High-Q HF microelectromechanical filters

IC-compatible microelectromechanical intermediate frequency filters using i ntegrated resonators with Q's in the thousands to achieve filter Q's in the hundreds have been demonstrated using a polysilicon surface micromachining technology: These filters are composed of two clamped-clamped beam microme chanical resonators coupled by a soft flexural-mode mechanical spring. The center frequency of a given filter is determined by the resonance frequency of the constituent resonators, while the bandwidth is determined by the co upling spring dimensions and its location between the resonators. Quarter-w avelength coupling is required on this microscale to alleviate mass loading effects caused by similar resonator and coupler dimensions. Despite constr aints arising from quarter-wavelength design, a range of percent bandwidths is still attainable by taking advantage of low-velocity spring attachment locations. A complete design procedure is presented in which electromechani cal analogies are used to model the mechanical device via equivalent electr ical circuits. Filter center frequencies around 8 MHz with Q's from 40 to 4 50 (i.e., percent bandwidths from 0.23 to 2.5%), associated insertion losse s less than 2 dB, and spurious-free dynamic ranges around 78 dB are demonst rated using low-velocity designs with input and output termination resistan ces on the order of 12 k Omega.