Circuit Design Using Multilayer Ceramic Capacitors Understanding the Vital Issue for a Wider Range of Applications
The two important key phrases in describing the history behind the widespread use of multilayer ceramic capacitors are "size reduction" and "capacitance enhancement." Manufacturers have created new markets by pursuing further reductions in size and capacitance enhancement. For electronics designers, however, there are other important specifications. Multilayer ceramic capacitors have both advantages and disadvantages. One should fully understand the pros and cons of the product's specifications and take all these factors into account in the actual design of electronic circuitry. Such efforts can reduce the cost of electronics design and shorten the development period.
Nearly 50 years have passed since the first multilayer ceramic capacitor was invented. During this time, manufacturers have steadily improved multilayer ceramic capacitors to make them smaller and provide higher capacitance by reducing the thickness of the dielectric layers and promoting the development of new dielectric materials. As a result, the domain of multilayer ceramic capacitors has been expanded as they have gradually taken over the market from aluminum and tantalum electrolytic capacitors and film capacitors, which were previously widespread (Fig. 1).
The figure shows the commercialization ranges of various types of capacitors, with rated voltage on the vertical axis and capacitance on the horizontal axis. The domain of monolithic ceramic capacitors is gradually being expanded by the rapid enhancement of capacitance. Meanwhile, aluminum and tantalum electrolytic capacitors are also barely managing to hold their own against the growth of monolithic ceramic capacitors as a result of improvements in withstand voltage and capacitance.
For example, regarding models with a capacitance ranging from 10 to 100 μF, the component ratio of multilayer ceramic capacitors was almost zero in 2002. In 2005, however, when new products were ready to be released as the reduction of size and the enhancement of capacitance progressed, the ratio grew to about 1/3 of the market and reached about 2/3 in 2007 (Fig. 2).
This figure shows the component ratios of monolithic ceramic, aluminum electrolytic and tantalum electrolytic capacitors. The graphs clearly indicate that the component ratio of monolithic ceramic capacitors among high-capacitance products is increasing year by year.
Currently, the market border between multilayer ceramic capacitors and aluminum and tantalum electrolytic capacitors lies around 100 μF for models with a rated voltage of about 10 V and around several dozen μF for those with a rated voltage of roughly several dozen V. This border will definitely move up to the higher capacitance side in the future.
Low ESR, Resistant to Abnormal Voltage
The reduction of size and the enhancement of capacitance helped to expand the domain of multilayer ceramic capacitors, but the dimensions and the capacitance are not the only characteristics that should be considered when selecting a capacitor for use in electronic devices. Multilayer ceramic capacitors are not always the perfect answer. Attention must be paid to various characteristics, because they have both advantages and disadvantages.
Table 1 shows a comparison between multilayer ceramic capacitors and aluminum and tantalum electrolytic capacitors. As shown in the table, multilayer ceramic capacitors have two distinct advantages.
One of the advantages is that multilayer ceramic capacitors have excellent frequency characteristics, thanks to their low equivalent series resistance (ESR). The term "ESR" refers to the resistance component of a capacitor's internal electrodes, etc. A high ESR not only degrades the frequency characteristics of impedance, which is a criterion for the noise absorption characteristics, but also causes the generation of a considerable amount of heat due to the resistance component. Thus, a low ESR is essential when a capacitor is mounted around a microprocessor, DSP, microcomputer, or other semiconductor chip for the decoupling purpose to absorb noise.
Another advantage is that they are highly resistant to abnormal voltage. When comparing products with a rated voltage of 16 V and a capacitance of 10 μF, for example, the DC breakdown voltage of an aluminum electrolytic capacitor is only 30 V and that of a tantalum electrolytic capacitor is 30-60 V. In contrast, a multilayer ceramic capacitor has an extremely high DC breakdown voltage (approximately 200 V). Thus, if a multilayer ceramic capacitor is mounted in an electronic device, the risk of failure due to dielectric breakdown can be minimized, even when a surge or pulse voltage is generated in the device for some reason.
To be continued in part 2 of 2, which will describe considering temperature and DC voltage characteristics.
* Indicated company and product names are the trademarks or the registered trademarks of each company.
* The content of this article, from the February to March 2010 issue of "Tech On!" Nikkei Business Publications, Inc., was restructured.
* For more details on Murata Manufacturing's multilayer ceramic capacitors, please refer to the following: