Sol-gel preparation and dielectric properties of lead iron niobate thin films

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Abstract
We have developed a new method to prepare lead iron niobate, Pb(Fe1/2Nb1/2)O3, by using organometallic precursors. The metal-containing sol was prepared by hydrolysis of the metal alkoxides. Homogeneous mixing of the constituents is achieved at the molecular level and densification of the ceramic occurs at temperatures considerably lower than that prepared by the conventional oxide power method. Due to the homogeneous mixing, the lead iron niobate gel forms a pyrochlore phase at temperatures as low as 300°C and ≥90% of it is converted to a perovskite phase at 700°C, and these conversion temperatures are about 100-200°C lower than those observed in samples prepared by conventional methods. In addition, we have prepared lead iron niobate capacitors on silicon wafers. This was achieved by spinning a prepared sol onto the silicon wafers, followed by gelation and pyrolysis of the precursor gels to give monolithic oxide films on the wafers. The maximum dielectric constant obtainable is ∼ 81, which is more than 20 times higher than the dielectric constant of SiO2 dielectric layers commonly used in the IC industry. However, this dielectric constant is considerably lower than the expected value of ∼ 2000 measured in sintered ceramic discs with an identical chemical composition. We then proceed to show that the low dielectric constant is due to the presence of a silicon dioxide layer beneath the ceramic, thus lowering the effective dielectric constant.

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