Mohamed A. Abdelmoneum

High-Q UHF micromechanical radial-contour mode disk resonators

A micromechanical, laterally vibrating disk resonator, fabricated via a technology combining polysilicon surface-micromachining and metal electroplating to attain submicron lateral capacitive gaps, has been demonstrated at frequencies as high as 829 MHz and with Qs as high as 23 000 at 193 MHz. Furthermore, the resonators have been demonstrated operating in the first three radial contour modes, allowing a significant frequency increase without scaling the device, and a 193 MHz resonator has been shown operating at atmospheric pressure with a Q of 8,880, evidence that vacuum packaging is not necessary for many applications. These results represent an important step toward reaching the frequencies required by the RF front-ends in wireless transceivers. The geometric dimensions necessary to reach a given frequency are larger for this contour-mode than for the flexural-modes used by previous resonators. This, coupled with its unprecedented Q value, makes this disk resonator a choice candidate for use in the IF and RF stages of future miniaturized transceivers. Finally, a number of measurement techniques are demonstrated, including two electromechanical mixing techniques, and evaluated for their ability to measure the performance of sub-optimal (e.g., insufficiently small capacitive gap, limited dc-bias), high-frequency, high-Q micromechanical resonators under conditions where parasitic effects could otherwise mask motional output currents. [1051].

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.

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.

Location-dependent frequency tuning of vibrating micromechanical resonators via laser trimming

Location-dependent, bidirectional laser trimming of the resonance frequencies of vibrating micromechanical resonators is demonstrated in steps as small as 21 ppm over it range of 20,200 ppm, and with targeting measures that suppress unwanted variations in Q and series motional resistance. Specifically, geometrically symmetrical laser targeting is shown to be instrumental in preserving high Q on the micro-scale, much more so than on the macro-scale. A semi-empirical model is used to model the trimming process and to identify the laser trim locations that most efficiently attain a desired shift in frequency with minimal Q reduction. Different micromechanical resonator types are trimmed to demonstrate the versatility of the technique, including a clamped-clamped beam and a wine glass disk.

UHF high-order radial-contour-mode disk resonators

A micromechanical, laterally vibrating disk resonator, fabricated via a technology combining polysilicon surface-micromachining and metal electroplating to attain sub-micron lateral capacitive gaps, has been demonstrated at frequencies as high as 829 MHz and with Qs as high as 23,000 at 193 MHz. Furthermore, the resonators have been demonstrated operating in the first three radial contour modes, allowing a significant frequency increase without scaling the device, and a 193 MHz resonator has been shown operating at atmospheric pressure with a Q of 8,880-evidence that vacuum packaging is not necessary for many applications. The geometric dimensions necessary to reach a given frequency are larger for this contour-mode than for the flexural-modes used by previous resonators. This, coupled with its unprecedented Q value, makes this disk resonator a choice candidate for use in the IF and RF stages of future miniaturized transceivers.

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.