Tailoring Mechanical and Optical Properties of Sputtered SiN/BN Coatings

The swift evolution of contemporary electronics products, such as flexible screens and wearable electronic devices, highlights the significance of flexible protective coatings, which combine superior mechanical and optical properties. Even though the recently developed polymer protective coatings can satisfy requirements for flexibility and transparency, their intrinsic nature often results in a hardness below 1 GPa, rendering them susceptible to scratches. On the other hand, traditional inorganic coatings, known for their high hardness and transparency, fall short of meeting flexibility requirements. In the present study, a SiN/BN periodical nanolayered coatings (PNCs) structure has been tailored to achieve high mechanical durability, transparency, and flexibility. In SiN/BN PNCs, the optical and mechanical properties of the single-layer SiN film are crucial to the overall performance of the PNCs. Therefore, pulse direct current (DC) magnetron sputtering was optimized first to enhance the ionization efficiency of Si and N, thereby promoting their reaction and diminishing the presence of elemental silicon in SiN. The effects of the pulse frequency and duty cycle on SiN were evaluated. Additionally, the influence of the thickness ratio and modulation periods on the overall performance of the SiN/BN PNCs was investigated. As a result, a SiN/BN coating with sapphire-grade hardness, almost no optical absorption in the visible-near-infrared (vis-NIR) range, high wear resistance, and exceptional flexibility was demonstrated.