Jize Yan

Enhancing Parametric Sensitivity in Electrically Coupled MEMS Resonators

In an array of identical resonators coupled through weak springs, a small perturbation in the structural properties of one of the resonators strongly impacts coupled oscillations causing the vibration modes to localize. Theoretical studies show that measuring the variation in eigenstates due to such vibration-mode localization can yield orders of magnitude enhancement in signal sensitivity over the technique of simply measuring induced resonant-frequency shifts. In this paper, we propose the application of mode localization for detecting small perturbations in stiffness in pairs of nearly identical weakly coupled microelectromechanical-system resonators and also examine the effect of initial mechanical asymmetry caused by fabrication tolerances in such sensors. For the first time, the variation in eigenstates is studied by coupling the resonators using electrostatic means that allow for significantly weaker coupling-spring constants and the possibility for stronger localization of vibration modes. Eigenstate variations that are nearly three orders of magnitude greater than the corresponding shifts in the resonant frequency for an induced perturbation in stiffness are experimentally demonstrated. Such high electrically tunable parametric sensitivities, together with the added advantage of intrinsic common-mode rejection, pave the way to a new paradigm of mechanical sensing.

Study of lateral mode SOI-MEMS resonators for reduced anchor loss

MEMS resonators fabricated in silicon-on-insulator (SOI) technology must be clamped to the substrate via anchoring stems connected either from within the resonator or through the sides, with the side-clamped solution often employed due to manufacturing constraints. This paper examines the effect of two types of commonly used side-clamped, anchoring-stem geometries on the quality factor of three different laterally-driven resonator topologies. This study employs an analytical framework which considers the relative distribution of strain energies between the resonating body and clamping stems. The ratios of the strain energies are computed using ANSYS FEA and used to provide an indicator of the expected anchor-limited quality factors. Three MEMS resonator topologies have been fabricated and characterized in moderate vacuum. The associated measured quality factors are compared against the computed strain energy ratios, and the trends are shown to agree well with the experimental data.

Low loss HF band SOI wine glass bulk mode capacitive square-plate resonator

This paper reports on the design and electrical characterization of a single crystal silicon micromechanical square-plate resonator. The microresonator has been excited in the anti-symmetrical wine glass mode at a resonant frequency of 5.166 MHz and exhibits an impressive quality factor (Q) of 3.7 × 106 at a pressure of 33 mtorr. The device has been fabricated in a commercial foundry process. An associated motional resistance of approximately 50 kΩ using a dc bias voltage of 60 V is measured for a transduction gap of 2 µm due to the ultra-high Q of the resonator. This result corresponds to a frequency-Q product of 1.9 × 1013, the highest reported for a fundamental mode single-crystal silicon resonator and on par with some of the best quartz crystal resonators. The results are indicative of the superior performance of silicon as a mechanical material, and show that the wine glass resonant mode is beneficial for achieving high quality factors allowed by the material limit.

Ultrasensitive mode-localized mass sensor with electrically tunable parametric sensitivity

We use the phenomena of mode localization and vibration confinement in pairs of weakly coupled, nearly identical microelectromechanical (MEMS) resonators as an ultrasensitive technique of detecting added mass on the resonator. The variations in the eigenstates for induced mass additions are studied and compared with corresponding resonant frequency shifts in pairs of MEMS resonators that are coupled electrostatically. We demonstrate that the relative shifts in the eigenstates can be over three orders of magnitude greater than those in resonant frequency for the same addition of mass. We also investigate the effects of voltage controlled electrical spring tuning on the parametric sensitivity of such sensors and demonstrate sensitivities tunable by over 400%.

A parametrically excited vibration energy harvester

In the arena of vibration energy harvesting, the key technical challenges continue to be low power density and narrow operational frequency bandwidth. While the convention has relied upon the activation of the fundamental mode of resonance through direct excitation, this article explores a new paradigm through the employment of parametric resonance. Unlike the former, oscillatory amplitude growth is not limited due to linear damping. Therefore, the power output can potentially build up to higher levels. Additionally, it is the onset of non-linearity that eventually limits parametric resonance; hence, this approach can also potentially broaden the operating frequency range. Theoretical prediction and numerical modelling have suggested an order higher in oscillatory amplitude growth. An experimental macro-sized electromagnetic prototype (practical volume of ~1800 cm3) when driven into parametric resonance, has demonstrated around 50% increase in half power band and an order of magnitude higher peak power density normalised against input acceleration squared (293 µW cm−3 m−2 s4 with 171.5 mW at 0.57 m s−2) in contrast to the same prototype directly driven at fundamental resonance (36.5 µW cm−3 m−2 s4 with 27.75 mW at 0.65 m s−2). This figure suggests promising potentials while comparing with current state-of-the-art macro-sized counterparts, such as Perpetuum’s PMG-17 (119 µW cm−3 m−2 s4).

