The application of combinatorial approach to the optimization of dielectric/ferroelectric materials

Combinatorial approaches are methods developed to facilitate the rapid discovery and optimization of materials by the simultaneous synthesis and screening of a large number of compounds within a short period of time. This work describes its application to dielectric and ferroelectric thin film materials, in particular, (Ba,SrCa)TiO3. New methods and instruments for thin film fabrication and measurement are developed to handle the synthesis and analysis of up to thousands of samples simultaneously.;Thin films are fabricated with a novel multilayer precursor method. Precursors of the various elemental components within the target compound, such as BaF 2 and TiO2 for BaTiO3, are deposited at room temperature as separate layers. These multilayers are thermally processed under a two step procedure. A low temperature treatment over a period of days interdiffuses the layers to form a homogeneous amorphous intermediate. This is followed by a high temperature crystallization step, which forms the final crystalline product. Effects of dopants on the dielectric constant and loss of (BaSr)TiO 3 are studied with the discrete combinatorial approach, where up to thousands of discrete thin film samples are fabricated on an individual single crystal substrate. A continuous combinatorial sample resembling a ternary phase diagram of (Ba,Sr,Ca)TiO3 is also fabricated in search of the lowest loss compositions that are useful for various applications such as the storage node capacitors in dynamic random access memories.;These combinatorial samples of (BaSr,Ca)TiO3 are measured with the newly developed scanning evanescent microwave microscope (SEMM). This instrument is capable of rapid and accurate non-contact characterization of the thin film dielectric constants and losses. The measured results show good agreement with results from more conventional methods such as the interdigital electrodes measurements.;Various issues concerning the combinatorial approach in materials science are addressed in this project. Although specific emphasis are placed on ferroelectric and dielectric properties of (BaSr,Ca)TiO3, the general procedures and precautions of combinatorial thin film synthesis and measurements are applicable to other classes of thin film materials.