Ph.D Thesis

Ph.D StudentKassie Adne
SubjectA Comprehensive Investigation of Electrostatic Micro
DepartmentDepartment of Mechanical Engineering
Supervisor PROF. David Elata
Full Thesis textFull thesis text - English Version


Resonators lay in the heart of modern-age technology. They give the rhythm to oscillators and clocks, form the core of RF filters, and are essential in many high-end sensors. Until recently, quartz resonators dominated the market. Quartz resonators, however, are difficult to integrate with the ever shrinking dimensions of silicon integrated circuits (ICs). Therefor in the last few decades, a formidable effort is made to replace quartz devices with mechanical resonators that are more compatible with ICs. The fruit of this effort is the emerging technology of micro electro mechanical (MEMS) resonators. This work focuses specifically, on MEMS electrostatic resonators.

Much of the current research in this field, is dedicated to investigating and improving temperature stability, minimizing packaging induced stress, developing non-disruptive characterization techniques, improving signal to noise ratios (SNR), finding methods to increase quality factor (Q), seeking effective ways to drive and sense resonators, and achieve tuneability. In this work we address some of these challenges, and present findings for three complementary topics.

The first topic addresses non-disruptive testing of micro resonators. It is shown experimentally and numerically that a laser vibrometer, which is often used for characterization of MEMS resonators at their development stages, may disrupt measurements in unexpected ways.

The second topic addresses driving and sensing of micro resonators. Here, the concept of Auto-resonance (AR) driving scheme is revisited, and a novel driving scheme, which we call 'Harmonic biasing', is proposed. It is shown that AR scheme can greatly expedite characterization of nonlinear electrostatic resonators, and that the method of 'Harmonic biasing' can improve SNR, in double-sided comb-drive (DSCD) resonators, by separating motional current from feedthrough in the frequency domain.

The third topic addresses parametric resonators and self-excited oscillators. We present a surprising scheme, for inducing a parametric response in DSCD resonators using an electrostatically floating rotor.

Finally, we conclude the third part, with an experimental investigation of methods for extending the life-span, of self-excited MEMS Franklin oscillators.