Ceramic Capacitors
Ceramic capacitors use a ceramic material as the dielectric. They are among the most common components in modern electronics because they can be made very small, have low lead inductance, and cover a wide range of capacitance values. Multilayer ceramic capacitors, usually abbreviated MLCC, place many thin electrode and dielectric layers inside one small package.
Why ceramics are used so often
- Small physical size.
- Very low series inductance in surface-mount packages.
- Wide range of capacitance and voltage ratings.
- Low cost in common values.
- Excellent availability for high-frequency bypassing and filtering.
Class 1 and Class 2 dielectrics
Not all ceramic capacitors behave alike. A useful first division is between Class 1 dielectrics, which emphasize stability and low loss, and Class 2 dielectrics, which emphasize higher capacitance in a smaller volume.
| Family | Typical examples | General behavior |
|---|---|---|
| Class 1 | C0G / NP0 | Very stable capacitance, low loss, low temperature coefficient, excellent for precision and RF use. |
| Class 2 | X7R, X5R | Much higher capacitance per volume, but capacitance varies more with voltage, temperature, and time. |
| Higher-change ceramic families | Y5V and similar types | Very compact and inexpensive, but capacitance can change substantially with operating conditions. |
Reading X7R and similar codes
The familiar three-character temperature code describes an operating temperature range and an allowed capacitance change over that range. For example, X7R is a Class 2 dielectric intended to remain within its specified capacitance-change band over a defined temperature range. The code does not describe DC-bias behavior, aging, tolerance, or voltage rating, so the datasheet is still required.
DC-bias effect
One of the most important facts about high-capacitance ceramic capacitors is that their capacitance may fall as DC voltage is applied. A capacitor marked 10 µF may provide considerably less than 10 µF in the actual circuit, especially when a small package is operated at a substantial fraction of its voltage rating.
Aging
Many Class 2 ceramic dielectrics show logarithmic aging: capacitance gradually decreases with time after manufacture or after the material has been heated above its characteristic transition temperature. Heating during soldering can temporarily reset part of this aging process. Precision circuits should use a dielectric appropriate to the required stability.
Microphonics and piezoelectric behavior
Some high-permittivity ceramic dielectrics are piezoelectric. Mechanical stress can create a small voltage, and an applied AC voltage can make the component physically vibrate. In sensitive audio, sensor, or high-gain circuits this can cause microphonic noise. In switching power supplies, groups of MLCCs can sometimes make an audible sound as the circuit board itself vibrates.
High-frequency decoupling
Small surface-mount ceramic capacitors are excellent for local IC decoupling because their short terminals and compact geometry keep inductance low. The complete current loop still matters: a good capacitor mounted far away through long traces may perform worse than a modest capacitor mounted directly beside the IC power and ground pins.
Cracking and board flex
MLCCs are rigid ceramic structures. Excessive board bending, rough depaneling, connector stress, or thermal shock can crack them. A crack may produce leakage or a short circuit. Flexible-termination versions are available for mechanically demanding equipment.
Typical applications
- Power-supply decoupling and bypassing.
- RF coupling and filtering.
- Oscillators and resonant circuits using stable C0G/NP0 parts.
- EMI filtering.
- Timing networks where the dielectric's stability is suitable.
- Switching-regulator input and output filtering.
Selection checklist
- Required capacitance under actual DC bias.
- Dielectric class: C0G/NP0, X7R, X5R, or another family.
- Voltage rating and transient margin.
- Temperature range.
- Tolerance and aging.
- Package size and mechanical stress.
- ESR, ESL, and self-resonant frequency for high-frequency work.
Further reading
- Murata — Ceramic capacitor basics
- Murata — MLCC characteristics and capacitance change
- For actual capacitance under bias, use the exact manufacturer's characteristic curves for the chosen part number.