Electrical insulation improvement using a CeYSZ/Al₂O₃ double ceramic layer underlayer for thin-film sensors

With the increasing application of thin-film sensors in high-temperature applications, there is an escalating demand for insulation layers that provide enhanced resistance to elevated temperatures. However, failure often occurs because of the mismatch in thermal expansion coefficients between the insulation layer and the substrate. This study proposes an underlayer comprising a double ceramic layer of CeYSZ and Al₂O₃, which preserves the high thermal expansion coefficient and corrosion resistance of CeYSZ while enhancing its electrical insulating properties. The high-temperature electrical insulation performance of underlayers with different ceramic layer structures was experimentally evaluated. The results indicate that the CeYSZ/Al₂O₃ double ceramic layer exhibits an electrical resistance of 2.1*10⁶ Ω at 800 °C and minimal drift after 5 h, demonstrating high stability. Finally, PdCr thin-film strain gauges were fabricated on CeYSZ/Al₂O₃ double ceramic layer, revealing the stability of the electrical resistance at high temperatures. The porosity of the underlayer cross-sections was also compared, revealing that the double ceramic layer coating effectively fills pores and cracks inherent in single-layer coatings. This mitigation of conductive pathways reduces the occurrence of such defects, thereby enhancing the high-temperature insulation performance of the underlayer.