Electrical insulation of ceramic thin film on metallic aero-engine blade for high temperature sensor applications

Fabricating sensor devices directly on metallic component requires the use of an electrical insulating ceramic layer between the sensor and the metal. However, most ceramics lose their electrical insulation with the increasing temperature. In this paper, electrical insulation properties of ceramic thin film were extensively analyzed in high temperature environment up to 1300 degrees C and a new ceramic coating with good high temperature insulation was developed. Results indicate that the ordinary YSZ ceramic film cannot maintain enough resistivity under high temperature above 600 degrees C. A new methodology is therefore proposed to compensate the possible errors of the sensors brought by the reduced resistivity in the ceramic. Meanwhile an improved ceramic coating recipe was developed to improve the electrical insulation which can meet the high temperature insulation requirement up to 1300 degrees C. Extensive numeric simulations considering electrical and thermal multi-physics interaction were conducted to analyze and estimate electrical performance under high temperature caused by the reduced resistivity of ceramic thin film onto which the thermal sensor is fabricated. Conduction current with the various thickness and defect situations in the ceramic thin film were studied through the extensive simulation, and a competitive behaviors of various current flows in this sensor/ceramic/metal composite structures is observed