Tunable curvature of large visible CMOS image sensors: Towards new optical functions and system miniaturization

Since few years, there has been an increasing interest and demand for foldable, stretchable and flexible electronics for different application areas, such as defense/military, astronomy, meteorology, medicine, biotechnologies and consumer applications. In this work, we propose a new packaging development on tunable curvature of CMOS image sensors. First, based on an existing fisheye design, the optical benefits of a Tunable Curved Focal Plane Array (T-CFPA) are detailed and quantified. T-CFPA technology allows to compensate for the Petzval Field Curvature Aberration (FCA) and drastically simplifies the optical design (by saving up to 35% of the number of required optical surfaces). Our CMOS sensor curving process is introduced to highlight new packaging constraints in comparison to conventional CMOS image sensors. Mechanical and thermomechanical Finite Element Analyses (FEA) have been performed to define, understand and optimize the T-CFPA packaging while curving. Using 3D-printing fast prototyping, T-CFPA prototypes have been realized. Thanks to topology characterizations, we proved that our packaging approach for T-CFPA is compatible with spherical shape curving. Moreover, the +infinity to 280 mm radius range capability was shown on a 100 mu m thick, 20*23 mm CMOS image sensor prototype.