13 May 2015 Microfabricated electrochemical sensors for combustion applications
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A new design for the miniaturization of an existing oxygen sensor is proposed based on the application of silicon microfabrication technologies to a cm sized O2 sensor demonstrated by Argonne National Laboratory and The Ohio State University which seals a metal/metal oxide within the structure to provide an integrated oxygen reference. The structural and processing changes suggested will result in a novel MEMS-based device meeting the semiconductor industry standards for cost efficiency and mass production. The MEMS design requires thin film depositions to create a YSZ membrane, palladium oxide reference and platinum electrodes. Pt electrodes are studied under operational conditions ensuring film conductivity over prolonged usage. SEM imaging confirms void formation after extended tests, consistent with the literature. Furthermore, hydrophilic bonding of pairs of silicon die samples containing the YSZ membrane and palladium oxide is discussed in order to create hermetic sealed cavities for oxygen reference. The introduction of tensile Si3N4 films to the backside of the silicon die generates bowing of the chips, compromising bond quality. This effect is controlled through the application of pressure during the initial bonding stages. In addition, KOH etching of the bonded die samples is discussed, and a YSZ membrane that survives the etching step is characterized by Raman spectroscopy.
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Vitor A. Vulcano Rossi, Vitor A. Vulcano Rossi, Max R. Mullen, Max R. Mullen, Nicholas A. Karker, Nicholas A. Karker, Zhouying Zhao, Zhouying Zhao, Marek W. Kowarz, Marek W. Kowarz, Prabir K. Dutta, Prabir K. Dutta, Michael A. Carpenter, Michael A. Carpenter, "Microfabricated electrochemical sensors for combustion applications", Proc. SPIE 9491, Sensors for Extreme Harsh Environments II, 94910J (13 May 2015); doi: 10.1117/12.2177335; https://doi.org/10.1117/12.2177335

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