Tunable MEMS capacitor

A MEMS tunable capacitor comprising:

• first and second opposing capacitor electrodes, wherein the second capacitor electrode is movable by a MEMS switch to vary spacing between the first and second opposing capacitor electrodes, and thereby tune the capacitance;
• a third electrode facing the movable second electrode;
• and a tunable dielectric material and a non-tunable dielectric material in series between the second and third electrodes, wherein the tunable dielectric material occupies a first dimension of the spacing, and the non-tunable dielectric material occupies a second dimension of the spacing, the third electrode being configured and arranged to electrically control the tunable dielectric material, an ac rf voltage source which includes a dc component and is connected to the third electrode, the voltage source being configured and arranged to apply a voltage to set a dielectric constant of the tunable dielectric material;
• and wherein the second capacitor electrode is configured and arranged to vary the spacing in response to a first applied voltage for a first continuous range of adjustment of the capacitance of the MEMS capacitor and wherein the tunable dielectric material is configured and arranged to be tuned, via the third electrode, in response to a second applied voltage, for a second continuous range of adjustment of the capacitance of the MEMS capacitor, thereby to provide a continuous analogue range of adjustment including the first and second ranges.

An apparatus comprising:

• a capacitor circuit having first, second, and third electrodes, the second electrode being separated from each of the first and third electrodes by an electrode spacing;
• a tunable dielectric material and a non-tunable dielectric material in series between the second and third electrodes, the tunable dielectric material occupying a first dimension of the spacing, and the non-tunable dielectric material occupying a second dimension of the spacing;
• a first circuit connected to the first and second electrodes and configured and arranged to apply a voltage across the first and second electrodes, the second electrode being configured and arranged to move in response to the voltage;
• a second circuit connected to the third electrode and configured and arranged to tune a dielectric constant of the tunable dielectric material by applying a voltage to the third electrode;
• and the first and second circuits being configured and arranged to tune the capacitance of the capacitor by applying a voltage across the first and second electrodes to move the second electrode relative to the first and third electrodes, and by applying a voltage to the third electrode to tune the dielectric constant of the tunable dielectric material.