D. V. Taylor

Discrimination between bulk and interface scenarios for the suppression of the switchable polarization (fatigue) in Pb(Zr,Ti)O3 thin films capacitors with Pt electrodes

A simple and reliable method which allows one to distinguish between the two major microscopic scenarios for the suppression of the switching polarization (Prs), i.e., pinning of ferroelectric domain walls (DWs) through the Pb(Zr,Ti)O3 film (PZT) (bulk scenario) and inhibition of the growth of opposite domains due to the nucleus suppression at the electrode interfaces (interface scenario), is proposed. In addition, a new electric treatment able to significantly suppress Prs in Pt–PZT–Pt ferroelectric capacitors (FECAPs) of thicknesses above 1.4 μm, was discovered and studied. It consists of the application of an external alternating electric field (Ee) which cycles the polarization at very low frequency (1.7 mHz). After only 10–20 cycles, Prs can be suppressed by a factor of 10. The same FECAP, when subjected to Ee at higher frequency (30 kHz), endures at least 108 switches, before attaining an equivalent Prs suppression (hereafter called fatigue). The fatigued states obtained with the two different proce...

Piezoelectric properties of rhombohedral Pb(Zr, Ti)O3 thin films with (100), (111), and “random” crystallographic orientation

The longitudinal d33 piezoelectric coefficient was studied in rhombohedral Pb(Zr0.6Ti0.4)O3 thin films with (111), (100), and “random” orientation. The largest d33 was found in (100)-oriented films and the smallest along the polarization direction in (111)-oriented films. These results are in a good qualitative agreement with recent theoretical predictions [Du, Zheng, Belegundu, and Uchino, Appl. Phys. Lett. 72, 2421 (1998)]. The field dependence of d33 was also investigated as a function of crystallographic orientation of the films. It was found that (100)-oriented films with the highest piezoelectric coefficient exhibit the weakest nonlinearity. Observed variation in the piezoelectric nonlinearity with film orientation can be fully explained by taking into account domain-wall contributions, which are dependent on film orientation.

Evidence of domain wall contribution to the dielectric permittivity in PZT thin films at sub-switching fields

Through the use of relations analogous to that of the Rayleigh law, it is demonstrated that the ac electric field dependence of the permittivity of ferroelectric thin films can be described. It is further shown that both reversible and irreversible components of the permittivity decrease linearly with the logarithm of the frequency of the ac field. The results demonstrate that the models describing the interaction of domain walls and randomly distributed pinning centers in magnetic materials can be extended to the displacement of domain walls in ferroelectric thin films.

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...

High resolution study of domain nucleation and growth during polarization switching in Pb(Zr,Ti)O3 ferroelectric thin film capacitors

The domain nucleation and growth during polarization switching in Pb(Zr,Ti)O3 (PZT) ferroelectric thin film capacitors with Pt top (TE) and bottom electrodes (BE) were studied by means of atomic force microscopy (AFM). The experimental configuration used in this study differs from that conventionally used (AFM tip/PZT/BE) where the AFM tip acts as a positionable TE. A small ac voltage was applied between the electrodes with a step by step increasing dc bias voltage. The induced piezoelectric vibration was detected by the AFM tip, its amplitude and phase determined with the lock-in amplifier. The phase difference between the applied ac voltage and the piezoelectric signal as a function of the x-y position was nearly locked at 0 or 180, representing film regions with parallel (in-phase) and antiparallel (antiphase) polarization direction, respectively. The polarization reversal was induced by application of a step by step increasing dc bias field opposite to the polarization of the prepoled sample. At each ...

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.

Domain wall pinning contribution to the nonlinear dielectric permittivity in Pb(Zr, Ti)O3 thin films

The ac field dependence of dielectric response of sol-gel derived Pb(Zr, Ti)O-3 thin films is presented. The analysis of amplitude and phase angle of first and third harmonic of the polarization at subswitching fields shows that a description of the dielectric nonlinearity by the classical polynomial approximation is inadequate. A qualitatively better description of many features of the experimental data is obtained using the Rayleigh relationship, indicating that the nonlinear behavior is associated with the pinning of domain walls on randomly distributed pinning centers

Fatigued state of the Pt-PZT-Pt system

Abstract The fatigued state of Pt-PZT-Pt ferroelectric capacitors (FECAP) was investigated by means of piezoelectric coefficient, polarisation charge and permittivity measurements. The suppression of switching polarisation Pr S appears to be the result of freezing of ferroelectric domains without affecting the lattice dielectric properties. The frozen polarised domains show a preferential orientation which is related to the electrode interface asymmetry. The fatigue mechanism in thin films is not assisted by a growing passive layer and is characterised by a substantial reversible character and adaptation to the used fatiguing field (field self-adjusting). With consideration of the frozen asymmetry and of the newly discovered slow cycling fatiguing effect in thicker samples, the fatigue mechanism was interpreted as inhibition of the nucleation at the top electrode interface. Since it is unlikely that the domain walls (DW) cross the grain boundaries, it is suggested that the effective suppression of Pr S oc...

Characterisation of the fatigued state of ferroelectric PZT thin-film capacitors

In the present study, piezoelectric, conductivity and dielectric measurements have been performed on virgin and fatigued ferroelectric PZT thin films prepared by spin-on sol-gel deposition process on Si/SiO2/Ti/Pt substrates. By fatiguing, the polarisation shows a strong exponential degradation, the hysteresis loops of the piezoelectric coefficient d(33) become smaller and asymmetric and the polarisation-induced asymmetry of the conductivity at low voltage and the relative permittivity both decrease. The ensemble of these results shows that the fatigued state is produced by the freezing of ferroelectric domains with the preferential orientation from the top to the bottom electrode. However, since the magnitude of the total polarisation after poling in the same direction in the fatigued state is smaller than that observed in the virgin state, it is concluded that part of the frozen polarisation is oriented in the opposite direction.

Interferometric study of piezoelectric degradation in ferroelectric thin films

Degradation of piezoelectric properties has been studied in ferroelectric PZT films by means of optical interferometry. The degradation under dc bias and aging of poled films have been observed. The decay of piezoelectric coefficient with time is described by a logarithmic law with aging rates comparable to those of switching polarization. The aging rates are shown to be sensitive to poling conditions and to orientation of the poling field with respect to the direction of preferred polarization. The fatigue measurements revealed a decrease of piezoelectric coefficient with a simultaneous shift of piezoelectric hysteresis loops. Degradation tests on thin membranes covered by PZT films have been reported.