Chemical solution deposition of (Pb1-xCax)TiO 3 thin films with x∼0.5 as new dielectrics for tunable components and dynamic random access memories

Abstract

Calcium lead titanate ((Pb,Ca)TiO3) thin films, with calcium contents of ∼50 at.%, have been prepared by chemical solution deposition (CSD). Different synthetic sol-gel methods have been used for the preparation of the precursor solutions. 1,3-propanediol, OH(CH2)3OH, and water, H2O, were used as solvents. Lead (II) acetate trihydrate, Pb(OCOCH3)2·3H2O, and titanium di-isopropoxide bis(acetylacetonate), Ti(OC3H7)2(CH3COCHCOCH3)2, were used as reagents of lead and titanium, respectively. Calcium was incorporated into the solutions as calcium acetate hydrate, Ca(OCOCH3)2·xH2O, or as calcium acetylacetonate hydrate, Ca(CH3COCHCOCH3)2·xH2O. Only the use of calcium acetate led to precipitate-free solutions. Pb(II)-Ti(IV)-Ca(II) sols were obtained when calcium acetate was refluxed with the lead and titanium reagents in a diol-water solvent. These sols led to films with a homogeneous compositional profile. Solutions obtained by mixing a water solution of calcium acetate with a Pb(II)-Ti(IV) sol led to films with a heterogeneous compositional profile in which an interface between the film and the Pt bottom electrode is formed. The films derived from the Pb(II)-Ti(IV)-Ca(II) sols have values of dielectric constant at room temperature of ∼500, which, together with their low leakage currents, low dielectric losses, and tunability, make these films promising for dynamic random access memories and tunable devices. © 2005 The American Ceramic Society.