From 2D to 3D: Strain- and elongation-free topological transformations of optoelectronic circuits

Significance We demonstrate a general method to transform planar electronic and optoelectronic devices fabricated by conventional photolithography into a strain-free but topologically different geometry. The method is used to demonstrate hemispherical, retina-like imagers whose pixel spacings are unaffected by the topological transformation. Our approach overcomes the critical limitation of distortion encountered in transforming a planar circuit to a nondevelopable, 3D shape. The process opens up additional possibilities for making a variety of electronic circuits that conform to randomly shaped surfaces, including high resolution, and large field of view imagers that have the shape and form factor of the human eye. Optoelectronic circuits in 3D shapes with large deformations can offer additional functionalities inaccessible to conventional planar electronics based on 2D geometries constrained by conventional photolithographic patterning processes. A light-sensing focal plane array (FPA) used in imagers is one example of a system that can benefit from fabrication on curved surfaces. By mimicking the hemispherical shape of the retina in the human eye, a hemispherical FPA provides a low-aberration image with a wide field of view. Due to the inherently high value of such applications, intensive efforts have been devoted to solving the problem of transforming a circuit fabricated on a flat wafer surface to an arbitrary shape without loss of performance or distorting the linear layouts that are the natural product of this fabrication paradigm. Here we report a general approach for fabricating electronic circuits and optoelectronic devices on nondevelopable surfaces by introducing shear slip of thin-film circuit components relative to the distorting substrate. In particular, we demonstrate retina-like imagers that allow for a topological transformation from a plane to a hemisphere without changing the relative positions of the pixels from that initially laid out on a planar surface. As a result, the resolution of the imager, particularly in the foveal region, is not compromised by stretching or creasing that inevitably results in transforming a 2D plane into a 3D geometry. The demonstration provides a general strategy for realizing high-density integrated circuits on randomly shaped, nondevelopable surfaces.