Preparation of piezoelectric PZT thin films by MOCVD for MEMS applications

Integration of piezoelectric Pb(Zr,Ti)O₃ (PZT) thin films promises to provide silicon-based microelectromechanical systems (MEMS) with added functionality. PZT films with compositions near the tetragonal/rhombohedral morphotropic boundary have been deposited on iridium-coated Si substrates by a thermal chemical vapor deposition (CVD) process using flash vaporized metalorganic precursors. Process variables including (A-site)-to-(B-site) ratios in the precursor mix and deposition times have been surveyed. Stoichiometric, perovskite films with nominal Zr/Ti ratios ranging from 40/60 to 60/40 were obtained. Parallel-plate capacitor structures have been fabricated by depositing Pt top electrodes using e-beam evaporation through shadow masks. Ferroelectric hysteresis loops were measured using a standard ferroelectric tester. Remnant polarization values in the range of 20 approx. 30 μC/cm² were obtained. For films of 0.5 μm or thicker, piezoelectric hysteresis loops were characterized by dual-beam interferometry. Longitudinal piezoelectric coefficients (d₃₃) of 30 approx. 60 pm/V were observed on the films deposited between 550 and 600°C.