| High-order beam-based micromechanical filters, employing for the first time "bridging" between nonadjacent resonators to effect loss poles for better filter shape factors, have been demonstrated with insertion loss less than 3 dB, sharper passband-to-stopband roll-offs than achievable by equivalent non-bridged filters, and around 50 dB of stopband rejection. In addition, these filters possess a demonstrated self-switching property by virtue of their dc-biased capacitive transducers that allow them to achieve zero-loss on/off filter switching without the need for lossy series switches, and with settling times down to 1.5 mus, 7X faster than that of RF MEMS switches.; To attain higher frequencies, a medium-scale integrated (MSI) fully differential vibrating micromechanical filter circuit that comprises 128 radial-mode disk and mechanical link elements to achieve low motional resistance while suppressing unwanted modes and feedthrough signals has been demonstrated with an insertion loss of 2.43 dB for 0.06% bandwidth, a 20 dB shape factor of 2.85, and a stopband rejection greater than 25 dB, all with a constituent resonator motional resistance Rx of only 977 O and filter termination impedances around 1.5 kO for each port. Furthermore, a method for realizing a high-order on-chip filter response that combines two fourth-order (i.e., two-pole) micro-mechanically-coupled MEMS-based disk-array sub-filters in a parallel configuration has been used to demonstrate a 163-MHz eighth-order (i.e., four-pole) bandpass filter with a 0.16%-bandwidth insertion loss of 2.73 dB, and a 20 dB shape factor of only 1.78.; To boost frequencies even past 1 GHz while maintaining reasonable impedances, vibrating polysilicon micromechanical spoke-supported ring resonators, obtained by removing quadrants of material from a solid disk resonator, but purposely leaving intact beams of material with quarter-wavelength dimensions to non-intrusively support the structure, have been demonstrated in several vibration modes spanning frequencies from HF (24.4 MHz), to VHF (72.1 MHz), to UHF (1.458 GHz), with Q's as high as 67,519, 48,026, and 8,832, respectively. Furthermore, the use of notched support attachments closer to actual extensional ring nodal points raises the Q to 15,248 in vacuum and 10,165 in air at 1.463 GHz, which is the highest yet achieved past 1 GHz, and which clearly illustrates the utility of notching for substantially higher Q. |
