ECA 521

Abstract

<strong>INTRODUCTION</strong> <br>Ceramic capacitors are those wherein the dielectric material -is a high-temperature, sintered, inorganic compound. As a general rule, these materials are based on mixtures of complex titanate or niobate compounds, including barium titanate, calcium titanate, strontium titanate, etc. Stannate and zirconate compounds are also used. Because of the great variety of electrical characteristics found in ceramic capacitors, the Electronic Industries Association (EIA) has categorized ceramic capacitors into four classes. <br>Class I capacitors are those of the stable and temperature-compensating type. They are available in a wide range of temperature coefficients (TC) with relatively linear characteristics. They are suited for applications where low-losses and high-stability are required. The capacitance ranges available in Class I are much lower than in the other classes. <br>Class II capacitors are typically more complex in formulation. They may be ferroelectric compounds, often based on barium titanate possessing a high dielectric constant. They are classified as having a semistable temperature characteristic and used over a wide temperature range. <br>Class III capacitors are also typically based on more complex formulations. Class III capacitors have the highest dielectric constant of all ceramic capacitors. They are the most volumetrically efficient of the standard ceramic dielectric types. They are used over a moderate temperature range in applications where high capacitance is required,but where moderate losses and capacitance changes can be tolerated. <br>Class IV capacitors are restricted to reduced titanate or barrier layer dielectrics. These capacitors have the highest apparent dielectric constant. The high dielectric constant is developed by creating a thin reoxidized dielectric layer, a PN semiconductor junction, and/or a thin intergranular insulating layer. They exhibit the same TC characteristics as the oxidized ceramic formulation <br>All class of ceramic capacitors are available in a variety of physical forms, ranging from disc or rectangular single layer to multilayer types. Tubular types, feedthrough styles, or variations of these are also produced. In all their variations, ceramic dielectric capacitors are used more than any other single dielectric family. High usage is the result of low cost, wide rang of characteristics, good volumetric efficiency, excellent high-frequency capabilities, and inherent reliability.