The role of printed electronics and related technologies in the development of smart connected products

The emergence of novel materials with flexible and stretchable characteristics, and the use of new processing technologies, have allowed for the development of new connected devices and applications. Using printed electronics, traditional electronic elements are being combined with flexible components and allowing for the development of new smart connected products. As a result, devices that are capable of sensing, actuating, and communicating remotely while being low-cost, lightweight, conformable, and easily customizable are already being developed. Combined with the expansion of the Internet of Things, artificial intelligence, and encryption algorithms, the overall attractiveness of these technologies has prompted new applications to appear in almost every sector. The exponential technological development is currently allowing for the ‘smartification’ of cities, manufacturing, healthcare, agriculture, logistics, among others. In this review article, the steps towards this transition are approached, starting from the conceptualization of smart connected products and their main markets. The manufacturing technologies are then presented, with focus on printing-based ones, compatible with organic materials. Finally, each one of the printable components is presented and some applications are discussed.This work has been supported by NORTE-06-3559- FSE-000018, integrated in the invitation NORTE59-2018-41, aiming the Hiring of Highly Qualified Human Resources, co-financed by the Regional Operational Programme of the North 2020, thematic area of Competitiveness and Employment, through the European Social Fund (ESF), and by the scope of projects with references UIDB/05256/2020 and UIDP/05256/2020, financed by FCT—Fundação para a Ciência e Tecnologia, Portugal

Development and Characterization of highly flexible and conformable electronic devices for wearable applications

As shown in the story, humanity has tried to develop objects, tools, and devices that could first help to survive in a difficult environment and then improve everyday life. The idea of creating objects that can be worn to restore or improve human abilities or to help during daily routine has fueled technological development and research since the beginning of technological advancement. Wearable technology goes back hundreds of years, and one of the first examples was the invention of glasses to restore the sight, or the wristwatch when big watches were reduced to something that people could take with them anywhere. However, it could be considered that, only when the computer age was established, wearable electronic devices were developed and started to spread out and get into the market. Wearable electronics are a category of technological devices that can be transferred into clothes or directly in touch with the body, typically as accessories or clothing, and these devices can be designed to provide different functionalities, such as notification sending, communication abilities, health and fitness monitoring, and even augmented or virtual reality experiences. In recent years, organic electronics have been deeply investigated as a technology platform to develop devices using biocompatible materials that can be deposited and processed on flexible and even ultra-flexible substrates. The high mechanical flexibility of such materials leads to a new category of devices going beyond wearable devices to more-than-wearable applications. In this context, epidermal electronics is a closely related field that focuses on developing electronic devices that can be directly attached to the skin with a minimally invasive, comfortable, and possibly enabling long-term application. The main object of this Ph.D. research activity is the development and optimization of a technology for the realization of wearable and more-than-wearable devices, able to meet all the new needs in this field, such as the low-cost production process and the mechanical flexibility of the devices and deposition over large areas on unconventional substrates, exploiting all the features and advantages of the organic electronic field, but also finding some solution to overcome the disadvantages of this technology. In this work, different application fields were studied, such as health monitoring through biopotential acquisitions, the development, and optimization of multimodal physical sensors able to detect simultaneously pressure and temperature for tactile and artificial skin applications, and the development of flexible high-performing transistors as a building block for the future of wearable and electronic-skin applications

Recent progress in piezotronic sensors based on one-dimensional zinc oxide nanostructures and its regularly ordered arrays: from design to application

Piezotronic sensors and self-powered gadgets are highly sought-after for flexible, wearable, and intelligent electronics for their applications in cutting-edge healthcare and human-machine interfaces. With the advantages of a well-known piezoelectric effect, excellent mechanical properties, and emerging nanotechnology applications, one-dimensional (1D) ZnO nanostructures organized in the form of a regular array have been regarded as one of the most promising inorganic active materials for piezotronics. This report intends to review the recent developments of 1D ZnO nanostructure arrays for multifunctional piezotronic sensors. Prior to discussing rational design and fabrication approaches for piezotronic devices in precisely controlled dimensions, well-established synthesis methods for high-quality and well-controlled 1D ZnO nanostructures are addressed. The challenges associated with the well-aligned, site-specific synthesis of 1D ZnO nanostructures, development trends of piezotronic devices, advantages of an ordered array of 1D ZnO in device performances, exploring new sensing mechanisms, incorporating new functionalities by constructing heterostructures, the development of novel flexible device integration technology, the deployment of novel synergistic strategies in piezotronic device performances, and potential multifunctional applications are covered. A brief evaluation of the end products, such as small-scale miniaturized unconventional power sources in sensors, high-resolution image sensors, and personalized healthcare medical devices, is also included. The paper is summarized towards the conclusion by outlining the present difficulties and promising future directions. This study will provide guidance for future research directions in 1D ZnO nanostructure-based piezotronics, which will hasten the development of multifunctional devices, sensors, chips for human-machine interfaces, displays, and self-powered systems

