Medium-permittivity ceramics

Multilayer, LTCC technology is now exploited in high speed digital circuitry for computer main frame equipment, the general form of the modules being still essentially as illustrated in Fig. 5.26. R.R. Tummala [5] and S.H. Knickerbocker et al. [6] review the glass-ceramic aspects of IBM TCM technology. 

The explosive growth in wireless technologies has been accompanied by a demand for specially tailored microwave dielectrics , and very recently by the exploitation of multilayer LTCC-based circuitry (see Section 5.6.5). 

Medium-permittivity ceramics are widely used as Class I dielectrics, and in order to be in this category they need to have low dissipation factors. This precludes the use of most ferroelectric compounds in their composition since ferroelectrics have high losses (tan S 0.003), particularly when subjected to high a.c. fields. 

Low-loss materials can be obtained with relative permittivities exceeding 500 but accompanied by high negative temperature coefficients, generally exceeding 

There are three principal areas in which these dielectrics are applied. 

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Class I dielectrics usually include low- and medium-permittivity ceramics with dissipation factors less than 0.003. Medium-permittivity covers an sr range of 15-500 with stable temperature coefficients of permittivity that lie between +100 and -2000 MK-1. 

MK. For most purposes medium-permittivity ceramics have 8r in the range 15-100. 

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