CHAPTER 2: No More Rigid Boxes—Fully Flexible and Transparent Electronics

Unlike today's electronics based on rigid silicon technologies, stretchable devices can conform to almost any kind of surface shape and provide unique functionalities, which are unreachable with a simple extension of conventional technologies. Flexible electronics are mechanically robust electronics that can be bent, folded, crumpled and stretched and are a major research focus of nanotechnology scientists towards next-generation wearable and implantable devices. This promises an entirely new design factor for novel devices: ultra-thin smartphones that wrap around the wrist; flexible displays that fold out as newspapers or as large as a television; photovoltaic cells and reconfigurable antennas that conform to the body parts of our cars; adhesive sensor patches for the skin; or flexible implants that can monitor and treat cancer. To get electronics out of their rigid casings and integrated into flexible materials such as textiles or even stretchable biomedical devices that interface directly with organs such as the skin, heart and brain, researchers have come up with solutions ranging from hydrogel electrodes in dielectric elastomers to stretchable supercapacitors using buckled carbon nanotube (CNT) macrofilms, CNT-coated cotton yarns and sponges. In order to fabricate entirely flexible electronic devices, the components that power them—such as batteries—not only need to be fully flexible as well, but they have to be compatible with commercially available manufacturing technologies. This would require achieving a high degree of deformability without using elastomeric materials.