetime, device reliability, simple device structure and operation mechanism and, most importantly, high power density. Along with the increasing interest in flexible/stretchable electronics, the supercapacitors with compatible mechanical properties have been also required. A eutectic gallium-indium (EGaIn) liquid metal could be a strong candidate as a soft electrode material of the supercapacitors because of its insulating surface oxide layer for electric double layer formation. Here, we report the electrochemical study on the charging/reaction process at the interface of EGaIn liquid metal and electrolyte. Numerical fitting of the charging current curves provides the capacitance of EGaIn/insulating layer/electrolyte (${\sim}38F/m^2$). This value is two orders of magnitude higher than a capacitance of a general metal electrode/electrolyte interface.

• 접착 및 계면
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• 제24권2호
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• pp.41-53
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• 2023

형태가변형 전자 소자는 늘림, 굽힘 등 기계적으로 변형된 상태에서도 초기 소자 특성이 유지되는 소자를 말한다. 형태가변형 전자 소자에 적용되는 여러 전도성 소재 중 갈륨 기반 액체 금속은 상온에서 액체 상태로 존재하며 우수한 형태가변성과 전기 전도성, 낮은 인체유해성으로 인해 최근 다양한 형태가변형 전자 소자에 적용되고 있다. 본 고에서는 최근 보고된 여러 연구들을 중심으로 갈륨 기반 액체 금속을 소개하고 이를 활용한 다양한 형태가변형 전자 소자 및 제조 공정에 대해 논하고자 한다.

• 전자통신동향분석
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• 제34권5호
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• pp.14-25
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• 2019

As the Internet of Things, artificial intelligence and big data have received a lot of attention as key growth engines in the era of the fourth industrial revolution, data acquisition and utilization in mobile, automotive, robotics, manufacturing, agriculture, health care and national defense are becoming more important. Due to numerous data-based industrial changes, demand for sensor technologies is exploding, especially for intelligent sensor technologies that combine control, judgement, storage and communication functions with the sensors's own functions. Intelligent sensor technology can be defined as a convergence component technology that combines intelligent sensor units, intelligent algorithms, modules with signal processing circuits, and integrated plaform technologies. Intelligent sensor technology, which can be applied to variety of smart IT convergence services such as smart devices, smart homes, smart cars, smart factory, smart cities, and others, is evolving towards intelligent and convergence technologies that produce new high-value information through recognition, reasoning, and judgement based on artificial intelligence. As a result, development of intelligent sensor units is accelerating with strategies for miniaturization, low-power consumption and convergence, new form factor such as flexible and stretchable form, and integration of high-resolution sensor arrays. In the future, these intelligent sensor technologies will lead explosive sensor industries in the era of data-based artificial intelligence and will greatly contribute to enhancing nation's competitiveness in the global sensor market. In this report, we analyze and summarize the recent trends in intelligent sensor technologies, especially those for four core technologies.

• 한국기계가공학회지
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• 제19권1호
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• pp.63-71
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• 2020

Recently, to improve convenience, flexible electronics are quickly being developed for a number of application areas. Flexible electronic devices comprise characters such as being bendable, stretchable, foldable, and wearable. Effectively manufacturing flexible electronic devices requires high efficiency, low costs, and simple processes for manufacturing technology. Through this study, we enabled the rapid production of multifunctional flexible bending sensors using a simple, low-cost Fused Deposition Modeling (FDM) 3D printer. Furthermore, we demonstrated the possibility of the rapid production of a range of functional flexible bending sensors using a simple, low-cost FDM 3D printer. Accurate and reproducible functional materials made by FDM 3D printers are an effective tool for the fabrication of flexible sensor electronic devices. The 3D-printed flexible bending sensor consisted of polyurethane and a conductive filament. Two patterns of electrodes (straight and Hilbert curve) for the 3D printing flexible sensor were fabricated and analyzed for the characteristics of bending displacement. The experimental results showed that the straight curve electrode sensor sensing ability was superior to the Hilbert curve electrode sensor, and the electrical conductivity of the Hilbert curve electrode sensor is better than the straight curve electrode sensor. The results of this study will be very useful for the fabrication of various 3D-printed flexible sensor devices with multiple degrees of freedom that are not limited by size and shape.

• 센서학회지
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• 제28권3호
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• pp.198-204
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• 2019

In this study, we propose a wearable force sensor using 3D printed mold and liquid metal. Liquid metal, such as Galinstan, is one of the promising functional materials in stretchable electronics known for its intrinsic mechanical and electronic properties. The proposed soft force sensor measures the external force by the resistance change caused by the cross-sectional area change. Fused deposition modeling-based 3D printing is a simple and cost-effective fabrication of resilient elastomers using liquid metal. Using a 3D printed microchannel mold, 3D multichannel Galinstan microchannels were fabricated with a serpentine structure for signal stability because it is important to maintain the sensitivity of the sensor even in various mechanical deformations. We performed various electro-mechanical tests for performance characterization and verified the signal stability while stretching and bending. The proposed sensor exhibited good signal stability under 100% longitudinal strain, and the resistance change ranged within 5% of the initial value. We attached the proposed sensor on the finger joint and evaluated the signal change during various finger movements and the application of external forces.

• 센서학회지
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• 제31권5호
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• pp.307-311
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• 2022

With the development of Internet of Things (IoT) technologies, numerous people worldwide connect with various electronic devices via Human-Machine Interfaces (HMIs). Considering that HMIs are a new concept of dynamic interactions, wearable electronics have been highlighted owing to their lightweight, flexibility, stretchability, and attachability. In particular, wearable strain sensors have been applied to a multitude of practical applications (e.g., fitness and healthcare) by conformally attaching such devices to the human skin. However, the stretchable elastomer in a wearable sensor has an intrinsic stretching limitation; therefore, structural advances of wearable sensors are required to develop practical applications of wearable sensors. In this study, we demonstrated a 3-dimensional (3D), porous, and piezoelectric strain sensor for sensing body movements. More specifically, the device was fabricated by mixing polydimethylsiloxane (PDMS) and polyvinylidene fluoride nanoparticles (PVDF NPs) as the matrix and piezoelectric materials of the strain sensor. The porous structure of the strain sensor was formed by a sugar cube-based 3D template. Additionally, mixing methods of PVDF piezoelectric NPs were optimized to enhance the device sensitivity. Finally, it is verified that the developed strain sensor could be directly attached onto the finger joint to sense its movements.