Ceramic multilayer capacitors

T. L. Rutt andJ. A. Syne, "Fabrication of Multilayer Ceramic Capacitor by Metal Impregnation," IEEE Trans. Parts Hybrids Packag., PHP-9, 144-147 (1973). 

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. 

Electronic Applications. The PGMs have a number of important and diverse appHcations in the electronics industry (30). The most widely used are palladium and mthenium. Palladium or palladium—silver thick-film pastes are used in multilayer ceramic capacitors and conductor inks for hybrid integrated circuits (qv). In multilayer ceramic capacitors, the termination electrodes are silver or a silver-rich Pd—Ag alloy. The internal electrodes use a palladium-rich Pd—Ag alloy. Palladium salts are increasingly used to plate edge connectors and lead frames of semiconductors (qv), as a cost-effective alternative to gold. In 1994, 45% of total mthenium demand was for use in mthenium oxide resistor pastes (see Electrical connectors). 

Figure 4-4 Cross-section of a Multilayer Ceramic Capacitor...

The equivalent series resistance (ESR) and equivalent series inductance (ESL) of the output capacitor substantially control the output ripple. Use an output capacitor with low ESR and ESL. Surface mount Tantalums, surface mount polymer electrolytic and polymer electrolytic and polymer Tantalum, Sanyo OS-CON, or multilayer ceramic capacitors are recommended. Electrolytic capacitors are not... 

Multilayer cast-film extrusion, VDC copolymers in, 25 725, 729-733 Multilayer ceramic capacitors (MLCC), platinum- group metals in,... 

Ag-Pd Alloy Powders (7,27). Bimetallic colloids, namely, Ag-Pd and Au-Pt, can be obtained by the polyol process. The composition Ag7oPdx> is of particular interest to make the internal electrodes of multilayer ceramic capacitors (MLCC). Polymer-protected, monodisperse, nanoscale Ag70Pd30 particles have been obtained... 

A particularly important application for aluminium electrolytic capacitors is in switch mode power supplies (SMPSs) which are now extensively used, especially in computer systems. In this application the capacitor is used essentially to smooth a rectified voltage, but it inevitably passes a ripple current I which, because of the capacitor s e.s.r., rs, leads to power losses I2rs. The switching frequency determines the size of an SMPS, and frequencies have increased from about 50 kHz to about 300 kHz over the past decade. This has led to the multilayer ceramic capacitor s challenging the aluminium electrolytic in this important application, and the signs are that it will continue to do so. 

Since the first multilayer ceramic capacitor (MLCC) was introduced in the early part of World War II there have been two principal development trends. One is towards smaller sizes and higher capacitance values, that is towards maximizing volumetric efficiency, and the other is cost reduction. These developments have had to be accompanied by improved reliability, which assumes increasing relevance as the number of capacitors in a given piece of equipment, for example a PC or mobile phone, steadily increases. 

Fig. 5.11 Schematic diagram of a multilayer ceramic capacitor construction.

Fig. 5.12 Outline of the fabrication process for multilayer ceramic capacitors.

We will focus on modem MLCCs (multilayer ceramic capacitors). The basic principle behind these is very simple. Let us start with a simple capacitor with two plates. Its capacitance is proportional to Aid, and it occupies a volume ofAxd, Suppose we then split this available volume Axd into two capacitors, each of area A, but thickness dH, Then each capacitor will have a capacitance of 2A d, and the overall volume will be unchanged. Now, if we parallel these two capacitors (by fine internal electrical connections), we will get a resultant capacitance of AAld in the same volume. By dividing the thickness progressively into finer and finer layers, we can thus keep increasing the capacitance. See Figure 4-4. But... 

We thank W. W. Rhodes of AT T Bell Laboratories at Murray Hill, New Jersey for supporting our work in the relaxor materials. Subsequent work on the processing and reliability of multilayer ceramic capacitors was achieved through many useful collaboration and discussions with our colleagues at AT T Bell Laboratories Engineering Research Center at Princeton, New Jersey. 

Ling, H. C., and Jackson, A. M., Correlation of silver migration with temperature-humidity-bias (THB) failures in multilayer ceramic capacitors, lEEE-CHMT, 12, 130 (1989). 

Ochi, A., Mori, T., Nakanishi, M., Utsumi, K., Abe, S., and Yoshimoto, T., Y5V multilayer ceramic capacitors with high specific capacitance and low-equivalent series resistance, lEEE-CHMT, 8, 572 (1991). 

Chang, D. D., Electrical characteristics and reliability study of high-K lead-based multilayer ceramic capacitors, in Ceramic Dielectrics Composition, Processing and Properties, Ceramic Transactions, Vol. 8, (H. C. Ling and M. F. Yan, eds.). Am. Ceram. Society, Westerville, OH 1990, p. 88. 

FIGURE 37.3 Multilayer ceramic capacitor-sized trends. 

Multilayer ceramic capacitors Orthopedics Scratch-resistant coatings... 

Ferroelectrics BaTiOs, SrTiOs Multilayer ceramic capacitors... 

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. 

Sakabe, Y. Multilayer ceramic capacitors. Curr. Opin. Solid State Mater. Sd. 2, 584—587... 

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