A 6 to 24 GHz continuously tunable, microfabricated, high-Q cavity resonator with electrostatic MEMS actuation

An all-silicon capacitive-post loaded cavity tunable resonator, continuously tunable from C to K frequency bands is presented for the first time. All parts of the resonator are fabricated using silicon microfabrication techniques. The presented device is tuned electrostatically from 6.1 to 24.4 GHz (4∶1 tuning range) with a measured unloaded quality factor (Q
u
) from 300–1,000. The resonator includes an evanescent capacitive-post section with a thin film of low-loss dielectric (Parylene-N) as a spacer between the optically smooth, gold coated silicon post-top and single-crystal-silicon diaphragm to create sub-micrometer initial gaps. Consequently, the resonator achieves a capacitance density of 47 pF/mm
²
at its lowest frequency. This is 5.6× higher than the state-of-the-art tunable filter designs. It is considered that precision and tight tolerances associated with the microfabrication techniques hold the key in achieving high-Q, widely tunable filters. To the best of the authors' knowledge, this is the widest tuning high-Q resonator presented today.