Low-temperature growth of Si and Si₁Ge (001) by ultrahigh vacuum ion-beam sputter deposition

이내응 University of Illinois, Urbana-Champaign 1996 국내박사

Physical sensing using functional organic and reduced graphene oxide field-effect transistor

Tran Quang Trung Sungkyunkwan University 2013 국내박사

Physical sensing devices with high sensitivity, stability, and repeatability may play an importance role in telecommunication, thermal imaging, remote sensing, thermal photovoltaics, personal health monitoring, electronic skins, robot sensors, “smart” surgical gloves, and other human-machine interface applications. There have been many methods to achieve physical sensing devices such as developing device structure, materials, and possessing the buckling geometry of devices by transferring or depositing them on a stretchable substrate. The physical sensing devices based on external sensing part structure in which FETs were used to read out the signals from sensor elements have received considerable attention in recent years. However, there have been some limitations in physical sensing-based external sensing part structure. Example the physical stimulus is insulated on sensor element, additional interconnect between sensor element and FET is required, structure is complicated, high signal to noise ratio, and power consumption. Another issue in the sensing application of physical sensing devices is the electrical stability of the devices is also of critical importance. There are two main problems that need to be addressed for stability during operation. First, charge carrier trapping at the interfaces between component layers in the device may occur from dipolar adsorbates. Second, oxygen and moisture diffusion from the ambient environment into the sensing layer operation affects the device characteristics, as observed for sensor devices operated in the air. Therefore, to fabricate devices and develop stimuli responsive layer materials for physical sensing applications with no environmental effects is a great challenge. A solution for mitigating the instability in the electrical properties of physical sensing devices due to environmental effects is required. Therefore, the motivation in this thesis was an approach of directly integrating physical sensing layers such as co-polymer poly(vinylidene fluoridetrifluoroethylene) (P(VDF‐TrFE)) as gate dielectrics into organic filed-effect transistors (OFETs), and reduce graphene oxide (R-GO) and R-GO nanocomposite as active layer into field-effect transistors (FETs) leading to physical sensing FETs with a simple structure was introduced. In additional, to improve stability, reproducibility, and eliminate oxygen and moisture diffusion from ambient condition, the encapsulation layer was deposited on the top of physical sensing FETs, or hydrophobic sensing layer was integrated in FETs. For physical sensing FETs with directly integrating P(VDF-TrFE) into OFETs as a multi-functional gate dielectric layer, we demonstrate that the device was transparent, flexible, and multi-modal sensing capability of detecting infrared (IR) light, pressure, and strain simultaneously. To decoupling of pyro- and piezoelectric responses in a single device under simultaneous stimulations of IR exposure and strain, an approach of determining two input stimuli by separating the polarization changes inside the gate dielectric (Vo) and the modulation in the product of effective field-effect channel mobility and gate capacitance (C). In additional, the devices were highly responsive to IR radiation from the human body, which may also enable the devices to be applied for the realization of artificial intelligence that contacts directly with human body such as artificial e-skin, biomedical monitoring, and tactile sensing. According to physical sensing FET based on the incorporation of an R-GO channel as a sensing layer, a reduced graphene oxide field-effect transistor (R-GO FET) with high sensitivity, stability, and reproducible detection of physical stimuli was demonstrated. The R-GO FET device has a uniformly self-assembled network channel of R-GO nanosheets that are highly responsive to physical stimuli such as temperature variation, infrared (IR) irradiation, and strain. Encapsulation of the device by an organic layer and thermal annealing in a vacuum led to very low hysteresis, improved stability, and good reproducibility. The novelty of the R-GO FET physical sensing is R-GO channel as a sensing layer in which the electrical resistance can be greatly modified upon application of physical stimuli. Due to weak coupling between adjacent nanosheets in R-GO thin film, therefore, upon applying physical stimuli into the R-GO thin film, a modulation of the internanosheet resistance (Rinter) is expected, inducing a large change in the transconductance of the R-GO FET. Regarding to physical sensing FET based R-GO nanocomposite, a transparent nanocomposite channel of reduced graphene oxide (R-GO) and P(VDF-TrFE) copolymer was used to develop field-effect transistor (FET) for high sensitivity, stability, and reproducible detection of thermal stimuli. The sensing channel layer, R-GO/P(VDF-TrFE) nanocomposite, is synthesized by highly uniform dispersion of R-GO nanosheets in hydrophobic polymer matrix (P(VDF-TrFE)) which minimizes environment effects such as polar solvents, moisture, and water vapor on sensing layer in ambient condition, and enhances absorption of incident infrared (IR) and IR radiation from human body. The effects of thickness and R-GO content in R-GO/P(VDF-TrFE) nanocomposite channel on sensitivity of FET is investigated. And the increase in responsivity of device to IR and IR from human body was attributed to the enhancement in IR of P(VDF-TrFE).

