Sinterability and Dielectric Properties of ZnNb2O6 – Glass Ceramic Composites

Abstract

In the new era of communication technology there are revolutionary developments in satellite communication, global positioning systems and mobile communication systems, which has helped the developments in multilayer technologies like low temperature cofired ceramics (LTCC). The microwave electronic devices have achieved significant miniaturisation, light weight and became very cost effective using LTCC. The characteristic properties required for dielectric materials which are used in multilayers are (a) high dielectric permittivity( r e ), (b) high quality factor (Q×f) and (c) low temperature coefficient of resonant frequency (τf). The size of the resonator is inversely related to the r e . Dielectric materials should posses near zero temperature coefficient of resonant frequency (τf) for thermally stable electronic devices [1-7]. Generally most of the dielectric ceramic materials are known to posses the above said properties but will sinter at temperatures above 1000 oC. Zinc niobates, ZnNb2O6 (ZN) is a low loss dielectric material with columbite structure having excellent dielectric permittivity, high quality factor and low temperature coefficient of resonant frequency. Sintering temperature of ZN is comparatively lower (~1200 oC) [8]. Hence it is widely used as dielectric resonators in microwave communication devices. In multilayer ceramic structures, the low melting electrodes such as Ag (melting point ~961 oC), Cu (melting point ~1083 oC) and Au (melting point ~1064 oC) are co-fired with these ceramic materials [9,10]. In the case of Ag electrodes, processing temperature of the material must be below 950 oC. There are several approaches to reduce the sintering temperature of the ceramics viz. (i) usage of ultra-fine particles/powders as synthesized by wet chemical methods as starting materials (ii) addition of low melting glasses to obtain a low temperature sintering composite [11-14]. Glass addition is known to be the most popular and least expensive method and hence ZN is widely used in ceramic technology. Even though the ZN ceramics prepared by conventional ceramic route [1-6] shows excellent properties, high sintering temperature preclude its application potential in the LTCC. Usage of nano sized ZN powders (instead of micron size powders) in multi layer technology can bring down the sintering temperature to a lower value. Hence the procedure for preparing