Origami technique turns flat optical sensors into hemispherical eyes

November 30, 2017 // By Julien Happich
Origami technique turns flat optical sensors into hemispherical eyes
Today's planar digital image sensors simply inherit their form factor from the substrates and semiconductor processes used in their volume manufacture. But more and more research groups are pursuing the benefits of curved hemispherical sensors, mimicking the optimized optics of biological eye systems.

While vertebrates evolved with globe-shaped eyes, with a concave retina behind a spherical lens (and the iris as a pin-hole), insects mostly sport convex multi-faceted compound eyes. Both approaches offer a wider field of view and lower aberrations than our made-made planar sensors. Yet, conforming high-resolution semiconductor-based sensors into hemispherical domes (inward or outward) presents its own challenges.

Now, a team of researchers from the University of Wisconsin Madison leveraged Japanese paper folding technique "origami" to shape silicon optoelectronic sensors into near perfect hemispherical sensor arrays.

The origami shaping process: a net of half truncated
icosahedron based on silicon nano-membranes is
pressed into hemispherical concave or convex molds.

Publishing their results in Nature Communications under the title "Origami silicon optoelectronics for hemispherical electronic eye systems", the researchers explain how they took advantage of traditional planar fabrication techniques to design an array of silicon-based lateral P–i–N photodiodes, laid out to form a large net of pentagon- and hexagon-shaped single photodetectors forming the flattened subdivisions of a half-truncated icosahedron (think of a soccer ball cut along carefully chosen seams).

Once lifted off their original substrate and transfer-printed to a flexible one, the thin-film array of photodiodes was cut-out along specific contours using a precision laser so the subdivisions' edges could then be jointly folded into a perfectly matching concave or convex hemispherical mould.

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