Fused Deposition Modeling 3D Printing-based Flexible Bending Sensor

Sun Kon Lee(이선곤),Young Chan Oh(오영찬),Joo Hyung Kim(김주형) 한국기계가공학회 2020 한국기계가공학회지 Vol.19 No.1

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.

유연전자소자를 위한 차세대 유연 투명전극의 개발 동향

김주현,천민우,좌성훈,Kim, Joo-Hyun,Chon, Min-Woo,Choa, Sung-Hoon 한국마이크로전자및패키징학회 2014 마이크로전자 및 패키징학회지 Vol.21 No.2

Flexible transparent conductive electrodes (TCEs) have recently attracted a great deal of attention owing to rapid advances in flexible electronic devices, such as flexible displays, flexible photovoltanics, and e-papers. As the performance and reliability of flexible electronics are critically affected by the quality of TCE films, it is imperative to develop TCE films with low resistivity and high transparency as well as high flexibility. Indium tin oxide (ITO) has been the most dominant transparent conducting material due to its high optical transparency and electrical conductivity. However, ITO is susceptible to cracking and delamination when it is bent or deformed. Therefore, various types of flexible TCEs, such as carbon nanotube, conducting polymers, graphene, metal mesh, Ag nanowires (NWs), and metal mesh have been extensively investigated. Among several options to replace ITO film, Ag NWs and metal mesh have been suggested as the promising candidate for flexible TCEs. In this paper, we focused on Ag NWs and metal mesh, and summarized the current development status of Ag NWs and metal mesh. The several critical issues such as high contact resistance and haze are discussed, and newly developed technologies to resolve these issues are also presented. In particular, the flexibility and durability of Ag NWs and metal mesh was compared with ITO electrode.

Flexible heatsink based on a phase-change material for a wearable thermoelectric generator

Lee, Gyusoup,Kim, Choong Sun,Kim, Seongho,Kim, Yong Jun,Choi, Hyeongdo,Cho, Byung Jin Elsevier 2019 ENERGY Vol.179 No.-

<P><B>Abstract</B></P> <P>Thermoelectric generators (TEGs) represent a promising technology for self-powered wearable systems. Since the conventional TEGs have limitation to be used on the human body due to its structural rigidity, flexible TEGs have been studied and developed so that TEGs can be attached to an arbitrarily shaped surface on the human body. However, flexible TEGs require a good heatsink with good flexibility to allow them to produce enough power for wearable devices. In this study, a high-performance flexible heatsink based on a phase-change material (PCM) was proposed. PCM blocks were arranged in an array and good flexibility was realized with an elastomer that filled the space between the PCM blocks. Given that PCM can absorb a large amount of heat at the phase-change temperature, the heatsink can hold the temperature difference across the TEG constant for a relatively long period of time. Thus, the generated power from the flexible TEG was maintained at around 20 μW/cm<SUP>2</SUP> for 33 min. The flexible heatsink can be reused because the PCM solidifies at room temperature. Furthermore, the PCM-based flexible heatsink is smaller and lighter than the conventional metal heatsink. The proposed heatsink is expected to contribute to the commercialization of self-powered wearable devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A phase-change material based flexible heatsink (f-HS) is developed. </LI> <LI> Design guideline of the f-HS for wearable applications is proposed. </LI> <LI> Performance of the f-HS is better than that of the metal heatsink of the same size. </LI> <LI> A thermoelectric generator with the f-HS generates high power for 33 min. </LI> </UL> </P>

유연성 소자용 금속 전극의 신뢰성 연구 동향

김병준,Kim, Byoung-Joon 한국마이크로전자및패키징학회 2013 마이크로전자 및 패키징학회지 Vol.20 No.4

Recently, various types of flexible devices such as flexible displays, batteries, e-skins and solar cell panels have been reported. Most of the researches focus on the development of high performance flexible device. However, to realize these flexible devices, the long-term reliability should be guaranteed during the repeated deformations of flexible devices because the direct mechanical stress would be applied on the electronic devices unlike the rigid Si-based devices. Among various materials consisting electronics devices, metal electrode is one of the weakest parts against mechanical deformation because the mechanical and electrical properties of metal films degrade gradually due to fatigue damage during repeated deformations. This article reviews the researches of fatigue behavior of thin metal film, and introduces the methods to enhance the reliability of metal electrode for flexible device.

