Ultraconformable Freestanding Capacitors Based on Ultrathin Polyvinyl Formal Films

Conformable electronics refers to a class of electronic devices that have the ability to conformally adhere onto nonplanar surfaces and materials, resulting particularly appealing for skin-contact applications, such as the case of skin-worn unobtrusive (bio)sensors for healthcare monitoring. Conformability can be addressed by integrating basic electronic components on ultrathin polymeric film substrates. Among other basic electronic components, capacitors are fundamental ones for energy storage, sensing, frequency tuning, impedance adaptation, and signal processing. In this work, a novel approach for conformable capacitors based on a freestanding, ultrathin, and ultraconformable nanosheet of poly(vinyl formal), which serves as both structural and dielectric component of the capacitor, is presented. A novel fabrication approach is proposed and applied to produce fully freestanding ultrathin capacitors, having an overall thickness as low as 200 nm, which represents the thinnest freestanding capacitors ever reported. Thanks to the ultralow thickness, the proposed capacitors are able to sustain flexure to extremely small curvature radii (as low as 1.5 µm) and to conform to complex surfaces without compromising their operation.