Piezoelectric properties of sol-gel derived ZnO thin films

ZnO films exhibit a wide range of interesting material properties. Recently, ZnO films have been studied for sensing applications based . on their piezoelectric and pyroelectric behaviors. Reported literature values of piezoelectric and pyroelectric coefficients of ZnO films are in the range of 11-12 pm/V and 1.0-1.4 nC/cm²-K respectively. In this study, the piezoelectric properties of sol-gel derived ZnO thin films were measured. These films were prepared on platinized Si wafers and fired to temperatures ranging from 550°C to 750°C. Multiple spincoating was performed with an intermediate/king at 400°C between coatings to obtain films up to 6000 A thick. Top Pt electrodes were sputtered to form monolithic capacitors. XRD indicated that the films consisted of crystalline wurtzite at firing temperatures as low as 400°C, and that the c-axis orientation increased with increasing firing temperature. A dielectric constant of 10 was obtained, while piezoelectric characterization indicated d₃₃ values as large as 12 pm/V i.e., values similar to those of bulk ZnO.