Layer by layer printing of nanomaterials for large-area, flexible electronics

Large-area electronics, including printable and flexible electronics, is an emerging concept which aims to develop electronic components in a cheaper and faster manner, especially on those non-conventional substrates. Being flexible and deformable, this new form of electronics is regarded to hold great promises for various futuristic applications including the internet of things, virtual reality, healthcare monitoring, prosthetics and robotics. However, at present, large-area electronics is still nowhere near the commercialisation stage, which is due to several problems associated with performance, uniformity and reliability, etc. Moreover, although the device’s density is not the major concern in printed electronics, there is still a merit in further increasing the total number of devices in a limited area, in order to achieve more electronic blocks, higher performance and multiple functionalities. In this context, this Ph.D. thesis focuses on the printing of various nanomaterials for the realisation of high-performance, flexible and large-area electronics. Several aspects have been covered in this thesis, including the printing dynamics of quasi-1D NWs, the contact problem in device realisation and the strategy to achieve sequential integration (3D integration) of the as-printed devices, both on rigid and flexible substrates. Promisingly, some of the devices based on the printed nanomaterial show a comparable performance to the state-of-the-art technology. With the demonstrated 3D integration strategy, a highly dense array of electronic devices can be potentially achieved by printing method. This thesis also touches on the problem associated with the circuit and system realisation. Specifically, graphene-based logic gates and NW based UV sensing circuit has been discussed, which shows the promising applications of nanomaterial-based electronics. Future work will be focusing on extending the UV sensing circuit to an active matrix sensor array

Mechanical and electrical characterization of wearable textile pressure and strain sensors based on PEDOT:PSS

Il termine tecnologia indossabile si riferisce a quei dispositivi elettronici incorporati negli indumenti od accessori che possono essere comodamente indossati. Essi sono ampiamente utilizzati in campo medico, sportivo, educativo o per monitorare disabilità. In questa tesi sono stati sviluppati sensori di pressione e di deformazione tessili, proponendo il modello teorico che ne descrive il comportamento. L'elemento attivo di tali sensori tessili è basato sul polimero intrinsecamente conduttivo (PEDOT:PSS). La soluzione conduttiva è stata depositata sui tessuti tramite il metodo drop-casting e la tecnica screen printing. La teoria sviluppata per il tessuto di cotone ha dimostrato che è possibile cambiare il range di pressione in cui i sensori rispondono cambiando la concentrazione di glicole etilenico presente nella soluzione di PEDOT:PSS pur mantenendo la geometria dei sensori inalterata. Per realizzare un'applicazione reale, il sensore di pressione tessile è stato fabbricato su un tessuto tecnico sportivo elastico. Comportamenti simili sono stati ottenuti dimostrando la validità del modello proposto. Successivamente, sono presentati i processi di fabbricazione e la caratterizzazione elettro-meccanica di sensori di deformazione tessili. Range tests e stability tests eseguiti su questi sensori di deformazione forniscono notizie circa le loro prestazioni:affidabilità e gauge factor. Il meccanismo di rilevamento è stato analizzato con un modello teorico basato sulle proprietà del tessuto e sulla deformazione della struttura wale-course tipica dei tessuti a maglia. I risultati ottenuti durante questo lavoro permettono lo sviluppo di una nuova generazione di sensori di pressione e di deformazione tessili che potranno essere comodamente indossati nella vita di tutti i giorni

Smart sensor systems for wearable electronic devices

Wearable human interaction devices are technologies with various applications for improving human comfort, convenience and security and for monitoring health conditions. Healthcare monitoring includes caring for the welfare of every person, which includes early diagnosis of diseases, real-time monitoring of the effects of treatment, therapy, and the general monitoring of the conditions of people's health. As a result, wearable electronic devices are receiving greater attention because of their facile interaction with the human body, such as monitoring heart rate, wrist pulse, motion, blood pressure, intraocular pressure, and other health-related conditions. In this paper, various smart sensors and wireless systems are reviewed, the current state of research related to such systems is reported, and their detection mechanisms are compared. Our focus was limited to wearable and attachable sensors. Section 1 presents the various smart sensors. In Section 2, we describe multiplexed sensors that can monitor several physiological signals simultaneously. Section 3 provides a discussion about short-range wireless systems including bluetooth, near field communication (NFC), and resonance antenna systems for wearable electronic devices

