טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentAlmog Ronen
SubjectNonlinear Dynamics in Nanomechanical Oscillators
DepartmentDepartment of Electrical Engineering
Supervisor Professor Eyal Buks
Full Thesis textFull thesis text - English Version


Abstract

    Micro/Nanoelectromechanical resonators are widely employed for applications such as sensing, switching, and filtering.
In particular, such resonators can be used for ultra-sensitive force/mass measurements. A possible technique to improve signal to noise ratio in such devices is to implement an on-chip mechanical amplification.

    In this work we have focused on the understanding of nonlinear dynamics in such devices and the development of novel amplification schemes. Two mechanisms of amplification were experimentally studied: (a) Small signal amplification in a bifurcating dynamical system, exploiting its high sensitivity to fluctuations near its bifurcation point. This amplification mechanism is known as Bifurcation Amplification.

(b) Stochastic resonance, in which an appropriate amount of noise is used to amplify periodic signal acting on a bistable nonlinear system.

    In the first amplification mechanism we have studied mechanical amplification and noise squeezing in a nonlinear nanomechanical resonator driven by an intense pump near its dynamical bifurcation point, namely, the onset of Duffing bistability. We have employed bifurcation amplification for the first time in nanomechanical resonators to demonstrate high signal gain, phase sensitive amplification and noise squeezing. Phase sensitive amplification is achieved by a homodyne detection scheme, where the output signal could be either amplified or deamplified, depending on a local oscillator phase.

    In the second amplification mechanism, we have studied stochastic resonance in a nonlinear bistable nanomechanical resonator. The resonator is tuned to its bistability region by an intense pump near a point of equal transition rates between its two metastable oscillation states. The pump is amplitude modulated, inducing thus modulation of the activation barrier between the states. When noise is added to the excitation, the resonator's response exhibits noise dependent amplification.

    The oscillator under study consists of a nonlinear doubly clamped Nan mechanical AuPd beam, excited capacitively by an adjacent gate electrode and its vibrations are detected optically.

    The work included fabrication, process development, setup of an optical system for displacement detection, measurements, analysis, and theory for selected subjects.