Believe it or not, capacitors are one of the fundamental building blocks of our modern world. These charge storage devices are at work in everything from your car’s speakers to the flash on your camera. One of the most important types of capacitors is the ceramic capacitor, which uses a ceramic layer as the dielectric between two or more conductive charge storage plates.
Ceramic Capacitors Versus Everything Else
Ceramic capacitors were first developed in the 1920s in Germany as a substitute for mica dielectrics. In the 21st century, the International Electrotechnical Commission (IEC) currently separates ceramic capacitors into two classes. Per the IEC guidelines:
- Class 1 capacitors are manufactured from finely ground paraelectric materials for high stability.
- Class 2 capacitors are manufactured using ferroelectric materials. Class 2 capacitors feature higher capacitance per volume when compared to class 1 components but offer less accuracy and stability.
We most often see ceramic capacitors in multilayer ceramic chip capacitor (MLCC) packages suitable for surface-mount soldering, or as single-layer ceramic disk capacitors, generally suitable for through-hole assembly. As of 2012, manufacturers produced more than a trillion of these components, and that number has almost certainly risen given their increased usage in electronic devices. Unfortunately, there still may not be enough capacitors available.
As abundant and useful as they are, ceramic capacitors aren’t the only charge-holding component available, and the other types come with unique advantages and disadvantages. Ceramic capacitors belong to the class of non-polarized capacitors. By contrast, polarized capacitors must connect properly in a positive and negative configuration.
Other Non-Polarized Dielectric Materials
Ceramic capacitors fall firmly into the class of non-polarized capacitors. When a dielectric separates two parallel plate conductors, they will exhibit capacitive qualities, storing charge on the plates. Due to their simplicity, we can use several alternative dielectric materials in place of the ceramic, such as:
- Polymer films
- In some situations, air or a vacuum
Each alternative dielectric material exhibits different permittivity, minimum dielectric thicknesses, and dielectric strength. Ceramic capacitors will generally have a higher permittivity and smaller minimum dielectric thickness – in the order of .5-1 micrometers (μm) – than the other materials in the list above. Ceramic capacitors also have a lower dielectric strength – at less than 100 V/μm – though air gap capacitors are one notable exception at 3.3 V/μm.
Polarized capacitors require attachment in a precise orientation to function properly. Normally this includes the following:
- An electrolytic cap, which uses a metal conductor to form the anode “plate” – to put things in terms of a ceramic capacitor
- An electrolytic solution that contacts a cathode
- An oxide layer that forms the dielectric material on the metallic anode, which is roughened to increase its surface area significantly
This increased surface area, as well as the fact that the oxide dielectric material can become very thin (less than less than .01 μm), means that a polarized capacitor can have a very high capacitance for a given physical size.
One disadvantage of polarized capacitors is that they are not suitable for use in applications where voltage oscillates between one contact and the other, such as some types of filtering. For these applications, ceramic and other non-polarized capacitors are the best choice.
Polarized capacitors can use aluminum, tantalum, or niobium to form the oxide layer. Each material exhibits a relatively high dielectric strength, with aluminum oxide exhibiting the highest performance at 710 V/μm. Their relative permittivity is similar to class 1 ceramic capacitors, in the order of 20 (niobium is greatest, followed by tantalum, then aluminum), though class 2 ceramic capacitors can exhibit much greater performance at well over 10,000 in some cases.
We can classify supercapacitors as one form of polarized capacitors because they contain positive and negative leads, but these devices are in somewhat of a class of their own. Supercapacitors use the movement of ions through an electrolyte to dynamically form a Helmholtz double layer. This double layer then acts as a very thin—less than .001 μm—dielectric. These capacitors provide excellent energy storage capabilities, but because of their relatively slow absorption and dissipation of charge when compared to ceramic and other types of capacitors, they are not appropriate for filtering. Additionally, they have a limited charge and discharge lifespan and a lower overall dielectric breakdown voltage.
Ceramic capacitors can maintain a constant rating well, but your application may require you to change your capacitance on the fly. If so, an adjustable, or tuning, capacitor may be the right component. Tuning capacitors are designed to move two parallel plates to increase or decrease capacitance. While largely replaced by other technologies, tuning capacitors once enabled our radios to tune, and you can still find them at work in certain niche and educational applications. You can even build your own tuning capacitor using these instructions.