<p>Flexible electronics isn&rsquo;t a new technology, but it has achieved a remarkable progress over the past years and has become increasingly important to many sectors such as consumer electronics, automotive, retail and healthcare. <a href="https://www.prnewswire.com/news-releases/idtechex-global-research-report-on-flexible-printed-and-organic-electronics-2019-2029-forecasts-players--opportunities-300799688.html" target="_blank">IDTechEx analysts forecast</a> that the total market for printed, flexible and organic electronics will grow from $31.7 billion in 2018 to $77.3 billion in 2029.&nbsp;</p><p>Flexible electronics is a technology that allows you to build electronic circuits on flexible substrates thus making them bendable and stretchable. It enables new product paradigms that aren&rsquo;t possible with conventional semiconductors and glass substrates. Here we explore some of the attributes of flexible electronics that make this tech attractive to product designers and consumers alike.</p><h2><strong>Flexible</strong></h2><p>Transistors can be made from either inorganic or organic materials, or a mix of both. FlexEnable fabricates transistors using organic materials which replace the silicon and hard ceramic materials with soft, carbon-based materials. The organic thin-film transistors (OTFTs) we use are known as&nbsp;<a href="https://www.flexenable.com/services/otft-materials/" target="_blank" title="FlexiOM™">FlexiOM&trade;</a> - they are inherently flexible and have greater performance than amorphous silicon. These high-performance OTFTs can be processed at temperatures lower than 100&deg;C allowing for the use of&nbsp;lower cost thin film substrates thus enabling flexible devices.</p><p>While flexible electronics have many applications, at FlexEnable we are primarily focused on flexible displays. Yet, our flexible OTFT platform can drive&nbsp;<a href="https://www.flexenable.com/technology/flexible-sensor-arrays/" target="_blank">flexible sensors</a> and other flexible devices. This platform has enabled the development of <a href="https://www.flexenable.com/technology/flexible-olcd/" target="_blank">flexible organic LCD</a>s&nbsp;(OLCDs) that can bend down to 10mm and be scaled to large areas making them suitable for a range of applications including automotive, consumer electronics, smart home appliances and digital signage.</p><h2><strong>Light and thin</strong></h2><p>Display thickness and weight are especially important features for applications that require large area displays such as automotive and digital signage. Using a flexible substrate (instead of glass) in combination with organic transistors helps make the whole stack very thin. For example at FlexEnable we use low-cost bio-based substrates such as TAC (tri acetyl cellulose) which are just a fraction of a tenth of a millimetre thick. As a result the entire OLCD is just 0.3mm thick (without the backlight). Moreover, the thinness and flexibility of&nbsp;<a href="https://www.flexenable.com/newsroom/breakthrough-in-glass-free-olcd-technology-enables-bezel-less-displays-for-notebooks/" target="_blank">OLCD enables bezel-less displays</a> through curved edges and folded borders. This brings huge value in applications like notebooks and tablets where borderless means bigger displays for the same sized device. <a href="https://www.flexenable.com/Blog/why-certain-plastic-substrates-are-an-ideal-alternative-to-glass-for-lcd/" target="_blank">The extreme thinness of TAC substrates also brings optical advantages to OLCD.</a></p><h2><strong>Unbreakable</strong></h2><p>One property of flexible electronics which deserves to be highlighted is their robustness. This makes a great difference for applications such as wearables, notebooks and other consumer electronics which traditionally feature glass-based displays or sensors. Incorporating an unbreakable, glass-free active matrix display could become a unique selling point for consumers.</p><h2><strong>Cost advantage</strong></h2><p>The processes and materials for manufacturing flexible electronics differ, but the aim is to make them lower cost than conventional electronics. <a href="https://www.flexenable.com/blog/enabling-flexible-electronics-from-the-roll/" target="_blank">Roll to roll printing</a> has been long considered the ultimate approach to the cost-effective manufacture of electronics over large and small areas. It will remove the waste of materials currently incurred in factories and will drive product costs down. However, there are a few steps to overcome before roll to roll printing becomes the norm.</p><p>At FlexEnable we have developed a practical approach to the cost-effective manufacture of flexible electronics for flexible displays and sensors. Our processes are compatible with existing flat panel display lines meaning that all of the existing equipment can be reused. A maximum processing temperature below 100&deg;C allows for the use of&nbsp;lower cost flexible substrates (e.g. TAC) and minimises&nbsp;distortion (improves yield), whilst enabling a low cost, high yield method of handling flexible substrates.</p><h2><strong>Innovation</strong></h2><p>For brands and designers to keep innovating and developing next generation products, they need tools and components that will enable them to do this. Flexible electronics allow the development of flexible components such as flexible displays and sensors which remove form factor constraints and give designers creative freedom. A typical example is the automotive industry where designers are already thinking outside the box by reinventing the car interior with the help of flexible displays. French company Novares, for example, has demonstrated how flexible display technology can help improve design and safety by integrating conformable OLCDs supplied by FlexEnable&nbsp;into the interior of their demo car&nbsp;<a href="https://www.novaresteam.com/our-solutions/novacar-2-an-open-innovation-lab/" target="_blank">Nova Car 2</a>.</p>

