  Conformable Electronics refers to a class of electronic devices that have the
ability to conformally adhere onto non-planar surfaces and materials, resulting
particularly appealing for skin 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 we present a novel approach for
conformable capacitors based on a free-standing, ultrathin and
ultra-conformable nanosheets of poly (vinyl formal) (PVF), which serve both as
structural and dielectric component of the capacitor. A novel fabrication
approach is proposed and applied to fully free-standing ultrathin capacitors
fabrication, having an overall thickness as low as 200 nm; that represents, to
the best of our knowledge, the thinnest free-standing capacitors ever reported.
Thanks to the ultra-low thickness, the proposed capacitors are able to sustain
flexure to extremely small curvature radii (as low as 1.5 {\mu}m) and to
conform to complex surfaces, such as a nylon mesh with micrometric texture
without compromising their operation.
