Thickness dependent dielectric properties of sol-gel prepared lead lanthanum titanate films

Abstract

A series of lead-lanthanum-titanate films (PLT, Pb0 65La0.28 2gTi096O3) films of differing thickness were prepared on Pt/Ti/SiO2/Si substrates using sol-gel techniques. One to six layer films with a layer thickness of 330 Mayer were deposited by spin-coating from a partially hydrolyzed metal alkoxide solution. After each layer was applied, the films were annealed using rapid thermal annealing (150 °C/sec temperature ramp, 1 minute at 700 °C, 02 atmosphere). The films were characterized by X-ray diffraction (XRD), electrical measurement of dielectric constant, dissipation factor and leakage current, and crosssectional transmission electron microscopy (TEM). For all films, only the perovskite phase of PLT was observed by both XRD and TEM. The films showed a strong [100] orientation on the [111] textured Pt substrates. Electrical measurements determined the dielectric constant at 200 kHz for films 1000 A thick and thicker to be -550. These films had leakage current densities of less than 1x10–7 amp/cm2 at 1 volt. The 1000 Å film has an equivalent oxide thickness of 7.2 Å and a capacitance per unit area of 48 fF/μm2. Films less than 1000 Å thick showed reduced dielectric constants and greatly increased leakage currents. The possible origins for the degradation in electrical properties of very thin films (stress, poorly crystallized interfacial layers, second phases, and electrode interactions) were evaluated using TEM. © 1995, Taylor & Francis Group, LLC. All rights reserved.