High tetragonality barium titanate-based compositions and methods of forming the same

Abstract

Barium titanate-based compositions having a high tetragonality and methods of forming the same are provided, as well as devices formed from the compositions. The barium titanate-based compositions advantageously have a high tetragonality and small particle sizes. For example, in some embodiments, the barium titanate-based compositions have a tetragonality of greater than about 2.0 and an average particle size of less than about 0.3 micron. Some methods involve achieving high tetragonality by limiting the concentration of certain metals (other than barium or titanium) in the compositions and / or heat treating the compositions at relatively high temperatures. In some methods, the A / B ratio of the composition may be adjusted prior to heat treatment to ensure that a small particle size is maintained during heat treatment. The barium titanate-based compositions may be processed to form dielectric layers in electronic devices, such as MLCCs, having excellent electrical properties as a result of the high tetragonality and relatively small particle sizes.

Description

[0001] The invention relates generally to dielectric materials and, more particularly, to barium titanate-based compositions having a high tetragonality and methods of forming the same.BACKGROUND OF INVENTION[0002] Barium titanate-based materials, which include barium titanate (BaTiO.sub.3) and its solid solutions, may be used as dielectric materials in electronic devices. For example, barium titanate-based particulate compositions may be processed to form dielectric layers in multilayer ceramic capacitors (MLCCs). Barium titanate-based materials are used in MLCC devices because barium titanate can have a high dielectric constant. The high dielectric constant arises, in part, because barium titanate can assume a tetragonal perovskite crystal structure at room temperature.[0003] Unit cells of crystal structures have dimensions a, b and c which correspond to the x, y and z axes of the cell. In tetragonal unit cells, a=b.noteq.c. The "tetragonality" of a tetragonal unit cell is related...

AI Technical Summary

Benefits of technology

[0027] As noted above, limiting the presence of metals other than barium or titanium (e.g., strontium and / or calcium) in barium titanate particle compositions may increase the tetragonality of the compositions. Contaminants (e.g., strontium and / or calcium) can be introduced into hydrothermally-produced barium titanate because such contaminants may be present in the barium source. Some hydrothermal methods of the present invention use barium sources that have low concentrations of contaminant metals, such as strontium and / or calcium, to limit the presence of such metals in the resulting composition. For example, in some cases, sources having a concentration of less than about 500 parts per million of strontium and / or calcium are used. In other cases, sources having a concentration of less than about 200 parts per million, or even less than about 50 parts per million, of strontium and / or calcium are used.

Problems solved by technology

However, the dielectric constant of MLCCs formed using small barium titanate-based particles may be sacrificed because of the relatively low tetragonality of such particles.

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