An image sensor consisting of a flat circuit board has served digital camera photographers well for many years. However, the ultimate image sensor -– the human eye -– is far from flat.
Does that mean there's a better way to create digital photographs, one that more closely mimics the human eye? Researchers at Northwestern University in Evanston, Ill., and at the University of Illinois at Urbana-Champaign are developing technologies for future cameras that could help answer that question in a few years.
The researchers are making use of a curved image sensor to create better images. The curved image sensor records images while working more like the inside of the human eye, which is naturally curved.
Unlike a flat image sensor, a curved sensor is able to provide sharp imaging of all aspects of photo. The curved sensor especially outperforms the flat sensor at the edges of the photo when using simple imaging optics.
Curved Image Sensor
Northwestern professors Yonggang Huang and Joseph Cummings teamed with Professor John Rogers of the University of Illinois to create the curved image sensor, which consists of silicon detectors and electronics that conform to the curved surface. When the digital camera takes a photo using this technology, the curved area captures the image by becoming the focal point for the camera lens, much like the back of the human eye is the focal point for light entering the eye.
With a flat image sensor, the camera lens must reflect an image several different times to strike the image sensor in the proper configuration to create the image. A curved sensor would not require numerous reflections, theoretically leading to greatly improved image quality.
In releasing their findings, the researchers say various designers have worked on creating a curved image sensor for more than 20 years. It has been a difficult process because silicon breaks under the pressure required to create curvature. The semiconductor materials used in an image sensor are brittle, too.
They worked around this problem by stretching a curved, thin, elastic polymer (elastomeric) membrane until it became flat; think of it like stretching a skin over a drum. The researchers then placed tiny digital photography electronics – sensors and associated circuitry – over the flat membrane.
With everything in place, they returned the elastic polymer to its curved shape. The brittle electronics are so small – measuring about 100 by 100 micrometers – that they aren't affected when the membrane is curved again. One micrometer is equal to a millionth of a meter, or about .00004 inches. To further take the stress off the electronics, the researchers connect the electronics with arc-shaped metal wires rather than brittle traces, as shown in the photo above.
During the early testing phase, the researchers found that more than 99% of the electronics continued to operate after the membrane's curvature was returned, providing promising early results.
The research into the capabilities of the curved electronics isn't limited to digital cameras and image sensors. Huang and Rogers are looking at using the curved electronics in items such as solar panels, or medical devices that must be attached to the curves of the human body.
Obviously, a curved image sensor is at least a few years away from finding its way into a digital camera that you can purchase. The researchers are still in the very early phases of developing the technology, although they say they have proven that a curved image sensor will work.
Next, the researchers must determine a way to add pixels to the curved sensor digital camera and continue to create electronics that will survive under the stress of a curved surface. They have to keep the technology cost effective, too; the National Science Foundation and U.S. Department of Energy have helped fund the research thus far.
Despite the remaining challenges, there's no doubt that it's worth keeping an eye on this technology.