Tungsten Bronze Application in Ceramic Capacitors I

A ceramic capacitor is a fixed value capacitor in which ceramic material acts as the dielectric. It is constructed of two or more alternating layers of ceramic and a metal layer acting as the electrodes. The composition of the ceramic material defines the electrical behavior and therefore applications. Ceramic capacitors, especially the multilayer style (MLCC), are the most produced and used capacitors in electronic equipment that incorporate approximately one trillion (1012) pieces per year. Ceramic capacitors of special shapes and styles are used as capacitors for RFI/EMI suppression, as feed-through capacitors and in larger dimensions as power capacitors for transmitters. Ceramic capacitors are divided into two application classes: Class 1 ceramic capacitors offer high stability and low losses for resonant circuit applications. Class 2 ceramic capacitors offer high volumetric efficiency for buffer, by-pass, and coupling applications.

Temperature stability is of great importance for the preparation of multilayer ceramic capacitors in electronic products application. Two or more than two of the polyhydric compounds having opposite temperature coefficient and dielectric constant (τ ε) are mixed to produce a solid solution with small temperature coefficient and dielectric constant, this method is frequently used to realize the temperature stability of the materials; or, such as capacitor for BaTiO3, mixed dopant is dispersed in the ceramic body to produce ferroelectric - paraelectric phase transition near room temperature and the relatively stable material has been obtained. Currently, BaTiO3 compound fits X7R standard, its dielectric constant does not exceed ± 15% in the temperature range of -55 ℃ ~125 ℃ compared to the change rate of dielectric constant at room temperature, the dielectric loss tan σ is less than 0.02 at 1MHz. However, if PbTiO3 (Tc = 4950C) is not doped, the maximum operating temperature does not exceed 130 ℃.

Recently, domestic and foreign researchers found that a number of tantalates with tungsten bronze structure having high dielectric constant (> 100) and low dielectric loss, is expected to be the dielectric materials with temperature stability being used in multilayer ceramic capacitors.

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