Ceramic capacitor
Encyclopedia
In electronics
, a ceramic capacitor is a capacitor
constructed of alternating layers of metal
and ceramic
, with the ceramic material acting as the dielectric
. The temperature coefficient
depends on whether the dielectric is Class 1
or Class 2
. A ceramic capacitor (especially the class 2) often has high dissipation factor
, high frequency coefficient of dissipation.
Ceramic capacitors come in various shapes and styles, including:
Class I capacitors: accurate, temperature-compensating capacitors. They are the most stable over voltage, temperature, and to some extent, frequency. They also have the lowest losses. On the other hand, they have the lowest volumetric efficiency. A typical class I capacitor will have a temperature coefficient of 30 ppm/°C. This will typically be fairly linear with temperature. These also allow for high Q filters—a typical class I capacitor will have a dissipation factor of 0.15%. Very high accuracy (~1%) class I capacitors are available (typical ones will be 5% or 10%). The highest accuracy class 1 capacitors are designated C0G or NP0.
Class II capacitors: better volumetric efficiency, but lower accuracy and stability. A typical class II capacitor may change capacitance by 15% over a −55 °C to 85 °C temperature range. A typical class II capacitor will have a dissipation factor of 2.5%. It will have average to poor accuracy (from 10% down to +20/-80%).
Class III capacitors: high volumetric efficiency, but poor accuracy and stability. A typical class III capacitor will change capacitance by -22% to +56% over a temperature range of 10 °C to 55 °C. It will have a dissipation factor of 4%. It will have fairly poor accuracy (commonly, 20%, or +80/-20%). These are typically used for decoupling
or in other power supply applications.
At one point, Class IV capacitors were also available, with worse electrical characteristics than Class III, but even better volumetric efficiency. They are now rather rare and considered obsolete, as modern multilayer ceramics can offer better performance in a compact package.
These correspond roughly to low K, medium K, and high K. Note that none of the classes are "better" than any others—the relative performance depends on application. Class I capacitors are physically larger than class III capacitors, and for bypassing and other non-filtering applications, the accuracy, stability, and loss factor may be unimportant, while cost and volumetric efficiency may be. As such, Class I capacitors are primarily used in filtering applications, where the main competition is from film capacitors in low frequency applications, and more esoteric capacitors in RF applications. Class III capacitors are typically used in power supply applications. Traditionally, they had no competition in this niche, as they were limited to small sizes. As ceramic technology has improved, ceramic capacitors are now commonly available in values of up to 100 µF, and they are increasingly starting to compete with electrolytic capacitors
, where ceramics offer much better electrical performance at prices that, while still much higher than electrolytic, are becoming increasingly reasonable as the technology improves.
Example: a label of "104K" indicates 10×104 pF = 100,000 pF = 100 nF = 0.1 µF ±10%
There is also an EIA
three character code that indicates temperature coefficient. For non-temperature-compensating capacitor, the code consists of three letters. The first character is a letter that gives the low-end operating temperature
. The second is a digit gives the high-end operating temperature. The final letter gives capacitance change over that temperature range:
For instance, a Z5U capacitor will operate from +10 °C to +85 °C with a capacitance change of at most +22% to −56%. An X7R capacitor will operate from −55 °C to +125 °C with a capacitance change of at most ±15%.
Temperature-compensated capacitors use a different EIA code. Here, the first letter gives the significant figure of the change in capacitance over temperature in ppm/°C. The second character gives the multiplier. The third character gives the maximum error from that in ppm/°C. All ratings are from 25 to 85 °C:
For instance, a C0G will have 0 drift, with an error of ±30 ppm/°C, while a P3K will have −1500 ppm/°C drift, with a maximum error of ±250 ppm/°C.
Note that in addition to the EIA capacitor codes, there are industry capacitor codes and military capacitor codes.
Sample self-resonant frequencies for one set of C0G and one set of X7R ceramic capacitors are:
and low capacitance aluminum electrolytic
capacitors in applications such as bypass or high frequency switching power supplies as their cost, reliability and size becomes competitive. In many applications, their low ESR allows the use of a lower nominal capacitance value.
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...
, a ceramic capacitor is a capacitor
Capacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
constructed of alternating layers of metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
and ceramic
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
, with the ceramic material acting as the dielectric
Dielectric
A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...
