Assessment of electromechanical properties of screen printed polymer nanopastes

Printed electronics has provided different printing techniques as environmentally friendly and cost-effective manufacturing methods of electronic components. The printed items can be produced on low cost, different types of flexible substrates, even when their surface is corrugated. This opens a new application range of printed electronics and makes them competitive with traditionally manufactured electronics. However, it is necessary to investigate new materials to continue the rapid progress in printed electronics. In our study, the electromechanical properties of polymer nanopastes consisted of carbon nanotubes and graphite platelet nanofibers mixed with a conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) were investigated. Their microstructure and the layer morphology were observed using a scanning electron microscope and an optical microscope. The thickness and average roughness of the layers printed on the foil and paper were determined with a contact profilometer. The mechanical durability of the screen printed layers was verified in a cyclic bending test. The highest mechanical durability was exhibited by the polymer pastes containing carbon nanotubes.     

Hybrid 3D Printing of Soft Electronics

Hybrid 3D printing is a new method for producing soft electronics that combines direct ink writing of conductive and dielectric elastomeric materials with automated pick‐and‐place of surface mount electronic components within an integrated additive manufacturing platform. Using this approach, insulating matrix and conductive electrode inks are directly printed in specific layouts. Passive and active electrical components are then integrated to produce the desired electronic circuitry by using an empty nozzle (in vacuum‐on mode) to pick up individual components, place them onto the substrate, and then deposit them (in vacuum‐off mode) in the desired location. The components are then interconnected via printed conductive traces to yield soft electronic devices that may find potential application in wearable electronics, soft robotics, and biomedical devices.     

金属纳米颗粒导电墨水制备与后处理工艺的研究进展

印刷电子技术是一种低成本、简捷高效、绿色环保的电子器件制造技术,已在柔性电子制造等诸多领域展现出巨大的潜力。近年来,导电墨水作为印刷电子技术迅速发展的关键材料受到了学术界的广泛关注和报道。结合印刷电子技术的应用和发展现状,对金属纳米颗粒导电墨水的各项性能指标及其机理进行概述,综述了金属纳米颗粒导电墨水的制备和后处理工艺的研究进展,着重介绍了部分有潜力的前沿技术,并分析了这些技术对应的优势与局限及其发展方向。最后结合印刷电子技术目前发展中存在的问题提出了一些观点。     

Direct flip-chip bonding of bare dies to polypropylene-coated paper substrates without adhesives or solders

Paper-based electronics is an emerging concept with the prospect of developing recyclable, low cost, flexible, and green products such as paper displays, smart labels, RFID tags, smart packages, electronic magazines, biological and medical devices. Compared to conventional printed circuit board (PCB) materials, utilizing paper as an electronics substrate has both physical and chemical challenges. Nowadays, the integration of components on papers are mainly conducted using adhesives [such as anisotropic conductive paste (ACP), isotropic conductive paste (ICP), and non-conductive pastes (NCP)] or low-temperature solders. The application of adhesives and solders in a roll-to-roll fabrication line of papers requires an additional dispensing or printing unit, which has its own drawbacks. Therefore, alternative approaches such as pre-applied adhesive films either on bare dies or papers can gain significant attention. In this study, by exploiting the unique properties of a paper coating material (i.e., polypropylene) as a non-conductive adhesive, it was shown that direct flip-chip bonding of the bare dies and devices could be successfully performed on paper without using any additional adhesives or solders. The electrical and mechanical performance of the flip chip-bonded dies on the polypropylene-coated paper substrate were assessed utilizing daisy-chain contact resistance measurement and die-shear analysis, respectively. Moreover, for an RFID tag application, RFID chips were flip chip bonded to the coated papers and functional tests via NFC communication were also successfully exerted. It was concluded that the polypropylene film on the paper can be considered as an intrinsic NCP layer for flip-chip integration of bare dies.

