The Microscopic Origin of Residual Stress for Flat Self-Actuating Piezoelectric Cantilevers

In this study, flat piezoelectric microcantilevers were fabricated under low-stress Pb(Zr0.52Ti0.48)O3 (PZT) film conditions. They were analyzed using the Raman spectrum and wafer curvature methods. Based on the residual stress analysis, we found that a thickness of 1 μm was critical, since stress relaxation starts to occur at greater thicknesses, due to surface roughening. The (111) preferred orientation started to decrease when the film thickness was greater than 1 μm. The d33 value was closely related to the stress relaxation associated with the preferred orientation changes. We examined the harmonic response at different PZT cantilever lengths and obtained a 9.4-μm tip displacement at 3 Vp-p at 1 kHz. These analyses can provide a platform for the reliable operation of piezoelectric microdevices, potentially nanodevice when one needs to have simultaneous control of the residual stress and the piezoelectric properties

Development of residual stress in sol-gel derived Pb(Zr,Ti)O3 films: An experimental study

Residual stresses develop in the sol-gel-derived ferroelectric thin films during the transformation of the metalorganic gel to the metal oxide upon thermal treatment and due to the thermal and elastic mismatch between the Pb(Zrx,Ti1-x)O3 (PZT) film and the substrate materials during cooling. In this study, residual stresses were determined using the wafer curvature method after the deposition of multilayer PZT film on platinized (100) silicon wafers. A multilayer model for stress analysis was used to calculate the residual stress in PZT films of three different compositions, x=0.4, x=0.52 and x=0.6. Orientation dependent residual stresses were found in compositions containing the tetragonal phase, with x=0.4 and x=0.52. Depending on the fraction of (100) orientated domains low compressive or low tensile stress was found in Pb(Zr0.4Ti0.6)O3 (PZT 40/60). Higher residual stress was found in PZT films consisting of only rhombohedral crystallographic structure (PZT 60/40) while the residual stress in PZT films with morphotropic boundary composition (PZT 52/48) was significantly dependent on the film orientation and the phase composition and could range from 17 MPa to 90 MPa. The effect of the film orientation on residual stress was found to be a function of the anisotropic thermal expansion coefficient of PZT. The contribution of the thermal and elastic properties of materials to the total wafer curvature was investigated and discussed. Finally, the residual stress results calculated with the four layers model were compared to the results calculated using the Stoney equation

The electromechanical properties of highly [100] oriented [Pb(Zr0.52ti0.48)O3, Pzt] thin films

Lead zirconate titanate [Pb(Zr0.52Ti0.48)O3, PZT] thin films were deposited on Pt (111)/Ti/SiO2/Si and Pt (200)/Ti/SiO2/Si substrates by sol-gel method. Pyrolysis temperature and time were used to control the orientation of the thin films. A PbO buffer layer was also used to enhance the growth of (100)/(001) orientation. Poling highly (100) oriented PZT 52/48 thin films deposited on Pt (111) led to cracking and/or incomplete poling as a consequence of the additional residual stresses introduced by the a to c domain orientation switching. These problems of cracking and incomplete poling did not occur for the (100)/(001)-oriented PZT films deposited on the Pt (200), which possess high piezoelectric coefficients with maximum e31,f and d33,f of −13.9± 4 C/m2 and ∼80± 25 pC/N, respectively. The elastic and electromechanical properties were measured using nanoindentation for films with different texture and compared with data obtained using a flexural method