Flexible electronics isn’t a new technology, but it has achieved a remarkable progress over the past years and has become increasingly important to many sectors such as consumer electronics, automotive, retail and healthcare.

Five benefits of flexible electronics for displays and sensors

<p>The rapid development of flexible and wearable electronics is giving rise to an exciting range of applications, from smart watches and flexible displays&mdash;such as smart phones, tablets, and TV&mdash;to smart fabrics, smart glass, transdermal patches, sensors, and more. With this rise, demand has increased for high-performance flexible batteries. Up to now, however, researchers have had difficulty obtaining both good flexibility and high energy density concurrently in lithium-ion batteries.&nbsp;</p><p><span class="fr-img-caption fr-fic fr-dib" style="width: 1114px;"><span class="fr-img-wrap"><img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1578070497445-fig1a-1b-newsite.jpg"><span class="fr-inner">Schematic of the structure and the fabrication process of Yang&#39;s spine-like battery. (a) Schematic illustration of bio-inspired design, the vertebrae correspond to thick stacks of electrodes and soft marrow corresponds to unwound part that interconnects all the stacks. (b) The process to fabricate the spine-like battery, multilayers of electrodes were first cut into designed shape, then strips extending out were wound around the backbone to form spine-like structure.&nbsp;<style type="text/css"></style><style type="text/css"></style><span data-sheets-userformat='{"2":769,"3":{"1":0},"11":3,"12":0}' data-sheets-value='{"1":2,"2":"Images And Video Courtesy: Yuan Yang/Columbia Engineering"}'>Images And Video Courtesy: Yuan Yang/Columbia Engineering</span>&nbsp;</span></span></span></p><p>A team led by Yuan Yang, assistant professor of <a href="http://apam.columbia.edu/materials-science-and-engineering-0" target="_blank">materials science and engineering</a> in the <a href="http://apam.columbia.edu/" target="_blank">department of applied physics and mathematics</a> at <a href="http://www.engineering.columbia.edu/" target="_blank">Columbia Engineering</a>, has developed a prototype that addresses this challenge: a Li-ion battery shaped like the human spine that allows remarkable flexibility, high energy density, and stable voltage no matter how it is flexed or twisted. The <a href="http://onlinelibrary.wiley.com/doi/10.1002/adma.201704947/full" target="_blank">study</a> is published today in <a href="http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1521-4095" target="_blank"><em>Advanced Materials</em></a>.</p><p>&ldquo;The energy density of our prototype is one of the highest reported so far,&rdquo; says Yang. &ldquo;We&rsquo;ve developed a simple and scalable approach to fabricate a flexible spine-like lithium ion battery that has excellent electrochemical and mechanical properties. Our design is a very promising candidate as the first-generation, flexible, commercial lithium-ion battery. We are now optimizing the design and improving its performance.&rdquo;</p><p><span class="fr-video fr-deletable fr-fvc fr-dvb fr-draggable" contenteditable="false" draggable="true"><iframe src="https://www.youtube.com/embed/JGpzSF0p1Xg?&wmode=opaque" frameborder="0" allowfullscreen="" class="fr-draggable" style="width: 1115px; height: 621px;"></iframe></span><em>Video demonstrating flexibility of Yang&#39;s lithium-ion battery powering a smart watch, in flat, flexed, and twisted configurations. <style type="text/css"></style><style type="text/css"></style><span data-sheets-userformat='{"2":769,"3":{"1":0},"11":3,"12":0}' data-sheets-value='{"1":2,"2":"Images And Video Courtesy: Yuan Yang/Columbia Engineering"}'>Images And Video Courtesy: Yuan Yang/Columbia Engineering</span>&nbsp;</em></p><p>Yang, whose <a