Masato Shimada

Thickness dependence of structural and ferroelectric properties of sol-gel Pb(Zr0.56Ti0.44)0.90(Mg1/3Nb2/3)0.10O3 films

Abstract Sol-gel Pb(Zr0.56Ti0.44)0.90(Mg1/3Nb2/3)0.10O3 (PZT-PMN) films were prepared onto the Ti/Pt/Ti bottom electrode by multilayer spin coating. The film thickness ranged from 0.22 to 0.88 μm. The Pt top electrodes were deposited on the PZT-PMN films by DC sputtering. The structural and ferroelectric properties of PZT-PMN films were investigated as a function of film thickness by X-ray diffraction (XRD), scanning electron microscopy (SEM), cross-sectional transmission electron microscopy (XTEM), and by measuring the relative permittivity. The film retains the tetragonal perovskite structure with the [111] and [100] preferred orientations perpendicular to the film surface independent of film thickness. The [100] texture increases with increasing film thickness although the [111] texture is always predominant. The film consists of columnar grains. The average grain size is nearly independent of film thickness. The surface layer containing fine grains about 30 nm in diameter is induced on the top of the film. As the film thickness exceeds 0.44 μm, the number of the fine grains decreases remarkably. The crystalline interface layer about 10 nm thick is formed between the film and the bottom electrode. This interface layer is composed of Pt, Pb, Zr, Ti and O, while it is rich in Ti and deficient in Pb and O as compared with the inside of the film. The measured relative permittivity of the film increases with increasing film thickness, following the low permittivity interface model. On the basis of this model, the relative permittivity is estimated to be 3200 for the intrinsic PZT-PMN film, 750 for the surface layer and 50 for the interface layer.

Structural, compositional and piezoelectric properties of the sol-gel Pb(Zr0.56Ti0.44)0.80(Mg1/3Nb2/3)0.20O3/Pb(Zr0.56Ti0.44)O3 composite films

A 750 nm-thick PZT-PMN/PZT composite film was prepared by sequential multiple spin-coatings. First, a 375 nm-thick sol-gel Pb(Zr0.56Ti0.44)O3 (PZT) layer was prepared on a Ti/Pt/Ti bottom electrode and then a 375 nm-thick Pb(Zr0.56Ti0.44)0.80(Mg1/3Nb2/3)0.20O3 (PZT-PMN) layer was prepared on the PZT layer. The structural, compositional and piezoelectric properties of the composite film were investigated by using X-ray diffraction, scanning electron microscopy, cross-sectional transmission electron microscopy and secondary ion mass spectrometry and by measuring the piezoelectric charge constant d31, the piezoelectric voltage constant g31 and the relative permittivity ϵ. The composite film retains the tetragonal perovskite structure with columnar grains. The lattice of the PZT-PMN layer smoothly connects to that of the PZT layer without forming any interfacial structure. However, the atomic composition, mainly in Mg and Nb, differs between PZT-PMN and PZT layers. The composite film has a higher piezoelectric charge constant d31 as compared with the PZT-PMN and PZT single films. The value of d31 is independent of the sequence of the PZT-PMN and PZT layers.

Structure and Piezoelectric Properties of 0.9 Pb(Zr,Ti)O3–0.1 Pb(Mg,Nb)O3 Films Prepared by Metalorganic Deposition Process

The 800-nm-thick 0.9 Pb(Zr,Ti)O3–0.1 Pb(Mg,Nb)O3 (PZT–PMN) were prepared by metalorganic deposition (MOD) process on Ti/Pt/Ti bottom electrodes. The structure of the films was investigated by scanning electron microscopy and X-ray diffraction. The piezoelectric properties of the films were characterized by measuring the electrically induced strain using the cantilever method to determine the piezoelectric charge constant (d31) and by measuring the mechanically induced voltage. The films retain the tetragonal perovskite structure with both [100] and [111] preferred orientations and are made up of columnar grains whose size ranges from 100 nm to 200 nm. The plot of strain versus electrical field shows a hysteresis loop, which reveals that the strain depends on the polarity of the top electrode. The unpoled film is virginally polarized toward the bottom electrode. As a result, d31 at an electrical field of 170 kV/cm is 190 pC/N for positive polarity and 166 pC/N for negative polarity.

Effect of the annealing temperature on structural and piezoelectric properties of the sol–gel Pb(Zr0.56Ti0.44)0.90(Mg1/3Nb2/3)0.10O3 films

Abstract Sol–gel Pb(Zr 0.56 Ti 0.44 ) 0.90 (Mg 1/3 Nb 2/3 ) 0.10 O 3 (PZT–PMN) films 1 μ m thick were prepared onto the Ti/Pt/Ti bottom electrodes by six layer spin-coatings. After the first triple layer coatings, a pre-annealing was carried out by rapid thermal process (RTP) with a step pattern of 600°C/5 min to 725°C/1 min. Finally, after the later triple layer coatings, the films were heat-treated by RTP with a step pattern of 650°C/5 min to 900°C/1 min (low-temperature annealing) or 650°C/5 min to 1050°C/1 min (high-temperature annealing). The structural and piezoelectric properties of the films were investigated by scanning electron microscopy (SEM), cross-sectional transmission electron microscopy (XTEM), and by measuring the piezoelectric charge constant d 31 , the piezoelectric voltage constant g 31 as well as the relative permittivity e . The films retain the tetragonal perovskite structure independent of the final annealing temperature. The interlayer caused at the middle depth of the film by the pre-annealing prevents the columnar grain growth through the film. Many fine grains are grown in the interlayer to be rich in Zr and deficient in Pb. The fine grains rich in Zr and deficient in Pb are also formed on the surface of the film. The growth of such the Zr-rich and Pb-deficient phase is effectively suppressed at the low temperature annealing rather than at the high temperature annealing. Thus, the piezoelectric films 1 μ m thick with high d 31 , g 31 and e are successfully obtained with the low- temperature annealing.

DEPENDENCE OF ELECTRICALLY INDUCED STRAIN ON ORIENTATION AND COMPOSITION IN PB(ZRXTI1-X)O3 FILMS

The effect of orientation and composition on electrically induced strain and relative permittivity of 600-nm-thick Pb(ZrxTi1-x)O3 (PZT) films was investigated. High permittivity was obtained near the morphotropic phase boundary (MPB) composition, unaffected by orientation. For films with mixed textures of [111] and [100], the electrically induced strain was maximum near the MPB composition. While the electrically induced strain showed a tendency to increase with increasing Zr concentration x in the films with [111] preferred orientation, for the Pb(Zr0.65Ti0.35)O3 film with [111] preferred orientation, an electrically induced strain of 0.54% was obtained under an electric field of 250 kV/cm.