Electromechanical Resonances in Ceramic Capacitor and Evaluation of the Piezoelectric Materials' Properties

Abstract

Impedance measurements as a function of frequency on ceramic capacitors with X7R and Z5U temperature characteristics show electromechanical resonances which are caused by the piezoelectric nature of the BaTiO{sub 3}-based dielectric materials. In contrast to BaTiO{sub 3}-based transducer materials, the dielectric materials cannot be permanently poled. Therefore, the resonances can only be observed during the application of a bias voltage. Resonances associated with the length, width, and thickness of the capacitor are clearly identified. Measurement of the characteristics of the width resonance as a function of bias field show that the dielectric ceramic is stiffened by the application of a bias field. The quality factor has a maximum at 200 V and 50 V for the X7R and Z5U capacitors, respectively. The materials constants for the dielectric materials derived from the width resonance are comparable to those published for BaTiO{sub 3}-based transducer materials.