The IMEC research institute has developed a novel pixel architecture that could impact image sensor design and performance. The architecture will be reported at the 2023 International Electron Devices Meeting in San Francisco.
IMEC has issued a call for industry partners to join it in creating a camera demonstrator for the technology. There appear to be no reasons why the pixel architecture cannot be applied to event-based image sensors.
Conventionally image sensors for light in the visible spectrum – wavelengths of 400nm to 700nm – have pixels at dimensions of several microns in order to collect enough light. Higher resolution image sensors therefore require larger and more expensive die.
While scaling pixels to sub-micron dimensions is desirable for cost and energy considerations it creates problems in terms of interference and diffraction effects and the numbers of photons collected and optical sensitivity in terms of color.
IMEC researchers are due to present a different way to render color allied to pixels with sub-micron dimensions that can be manufactured using standard back-end-of-line processing on 300mm-diameter wafers. The technology will allow higher spatial resolutions while delivering higher signal-to-noise ratio and enhanced color quality, the institute claims.
Getting the color right
Diffraction based color splitting – rather than the use of color filters – has already been shown to improve color sensitivity but this does not address image resolution. The general impasse is that small pixels while allowing higher image resolution would capture less light and are prone to artifacts from interpolating color values from neighboring pixels, IMEC said in a statement.
The sub-micron pixel architecture increases image resolution, collects nearly all photons and renders colors faithfully, IMEC said. The researchers have built an array of vertical Si3N4 multimode waveguides on an SiO2 matrix. The waveguides have a tapered, diffraction-limited input of 800nm by 800nm to collect all the incident light.
“In each waveguide, incident photons are exciting both symmetric and asymmetric modes, which propagate through the waveguide differently, leading to a unique “beating” pattern between the two modes for a given frequency. This beating pattern enables a spatial separation at the end of the waveguides corresponding to a specific color”, explained Professor Jan Genoe, scientific director at IMEC, in the statement. The total output light from each waveguide is estimated to reach over 90 percent within the range of human color perception making it superior to color filters. The location of an aperture at the reverse of the silicon-dioxide matrix determines what color of light exits.
IMEC has produced silicon with waveguides on a 1-micron pitch.
Robert Gehlhaar, principal member of the technical staff at IMEC, commented: “Because this technique is compatible with standard 300mm [wafer] processing, the splitters can be produced cost-efficiently. This enables further scaling of high-resolution imagers, with the ultimate goal to detect every incident photon and its properties. Our ambition is to become the future standard for color imaging with diffraction-limited resolution. We are welcoming industry partners to join us on this path towards full camera demonstration.”