. The temperature coefficient
Temperature coefficient
The temperature coefficient is the relative change of a physical property when the temperature is changed by 1 K.In the following formula, let R be the physical property to be measured and T be the temperature at which the property is measured. T0 is the reference temperature, and ΔT is the...
depends on whether the dielectric is Class 1
EIA Class 1 dielectric
The EIA Class 1 dielectric materials are ceramic dielectric materials used in ceramic capacitors of small values The EIA Class 1 dielectric materials are ceramic dielectric materials used in ceramic capacitors of small values The EIA Class 1 dielectric materials are ceramic dielectric materials...
or Class 2
EIA Class 2 dielectric
The EIA Class 2 dielectric materials are ceramic dielectric materials used in ceramic capacitors.The EIA Class 2 dielectrics in general are usually based on formulas with high content of barium titanate , possibly mixed with other dielectric electroceramics. Due to its piezoelectric properties,...
. A ceramic capacitor (especially the class 2) often has high dissipation factor
Dissipation factor
In physics, the dissipation factor is a measure of loss-rate of energy of a mode of oscillation in a dissipative system. It is the reciprocal of Quality factor, which represents the quality of oscillation....
, high frequency coefficient of dissipation.
Construction
A ceramic capacitor is a two-terminal non-polar device. The classical ceramic capacitor is the "disc capacitor". This device pre-dates the transistor and was used extensively in vacuum-tube equipment (e.g., radio receivers) from about 1930 through the 1950s, and in discrete transistor equipment from the 1950s through the 1980s. As of 2007, ceramic disc capacitors are in widespread use in electronic equipment, providing high capacity and small size at low price compared to other low value capacitor types.Ceramic capacitors come in various shapes and styles, including:
- disc, resin coated, with through-holeThrough-hole technologyThrough-hole technology, also spelled "thru-hole", refers to the mounting scheme used for electronic components that involves the use of leads on the components that are inserted into holes drilled in printed circuit boards and soldered to pads on the opposite side either by manual assembly by...
leads - multilayer rectangular block, surface mountSurface-mount technologySurface mount technology is a method for constructing electronic circuits in which the components are mounted directly onto the surface of printed circuit boards . An electronic device so made is called a surface mount device...
- bare leadless disc, sits in a slot in the PCB and is soldered in place, used for UHF applications
- tube shape, not popular now
Classes of ceramic capacitors
Three classes of ceramic capacitors are commonly available:Class I capacitors: accurate, temperature-compensating capacitors. They are the most stable over voltage, temperature, and to some extent, frequency. They also have the lowest losses. On the other hand, they have the lowest volumetric efficiency. A typical class I capacitor will have a temperature coefficient of 30 ppm/°C. This will typically be fairly linear with temperature. These also allow for high Q filters—a typical class I capacitor will have a dissipation factor of 0.15%. Very high accuracy (~1%) class I capacitors are available (typical ones will be 5% or 10%). The highest accuracy class 1 capacitors are designated C0G or NP0.
Class II capacitors: better volumetric efficiency, but lower accuracy and stability. A typical class II capacitor may change capacitance by 15% over a −55 °C to 85 °C temperature range. A typical class II capacitor will have a dissipation factor of 2.5%. It will have average to poor accuracy (from 10% down to +20/-80%).
Class III capacitors: high volumetric efficiency, but poor accuracy and stability. A typical class III capacitor will change capacitance by -22% to +56% over a temperature range of 10 °C to 55 °C. It will have a dissipation factor of 4%. It will have fairly poor accuracy (commonly, 20%, or +80/-20%). These are typically used for decoupling
Decoupling capacitor
A decoupling capacitor is a capacitor used to decouple one part of an electrical network from another. Noise caused by other circuit elements is shunted through the capacitor, reducing the effect they have on the rest of the circuit....
or in other power supply applications.
At one point, Class IV capacitors were also available, with worse electrical characteristics than Class III, but even better volumetric efficiency. They are now rather rare and considered obsolete, as modern multilayer ceramics can offer better performance in a compact package.
These correspond roughly to low K, medium K, and high K. Note that none of the classes are "better" than any others—the relative performance depends on application. Class I capacitors are physically larger than class III capacitors, and for bypassing and other non-filtering applications, the accuracy, stability, and loss factor may be unimportant, while cost and volumetric efficiency may be. As such, Class I capacitors are primarily used in filtering applications, where the main competition is from film capacitors in low frequency applications, and more esoteric capacitors in RF applications. Class III capacitors are typically used in power supply applications. Traditionally, they had no competition in this niche, as they were limited to small sizes. As ceramic technology has improved, ceramic capacitors are now commonly available in values of up to 100 µF, and they are increasingly starting to compete with electrolytic capacitors
Electrolytic capacitor
An electrolytic capacitor is a type of capacitor that uses an electrolyte, an ionic conducting liquid, as one of its plates, to achieve a larger capacitance per unit volume than other types. They are often referred to in electronics usage simply as "electrolytics"...
, where ceramics offer much better electrical performance at prices that, while still much higher than electrolytic, are becoming increasingly reasonable as the technology improves.
