Bespoke multispectral filter arrays based on Fabry-Perot optical cavities fabricated using large-area grayscale photolithography (Conference Presentation)

Abstract

Snapshot multispectral image sensors have been proposed as a key enabler for a plethora of multispectral imaging applications, from diagnostic medical imaging to remote sensing. With each application requiring a different set, and number, of spectral bands, the absence of a scalable, cost effective manufacturing solution of custom multispectral filter arrays (MSFAs) has prevented widespread MSI adoption. Despite recent nanophotonic-based efforts, such as plasmonic or high-index metasurface arrays, large-area MSFA manufacturing still consists of many-layer dielectric (Fabry Perot) stacks, requiring separate complex lithography steps for each spectral band and multiple material compositions for each. It is an expensive, cumbersome and inflexible undertaking, but yields optimal optical performance. Here, we demonstrate a manufacturing process that enables cost effective wafer-level fabrication of custom MSFAs in a single lithographic step, maintaining high efficiencies (~75%) and narrow linewidths (~25 nm) across the visible to near-infrared. By merging grayscale (analog) lithography with metal-insulator-metal (MIM) Fabry-Perot cavities, whereby exposure dose controls cavity thickness, we demonstrate simplified fabrication of MSFAs up to N-wavelength bands. The concept is first proven using low volume electron beam lithography, followed by the demonstration of large volume UV mask-based photolithography with MSFAs produced at the wafer-level. Our framework provides an attractive alternative to conventional MSFA manufacture, and metasurface-based spectral filters, by reducing both fabrication complexity and cost of these intricate optical devices, while increasing customizability.