Design of infrared anti-reflection thin film devices with compatibility of electromagnetic shielding

It is contradictory to satisfy the high-performance infrared transmittance and electromagnetic shielding in the optical window. A design method was proposed for high electromagnetic shielding and infrared transmission on a silicon substrate. Based on the equivalent circuit model theory, the equivalent circuit model of the Cu grid was modified. The infrared antireflection film was designed to further improve the infrared transmittance of the silicon-based grid. The overall transmittance of antireflection film devices compatible with electromagnetic shielding is discussed. The Cu grid was fabricated by photolithography mask and thermal evaporation deposition technology. The results show that the modified LZ equivalent circuit model can more accurately calculate the low-frequency shielding efficiency of metal grids. The simulation shows that the grid linewidth is more likely to affect the electromagnetic shielding effectiveness than the period, and the precise structure is conducive to higher electromagnetic shielding efficiency. Considering the refractive index, stress matching and convenient preparation of the film, the film system was finally selected as Sub/HL/Air (H: ZnSe, L: BaF₂), and the design center wavelength was 3514 nm. The average transmittance of the silicon-based grid (g=550 μm, 2a=50 μm) double-sided coated with the same anti-reflection film system is 81.7 % in the 3-5 μm, which is 36.2 % higher than that of the silicon-based grid (45.5 %), with the average electromagnetic shielding efficiency unchanged (SE_avg = 24.8 dB@ 1-12 GHz).