Friday, November 24, 2017

Curved Origami Image Sensor

University of Wisconsin-Madison reports that its researchers were able to make a curved image sensor:

A flat silicon sensor "just can’t process images captured by a curved camera lens as well as the similarly curved image sensor — otherwise known as the retina — in a human eye.

Zhenqiang (Jack) Ma has devised a method for making curved digital image sensors in shapes that mimic the convex features of an insect’s compound eye and a mammal’s concave “pinhole” eye.

To create the curved photodetector, Ma and his students formed pixels by mapping repeating geometric shapes — somewhat like a soccer ball — onto a thin, flat flexible sheet of silicon called a nanomembrane, which sits on a flexible substrate. Then, they used a laser to cut away some of those pixels so the remaining silicon formed perfect, gapless seams when they placed it atop a dome shape (for a convex detector) or into a bowl shape (for a concave detector).

“We can first divide it into a hexagon and pentagon structure, and each of those can be further divided,” says Ma. “You can forever divide them, in theory, so that means the pixels can be really, really dense, and there are no empty areas. This is really scalable, and we can bend it into whatever shape we want.”

Pixel density is a boon for photographers, as a camera’s ability to take high-resolution photos is determined, in megapixels, by the amount of information its sensor can capture.

This image shows how the researchers mapped pixels
onto the silicon, then cut some sections away so
the resulting silicon drapes over a dome shape, with
no wrinkles or gaps at the seams.

The open-access paper has been publishes in Nature Communications: "Origami silicon optoelectronics for hemispherical electronic eye systems" by Kan Zhang, Yei Hwan Jung, Solomon Mikael, Jung-Hun Seo, Munho Kim, Hongyi Mi, Han Zhou, Zhenyang Xia, Weidong Zhou, Shaoqin Gong & Zhenqiang Ma

A concave version of the digital image sensor (left)
bends inward for creating a hemispherical focal plane
array. A convex version (right) bends like a soccer
ball for mimicking an insect’s compound eye.
A silicon nanomembrane-based photodiode used for the
electronic eyes. An array of such photodiodes were
printed and fabricated on a pre-cut flexible polyimide


  1. i hope that someday these microfabrication techniques will find applications. They are too clever to waste!

  2. fascinating techniques!

  3. Amateur here: Would it be possible to have flat Si pixels, each as a separate tiny piece and they would be connected with metal "wires" only? :) Small gaps in between.. and maybe you can bend it then!

    1. It seems the reported device is an array of PN junctions so as an image sensor it won't work too well. To move to a more classic image sensor, there should be at least a switch in each pixel, complicating the fabrication and wiring. Perhaps that is next. I am not sure what the advantage of individual pixels wired together would be but maybe it could be more flexible. Passivation of the pixel sidewalls would be important. I think a cluster-based array makes more sense for flexibility and manufacturing, assuming there was an application for this. I did see an interesting presentation from a group of college students making a flexible array of solar cells. Different approach, but similar concepts, including DRIE for etch-thru.

      Stretchable Photovoltaics, University of Maryland
      Team Members: Sabrina Michelle Curtis, Alexander Randolph, Gabriel Anfinrud, Haotian Wang; Advisors: Ray Phaneuf, Nathan Lazarus
      Power Flex: Imagine wearing a traditional solar panel on your back. While useful for charging your smartphone, it's neither lightweight nor particularly comfortable. Now imagine a different kind of solar cell, one the thickness of a piece of paper and woven seamlessly into your clothing. This invention is a silicon solar cell with a unique serpentine structure able to stretch by 30 percent, just like human skin, opening a new era of wearable and renewable power generation.

    2. It could be installed around your beautiful Audi car and give you a warning when you are too close to something ... :)

  4. Awesome, can't imagine how this innovation will affect the adjacent field.

  5. While this is a very cool micro-fabrication technical achievement, I doubt it will affect the imaging that much.

    Nature has been able to form curved sensing surfaces for millions of years - the first "eye" was a concave pit of light sensors that was somewhat directional. To my knowledge, there are no examples of convex imaging surfaces in nature.

    What would the lens for a spherical sensing surface look like? It seems like the only lens solution would be a single lens over each pixel, or a lens over a small group of pixels. I.e. a fly's eye. We already have technologies for assembling arrays of small cameras. I think USD10 now buys you a kilogram of 1/10" VGA cameras in Shenzhen.


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