Nano-Floating Gate Memory Devices

Jang-Sik Lee 대한금속·재료학회 2011 ELECTRONIC MATERIALS LETTERS Vol.7 No.3

In recent decades, memory device technology has advanced through active research and the development of innovative technologies. Single transistor-based flash memory device is one of the most widely used forms of memory devices because their device structure is simple and the scaling is feasible. A nano-floating gate memory (NFGM) device is a kind of flash memory devices that uses nanocrystals as a charge-trapping element. The use of nanocrystals has advantages over memory devices that rely on other methods such as discontinuous trap sites and controllable trap levels. Nowadays considerable progress has been made in the field of NFGM devices, and novel application areas have been explored extensively. This review article focuses on new technologies that are advancing these developments. The discussion highlights recent efforts and research activities regarding the fabrication and characterization of nonvolatile memory devices that use a nanocrystal layer asa charge-trapping element. The review concludes with an analysis of device fabrication strategies and device architectures of NFGM devices for possible applicationto devices that are organic, printed, and flexible.

플렉서블 디스플레이 디바이스(상품) 신시장 창출을 위한 차세대사용자 의식조사 연구

이철호 ( Lee Cheol Ho ),정형기 ( Jung Hyeong Gi ) 한국상품문화디자인학회 2016 상품문화디자인학연구 Vol.46 No.-

2000년대 사회 전반적으로 의료, 건강, 인포테인먼트 등 다양한 분야에서 플렉서블 디스플레이가 확대될 것으로 보여지며, 향후 전자기기 디자인 융합기술, 인포테인먼트 및 게임디자인 융합기술, 산업 및 군사 디자인 융합기술 등에 적용된 사례개발 또한 급속도로 이루어질 것으로 예상된다. 특히, 스마트기기의 형태가 ‘소지’에서 ‘착용’형태로 확정되어가는 시점에서 등장한 플렉서블 디스플레이 기기는 관련 산업분야별 신시장 창출과 미래 신성장 동력엔진의 먹거리, 차세대 일자리 창출의 필요성으로 당면하고 있는 국가적 난제를 해결하기 위한 가장 훌륭한 대안으로 인정받고 있다. 본 연구는 이러한 관점에서 플렉서블 디스플레이 신시장 창출을 위한 차세대사용자의 의식을 조사, 분석하여 향후의 플렉서블 디스플레이 R&D기술과 디자인 융합연구 개발의 방향성 탐색의 단초 및 그 흐름을 제시하는데 그 배경과 목적이 있다. 연구의 방법 및 범위는 다음과 같다. 첫째, 국내외 플렉서블 디스플레이 관련 연구동향과 기대효과를 파악하고 예측하기 위하여 관련 선행연구 및 이론적 고찰을 행한다. 둘째, 플렉서블 디스플레이 디바이스에 대한 미래의 주사용자 즉, 차세대 집단의 의식조사 분석을 통한 태도연구를 실시하여 미래형 플렉서블 디스플레이 디바이스 시장에 대한 선도적 개발 방향과 시스템 구축에 필요한 향후의 실증적 자료로 활용한다. 구체적으로 웨어러블 디바이스의 차세대 의식조사 연구는 SAS 9.3 Chi-square & Fisher``s Exact test 설문응답의 기술통계로서, 신뢰성과 타당성을 갖는 설문조사를 위해서 조사계획, 설문지, 표본추출, 본 조사, 자료입력, 자료 분석 등의전 과정에서 가장 적절한 통계적 방법인 크론바흐 기법 을 이용한 신뢰도의 통계적 유의성을 분석하여 확인하였다. 셋째, 설문대상은 플렉서블 디스플레이 디바이스의 차세대 주 사용자인 수도권 20대 대학생 80명을 대상으로 일대일 심층면접 형태로 조사되었으며 설문항목은 정보 이해도, 관심도, 흥미욕구 정도, 구매욕구 정도, 구매용도, 구매요인, 구매부위, 비구매 요인, 구매 시 보완요인, 보완요인 해결 시 최종 구매의사 등이다. 연구결과 및 결론은 다음과 같다. 플렉서블 디스플레이 디바이스에 대한 정보 이해도, 관심도, 흥미욕구 정도, 구매욕구 정도, 구매용도, 구매요인, 구매부위, 비구매 요인, 구매 시 보완요인, 보완요인 해결 시 최종 구매의사 등 문항에서는 남녀구분 없이 긍정적인 응답이 통계적으로 유의하였고 각 문항 간 신뢰도 또한 높게 나타났다. 문항 간 상관관계 또한 독립적이지 않고 연관이 있음이 입증되었으며 또 주사용자인 차세대 집단의 플렉서블 디스플레이 디바이스 비구매시 가장 중요한요인은 가격과 디자인, 인터페이스, 기능 등 특히, 가격으로 확인되어 이에 대한 해결책이 필요한 것으로 보인다. In the 2000s, flexible display is considered to expand in various areas of society, including medical service, health, and infotainment. In addition, it is expected to apply rapidly flexible display to digital device design convergence technology, infotainment and game design convergence technology, and industrial and military design convergence technology. In particular, flexible display devices appearing at the time when smart devices type changed from ``belonging`` to ``wearing`` are accepted to be the best alternative to solve national impending issues, such as the creation of a new market in each industrial area, the drive engine for the future new growth, and the creation of the next-generation jobs. From the perspective, the purose of this study is to survey and analyze the next-generation users`` perception in order to create the new market of flexible display, and to lay the foundation for finding the direction of the future flexible display R&D technology and design convergence R&D. The study method and scope are presented as follows: First, related work and theoretical research are performed to find the domestic and foreign research trend of flexible display and to predict the expected effects. Secondly, by analyzing the perception of the next-generation users of flexible display devices and their attitudes, this study provides an empirical material necessary for setting the direction for the leading development of futuristic flexible display devices and establishing a system. More specifically, the survey on the next-generation users` perception of wearable devices is descriptive statistics of SAS 9.3 Chi-square & Fisher``s Exact Test Questionnaire. For reliable and valid questionnaire survey, Cronbach`s technique which is the most proper statistical method for all processes, including survey plan, questionnaire, sampling, main survey, data input, and data analysis, was applied. Based on that, statistical significance was analyzed. Thirdly, the study subjects participating in the questionnaire survey were 80 university students in their 20s living in the metropolitan areas, who are the main next-generation users of flexible display devices. They had person-to-person in-depth interview. The questionnaire items include information understanding, interest, a degree of interest desire, a degree of purchase desire, purchase purpose, purchase factor, purchase region, non-purchase factor, something to improve in non-purchase case, and purchase intention when improved. The study drew the following conclusions: In the questions about information understanding, interest, a degree of interest desire, a degree of purchase desire, purchase purpose, purchase factor, purchase region, non-purchase factor, something to improve in non-purchase case, and purchase intention when improved, they answered positively regardless of gender, and their answers were statistically significant. The reliability of each question was high. The correlation between questions was not independent, but was found. The most important factors of non-purchase of the next-generation users were found to be price, design, and interface. Therefore, it is necessary to improve them.

A new approach to high-performance flexible supercapacitors: Mesoporous three-dimensional Ni-electrodes

Kim, Sun-I.,Kang, Ji-Hun,Kim, Sung-Wook,Jang, Ji-Hyun Elsevier 2017 Nano energy Vol.39 No.-

<P><B>Abstract</B></P> <P>The demand for portable electronic devices is driving the development of flexible supercapacitor, while current devices still need to improve the performance for practical applications. Here, we report a cost-efficient flexible three-dimensional-Ni (3D-Ni) electrode for a flexible supercapacitor with excellent energy density and power density. The meso-porous 3D-Ni electrode provides a large number of active sites to store charges and good accessibility to the ions in polymer electrolytes, leading to excellent capacitance, high energy density, as well as high power density. The Ni(OH)<SUB>2</SUB>/3D-Ni positive electrode showed an outstanding specific capacitance of ~3400F/g at 10A/g and retained 80% of the initial capacitance at 200A/g. The negative MnO<SUB>2</SUB>/3D-Ni electrode exhibited a specific capacitance of 1250F/g at 10A/g and excellent capacitance retention of 82% at 200A/g. The Ni(OH)<SUB>2</SUB>/3D-Ni//MnO<SUB>2</SUB>/3D-Ni hybrid supercapacitor delivered an excellent energy density of 75Wh/kg and a high power density of 5.3kW/kg, and these values did not change under bending conditions. The 3D-Ni electrode introduced here represents a new type of ideal electrode that can be easily applied to various flexible/wearable electronic device with excellent performance.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The flexible solid-state supercapacitor delivered an outstanding specific capacitance of ~3400F/g at 10A/g, an excellent energy density of 75Wh/kg, and a high power density of 5.3kW/kg. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>The highly meso-porous 3D-Ni electrode provides a large number of active sites to store charges and provide good accessibility to the ions in electrolytes, leading to excellent electrochemical performance. The Ni(OH)2/3D-Ni electrode showed an outstanding specific capacitance of ~3400F/g at 10A/g and retained 80% of the initial capacitance at 200A/g. The flexible hybrid supercapacitor delivered an excellent energy density of 75Wh/kg and a high power density of 5.3kW/kg.</P> <P>[DISPLAY OMISSION]</P>

Indium-tin-oxide, free, flexible, nonvolatile memory devices based on graphene quantum dots sandwiched between polymethylsilsesquioxane layers

Ooi, Poh Choon,Lin, Jian,Kim, Tae Whan,Li, Fushan Elsevier 2016 ORGANIC ELECTRONICS Vol.32 No.-

<P><B>Abstract</B></P> <P>Indium-tin-oxide (ITO) free, nonvolatile memory (NVM) devices based on graphene quantum dots (GQDs) sandwiched between polymethylsilsesquioxane (PMSSQ) layers were fabricated directly on polyethylene terephthalate (PET) substrates by using a solution process technique. Current-voltage (<I>I-V</I>) curves for the silver nanowire/PMSSQ/GQD/PMSSQ/poly(3,4-ethylenethiophene):poly(styrene sulfonate)/PET devices at 300 K showed a current bistability. The ON/OFF ratio of the current bistability for the NVM devices was as large as 1 × 10<SUP>4</SUP>, and the cycling endurance time of the ON/OFF switching for the NVM devices was above 1 × 10<SUP>4</SUP> s. The Schottky emission, Poole-Frenkel emission, trapped-charge limited-current, and space-charge-limited current were dominantly attributed to the conduction mechanisms for the fabricated NVM devices based on the obtained <I>I-V</I> characteristics, and energy band diagrams illustrating the “writing” and the “erasing” processes of the devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> ITO-free, two-terminal, MIM, NVM devices containing GQDs sandwiched between PMSSQ layers were fabricated by using a simple solution process. </LI> <LI> <I>I-V</I> curves for the Ag NW/PMSSQ/GQD/PMSSQ/PEDOT:PSS/PET devices at 300 K showed a current bistability. </LI> <LI> ON/OFF ratio of the current bistability for the NVM devices was as large as 1 × 10<SUP>4</SUP>. </LI> <LI> Cycling endurance time of the ON/OFF switching for the NVM devices was above 1 × 10<SUP>4</SUP> s. </LI> <LI> Schottky and PF emissions, TCLC, and SCLC were the dominant carrier transport mechanisms for the MIM, NVM device. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Metal grid technologies for flexible transparent conductors in large-area optoelectronics

Fakharan Zahra,Dabirian Ali 한국물리학회 2021 Current Applied Physics Vol.31 No.-

Mechanically flexible optoelectronic devices such as flexible displays, touch-screens, wearable electronics and solar cells are attracting significant commercial interest. In these devices, a transparent conductor is an essential element that delivers or collects the electrical current to the active material while it allows light to enter or exit from the device. The transparent conductor is composed of a transparent conductive film and a metallic grid providing electrical conduction over the large area. In this article, we review the established processes used by the industry as well as emerging solution-based methods for processing metal grids. Furthermore, we review the issues and potentials of these emerging processes facing for large-area deployment. In the final section, we evaluate three applications of flexible transparent conductors in: perovskite-based solar cells, organic light emitting diodes and electrochromic windows.

Flexible Thermoelectric Device Using Thick Films for Energy Harvesting from the Human Body

Cho, Han Ki,Kim, Da Hye,Sin, Hye Sun,Cho, Churl-Hee,Han, Seungwoo The Korean Ceramic Society 2017 한국세라믹학회지 Vol.54 No.6

A flexible thermoelectric device using body heat has drawn attention as a power source for wearable devices. In this study, thermoelectric thick films were fabricated by cold pressing method using p-type antimony telluride and n-type bismuth telluride powders in accordance with specific loads. Thermoelectric thick films were denser and improved the electrical and thermoelectric properties while increasing the load of the cold pressing. The thickness of the specimen can be controlled by the amount of material; specimens were approximately 700 um in thickness. Flexible thermoelectric devices were manufactured by using the thermoelectric thick films on PI (Polyimide) substrate. The process is cheap, efficient, easy and scalable. Evaluation of power generation performance and flexibility on the fabricated flexible thermoelectric device was carried out. The flexible thermoelectric device has great flexibility and good performance and can be applied to wearable electronics as a power source.