Printed and Flexible Electronics for Wearables

Flexible electronics and sensors are a key enabling element for the realization of wearables and geometry adaptive devices needed to follow current trends such as the Internet of things or Industry 4.0. Within this paper, we present a new and flexible packaging platform by the fabrication of an ultra-thin and highly flexible printed circuit board (PCB).The thermoplastic polymer Parylene, which combines a variety of unique properties such as optical transparency, biostability and biocompatibility according to ISO 10993, thermal stability as well as low permeability for gases and water, was used as the base for the new PCB.Particularly, its mechanical properties, especially the absence of intrinsic stresses, as well as its low Young’s modulus and good bendability are advantageous when using Parylene films as a free-standing substrate for flexible applications. The chemical inertness of Parylene against all common acids, bases and solvents ensures its compatibility with established standard microsystem technologies.For the realization of ultra-thin flexible PCBs, Parylene was used as a substrate as well as for the encapsulation and protection layer, respectively. Furthermore, Parylene was the dielectric between the metallic conductive layers. These redistribution layers (RDL) were deposited and patterned by standard microsystem technologies, such as sputtering, lithography and wet chemical etching. Hence, structure sizes of down to 10 µm were successfully realized. Different metals, such as gold, copper, and aluminum were tested for the RDL. Alternatively, printing technologies such as screen printing and aerosol jet printing were successfully demonstrated for the if conductive silver layerse. The electrical connection between the various RDL was of special interest throughout the study and was realized by etching vertical vias through the Parylene using oxygen plasma. Due to the low total thickness of the flexible Parylene PCB of 20 µm or even less, the obtained vias through the Parylene feature an advantageous low aspect ratio. For the contact formation through the vias, different methods were investigated, e. g. sputtering, printing and electrochemical deposition.Finally, the fabricated flexible Parylene PCB were characterized with respect to their bendability and electrical properties. Doing so, the resistivity and capacitance were measured as well as the frequency response between 20 kHz and 500 MHz. Particularly, for frequencies below 1 MHz the realized flexible Parylene PCBs show a good electrical performance.A third function of Parylene with respect to the realization of an ultra-thin and flexible PCB is its usage as a barrier or capping layer. Doing so, new approaches such as embedding electronic or sensor components in the flexible PCB can be enabled. Other integration technologies such as wire bonding, printing or gluing were investigated with respect to their usability for the new flexible PCB as well. Besides, also the direct fabrication of sensors on the Parylene flexible PCB was successfully demonstrated by the realization of a flexible potentiometric pH sensor.The presented new type of ultra-thin PCB is a versatile platform for the realization of flexible electronics, sensors and devices. Due to its biocompatible properties, the flexible Parylene PCB can be used for medical applications but also for the integration of MEMS, chemical sensors and optical components, respectively. Doing so, it enables the realization of smart systems for wearable applications and their integration into light weight constructions. Within this paper, the concept of this new approach, the respected fabrication and integration technologies as well as possible applications are presented in detail. Figure 1

Technological innovation is viewed as one of the main economic multipliers. In high-technology sectors, with intense competition and short product life cycles, failure to detect an emerging technology could be devastating to both incumbent technology pursuers and innovators. Firms typically employ methods such as a Delphi method, Technology growth curves or technology road-mapping methods to identify and forecast growth. Some of these methods are based on a life cycle approach where a technology is expected to follow an S-curve and then become obsolete in due time, which is analogous to market diffusion of products. In the case of emerging technologies, forecasting methods are not always reliable due to lack of historical data. Hence, both qualitative and quantitative methods are employed to forecast; however, there are risks associated with both of these methods. A general consensus in technology forecasting community is to apply multiple methods for forecasting. In the last few decades there has been explosion of new technologies, especially in the high-technology sector of electronics. Several new applications such as Large Area Displays (several square feet in area), low cost electronics (e.g. RFID tags being manufactured for pennies or cents per unit) and body conformable electronic applications are a few of a long and growing list. The aforementioned applications could broadly be categorized to form a new and emerging field of electronics called flexible electronics. These applications utilize the rugged lightweight plastics to potentially offer attractive characteristics such as low-cost processing, mechanical flexibility, large area coverage, etc. these characteristics are not easily implemented with established silicon technologies. This research analyzes flexible electronics technology by first identifying a few key innovations. Patent and publications data are collected and technology growth curves based on the indicators would be generated, and compared with those of incumbent technology innovations, to assess technology growth potential. Based on the study, technology adoption strategies would also be recommended by which business leaders could anticipate and plan for the effects of these innovations.

