Fabricating bi-layered metallic wire-grid polarizers by nanoimprint and O ₂ plasma etching

This paper proposes an efficient process for fabricating bi-layered metallic wire-grid polarizers (WGP), which consist of a metallic (aluminum) layer on the top and a dielectric (PMMA) layer at the bottom. The proposed architecture was fabricated from the insertion structure, which was accomplished through only three steps, i.e., nanoimprint, aluminum deposition and chemical mechanical polishing (CMP), to embed the Al wire grating into PMMA substrate. By taking the advantage of the characteristic of the insertion structure, this technique fabricated PMMA wires with O ₂ plasma etching by employing the nano-scale Al wire gratings as a mask to achieve bi-layered structures. The proposed bi-layered structures of metallic WGP can achieve superior optical performance, such as the extinction ratio of 497 and brightness gain of 1.18, from 0°to 40°of incident angles at a wavelength of 650 nm of incident light. In this paper, FE-SEM and FIB images show that the bi-layered wire-grid structure with wire gratings 100 nm in linewidth, 240 nm in pitch, and 300 nm in total height, i.e., 150 nm each for Al and PMMA wire gratings, was successfully replicated on a PMMA substrate of 1 cm ². Various O ₂ plasma etching periods were employed to accomplish the desirable bi-layered structures as well as its optical performance. In addition, we demonstrate that the deeper PMMA wire gratings of bi-layered structures cannot acquire the higher extinction ratio because of the increases of the P-polarization as well as the S-polarization.