Multilayer ceramic capacitors titanate

The most significant commercial product is barium titanate, BaTiO, used to produce the ceramic capacitors found in almost all electronic products. As electronic circuitry has been rniniaturized, demand has increased for capacitors that can store a high amount of charge in a relatively small volume. This demand led to the development of highly efficient multilayer ceramic capacitors. In these devices, several layers of ceramic, from 25—50 ]lni in thickness, are separated by even thinner layers of electrode metal. Each layer must be dense, free of pin-holes and flaws, and ideally consist of several uniform grains of fired ceramic. Manufacturers are trying to reduce the layer thickness to 10—12 ]lni. Conventionally prepared ceramic powders cannot meet the rigorous demands of these appHcations, therefore an emphasis has been placed on production of advanced powders by hydrothermal synthesis and other methods. 

The information about nanocrystalline ferroic powders fabricated by various chemical synthesis technologies is reported in Table 5.2. Their possible applications are also listed. Powders of the same ferroics for two different applications might be obtained by different techniques since the requirements of size distribution, morphology, agglomeration and impurity composition are determined by different technological conditions. For example, barium titanate is a dielectric with high dielectric constant and it is widely used in multilayer ceramic capacitors, whereas semiconducting properties of rare-earth doped BaTiOs are important for thermistors. 

In addition to the multilayered ceramic capacitors just described, many of the barium titanate-based compounds that exhibit high dielectric constants are used in single-layer tape-cast capacitor devices. Relaxor materials such as lead magnesium niobate (PMN), which are characterized by high dielectric constants, broad dielectric maxima, and low sintering temperatures, have been manufactured in thin sheets by tape casting. 

Barium titanate is also the first material with the ferroelectricity studied theoretically by Devonshire (1949). Theoretical description is based on the idea of the thermodynamic potentials known from the Landau-Ginzburg theory of phase transitions (Devonshire 1949, 1951). Barium titanate is mainly used in multilayer ceramic capacitors and in positive temperature coefficient (PTC) elements (Bhalla et al. 2000). 

Ceramic capacitors are fabricated in four general processes thin-fihn, thick-film, single layer, and multilayer. Thin-fihn capacitors were developed out of a need to embed passive components into electronic packaging in hybrid circuits. Dielectrics such as SiO, SiOj, Ta20j, Ti02, titanates, and aluminosihcates can be vacuum deposited with a variety of electrode metallizations. 

Thin film ceramic materials with important magnetic, optical, electronic, and mechanical properties are often highly anisotropic. Thus, the ability to control orientation is critically important in thin film applications. For many of the oxide materials, as well as Ae ionic materials, aqueous solution or sol-gel routes are the most convenient or the only method of preparation. Examples of these include barium titanate (BaTiOs) used in multilayer capacitors, lead-zirconate-titanate (Pb(Zr,Ti)03, "PZT") used as a piezoelectric material, and zinc oxide (ZnO) used in varistors. Thus, the use of substrates to control orientation can eliminate major problems in deposition of thin films. In some cases, e.g., the many magnetic and non-magnetic phases of iron oxide, the ability to control the phase formed is critical to production of the desired properties. While this can be controlled by solution conditions, the proper surface can add an additional and very effective mechanism of control. 

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