Ultrasensitive biosensing by organic and graphene based transistors for disease diagnosis

Kim, Duck-Jin Sungkyunkwan Univercity 2012 국내박사

Detection of specific protein biomarkers are extremely urgent issue for disease diagnosis and monitoring. Many studies have been developed various signal transducer based on optical, mechanical, electrochemical and electrical method. Recently, electrical detection of disease biomarkers is significantly studied to overcome the technical limitation of optical and mechanical detection method such as large instrumentation, long analysis time, and constraints of nanofabrication. The biosensor require the high sensitivity, high specificity, high stability, low limit of detection, wide dynamic range, real-time detection, simple fabrication for the realization of the point-of-care (POC) disease diagnostic system as well as biological study of proteomics and cellomics. To achieve this requirement, the development of transducing materials, recognition receptors with high affinity and high dense immobilization method are necessary. Here, the suggested different strategies and devices for the improvement of detection sensitivity based on organic material and graphene based transistors enabling the minimum quantification of various biomarkers. This thesis is divided into three experimental part where 1) organic electrochemical transistor (OECT) with conjugated polymer for detection of prostate specific antigen/α1-antichymotrypsin (PSA-ACT) complex combined with the signal amplification by gold nanoparticle; 2) reduced graphene oxide field effect transistor (RGO-FET) for detection of PSA-ACT complex; 3) aptamer modified RGO-FET for detection of protective antigen (PA) in anthrax with signal amplification. The first purpose of this thesis was that the first development of OECT immunosensor for detection of cancer biomarker. The conjugated polymer, poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), was applied to the detection of cancer biomarker with the secondary PSA polyclonal antibody conjugated gold nanoparticle (PSA pAb-AuNP) for signal amplification. The calixcrown based self-assembled monolayer (SAMs) for the linker molecule was selectively functionalized on the aminated PEDOT:PSS. The PSA mAb was immobilized on the PEDOT:PSS and then the sensing characteristics was obtained varying by the concentration of PSA-ACT complex in PBS solution. The second purpose of this thesis was that the first development of highly sensitive reduced graphene oxide field-effect transistor (RGO-FET) for detection of cancer biomarker. The ultrathin nature and large reactive area of graphene induced the very sensitive response to biomolecule. The scalable and facile fabrication of RGO-FET have the capability of label-free, ultrasensitive electrical detection of a cancer biomarker, PSA-ACT complex, in which the ultrathin R-GO channel was formed by a uniform self-assembly of two-dimensional RGO nanosheets. The third purpose of this thesis was that the enhancement of RGO-FET performance by aptamer as recognition receptor and signal amplification by gold nanoparticle. In this experiment, the RGO-FET was applied to the detection of anthrax exotoxin, i.e. protective antigen (PA). This study demonstrates the Debye screening effect, which are critical issue in electrical sensor, varying by the concentration of PBS solution. The use of aptamer for the RGO-FET provide the one way to overcome the Debye screening as well as the highly dense immobilization due to comparably small size. And the signal amplification was achieved by the aptamer conjugated gold nanoparticle for the realization of very ultrahigh sensitive biosensor. These results indicated that I have successfully developed and exploited OECT and RGO-FET based biosensor that enable the detection of biomolecules with ultralow limit of detection (LOD), high sensitivity, and wide dynamic range. These organic material and graphene based biosensor is good candidate for the early diagnosis of disease as well as biological studies.

