The DC Bias Phenomenon Explained

When constructing multilayer ceramic capacitors (MLCCs), there are two classes of dielectrics electrical engineers typically select from depending on the application – Class 1, which consists of non-ferroelectric materials such as C0G/NP0, and Class 2, which are ferroelectric materials such as X5R and X7R. One key difference between these materials comes in the form of capacitance stability as voltage and temperature increase.

With Class 1 dielectrics, capacitance will remain stable when DC voltage is applied and operational temperature increases. On the other hand, Class 2 dielectrics, which have a higher dielectric constant (K), are less stable with regards to temperature, voltage, frequency, and time.

While a variety of modifications can be made to increase capacitance, including changing the surface area of the electrode layers, the number of layers, the K, or the distance between the two electrodes, capacitance will still eventually dramatically decrease for Class 2 dielectrics when DC voltage is applied. This is because of a phenomenon called DC bias that causes Class 2 ferroelectric formulations to eventually experience a decrease in dielectric constant as DC voltage is applied.