Manipulating Vibration Energy Confinement in Electrically Coupled Microelectromechanical Resonator Arrays

This paper reports the first detailed experimental evidence of the phenomena of eigenvalue loci veering and vibration mode localization in microelectromechanical resonator arrays subjected to weak electroelastic coupling. A rapid but continuous interchange of the eigenfunctions associated with the eigenvalues is experimentally observed during veering as the variations in the eigenvalues are studied for induced stiffness variations on one of the coupled resonators. It is also noticed that the electrical tunability of the coupling spring constant in such microsystems enables a manipulation of the severity of modal interchange during veering and in consequence, the extent of energy confinement within the system. These results, while experimentally confirming the elastic behavior of such electrical coupling elements, also suggest that such microsystems provide a unique platform for investigating the general nature and properties of these dynamic phenomena under significantly weaker tunable coupling spring constants that are very difficult to implement in corresponding “macroscopic” systems.

Limits to mode-localized sensing using micro- and nanomechanical resonator arrays

In recent years, the concept of utilizing the phenomenon of vibration mode-localization as a paradigm of mechanical sensing has made profound impact in the design and development of highly sensitive micro- and nanomechanical sensors. Unprecedented enhancements in sensor response exceeding three orders of magnitude relative to the more conventional resonant frequency shift based technique have been both theoretically and experimentally demonstrated using this new sensing approach. However, the ultimate limits of detection and in consequence, the minimum attainable resolution in such mode-localized sensors still remain uncertain. This paper aims to fill this gap by investigating the limits to sensitivity enhancement imposed on such sensors, by some of the fundamental physical noise processes, the bandwidth of operation and the noise from the electronic interfacial circuits. Our analyses indicate that such mode-localized sensors offer tremendous potential for highly sensitive mass and stiffness detection with ultimate resolutions that may be orders of magnitude better than most conventional micro- and nanomechanical resonant sensors.

Narrow Bandwidth Single-Resonator MEMS Tuning Fork Filter

We present a solution for a fourth-order, narrow-bandwidth filter comprising of a single silicon tuning fork resonator driven using one electrode only. Voltage controlled electrical spring tuning is employed to match the primary and secondary modes of the resonator to achieve filter response. A narrow bandwidth single resonator MEMS tuning fork filter is demonstrated with a center frequency of 1.2866 MHz, a 3 dB-bandwidth of 0.0085% and a 1.5 dB ripple.

Parametrically excited MEMS vibration energy harvesters with design approaches to overcome the initiation threshold amplitude

Resonant-based vibration harvesters have conventionally relied upon accessing the fundamental mode of directly excited resonance to maximize the conversion efficiency of mechanical-to-electrical power transduction. This paper explores the use of parametric resonance, which unlike the former, the resonant-induced amplitude growth, is not limited by linear damping and wherein can potentially offer higher and broader nonlinear peaks. A numerical model has been constructed to demonstrate the potential improvements over the convention. Despite the promising potential, a damping-dependent initiation threshold amplitude has to be attained prior to accessing this alternative resonant phenomenon. Design approaches have been explored to passively reduce this initiation threshold. Furthermore, three representative MEMS designs were fabricated with both 25 and 10 ?m thick device silicon. The devices include electrostatic cantilever-based harvesters, with and without the additional design modification to overcome initiation threshold amplitude. The optimum performance was recorded for the 25 ?m thick threshold-aided MEMS prototype with device volume ?0.147?mm3. When driven at 4.2?ms?2, this prototype demonstrated a peak power output of 10.7 nW at the fundamental mode of resonance and 156 nW at the principal parametric resonance, as well as a 23-fold decrease in initiation threshold over the purely parametric prototype. An approximate doubling of the half-power bandwidth was also observed for the parametrically excited scenario.

Electrically Addressed Dual Resonator Sensing Platform for Biochemical Detection

Chemically functionalized silicon microresonators provide the potential for sensitive, label-free biomolecular detection by coupling small induced perturbations in stiffness, mass, and dissipation due to surface bound analyte to their measured frequency response. However, several implementation challenges arise from the necessity of operation in compatible biological buffer solutions. These challenges include minimizing undesired effects of fluid-structure interaction and buffer interference with signal transduction. In this paper, we present a novel dual resonator sensing platform (DRP) to address these challenges, wherein electrical transduction and biochemical sensing are spatially separated onto two different mechanically coupled resonators. This enables electrical interrogation of the sensor without compromising the sensing environment, allowing for relative ease of fabrication and the possibility of integration with on-chip electronics. We demonstrate the functionality of the DRP as a mass sensing platform, with a mass responsivity of 34 Hz/ng in air. The viscous effects on dynamic response of the DRP were investigated by comparing the measurements with theoretical values, and a quality factor of 221 in water is demonstrated. Furthermore, characterization of the DRP was preformed with streptavidin-coated microbeads, and the measured response is in close agreement with the model. Finally, the use of DRP for measurement of dried cell mass and accurate cell counting is demonstrated with a detection limit of 1.46 ng.