Reduced graphene oxide field-effect transistor with indium tin oxide extended gate for proton sensing

Thuy, Kieu Truong Sungkyunkwan University 2013 국내석사

In this study, reduced graphene oxide field-effect transistor (R-GO FET) with indium tin oxide (ITO) extended gate electrode was demonstrated as a transducer for a proton sensing application. In this structure, the sensing area is isolated from the active area of the R-GO FET. The ITO extended gate electrode was also used as a proton sensing area. The proton sensing properties based on the R-GO FET transducer were analyzed. The R-GO FET device with the encapsulation by tetratetracontane (TTC) layer showed a good stability in the electrolytic solutions. The device showed an ambipolar behavior with the Dirac point shift versus the pH change in the electrolyte. pH sensitivity based on the Dirac point shift as a sensing parameter was about 43 ~ 50 mV/pH in a wide range of pH value 2~12. The sensor has offered a potential for sensing of H+ in the electrolytes and the sensing area can be modified further for various ions sensing applications.

Synaptic organic electrochemical transistors with ionic liquids and ionic gels

Lee Donghyun Sungkyunkwan university 2021 국내석사

시냅스는 인간 감각기관에서부터 전달된 신경 신호 및 데이터를 전송하는 기관입니다. 시냅스에서는 시냅스 가소성을 통해 자극을 기억, 필터링 등의 기능을 하며 신호 처리의 효율성을 높입니다. 이를 모방한 시냅스 모방 소자들은 높은 효율성과 낮은 전력 소비의 이점을 가지고 많은 연구가 이루어 지고 있습니다. 폴리(3,4-에틸렌 디옥 시티 오펜) 폴리스티렌 설포네이트 (PEDOT:PSS)를 사용하는 유기전기 화학 트랜지스터(OECT)는 뛰어난 전기적 특성 및 장기 가소성, 단기 가소성등을 보여주어 새로운 시냅스 모방소자로 주목받고 있습니다. 이 연구에서, 우리는 이온 리퀴드와 자외선 경화 이온 젤과 PEDOT:PSS를 이용하여 전기적 특성 및 시냅스 가소성이 향상된 OECT를 보고합니다. 이온 리퀴드는 상온에서 액체상태로 존재하는 물질로써 양이온 및 음이온으로 가득 차있으며 높은 전도성 및 비휘발성 등의 장점으로 액체 전해질 대체 물질로 적합합니다. 이온 젤은 1-에틸-3-메틸리미다졸륨비스(트리플루오로메틸설포닐)이미드 ([EMIM] [TFSI]) / 폴리(에틸렌글리콜) 디아크릴레이트 (PEGDA) / 1-하이드록시실로헥실페닐 케톤 (광개시제) 를 첨가하여 제작하였다. 이온 리퀴드 및 기타 첨가 폴리머의 양 비율에 따라 진폭, 펄스 수 또는 펄스 지속 시간 등 게이트 바이어스 펄스에 따라 시냅스 가소성의 변화를 검증할 수 있었다. 이온 리퀴드 함량이 90% 인 이온젤의 경우엔 대체적으로 이온 리퀴드 및 리퀴드 함량이 더 적은 이온 젤 보다 높은 시냅스 가소성을 보여주었습니다. 이온 리퀴드의 경우 시냅스 모방 소자 뿐 아니라 가스 센서로도 많은 연구가 되고 있는 물질로써 위 연구에서도 이산화질소 가스를 이용하여 가스 센싱 테스트를 하였고, 이에 따라 소자의 전기적 특성 및 시냅스 가소성 변화를 확인하였습니다. In neuronal system, synapses are major components which can transmit and process data from human sensory neuron. Action potentials which are transferred from pre-synapse to post-synapse change according to stimulation strength, called synaptic plasticity, are the signal transmitted to brain. Through the changes of synaptic plasticity, synapses plays a role in memorizing the strength of stimuli. By mimicking synapse memory adaptation and filtering properties, a lot of synaptic devices are being studied and developed these days. Especially organic electrochemical transistors (OECTS) have been recently researched as synaptic devices. In particular, the OECTs with poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate)(PEDOT:PSS) have been studied with its outstanding neuromorphic functions like long-term plasticity and short-term plasticity. In this study, an OECT with ionic liquid and ultraviolet (UV)-cured ionic gel as an electrolyte and PEDOT:PSS as channel layer was investigated. Ionic liquid is a molten salt at room temperature and can be used as substitute of electrolyte with advantages of high conductivity, bifunctionality and non-volatility. UV-cured ionic gel was formed with ionic liquid / poly(ethylene glycol) diacrylate (PEGDA, crosslinker) / 1-hydroxycylohexyl phenyl ketone (photoinitiator). According to ratio of amount of ionic liquid and other additives, the synaptic plasticity changes at different gate bias pulsing like amplitude, number of pulses or duration time were verified. Many studies have already shown the Gas sensing property of ionic liquids. Due to IL's gas sensing property, we tested the detection of NO2 gas with our device. NO2 gas can absorb in EMIM TFSI IL by a reversible reaction. Specific ionic liquids show sensitivity and selectivity towards each different target gases. When target gas is applied, the gas reacts with the ions of IL, resulting in difference in ion proportion penetrating in the channel. As a result, the conductance of the channel is modulated. Here electrical properties of the device were measured by the flow of different concentration of NO2 gas.

