Ceramic Capacitors

Ceramic capacitors are constructed with materials such as titanium acid barium used as the dielectric. Internally, these capacitors are not constructed as a coil, so they can be used in high frequency applications. Typically, they are used in circuits which bypass high frequency signals to ground. Ceramic Capacitors are typified by their small size and high-dielectric strength. Ceramic capacitors generally come in the shape of a flat disk (disk ceramics), or cylindrical shapes. These capacitors are also compact, moisture-proof, and durable. Typical available ranges having 1,000 V ratings are from approximately 5 pF to about 5,000 pF. At lower voltage ratings, higher capacitance values are available. Because of good dielectric characteristics, both mica and ceramic capacitors can be used in applications from the audio-frequency range up to several hundred megahertz.

Multi Layer Ceramic Capacitors

The multilayer capacitors consist of a monolithic ceramic block with comb-like sintered electrodes. These electrodes come to the surface at the face ends of the ceramic block where an electrical contact is made by burnt-in metallic layers.

Capacitance of MLCC is:

Multilayer ceramics have a superficially similar construction to film capacitors, but instead of being wound, layers of dielectric and electrode material are built up individually and then fired to produce a solid block with terminations at each end. For this reason they are often called “monolithic” capacitors. They can be supplied either in chip form or encapsulated with leads; the encapsulant can be a moulded body or a dip coating.

The multilayer ceramic capacitor has a many-layered dielectric. These capacitors are small in size, and have good temperature and frequency characteristics.

Depending on the chemical composition of their ceramic dielectrics, which determine the main electric properties, ceramic capacitors are classified as follows:

Class-1 Ceramic Capacitors Characteristics

  • The dielectric (e<200) primarily consists of a mixture of metal oxides and titanates.
  • Defined linear temperature coefficient with reversible temperature dependence
  • Capacitance does not vary with voltage.
  • Low losses at frequencies up to the UHF range
  • High insulation resistance
  • Applications: resonant circuits, filters, timing elements

Temperature characteristics of capacitance for class-1 ceramics

Class-2 Ceramic Capacitors Characteristics

  • The dielectric (e = 200 to 10000) primarily consists of titanates (barium, calcium, strontium) and zirconates.
  • Non-linear dependence of capacitance on temperature and voltage
  • Somewhat higher losses and lower insulation resistance than class-1 capacitors
  • Capacitance decreases according to a logarithmic function (ageing)
  • Relatively high capacitance values even with small-size capacitors
  • Applications: coupling, blocking, filtering

Temperature characteristics of capacitance for class-2 ceramics

Summery of Multilayer Ceramic Capacitors

  • Ceramic capacitors change their capacitance more (class 2) or less (class 1) with temperature.
  • Due to a change in the crystalline structure, the capacitance value of high K materials (with a high dielectric constant, e.g. X7R, Z5U) drastically decreases above the Curie point (order of magnitude approximately 50 % at 150 °C). With low K materials (with a low dielectric constant, e.g. C0G) the dissipation factor increases considerably at high temperatures.
  • By owing to the high temperature, moreover, an acceleration of failure mechanisms and thus a shorter service life of the capacitor is to be expected.
  • The capacitance of class-2 capacitors decreases with aging.
  • High dc voltages applied to class-2 capacitors also result in capacitance deviation.
  • Capacitance of class-2 capacitors changes with voltage and/or temperature load.
  • COG is the highest quality dielectric but has a lower permittivity, which means that its capacitance range is more restricted. It exhibits a near-zero temperature coefficient, negligible capacitance and dissipation factor change with voltage or frequency, and its dissipation factor is around 0.001. These features make it the leading contender for high-stability applications, though polycarbonate can be used in some cases.
  • X7R is a reasonably stable high-permittivity (Hi-K) dielectric, which allows capacitance values up to 1 uF to be achieved within a reasonable package size. It can be used over the same temperature range as COG but it exhibits a non-linear and quite marked change of both capacitance and dissipation factor over this range.
  • Virtually the only redeeming feature of class-2 ceramics is their high permittivity which allows high capacitance values, up to 22uF, to be achieved.