Frequency dependent capacitance of metal semiconductor metal varactor diode and its tunable filter application

The structure of metal semiconductor metal varactor diode is presented. The capacitance dependent of the varactor on external voltage has been described. Also the frequency dependent capacitance of the varactor has been measured by Network Analyzer. We also build a tunable filter with applied bias on the varactor to investigate the frequency dependent capacitance. This shows that the capacitance reduces very fast when the frequency increases. The ratio of the capacitance from no bias to maximum bias, however, does not reduce too much. This makes the varactor useful for microwave frequency applications to protecting from electrostatic discharge, lightning, and electromagnetic pulse.