Development of tough and stretchable materials for wearable electronics

Gargi, Ghosh Sungkyunkwan University 2023 국내박사

New generations of wearable electronics are rapidly merging with bioelectronics offering a robust and emerging framework for invasive and on-skin electronics that are expected to be flexible, stretchable, conformable, lightweight, and long-lasting. These wearable devices can be worn comfortably on human skin (3-55% in elongation) without causing user discomfort, delamination, and device failure. Mostly, the advances that are made in the field of wearable soft electronics have been achieved on substrates. The prevalence of these synthetic polymers in wearable soft electronics can bring tremendous benefits to daily life due to their structural integrity. Consequently, this prevalent use of synthetic polymers in soft electronics has been a major cause for landfills and oceanfills with far-reaching consequences for the environment as well as humankind. Hence, it is highly essential for these materials to be seamlessly integrated with the environment and human health. In fact, their successful integration into our ecosystem depends on the creation of materials that are recyclable, environmentally relevant in terms of degradability, and interface with biological systems without causing harm. Moreover, the development of sustainable material with recyclability or transient nature and their incorporation into electronics is essential for the progression of new technologies, environmental protection, human health, and a sustainable future. However, creation of such materials has been hampered due to the challenges of balancing these properties. Here, we have utilized both intrinsic and extrinsic methods to develop materials with stretchability, toughness and sustainability (recyclability/ biodegradability/ bio-disintegrability). First, we developed an intrinsically stretchable thermoplastic copolymer with a random sequence of hard and soft domains in the polyimide backbone in which their superior traits are harnessed to enable the properties of the copolymer to be tunable and balanced. In addition, the polymer is recyclable and shows excellent processability. Furthermore, the utility of the copolymer was successfully demonstrated for a wearable temperature sensor on the stretchable copolymer and a copolymer-based fully stretchable sweat collection patch, suggesting that they have great potential in soft electronics. Secondly, we developed a biodegradable, biocompatible and stretchable composite microfiber of poly(glycerol sebacate) (PGS) and polyvinyl alcohol (PVA) for transient stretchable device applications. As an application, the stretchable microfiber-based strain sensor was fabricated by incorporation of Au nanoparticles (AuNPs) in the composite microfiber. Finally, we developed a bio-disintegrable substrate (NFR-WPU) embedded with biodegradable nanofibers which acts as a reinforcement to render a non-degradable substrate bio-disintegrable. An optimal loading amount of NFs into the NFR-WPU significantly enhanced the toughness by 19 times and also has a disintegration rate nine times greater than that of pristine non- degradable WPU. Finally, disintegrable and stretchable triboelectric and capacitive touch sensors on the NFR-WPU were fabricated and demonstrated for potential use in transient wearable electronics. In conclusion, the results of this study will open up new horizons of material designing for future electronics by addressing the currently existing limitations in harnessing a material with balanced properties. 새로운 세대의 웨어러블 전자 제품은 빠르게 바이오 전자 제품과 병합되어 침입 및 피부 위 전자 제품을 위한 강력하고 새로운 프레임워크를 제공하고 있다. 이러한 웨어러블 기기는 사용자 불편, 박리 및 기기 고장을 유발하지 않고 사람 피부에 편안하게 착용할 수 있다(신장 3-55%). 대부분 웨어러블 소프트 일렉트로닉스 분야의 발전은 기판에서 이루어졌다. 웨어러블 소프트 일렉트로닉스에서 이러한 합성 중합체의 보급은 구조적 무결성으로 인해 일상 생활에 엄청난 이점을 가져올 수 있다. 결과적으로, 소프트 일렉트로닉스에서 이러한 합성 중합체의 널리 사용은 환경과 인류에게 광범위한 결과를 초래하는 매립지와 해양 매립지의 주요 원인이 되었다. 따라서, 이러한 물질들이 환경 및 인간의 건강과 원활하게 통합되는 것은 매우 중요하다. 사실, 재활용 가능성 또는 일시적인 특성을 가진 지속 가능한 물질의 개발과 그것들의 전자공학으로의 통합은 신기술, 환경보호, 인간의 건강, 그리고 지속 가능한 미래의 발전을 위해 필수적이다. 그러나, 이러한 특성들의 균형을 맞추는 문제로 인해 이러한 재료들의 생성이 방해를 받고 있다. 여기서, 우리는 신축성, 강인성 및 지속 가능성(재활용성/생분해성/바이오 분해성)을 가진 재료를 개발하기 위해 내재적 및 외재적 방법을 모두 사용했다. 먼저, 우리는 폴리이미드 골격에서 하드 도메인과 소프트 도메인의 무작위 시퀀스를 가진 본질적으로 신축성이 있는 열가소성 공중합체를 개발했는데, 이는 공중합체의 특성이 조정 가능하고 균형을 이룰 수 있도록 우수한 특성을 이용한다. 또한, 신축성 공중합체 상의 웨어러블 온도 센서 및 공중합체 기반의 완전 신축성 땀 포집 패치에 대하여 공중합체의 유용성이 성공적으로 입증되어 소프트 일렉트로닉스 분야에서 큰 잠재력을 가지고 있음을 시사하였다. 둘째로, 우리는 일시적인 신축성 장치 애플리케이션을 위한 폴리(글리세롤 세바세이트)와 폴리비닐알코올(PVA)의 생분해성, 생체적합성 및 신축성 복합 마이크로파이버를 개발했다. 애플리케이션으로는, 복합 마이크로파이버에 Au 나노입자(AuNPs)를 혼입시켜 신축성 마이크로파이버 기반의 스트레인 센서를 제작하였다. 마지막으로, 우리는 생물 분해성 나노 섬유가 내장된 생물 분해성 기판(NFR-WPU)을 개발했는데, 이는 분해 불가능한 기판을 생물 분해성으로 만드는 강화제 역할을 한다. 마지막으로, NFR-WPU의 분해 가능하고 신축 가능한 트라이보 전기 및 용량성 터치 센서는 일시적인 웨어러블 전자 장치에서 잠재적으로 사용할 수 있도록 제작되고 시연되었다. 결론적으로, 본 연구의 결과는 균형잡힌 특성을 가진 재료를 활용하는 데 있어 현재 존재하는 한계를 해결함으로써 미래 전자공학에 대한 재료 설계의 새로운 지평을 열 것이다.

