Characterization and aging response of the d(31) piezoelectric coefficientof lead zirconate titanate thin films

The wafer flexure technique was used to characterize the d(31) coefficient of a number of sol-gel and radio frequency (rf) sputtered lead zirconate ti tanate (PZT) thin films with thicknesses between 0.6 and 3 mu m. Typical d( 31) values for well-poled 52/48 sol-gel films were found to be between -50 and -60 pC/N. The rf sputtered films possessed large as-deposited polarizat ions which produced d(31) coefficients on the order of -70 pC/N in some unp oled films. The subsequent poling of the material, in a direction parallel to the preferred direction increased the d(31) coefficient to values of abo ut -85 pC/N. The aging behavior of the d(31) coefficient was also investiga ted. For sol-gel films the aging rate was found to be independent of poling direction and to range from 4% per decade for a 2.5 mu m film to 8% per de cade for a 0.6 mu m film. In contrast, the aging rate of sputtered films wa s strongly dependent on poling direction, with maximum and minimum rates of 26% and 2% per decade recorded. These aging rates are very high in light o f the limited twin wall motion in PZT films, and are believed to result fro m the depolarizing effects of internal electric fields in the rf sputtered films and interfacial defects in the sol-gel films. (C) 1999 American Insti tute of Physics. [S0021-8979(99)04609-5].