a device for varying the capacitance of an electronic circuit is disclosed . the device comprises a flexible membrane located above the electronic circuit , a metal layer connected to the flexible membrane , and bias circuitry located above the membrane . variation of the capacitance of the electronic circuit is obtained by pulling the membrane upwards by means of the bias circuitry . the disclosed device provides a sizeable capacitance variation and high q factor , resulting in overall low filter insertion loss . a nearly constant group delay over a wide operating bandwidth is also obtained .