The farad (F) is the capacitance unit of measurement for ceramic capacitors.
It represents how much charge is stored in a capacitor. The capacitance is often described in the product description as "nominal value."
Please note that among ceramic capacitors, the capacitance, especially of capacitors classified as high dielectric constant (B/X5R, R/X7R characteristic), may differ from the nominal value when a DC voltage is applied.
For example, as shown in the chart, the larger the DC voltage applied to the high dielectric constant capacitors, the more effective capacitance is reduced.
In the following chart, the horizontal axis shows the DC voltage applied to the capacitor (V), and the vertical axis shows the capacitance change ratio against the initial value.*
Thus, the characteristic of change in capacitance according to the applied voltage is called "DC (direct current) bias characteristic."
The change ratio in capacitance varies depending on the product.
Based on the above, the characteristics should be well considered when using high dielectric constant capacitors. Also, whether the use is appropriate or not should be confirmed based on actual conditions as well as actual equipment.
For your information, it is not only our products that have DC bias; it is a phenomenon commonly observed in high dielectric constant capacitors.
Bias characteristics, temperature characteristics, frequency characteristics, etc. can be confirmed with this software. (SimSurfing)
The mechanism of DC bias characteristic
In the high dielectric constant capacitor type of ceramic capacitors, at present mainly BaTiO3 (barium titanate) is used as a principal component of high dielectric.
As shown below, BaTiO3 has a perovskite shaped crystal structure and above the Curie temperature it becomes a cubic shape with Ba2+ ions to the vertices, O2- ion to face center and Ti4+ ion in a body centered position.
The crystal structure of ceramics BaTiO3
At the Curie temperature (approx 125°C) or more, it has a cubic crystal structure, and below the Curie temperature and within an ambient temperature range, one axis (axis C) stretches and other the axes shrink and turn to a tetragonal crystal structure.
In this case, polarization occurs as a result of the unit shift of axially elongated Ti4+ ion crystal. This polarization occurs without applying an external electric field or pressure, and is known as "spontaneous polarization." As explained above, a characteristic that has a spontaneous polarization and a property of changing orientation of spontaneous polarization by an external electric field to reverse is called "ferroelectricity."
The reversal of the spontaneous polarization per unit volume is equivalent to relative permittivity. Relative permittivity is observed as a capacitance.
Without a DC voltage, spontaneous polarization can happen freely. However, when a DC voltage is externally applied, spontaneous polarization is tied to the direction of the electric field in the dielectric, and independent reversal of spontaneous polarization is inhibited. As a result, the capacitance becomes lower than before applying the bias.
This is a mechanism of decrease in the capacitance after applying DC voltage.
For your information, in temperature compensation capacitors (CH, C0G characteristics, etc.), capacitance doesn't change because paraelectric ceramic is used as its main material and that gives the DC voltage characteristic to the capacitors.