Kenji Ishikawa

Thickness dependence of stress in lead titanate thin films deposited on Pt-coated Si

Thickness dependence of the soft mode E(1TO) of tetraganol lead titanate thin film, deposited on Pt-coated Si by a chemical solution deposition, was determined with Raman scattering measurements. A downshift of the soft mode was attributed to the residual stress in the thin film, which was estimated in the range of 1.3–2.6 GPa, corresponding to film thickness of 400–50 nm. The variation of the clamped dielectric constants determined by observed mode frequencies was found to agree with the prediction of stress dependence of dielectric constants by Devonshire theory.

High-piezoelectric behavior of c-axis-oriented lead zirconate titanate thin films with composition near the morphotropic phase boundary

The piezoelectric responses of c-axis-oriented Pb(Zr0.53Ti0.47)O3 (PZT) thin films have been studied by measuring the stress-induced charge with an accurate charge integrator. These measurements reveal that the c-axis-oriented PZT films have high values of d33, which are several times those of ceramic materials. The intrinsic d33 values of poled films are about 680 and 800 pC/N for the c-axis-oriented films on Si and MgO single-crystal substrates, respectively. It shows that the thin-film deposition technique opens an approach for exploring the potential superior properties of PZT near the morphotropic phase boundary.

Observation of Piezoelectric Relaxation in Ferroelectric Thin Films by Continuous Charge Integration

A continuous charge integration technique is used to measure the effective longitudinal piezoelectric coefficient (d33) of thin films. Measurements are performed by applying a static force normal to the films and recording the stress-induced polarization with a charge integrator. Measurements for the as-deposited PbZr0.53Ti0.47O3 (PZT) thin films show that the piezoelectric effect is strongly time-dependent and the relaxation is well described by the stretched exponential law. It was demonstrated that the continuous charge integration technique is highly useful for the characterization of the piezoelectric properties of thin films.

Thickness Dependence of Residual Stress in Alkoxide-Derived Pb(Zr0.3Ti0.7)O3 Thin Film by Chemical Solution Deposition

Ferroelectric thin films of Pb(Zr0.3Ti0.7)O3 (PZT30) with different thicknesses were deposited on a Pt/Ti/SiO2/Si substrate by chemical solution deposition (CSD). The residual stress in the PZT30 thin films was estimated by the phonon mode shift of Raman scattering. The stress dependence of the optical phonon mode of ferroelectric tetragonal PZT30 was calibrated by a gasketed diamond anvil cell (DAC) system. As a result, the A(2TO) mode for PZT30 was downshifted at a rate of 13.9 cm-1/GPa. By using this calibration result, the residual stress in the PZT30 thin films with different thickness was estimated. The residual stress in PZT30 thin films increased with decreasing film thickness and reached approximately 1.14 GPa in the case of a film 280 nm thick. Moreover, the residual stress in the PZT30 thin films was compared with that of a lead titanate (PT) thin film to discuss the origin of the residual stress.

Residual stress in lead titanate thin film on different substrates

This paper describes the effect of thermal expansion coefficients of the substrates on the residual stress in lead titanate (PT) thin film. The residual stress in the film on the different substrates was calculated from the phonon mode shift. In addition, the dielectric constant for the film was calculated from the lattice mode frequency. As a result, the residual stress and the dielectric behavior depended upon the substrates.

Size effect for lead zirconate titanate nano-particles with PZT (40/60) composition

This paper focuses on the size effect of lead zirconate titanate. Pb (Zr0.4 Ti0.6) O3 (PZT40) nano-partilces with different sizes were prepared by the sol–gel method. The crystal size and structure were determined by X-ray diffraction. As a result the c/a ration (terragonality) was close to 1 with decreasing particle size. Raman spectra for PZT40 nano-particle of various sizes have been observed to exhibit a decrease in the soft mode at around 35 nm, suggesting the existence of a critical size of the PZT40 particle. The temperature dependence of Raman spectra clearly revealed that the Curie temerature for PZT40 nano-partilces shifted toward lower temperatures due to the size effect. The intrinsic dielectric onstants of PZT40 nano-particles calculated by the Laddne–Saches–Teller relation increased with decreasing particle size. These results show that Raman scattering is a powerful tool to investigate forrelectric materials.

Size Effect for Lead Zirconium Titanate Nanopowders with Pb(Zr0.3Ti0.7)O3 Composition

This paper focuses on the size effect for lead zirconate titanate. Pb(Zr0.3Ti0.7)O3 (PZT30) nanopowders with different sizes were prepared by chemical solution deposition. The crystal sizes of the prepared samples were determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The crystal structures were identified by XRD. The c/a ratio or tetragonality for PZT30 nanocrystals was close to 1 with decreasing crystal size. Raman spectra for PZT30 nanocrystals with various grain sizes have been observed to show the sudden decrease in the soft mode frequencies E(1TO) and A1(1TO) at around 25 nm, suggesting the existence of the critical size for PZT30 nanopowders. The intrinsic dielectric constant which was calculated from the phonon mode shift by using the Lyddane-Sachs-Teller (LST) relation increased with decreasing crystal size. The temperature dependence of Raman spectra clearly revealed that Tc for PZT30 nanopowder shifted due to the size effect.

Effect of Back-Etching on Residual Stress in Lead Titanate Thin Films on Si Wafer

This paper forcuses on the effect of back-etching on the residual stress in lead titanate (PT) thin film. The PT thin films were deposited by a chemical solution deposition (CSD) on a Pt/Ti/SiO2/Si substrate with different back-etching depth. The part of the Si substrates of 500 µm thickness was etched from back side (back-etching) with a wet etching process. The depth of the back-etching was controlled by changing the etching time in the range from 481.5 µm to 250 µm (residual Si; 18.5–250 µm). The residual stress in PT thin film was calculated from the phonon mode shift of raman scattering. In addition, the intrinsic dielectric constant for PT thin film was also calculated from the lattice mode frequencies. As a result, the residual stress in PT thin films abruptly increased with increasing depth of back-etching at around 300 µm (residual Si; 200 µm) and reached about 1.7 GPa.

Size Effect for Ba(ZrxTi1 − x)O3 (x = 0.05) Nano-Particles

This paper focuses on the size effect for barium zirconate titanate (BZT) prepared by a sol-gel method. BZT particles with different crystal sizes were prepared by carefully controlling the annealing temperatures and times of the alkoxide-derived precursor particles. Particle size was calculated from the XRD patterns using Scherrers equation. The change in the Curie temperature was estimated by XRD pattern measured at different temperatures, and the intrinsic dielectric permittivity for BZT nano-particles were calculated from the phonon mode frequencies using the Lyddane-Sachs-Teller (LST) relation.

Long-Time Piezoelectric Relaxation in Lead Zirconate Titanate Thin Film

The piezoelectric responses of tetragonal (001)&(100)- and (111)-oriented PbZr0.3Ti0.7O3 thin films have been measured in the time domain. A long-time relaxation is observed for the (111)-oriented films; in contrast, the (001)&(100)-oriented films exhibit only a rapid response. This piezoelectric relaxation is considered to be related to the motion of non-180° domain walls. It shows that the (001)&(100)-oriented film is a suitable material for time-stable microelectromechanical devices.