Stretchable physical sensors using piezoresistive nanomaterials and conductive paste electrodes

Roh, Eun Sungkyunkwan university 2019 국내박사

Nowadays the smart personal healthcare devices for disease prevention, early diagnosis, customized health management and etc. are rapidly emerging as adopting information and communication technologies and sensing technologies. The trend of medical service paradigm, as well as, has been changed from cure- and hospital-centric to precaution- and user-centric. Among diverse sensing devices, physical sensors easily and directly detect parameters such as blood pressure, respiration, heart rate, etc. from human skin which is composed of successive curvilinear surfaces. Furthermore, physical sensors based on stretchable platforms give more accurate and stable data, body information, on the skin. Stretchable physical sensors are fundamentally composed of stretchable sensing layer and stretchable electrode/electrical wiring. Above all, stretchable piezoresistive physical sensors have been extensively applied and studied due to diverse advantages such as simple device structures and easy read-out of electrical responses in today. However, challenges are still remained such as electrical stability by piezoresistive responses of materials under external stimuli. Herein, three categories to realize stretchable piezoresistive physical sensors were investigated using piezoresistive nanomaterials and conductive paste electrodes. Those three categories are as follows; first, stretchable piezoresistive strain sensors based on patchable platforms were developed using PU-PEDOT:PSS as conductive elastomeric composite and CNTs conductive nanofillers. All materials were layer-by-layer coated on PDMS substrate by solution process, and sensor detected low strain range with high sensitivity to possible to detect facial expressions and eye movements. Secondly, an omnidirectionally stretchable pressure sensors were developed on a 3D microstructured curvilinear surface patterned elastomeric PDMS substrate via solution processing of a PEDOT:PSS-SWCNTs nanocomposite for piezoresistive materials and diluted Ag paste as an electrode. High electrical stability under stretching (G.F.~0.17 at 30%) and pressure sensitivity of 0.5 kPa-1 were obtained and device could simultaneously detect dynamic and static pressures. Detection of tremor which is small skin vibration on skin and evaluation of relative skin elasticity were demonstrated. Thirdly, a stretchable electrical wiring/electrode was developed on rill-patterned Ecoflex substrate, motived from nature, using modified carbon paste. This substrate engineering technique, rill-patterned substrate, is very simple and noninvasive method. Furthermore, development of stretchable carbon paste from commercial products was first trial and modified carbon paste on rill patterned Ecoflex substrate showed high electrical stability under stretching. (G.F.~0.7 at 30%) Based on those results, stretchable strain and pressure sensors based on piezoresistive nanomaterials and conductive paste electrodes were successfully demonstrated. As integration of developed element technologies, stretchable physical sensors have great potential for various applications in healthcare device for daily activity monitoring, earlier diagnosis and management of diverse diseases as conformably attached on skin.

