The Development of Lead Zirconate Titanate Thin Films for Piezoelectric Microactuators

Piezoelectric actuation of a thin film is one means used for electrical-mechanical transduction in Microelectromechanical systems (MEMS). Currently, the most commonly employed piezoelectric thin-film material is ZnO. Replacing ZnO with certain compositions of lead zirconate titanate (PZT) should improve the performance of many MEMS devices due to the significantly greater piezoelectric coefficients of PZT (-20 times greater than ZnO).
In this dissertation I investigate the growth and properties-particularly piezoelectric properties-of PZT thin films. I also fabricate a PZT-based MEMS structure, a flexural plate wave (FPW) pump, and compare its performance with similar ZnO-based devices.
PZT films of two compositions, Pb(Zr0.7Ti0.3)O3 and Pb(Zr0.5Ti0.5)O3, were grown using reactive, multi-target, RF-magnetron sputtering on Pt-coated silicon wafers. Films were deposited at temperatures from 200C to 400C and rapid thermally annealed between 450C and 700C to crystallize perovskite PZT. The effects of as-deposited lead excess and deficiency on perovskite phase formation and film properties were studied. Films of composition Pb(Zr0.5Ti0.5)O3 with relative dielectric constants of 1000, remanent polarizations of 20 uC/cm^2, coercive fields of 60 kV/cm, and effective piezoelectric d33 coefficients of 50 pm/N were obtained. These films show promise for use in MEMS.
PZT films also were grown on a series of substrates using pulsed laser deposition (PLD). Epitaxial (100) films were obtained on LaAlO3 single crystal substrates, and randomly oriented films were obtained on Pt-coated silicon wafers. A conducting oxide electrode, (La0.5Sr0.5)CoO3, was used for these films. Good structural and ferroelectric properties were obtained, however these films have limitations for use in MEMS.
An FPW pump was fabricated using a sol-gel PZT thin film. Measured wave amplitudes were significantly higher than those of a similar ZnO-based device at the same driving voltage-250 A on a 5-finger pair PZT device as compared to 145 A on a 25-finger pair ZnO device. Estimations of pumping speed indicate that the PZT device should have a pumping speed more than an order of magnitude greater than the ZnO device.
Annabel Susan Nickles
Eugene E. Haller
Timothy D. Sands
Publication date: 
June 30, 1998
Publication type: 
Ph.D. Dissertation
Nickles, A. S. (1998). The Development of Lead Zirconate Titanate Thin Films for Piezoelectric Microactuators. United States: University of California, Berkeley.

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