Solar panels convert light into electricity, image sensors also convert light into electricity. Trying to combine them in a single chip would create a fully autonomous camera. University of Michigan engineers Euisik Yoon and Sung-Yun Park recently came up with just that – a microscopic sensor that both captures the image and stores energy from incident light. The technology was detailed in a study published in IEEE Xplore.
Image: University of Michigan
This is not the first attempt to create such a sensor, but the first prototypes were labor-intensive and had low efficiency. One of the manufacturing techniques involved placing additional photodiodes on the photosensitive surface to store energy, which reduced the amount of light used to form the image.
The prototype sensor created by Yoon and Park is devoid of all these drawbacks. Continuing their research, engineers noticed that some photons slip through a photosensitive diode Photo-Detection diode without causing a build-up of charge. So underneath this diode, they placed an additional photo-voltaic diode, which used the slipping photons to store energy. “It’s not reuse, it’s more like harvesting leftovers,” says Yoon, “It’s actually free energy.”
Image quality at 15 fps left and at 7.5 fps right
Image: University of Michigan.
Since the photoelectric diode layer is located underneath the light-sensitive layer, almost the entire area of the sensor is used for image formation. At the same time, the photoelectric layer captures unused photons, converting them into electricity. The final chip based on this principle is 5 micrometers wide and delivers 998 pW /klx /mm2. In intense daylight of 60000 lux, this is enough to capture images at 15k/s. In normal daylight between 20,000 and 30,000 lux this goes down to 7.5 fps.
The sensor was made primarily to validate the concept itself, and could be further optimized to increase the frame rate or improve low-light performance. The continuation of the project could lead, in the future, to a self-contained camera based on an advanced sensor that would power a tiny microprocessor and a wireless transceiver.
This is fascinating! How exactly does this image sensor function and what specific features make it capable of creating an autonomous camera? Additionally, what potential applications can this technology have in various fields?