Characterization of sol-gel Pb(Zr0.53Ti0.47)O3 in thin film bulk acoustic resonators

The behavior of {111}-textured Pb(Zr_0.53Ti_0.47)O₃ (PZT) deposited by the sol-gel technique in thin film bulk acoustic resonators (TFBAR´s) was investigated at a resonance frequency of about 1 GHz. The resonators were fabricated on Si wafers using deep silicon etching to create a membrane structure and using platinum as top and bottom electrodes. The best response of the resonators was observed at a bias voltage of -15 kV/cm with values of about 10% for the coupling constant and about 50 for the quality factor. This voltage corresponds to optimal values of piezoelectric constant d₃₃ and dielectric constant measured as a function of the electric field. The influence of a bias voltage on the resonance frequency, antiresonance frequency, and coupling constant were observed. Both the resonance and antiresonance frequency show a hysteretic change with applied bias. This effect can be used to shift the whole band of a filter by applying a voltage. The TFBAR structure also allowed us to extract values for materials parameters of the PZT film. Dielectric, piezoelectric, and elastic properties of the {111}-textured PZT film are reported and compared to direct measurements and to literature values.