Characterization of single layer PZT (53/47) films prepared from an air-stable sol-gel route
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Single layer Pb(Zr0.53Ti0.47)O3 films up to 0.7 /xm thick have been prepared from air-stable titanium and zirconium precursors using a diol-based sol-gel route. Information on film crystallization, surface microstructure, and electrical properties under different firing temperatures and three different heating rates including rapid thermal annealing are presented. Films exhibited (111) preferred orientation, the extent of which reduced with increasing firing temperature or heating rate. It is possible that a PbPt^ interfacial reaction product was formed during the prefiring step at 350 °C and this, together with the influence of the 111 bottom platinum electrode, contributed to (111) orientation in the PZT films. Surface microstructure was also influenced by firing temperature and heating rate as well as by film thickness. The 0.4 /xm thick films used for electrical measurement had a grain size of =50.1 /xm, whereas 0.7 /xm thick films made from concentrated sols exhibited "rosette" microstructures with grain sizes up to 0.5 /xm. Among the three firing schedules studied, directly inserting the gel coatings in a furnace preset at 700 °C produced films with the most favorable electrical properties. A 0.4 /xm thick film gave rise to a remanent polarization, Pr, of 33 /xC cm" 2 coercive field, Ec, of 46 kV cm" 1 ; relative permittivity, er, of 1100; and dissipation factor, D, of 0.05. For a 0.7 /xm single layer film, the respective values were 21 /xC cm" 2 , 36 kV cm" 1 , 1300, and 0.05.
I. INTRODUCTION The market potential for exploiting the ferroelectric and piezoelectric properties of thin films of lead zirconate titanate and related compositions has made them the subject of extensive research activity. A wide range of film fabrication techniques have been developed, including various chemical and physical vapor deposition techniques and solution-based sol-gel routes. The latter offers researchers a relatively inexpensive means of producing inorganic thin films, since, unlike most other methods, the setup costs are relatively low. Moreover, for multicomponent systems such as PZT, sol-gel routes may under optimum conditions offer good control of film composition and chemical homogeneity. The basic steps in sol-gel processing involve the synthesis of a gel-precursor solution, or sol, which is applied to a substrate using spin or dip-coating techniques; the resulting gel layer is then thermolyzed to form a ceramic film. Usually thermolysis is carried out in two stages employing a hot-plate prefiring step at —300 °C followed by a treatment at 600 °C-700 °C. The first sol-gel techniques for producing PZT films were reported in the mid 1980s.1 A route using methoxyethanol solutions of lead acetate, titanium propoxide, and zirconium propoxide has since found widespread use.2 In the methoxyethanol, or MEO, route, polymeric sols are formed as a result of carefully 3222
J. Mater. Res., Vol. 10, No. 12, Dec 1995
controlled hydrolysis and condensation reactions. This is also true of a variety of closely related routes includ
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