Flexible Electronics: Status, Challenges and Opportunities

Abstract

The concept of flexible electronics has been around for several decades. In principle, anything thin or very long can become flexible. While cables and wiring are the prime example for flexibility, it was not until the space race that silicon wafers used for solar cells in satellites were thinned to increase their power per weight ratio, thus allowing a certain degree of warping. This concept permitted the first flexible solar cells in the 1960s (Crabb and Treble, 1967). The development of conductive polymers (Shirakawa et al., 1977), organic semiconductors, and amorphous silicon (Chittick et al., 1969; Okaniwa et al., 1983) in the following decades meant huge strides toward flexibility and processability, and thus these materials became the base for electronic devices in applications that require bending, rolling, folding, and stretching, among other properties that cannot be fulfilled by conventional electronics (Cheng and Wagner, 2009) (Figure 1). Presently there is great interest in new materials and fabrication techniques which allow for highperformance scalable electronic devices to be manufactured directly onto flexible substrates. This interest has also extended to not only flexibility but also properties like stretchability and healability which can be achieved by utilizing elastomeric substrates with strong molecular interactions (Oh et al., 2016; Kang et al., 2018). Likewise, biocompatibility and biodegradability has been achieved through polymers that do not cause adverse effect to the body and can be broken down into smaller constituent pieces after utilization (Bettinger and Bao, 2010; Irimia-Vladu et al., 2010; Liu H. et al., 2019). This new progress is now enabling devices which can conform to complex and dynamic surfaces, such as those found in biological systems and bioinspired soft robotics. These next-generation flexible electronics open up a wide range of exciting new applications such as flexible lighting and display technologies for consumer electronics, architecture, and textiles, wearables with sensors that help monitor our health and habits, implantable electronics for improved medical imaging and diagnostics, as well as extending the functionality of robots and unmanned aircraft through lightweight and conformable energy harvesting devices and sensors. While conventional electronics are very capable of these functions, flexible electronics are intended to expand the mechanical features to adhere to novel form factors through hybrid strategies, or as standalone solutions where the application does not require high computation power, intended to be highly robust to deformation, low cost, thin, or disposable. The definition of flexibility differs from application to application. From bending and rolling for easier handling of large area photovoltaics, to conforming onto irregular shapes, folding, twisting, stretching, and deforming required for devices in electronic skin, all while maintaining device performance and reliability. While early progress and many important innovations have alre...

Mechanical Properties of Organic Electronic Polymers on the Nanoscale

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electronic polymers, have played a pivotal role in the development of flexible and printed electronics over the last two decades. [1][2][3] Composed from rings and chains of carbon atoms, these materials sport a low mass density, as well as electronic, optical, and mechanical properties that are tailored through the chemical design of their constituent molecular units. Weak inter-chain van der Waals bonding within thin films of stacked conjugated organic polymers renders them soft, with intrinsically low Young's moduli several orders of magnitude smaller than conventional inorganic semiconductors such as silicon.

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A compact evolved antenna for 5G communications

“…With the advent of 5G and new 6G network infrastructures, flexible and bendable IoT devices are becoming increasingly popular 1 , 2 . In this regard, the conception of wearable and bendable antennas is a crucial issue to overcome 3 , 4 .…”

An Aptasensor Based on a Flexible Screen-Printed Silver Electrode for the Rapid Detection of Chlorpyrifos

“…Ag ink was chosen over gold because of its cost-effectiveness and over the well-studied carbon because of its higher conduction and faster electron transfer rate [ 33 , 34 ]. The screen printing technique provides several extra benefits, such as roll-to-roll large production, ability to withstand mechanical stress, easy implementation, and adaptability, if compared to other printing methods [ 35 , 36 , 37 , 38 , 39 ]. Moreover, a flexible and low-cost polymeric (polyethylene terephthalate (PET)) substrate was used, in order to pave the way to the use of scalable fabrication techniques and achieve advantages such as being unbreakable, light, and thin in weight, as well as the possibility to apply innovative ideas [ 40 ].…”