Editing Varicap (section)

== Operation ==
[[File:Varactor function.svg|right|thumb|Operation of a varicap. [[Electron hole|Holes]] are blue, electrons are red, [[depletion zone]] is white. The electrodes are at the top and bottom.]]
Varactors are operated in a [[reverse-biased]] state, so no DC current flows through the device.  The amount of reverse bias controls the thickness of the [[depletion zone]] and therefore the varactor's junction capacitance. Capacitance change characteristic depends on doping profile. Generally, for abrupt junction profile, the depletion region thickness is proportional to the [[square root]] of the applied voltage, and [[capacitance]] is inversely proportional to the depletion region thickness. Thus, the capacitance is inversely proportional to the square root of applied voltage. For hyperabrupt junction profile capacitance change is more non-linear, but hyperabrupt varicaps have larger capacitance variation and can work with lower voltages.

All diodes exhibit this variable junction capacitance, but varactors are manufactured to exploit the effect and increase the capacitance variation.

The figure shows an example of a cross section of a varactor with the depletion layer formed of a p–n junction. This depletion layer can also be made of a [[MOSFET|MOS]] or a [[Schottky diode]]. This is important in [[CMOS]] and [[MMIC]] technology.