Surface and mechanical analysis of metallized poly(dimethylsiloxane) gel for varifocal micromirrors

Abstract

Varifocal micromirrors are alternative and miniaturized mirror systems that are used for imaging procedures in biomedical diagnostics, mirror‐based tunable lenses, or the correction of spherical aberration. In this study, we demonstrate a new concept for focal length variation by electrostatic mirror deformation of a compact and integrated electroactive polymer actuator based on metallized poly(dimethylsiloxane) (PDMS) gel thin films. The varifocal micromirrors have a lateral size of 70 × 70 μm2 and are capable of deforming in either convex or concave direction, depending on a defined surface treatment by O2‐plasma or UV/ozone of the PDMS prior to metallization by physical vapor deposition (PVD). Surface and interface analysis by wetting experiments, sputter depth‐profiling X‐ray photoelectron spectroscopy (XPS) combined with scanning electron microscopy (SEM) on cross‐sections processed with focused ion beam (FIB) as well as polymer and metal surfaces are used to understand and to improve the metal film growth and quality with respect to high reflectivity and conductivity. In addition to the high quality of the metallic mirror layer, the mirror displacement is important and inevitably depends on the gel stiffness of the actuator. Therefore, we investigate the gel mechanics and the performance of the actuator with rheology, confocal microscopy, and image formation on the electrically deformed mirrors. Our concept of varifocal micromirrors offers a wide range of applications for tunable mirror‐based optics due to their simple and compact design.