Microelectromechanical resonators and filters for communications applications.

This dissertation explores the performance capabilities and limitations of micromechanical resonators and filters for wireless communications applications. The design, simulation, fabrication, characterization, and verification of polysilicon versions of such devices are discussed, with a particular focus on achieving high performance high order filters and high quality factor ( Q) high frequency resonators. Technological developments are presented for fabrication and for frequency tuning of micromechanical. resonators. A brief review is given for macroscopic mechanical components used in current transceiver design. The first high-order, acoustically-coupled micromechanical filter is developed with percent bandwidths less than 0.09%, stopband rejection larger than 64dB, and insertion loss less than 0.2dB in the medium frequency (MF - 300kHz to 3MHz) range. Design strategies that prove instrumental in achieving these filters include (1) quarter-wavelength coupling beams to eliminate passband distortion caused by non-ideal coupling elements, (2) low-velocity coupling to extend the range of achievable filter bandwidths, (3) ratioed, folded-beam micromechanical resonators to achieve a wide range (six orders of magnitude) of stiffnesses at resonator coupling locations, (4) parallel-plate capacitive transducers for individual frequency tuning of constituent resonators, and (5) differential operation to reduce the effect of parasitic feedthrough capacitors. In addition, free-free beam, flexural-mode, micromechanical resonators are demonstrated for the first time, utilizing non-intrusive supports to achieve measured Q's as high as 14,000 at VHF frequencies from 30--90MHz. These microresonators feature torsional-mode support springs that effectively isolate the resonator beam from its anchors via quarter-wavelength impedance transformations, thus minimizing anchor dissipation and allowing these resonators to achieve high Q with high stiffness in the VHF frequency range. Finally, a batch-compatible, post-fabrication annealing technique based upon filament-like heating of microstructures is demonstrated as an effective means for trimming the resonance frequencies (fO's) and increasing the quality factors (Q's) of surface-micromachined, polysilicon, mechanical resonators, with frequency trim ranges of over 2.7% and Q increases of up to 600%, depending upon resonator fabrication history. By pulsing anneal voltage waveforms, controlled frequency trims of less than 16 ppm per trial are demonstrated.Ph.D.AcousticsApplied SciencesElectrical engineeringMechanical engineeringPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/132270/2/9959883.pd