Printing Beyond sRGB Color Gamut by Mimicking Silicon Nanostructures in Free-Space

Localized optical resonances in metallic nanostructures have been increasingly used in color printing, demonstrating unprecedented resolution but limited in color gamut. Here, we introduce a new nanostructure design, which broadens the gamut while retaining print resolution. Instead of metals, silicon nanostructures that exhibit localized magnetic and electric dipole resonances were fabricated on a silicon substrate coated with a Si₃N₄ index matching layer. Index matching allows a suppression of substrate effects, thus enabling Kerker's conditions to be met, that is, sharpened transitions in the reflectance spectra leading to saturated colors. This nanostructure design achieves a color gamut superior to sRGB, and is compatible with CMOS processes. The presented design could enable compact high-resolution color displays and filters, and the use of a Si₃N₄ antireflection coating can be readily extended to designs with nanostructures fabricated using other high-index materials.