href="http://blogs.cuit.columbia.edu/yanggroup/" target="_blank">group</a> explores the composition and structure of battery materials to realize high performance, was inspired by the suppleness of the spine while doing sit-ups in the gym. The human spine is highly flexible and distortable as well as mechanically robust, as it contains soft marrow components that interconnect hard vertebra parts. Yang used the spine model to design a battery with a similar structure. His prototype has a thick, rigid segment that stores energy by winding the electrodes (&ldquo;vertebrae&rdquo;) around a thin, flexible part (&ldquo;marrow&rdquo;) that connects the vertebra-like stacks of electrodes together. His design provides excellent flexibility for the whole battery.</p><p align="left">&ldquo;As the volume of the rigid electrode part is significantly larger than the flexible interconnection, the energy density of such a flexible battery can be greater than 85 percent of a battery in standard commercial packaging,&rdquo; Yang explains. &ldquo;Because of the high proportion of the active materials in the whole structure, our spine-like battery shows very high energy density&mdash;higher than any other reports we are aware of. The battery also successfully survived a harsh dynamic mechanical load test because of our rational bio-inspired design.&rdquo;</p><p align="left"><span class="fr-video fr-deletable fr-fvc fr-dvb fr-draggable" contenteditable="false" draggable="true"><iframe src="https://www.youtube.com/embed/CDJpnqT_Y0c?&wmode=opaque" frameborder="0" allowfullscreen="" class="fr-draggable" style="width: 1115px; height: 630px;"></iframe></span><em>Video of the dynamic mechanical load test demonstrating flexibility of Yang&#39;s lithium-ion battery. <style type="text/css"></style><style type="text/css"></style><span data-sheets-userformat='{"2":769,"3":{"1":0},"11":3,"12":0}' data-sheets-value='{"1":2,"2":"Images And Video Courtesy: Yuan Yang/Columbia Engineering"}'>Images And Video Courtesy: Yuan Yang/Columbia Engineering</span>&nbsp;</em></p><p>Yang&rsquo;s team cut the conventional anode/separator/cathode/separator stacks into long strips with multiple &ldquo;branches&rdquo; extending out 90 degrees from the &ldquo;backbone.&rdquo; Then they wrapped each branch around the backbone to form thick stacks for storing energy, like vertebrae in a spine. With this integrated design, the battery&rsquo;s energy density is limited only by the longitudinal percentage of vertebra-like stacks compared to the whole length of the device, which can easily reach over 90 percent.</p><p>The battery shows stable capacity upon cycling, as well as a stable voltage profile no matter how it is flexed or twisted. After cycling, the team disassembled the battery to examine the morphology change of electrode materials. They found that the positive electrode was intact with no obvious cracking or peeling from the aluminum foil, confirming the mechanical stability of their design. To further illustrate the flexibility of their design, the researchers continuously flexed or twisted the battery during discharge, finding that neither bending nor twisting interrupted the voltage curve. Even when the cell was continuously flexed and twisted during the whole discharge, the voltage profile remained. The battery in the flexed state was also cycled at higher current densities, and the capacity retention was quite high (84 percent at 3C, the charge in 1/3 of an hour). The battery also survived a continuous dynamic mechanical load test, rarely reported in earlier studies.</p><p align="left">&ldquo;Our spine-like design is much more mechanically robust than are conventional designs,&rdquo; Yang says. &ldquo;We anticipate that our bio-inspired, scalable method to fabricate flexible Li-ion batteries could greatly advance the commercialization of flexible devices.&rdquo;</p>

