Electronic Ceramic Thin Films: Trends in Research and Development

Abstract

Electronic ceramic materials research is one of the fastest growing, most highly publicized areas of materials science. Subjects receiving considerable attention include high temperature superconductors, multilayer ceramic composites for high density microelectronics packaging, and ferroelectric electro-optic thin films. A complete review of all aspects of electronic ceramics research is beyond the scope of this article, which will focus on two general topics whose development is representative of recent contributions to the field. These two areas are synthesis and characterization of electronic ceramic films,1 and controlled use of low level dopants (1,000 ppm or less) in bulk polycrystalline ceramics, thin films, and single crystals to achieve desired properties. Perspective of the progress in ceramic film development is given by a review of single-crystal synthesis and properties. Several examples of the impact that low level dopants and thin film synthesis have on electronic ceramics development are presented. Dopant concentrations of 1,000 ppm or less can have a dramatic effect on microstructural, optical, and electrical properties. For example, a decrease in aluminum content of 150 ppm resulted in an increase in grain size from 1 to 25 microns in otherwise identical ZnO varistors. Background aluminum concentrations for these varistors were less than 10 ppm. In another example, the photorefractive effect, the change in refractive index with optical light intensity, has been shown to be altered by orders of magnitude with ppm doping levels in ferroelectric electro-optic materials. Several electronic ceramic devices have recently been developed due to improvements in ceramic film processing. Examples of these devices include: 1. multilayer PZT transformers, which allow fabrication of complex monolithic passive multicom-ponent networks, 2. liquid cooled multilayer ceramic substrates, with 400×800 micron liquid transfer capillaries integrated into the multilayer structure via ceramic processing techniques for high density VLSI packaging, and 3. ferroelectric electrooptic thin films that are compatible with silicon or III-V technology. For all the above applications, synthesis of electronic ceramic materials into high purity films is essential.