What are ceramic capacitors?
A ceramic capacitor uses a ceramic material as the dielectric. Ceramics were one of the first materials to be used in the producion of capacitors, as it was a known insulator. Many geometries were used in ceramic capacitors, of which some, like ceramic tubular capacitors and barrier layer capacitors are obsolete today due to their size, parasitic effects or electrical characteristics. The types of ceramic capacitors most often used in modern electronics are the multi-layer ceramic capacitor, otherwise named ceramic multi-layer chip capacitor (MLCC) and the ceramic disc capacitor. MLCCs are the most produced capacitors with a quantity of approximately 1000 billion devices per year. They are made in SMD (surface-mounted) technology and are widely used due to their small size. Ceramic capacitors are usually made with very small capacitance values, typically between 1nF and 1µF, although values up to 100µF are possible. Ceramic capacitors are also very small in size and have a low maximum rated voltage. They are not polarized, which means that they may be safely connected to an AC source. Ceramic capacitors have a great frequency response due to low parasitic effects such as resistance or inductance.
Ceramic capacitor definition
A ceramic capacitor is a capacitor which uses a ceramic material as the dielectric. The two most common types are multi-layer ceramic capacitors and ceramic disc capacitors.
Precision and tolerances
There are two classes of ceramic capacitors available today: class 1 and class 2. Class 1 ceramic capacitors are used where high stability and low losses are required. They are very accurate and the capacitance value is stable in regard to applied voltage, temperature and frequency. The NP0 series of capacitors has a capacitance thermal stability of ±0.54% within the total temperature range of -55 to +125 °C. Tolerances of the nominal capacitance value can be as low as 1%.
Class 2 capacitors have a high capacitance per volume and are used for less sensitive applications. Their thermal stability is typically ±15% in the operating temperature range, and the nominal value tolerances are around 20%.
When high component packing densities are required, as is the case in most modern printed circuit boards (PCBs), MLCC devices offer a great advantage compared to other capacitors. To illustrate this point, the “0402” multi-layer ceramic capacitor package measures just 0.4 mm x 0.2 mm. In such a package, there are 500 or more ceramic and metal layers. The minimum ceramic thickness as of 2010 is on the order of 0.5 microns.
High voltage and high power
Physically larger ceramic capacitors can be made to withstand much higher voltages and these are called power ceramic capacitors. These are physically much larger than those used on PCBs and have specialized terminals for safe connection to a high voltage supply. Power ceramic capacitors can be made to withstand voltages in the range of 2kV up to 100 kV, with a power specified at much higher than 200 volt-amperes.
Smaller MLCCs used in printed circuit boards are rated to voltages from only a few volts up to several hundreds of volts, depending on the application.
Construction and properties of ceramic capacitors
Ceramic disc capacitors
Ceramic disc capacitors are manufactured by coating a ceramic disc with silver contacts on both sides. To achieve larger capacitances, these devices can be made from multiple layers. Ceramic disc capacitors are usually through-hole components and are falling out of favor due to their size. MLCCs are used instead, if capacitance values allow. Ceramic disc capacitors have a capacitance value of 10pF to 100μF with a wide variety of voltage ratings, between 16 volts to 15 kV and more.
Multi-layer ceramic capacitor (MLCC)
MLCCs are manufactured by accurately mixing finely ground granules of paraelectric and ferroelectric materials and alternatively layering the mix with metal contacts. After the layering is complete, the device is brought to a high temperature and the mixture is sintered, resulting in a ceramic material of desired properties. The resulting capacitor basically consists of many smaller capacitors connected in parallel, increasing the capacitance. MLCCs consist of 500 layers and more, with the minimum layer thicknes of approximately 0.5 micron. As technology progresses, the layer thickness decreases and higher capacitances are achievable for the same volume.
Applications for ceramic capacitors
Having in mind that MLCCs are the most widely produced capacitor in the electronics industry, it goes without saying that there are countless applications for these capacitors. An interesting high-precision, high-power application is a resonant circuit in transmitter stations. Class 2 high-power capacitors are used in high voltage laser power supplies, power circuit breakers, induction furnaces etc. Small-form SMD (surface mount) capacitors are often used in printed circuit boards and high density applications use capacitors which are comparable to the size of a grain of sand. They are also used in DC-DC converters which put a lot of stress on the components in the form of high frequencies and high levels of electrical noise. Ceramic capacitors can also be used as a general purpose capacitor, since they are not polarized and are available in a large variety of capacitances, voltage ratings and sizes. Many hobbyists, especially in the field of robotics, are familiar with ceramic disc capacitors used across brush DC motors to minimize RF noise.