Highly Selective Color Filters Based on Hybrid Plasmonic–Dielectric Nanostructures

We demonstrate a novel transmission color filter design that exploits both dielectric and plasmonic resonances to establish a highly color-selective device, reaching an experimental full-width at half-maximum (fwhm) that is only half that of previously demonstrated cost-effective color filter devices for the same peak transmission and better out-of-band rejection. The measured fwhm is only 25 nm, and the peak transmission reaches up to 53%. The filter uses the interference of Fabry-Pérot resonances and guided-mode resonances in two separated dielectric slabs to achieve this excellent fwhm while relying on propagating surface plasmon polaritons to achieve the excellent out-of-band rejection. A simulation study elucidates the nature of the optical modes in the device and their interference mechanisms and reveals the most important design considerations. Fabrication was done in a CMOS pilot line and is cost-effective, as it requires only two metal patterning steps. Fabrication imperfections are discussed, together with strategies to mitigate them. We show the correct mitigation of these imperfections leads to further performance gain, enabling a full-width at half-maximum down to 20 nm and a peak transmission beyond 60%. We believe this novel filter design is a powerful concept to improve the spectral resolution of color filters for cost-effective multispectral imaging. Beyond multispectral imaging, the design could be adapted for other applications that require on-chip spectral filtering in a thin form factor.