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|Structural Design of Future MLCCs using Computer Simulation|
|Keywords: multilayer ceramics capacitor, computer simulation, barium titanate|
|Multilayer ceramics capacitors (MLCCs) are widely in modern electronic circuits. To increase the capacitance density of MLCCs, the dielectric layer thickness in MLCCs has been reducing every year and now reaches under 1 micron in high-capacitance products. The dielectric permittivity reduces with the size of barium titanate grains in the dielectric layers, which is known as the size effect of barium titanate. It is also known that several grains should be necessary in one dielectric layer to obtain the reliability and/or life time enough for capacitor applications under DC-fields. These two facts mean that the reduction of the dielectric layer thickness needs the reduction of grain size of barium titanate, which gives rise to the reduction of dielectric permittivity by the size effect. Consequently, it should be expected that there must be a limit of dielectric layer thickness or a limit of capacitance density in the future MLCCs. In this study, we have tried to see the limit of capacitance density of MLCCs using a computer simulation technique. Dielectric properties of MLCCs with different particle size of barium titanate were measured. The data were analyzed using B-SPLINE fitting to predict dielectric permittivity at arbitral temperature and AC-fields. The dielectric properties of barium titanate grains smaller then 100 nm were predicted using least squares fitting of the B-SPLINE coefficients. It was found from the simulation that the usage of barium titanate grains smaller than 80 nm did not have any meanings to increase the capacitance density as well as temperature stability of the MLCCs. The maximum capacitance was predicted for a certain chip size. The usage of lead-free relaxors was proposed as a new concept to overcome the limit of capacitance density of future MLCCs.|
|Takaaki Tsurumi, Professor
Tokyo Institute of Technology
Meguro, Tokyo 152-8552,