PIEZOELECTRIC PROPERTIES OF SPUTTERED PBTIO3 FILMS - GROWTH TEMPERATURE AND POLING TREATMENT EFFECTS

Thin films of lead titanate (PbTiO3) were prepared on silicon substrat es by sputtering. Two processes have been developed; (a) the in situ p rocess (the growth temperature was 440 degrees C) and (b) the depositi on at room temperature followed by a conventional annealing at 680 deg rees C. The dielectric constant, the ferroelectric, and the piezoelect ric properties were evaluated and compared. The dielectric constant of films deposited in situ was higher than those of postannealed films l ikely due to the dense microstructure with fine and homogeneous grains . The embedded beam method and the Berlincourt piezometer were used to measure the e(31) and the d(33) piezoelectric coefficients, respectiv ely. The PbTiO3 films were naturally polarized, in particular the film s grown in situ have large piezoelectric constants: e(31) = -0.49 C/m( 2) and d(33) = 20 pC/N. These values agree broadly with data of bulk c eramics, however, with bulk material a poling treatment is necessary t o attain these values. The poling of the postannealed films leads to a substantial increase of their piezoelectric properties; e(31) = -0.26 C/m(2) and d(33) = 8 pC/N for virgin film and e(31) = -0.41 C/m(2)-d( 33) = 18 pC/N for an applied electric field of 110 kV/cm (close to sat uration) and a poling time of 30 min. The piezoelectric response was f ound to depend on the direction of the poling field. Note d(33) and e( 31) decreased when the poling field was applied against the preferred polarization direction; the polar domains were oriented from the film surface to the substrate. (C) 1998 American Vacuum Society.