Ferroelectric varactors suitable for capacitive shunt switching

Patent, 2007

A ferroelectric varactor suitable for capacitive shunt switching is disclosed. High resistivity silicon with a SiO2 layer and a patterned metallic layer deposited on top is used as the substrate. A ferroelectric thin-film layer deposited on the substrate is used for the implementation of the varactor. A top metal electrode is deposited on the ferroelectric thin-film layer forming a CPW transmission line. By using the capacitance formed by the large area ground conductors in the top metal electrode and bottom metallic layer, a series connection of the ferroelectric varactor with the large capacitor defined by the ground conductors is created. The large capacitor acts as a short to ground, eliminating the need for vias. The varactor shunt switches can be used to create a bandpass filter and a tunable notch filter. The bandpass filter is implemented by cascading the switches, and the bandpass filter implemented through the use of a resonance circuit.