     

Rheological properties and screen printability of UV curable conductive ink for flexible and washable E-textiles

As a critical component for the realization of flexible electronics,multifunctional electronic textiles(etextiles)still struggle to achieve controllable printing accuracy,excellent flexibility,decent washability and simple manufacturing.The printing process of conductive ink plays an important role in manufacturing e-textiles and meanwhile is also the main source of printing defects.In this work,we report the preparation of fully flexible and washable textile-based conductive circuits with screen-printing method based on novel-developed UV-curing conductive ink that contains low temperature and fast cure features.This work systematically investigated the correlation between ink formulation,rheological properties,screen printability on fabric substrates,and the electrical properties of the e-textile made thereafter.The rheological behaviors,including the thixotropic behavior and oscillatory stress sweep of the conductive inks was found depending heavily on the polymer to diluent ratio in the formulation.Subsequently,the rheological response of the inks during screen printing showed determining influence to their printability on textile,that the proper control of ink base viscosity,recovery time and storage/loss modulus is key to ensure the uniformity of printed conductive lines and therefore the electrical conductivity of fabricated e-textiles.A formulation with 24 wt%polymer and 10.8 wt%diluent meets all these stringent requirements.The conductive lines with 1.0 mm width showed exceptionally low resistivity of 2.06×10^-5Ωcm Moreover,the conductive lines presented excellent bending tolerance,and there was no significant change in the sample electrical resistance during 10 cycles of washing and drying processes.It is believed that these novel findings and the promising results of the prepared product will provide the basic guideline to the ink formulation design and applications for screen-printing electronics textiles.     

EGaIn‐Assisted Room‐Temperature Sintering of Silver Nanoparticles for Stretchable,Inkjet‐Printed,Thin‐Film Electronics

Coating inkjet‐printed traces of silver nanoparticle (AgNP) ink with a thin layer of eutectic gallium indium (EGaIn) increases the electrical conductivity by six‐orders of magnitude and significantly improves tolerance to tensile strain. This enhancement is achieved through a room‐temperature “sintering” process in which the liquid‐phase EGaIn alloy binds the AgNP particles (≈100 nm diameter) to form a continuous conductive trace. Ultrathin and hydrographically transferrable electronics are produced by printing traces with a composition of AgNP‐Ga‐In on a 5 µm‐thick temporary tattoo paper. The printed circuit is flexible enough to remain functional when deformed and can support strains above 80% with modest electromechanical coupling (gauge factor ≈1). These mechanically robust thin‐film circuits are well suited for transfer to highly curved and nondevelopable 3D surfaces as well as skin and other soft deformable substrates. In contrast to other stretchable tattoo‐like electronics, the low‐cost processing steps introduced here eliminate the need for cleanroom fabrication and instead requires only a commercial desktop printer. Most significantly, it enables functionalities like “electronic tattoos” and 3D hydrographic transfer that have not been previously reported with EGaIn or EGaIn‐based biphasic electronics.     

The potential of molecular self-assembled monolayers in organic electronic devices

Functionalized molecules that organize to self-assembled monolayers (SAMs) are gaining importance in organic electronic devices. They are fully compatible with flexible substrates, are amenable to low-cost processing, and show reliable film-forming behavior. Highly integrated devices, such as sensor arrays or memories, have also been demonstrated. Starting from auxiliary layers, which improve and modify surfaces and interfaces in traditional thin-film devices, the applications of SAMs develop towards molecular scale electronics, including active molecular device layers and multifunctional SAMs, which fulfill several layer functions of a device within one monolayer. Mixed SAMs make new and tunable device features possible, by stoichiometric control of the composition of different SAM-forming molecules.     

