Electrical insulation enhancement of the Al 2 O 3 composite films at high temperature by oxygen vacancy suppression

The electrical insulation film is critical for the reliable operation of Ultra-high temperature thin-film sensors (UTTSs) at elevated temperatures. However, the resistance of the insulation film easily decline at high temperatures due to the formation of the oxygen vacancy and through-type defects, which will affect the long-term stability and reliability of the UTTSs. Here, we report a novel gas-liquid phase composite strategy to fabricate Al2O3 composite insulation films. An Al2O3 bottom film was first deposited by liquid-phase electrohydrodynamic jet printing, followed by the deposition of a dense Al2O3 film by magnetron sputtering. This design not only effectively repairs through-type defects in the liquid-phase film and improves overall densification, but also suppresses the formation of oxygen vacancy in films. The gas-phase Al2O3 (G-Al2O3)/liquid-phase Al2O3 (L-Al2O3) composite film exhibits a smooth surface with substantially reduced micro-cracks and porosity. X-ray photoelectron spectroscopy reveals a significantly lower relative oxygen-vacancy level in the composite films compared with the pure L-Al2O3 film. Consequently, the G-Al2O3/L-Al2O3 film achieves an insulation resistance of 44 kΩ at 1400 °C, an order of magnitude higher than that of the pure L-Al2O3 film. In addition, three thermal cycles between 800 and 1200 °C demonstrate excellent repeatability of the insulation resistance within this temperature range. Practically, the Al2O3 composite films were applied to the thin-film strain gauges (TFSGs) , and the TFSGs exhibited excellent performance at high temperatures.