Ge/ZnS-Based Micromachined Fabry-Perot Filters for Optical MEMS in the Longwave Infrared

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    Abstract

    This paper reports on the successful demonstration of Ge/ZnS-based Fabry–Perot filters operating in the longwave infrared (LWIR). The suitability of thermally deposited Ge and ZnS as thin-film mirror materials for micromachined LWIR Fabry–Perot filters has been fully investigated, and it is shown that a film growth temperature higher than 150 °C is key to depositing durable ZnS films. The optical constants of Ge and ZnS films in the LWIR band reveal that the material pair possesses high refractive index contrast and excellent LWIR transparency. Fixed-cavity LWIR Fabry–Perot filters with a 150- μm circular single-layer Ge top mirror and a four-layer Ge/ZnS/Ge/ZnS bottom mirror were fabricated. Curvature in the suspended top mirror was corrected using a thin SiNx stress-compensation layer. After curvature correction, a mirror flatness of 550 nm was achieved, and the filter demonstrated a 60% peak transmission with a full-width at half-maximum of 700 nm as well as a out-of-band rejection of 24:1. [2015-0143]
    Original languageEnglish
    Pages (from-to)2109-2116
    Number of pages8
    JournalIEEE Journal of Microelectromechanical Systems
    Volume24
    Issue number6
    Early online date25 Nov 2015
    DOIs
    Publication statusPublished - Dec 2015

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