(A) versatile, wireless, flexible potentiostat platform for electrochemical wearable biosensors

Zabeeb, Arsalan Sungkyunkwan university 2020 국내석사

Wearable flexible biosensors are a prominent candidate for the e-health care system. Specifically, for Sensor internet of thing (SIoT) encompassing skin-attachable stretchable/flexible hardware, onbody electroanalytical analysis, user interface, and cloud database through a mobile device. However, existing benchtop commercial and standalone potentiostats exhibit constraints in terms of onbody electroanalytical analysis capability and hardware flexibility. Which are vital for wearable wireless flexible biosensors respectively. Herein, i present flexible versatile potentiostat capable of performing, linear sweep, cyclic voltammetry, chronoamperometry, square wave voltammetry, and electrochemical impedance spectroscopy. The hardware design contains off-the-shelf components and Bluetooth low energy (BLE) module for wireless connectivity. All mounted on a flexible printed circuit board (FPCB) which induces hardware conformity essential for wearable wireless flexible biosensing systems. Comparative experiments performed with commercial benchtop potentiostat proved its analytical performance of R^2=0.9898 with an operating electrical range of ±1.0 Volts and ±180uA, sufficient for most sensors.

(A) study on skin-inspired substrates for stretchable electronics

Adeela, Hanif Sungkyunkwan university 2020 국내박사

피부 장착형 및 웨어러블 전자 장치는 인체와의 상호 작용 및 장기 모니터링 기능으로 인해 주목할 만한 관심을 끌었다. 유연한 피부에 영감을 받은 전자기기는 연성 로봇, 임플란트 의료 시스템, 인간 기계 인터페이스, 건강 모니터링 및 바이오 일렉트로닉스 등에 적합하다. 물리적, 화학적 및 생물학적 시스템을 모니터링하기 위해 고효율 및 최소의 불편함을 갖는 다양한 신축성 센서가 사용되었다. 이러한 신축성 전자 장치는 신축성 기판 상에 제조되어 인간의 피부에 착용될 때 굽히거나 늘어남 및 복잡한 곡선 형태로 변형하기위한 요건을 충족시킬 수 있다. 미래의 신축성 전자 장치의 피부 부착 가능 응용을 위해, 신축성 기판은 발생하는 큰 기계적 변형에 반응하여 장치의 층의 무결성 및 착용자의 신체 활동 중에 발생하는 거대한 기계적 변형에 반응하여 소자 성능의 수준이 유지되도록 자체 제한 기능을 가져야 한다. 따라서, 이 논문에서는 낮은 변형률에서는 높은 신축성을 가지지 만 큰 변형률에서는 높은 인성을 갖는 비 생분해성 및 초박형의 생분해성을 가진, 강인하고 자기-제한성 피부에 영감을 받은 유연성 있는 기판을 보여준다. 사람의 피부는 역동적이며 순응적이고, 생분해성이며 신축성이 뛰어나다. 사람의 피부는 비선형 및 자기 제한적 기계적 성질을 모방한다. 이는 낮은 변형률에서 높은 신축성을 갖지만 표피 아래 조직 내부의 딱딱한 콜라겐 나노 섬유 네트워크의 정렬로 인한 경화로 인해 큰 변형률에서 변형될 때 자체 제한이 된다. 인간 피부의 이러한 기계적 거동을 모방하기 위해, 우리는 높은 탄성률을 가지고, 투명하고, 강인하고, 매우 얇으며, 기능적이고 자가 제한적인 특징을 탄성 중합체의 폴리 디메틸실록산의 낮은 계수의 매트릭스 내로의 압전과 높은 계수를 결정질의 폴리(vinyldenefluoride-cotrifluoroethylene) 를 포함함으로써 제작했다. 탄성중합체 매트릭스에 무작위로 분포된 나노 섬유는 강화 필러로서 기능하여 피부와 같은 기판을 높은 내구성으로 부여하였기 때문에 낮은 압력에서 쉽게 늘어날 수 있지만 응력 감지에 신속하게 파열에 대응하고 유연성 감지를 용이하게 한다. 나노 섬유의 로딩을 제어함으로써 높은 광학 투명도 (80 %)를 갖는 초박형 (~ 62 μm) 피부형 기판의 신축성, 인성 및 영률을 조정할 수있다. 또한 초박형의 피부와 유사한 기판에 신축성 온도 센서를 제작하여 인체 피부의 감각적 기능과 기계적 행동을 모두 모방했다. 이 새로운 신축성 전자 장치는 감지 기능을 유지하면서 신체 움직임을 수용할 수 있다. 또한, NF 로 강화된 복합재는 인간 피부의 기계적 성질을 모방하기 위해 개발되었다. 뻣뻣한 NF 를 탄성중합체 매트릭스에 삽입하면 인성이 증가하지만 신축성이 좋지 않아진다. 이러한 어려움을 극복하기 위해, 우리는 스파게티와 같이 폴리 디메틸 실록산 (PDMS) 탄성중합체에 삽입된 NF 층을 뻣뻣한 폴리 (vinyldenefluoride-cotrifluoroethylene) (PVDF-TrFE )사이에 탄력 있는 폴리우레탄(PU) NFs 의 다중적인 나노 섬유 네트워크(SMNN)를 기반으로 하는 피부에 영감을 받은 디자인을 보고한다. 