Electrostriction in Ceramics and Glass

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9634101 Newnham The electrical, mechanical, and thermal properties of packaging materials have been investigated thoroughly over the years, but reliable data on the electrostriction coefficients of low-permittivity oxides and nitrides are scarce. Electrostriction is a fourth rank tensor property relating mechanical strain to the square of the electric field. The principal goal of this project is to carry out electromechanical measurements on ceramics and glasses representative of the inorganic materials used in multilayer packaging, metal-on-silicon devices, high voltage insulators, optical fibers, micro-electrical mechanical systems, and thick film substrates. Among the materials to be studied are silica, silicon nitride, alumina, aluminum nitride, forsterite, spinel, mullite, cordierite, silicate glasses, mica, and porcelain. The PI and his group have developed two techniques for measuring the electrostriction coefficients of ceramics and glasses. The 'direct' method involves measuring the field-induced strain with a carefully calibrated optical interferometer. The 'converse' method entails monitoring the dielectric constant as a function of mechanical stress. The principal purpose of this project is to formulate structure-property relationships describing the dependence of the electrostrictive coefficient on atomic bond type, atomic bond length, crystal structure, and chemical composition of the material. Since electrostriction is the primary coupling mechanism between electric polarization and mechanical strain, the PI hopes to identify correlations between electrostriction coefficients, elastic compliance, and dielectric permittivity. %%% The electrical, mechanical, and thermal properties of packaging materials have been investigated thoroughly over the years, but reliable data on the electrostriction coefficients of low-permittivity ceramics and glasses are scarce. The goal of the proposed research is to measure the electrostriction coefficient of a variety of ceramic and glass materials. Electrostriction is a fourth rank tensor property relating mechanical strain to the square of the electric field. It is present in all insulators and becomes especially important in the ferroelectric ceramics used as capacitors and transducers, and in electronic and optical devices where extremely high fields are present. This includes optical fibers, high voltage insulators, laser windows, multilayer electronic packages, thin film components and thick film substrates. In these materials the stresses and strains caused by electric fields are often surprisingly large, making electrostriction an important degradation mechanism. If materials having a zero electrostrictive coefficient could be found, the reliability of electronic and optical devices based on that material could be significantly improved. ***