Piezoelectric Measurements on Ceramic Multilayer Capacitors

Piezoelectric measurements are reported for a series of commercial multilayer capacitors which had been previously tested and sold for high-reliability applications. The capacitors conformed to BX specifications and were fabricated from various combinations of barium titanate based dielectric compositions with different electrode materials. Dielectric properties are reported, including distributions in capacitance values and variations in Curie-Weiss behavior. Piezoelectric measurements were made of the d13and d33coefficients; and data are reported for their distribution in values, and temperature and voltage dependencies. Significant piezoelectric coefficients were detected for capacitors in their as-received conditions. In certain cases the piezoelectric coefficients approached 1000 pC/N. The results are discussed in the context of what effects life-testing conditions may have on dielectric quality. Experiments are also reported for the electric-poling and thermal-depoling of multilayer ceramic capacitors. Concern is expressed for the over-testing of thin layer ceramic devices. Calculations indicate the strain deformation can exceed the elastic limit in certain conditions, resulting in mechanical failure. In addition, the generation of electric charge or potential by mechanical vibration contributes a significant noise to circuit applications. Voltage levels were in the millivoltage range. The study indicates that significant problems may arise in commercial ceramic multilayer capacitors due to a generally unrecognized piezoelectric effect.