Lead-free piezoelectric K0.5Na0.5NbO3 thin films for microelectromechanical systems were fabricated via chemical solution process using metal alkoxide. Perovskite K0.5Na0.5NbO3 (KNN) single-phase thin films with good leakage current properties were successfully prepared by optimizing the KxNaxNbO3 (x≧0.5) composition of the precursor solution. The KNN thin films prepared from the solution with K0.55Na0.55NbO3 composition showed typical ferroelectric P–E hysteresis and field-induced strain loops. The 2Pr and 2Ec values of the K0.55Na0.55NbO3 films were 14 µC/cm2 and 140 kV/cm, respectively. From the slope of the field-induced butterfly loop, the effective d33 was found to be 46 pm/V.

Neodymium-doped Bi4Ti3O12 (BNT) films are evaluated for use as lead-free thin-film piezoelectrics in microelectromechanical systems. Bi4Ti3O12, Bi3.25La0.75Ti3O12, and Bi3.25Nd0.75Ti3O12 films were fabricated by chemical solution deposition on Pt/TiOx/SiO2/Si substrates. Nd substitution promoted random orientation with low (00l) diffraction peaks. The 1-μm-thick Bi3.25Nd0.75Ti3O12 film annealed at 750 °C exhibited a remanent polarization of 26 μC/cm2. Typical butterfly field-induced strain loops were obtained in the BNT film capacitors. The electrically induced strain is 8.4×10−4 under the bipolar driving field of 220 kV/cm. These results show that BNT is a promising candidate for use in lead-free thin-film piezoelectrics.

Ferroelectric BaTiO3 thin films were prepared on Pt(111)/ SiO2/Si(100) substrates at 650° C by the sol-gel method. Film thickness could be varied by repeating a dip coating/heating cycle. The texture of the BaTiO3 thin films became more dense and homogeneous when the film thickness increased. The crystalline thin films showed microstructure with grains as small as 20–30 nm. The dielectric properties could be measured for films thicker than 0.25 µ m. With increasing film thickness, the dielectric constant and remanent polarization increased and the coercive field decreased. Loss tangent of the thin films was independent of the film thickness. BaTiO3 thin film with a thickness of 0.58 µ m exhibited a dielectric constant of 1000, remanent polarization of 8 µ C/cm2 and coercive field of 30 kV/cm.

An atomic force microscope (AFM) is used to measure the magnitude of the effective longitudinal piezoelectric constant (d33) of thin films. Measurements are performed with a conducting diamond AFM tip in contact with a top electrode which is driven by an externally applied voltage. The interaction between the tip and electric field present is a potentially large source of error that is eliminated through the use of this configuration and the conducting diamond tips. Measurements yielded reasonable piezoelectric constants of X-cut single crystal quartz, thin film ZnO, Pb(Zr,Ti)O3 (Zr/Ti = 30/70), and nonpiezoelectric amorphous SiO2 thin films. The system was also used to measure d33 hysteresis loops for Pb(Zrx,Ti1−x)O3 thin films.

The electrocaloric properties of Pb(Zr,Ti)O 3 (PZT)-based and Ba(Zr,Ti)O 3 ceramics and Pb(Mg,Nb)O 3 -PbTiO 3 (PMN-PT) crystals were investigated by the indirect estimation and direct measurement of temperature-electric field (T-E) hysteresis loops. The measured T-E loops showed a similar shape to strain-electric field (s-E) loops. The adiabatic temperature change ΔT due to electrocaloric effects was estimated from the polarization change of these samples. ΔTs of 0.48 and 0.66 K were estimated for the (Pb,La)(Zr,Ti)O 3 (PLZT)(9.1/65/35) ceramics and PMN-PT crystals under a field of 30 kV/cm, respectively. The measured temperature changes ΔTs in these samples upon the release of the electric field from 30 kV/cm to zero were 0.39 and 0.36 K, respectively.