A. L. Kholkin

Interferometric measurements of electric field-induced displacements in piezoelectric thin films

Interferometric measurements of electric field‐induced displacements in piezoelectric thin films using single‐beam and double‐beam optical detection schemes are reported. It is shown that vibrational response measured with a single‐beam interferometer includes a large contribution of the bending motion of substrate. Therefore, it is difficult to apply single‐beam technique for piezoelectric measurements in thin films. To suppress the bending effect a high‐resolution double‐beam interferometer is proposed. The sensitivity of the interferometer is significantly improved in comparison with previously reported system. The interferometer is shown to resolve small displacements without using a lock‐in technique. An example of the interferometric capabilities is demonstrated with experimental results on electric field, frequency, and time dependences of piezoelectric response for quartz and Pb(Zr,Ti)O3 thin film.

Nanoscale ferroelectrics : processing, characterization and future trends

This review paper summarizes recent advances in the quickly developing field of nanoscale ferroelectrics, analyses its current status and considers potential future developments. The paper presents a brief survey of the fabrication methods of ferroelectric nanostructures and investigation of the size effects by means of scanning probe microscopy. One of the focuses of the review will be the study of kinetics of nanoscale ferroelectric switching in inhomogeneous electrical and elastic fields. Another emphasis will be made on tailoring the electrical and mechanical properties of ferroelectrics with a viewpoint of fabrication of nanoscale domain structures.

Effect of diamagnetic Ca, Sr, Pb, and Ba substitution on the crystal structure and multiferroic properties of the BiFeO3 perovskite

In this work, we studied the effect of heterovalent Ca, Sr, Pb, and Ba substitution on the crystal structure, dielectric, local ferroelectric, and magnetic properties of the BiFeO3 multiferroic perovskite. Ceramic solid solutions with the general formula Bi0.7A0.3FeO3 (A is a doping element) were prepared and characterized by x-ray diffraction, dielectric, piezoresponse force microscopy (PFM), and magnetic measurements. It is shown that the crystal structure of the compounds is described within the space group R3c, permitting the spontaneous polarization, whose existence was confirmed by the PFM data. Magnetic properties of the solid solutions are determined by the ionic radius of the substituting element. Experimental results suggest that the increase in the radius of the A-site ion leads to the effective suppression of the spiral spin structure of BiFeO3, resulting in the appearance of net magnetization.

Piezoelectric actuation of PZT thin-film diaphragms at static and resonant conditions

The piezoelectric response of silicon diaphragms covered with sputter-deposited PbZr0.45Ti0.55O3 (PZT) films has been investigated in view of their application in ultrasonic micro-actuators. The behaviour of resonance frequencies and quasistatic deflections has been studied as a function of membrane thickness and d.c. bias. The total stress in the films and the piezoelectric constant, d(31), have been derived by means of two different methods. The results are consistent with direct strain measurements by optical interferometry and with bulk ceramic values of identical composition.

Fabrication and Characterization of Pzt Thin-Film Vibrators for Micromotors

For the first time we have characterized a micromotor driven by a piezoelectric PZT (PbZrxTi1-xO3) thin film. Sputter and sol-gel techniques have been applied for the deposition of the PZT films onto a silicon stator membrane, which is 20-30 mu m thick and has a diameter of 4 mm. The amplitudes of the membrane deflections are measured by means of laser interferometry. They are as large as 800 nm V-1 at the first resonance (26 kHz) and 60 nm V-1 at 1 kHz. This is one order of magnitude larger than previously reported for a ZnO-activated device of similar geometry. The motor operates at 1-3 V-r.m.s., with speeds of up to 200 rpm at 1.1 V-r.m.s. and torques of 35 nN m at 2.5 V-r.m.s. and 1 mN force between rotor and stator. Compared with the conceptually identical ZnO version published by Racine et al., this is an improvement by a factor of three in speed per volt. Taking into account the linear increase of the torque with the stator vibration frequency, the torque per volt is a factor of two higher. A long-term test of 100 h showed no degradation of the motor performance.

