A method to determine the ageing rate of thick-film PZT layers

Screen printed lead zirconate titanate (PZT) layers offer possibilities for both sensing and actuation applications. PZT materials are known to suffer a long-term ageing process that can affect their performance as functional materials. Measuring the rate of this ageing on thick-film piezoelectric materials is difficult due to the presence of a substrate, and suitable methods have not been reported in the literature. A technique for measuring the ageing rate of the d31 coefficient is described in this paper, and includes a composite test structure based on a steel substrate. The d31 coefficient is found to age at −4.4 % per time decade after polarization with no external stresses (for PZT-5H, a soft piezoelectric material). A method is also presented for measuring the ageing of the dielectric constant, K33, and this is found to have an ageing rate of −1.34 % per time decade. Techniques for exploring cyclical stress induced ageing of d31 are further described, and an interesting linear ageing characteristic is demonstrated