Single-resonator fourth-order micromechanical disk filters

A method for realizing a fourth-order micromechanical filter response using only a single, mass-loaded, flexural-mode disk resonator has been used to demonstrate a 20.26-MHz fourth-order Butterworth filter with a tiny 0.03% bandwidth and only 2.56 dB of insertion loss. The basic design technique uses orthogonal mode-splitting and recombining to achieve a parallel-class filter that dispenses with the need for multiple resonators and coupling links in previous filters. The single-resonator disk structure has a measured temperature coefficient of frequency TC_f of -14.2ppm/°C and a third order intercept point IIP₃ of +20.6dBm, which indicates very good device linearity.