Design and fabrication of silicon-tessellated structures for monocentric imagers

Abstract

Compared with conventional planar optical image sensors, a curved focal plane array can simplify the lens design and improve the field of view. In this paper, we introduce the design and implementation of a segmented, hemispherical, CMOS-compatible silicon image plane for a 10-mm diameter spherical monocentric lens. To conform to the hemispherical focal plane of the lens, we use flexible gores that consist of arrays of spring-connected silicon hexagons. Mechanical functionality is demonstrated by assembling the 20-μm-thick silicon gores into a hemispherical test fixture. We have also fabricated and tested a photodiode array on a siliconon-insulator substrate for use with the curved imager. Optical testing shows that the fabricated photodiodes achieve good performance; the hemispherical imager enables a compact 160°field of view camera with 480% fill factor using a single spherical lens.

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

“…3D presents the EQE spectrum of a photodiode. We observe EQE > 80% at λ > 650 nm, which to our knowledge is above those reported for other hemispherical imagers (5,8,22,27,32). The photodetector noise equivalent power (NEP) is NEP = ffiffiffiffiffiffiffiffiffi ffi 2qI D p =RðλÞ under shot-noise-limited detection at −1 V, where q is the electron charge, I D is the dark current, and RðλÞ is the responsivity at a given wavelength λ.…”

“…to correct these aberrations that increase the complexity, weight, and cost, while often decreasing the functionality of the imaging system. Many efforts, therefore, have been made to shape the FPA into a hemisphere (1,4,5,8,19,22,(26)(27)(28)(29). Fabricating arrays on retina-like hemispherical surfaces (5,22,30,31), however, introduces significant challenges.…”

“…However, the gaps between pixels reserved for the bridges result in a loss of resolution, particularly near the central "fovea" at the point of maximum strain. Recently, origami-inspired hemispherical FPAs were reported (8,27,32) with high deformability and pixel counts that were achieved by cutting, folding, and mating sections to form an approximately hemispherical shape. This process does not result in a perfect conformation to a hemisphere, leading to undesirable optical aberrations and image stitching errors.…”

Bioinspired Artificial Eyes: Optic Components, Digital Cameras, and Visual Prostheses

“…i) Magnified view of the kirigami‐based device's high pixel density. Reproduced with permission . Copyright 2016, Nature Publishing Group.…”

“…In this scheme, a photodetector array with an elaborate petal pattern is fabricated (Figure g, left) and then transferred to a concave hemispherical holder (Figure g, right). Recently, Wu et al reported a hemispherical Si‐based photodetector array by applying the kirigami method (Figure h) . Si of thickness <20 µm supplies material flexibility, and the tessellated hexagonal structures enable structural flexibility, both of which help form a hemispherical imager.…”