Piezoelectric properties of sol-gel derived ZnO thin films

Abstract

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 firing 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 temperature 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.

Key Words:

• piezoelectric
• films
• ZnO
• sol-gel