Electrodeposition of PEDOT-Cl film on a fully printed Ag/polyaniline electrode

Electrodeposition of poly(3,4-ethylenedioxythiophene) doped with chloride (PEDOT-Cl) on a paper substrate is demonstrated. A fully printed silver/polyaniline (Ag/PANI) layer-by-layer structure on a pigment coated paper acted as a working electrode, on which a layer of PEDOT-Cl was galvanostatically grown in an electrochemical cell. The deposited PEDOT-Cl appeared as a dark-blue circular area on a green Ag/PANI electrode. The electrodeposition was further confirmed by chemical and topographical analyses. The results demonstrate the potential of low-cost paper substrates and roll-to-roll mass-manufacturing methods in electrochemical applications.     

Paper electronics

Paper is ubiquitous in everyday life and a truly low-cost substrate. The use of paper substrates could be extended even further, if electronic applications would be applied next to or below the printed graphics. However, applying electronics on paper is challenging. The paper surface is not only very rough compared to plastics, but is also porous. While this is detrimental for most electronic devices manufactured directly onto paper substrates, there are also approaches that are compatible with the rough and absorptive paper surface. In this review, recent advances and possibilities of these approaches are evaluated and the limitations of paper electronics are discussed.     

Electroless copper deposition on aluminum-seeded ABS plastics

We report a method of converting non-conductive plastic surfaces into conductive by coating either aluminum or aluminum-carbon black containing enamel pastes onto acrylonitrile-butadiene-styrene (ABS) plastics to create aluminum-seeded surfaces for a subsequent copper deposition. Through a simple electroless procedure, copper ions were reduced on the Al seeds and deposited on the ABS surface to develop a conductive layer in about 10-min deposition time. We demonstrate that addition of carbon black particles to the pastes shorten the time to reach the maximum conductivity and enhance the adhesion of electrolessly deposited copper layer to the ABS substrate surface. The electroless copper deposition process developed in this study may open up a new route of plating on plastics (POP) for printed circuit boards, electromagnetic interference shielding, and many other applications.     

柔性电子器件集成与其在包装上的应用

目的 分析柔性电子和柔性基底的发展现状、趋势和前景,为促进智能包装的进一步发展提供参考.方法 先从柔性基底材料入手,梳理常见基底材料性能;再综述柔性电子器件集成的研究现状及主要的集成技术,并讨论其在包装上的应用.结论 具有较好柔韧性和降解性的纸基可作为柔性电子集成的基底材料,结合柔性印刷电子技术和传统硅基电子技术的优势,将柔性电子器件通过蛇形互联结构集成并封装在柔性基底上,从而制备集成可拉伸的微系统,且随着新型印刷电子材料、印刷工艺、新技术和新设备的不断涌现,柔性电子器件集成于柔性基底上并应用于包装将成为一大研究热点.     

Printable Transparent Conductive Films for Flexible Electronics

Printed electronics are an important enabling technology for the development of low‐cost, large‐area, and flexible optoelectronic devices. Transparent conductive films (TCFs) made from solution‐processable transparent conductive materials, such as metal nanoparticles/nanowires, carbon nanotubes, graphene, and conductive polymers, can simultaneously exhibit high mechanical flexibility, low cost, and better photoelectric properties compared to the commonly used sputtered indium‐tin‐oxide‐based TCFs, and are thus receiving great attention. This Review summarizes recent advances of large‐area flexible TCFs enabled by several roll‐to‐roll‐compatible printed techniques including inkjet printing, screen printing, offset printing, and gravure printing using the emerging transparent conductive materials. The preparation of TCFs including ink formulation, substrate treatment, patterning, and postprocessing, and their potential applications in solar cells, organic light‐emitting diodes, and touch panels are discussed in detail. The rational combination of a variety of printed techniques with emerging transparent conductive materials is believed to extend the opportunities for the development of printed electronics within the realm of flexible electronics and beyond.     

