Electrical insulation improvement of Al2O3 composite films at high temperatures utilizing electrohydrodynamic jet printing technique

Ultra-high temperature thin-film sensors ( UTTSs ) offer advantages such as high sensitivity, rapid thermal response, and minimal environmental interference in multi-physical parameter monitoring of the hot sections. As one of the key parts of the UTTSs , the insulation films are of significance to their property and reliability to provide high temperature electrical isolation between workpiece and the sensitive film. However, the resistance of the insulation films will decrease at high temperatures, which causes the failure of the UTTSs . In this study, Al 2 O 3 composite films were fabricated using electrohydrodynamic jet (E-jet) printing technology combining Al 2 O 3 mixture and Al 2 O 3 sol. The S-Al 2 O 3 film prepared with the superior fluidity Al 2 O 3 sol can effectively repair the defect existing in the M-Al 2 O 3 film prepared with the Al 2 O 3 mixture. Consequently, it reduced the surface roughness of the insulation films from 1.496 μm to 1.086 μm and finally repaired their through defects. Experimental results demonstrated that the Al 2 O 3 composite films exhibited significantly improved performance compared to pure M-Al 2 O 3 . The insulation resistances can reach up to 25 MΩ, 199 kΩ at 800 °C and 1200 °C, respectively. The normalized resistance of the Al 2 O 3 composite films is up to 476 times higher than that in the existing literatures at 800 °C. Practically, the Al 2 O 3 composite films were applied to the thin-film strain gauges ( TFSGs ) and the tungsten-rhenium coaxial thermocouples ( TRCTs ). Both of the TFSGs and the TRCTs exhibited excellent performance at high temperatures.