Printing practice for the fabrication of flexible and stretchable electronics

Recently, flexible and stretchable electronics have experienced tremendous surge due to their promised applications in fields such as wearable electronics, portable energy devices, flexible display, and human-skin sensors. In order to fabricate flexible and stretchable electronics, a high-throughput, cost-saving, and eco-friendly manufacturing technology is required. Printing, which is an additive patterning process, can meet those requirements. In this article, printing fabrication is compared with conventional lithography process. Practices at the author's group utilizing printing for the fabrication of flexible thin-film transistors, flexible hybrid circuits and stretchable systems are presented, which has proven that printing can indeed be a viable method to fabricate flexible and stretchable electronics.     

Flexible electronics manufacturing technology and equipment

Flexible electronics such as mechanically compliant displays, sensors and solar cells, have important applications in the fields of energy, national defence and biomedicine, etc. Various types of flexible electronics have been proposed or developed by the improvements in structural designs, material properties and device integrations. However, the manufacturing of flexible electronics receives little attention, which limits its mass production and industrialization. The increasing demands on the size, functionality, resolution ratio and reliability of flexible electronics bring several significant challenges in their manufacturing processes. This work aims to report the state-of-art technologies and applications of flexible electronics manufacturing. Three key technologies including electrohydrodynamic direct-writing, flip chip and automatic optical inspection are highlighted. The mechanism and developments of these technologies are discussed in detail. Based on these technologies, the present work develops three kinds of manufacturing equipment, i.e., inkjet printing manufacturing equipment, robotized additive manufacturing equipment, and roll-to-roll manufacturing equipment. The advanced manufacturing processes, equipment and systems for flexible electronics pave the way for applications of new displays, smart sensing skins and epidermal electronics, etc. By reviewing the developments of flexible electronics manufacturing technology and equipment, it can be found that the existing advances greatly promote the applications and commercialization of flexible electronics. Since flexible electronics manufacturing contains many multi-disciplinary problems, the current investigations are confronted with great challenges. Therefore, further developments of the reviewed manufacturing technology and equipment are necessary to break the current limitations of manufacturing resolution, efficiency and reliability.

     

Preparation and application of gallium-based conductive materials in the very recent years

Gallium and its alloys are a group of metallic materials with low-melting points at or around room temperature. Apart from the good electrical conductivity, the unique liquid state endows those metals with excellent compliance and self-healing capacity,which present great value in the development of flexible and stretchable electronics. Constrained by the high surface tension and low viscosity, however, liquid metals cannot be applied to some common microelectronics manufacturing technologies such as micro-electro mechanics in the preceding years, which impedes their mass production in electronic devices. To address these issues and broaden the applications of liquid metals in electronics devices, numerous efforts have been taken and great progress has been made especially in the very recent years. This review summaries the recent development of liquid metal-based conductive materials from the aspects of preparation or modification methods and their accommodative fabrication techniques in flexible electronic applications. Further outlook including expectations and challenges of liquid metal-based conductive materials are also presented.     

Flexible smart sensing skin for “Fly-by-Feel” morphing aircraft

Flexible smart sensing skin is a key enabling technology for the future “Fly-by-Feel” control of morphing aircraft. It represents the next-generation skin of aircraft that can exhibit a more powerful sensing function than a conventional one and could be mounted on arbitrary curvilinear surfaces, especially for advanced autonomic, morphing aircraft. Recent significant technical advances in flexible electronics have overcome many historic drawbacks of conventional smart skin, e.g., only a limited number of discrete block sensors can be integrated due to the inevitable structural damage and heavy guidelines. Herein, we review the key developments in flexible sensors technology and highlight both the state-of-the-art devices and the potential applications for the measurement of aircraft. We begin with the importance of flexible smart skin for morphing aircraft and then expand to the latest progress in various types of flexible sensors. Then we highlight flexible sensors as smart skin to measure aerodynamic parameters and monitor the structural health, and further to achieve the Fly-by-Feel control. Finally, the challenges and opportunities on flexible smart sensing skin are discussed, from the functional design to practical applications.

     

纳米压印光刻工艺的研究进展和技术挑战

图形化技术是微纳制造过程的核心工艺之一.目前,作为微纳加工主流工艺的光学光刻技术由于受曝光波长衍射极限的物理限制,其技术复杂性和设备制造成本大幅增加.纳米压印将传统的模板复型原理应用到微观制造领域,以其高分辨率、高效率、低成本和工艺过程简单的特点,引起了各国研究人员的广泛关注.作为一种接触式几何约束流变成形方式,纳米压印必然衍生出许多新的挑战性问题.在阐述纳米压印工艺构成要素的基础上,对目前的若干主要压印技术工艺变种进行了简要综述,总结出了纳米压印所涉及的基本理论问题,并对纳米压印在集成电路制造中所面临的挑战进行了分析.     

