Kunio Nishida

First-Principle Studies on Elastic Properties and Spontaneous Polarizations of PbTiO3.

The elastic properties of the tetragonal phase of PbTiO3 were investigated using the full-potential linearized argumented plane wave (FLAPW) method. The geometric optimization calculations were performed against the lattice deformations. It is shown that the elastic properties including the sublattice relaxations can be well described by the simple Hooks law. The value of the spontaneous polarization using Berrys phase approach based on the optimized geometry fairly reproduced the experimental value.

Preparation and Characterization of Lead Zirconate Titanate Thin Films on Si Substrate by Metal-Organic Chemical Vapor Deposition

The effect of a gradient-composition lead zirconate titanate (PZT) layer functioning as a buffer layer and having a Zr/(Zr+Ti) ratio of from 10 to 50 atomic % to prepare PZT thin films was investigated. [001]-oriented PZT films were prepared on (111)Pt/Ti/SiO2/Si substrates with gradient-composition PZT layers by metal-organic chemical vapor deposition (MOCVD). A post-annealing process improved the insulation resistance and crystallinity of the films with buffer layers. They had a dielectric constant of 948, a dielectric loss of 6.7 %, a remanent polarization of 23 μC/cm, a coercive field of 35 kV/cm, and a piezoelectric constant (d31 ) of –136 pC/N. INTRODUCTION Lead zirconate titanate (PZT) is one of the most promising ferroelectric and piezoelectric materials, and there have been many experimental studies on the characteristics of PZT films prepared by various methods such as metal-organic chemical vapor deposition (MOCVD), pulsed-laser deposition (PLD), sol-gel, or sputtering [1-2]. Films with excellent ferroelectric properties have been obtained by preparing them on single-crystal such as MgO, SrTiO3 substrates covered with epitaxial Pt [3-4], but we will need high-quality PZT films on SiO2/Si substrates if we are going to use them in miniaturized devices made with Si micromachining processes and/or smart sensors with IC circuits. In recent years, there have been many studies on the preparation of oriented PZT thin film using a buffer layer, such as PbTiO3, (Pb,La)TiO3, SrTiO3 and (Ba,Sr)TiO3, prepared by MOCVD and the sol-gel method [5]. In this paper, we describe the preparation of [001]-oriented PZT films on SiO2/Si substrates using a gradient-composition PZT thin film as a buffer layer by MOCVD. We also describe some MFC