피부 부착이 가능한 생체 통합 센서, 전하 트랩 메모리, 및 양자점 정보 디스플레이의 개발

학위논문 (박사)-- 서울대학교 대학원 : 화학생물공학부, 2017. 2. 김대형.최근 다양한 생리학적 데이터를 얻을 목적으로 인체에 붙일 수 있는 전자 장치를 개발하기 위해 많은 연구자들이 지속적인 노력을 기울여 왔습니다. 그러나 부드럽고 곡면으로 이루어 진 인체의 피부에 딱딱한 전자 장치를 장착하기 어려운 까닭에, 변형 가능한 전자 장치의 개발에 대한 필요성이 대두 되었습니다. 이와 관련하여, 유기 반도체 물질과 같은 본질적으로 유연한 물질뿐만 아니라 벌크 형태일 때에는 변형성이 부족하지만 그 두께 및 크기를 조절하여 변형이 용이하게 만들어진 나노 입자, 나노 와이어 및 나노 리본과 같은 초박형/초소형 물질이 인체 부착 형 전자 장치의 고성능 동작을 위한 주요 물질로 사용되기 시작하였습니다. 본 논문은 이러한 나노 물질을 다양한 목적으로 통합시킨, 피부와 유사한 기계적 성질을 가지는 피부 부착 형 전자 장치의 세 가지 예에 대한 연구 내용을 소개하고 있습니다. 첫 번째로, 초박막, 단결정 실리콘 나노 리본을 활용한 변형률, 압력 및 온도 센서 어레이와 더불어, 눅눅한 정도를 느낄 수 있는 습도 센서, 체온 모사를 위한 히터 및 신경 자극을 위한 신축성 다중 전극 어레이가 활용 된 스마트 인공 피부 보철 장치를 개발 하였습니다. 본 연구에서 개발된 피부 보철 장치는 사람의 피부와 비슷한 신축성을 가진 동시에, 사람의 피부가 느낄 수 있는 외부 자극을 느낄 수 있고, 사람의 체온을 모사 하는 등, 최대한 사람의 피부와 비슷한 특성 및 성능을 지니도록 고안되어 향후 로봇 팔, 의수 등에 적용 가능할 거라 기대합니다. 두 번째로, 나노 결정으로 이루어진 플로팅 게이트를 갖춘 피부 부착 형 비휘발성 메모리 어레이를 개발 하였습니다. 나노 결정 플로팅 게이트는 Langmuir-Blodgett 방법을 사용하여 넓은 영역에 걸쳐 균일하게 조립됩니다. 균일한 나노 결정 플로팅 게이트는 성능의 균일성을 향상시킴과 동시에, 메모리 윈도우 마진과 정보 저장 성능을 향상시킵니다. 또한, 초박형 실리콘 나노 멤브레인으로 제작 된 회로를 기반으로 한 증폭기와 늘일 수 있는 피부 부착 형 전극을 이용하여 심전도를 측정하고 심장 박동 수의 변화를 개발된 메모리에 저장하는 데모를 선보였으며, 이는 향후에 피부 부착 형 소자를 의료 어플리케이션에 적용할 수 있는 가능성을 열었다 할 수 있습니다. 세 번째로, 피부에 붙일 수 있는 초박형 양자점 발광 다이오드 디스플레이를 개발하였습니다. 먼저 낮은 작동 전압으로 높은 휘도를 얻기 위해 양자점을 구조적으로 최적화 시켰습니다. 이렇게 최적화된 양자점을 활용하여 양자점 발광 다이오드 어레이로 구성된 양자점 디스플레이를 디자인 하였으며 이의 활용성을 보이기 위하여 문자, 숫자, 기호 및 애니메이션으로 구성된 다양한 패턴이 피부에 부착된 양자점 디스플레이를 통해 보여 질 수 있음을 시연 하였습니다. 개발된 양자점 디스플레이의 사용 중 안정성을 입증하기 위해 구겨짐 및 반복되는 구부림과 같은 다양한 기계적 변형에도 성능에 영향이 없음을 확인 하였습니다. 또한, 입을 수 있는 전자 소자로의 활용성을 보이기 위하여 유연한 전자 장치를 디스플레이와 함께 집적하여 주변 온도 및 걸음 수를 측정하고 곧바로 피부에 부착된 디스플레이로 이를 확인할 수 있음을 시연 하였습니다. 본 논문에서 개발된 세 전자 장치는 미래의 피부 부착 형 전자 장치의 실현에 중요한 구성 요소입니다. 이번 연구 결과를 활용하여 변형 가능한 센서, 액추에이터, 데이터 저장 장치 및 디스플레이 분야에서 새로운 기회가 창출 되고, 완전히 통합된 피부 부착 형 전자 장치의 개발이 가속화되기를 기대합니다.1. Recent advances in deformable devices with integrated functional nanomaterials for wearable electronics 1 Preface 1 1.1 Introduction 3 1.2 Wearable sensors and actuators 6 1.3 Wearable memories 18 1.4 Wearable displays 23 1.5 Conclusion 26 References 27 2. Stretchable silicon nanoribbon based sensor array for skin prosthesis 39 2.1 Introduction 39 2.2 Experimental section 42 2.3 Results and discussion 49 2.4 Conclusion 94 References 95 3. Skin mountable multiplexed silicon nonvolatile memory for storing physiological information 101 3.1 Introduction 101 3.2 Experimental section 105 3.3 Results and discussion 109 3.4 Conclusion 145 References 147 4. Skin mountable quantum dot light emitting diode display for indicating measured data 154 4.1 Introduction 154 4.2 Experimental section 157 4.3 Results and discussion 161 4.4 Conclusion 190 References 191 국문 초록 (Abstract in Korean) 198Docto