Schematic of the structure and the fabrication process of Yang's spine-like battery. (a) Schematic illustration of bio-inspired design, the vertebrae correspond to thick stacks of electrodes and soft marrow corresponds to unwound part that interconnects all the stacks. (b) The process to fabricate the spine-like battery, multilayers of electrodes were first cut into designed shape, then strips extending out were wound around the backbone to form spine-like structure. Images And Video Courtesy: Yuan Yang/Columbia Engineering

Shaped like a spine, new design enables remarkable flexibility, high energy density, and stable voltage no matter how it is flexed or twisted

Engineers Develop Flexible Lithium Battery for Wearable Electronics

<p>Researchers from Carnegie Mellon University&rsquo;s College of Engineering and the Institute of Systems and Robotics of the University of Coimbra, Portugal have developed a simple, efficient method to make robust, highly flexible, tattoo-like circuits for use in wearable computing. The low-cost process adds trace amounts of an electrically-conductive, liquid metal alloy to tattoo paper that adheres to human skin. These ultrathin tattoos can be applied easily with water, the same way one would apply a child&rsquo;s decorative tattoo with a damp sponge.</p><p>Other tattoo-like electronics either require complex fabrication techniques inside a cleanroom or lack the material performance required for stretchable digital circuit functionality on skin.</p><p><img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1573729030390-1011-em-carmel-tattoo-1.png" style="width: 1114px;" class="fr-fic fr-dib"></p><p><em>The tattoos can conform and adhere to highly curved 3D surfaces, like a model of the human brain.</em></p><p>Carmel Majidi, an associate professor of mechanical engineering and the director of the&nbsp;<a href="http://sml.me.cmu.edu/" rel="noopener" target="_blank">Soft Machines Lab</a> at Carnegie Mellon, and Mahmoud Tavakoli, the director of the&nbsp;<a href="https://sites.google.com/site/fsrlabisr/" rel="noopener" target="_blank">Soft and Printed Microelectronics Laboratory</a> <a href="https://sites.google.com/site/fsrlabisr/" target="_blank"></a>at the University of Coimbra, teamed up to develop methods for direct printing of stretchable electronic circuits.</p><p>Their collaboration succeeded.&nbsp;</p><p>&ldquo;This is a breakthrough in the printed electronics area,&rdquo; said Tavakoli. &ldquo;We showed for the first time that inkjet-printed patterns of silver nano particles can be sintered at room temperature using the gallium indium alloy. Removing the need for high temperature sintering makes our technique compatible with thin-film and heat sensitive substrates.&rdquo;</p><blockquote><p>The technique is simple. The tattoos are ultrathin, very stretchable, and inexpensive to produce.</p></blockquote><p>In addition to low-cost processing, these tattoos provide other advantages. Because they have mechanical properties similar tolightweight fabrics, they remain functional under bending, folding, twisting, and strains above 30% (which is the typical stretchability of human skin). They can conform and adhere to highly curved 3D surfaces, like a model of a human brain or a lemon.</p><p>Applications for ultrathin, compliant tattoos include epidermal biomonitoring, soft robotics, flexible displays, and 3D-transferable printed electronics.</p><p>The findings were published in <em>Advanced Materials&nbsp;</em>in a paper titled &ldquo;<a href="https://doi.org/10.1002/adma.201801852" rel="noopener" target="_blank">EGaIn‐Assisted Room‐Temperature Sintering of Silver Nanoparticles for Stretchable, Inkjet‐Printed, Thin‐Film Electronics</a>.&rdquo;</p><p><br></p><p>Carmel Majidi explains the technology behind the electronic tattoos:</p><p><span class="fr-video fr-deletable fr-fvc fr-dvb fr-draggable" contenteditable="false" draggable="true"><iframe src="https://www.youtube.com/embed/OaITzyMptFQ?&wmode=opaque" frameborder="0" allowfullscreen="" class="fr-draggable" style="width: 1115px; height: 619px;"></iframe></span><em>Video credit: Institute of Systems and Robotics of the University of Coimbra, Portugal and College of Engineering, Carnegie Mellon University</em> </p>

The ultrathin tattoos can be applied and removed easily with water, similar to deorative, temporary tattoos.

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Five benefits of flexible electronics for displays and sensors

Engineers Develop Flexible Lithium Battery for Wearable Electronics

Electronic tattoos for wearable computing