镓基液态金属导电油墨及其图形化应用

目的 提出发展液态金属导电油墨的基本途径及其对信息产业发展重要性。方法 从导电油墨的制备方法、液态金属粒子的物理特性、液态金属油墨图形化及其应用展开论述,全面总结液态金属导电油墨的技术现状以及深化对其的认识。结果 液态金属基导电油墨将比目前贵金银基导电油墨的成本低50倍,基于液态金属的导电油墨图形化印刷电子在智能防伪包装、柔性电子、生物医用等领域呈快速发展趋势。结论 镓基液态金属导电油墨及其印刷技术是一个崭新的技术革命,具有重要的研究价值和经济意义。     

电弧放电法制备石墨烯及其在导电油墨中的应用

导电油墨是印刷电子技术中使用的关键电子材料, 而导电填料作为导电油墨的主要成分要求其化学性能稳定且电导率高。其中, 基于石墨烯的导电油墨因为其、透射电子显微镜、拉曼光谱等手段对制备的石墨烯进行了表征。结果表明: 直流电弧放电法制备的石墨烯为2~10层、尺寸在100~200 nm范围且纯度高、结晶性好。在此基础上, 研究了涂层厚度、热处理温度以及弯曲角度等对石墨烯导电油墨导电性能的影响。研究发现, 石墨烯导电油墨电阻率与涂层厚度、热处理温度成反比, 且随着厚度、温度的增加石墨烯导电油墨的电阻率逐渐降低。并且样品在柔性基底上经过不同角度的弯曲折叠后电阻率没有明显变化。当厚度为170 μm的样品经过360℃ (30 min) 热处理后, 石墨烯导电油墨的电阻率仅为0.003 Ω·cm。上述结果表明, 电弧法制备的石墨烯导电油墨有望成为未来印制电子领域的关键材料。     

A New Facile Route to Flexible and Semi‐Transparent Electrodes Based on Water Exfoliated Graphene and their Single‐Electrode Triboelectric Nanogenerator

Wearable technologies are driving current research efforts to self‐powered electronics, for which novel high‐performance materials such as graphene and low‐cost fabrication processes are highly sought.The integration of high‐quality graphene films obtained from scalable water processing approaches in emerging applications for flexible and wearable electronics is demonstrated. A novel method for the assembly of shear exfoliated graphene in water, comprising a direct transfer process assisted by evaporation of isopropyl alcohol is developed. It is shown that graphene films can be easily transferred to any target substrate such as paper, flexible polymeric sheets and fibers, glass, and Si substrates. By combining graphene as the electrode and poly(dimethylsiloxane) as the active layer, a flexible and semi‐transparent triboelectric nanogenerator (TENG) is demonstrated for harvesting energy. The results constitute a new step toward the realization of energy harvesting devices that could be integrated with a wide range of wearable and flexible technologies, and opens new possibilities for the use of TENGs in many applications such as electronic skin and wearable electronics.     

ZnO-nanowires/PANI inorganic/organic heterostructure light-emitting diode

In this paper, we report a flexible inorganic/organic heterostructure light-emitting diode, in which inorganic ZnO nanowires are the optically active components and organic polyaniline (PANI) is the hole-transporting layer. The fabrication of the hybrid LED is as follows, the ordered single-crystalline ZnO nanowires were uniformly distributed on flexible polyethylene terephthalate (PET)-based indium-tin-oxide-coated substrates by our polymer-assisted growth method, and proper materials were chosen as electrode and carrier. In this construction, an array of ZnO nanowires grown on PET substrate is successfully embedded in a polyaniline thin film. The performance of the hybrid device of organic-inorganic hetero-junction of ITO/(ZnO nanowires-PANI) for LED application in the blue and UV ranges are investigated, and tunable electroluminescence has been demonstrated by contacting the upper tips of ZnO nanowires and the PET substrate. The effect of surface capping with polyvinyl alcohol (PANI) on the photocarrier relaxation of the aqueous chemically grown ZnO nanowires has been investigated. The photoluminescence spectrum shows an enhanced ultraviolet emission and reduced defect-related emission in the capped ZnO NWs compared to bare ZnO. The results of our study may offer a fundamental understanding in the field of inorganic/organic heterostructure light-emitting diode, which may be useful for potential applications of hybrid ZnO nanowires with conductive polymers.     