Pi-conjugated polymer light emitting devices have the potential to be the next generation of solid state lighting. In order to achieve this goal, a low cost, efficient and large area production process is essential. Polymer based light emitting devices are generally deposited using techniques based on solution processing e.g.: spin coating, ink jet printing. These techniques are not well suited for cost-effective, high throughput, large area mass production of these organic devices. Ultrasonic spray deposition however, is a deposition technique that is fast, efficient and roll to roll compatible which can be easily scaled up for the production of large area polymer light emitting devices (PLEDs). This deposition technique has already successfully been employed to produce organic photovoltaic devices (OPV)¹. Recently the electron blocking layer PEDOT:PSS² and metal top contact³ have been successfully spray coated as part of the organic photovoltaic device stack. In this study, the effects of ultrasonic spray deposition of polymer light emitting devices are investigated. For the first time – to our knowledge -, spray coating of the active layer in PLED is demonstrated. Different solvents are tested to achieve the best possible spray-able dispersion. The active layer morphology is characterized and optimized to produce uniform films with optimal thickness. Furthermore these ultrasonic spray coated films are incorporated in the polymer light emitting device stack to investigate the device characteristics and efficiency. Our results show that after careful optimization of the active layer, ultrasonic spray coating is prime candidate as deposition technique for mass production of PLEDs.

Equipment to enjoy a 3D image, such as a movie theater, television and so on have been developed many. So 3D video are widely known as a familiar image of technology now. The display representing the 3D image are there such as eyewear, naked-eye, the HMD-type, etc. They has been used for different applications and location. But have not been widely studied for the transparent 3D display. If transparent large 3D display is realized, it is useful to display 3D image overlaid on real scene in some applications such as road sign, shop window, screen in the conference room etc. As a previous study, to produce a transparent 3D display by using a special transparent screen and number of projectors is proposed. However, for smooth motion parallax, many projectors are required. In this paper, we propose a display that has transparency and large display area by time multiplexing projection image in time-division from one or small number of projectors to active screen. The active screen is composed of a number of vertically-long small rotate mirrors. It is possible to realize the stereoscopic viewing by changing the image of the projector in synchronism with the scanning of the beam.3D vision can be realized by light is scanned. Also, the display has transparency, because it is possible to see through the display when the mirror becomes perpendicular to the viewer. We confirmed the validity of the proposed method by using simulation.

Hydrogen reduced graphene oxide/metal grid hybrid film: towards high performance transparent conductive electrode for flexible electrochromic devices

Printed electronics is a rapidly growing field that involves the use of printing technologies to create electronic devices such as sensors, displays, and solar cells 1. Unlike traditional electronics, which rely on rigid and bulky components, printed electronics can be obtained on flexible and lightweight substrates such as plastic and paper, allowing the development of novel applications such as wearable electronics, smart packaging, and medical sensors. Printing technologies uniquely feature miniaturization and patterning capability at low-cost and high-throughput production. Among them, screen-printing, inkjet printing (IJP) and aerosol jet printing (AJP) are the most employed to fabricate conductive metallic patterns of Ag, Au, Cu and other metal nanoparticles (NPs). These printing techniques typically requires concentrated ink of metal NPs. However, specially in the case of IJP and AJP the synthesis of very small NPs (d < 100 nm) as well as proper ink formulation and long-time stability are major limitations to printing conductive metallic patterns 2.In this work, we propose an innovative method to produce 2D and 3D patterns and structures of Ag NPs by reactive Aerosol Jet Printing (r-AJP) on different substrates, using a custom-built aerosol jet printer. Ag NPs were in-situ reduced coupling two aerosol streams carrying the Ag precursor and a reducing agent, respectively. The process is fast, scalable and cheap. The electrical properties, in terms of both linear and areal electrical conductivity, of the r-AJP silver structures metallization patterns were investigated. Furthermore, the effect of both process parameters and precursor solution physical properties on printed Ag structure and morphology was assessed by x-ray diffraction (XRD) and scanning electron microscopy (SEM) in order to define the optimized condition for high definition 2d and 3D patterns by r-AJP. Bibliography P. Martins et al., Advanced Functional Materials, 33, 2213744 (2023).Y. Sui and C. A. Zorman, J. Electrochem. Soc., 167, 037571 (2020).

