Ceramic capacitors are fixed-value capacitors that use ceramic or porcelain materials as the dielectric and metal as its electrodes. These are also known as “Workhorses” of the capacitor world as they are widely used due to their small size and charge storage capacity. Ceramic capacitors have a capacitance range between 1uF and 1 nF with a low-voltage rating. These are non-polarized devices and can be used with an AC source as the negative cycle of the voltage will not damage the capacitor.

Applications of ceramic capacitors:

• Ceramic Capacitors are used in bypass and decoupling applications. 
• They are also used in DC motors to minimize RF noise. 
• Ceramic capacitors are used in transmitter stations for resonant circuit applications.
• They are used for high voltage power supplies in laser applications, in power distribution lines, etc.
• Since ceramic capacitors are non-polarized and come in a wide range of capacitances, voltage ratings, and sizes, they can also be used as general-purpose capacitors.

Ceramic Capacitors can be classified into four classes based on the type of ceramic material used as the dielectric.

CLASS I

Paraelectric materials like Titanium dioxide are used as the basic dielectric material. These capacitors have low capacitance values when compared to other classes and are the most accurate. Paraelectric materials have low permittivity which results in the lowest volumetric efficiency among ceramic capacitors. 

The permittivity of a dielectric refers to the electric dipole moment of charged particles (polarization) when an external electric field is applied. The larger the tendency of electric dipole moment, the larger the permittivity value and the larger the charge storage capacity. Paraelectric materials generate polarization when an external electric field is applied and loses the polarization when the field is removed. This is why Paraelectric materials as dielectrics have low permittivity and low losses also. 

The capacitance value of Class 1 Capacitors is almost completely independent of the applied voltage. They are used in resonant circuit applications because of their high stability and low losses.

CLASS II

Class II ceramic capacitors use ferroelectric materials like barium titanate as dielectric. They have high permittivity and in turn better volumetric efficiency than class I capacitors. Ferroelectric materials have some polarization of their own, when an electric field is applied, the polarization increases. Ferroelectric materials remain polarized even after the electric field is removed. Ferroelectric materials are sensitive to voltage and temperature changes. The capacitance of class 2 capacitors changes with the applied voltage. The voltage that is applied affects the ferroelectric material. Higher applied voltages result in lower permittivity. When measured or applied at higher voltages, capacitance can fall to levels that are 80% lower than those at the standardized 0.5 or 1.0 V measuring voltage. Class 2 capacitors also deteriorate with time.

When the rated capacitance and voltage are the same, class II capacitors are significantly smaller than class I capacitors. They are appropriate for uses like buffering, filtering, coupling, and decoupling of electric signals that only need the capacitor to maintain a minimum value of capacitance.

CLASS III

These are known as semiconductive ceramic capacitors. They use doped ferroelectric materials such as Barium titanate as the dielectric. They have very high permittivity which results in better volumetric efficiency than class I and class II.

These capacitors, however, have worse electrical properties, such as decreased accuracy and stability. A very high nonlinear change in capacitance across the temperature range is a characteristic of the dielectric. The voltage applied also affects the capacitance value as doped ferroelectric materials change polarization when the field strength increases or decreases. Additionally, they age over time and suffer from high losses.

CLASS IV

These capacitors are known as barrier layer capacitors. They exhibit very high losses and are the least accurate.

Types of ceramic capacitors:

There are two main types of ceramic capacitors based on their shape – MLCC and disc-shaped capacitors.

• Multi-layer Ceramic capacitors (MLCC): MLCC or Multi-layer Ceramic capacitors are manufactured by stacking individual capacitors together in parallel and connected via terminal surfaces(connecting ends of each capacitor). The production of MLCCs involves precisely combining finely ground paraelectric and ferroelectric granules and alternately layering the mixture with metal contacts. The device is heated to a high temperature after layering is finished, and the mixture is sintered to produce a ceramic material with the desired properties. To increase capacitance, many smaller capacitors are connected in parallel to create the final capacitor. An MLCC has at least 500 layers, with a minimum layer thickness of about 0.5 microns.

Manufacturing process of MLCC

The total capacitance is the product of the capacitance of each layer and the total number of layers in MLCC. MLCCs produce ideal-frequency capacitors when combined with surface-mount technology. The small spacing between the individual capacitors limits the voltage rating. The layer thickness between the capacitors can be decreased to increase the capacitance of MLCC Capacitors

• Disc-type Ceramic Capacitor: These are through-hole capacitors manufactured by coating a ceramic disc with silver contacts on both sides. They have a capacitance range of 10 to 100 pF with a voltage rating of 16 V to 15 kV. They are used as safety capacitors in electromagnetic interference(unwanted noise in a circuit) suppression applications.

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