Graphene-based conducting inks for direct inkjet printing of flexible conductive patterns and their applications in electric circuits and chemical sensors

A series of inkjet printing processes have been studied using graphene-based inks. Under optimized conditions, using water-soluble single-layered graphene oxide (GO) and few-layered graphene oxide (FGO), various high image quality patterns could be printed on diverse flexible substrates, including paper, poly(ethylene terephthalate) (PET) and polyimide (PI), with a simple and low-cost inkjet printing technique. The graphene-based patterns printed on plastic substrates demonstrated a high electrical conductivity after thermal reduction, and more importantly, they retained the same conductivity over severe bending cycles. Accordingly, flexible electric circuits and a hydrogen peroxide chemical sensor were fabricated and showed excellent performances, demonstrating the applications of this simple and practical inkjet printing technique using graphene inks. The results show that graphene materials-which can be easily produced on a large scale and possess outstanding electronic properties-have great potential for the convenient fabrication of flexible and low-cost graphene-based electronic devices, by using a simple inkjet printing technique.      

基于导电纤维的柔性电子器件研究进展

柔性电子器件具有优异的灵活性,实现了与服装的无缝集成,在各种实际的可穿戴应用中具有巨大的潜力。一维纤维状电子器件由于其优异的柔韧性、可编织性及舒适性成为智能可穿戴领域的研究热点。首先,综述了用于纤维状柔性电子器件的一维可拉伸电极的研究进展,然后详细介绍了高性能一维纤维状柔性电子器件制备过程中具有代表性的导电材料、制造技术及一维柔性纤维进一步应用于各类电子器件的主要制备方法,另外总结了近年来基于柔性纤维状电子器件在智能可穿戴领域的应用。最后对一维纤维基智能可穿戴电子器件的机遇和挑战进行了批判性思考。      

Laser–Material Interactions for Flexible Applications

The use of lasers for industrial, scientific, and medical applications has received an enormous amount of attention due to the advantageous ability of precise parameter control for heat transfer. Laser‐beam‐induced photothermal heating and reactions can modify nanomaterials such as nanoparticles, nanowires, and two‐dimensional materials including graphene, in a controlled manner. There have been numerous efforts to incorporate lasers into advanced electronic processing, especially for inorganic‐based flexible electronics. In order to resolve temperature issues with plastic substrates, laser–material processing has been adopted for various applications in flexible electronics including energy devices, processors, displays, and other peripheral electronic components. Here, recent advances in laser–material interactions for inorganic‐based flexible applications with regard to both materials and processes are presented.     

Solution-Processed Centimeter-Scale Highly Aligned Organic Crystalline Arrays for High-Performance Organic Field-Effect Transistors

Solution-printed organic single-crystalline films hold great potential for achieving low-cost manufacturing of large-area and flexible electronics. For practical applications, organic field-effect transistor arrays must exhibit high performance and small device-to-device variation. However, scalable fabrication of highly aligned organic crystalline arrays is rather difficult due to the lack of control over the crystallographic orientation, crystal uniformity, and thickness. Here, a facile solution-printing method to fabricate centimeter-sized highly aligned organic crystalline arrays with a thickness of a few molecular layers is reported. In this study, the solution shearing technique is used to produce large-area, organic highly crystalline thin films. Water-soluble ink is printed on the hydrophobic surface of organic crystalline films, to selectively protect it, followed by etching. It is shown that the addition of a surfactant dramatically changes the fluid drying dynamics and increases the contact line friction of the aqueous solution to the underlying nonwetting organic crystalline film. As a result, centimeter-scale highly aligned organic crystalline arrays are successfully prepared on different substrates. The devices based on organic crystalline arrays show good performance and uniformity. This study demonstrates that solution printing is close to industrial application and also expands its applicability to various printed flexible electronics.