Post-fabrication laser trimming of micromechanical filters

Semi-automatic post-fabrication laser trimming of a second order vibrating micromechanical clamped-clamped beam (CCB) filter has been demonstrated via a pole-correcting algorithm that identifies the individual resonators associated with each peak in a distorted filter response, then uses this information to compute correction factors needed to trim each resonator towards the desired filter passband. Both increases or decreases in resonator frequency are possible via the laser trimming due a geometrically-derived location-dependence, where the direction of the frequency change depends strongly on the location at which the laser removes material. By compensating for dimensional errors due to finite absolute and matching tolerances in planar processes, this trim procedure might eventually be instrumental in making available the banks of very small percent bandwidth micromechanical filters presently targeted for RF-channel selection in future multi-band wireless handsets.