This articles in this special issue on flexible hybrid electronics provides insight into the technical problems that must be overcome as well as the new capabilities they will provide. The term, 'flexible hybrid electronics' means different things based on the context in which it is being discussed. It could mean adaptable for multiple applications, but, here the term refers to mechanical properties, although not necessarily precisely defined. Mechanically flexible might mean anything from conformable (nonlinear shape) to bendable or rollable (around a defined radius of curvature), or even foldable and stretchable. Although not well defined, the intent is to differentiate from the rectangular, rigid form factor of conventional semiconductor electronics. Hybrid means heterogeneous integration of conventional electronics with other electronic components (passive devices, sensors, etc.) that could be fabricated using conventional thin-film transistor (TFT) process technology by additive printing (ink jet, gravure, etc.). The purpose is to provide an electronics solution that has adequate performance, but in a low cost, novel form factor because printing offers the ability to inexpensively fabricate structures over large areas on mechanically flexible substrates (plastics, metal sheets, bendable glass). However, integration with conventional electronics such as silicon CMOS is necessary to achieve required performance because TFT and printed devices are ignificantly inferior to conventionally fabricated devices.

In this work, the stability, electrical conductivity, and versatility of graphite-based inks were taken advantage of to fabricate a nitrate potentiometric sensor. One other key property that was exploited for the design of an ion-selective electrode was the hydrophobicity of graphite. This prevented the formation of a water layer between the solid contact and the polymeric selective membrane. Moreover, given the use of printing technologies for electrode fabrication, it was possible to easily miniaturize the sensors and achieve lower fabrication costs. In this article, a printed sensor, composed of a graphite working electrode and a Ag/AgCl reference electrode, is presented and thoroughly characterized. The working electrode was modified with a well-known PVC-ionophore membrane, and the reference electrode was protected with a PVB-NaCl saturated membrane. It showed almost-Nernstian sensitivity of −(55.4 ± 0.7) mV/dec to NO3−, stability of up to 25 days of operation, limit of detection of 0.204 ± 0.009 mM, and repeatability of 99.02 % (N = 3). Coupled with its high selectivity compared with other anions, this low-cost, mass-producible sensor is a great alternative for environmental and industrial applications.

<p indent="0mm">Microfluidic chips have attracted increasing research attention in biology, chemistry, and medicine; in particular, microfluidic pipes containing metal electrodes have broad prospects in capillary electrophoresis, electrochemical microdetection, biomedical engineering, and flexible electronics. In this study, a simple on-demand method for fabricating arrayed flexible microfluidic pipes with embedded metal electrodes was proposed. The method is based on the direct-writing technology of electrohydrodynamic jet printing (E-jet), which is combined with the conventional mold turning and wet etching processes to obtain flexible microfluidic pipe arrays with embedded metal electrodes. First, a linear convex microstructure with a smooth surface (line width of 10–100 μm and aspect ratio &gt;1:2) was prepared by stacking direct-writing polyvinyl alcohol fibers using the E-jet printing system with a linear rotation-receiving substrate to serve as a template. Using the template, the arrayed microfluidic channels were obtained. Second, a flexible metal patterned conductive electrode (line width &lt;5 μm) was printed on the flexible microfluidic pipe array substrate using the E-jet printing system with a linear translation-receiving substrate and the wet etching process, with a direct-writing photoresist as the protective layer. Finally, the microfluidic pipes were electrically tested with different salt solution concentrations to verify the conductivity of the pipes and the metal electrode. The results indicate that the integrated manufacturing process based on the E-jet printing could be used to simply and efficiently fabricate flexible microfluidic pipe arrays embedded with gold electrodes on-demand and at a low cost. These arrays can be broadly applied in biomedical engineering and flexible electronics.

