Flexible Thin-Film InGaAs Photodiode Focal Plane Array

Natural imaging systems such as the retina and the compound eye employ a conformal architecture that provides an aberration-free image with wide field of view (FOV) and very low f /number. However, most artificial imagers such as conventional cameras are limited to a planar architecture demanded by the use of brittle semiconductor focal plane arrays (FPAs). High-resolution image formation on this flat field requires multiple bulky optical elements. Here we demonstrate a general approach to fabricating complex circuits and in particular FPAs on flexible and/or conformable substrates that can be shaped to overcome these fundamental limitations. An 8 × 100, lightweight, thin-film In 0.53 Ga 0.47 As p - i - n photodiode FPA with sensitivity to wavelengths as long as λ = 1650 nm is fabricated on a thin flexible plastic foil following transfer by adhesive-free bonding of the epitaxial layers that are subsequently lifted off from the parent InP substrate. The array is shaped into either a convex cylindrically curved imager to achieve a 2π FOV or, when formed into a concave shape, to provide high-resolution and compact spectral decomposition over a wide wavelength range. The array exhibits ∼99% fabrication yield with ∼100% peak external quantum efficiency at λ = 1300 nm. The unique features of this flexible thin-film FPA provide a new paradigm for realizing advanced electronic and imaging applications.