Ferroelectricity and voltage-capacitance behaviour

Würth Elektronik has implemented the voltage-capacitance behaviour of ferroelectric MLCCs in the LTspice files of its products, which greatly improves the accuracy of simulations. The Application Note 'ANP114' published by the electronic and electromechanical components supplier describes the model development for ferroelectric class-2 MLCCs, explaining their dependence on voltage and frequency. The use of MLCCs, e.g., in filtering circuits, is greatly simplified for the developer.

Ferroelectric MLCCs are electronic components that display the property of ferroelectricity. They can maintain stable electric polarisation without an external electric field and, therefore, have a voltage-dependent capacitance. The Application Note gives an in-depth explanation of the voltage and frequency dependence of ferroelectric MLCCs. The AppNote starts with an introduction to the world of ferroelectricity before going on to derive a mathematical model for the capacitance-voltage behaviour of ceramic MLCCs from a dipole polarisation model, in which the model's parameters are reduced to two fitting parameters.

Comprehensive measurements tested the model on a selection of MLCCs from the company's portfolio to demonstrate the practical applicability. Since the integral of the capacitance-voltage model mathematically contains only basic trigonometric expressions, it can be readily implemented in software that needs functions of charge instead of capacitance, such as the simulation software LTspice. Also, it is shown that the model is extremely useful in describing the capacitance spectra of MLCCs at different DC voltages.

The AppNote is part of a comprehensive collection of publications on the complex of issues regarding multilayer ceramic capacitors and can be directly downloaded from the company's website.