Temperature resistant anti-reflective coating on Si-wafer for long-wave infra-red imaging

• Published in: Heliyon Vol. 9; no. 5; p. e15888
• Main Authors: Papatzacos, Phillip H., Akram, M. Nadeem, Hector, Olivier, Lemarquis, Frédéric, Moreau, Antonin, Lumeau, Julien, Ohlckers, Per
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.05.2023; Elsevier
• Subjects: Anti-reflective coatings; Electron beam deposition; Long wave IR; Microbolometers; Physics; Thermal camera; Long wave IR; Anti-reflective coatings; Electron beam deposition; Si; Microbolometers; Thermal camera; Long Wave IR Anti-Reflective coatings Thermal Camera Microbolometers electron beam deposition Si; Anti-Reflective coatings; Long Wave IR; Thermal Camera; electron beam deposition
• ISSN: 2405-8440; 2405-8440
• DOI: 10.1016/j.heliyon.2023.e15888

A micromachined Silicon lid, sealed by CuSn solid liquid interdiffusion bonding is a promising approach for hermetic sealing of microbolometers for use in low-cost thermal cameras. However, since ∼30% of long-wave infrared light is reflected at an uncoated single Si-air interface, anti-reflective treatments are required. Traditional anti-reflective coatings are inapplicable since CuSn solid liquid interdiffusion bonding requires heating to about 270 °C and these multi-layer coatings fail due to differing coefficients of thermal expansion for the different layers and the substrate. For this purpose, an anti-reflective coating that maintains its anti-reflective properties after being heat-cycled to 300 °C has been developed. This coating was developed using a simple 2-layer structure composed of ZnS and YF3 and deposited at 100 °C. The development process that led to the successful coating has also been described in this paper. The final sample shows a 30% average increase in transmission in the 8–12 μm wavelength range as compared to an uncoated wafer.