Multifunctional vertical interconnections of multilayered flexible substrates for miniaturised POCT devices

Point-of-care testing (POCT) is an emerging technology which can lead to an eruptive change of lifestyle and medication of population against the traditional medical laboratory. Since living organisms are intrinsically flexible and malleable, the flexible substrate is a necessity for successful integration of electronics in biological systems that do not cause discomfort during prolonged use. Isotropic conductive adhesives (ICAs) are attractive to wearable POCT devices because ICAs are environmentally friendly and allow a lower processing temperature than soldering which protects heat-sensitive components. Vertical interconnections and optical interconnections are considered as the technologies to realise the miniaturised high-performance devices for the future applications. This thesis focused on the multifunctional integration to enable both electrical and optical vertical interconnections through one via hole that can be fabricated in flexible substrates. The functional properties of the via and their response to the external loadings which are likely encountered in the POCT devices are the primary concerns of this PhD project. In this thesis, the research of curing effect on via performance was first conducted by studying the relationship between curing conditions and material properties. Based on differential scanning calorimetry (DSC) analysis results, two-parameter autocatalytic model (Sestak-Berggren model) was established as the most suitable curing process description of our typical ICA composed of epoxy-based binders and Ag filler particles. A link between curing conditions and the mechanical properties of ICAs was established based on the DMA experiments. A series of test vehicles containing vias filled with ICAs were cured under varying conditions. The electrical resistance of the ICA filled vias were measured before testing and in real time during thermal cycling tests, damp heat tests and bending tests. A simplified model was derived to represent rivet-shaped vias in the flexible printed circuit boards (FPCBs) based on the assumption of homogenous ICAs. An equation was thus proposed to evaluate the resistance of the model. Vias with different cap sizes were also tested, and the equation was validated. Those samples were divided into three groups for thermal cycling test, damp heat ageing test and bending test. Finite element analysis (FEA) was used to aid better understanding of the electrical conduction mechanisms. Based on theoretical equation and simulation model, the fistula-shape ICA via was fabricated in flexible PCB. Its hollow nature provides the space for integrations of optical or fluidic circuits. Resistance measurements and reliability tests proved that carefully designed and manufactured small bores in vias did not comprise the performance. Test vehicles with optoelectrical vias were made through two different approaches to prove the feasibility of multifunctional vertical interconnections in flexible substrates. A case study was carried out on reflection Photoplethysmography (rPPG) sensors manufacturing, using a specially designed optoelectronic system. ICA-based low-temperature manufacture processes were developed to enable the integration of these flexible but delicate substrates and components. In the manufacturing routes, a modified stencil printing setup, which merges two printing-curing steps (vias forming and components bonding) into one step, was developed to save both time and energy. The assembled probes showed the outstanding performance in functional and physiological tests. The results from this thesis are anticipated to facilitate the understanding of ICA via conduction mechanism and provide an applicable tool to optimise the design and manufacturing of optoelectrical vias