Crackle template based metallic mesh with highly homogeneous light transmission for high-performance transparent EMI shielding

Abstract

Our daily electromagnetic environment is becoming increasingly complex with the rapid development of consumer electronics and wireless communication technologies, which in turn necessitates the development of electromagnetic interference (EMI) shielding, especially for transparent components. We engineered a transparent EMI shielding film with crack-template based metallic mesh (CT-MM) that shows highly homogeneous light transmission and strong microwave shielding efficacy. The CT-MM film is fabricated using a cost-effective lift-off method based on a crackle template. It achieves a shielding effectiveness of ~26 dB, optical transmittance of ~91% and negligible impact on optical imaging performance. Moreover, high-quality CT-MM film is demonstrated on a large-calibre spherical surface. These excellent properties of CT-MM film, together with its advantages of facile large-area fabrication and scalability in processing on multi-shaped substrates, make CT-MM a powerful technology for transparent EMI shielding in practical applications.

Figure 1. Fabrication process and optical and SEM characterizations of the CT-MM film.

(a) Schematic illustration of the fabrication steps for a large-area CT-MM film. The SEM image shows the highly connected metallic networks. (b) Optical images of crackle templates with different values of R_MM-B, showing that the crack width and cell size can be controlled by the amount of monomers. (c) Experimental curves of crack width and crack spacing of the dried CEs with different values of R_MM-B. (d) Variations in crack width and crack spacing with respect to coating thickness. (e) Drying process of crackle template. Inset: SEM image showing the fine cracks with ignorable buckling.

Figure 2. Optical images and light transmissivities of representative CT-MM films and square mesh.

(a) Photograph of a fabricated large-area CT-MM film sample (200 ×  200 mm²). Inset: optical morphology image showing the metallic networks patterned on the substrate. (b) A typical square mesh sample (φ 100 mm) with magnified pattern geometry. The relative optical transmittance of CT-MM and square mesh films as a function of wavelength measured in the ranges of (c) 300–800 nm and (d) 1.5–4 μ m. Light transmissivity at λ  =  633 nm as a function of coated CE thickness.

Figure 3. The simulated stray light distributions of square mesh and CT-MM.

(a,c) Diffraction pattern spectrograms of (a) the square mesh sample (g =  250 μ m and w =  5 μ m) and (c) the CT-MM film (CT-MM3). (b,d) Normalized intensity spectra of diffraction spots related to the diffraction patterns and their partial enlarged drawings, respectively.

Figure 4. Stray light distribution testing with different samples.

Detected diffraction patterns with digital grey level graphs (along dash lines) of (a) a bare quartz, (b) a square mesh/quartz sample and (c) the CT-MM3/quartz sample. Insets in (a,c) are the enlarged grey level graphs at high–order regions.

Figure 5. Microwave shielding performances of CT-MM films and the testing schematic.

(a) Schematic illustration of the EMI shielding measurement setup. The sample was installed in a centre-hollowed EMW absorber (foam, 500 ×  500 ×  5 mm³). (b) EMI SE of CT-MM films measured in the frequency range of 12–18 GHz. (c) EMI SE at a frequency of 18 GHz of CT-MM films fabricated by CE3 with different thicknesses.

Figure 6. Photographs and performances of a large-calibre CT-MM dome.

(a) A photograph and (b) surface profile of a large-calibre quartz dome coated with CT-MM film. The dome is a spherical cap with an outer diameter of 220 mm, a cap height of 85 mm and a wall thickness of 7 mm. The inset shows a macrophotograph of the CT-MM dome. (c) The optical transmittance spectrum in 300–800 nm regions and (d) the EMI SE in the Ku-band of the CT-MM dome, respectively.