Wire Grid Polarizer by Angled Evaporation Method Using Nanoimprint Lithography.

Abstract

I report the development of a nanoimprint-lithography-based method of fabricating a wire grid polarizer (WGP), which greatly relaxes patterning and etching requirements and can be easily applied to produce flexible WGPs. Nanoimprinting is a simple and cheap large-area nanofabrication process. To date, WGPs were fabricated by electron beam lithography. Although electron beam lithography has a high resolution and good profile, it is slow and expensive. Therefore, electron beam lithography is not suitable for large-area nanofabrication. To fabricate larger WGPs, nanoimprinting lithography is one of the best processes. WGP resolution and material brittleness have somewhat limited the choice of previous resists used for nanoimprinting. Hence, I developed an epoxy resist whose physical properties were tuned by adjusting the ratio of bisphenol F-type to acrylonitrile-butadiene rubber (NBR)-based epoxy resins in the resist formulation. The mechanical properties of the resist were tuned to obtain various aspect ratios and mold flexibility for conformal contact over nonplanar surfaces and large areas. Roll-to-roll nanoimprint lithography is a very attractive method of manufacturing micro- and nanopatterns owing to its large-area patterning capabilities. Material flexibility is one of the most important requirements in roll-to-roll nanoimprint lithography. Commercially available bisphenol F-type epoxy resin is much less expensive than other resins, so it is a widely used construction polymer. NBR rubber is also widely used. Hence, the resist formulation I developed could be used to industrially mass-produce nanostructures. In addition, I used atomic layer deposition to fabricate 20-nm-linewidth, 9:1-aspect-ratio ultrasmall nanostructures. I used nanoimprint lithography to pattern a high-aspect-ratio, narrow-linewidth grating and subsequently deposited two aluminum layers angled in opposite directions to efficiently fabricate the large-area WGP. Anisotropic reactive-ion etching was used to remove the aluminum layer deposited on top of the grating while retaining that on the grating sidewalls, thereby forming a metal wire grid whose spacings were much smaller than those of a lithographically defined grating. The WGP showed good optical properties in the visible range. I encapsulated the WGP in a thin layer of poly(methyl methacrylate) (PMMA) for practical use, and the encapsulated WGP worked well in the visible range.