Othman, Masuri Bin (1986) Silicon-based micromechanical resonators. University of Southampton, Doctoral Thesis.
Abstract
This thesis describes the analysis, design, fabrication and evaluation of on-chip silicon micromechanical resonators. The basic device consists of a vibrating cantilever beam etched out of single crystal silicon, with overlying layers of silicon dioxide and polysilicon. The mechanical excitation of the beam is achieved by localised thermal expansion and the resulting motion is detected by the piezoresistive effect in the polysilicon. In order to produce the structure it was necessary to develop suitable etching techniques and so a detailed study has been made of the concentration and orientation dependence of ethylenediamine pyrocatechol etch. Resonators with a thickness of 2 μm and lengths of 50 μm to 80 μm have been fabricated and have resonant frequencies in the range 300 KHz to 1 MHz. The maximum Q observed is 1600 in vacuum and reduced to 300 at atmospheric pressure. The temperature coefficient of resonant frequency is in the range 11 to 20 ppm/K. An analysis of these devices is presented based on the use of Rayleigh method, and it is shown that it should be possible to achieve a zero temperature coefficient of frequency if an optimised structure is used. An equivalent electrical network is proposed for the resonator and shown to agree well with measurements. Finally some preliminary results are presented on the use of the resonator as a pressure sensor. (D73136/87)
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