New CO₂ filters fabricated by anodic bonding at overpressure in CO₂ atmosphere

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• 作者：Huiku ; M. ; Weckströ ; m ; K. ; Merilä ; inen ; P. ; Corman ; T. ; Kä ; lvesten ; E. ; Stemme ; G.
• 关键词：CO₂ filter ; Gas encapsulation ; Antireflective coating ; Optical transmission ; Infrared
• 刊名：Sensors and Actuators A: Physical
• 出版年：1998
• 出版时间：August 15, 1998
• 年：1998
• 卷：69
• 期：2
• 页码：166-171
• 全文大小：577 K

文摘

New bulk micromachined CO₂ infrared filters are presented. The filters consist of a chamber in which CO₂ is encapsulated during an anodic bonding procedure. The chamber is formed by three fusion bonded silicon wafers joined to a glass wafer by anodic bonding at overpressure in a CO₂ atmosphere. The two central silicon wafers are etched in KOH to form a cavity. The high temperature anodic bonding process (430°C) is performed at overpressures up to 2 bar, enabling an optimized gas absorption at a final CO₂ chamber pressure up to 1 bar at room temperature. CO₂ filters of different bonding pressures were fabricated and evaluated. An experimental investigation was conducted to improve the optical performances of the device at the wavelength of interest, i.e., 4.23 μm, where the absorption peak of CO₂ is located. We studied both the influence of the glass thickness and antireflective coatings on optical losses. Theoretical calculations for transmission with antireflective coating materials are presented. From these calculations, the thickness of two antireflective coating layers (silicon nitride and silicon dioxide) was optimized to obtain a maximum transmission at 4.23 μm. Finally, an optimized filter with thinner glass and silicon dioxide as antireflective coating is presented.