S. Corkovic

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 metal-organic 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 fil...

Comparative measurements of piezoelectric coefficient of PZT films by berlincourt, interferometer, and vibrometer methods

Chemical solution deposition (CSD) techniques were used to prepare lead zirconate (Zr) titanate (Ti) (PZT) thin films with Zr/Ti ratios of 30/70 and 52/48. Usually CSD processing is restricted to making crack-free, single-layer films of 70-nm thick, but modifications to the sol-gel process have permitted the fabrication of dense, crack-free, single layers up to 200 to 300 nm thick, which can be built-up into layers up to 3-mum thick. Thicker PZT films (>2-mum single layer) can be produced by using a composite sol-gel/ceramic process. Knowledge of the electroactive properties of these materials is essential for modeling and design of novel micro-electromechanical systems (MEMS) devices, but accurate measurement of these properties is by no means straightforward. A novel, double-beam, common-path laser interferometer has been developed to measure the longitudinal (d33) piezoelectric coefficient in films; the results were compared with the values obtained by Berlincourt and laser scanning vibrometer methods. It was found that, for thin-film samples, the d33,f values obtained from the Berlincourt method are usually larger than those obtained from the interferometer and the vibrometer methods; the reasons for this are discussed

Enhanced pyroelectric coefficient of antiferroelectric-ferroelectric bilayer thin films

In this study, the pyroelectric coefficient and the figure of merit (FOM) of the ferroelectric (FE) PbZr0.3Ti0.7O3 (PZT 30/70) thin films were found to be greatly enhanced by introducing a thin antiferroelectric (AF) PbZr0.95Ti0.05O3 (PZT 95/05) layer underneath the FE film and thus creating a bilayer structure on platinized silicon substrates. The film properties were investigated as a function of the FE layer thickness when the thickness of AF layer remained unchanged. The highest pyroelectric coefficient of 1 μm thick PZT 30/70 film was 3.18×10−4 cm−2 K−1. However, the highest pyroelectric coefficient for 1 μm thick bilayer film was 3.5×10−4 or 2.5×10−4 cm−2 K−1 for only 280 nm thick bilayer film. The enhancement of pyroelectric coefficient suggests switching of AF into FE phase during poling and following stabilization of FE phase at room temperature. The reduction in dielectric constant in bilayer films after poling, compared to pure PZT 30/70, showed a FOM of 2.94×10−5 Pa−0.5, which is the double of...

Reversible charge injection in antiferroelectric thin films

High-energy storage antiferroelectric capacitors operated in a high speed require the quick release of stored charges after the removal of the electrical field accompanying ferroelectric-to-antiferroelectric phase transition. However, the phase-transition time can vary from a few nanoseconds to milliseconds due to the reversible charge injection into the film to temporally stabilize the high-field ferroelectric phase. The consequent theoretical modeling discloses the nearly Ohmic contact of an antiferroelectric Au/Cr/Pb(Zr0.95Ti0.05)O3/Pt thin-film capacitor for the charge injection unlike the Schottky emission of a typical ferroelectric capacitor.

THE ELECTROMECHANICAL PROPERTIES OF HIGHLY [100] ORIENTED [Pb(Zr0.52Ti0.48)O3, PZT] THIN FILMS

ABSTRACT 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.

SOL-GEL FABRICATION OF PZT THICK FILMS FOR MEMS

ABSTRACT Pb(ZrxTi1 – x)O3 (PZT) sol (≥ 0.6M) was spun onto platinised silicon substrate. The single layer thickness of a dense, crack-free film up to 500 nm could be obtained. It was found that the key factor in obtaining thick crack-free films was to choose an appropriate heating profile, using a method based on the wafer deflection measurement. By using the temperature profile to thermally treat each single layer, it was possible to obtain thick crack-free films by repeatedly spin-coating. The dielectric and piezoelectric properties of the films with different thicknesses and orientations were measured and compared.