기판의 영률은 쌓인 층에서 뻣뻣하고 부드러운 나노 섬유 적재량을 조정하여 피부 유형에 따라 조정할 수 있다. 폴리 우레탄 나노 섬유는 또한 뻣뻣한 P (VDF-TrFE)를 첨가한 후에도 전체 기판의 신축성을 유지한다. 이러한 높은 유연성, 조절 가능하며, 자기-제한이 가능한 기판은 각각 적재량을 변화시켜서 0.09 ~ 0.06 MPa 의 탄성률 값을 갖는다. 이는 다양한 유형의 피부 속성을 모방할 수 있는 전략을 개발하는 기회를 제공한다. 또한 피부에서 영감을 얻은 기판 위의 금속 막 코팅은 주기적 (30 %에서 최대 7000 사이클) 및 동적 연신하에서 변화를 보이지 않았다. 게다가, 다양한 농도에서의 NO2 가스 감지 반응이 최대 30 %의 다양한 변형률 하에서 영향을받지 않음을 입증하는 화학 작용 가스 센서를 제조했다. 피부에서 영감을 얻은 이 기판은 의료 진단 고안 및 착용 형 센서에 적용할 수 있다. 환경 영향을 줄이고 의료용 임플란트를 위한 2 차 장치 제거 필요성을 제거하기 위해 우리는 높은 신축성, 순응성 및 조정 가능한 생분해성을 가진 피부에서 영감을 얻은 생분해성 기판을 제작했다. 여기서, PGS 와 PVA 나노 섬유 합성물은 전기 방사되었고 PEG 부드러운 탄성 중합체에 내장되어 신축성 있고 순응적이며, 얇고 및 생분해성인 인간 피부를 모방한다. 완전한 기판은 생분해성이며 피부에서 영감을 얻은 기계적 성질을 성공적으로 보여줍니다. 전도성 있는 생분해성 및 호환 가능한 마이크로 파이버 또한 바이오 응용을 위해 제조되었다. Skin mountable and wearable electronics have attracted incredible attention because of their possible interaction with the human body and long-term monitoring capabilities. Stretchable skin-inspired electronics are considerable for soft robotics, implantable medical systems, human-machine interfaces, health monitoring, and bioelectronics. Diverse stretchable sensors with high efficiency and minimum discomforts have been used to monitor physical, chemical, and biological systems. These stretchable electronic devices have been fabricated on stretchable substrates that can fulfill the requirements for bending, stretching, and deforming into complex curvilinear shapes when worn on human skin. For the future skin-attachable application of stretchable electronic devices, the stretchable substrate must possess self-limiting functions so that the integrity of layers in the devices as well as the reliability and level of device performance are maintained in response to large mechanical deformations that occur during physical activity of the wearer. Therefore, in this thesis, the development of synthetic and biodegradable ultrathin, tough, and self-limiting skin-inspired stretchable substrates that have high stretchability at low strain, but high toughness at large strain, are presented. Human skin is dynamic, conformal, biodegradable, and highly stretchable. Human skin mimics non-linear and self-limiting mechanical properties. It is highly stretchable at low strain but becomes self-limiting when deformed at large strain due to stiffening caused by the alignment of a network of stiff collagen nanofibers inside tissue beneath the epidermis. To imitate this mechanical behavior of human skin, we fabricated a skin-like substrate with highly stretchable, transparent, tough, ultrathin, functional, and self-limiting properties by incorporating crystalline poly(vinyldenefluoride-co-trifluoroethylene) nanofibers with a high modulus and piezoelectricity into the low modulus matrix of elastomeric polydimethylsiloxane. Randomly distributed nanofibers in the elastomer matrix functioned as a reinforcing filler, conferring the skin-like substrate with high