Chun Zhao

Experimental Observation of Noise Reduction in Weakly Coupled Nonlinear MEMS Resonators

In this paper, we present the strongly nonlinear behavior of a 2-degree-of-freedom weakly coupled microelectromechanical systems (MEMS) resonator system in a mixed nonlinear regime, using a closed-loop phase feedback oscillator approach. Three out of four nonlinear bifurcation points within a strongly nonlinear coupled resonator system, with both electrical and mechanical nonlinearities, were revealed. Furthermore, we are able to study the amplitude and frequency stabilities of the resulting system when biased at the bifurcation points. Specifically, we discover that, as compared with the linear case, orders of magnitude improvement in amplitude and frequency signal resolution can be observed at the nonlinear bifurcation points, demonstrating that coupled nonlinear MEMS resonators can be useful for enhancing the amplitude and frequency stability for relevant applications. [2017-0092]

A Closed-Loop Readout Configuration for Mode-Localized Resonant MEMS Sensors

This letter presents the first experimental results on the closed-loop characterization of a mode-localized microelectromechanical resonator system. Comparisons between the closed-loop oscillator approach and the open-loop frequency sweep approach show good agreement of output metrics including the amplitude ratios and mode frequencies. This new approach enables real-time measurements using emerging mode-localized resonant sensors and represents an important step toward realizing sensors based on this measurement principle. [2016-0307]

Investigation on the Quality Factor Limit of the (111) Silicon Based Disk Resonator

Quality factor is one of the most important parameters for a MEMS resonator. Most MEMS resonators are dominated by thermoelastic dissipation (TED). This paper demonstrates that the TED in a disk resonator that is made of (111) single-crystal silicon is surpassed by clamping loss. The stiffness-mass decoupling design method, combined with reducing the beam width, was used to engineer high QTED. Experiments show that Q of the (111) disk resonator have an upper boundary that is determined by the clamping loss caused by the unbalanced out-of-plane displacement. The origin of the out-of-plane displacement is explained by theory and simulation.

Closed-loop tracking of amplitude and frequency in a mode-localized resonant MEMS sensor

In this paper, the amplitude and frequency stability of a mode-localized sensor are characterized in a closed loop setup. The system describes an absolute amplitude ratio sensitivity of 5250 to stiffness perturbations in linear operation. A stability of 432ppm at 500s integration time is observed for amplitude ratio measurements. A resolution of 85ppb corresponding to normalised stiffness perturbations in amplitude ratio measurements is thus demonstrated at 500s integration time. Comparisons to frequency shift sensing within the same device shows that amplitude ratio sensing provides higher accuracies for long term measurements due to intrinsic common mode rejection properties in a mode-localized system.

Nonlinear cancellation in weakly coupled MEMS resonators

For the first time, this paper demonstrates the cancellation of nonlinear response in weakly coupled resonators. It has been observed that by working in the region where the mechanical nonlinearity of the resonators and the electrical nonlinearity of the electrostatic coupling cancel, the output current amplitudes are increased by 4x while the trend of vibration amplitude variation upon stiffness perturbations is preserved as seen in the linear regime of the resonators.

Edge-anchored mode-matched micromachined gyroscopic disk resonator

This paper reports on a vacuum packaged circular disk gyroscopic resonator with T-shape anchors fabricated in a (100) single crystalline silicon substrate. This device topology simplifies the fabrication process as compared to previous approaches to realize center-anchored disk gyroscopes. Mode-matching of the trigonal modes of the disk is realized with open-loop characterization results demonstrating a Quality factor exceeding 1.5 million with an initial modal frequency split of 4.7 Hz and a natural frequency of approximately 0.976 MHz (4.81 ppm split). An approach to effective mode matching of such devices is described.

Parametric Noise Reduction in a High-Order Nonlinear MEMS Resonator Utilizing Its Bifurcation Points

An electrostatically actuated non-linear microelectromechanical systems (MEMS) resonator can describe double hysteresis behavior in the measured frequency response due to the interplay between electrical and mechanical non-linearities in the system. This paper provides the first experimental mapping of the stable and unstable branches of the frequency response of a MEMS resonator describing a double hysteretic frequency response using a closed-loop phase feedback oscillator. Furthermore, the frequency stability of the oscillator is compared for varying amplitude and phase feedback conditions, and it is experimentally demonstrated that parametric noise up-conversion can be suppressed in such a system by suitably biasing the resonator at one of the four bifurcation points in such a system. This result is qualitatively consistent with theoretical prediction and demonstrates that improved frequency stability in a non-linear MEMS oscillator is possible by suitably biasing the resonator using simultaneous amplitude and phase feedback.