Asymmetric nanoscale switching in ferroelectric thin films by scanning force microscopy

Scanning force microscopy (SFM) has been used to perform nanoscale studies of the switching behavior of Pb(Zr, Ti)O3 thin films via the direct observation of their domain structures. The study revealed a significant asymmetry of a switching pattern which is a function of the voltage polarity and original domain structure of individual grains. The phenomenon of asymmetric switching is attributed (1) to the presence of an internal built-in electric field at the bottom interface and (2) to the mechanical stress exerted by the SFM tip. The former effect results in incomplete 180° switching, while the latter effect leads to a 90° rotation of the polarization vector. The resulting shear stress deformation of the grain underneath the tip combined with the applied field effect propels polarization reversal in the adjacent grains.

Synthesis and multiferroic properties of Bi0.8A0.2FeO3 (A=Ca,Sr,Pb) ceramics

Bi1−xAxFeO3 ceramics (A=Ca,Sr,Pb) were sintered by conventional mixed oxide route. The crystallographic structure of all samples is characterized by the rhombohedral symmetry (space group R3c). The existence of switchable ferroelectric polarization is verified by piezoresponse force microscopy that is proven to be a useful technique in semi-insulating ferroelectrics. Magnetic properties of Ca and Sr-doped ceramics are found to reproduce the antiferromagnetic behavior of undoped BiFeO3 without any enhancement of the magnetization. On the contrary, Pb-doped compound demonstrates appearance of a weak ferromagnetism. It is thus shown that Pb doping of BiFeO3 is a promising way for preparing multiferroic materials.

Self-polarization effect in Pb(Zr,Ti)O3 thin films

Abstract The self-polarization effect is investigated in Pb(Zr,Ti)O3 (PZT) thin films deposited by sol-gel and magnetron sputtering techniques. The effective piezoelectric coefficient of as-grown films, which is proportional to their initial polarization (self-polarization), is measured by a sensitive interferometric technique as a function of the annealing temperature, PZT composition, film thickness and bottom electrode material. The results indicate that the films are self-polarized by an internal bias field upon cooling through the phase transition temperature. It is suggested that a built-in field of a Schottky barrier between the PZT film and the bottom electrode is responsible for the observed effect. Self-polarization of the films is found to be very stable and in some cases to be as high as 90% of that produced by the subsequent room temperature poling. This property is very useful for piezoelectric and pyroelectric applications of PZT films since the poling procedure can be avoided. The properti...

Crystal structure and multiferroic properties of Gd-substituted BiFeO3

Room-temperature crystal structure, local ferroelectric, and magnetic properties of the Bi1−xGdxFeO3 (x=0.1,0.2,0.3) polycrystalline samples have been investigated by x-ray diffraction, piezoresponse force microscopy, and magnetometry techniques. Performed measurements have revealed a sequence of the composition-driven structural phase transitions R3c→Pn21a (occurs at x∼0.1) and Pn21a→Pnma (takes place within the concentrational range of 0.2<x<0.3). The latter structural transformation is attributed to the substitution-induced suppression of the polar displacements. Gd substitution has been shown to effectively induce the appearance of the spontaneous magnetization, thus indicating a promising way for improving multiferroic properties of antiferromagnetic BiFeO3.

FATIGUE OF PIEZOELECTRIC PROPERTIES IN PB(ZR,TI)O3 FILMS

Piezoelectric properties of Pb(Zr,Ti)O3 thin films are investigated as a function of the number of bipolar (switching) and unipolar (nonswitching) voltage pulses. The longitudinal piezoelectric coefficient d33 decreases with bipolar fatigue reflecting the decrease of switchable polarization. Simultaneously, a strong vertical shift of piezoelectric hysteresis loops is observed, which is considered as the buildup of fixed internal polarization due to the pinning of ferroelectric domains in a preferred orientation. Piezoelectric fatigue induced by unipolar (nonswitching) pulses is considerably smaller than the fatigue under bipolar conditions and can be described by the internal bias field which shifts piezoelectric hysteresis loops along the field axis.