Mustafa U. Demirci

Mechanically Corner-Coupled Square Microresonator Array for Reduced Series Motional Resistance

Substantial reductions in vibrating micromechanical resonator series motional resistance Rx have been attained by mechanically coupling and exciting a parallel array of corner-coupled polysilicon square plate resonators. Using this technique with seven resonators, an effective Rx of 480 Omega has been attained at 70 MHz, which is more than 5.9X smaller than the 2.82 kOmega exhibited by a stand-alone transverse-mode corner-supported square resonator, and all this achieved while still maintaining an effective Q>9000. This method for Rx-reduction is superior to methods based on brute force scaling of electrode-to-resonator gaps or dc-bias increases, because it allows a reduction in Rx without sacrificing linearity, and thereby breaks the Rx versus dynamic range tradeoff often seen when scaling. This paper also compares two types of anchoring schemes for transverse-mode square micromechanical resonators and models the effect of support beam parameters on resonance frequency

Stemless wine-glass-mode disk micromechanical resonators

Polysilicon wine-glass mode micromechanical disk resonators using a stemless, non-intrusive suspension structure have been demonstrated in both vacuum and atmospheric pressure at frequencies around 73.4 MHz with Qs as high as 98,000 in vacuum, and 8,600 in atmosphere-the highest ever reported Qs at this frequency range and in these environments for any on-chip micro-scale resonator. The Q of 98,000 in vacuum for this wine-glass mode resonator is more than 10X higher than measured on radial contour mode counterparts, and more than 8X higher than exhibited by published free-free beams at 70 MHz.

A 10-MHz Micromechanical Resonator Pierce Reference Oscillator for Communications

A modified Pierce circuit topology has been used to first demonstrate a 9.75 MHz μmechanical resonator reference oscillator, then to assess the ultimate frequency stability of such an oscillator via accurate measurement of its close-to-carrier phase noise, which seems to exhibit an unexpected 1/f 3 dependence that limits the phase noise to −80 dBc at a 1 kHz offset from the carrier—a value that must be improved before use in most communications applications. Through theoretical analysis, this 1/f 3 dependence seems to derive from aliasing of active circuit 1/f noise onto the carrier caused by nonlinearity in the capacitive transducer of the μmechanical resonator.

Mechanically corner-coupled square microresonator array for reduced series motional resistance

Substantial reductions in vibrating micromechanical resonator series motional resistance R/sub x/ have been attained by mechanically coupling and exciting a parallel array of corner-coupled polysilicon square plate resonators. Using this technique with five resonators, an effective R/sub x/ of 4.4 k/spl Omega/ has been attained at 64 MHz, which is more than 4.8 X smaller than the 21.3 k/spl Omega/ exhibited by a stand-alone transverse-mode square resonator, and all this achieved while still maintaining an effective Q>9,000. This method for R/sub x/-reduction is superior to methods based on brute force scaling of electrode-to-resonator gaps or DC-bias increases, because it allows a reduction in R/sub x/ without sacrificing linearity, and thereby breaks the R/sub x/ versus dynamic range trade-off often seen when scaling.

Higher-mode free-free beam micromechanical resonators

Polysilicon free-free beam micromechanical resonators based on MEMS technology operating in second and third-mode flexural vibrations have been demonstrated at frequencies as high as 102 MHz with Qs on the order of 11,500. Via strategic placement of electrodes, and careful determination of the exact support beam attachment locations that minimize anchor loss, these new resonators actually exhibit higher Q in the second mode than in the fundamental at the same frequency. Experiments to gauge the effect of variations in support beam dimensions and attachment locations on free-free beam microresonator performance show that an offset of only 0.6 /spl mu/m in the support beam attachment location results in a 7X degradation in the Q. In addition, measured temperature coefficients for second-mode free-free beam /spl mu/resonators are on the order of -13.1 ppm//spl deg/C, which is on par with that for fundamental mode resonance.

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/sub f/ of -14.2ppm//spl deg/C and a third order intercept point IIP/sub 3/ of +20.6dBm, which indicates very good device linearity.

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.