Fabrication of Optically Transparent Millimeter-Wave Micromesh Structures

Global trends toward mobility and miniaturization along with increasing demands to improve the performance and efficiency of sensor systems, especially in autonomous systems, have led to a need to decrease their size, weight, and power (SWaP). For millimeter wave (mmWave) and optical sensing, optically transparent mmWave antennas provide a solution to meet this need by offering a multi-modal, single aperture system with applications in vehicle windshields, solar cells on satellites, and drone camera lenses, among others. However, integrating these sensing systems while optimizing both the mmWave properties and optical sensing capabilities forces competing design and fabrication requirements. Currently, there also exists limited research and literature on a fabrication procedure for these micromesh structures. This paper presents a photolithographic procedure for fabricating micro-scale optically transparent mmWave transmission lines (TLs) and antennas suitable for use in the design optimization processes. It investigates the fabrication of varying line width versus line gap dimensions as well as the fabrication of different mesh unit cell designs. The fabrication procedure was designed to achieve down to 1-2 μm features and is replicable for both single-sided and dual-sided designs. The fabricated micro-mesh structures exhibit strong performance in both operating regimes, having optical transmittance ranging from 80-95% transmittance in the visible spectrum and high conductivity with sheet resistance less than 1 ohmper- square.