The electromagnetic interference (EMI) shielding window is of great significance for precision aeronautic, medical, civilian, and research facilities. There are tremendous world-wide efforts in searching new structures and materials with excellent shielding performances. However, how to achieve high optical transmittance and strong microwave shielding performance simultaneously is still a great challenge.

Besides, most of manufacture methods generally adopt ultraviolet mask lithography or electron beam direct writing methods, which make the fabricated meshes deposit only on the surface of the substrate and result in low firmness and durability to shorten the operating life. Also, harsh environment, such as erosion of wind, rain, sand and stone, can make the shielding layer easy to be scuffed off, resulting in the decrease of shielding performance.

Recently, the research team led by Shanghai Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences, has demonstrated a high-performance EMI shielding window with double-layer metal mesh etched by femtosecond laser. The result was published in RSC Advances.

In their experiment, the transparent EMI shielding window contains an excellent double-layer Au-Ni composite mesh with high optical transparency and strong EMI shielding performance.

By focusing femtosecond laser under the surface of quartz glass coated with photoresist, grids with grooved structure were etched deeply to enhance the adhesion of metal film and prevent it from being scuffed off.

Following this, Ni layer was evaporated on the surface of quartz glass by electron beam evaporation method, and Au layer was evaporated on the top of the Ni layer. The sample was placed in N-Methyl pyrrolidone (NMP) solution with ultrasonic heating to remove residual photoresist, and obtain a complete metal mesh.

The results show that the measured SE of the double-layer mesh reacheed over 37.61 dB from 150 MHz to 5 GHz, with a maximal SE of 75.84 dB at 3.58 GHz.

More importantly, the normalized visible transmittance of the double-layer mesh remains ~76.35% over spectrum ranging from 400 nm to 900 nm.

Furthermore, femtosecond laser direct-writing processing was used to fabricate the double-layer mesh, forming a "deep surface-embedded" metal grids, which possess high durability and longer operating life.

These excellent properties are promising for use in high-performance transparent EMI shielding materials, which are highly desirable for modern optoelectronic systems.

These works were supported by the National Natural Science Foundation of China, the Hongxing Dong acknowledges the Youth Top-notch Talent Support Program in Shanghai, and Shanghai Rising-star Program and Shanghai Sailing Program.

Schematic diagram and shielding effectiveness of the double-layer Au-Ni composite mesh (Image by SIOM)