durability so that it could easily stretch at low strain but swiftly counteract rupturing in response to stretching, and facilitated strain sensing. The stretchability, toughness, and Young’s modulus of the ultrathin (~62 m) skin-like substrate with high optical transparency (80%) could be tuned by controlling the loading of nanofibers. Moreover, we fabricated a stretchable temperature sensor on the ultrathin skin-like substrate that mimicked both the sensory capabilities and mechanical behavior of human skin. This novel stretchable electronic device was capable of accommodating body movements while maintaining its sensing functionalities. Furthermore, composites reinforced with nanofibers (NFs) have been developed to mimic the mechanical properties of human skin. Embedding stiff NFs into an elastomeric matrix led to an increase in the toughness but compromised the stretchability. To overcome this challenge, we report the design of a skin-inspired substrate based on a spaghetti-like multi-nanofiber network (SMNN) of elastic polyurethane (PU) NFs sandwiched between stiff poly(vinyldenefluoride-co-trifluoroethylene) (PVDF-TrFE) NFs layers embedded in polydimethylsiloxane (PDMS) elastomer. Young’s modulus of substrate can be tuned according to skin type by adjusting the stiff and soft nanofiber loadings in stacked- layers. Polyurethane nanofibers also maintain the stretchability of overall substrate even after adding the stiff P(VDF-TrFE). This highly stretchable, tunable, and self-limiting substrate has elastic modulus values of 0.09~0.06 MPa by varying loading volumes, respectively. This provides the opportunity to develop a strategy which can mimic the properties of different type of skins. Further, the metal film coating onto the skin-inspired substrate showed no change under cyclic (up to 7000 cycles @ 30 %) and dynamic stretching. Moreover, we fabricated a chemoresistive gas sensor which demonstrated that the NO2 gas sensing response at various concentrations remained unaffected under various degrees of strains up to 30 %. This skin-inspired substrate may find applications in medical diagnostic devise and wearable sensors. To reduce the environmental impact and obviating the need for secondary device removal for medical implants we fabricated the skin-inspired biodegradable substrate with high stretchability, conformity, and tunable biodegradability. Herein, composite of stretchable Poly (Glycerol Sebacate) PGS and (Polyvinyl Alcohol) PVA nanofibers were electrospun and embedded in (Polyethylene Glycol) PEG soft elastomer to mimic stretchable, conformal, thin, and biodegradable human skin. The complete substrate is biodegradable and successfully represents the skin-inspired mechanical properties with tunable mechanical properties and time for degradation.

Nanocomposite of oxide nanoparticles and polyimide for ultra-thin, hybrid gate insulator for flexible thin film transistors

Kim, Juhyun Sungkyunkwan university 2017 국내석사