차세대 항공전자 시스템은 표준화 모듈의 데이터통신에 기반한 개방형 아키텍처와 범용성을 위한 새로운 시스템 개발이 요구된다. 본 논문에서는 차세대 항공전자 비행운영 프로그램을 지원하기 위한 메시지 기반 미들웨어를 설계하고 이에 대한 구현 및 테스트를 통한 적용성을 검증한다. 시스템 구성은 임무컴퓨터 (Mission Computer, MC)와 대화면 시현기 (Large Area Display, LAD)를 포함하며 고신뢰의 이더넷기반의 소켓통신이 사용하였다. 마지막으로 실험결과 제안된 방법은 모든 패킷이 20msec의 데드라인에 패킷 손실이 전혀 없이 전달됨으로써 실시간성과 신뢰성 요구사항을 만족시키는 것으로 판명되었다. It is require to design the next generation avionics system while considering applicability under open architecture where standerd communication module is used. In this situation, if the existing schemes cannot guarantee new requirement, new system development is demanded. In this paper, we present design, implementation, and testing procedure for message based middleware to support operational flight program on avionics. System architecture include mission computer (MC) and large area display (LAD) over standard socket communication based on reliable Ethernet. Finally, experimental results demonstrate that the proposed middleware can guarantee real-time with 20msec as well as reliability requirements with no lost packet.

Electronic printing is an interdisciplinary technology of traditional printing technology and microelectronics manu- facturing. The development of electronic printing has mostly benefited from the progress of nanomaterials research. Graphene, a novel two-dimensional carbon nanomaterial, has shown excellent electrical, thermal, optical properties in flexible electrical devices. Graphene with traditional metals or polymer materials together could act as the main conductive components in conductive ink. Printing of graphene ink represents a cost-effective deposition technique to obtain patterned conductive graphene films, and further assemble them into functional electrical devices. Therefore, electronic printing based on graphene conductive ink is one of the recent research hotspots. In this paper, we review recent developments and advances in research of graphene conductive ink. This review begins with an introduction of different preparation strategies for graphene conductive inks. For printing, the three major pathways for producing graphene sheets are oxidation-reduction, solvent exfoliation and electrochemical expansion of graphite. Different preparation strategies for conductive inks are classified into three major methods: Graphene inks stabilized by surfactants or functional groups, and graphene-based composite conductive ink. The detailed review of graphene conductive ink preparation is discussed with specific examples. Preparation of graphene conductive inks of high concentrations, stability and printing adaptability is the key issue in electronic printing. Subsequently, an introduction of common printing methods and principles is given. Five printing methods are discussed in this review, including inkjet printing, gravure printing, transfer printing, direct writing and three- dimensional (3D) printing. Printing is kind of additive manufacturing, by depositing graphene onto substrates of various materials, sizes, flexibility and roughness for conductive pattern. Different printing techniques have unique requirements of ink rheological properties. The inkjet printing is becoming the most common technique employed in both academic research and industrial application. The realization of rapid, accurate, simple and controllable printing has important influence on the application of graphene conductive ink. Finally, applications of printed graphene conductive ink in flexible functional devices, including basic electrical circuits, energy storage devices and mechanical/chemical sensing devices, are envisioned. Basic electrical circuits, like flexible conductive patterns, field-effect transistors and radio-frequency circuits, play an important role in the fabrication of wearable devices. Printing also offers a cheap, scalable method of fabricating energy storage devices, including supercapacitor and lithium battery. The unique structure of graphene makes possible the fabrication of different kinds of sensors, including strain, temperature, chemical, electrochemical, photo-electricity sensors and biosensors. An outlook of potential future trends in printing graphene conductive ink research and technology is followed. In summary, printing graphene conductive ink has made many significant advances in a wide range of applications. However, the industrial-level application is still limited, and the preparation and application of graphene conductive ink still need further study. A number of key issues should be solved, including stability of graphene ink, electronic conductivity of printed circuit, limited printing resolution, etc. Overall, electronic printing technology based on graphene conductive ink is not meant as a replacement for microelectronic manufacturing engineering, but instead provides an opportunity to produce large-area flexible electronic devices at low cost. Electronic printing of graphene conductive ink will result in a diverse range of novel applications in many fields, and it calls for more research in the future.

