Why do we use polarized capacitors?
The physical size of a capacitor is a function of the thickness of the dielectric (among other things).

Early on, it was discovered that the oxides of certain metals (aluminum and tantalum in particular) made good dielectrics, and could be made very thin through a chemical process &mdash; orders of magnitude thinner than other dielectrics such as waxed/oiled paper and plastic film. Therefore, the electrolytic capacitor was invented to provide high capacitance in a reasonable volume.

Unfortunately, the chemical process requires that the voltage across the capacitor must have only a single polarity, so these capacitors are "polarized". Reversing the polarity degrades and eventually destroys the oxide layer. It's something we just have to live with in order to take advantage of this technology.



The ability to produce high-value capacitors in nonpolarized technologies such as multilayer ceramic means that it is now possible to use them where only a polarized capacitor would have been previously available. There is generally no problem with making this substitution, although you may need to consider some of the quirks of the technology you're switching to.

For example, some high-K (high dielectric constant) ceramics exhibit significant capacitance changes with voltage. This might be acceptable in a coupling or bypass application, but completely unacceptable in a filter design.