Silicon-micromachined spacers for UHF cavity resonators

This paper reports on a novel hybrid integration concept that enables the realization of high-quality (Q) factor, low-frequency coaxial cavity resonators with well-defined capacitive-loading and variable center frequency. It is based on a silicon-micromachined spacer that is mounted on top of a conventional CNC-machined metallic cavity to functionalize the resonator's capacitance. For the first time, it is demonstrated that low-frequency resonators with micrometer-scale gaps (10s of microns), relatively large Q-factor (459-505) and tunable response (18.5%) can be constructed without the need for post-fabrication tuning. To demonstrate these benefits, a resonator assembly was designed, built and experimentally tested at the UHF band and for a frequency tuning range between 1424-1711 MHz.