Effect of processing conditions on the piezoelectric properties of sol-gel derived Pb(Zr,Ti)O 3 films for micromechanica
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J. Manuel Herrero and C. Zaldo Instituto de Ciencia de Materiales de Madrid CSIC, Cantoblanco, 28049 Madrid, Spain (Received 1 February 2005; accepted 17 February 2005)
Lead zirconate titanate (PZT) films of composition close to the morphotropic phase boundary were deposited onto standard Si/SiO2/Ti/Pt substrates using a modified sol-gel process. The preparation conditions were optimized to obtain high-quality films at sufficiently low temperature (Ta ⳱ 500 °C). The dielectric, ferroelectric, and piezoelectric properties of the films were then measured as a function of the annealing temperature and the number of distillations to evaluate their suitability for micromechanical applications. The maximum values of the longitudinal charge and voltage piezoelectric coefficients were d33 ∼ 65 pm/V and g33 ∼ 4 × 10−3 Vm/N, respectively. The results indicate that the piezoelectric properties improved and became saturated with increasing number of distillations and are almost independent on Ta. Only moderate decrease of the piezoelectric response with frequency suggests that the investigated PZT films can be used in high-frequency piezoelectric applications. The results are discussed in terms of the microstructure and interface effects on the piezoelectric deformation in ferroelectric thin films.
I. INTRODUCTION
Lead zirconate titanate (PZT) in a thin-layer form is extensively investigated for a variety of applications ranging from non-volatile memories to microelectromechanical systems (MEMS).1 Most of these applications require processing compatibility of PZT with major fabrication procedures used in semiconductor industry. The general problem is a high crystallization temperature of lead-based perovskite materials, which attains over 1000 °C for bulk PZT ceramics. In thin films, this temperature is typically below 700 °C,2 but it is still sufficiently high to cause electrode oxidation and Pb interdiffusion during back end process.2,3 High processing temperatures of PZT necessitate use of various barrier layers to prevent degradation of both the electrode and ferroelectric materials. This is detrimental for micromechanical applications where the introduction of additional interlayers and mechanical stress produced by the hightemperature annealing apparently decrease the actuation and sensing capabilities of microdevices. In addition, it is a)
Address all correspondance to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0203 1428
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 6, Jun 2005 Downloaded: 18 Mar 2015
believed that if the processing temperature is lowered below 500 °C, Si can be replaced with inexpensive glass and even plastic substrates, thus allowing novel devices to be achieved (e.g., thin film MEMS4). Wet-chemical techniques have been widely used to achieve lowtemperature deposition of PZT films.5,6 Typical approaches to reduce the processing temperature include introduction of seed layers/particles,7–9 use of special substrates having a perfect lattice match with PZT,10 and modifi
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