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New for December 2018: capacitor manufacturing is a multi-billion dollar business. If you are a microwave engineer, it pays to understand all parts of the microwave supply chain. Capacitors require three things: two matal contacts, and dielectric material between them. The Devil is in the details.
Note: In the case of electrolytic caps, which are "polarized", one side is the anode and the other is the cathode. You always connect the positive DC voltage to the anode. If you are a dog lover, you might think that "cats are negative" to remember this. Non-polarized capacitors don't care how you hook up DC voltage, their leads are both called electrodes.
Multi-layer ceramic capacitors (MLCCs)
MLCCs (also abreviated MLCs) are fabricated by mixing a capacitor powder with binders, rolling it into a tape, printing electrodes, firing, testing... and in the end you need to produce a capacitor that is made for less than $0.01 each.
Having troubles procuring chip caps lately? Recently the sheer amount of electronic hardware in commercial products has driven the need for capacitors through the roof. Read about the 2018 multi-layer chip capacitor shortage here.
There are many dielctrics used for MLCs, and we'll add a page on that topic soon. The relative permittivity of some of them are in the thousands!
Enjoy a video from KEMET on their MLCC process below:
KEMET Electronics' multi-layer ceramic capacitor process
Aluminum electrolytic capacitors
These are used in microwave systems as charge storage in pulsed transmitter applications. They don't store as much charge as tantalum caps. They are made from aluminum foil that is specially treated to provide up to 100X the surface area of raw foil, to increase capacitance density. The dielectric is aluminum oxide (so-called alumina, relative permittivity of ~9.5) that is grown to specified thickness.
Aluminum electrolytics are almost always provided in a "can" format, as they are fabricated by rolling up sheets of aluminum/dielectric/aluminum sandwich. Not unlike a fruit roll-up!
Here is a video from KEMET on their aluminum electrolytic capacitor process.
KEMET Electronics' aluminum electrolytic capacitor process
Wet tantalum capacitors
These are also used for charge storage, and they have highest capacitance density. They must be carefully screened for reliabiltiy; when they fail, you may see the "magical blue smoke" of electronics released. If you don't see smoke or flames, or hear the combustion (it sounds like something cracking), you may unfairly accuse your co-worker of passing gas due to the unpleasant odor.
Tantalum is not exactly abundent on Earth. About 50% of current production is mined in Congo. You can guess how that works out for the local populace. Read about "resource curse" on Wikipedia.
Tantalum caps are made starting with powdered tantalum that is sintered into a sponge-like material to form the anode. It is baked in an oxygen atmosphere so that tantalum pentoxide (Ta2O5) grows over the considerable surface area, forming the dielectric layer. Ta2O5 has relaitive permittivity of 41. Then another material is flooded into the matrix to form the cathode. In the past, MnO2 was used. KEMET has a version that uses a conductive polymer, as shown in the video below, and is supposed to prevent the ignition failure mode.
KEMET Electronics' KO-CAP tantalum capacitor process
Metal insulator metal capacitors
In this style of capacitor, a silicon wafer is processed witth many thousands of small value (100pF for example) capacitors on top using silcon nitride or silicon oxide dielectric. The top metal is plated in such a way that it is wirebondable.
Single-layer ceramic capacitors
More to come!