Crystal structures and phase equilibria of ceramics for low temperature co-fired ceramics. (General Developments).

The primary technology drivers for wireless consumer devices and computer applications are miniaturization, higher frequency, lower operating voltages, reduction of component part count, and increased functionality. For example, multiband wireless telephones will require the packaging of two or three radios within the same cell phone format. One solution to this challenge is multilayer ceramic integrated circuit (MCIC) technology, which organizes the components into a single module containing all the passive and active components. MCIC technology requires the development of ceramic dielectrics which may be co-fired with high-conductivity metals; that is, low temperature co-fired ceramics (LTCC).

Currently available LTCC materials have relatively low dielectric constants of about 10; new ceramics with higher permittivities are required to develop integrated filters and capacitors. As part of an ongoing program on dielectric ceramics, NIST researchers applied high-resolution electron microscopy and x-ray diffraction to determine crystal structures and phase equilibria of a new, low-sintering-temperature dielectric ceramic in the Li-Nb-Ti-O system. This material is based on the solid solution [Li.sub.1+x-y] [Nb.sub.1-x-3y] [Ti.sub.x+4y] [O.sub.3], and exhibits excellent dielectric properties including chemically tunable dielectric constants of 55 to 78, near-zero temperature coefficients of the resonant frequency, and dielectric losses of less than [10.sup.-3] at frequencies above 1 GHz. Moreover, the sintering temperature of these ceramics can be reduced to 950 [degrees]C by small additions of [V.sub.2][O.sub.5], which permits co-firing with silver electrodes, thus making this material an attractive c andidate for low-temperature co-fired ceramic (LTCC) technology.

NIST research on [Li.sub.1+x-y][Nb.sub.1-x-3y][Ti.sub.x+4y][O.sub.3] ceramics has demonstrated that what actually forms is not a solid solution but rather a homologous series of distinct compounds which feature intergrowths of [LiNbO.sub.3]-type blocks and corundum-type layers. Successive compounds differ in the thickness of the [LiNbO.sub.3] blocks, expressed as the number of cation (or anion) layers, n, which increases with decreasing Ti/(Li+Nb) ratio. The phase field containing these compounds was confirmed to encompass a series of such ordered commensurate intergrowths, with n ranging from 5 to 54. The structural nature of these ceramics bears important implications for their processing and properties as LTCC ceramics, since the complexity and large number of possible phases considerably extend the "tunability" of properties.

CONTACT: Igor Levin, [phone]; [e-mail].