Variation of the vibration profile of piezoelectric resonant sensors with different electrode conductivity at high temperatures

Abstract

Gas sensors for applications at elevated temperatures provide improved gas selectivity if fabricated using high-temperature stable piezoelectric resonators. The high-temperature and chemical stability of devices based on langasite coated with metal oxide films supports their application at extreme environments. The vibrational behavior of these resonators is influenced by changes in the electrical and mechanical properties of the metal oxide film.Measurements of the spatial distribution of the displacement characteristics of thickness shear mode resonators are realized using a laser Doppler interferometer at high temperatures and oxygen partial pressures (pO2) down to 10−27bar. The pO2 dependent changes of the properties of a CeO2−x sensor film and the influence on the vibration profile of the resonator are determined. At low pO2 the conductivity of the film increases. Due to the design of the device, the increase of the conductivity results in an enlargement of the effective electrode area of up to 18%. This is reflected in a broadening of the vibration profile of the resonator. Impedance spectroscopy provides comparable results for a pO2 dependent increase of the effective electrode area. The influence of the electrode thickness on the vibration profile is investigated and a decrease of the profile width of up to 11% with increasing thickness is demonstrated. The latter is attributed to an increased energy trapping.