Coding
There is a three digit code printed on a ceramic capacitor specifying its value. The first two digits are the two significant figures and the third digit is a base 10 multiplier. The value is given in picofarads (pF). A letter suffix indicates the tolerancehttp://staff.bcc.edu/eet/Capacitor_Coding.html:| C | ± 0.25 pF | M | ±20% |
|---|---|---|---|
| D | ± 0.5 pF | P | +100 −0% |
| J | ± 5% | Y | −20 +50% |
| K | ±10% | Z | −20 + 80% |
Example: a label of "104K" indicates 10×104 pF = 100,000 pF = 100 nF = 0.1 µF ±10%
There is also an EIA
Electronic Industries Alliance
The Electronic Industries Alliance was a standards and trade organization composed as an alliance of trade associations for electronics manufacturers in the United States. They developed standards to ensure the equipment of different manufacturers was compatible and interchangeable...
three character code that indicates temperature coefficient. For non-temperature-compensating capacitor, the code consists of three letters. The first character is a letter that gives the low-end operating temperature
Operating temperature
An operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the...
. The second is a digit gives the high-end operating temperature. The final letter gives capacitance change over that temperature range:
| Letter (low temp) | Digit (high temp) | Letter (change) |
|---|---|---|
| X= −55 °C (−67 °F) | 2= +45 °C (+113 °F) | D= ±3.3% |
| Y= −30 °C (−22 °F) | 4= +65 °C (+149 °F) | E= ±4.7% |
| Z= +10 °C (+50 °F) | 5= +85 °C (+185 °F) | F= ±7.5% |
| 6=+105 °C (+221 °F) | P= ±10% | |
| 7=+125 °C (+257 °F) | R= ±15% | |
| 8=+150 °C (+302 °F) | S= ±22% | |
| T= +22 to −33% | ||
| U= +22 to −56% | ||
| V= +22 to −82% |
For instance, a Z5U capacitor will operate from +10 °C to +85 °C with a capacitance change of at most +22% to −56%. An X7R capacitor will operate from −55 °C to +125 °C with a capacitance change of at most ±15%.
Temperature-compensated capacitors use a different EIA code. Here, the first letter gives the significant figure of the change in capacitance over temperature in ppm/°C. The second character gives the multiplier. The third character gives the maximum error from that in ppm/°C. All ratings are from 25 to 85 °C:
| Significant Figure | Multiplier | Tolerance |
|---|---|---|
| C: 0.0 | 0: -1 | G: ±30 |
| B: 0.3 | 1: -10 | H: ±60 |
| L: 0.8 | 2: -100 | J: ±120 |
| A: 0.9 | 3: -1000 | K: ±250 |
| M: 1.0 | 4: +1 | L: ±500 |
| P: 1.5 | 6: +10 | M: ±1000 |
| R: 2.2 | 7: +100 | N: ±2500 |
| S: 3.3 | 8: +1000 | |
| T: 4.7 | ||
| V: 5.6 | ||
| U: 7.5 |
For instance, a C0G will have 0 drift, with an error of ±30 ppm/°C, while a P3K will have −1500 ppm/°C drift, with a maximum error of ±250 ppm/°C.
Note that in addition to the EIA capacitor codes, there are industry capacitor codes and military capacitor codes.
HF use
Ceramic capacitors are suitable for moderately high-frequency work (into the high hundreds of megahertz range, or, with great care, into the low gigahertz range), as modern ceramic caps are fairly non-inductive compared to the other major classes of capacitors (film and electrolytic). Capacitor technologies with higher self-resonant frequencies tend to be expensive and esoteric (typically, mica or glass capacitors).Sample self-resonant frequencies for one set of C0G and one set of X7R ceramic capacitors are:
| 10 pF | 100 pF | 1 nF | 10 nF | 100 nF | 1 µF | |
|---|---|---|---|---|---|---|
| C0G (Class 1) | 1550 MHz | 460 MHz | 160 MHz | 55 MHz | ||
| X7R (Class 2) | 190 MHz | 56 MHz | 22 MHz | 10 MHz |
Tantalum capacitor replacement use
Multilayer ceramic capacitors are increasingly used to replace tantalumTantalum capacitor
The tantalum capacitor is a highly reliable type of electrolytic capacitor, available in both solid-bodied and separately encased forms. The encased "wet" variant is not used often in modern designs...
and low capacitance aluminum electrolytic
Electrolytic capacitor
An electrolytic capacitor is a type of capacitor that uses an electrolyte, an ionic conducting liquid, as one of its plates, to achieve a larger capacitance per unit volume than other types. They are often referred to in electronics usage simply as "electrolytics"...
capacitors in applications such as bypass or high frequency switching power supplies as their cost, reliability and size becomes competitive. In many applications, their low ESR allows the use of a lower nominal capacitance value.