Investigation of high temperature electrical insulation property of MgO ceramic films and the influence of annealing process

Abstract MgO ceramic films were deposited as insulating films for thin film sensors by electron beam evaporation on Ni-based substrate at 25 °C, 200 °C and 300 °C (denoted as MgO-25, MgO-200, and MgO-300). The structures and morphologies of the MgO ceramic films were investigated by X-ray diffraction and scanning electron microscopy, which indicated that MgO films exhibited (111) and (222) preferential orientation growth and a more compact microstructure with increasing substrate temperature. Furthermore, the insulation resistance of MgO films was enhanced at higher substrate temperature, the MgO-300 ceramic film increased by approximately one order of magnitude compared to MgO-25 ceramic film. Notably, the insulation resistance of the MgO-300 ceramic film was 1.5 MΩ when the test temperature reached 1000 °C. Additionally, the influence of annealing on the electrical insulation properties of MgO-300 was evaluated via a leakage current test at 25–1000 °C. The results showed that the stability of the electrical insulation performance was improved mainly due to the growth of grains and repair of defects. Moreover, the conductivity was below 1.2 × 10−6 S/m and the calculated insulation resistance was greater than 0.55 MΩ at 1000 °C after the fourth annealing, which displays that the relative error of the apparent resistance is less than 0.03% by the shunt circuit law. Therefore, their excellent electrical insulation performance demonstrated that MgO films have the potential to be employed as an insulating layer for thin film sensors at high temperature.