According to imec, this technology will elevate high-end camera performance, delivering higher signal-to-noise ratio, enhanced colour quality with spatial resolution.
Designing next-generation CMOS imagers requires striking a balance between collecting all incoming photons, achieving a resolution down to photon size or diffraction limit, and accurately recording the light colour.
Traditional image sensors with colour 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 colour values from neighbouring pixels.
Even though diffraction-based colour splitters represent a leap forward in increasing colour sensitivity and capturing light, they are still unable to improve image resolution.
Imec has proposed a fundamentally new way for splitting colours at sub-micron pixel sizes (i.e., beyond the fundamental Abbe diffraction limit) using standard back-end processing.
Their approach works by collecting nearly all photons, increasing resolution by utilising very small pixels, and rendering colours faithfully.
To achieve this, imec researchers have built an array of vertical Si3N4 multimode waveguides in an SiO2 matrix. The waveguides have a tapered, diffraction-limited sized input (e.g., 800nm2) 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 Pwaveguides corresponding to a specific colour", explained Prof. Jan Genoe, Scientific Director at imec.
The total output light from each waveguide is estimated to reach over 90% within the range of human colour perception (wavelength range 400-700nm), making it superior to colour filters.
Robert Gehlhaar, Principal Member of Technical Staff at imec said, “Because this technique is compatible with standard 300-mm processing, the splitters can be produced cost-efficiently. This enables further scaling of high-resolution imagers, with the goal to detect every incident photon and its properties. Our ambition is to become the future standard for colour imaging with diffraction-limited resolution. We are welcoming industry partners to join us on this path towards full camera demonstration.”
Image: RGB camera measurement (100x magnification) of an array of waveguides with alternating 5 left-side-open-aperture and 5 right-side open-aperture (the others being occluded by TiN) waveguides at a 1-micron pitch. Yellow light exits at the right part of the waveguide, whereas the blue exits at the left. The wafer is illuminated using plane wave white light.
