Imec touts sub-micron pixels for superior imaging

Paul van Gerven
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Imec has unveiled a method to enable sub-micron pixel CMOS imagers. At the 2023 IEDM in San Francisco, researchers from the Leuven-based institute demonstrated a way of faithfully splitting colors with sub-micron resolution using standard back-end-of-line processing on 300mm wafers. The technology is claimed to elevate camera performance, delivering a higher signal-to-noise ratio and an enhanced color quality with unprecedented spatial resolution.

CMOS imaging strikes a balance between collecting incoming photons, achieving a resolution down to photon size or diffraction limit, and accurately recording the light color. Traditional image sensors with color filters on the pixels are still limited in combining all three requirements. While higher pixel densities would increase the overall image resolution, smaller pixels capture even less light and are prone to artifacts that result from interpolating color values from neighboring pixels. Even though diffraction-based color splitters represent a leap forward in increasing color sensitivity and capturing light, they’re still unable to improve image resolution.

3D visualization (left) en TEM cross-section (right) of the vertical waveguide. Credit: Imec

Imec researcher proposed a fundamentally new way for splitting colors at sub-micron pixel sizes, beyond the fundamental Abbe diffraction limit. Their approach ticks all the boxes for next-generation imagers by collecting nearly all photons, increasing resolution by utilizing very small pixels and rendering colors faithfully. The amount of captured light is estimated to reach over 90 percent within the range of human color perception, making it superior to color filters.

To achieve this, the researchers built an array of vertical Si3N4 multimode waveguides in a SiO2 matrix. The waveguides have a tapered, diffraction-limited sized input 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,” explains Jan Genoe, scientific director at Imec.

Robert Gehlhaar, principal member of technical staff at Imec: “Because this technique is compatible with standard 300mm 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.”

Imec is inviting industry to work together on demonstrating the technology in a real camera.

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