Integrated piezoelectric thin films for microactuators

Abstract

Thin films of (1-x)Pb(Mg_1/3Nb_2/3)O₃ - xPbTiO₃ (x = 0.1 to 0.3) (PMN-PT) were grown on the platinum coated silicon substrate by pulsed excimer laser ablation technique. The composition and the structure of the films were modulated via proper variation of the deposition parameters. A room temperature dielectric constant varying from 2000 to 4500 was noted for different composition of the films. The dielectric properties of the films were studied over the frequency range of 100 Hz - 100 kHz over a wide range of temperatures. The films exhibited the relaxor- type behavior that was characterized by the frequency dispersion of the temperature of dielectric constant maxima (T_m) and also diffuse phase transition. This relaxor nature in PMN-PT thin films was attributed to freezing of the dipole moment, which takes place below a certain temperature. This phenomenon was found to be very similar to spin glass systems, where spins are observed to freeze after certain temperature. Antiferroelectric lead zirconate (PZ) thin films were deposited by pulsed laser ablation technique on Pt coated Si substrates. The films that were deposited at a lower temperature of 300° C with subsequent post annealing at 650° C for 5 min. (ex-situ films) exhibited polycrystalline multi-grained microstructure, whereas the films that were deposited at a higher substrate temperature (in-situ films) of 550° C exhibited highly oriented (110) columnar microstructure. The antiferroelectric nature of the PZ films was confirmed by the double hysteresis behavior in polarization vs. applied electric field characteristics. These two films showed a difference in the dielectric and electrical properties and were attributed to the difference in their microstructure.