Al₂O₃-Modified Polymer-Derived Ceramic SiCN High-Temperature Anti-Oxidative Composite Coating Fabricated by Direct Writing

A reliable protective layer is one of the main challenges in preventing oxidation of thin film sensors to achieve accurate, effective, and stable readings at high temperatures. In this work, an Al₂O₃-modified polymer-derived ceramic SiCN composite coating fabricated by a direct-writing technique is utilized as a protective layer for thin film sensors. The microstructure evolution of the Al₂O₃/SiCN films is examined herein. The protective layer exhibits excellent oxidation resistance and thermal stability at high temperatures up to 1000 °C, which contributes to improving the stability and lifetime of thin film sensors in extreme environments. The TiB₂/SiCN thin film resistive grid with the Al₂O₃/SiCN composite film as a protective layer is fabricated and tested. The results indicate that the coating can protect the TiB₂/SiCN thin film resistive grid at high temperatures up to 1000 °C, which is about 200 °C higher than that of the TiB₂/SiCN thin film resistive grid without a protective layer. The resistance change rates of the TiB₂/SiCN thin film resistive grid with a protective layer are 0.5%/h at 900 °C and 10.7%/h at 1000 °C.