Influence of Platinum Bottom Electrodes on the Piezoelectric Performance of PZT Thin Films Hot Sputtered in a High Volum
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Influence of Platinum Bottom Electrodes on the Piezoelectric Performance of PZT Thin Films Hot Sputtered in a High Volume Production Tool Dirk Kaden1, Hans-Joachim Quenzer1, Martin Kratzer2, Lorenzo Castaldi2, Bernhard Wagner1, Bernd Heinz2, Robert Mamazza2 1 Fraunhofer Institute for Silicon Technology (ISiT), 25524 Itzehoe, Germany. 2 OC Oerlikon Balzers AG, 9496 Balzers, Liechtenstein.
ABSTRACT In this work high quality ferroelectric PZT films have been prepared in-situ by hot RF magnetron sputtering. 200 mm wafer were coated with PZT films of 1 µm and 2 µm thickness at sputter rates of 45 nm/min in a high volume production sputtering tool. The films were grown on oxidized Si substrates prepared either with sputtered Ti/TiO2/Pt, sputtered Ti/TiO2/Pt/TiO2 or evaporated Ti/Pt bottom electrodes at substrate holder temperatures in the range from 550 °C to 700 °C. At these temperatures, the material nucleates in the requisite piezoelectric perovskite phase without need of an additional post annealing treatment. The films were investigated with respect to their chemical composition and their crystallographic, piezoelectric and dielectric properties. At an intermediate chuck temperature of 600 °C the PZT thin films were characterized by a minimum volume fraction of secondary nonpiezoelectric phases. A Zr/(Zr+Ti) ratio of 0.53 has been achieved matching the morphotropic phase boundary. By improving the deposition process and poling procedure, a notable high e31,f coefficient of -17.3 C/m² has been obtained. The corresponding longitudinal piezoelectric constant was determined to have an effective longitudinal piezoelectric coefficient d33,f of 160 pm/V. INTRODUCTION Piezoelectric thin films are of great interest in the field of MicroElectroMechanical Systems (MEMS). Lead zirconate titanate (PZT) is, and will remain, the most favorable ferroelectric material [1] when fast microactuators for large forces, momenta and motions at low power consumption are required. The obstacles to prevalence of MEMS fabricated PZT thin film actuators include integration difficulties into a fabrication process and the material complexity of PZT that results in demanding deposition technologies. The possibility of depositing PZT thin films directly by magnetron sputtering would overcome these obstacles. In this work, an in-situ hot sputtering process for the deposition of high quality PZT films on large area substrates has successfully been developed on a high volume sputter tool. The influences of the deposition temperature and the bottom electrode on the stoichiometry of subsequently deposited PZT films and their correlations between the crystallographic, ferroelectric and dielectric properties of the prepared PZT layers have been studied. Finally the reliability of the process was demonstrated. EXPERIMENTS For subsequent sputtering of PZT thin films, three different types of Pt bottom electrodes were used. The metallic films were deposited on (100) oriented 8” silicon substrates passivated
with a thermally grown silicon oxide of 200 nm an
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