There have been recent remarkable developments in communication systems that use microwave frequencies with a range of 300 MHz to 300 GHz in mobile communications such as wireless telephone sets and car-phones, satellite broadcastings, satellite communications and the like. With the development of personal portable communications, miniaturization of terminals has become generalized. Thus, laminated parts are increasingly required to accomplish miniaturization, high light weighting, and surface mounting of terminal parts. Particularly, passive elements such as filters, duplexers, resonators and antennas, which are essential parts of communication equipment, were difficult to miniaturize. However, miniaturized thick film laminated chip elements were obtained with the use of low temperature sintering materials that can be co-fired with an electrode, such as silver (Ag) or copper (Cu). High dielectric constant and high frequency are required for miniaturization of parts because the wavelength of microwaves within dielectric ceramics is inversely proportional to the square root of a dielectric constant, and the frequency. Generally, a dielectric constant (εr) is inversely proportional to a quality factor (Q) value, and dielectric materials having a high dielectric constant are required for miniaturization of parts. However, as the frequency in use is increased to ≧1˜2 GHz, the parts are sufficiently miniaturized. Thus, materials having dielectric constants with a range of 20˜40 are now actively applied to a variety of chip antennas, chip filters and the like.
The representative examples of low temperature sintering dielectric ceramics for high frequency, which have been developed, include CuO and V2O5 containing the BiNbO4 system, of which the Q·f0 value is 18,300 GHz, the dielectric constant is 43, and the temperature coefficient of resonant frequency is +38 ppm/° C. These types of dielectric ceramics have sintering temperatures as low as 875° C., but have very high temperature coefficients of resonant frequency. Thus, they are impossible to apply to actual parts. Therefore, study of adding various additives to the BiNbO4 system to stabilize the temperature coefficient of resonant frequency is now in energetic progress (See, H. Kagata, Jpn. J. Appl. Phys., 31, p.3152, 1992). Bismuth (Bi) reacts with electrodes when a BiNbO4 system is in laminated sintering, causing a characteristic deterioration of the BiNbO4 system (see, K. B. Shim, J. Mater. Sci., 35, p.813, 2000). Thus, a demand is rising for low temperature sintering dielectric ceramics materials that do not include Bi.