Synthesis of Ag/RGO composite as effective conductive ink filler for flexible inkjet printing electronics

Flexible electronics have received considerable attention in academies and industries for their promising applications in enormous fields, such as flexible displays, wearable sensors, artificial skins, and flexible energy devices. Challenges remain in developing a flexible and scalable manufacturing method to facilitate the fabrication of multi-functional structures in a flexible electronic system. Nanoimprint lithography is a high resolution and low-cost approach to fabricate nanostructures over a large area. This paper reviews recent progress of nanoimprint lithography and its applications in flexible electronics. The basic principles, classification, research focus, and critical issues of nanoimprint lithography are elaborated. Then, the advantages of nanoimprint lithography are demonstrated in several typical applications related to flexible electronics, including conductive films, optoelectronic devices, flexible sensors, energy harvesting and storage devices, and bioinspired electronic devices. Finally, the challenges and perspectives of nanoimprint lithography in flexible electronic systems are discussed.

Seamless and minimally invasive three-dimensional interpenetration of electronics within artificial or natural structures could allow for continuous monitoring and manipulation of their properties. Flexible electronics provide a means for conforming electronics to non-planar surfaces, yet targeted delivery of flexible electronics to internal regions remains difficult. Here, we overcome this challenge by demonstrating the syringe injection (and subsequent unfolding) of sub-micrometre-thick, centimetre-scale macroporous mesh electronics through needles with a diameter as small as 100 μm. Our results show that electronic components can be injected into man-made and biological cavities, as well as dense gels and tissue, with >90% device yield. We demonstrate several applications of syringe-injectable electronics as a general approach for interpenetrating flexible electronics with three-dimensional structures, including (1) monitoring internal mechanical strains in polymer cavities, (2) tight integration and low chronic immunoreactivity with several distinct regions of the brain, and (3) in vivo multiplexed neural recording. Moreover, syringe injection enables the delivery of flexible electronics through a rigid shell, the delivery of large-volume flexible electronics that can fill internal cavities, and co-injection of electronics with other materials into host structures, opening up unique applications for flexible electronics.

Printed and flexible electronics promises smart devices for application domains, such as smart fast moving consumer goods and medical wearables, which are generally untouchable by conventional rigid silicon technologies. This is due to their remarkable properties such as flexibility, non-toxic materials, and having low-cost per area. Combined with neuromorphic computing, printed neuromorphic circuits pose an attractive solution for these application domains. Particularly, the additive printing technologies can reduce large amount of fabrication complexities and costs. On the one hand, high-throughput additive printing processes, such as roll-to-roll printing, can reduce the per-device fabrication time and cost. On the other hand, jet-printing can provide point-of-use customization at the expense of lower fabrication throughput. In this work, we propose a machine learning based design framework, that respects the objective and physical constraints of split additive manufacturing for printed neuromorphic circuits. With the proposed framework, multiple printed neural networks are trained jointly with the aim to sensibly combine multiple fabrication techniques (e.g., roll-to-roll and jet-printing). This should lead to a cost-effective fabrication of multiple different printed neuromorphic circuits and achieve high fabrication throughput, lower cost, and point-of-use customization.