Color filters are often made of thin films or dye coatings, but are limited by optical diffraction restrictions, they have low resolution and are sensitive to high temperatures and prolonged ultraviolet (UV) ray exposure. Meanwhile, microstructure-based color filters are more adaptable under application scenarios since they may get the necessary light wavelengths by modifying structural or material factors. Microstructure-based color filters have the advantages of stable performance, tunability, and manufacturability over conventional color filters. Additionally, they are usually made of inorganic or high-temperature durable materials, which have a longer service life with extensive applications in many fields, such as complementary metal oxide semiconductor (CMOS) image sensors, liquid crystal screens, and pixel development.

A top double-layer cross circle and a bottom buffer layer comprise the color filter presented in our study. The metal Al and the hydrogen silsesquioxane (HSQ) polymers make up the double-layer cross circle. The bottom is made up of three dielectric layers: a buffer layer of TiO₂, a waveguide layer of Al₂O₃, and a substrate layer of SiO₂. The finite difference time domain (FDTD) method is adopted to conduct a comparative investigation into the transmission spectra and color display patterns of four different structural filters. The effects of the structural period, cross ring diameter, cross width, and polarization angle on the transmission spectra and filtering characteristics are also examined.

Compared to single-layer construction, the designed color filter using a double-layer cross circle structure has a greater transmittance and reduced full width at half maximum (FWHM). The filter can achieve high transmittance of up to 90.5% at vertical incidence [Fig. 5(b)] and the minimum FWHM at the structural period is L₁=W₁=360 nm [Fig. 1(a)]. Meanwhile, the resonance wavelength of the transmission peak remains essentially constant over the polarization range of 0-90° (Fig. 5), and the transmittance remains above 50 when the angle of incidence is varied from 0 to 30° (Fig. 6).

We propose a polarization-insensitive and highly selective color filter. FDTD numerical simulation is adopted to investigate and compare the cross ring double-layer subsurface structure to the single-layer plasmonic structure. The results show that combining the double-layer subsurface structure with the dielectric can result in a higher transmittance and narrower FWHM, thus leading to a more effective color selection in the visible wavelength range and robust interference resistance. When the angle of the polarized light is changed from 0 to 90°, the resonance peak position of the simulated transmission spectrum varies somewhat, and the accompanying chromaticity coordinate point moves within a small range. This means that the output properties of the filter are consistent across polarization angles, allowing the filter to be employed in structural applications.