Abstract
High-temperature surface acoustic wave (SAW) sensors for multi-parameter simultaneous measurement are widely needed in the fields of aerospace and energy. For the SAW sensors that can be operated up to 1200 °C, high temperature conductive coatings are required to match with the YCa4O(BO3)3 (YCOB) single crystal, which is the only available piezoelectric ceramics now for use at 1200 °C. Promising high temperature conductive films comprised of SiBCN ceramics were coated via chemical vapor deposition (CVD), polymer-derived ceramic (PDC) route and PDC plus CVD method, respectively. The microstructure, morphology and electrical properties of the films were characterized in detail. It was found that a film with few defects and good conductive performance can be obtained at 1000 °C by PDC plus CVD route. However, a BN film has to be deposited on YCOB wafer first to suppress its decomposition in inert atmospheres around 1000 °C in the case of using CVD method. The overall conductivity change is primarily due to the increase in graphitization degree of free carbon in PDC-SiBCN.
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