Flexible hybrid electronics: Enabling integration techniques and applications

The conventional electronic systems enabled by rigid electronic are prone to malfunction under deformation, greatly limiting their application prospects. As an emerging platform for applications in healthcare monitoring and human-machine interface (HMI), flexible electronics have attracted growing attention due to its remarkable advantages, such as stretchability, flexibility, conformability, and wearing comfort. However, to realize the overall electronic systems, rigid components are also required for functions such as signal acquisition and transmission. Therefore, flexible hybrid electronics (FHE), which simultaneously possesses the desirable flexibility and enables the integration of rigid components for functionality, has been emerging as a promising strategy. This paper reviews the enabling integration techniques for FHE, including technologies for two-dimensional/three-dimensional (2D/3D) interconnects, bonding of rigid integrated circuit (IC) chips to soft substrate, stress-isolation structures, and representative applications of FHE. In addition, future challenges and opportunities involved in FHE-based systems are also discussed.

     

生物质基储能材料在柔性器件中的应用

随着柔性器件和可穿戴设备的发展及人类环保意识的提高,开发高能效、高能量和功率密度、绿色环保的新型柔性储能装置受到了广泛的关注.然而,传统的有机聚合物、贵金属等材料不仅价格昂贵而且面临资源枯竭的危机,难以满足柔性器件发展的需要.生物质资源具有储量丰富、可再生、环境友好、生物相容性好、价格低廉等特点,是制备柔性储能材料的理...     

风力发电中电力电子技术的应用

风能是可再生能源中最重要的组成部分。风力发电由于清洁无污染。施工周期短，投资灵活，占地少，具有较好的经济效益和社会效益，已受到世界各国政府的高度重视。随着现代电力电子技术以及变频调速技术的迅速发展，其在风力发电中的应用也更为广泛。本文介绍了电力电子技术在风力发电中的主要应用，包括风力发电系统的分类，风电机组的控制技术以及风力发电的输电方式等，并对风力发电前景进行了展望。     

接地技术在电力电子技术实践应用中的探讨

接地技术是保证电力电子装置可靠工作的关键技术之一,研究了有关接地的系列问题。详述了接地的分类、定义、目的,引入接地阻抗概念来解释接地出现的各种现象,并给出了解决接地技术的应用策略,最后,设计了一种较佳的接地技术方案,以期实践者能较好地解决接地技术在电力电子技术实践应用中遇到的大多数问题。     

Transient of power pulse and its sequence in power electronics

Various failures and destructions occur in the applications of the power electronic converter. The real practice shows that these failures are connected with the con-centration of the transient power pulse. In allusion to the physical characteristics of power electronic converters,this paper proposed that the power pulse and its se-quence are the basis for power electronics in the perspective of electromagnetic energy. The authors analyzed the transient processes in the power semiconductors,electric conduction loops and controller system and illustrated the power pulse phenomena in high voltage and high power inverters. This investigation on the power pulse sequence is very meaningful for the failure analysis and device pro-tection and has become an important topic in power electronics.     

Review: Wearable Sweat Sensors for Diseases Prevention and Monitoring

Advanced in wireless technologies and flexible materials with great biocompatibility, wearable devices have been utilized in the field of healthcare, sports management, and diseases prevention, which have been widely applied in current electronic equipment. Sweat, as a common metabolite on the skin surface, contains a wealth of biomarkers for disease detection and diagnosis. Therefore, developing wearable sweat sensors can provide a non-invasive method for health data collecting, sports monitori...     

导电油墨在印刷电子方面的研究进展

随着新型柔性电子器件的出现、发展与应用,印刷电子的制备工艺相对于其他传统技术表现出成本低、效率高以及可大面积生产等比较优势,逐步受到广泛关注.而导电油墨作为印刷电子工艺中的重要组成部分,越来越多的科研工作者对其进行了研究.为此针对导电油墨进行了相关论述,并阐明了未来导电油墨的发展方向,其中重点介绍了金属纳米颗粒型、金属有机分解型和金属纳米线型等不同导电体系的导电油墨,评述了它们的整体特点、制作方法和应用实例,并针对各油墨体系提出了改进其在基材上的附着力设计方法.可以看出:在印刷电子工艺中所使用的导电油墨,其性质与特征决定了整个制备工艺的流程和最终产品性能,并且将会继续沿着低成本、环境友好型和高导电性等方向进行发展.     

Spraying printing of liquid metal electronics on various clothes to compose wearable functional device

Liquid metal printing is emerging as an important tool for making wearable electronics. However, very limited academic efforts were made to fulfill such an increasing need. This paper is dedicated to present relatively complete theoretical and experimental characterizations for liquid metal spraying printing towards developing wearable electronic textile. The practical conditions of liquid metal droplets in the spraying printing process such as the jet velocity, the size distribution of droplets and their evenness degree, the morphology of droplets and their unrolling areas after impacting the substrate are quantified. The dominating factors, including the oxidation of liquid metal and the pressure force on cloth substrate during the impacting process, which ensure liquid metal firmly adhere to the cloth, are clarified. Further, various clothes are comparatively investigated to test their capabilities in printing liquid metal conductors, where the resistance difference can be over thousand-fold. In addition to interpreting the basic mechanisms and performances of the spraying printing, two programmable flexible circuits with specifically designed functions such as blinking LED lighting and wireless infrared temperature measurement via current manufacture technology were also demonstrated and evaluated for their washable ability. With the realization of wearable modules via liquid metal printing technology, it can be expected that flexible functional devices on cloth fabricated quickly and directly would witness more broad applications in the coming time.     

