Integrated Resonant Micro/Nano Gravimetric Sensors for Bio/Chemical Detection in Air and Liquid

Resonant micro/nanoelectromechanical systems (MEMS/NEMS) with on-chip integrated excitation and readout components, exhibit exquisite gravimetric sensitivities which have greatly advanced the bio/chemical sensor technologies in the past two decades. This paper reviews the development of integrated MEMS/NEMS resonators for bio/chemical sensing applications mainly in air and liquid. Different vibrational modes (bending, torsional, in-plane, and extensional modes) have been exploited to enhance the quality (Q) factors and mass sensing performance in viscous media. Such resonant mass sensors have shown great potential in detecting many kinds of trace analytes in gas and liquid phases, such as chemical vapors, volatile organic compounds, pollutant gases, bacteria, biomarkers, and DNA. The integrated MEMS/NEMS mass sensors will continuously push the detection limit of trace bio/chemical molecules and bring a better understanding of gas/nanomaterial interaction and molecular binding mechanisms.

Characterizing the Spatially Dependent Sensitivity of Resonant Mass Sensors Using Inkjet Deposition

Micro- and millimeter-scale resonant mass sensors have received widespread attention due to their robust and sensitive performance in a wide range of detection applications. A key performance metric for such systems is the sensitivity of the resonant frequency of a device to changes in mass, which needs to be calibrated. This calibration is complicated by the fact that the position of the added mass on a sensor can have an effect on the measured sensitivity—therefore, a spatial sensitivity mapping is needed. To date, most approaches for experimental sensitivity characterization are based upon the controlled addition of small masses, e.g., the direct attachment of microbeads via atomic force microscopy or the selective microelectrodeposition of material, both of which are time consuming and require specialized equipment. This work proposes a method of experimental spatial sensitivity measurement that uses an inkjet system and standard sensor readout methodology to map the spatially dependent sensitivity of a resonant mass sensor—a significantly easier experimental approach. The methodology is described and demonstrated on a quartz resonator. In the specific case of a Kyocera CX3225 thickness-shear mode resonator, the location of the region of maximum mass sensitivity is experimentally identified.

Characterization of Resonant Mass Sensors Using Inkjet Deposition

Micro- and millimeter-scale resonant mass sensors have received widespread research attention due to their robust and highly-sensitive performance in a wide range of detection applications. A key performance metric associated with such systems is the sensitivity of the resonant frequency of a given device to changes in mass, which needs to be calibrated for different sensor designs. This calibration is complicated by the fact that the position of any added mass on a sensor can have an effect on the measured sensitivity, and thus a spatial sensitivity mapping is needed. To date, most approaches for experimental sensitivity characterization are based upon the controlled addition of small masses. These approaches include the direct attachment of microbeads via atomic force microscopy or the selective microelectrodeposition of material, both of which are time consuming and require specialized equipment. This work proposes a method of experimental spatial sensitivity measurement that uses an inkjet system and standard sensor readout methodology to map the spatially-dependent sensitivity of a resonant mass sensor — a significantly easier experimental approach. The methodology is described and demonstrated on a quartz resonator and used to inform practical sensor development.

Mass and Position Determination in MEMS Resonant Mass Sensors: Theoretical and Experimental Investigation

We present a method to determine accurately the position and mass of an entity attached to the surface of an electrostatically actuated clamped-clamped microbeam implemented as a mass sensor. In the theoretical investigation, the microbeam is modeled as a nonlinear Euler-Bernoulli beam and a perturbation technique is used to develop a closed-form expression for the frequency shift due to an added mass at a specific location on the microbeam surface. The experimental investigation was conducted on a microbeam made of Polyimide with a special lower electrode to excite both of the first and second modes of vibration. Using an ink-jet printer, we deposited droplets of polymers with a defined mass and position on the surface of the microbeam and we measured the shifts in its resonance frequencies. The theoretical predictions of the mass and position of the deposited droplets match well with the experimental measurements.

Dynamics of Globally and Dissipatively Coupled Resonators

This work explores the dynamics of arrays of globally and dissipatively coupled resonators. These resonator arrays are shown to be capable of exhibiting seemingly new collective behaviors which are highly sensitive to the dispersion of the natural frequencies of the constituent resonators in the array, the intrinsic damping of the resonators in the array, and the magnitude of the global coupling coefficient that captures the strength of the dissipative coupling. These behaviors have been identified within the work as group attenuation, confined attenuation, and group resonance. Group and confined attenuation are associated with an absence of energy and are strongly dependent on the dispersion of the natural frequencies. In cases of moderate dissipative coupling, the effects of group and confined attenuation could be interpreted as frequency-dependent damping. In cases where the global coupling coefficient is large, group resonance is significant. This effect is synonymous with the resonances of the constituent resonators being shared and occurring at frequencies in between the isolated resonators' natural frequencies. Accordingly, one could view group resonance as the antithesis of localization, in that the localization of the modes of a conservatively coupled system with a finite dispersion of the constituent resonators' natural frequencies is most significant when the coupling is weak. The authors believe that collective behaviors, such as those described herein, have direct applicability in new single-input, single-output resonant mass sensors, and, with extension, a variety of other sensing and signal processing systems.