Stability of Glass Seals for Pt Thin-film Resistance Temperature Detector

Noting the airtight, insulation and other performance issues of platinum thin-film resistance temperature sensors in the insulation encapsulation process, two kinds of glass and platinum thin-film temperature sensors were evaluated, focusing on the infiltration of the performance, airtightness, insulation and thermal cycling stability, so as to optimize the performance of the glass sealing materials for the platinum thin-film temperature sensors. The two glass-ceramics, SiO₂-BaO-Al₂O₃-CaO glass and SiO₂-B₂O₃-Al₂O₃-CaO glass, with different thermal stability, have high wettability with the alumina substrate at 800-1000 ℃. At 800 ℃, the air leakage rates were about 0.0073 sccm·cm^-1 and 0.0065 sccm·cm^-1, at the vent pressure of 20.7 kPa, while the insulation resistivities were about 21.6×10⁶ Ω·cm and 31.1×10⁶ Ω·cm, respectively. In addition, the size of holes on the surfaces of the two types of glass appeared to be different after 500 thermal cycling from 30 to 800 ℃. Specifically, the pore size of the SiO₂-BaO-Al₂O₃-CaO glass increased from 0.13 μm to 15.62 μm after 500 thermal cycles, whereas that of the SiO₂-B₂O₃-Al₂O₃-CaO glass showed a smaller change and the surface morphology was more denser. It is therefore concluded that the SiO₂-B₂O₃-Al₂O₃-CaO glass has more excellent sealing performance, high-temperature insulation performance and thermal cycle stability, and hence is more suitable for the encapsulation process of platinum thin-film resistance temperature sensors.