Microelectromechanical systems (MEMS) incorporating active piezoelectric layers offer integrated actuation, sensing, and transduction. The broad implementation of such active MEMS has long been constrained by the inability to integrate materials with giant piezoelectric response, such as Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) (PMN-PT). We synthesized high-quality PMN-PT epitaxial thin films on vicinal (001) Si wafers with the use of an epitaxial (001) SrTiO(3) template layer with superior piezoelectric coefficients (e(31,f) = -27 ± 3 coulombs per square meter) and figures of merit for piezoelectric energy-harvesting systems. We have incorporated these heterostructures into microcantilevers that are actuated with extremely low drive voltage due to thin-film piezoelectric properties that rival bulk PMN-PT single crystals. These epitaxial heterostructures exhibit very large electromechanical coupling for ultrasound medical imaging, microfluidic control, mechanical sensing, and energy harvesting.

Vanadium oxide (VOx) thin films were deposited on thermally grown silicon oxide substrates using a pure vanadium target in a pulsed dc sputtering technique. Film microstructure, electrical resistivity, temperature coefficient of resistance (TCR) and activation energy were studied as a function of the oxygen partial pressure (pO2) and growth temperatures. The mixed valence VOx thin films deposited at various substrate temperatures between 40 and 300 °C exhibited columnar grain structure even though the samples were found to be x-ray amorphous. The TCR and activation energies of the films increased from 0.4% (K−1) to 2.4% (K−1) and 0.04 eV to 0.28 eV, respectively, by controlling the pO2 content between depositions. The charge carrier transport in the VOx thin films was found to exhibit conventional and inverse Meyer–Neldel compensation mechanisms depending on the growth conditions.

Dielectric and piezoelectric properties of morphotropic phase boundary (Bi,Na)TiO 3-(Bi,K)TiO 3-BaTiO 3 epitaxial thin films deposited on SrRuO 3 coated SrTiO 3 substrates were reported. Thin films of 350 nm thickness exhibited small signal dielectric permittivity and loss tangent values of 750 and 0.15, respectively, at 1 kHz. Ferroelectric hysteresis measurements indicated a remanent polarization value of 30 µC/cm 2 with a coercive field of 85-100 kV/cm. The thin film transverse piezoelectric coefficient e 31,f of these films after poling at 600 kV/cm was found to be-2.2 C/m 2. The results indicate that these BNT-based thin films are a potential candidate for lead-free piezoelectric devices.

Piezoelectric thin films are of increasing interest in low-voltage micro electromechanical systems for sensing, actuation, and energy harvesting. They also serve as model systems to study fundamental behavior in piezoelectrics. Next-generation technologies such as ultrasound pill cameras, flexible ultrasound arrays, and energy harvesting systems for unattended wireless sensors will all benefit from improvements in the piezoelectric properties of the films. This paper describes tailoring the composition, microstructure, orientation of thin films, and substrate choice to optimize the response. It is shown that increases in the grain size of lead-based perovskite films from 75 to 300 nm results in 40 and 20% increases in the permittivity and piezoelectric coefficients, respectively. This is accompanied by an increase in the nonlinearity in the response. Band excitation piezoresponse force microscopy was used to interrogate the nonlinearity locally. It was found that chemical solution-derived PbZr(0.52)Ti(0.48)O(3) thin films show clusters of larger nonlinear response embedded in a more weakly nonlinear matrix. The scale of the clusters significantly exceeds that of the grain size, suggesting that collective motion of many domain walls contributes to the observed Rayleigh behavior in these films. Finally, it is shown that it is possible to increase the energy-harvesting figure of merit through appropriate materials choice, strong imprint, and composite connectivity patterns.

Low temperature charge transport in vanadium oxide (VOx) thin films processed using pulsed dc sputtering is investigated to understand the correlation between the processing conditions and electrical properties. It is identified that the temperature dependent resistivity ρ(T) of the VOx thin films is dominated by a Efros–Shklovskii variable range hopping mechanism [Efros and Shklovskii, J. Phys. C 8, L49 (1975)]. A detailed analysis in terms of charge hopping parameters in the low temperature regime is used to correlate film properties with the pulsed dc sputtering conditions.

Antiferroelectric lead zirconate ͑PZ͒ thin films were deposited by pulsed laser ablation on platinum-coated silicon substrates. Films showed a polycrystalline pervoskite structure upon annealing at 650°C for 5-10 min. Dielectric properties were investigated as a function of temperature and frequency. The dielectric constant of PZ films was 220 at 100 kHz with a dissipation factor of 0.03. The electric field induced transformation from the antiferroelectric phase to the ferroelectric phase was observed through the polarization change, using a Sawyer-Tower circuit. The maximum polarization value obtained was 40 C/cm 2 . The average fields to excite the ferroelectric state, and to reverse to the antiferroelectric state were 71 and 140 kV/cm, respectively. The field induced switching was also observed through double maxima in capacitance-voltage characteristics. Leakage current was studied in terms of current versus time and current versus voltage measurements. A leakage current density of 5ϫ10 Ϫ7 A/cm 2 at 3 V, for a film of 0.7 m thickness, was noted at room temperature. The trap mechanism was investigated in detail in lead zirconate thin films based upon a space charge limited conduction mechanism. The films showed a backward switching time of less than 90 ns at room temperature.

The dielectric and ferroelectric switching properties of high temperature-high energy density (1-x)BaTiO(3)-xBiScO(3) (0.1 <= x <= 0.4) dielectrics were investigated over a broad temperature range. It was found that these ceramics possess dipole glass features such as critical slowing down of the dielectric relaxation, polarization hysteresis aging, rejuvenation, and holelike memory below the dipole glass transition temperature (T(DG)). The dielectric relaxation behavior is consistent with a three-dimensional Ising model with critical slowing exponents (z nu) = 10 +/-1 and composition-dependent glass transition temperatures. At lower temperatures, (1-x)BaTiO(3)-xBiScO(3) ceramics transform into a reentrant dipole glass state owing to the breakup of local polar ordering. A phase diagram is developed marking the paraelectric, ferroelectric, and dipole glass regimes as a function of composition with the reentrant features.

Dielectrics that provide higher electrostatic energy densities are urgently required for power electronic applications; recent observations in the solid solution of (1 − x)BaTiO3 − xBiScO3 show promise, and low temperature re-entrant dipole glass behavior is inferred. Here, direct observations of switchable polarization freezing in the reentrant dipole-glass (1 − x)BaTiO3 − xBiScO3, 0.1 ≤ x ≤ 0.4 are reported. As the temperature is decreased, the switchable polarization increases rapidly, reaches a maximum value at the reentrant temperature (TR) before disappearing at low temperatures. With measurement electric field (E), the TR is found to increase in (1 − x)BaTiO3 − xBiScO3, 0.1 ≤ x ≤ 0.4, as a function of x.