Tadashi Yonezawa

Preparation of Bi-Based Ferroelectric Thin Films by Sol-Gel Method

The effects of Bi/Ta and Sr/Ta mole ratios on ferroelectric properties of Srx Biy Ta2Oz [ SBIT(x/y/2.0); 0.7≤x≤1.0, 2.0≤y≤2.6] thin-film capacitors were investigated. The SBIT films were grown by the sol-gel method using a spin-on coating on Pt/Ta/SiO2/Si and Pt/Ti/SiO2/Si substrates. The films were annealed at 800° C for one hour in oxygen atmosphere. Remanent polarization (Pr) depended strongly on the Sr/Ta mole ratio, and increased with decrease of the Sr/Ta mole ratio. On the other hand, Pr was almost independent of the Bi/Ta mole ratio. Scanning electron microscopy (SEM) images show that crystal grains grew with decrease of the Sr/Ta mole ratio. Electron probe micro analyzer (EPMA) analysis revealed that Bi content in SBIT films increased with decrease in Sr composition from stoichiometry.

Surface morphology of lead-based thin films and their properties

Surface morphology of lead-zirconate-titanate [PZT(52/48)] thin films prepared by sol-gel processing on Pt/Ti/ SiO2/Si substrates was studied. When the atomic ratio [Pb/(Zr+Ti)] of PZT gel films was 1, rosette structure was observed in the films after annealing at 600° C for one hour. The crystal structure of the rosette was identified as perovskite and that of the other area was nonperovskite, by electron diffraction analysis. Lead deficiency in the non-perovskite phase caused by lead diffusion into the bottom electrode was detected by energy dispersive X-ray spectroscopy and Auger electron spectroscopy. In order to prepare PZT films with a smooth surface, the following four means were efficient: addition of lead excess, rapid thermal annealing (RTA), adoption of buffer layer, and preparation of crystal nucleus on the substrate.

Influence of buffer layers on microstructural and ferroelectric characteristics of sol-gel derived PbZrxTi1-xO3 thin films

Pb(Zr, Ti)O3 (PZT) films with very thin PbTiO3 (PT) and ( Ba0.5Sr0.5)TiO3 (BST) buffer layers inserted between the film and Pt/Ti/ SiO2/Si substrate were synthesized by the sol-gel technique, and effects of variation in thickness upon microstructural and ferroelectric characteristics were investigated. Insertion of buffer layers was found to exert marked effects. PT buffer layers with thicknesses as thin as 2–4 nm yield PZT films with dense, homogeneous microstructure and good ferroelectric properties such as large remanent polarization, small coercive field and low leakage current densities. On the other hand, use of (2–4)-nm-thick BST buffer layers yields PZT films with dense microstructure and good dielectric properties such as increased permittivity, small coercive field and good leakage current characteristics. However, fatigue behavior of PZT films was not improved through insertion of PT or BST buffer layer.

Ionic conductivity and morphology in Sc2O3 and Al2O3 doped ZrO2 films prepared by the sol–gel method

Abstract We used the sol–gel method to deposit zirconia films doped with Sc2O3 and Al2O3 on alumina substrates. We investigated the annealing temperature dependence of the ionic conductivity and morphology in the films whose composition was 0.85ZrO2–0.11Sc2O3–0.04Al2O3. The film thickness was controlled from about 0.1 to 1.0 microns by controlling the coating time. The films prepared by this method are stabilized in the cubic phase. Annealing at 1200°C produces isotropic and well-sintered films. The ionic conductivity of the annealed film was 7.6×10−2 S/cm at 800°C, which is comparable to that of bulk samples prepared by solid reaction at 1620°C.

Ultrasonic Properties of Lead Zirconate Titanate Thin Films in UHF-SHF Range

We describe the ultrasonic properties of lead zirconate titanate (PZT) thin films prepared by the sol-gel method. It is shown that the PZT thin film exhibits efficient transduction of bulk and surface acoustic waves in UHF-SHF range. A conversion loss of less than 4 dB is achieved for bulk wave excitation and detection at 1.7 GHz, where the electromechanical coupling factor k t reaches 30%. This indicates that the PZT thin film is promising for use in the development of large-bandwidth resonators and filters in modern communication systems as well as for high-frequency ultrasonic transducer applications.

Preparation of Dielectric Thin Films from Photosensitive Sol-Gel Solution

Fine-patterned Bax Sr1-x TiO3 (BST) thin films were successfully fabricated from a photosensitive sol-gel solution by means of UV irradiation. This solution was prepared from barium acetate, strontium acetate, and titanium isopropoxide. BST gel films on substrates formed from the solution by spin-coating were irradiated with UV rays through a mask pattern and developed with a mixture of ethanol and water. The obtained patterns were a negative of the mask. The films were finally annealed for crystallization. The obtained films had perovskite structure and good properties.