高保真度压印光刻图形质量研究

为提高纳米压印工艺的图形质量,在抗蚀剂涂铺之前,对硅基材料进行氧离子轰击表面改性,有效增强硅基材料对抗蚀剂的亲和性;采用PDMS软模具,脱模性能好,而且能够很好的清除图型母版和自身表面的杂质;利用高保真度加载工艺,图型横向和纵向复型误差小于14 nm;运用多元回归方法建立了所选温度测点的温度值与模具中心z向热误差之间的关系模型,并对热误差进行了补偿。实验结果表明,压印光刻工艺实现了图型特征的高保真度复制。     

A triboelectric/electromagnetic hybrid generator for efficient wind energy collection and power supply for electronic devices

Harvesting energy from ambient environment has been considered as a promising strategy for driving portable electronic devices in a sustainable way. A wind driven triboelectric-electromagnetic hybrid nanogenerator has been fabricated to convert wind energy into electricity. It is composed of an electromagnetic generator(EMG) and a triboelectric nanogenerator(TENG) with the output power of 35 and 0.32 mW, respectively when the wind speed is 5 m/s. Generally, TENG shows a low current output with a high voltage output characteristic, on the contrary the EMG shows a high current output and a low voltage output. This hybrid nanogenerator overcomes these problems and exhibits comprehensive and efficient performance on scavenging energy.Moreover, in view of the output performance and charging ability of the hybrid nanogenerator, it shows high stability, making it suitable for charging capacitors or batteries and driving portable electronics sustainably. A new structure of integrated TENG and EMG was designed to harvest wind energy, which shows potential applications in portable and small device power supply system, especially in the areas of remote mountains, deserts, islands, etc., as emergency power supply.     

分子电子学及其LB膜技术

分子电子学是近年来迅速发展起来的崭新学科,理论上的成功将必然导致新型的分子电子器件的产生,而LB膜技术已成为一种对广义分子电子器件进行组装的新技术。文中叙述了分子电子学的发展状况和LB技术在分子电子学中的应用,探讨了该领域的发展前景。     

Ionic conductive hydrogels toughened by latex particles for strain sensors

Conductive hydrogels have attracted tremendous attention due to their excellent softness and stretchability as wearable strain sensing devices. However, most of hydrogel-based strain sensors suffered from poor self-recoverability and fatigue resistance,resulting in significant decrease of strain sensitivity after recycling. Here, a soft and flexible wearable strain sensor is prepared by using an ionic conductive hydrogel with latex particles as physical cross-linking centers. The dynamic physical cross-linking structure can effectively dissipate energy through disruption and reconstruction of molecular segments, thereby imparting excellent stretchability, self-recoverability and fatigue resistance. In addition, the hydrogel exhibits excellent strain-sensitive resistance changes, which enables it to be assembled as a wearable sensor to monitor human motions. As a result, the hydrogel strain sensor can provide precise feedback for a wide range of human activities, including large-scale joint bending and tiny phonating. Therefore, the tough ionic conductive hydrogel would be widely applied in electronic skin, medical monitoring and artificial intelligence.     

A highly conductive and stretchable wearable liquid metal electronic skin for long-term conformable health monitoring

Conventional rigid electronics are usually unconformable with soft skins and tend to fail in accurate physiological monitoring and precise treatment. Electronic skins (e-Skins) made by conductive and stretchable materials offer mechanical compliance for fabricating flexible and conformable wearables. Compared to common organic or inorganic conductive materials, gallium-based liquid metals alone own superior conductivity and compliance. Here, we demonstrate a highly conductive and stretchable electronic skin with liquid metal circuits (LMCs) embedded in silicone rubber film, which are functionalized for physiological signals monitoring. Through the designs of serpentine structure, LMCs maintained good electrical conductivity and functionality under over 100% strain. Also, a wearable electrocardiogram (ECG) recording device was fabricated and tested. The device was able to acquire steady signals during real-time measurement of physical activities. The proposed liquid metal e-Skin can be further extended to conformable bio-integrated healthcare devices and intelligent health monitoring networks.     

人体动能收集的发电装置研究

传统的化学电池已不能满足现代便携式电子设备快速发展的要求,由此出现了收集人体动能用于发电的技术。借助电场、磁场和压电转换材料,通过直接驱动或振动驱动的方式,将人体动能转换为电能,对便携式电子设备进行充电或构成自供电系统。文章对人体动能收集技术的各类微型发电装置的基本工作原理、发展现状以及微电源管理等进行了综述,探讨了相关的研究方向。     

磁电阻效应的原理及其应用

对几种磁阻效应作用机理和磁阻元件在传感器中的应用进行了综述,详细介绍了几种磁阻传感器的工作原理,对几类常用的磁阻传感器的性能进行了比较,并对磁阻传感器的发展进行了展望.