Exploiting Thickness Shear Mode Acoustic Resonance in Piezoelectric-on-Si Unreleased Micromechanical Resonators for Gravimetric Biosensing in Fluid-Damped Media

Description

Mechanical resonance is an age-old physical effect, describing the amplification of amplitudefor a mechanical system in vibration at a characteristic frequency, referred to as the resonantfrequency. Incremental mass loaded on the mechanical system is detected via the resultingresonant frequency shift. This sensitivity increases when reducing the size of the mechanicalsystem. Over the last ~20 years, advances in micro/nanofabrication have allowed realizationof micro/nano-scale mechanical systems, affording impressive gains in the sensitivity. Whilesuch benefits have been repeatedly demonstrated in vacuum and air, operating such devicesin liquid (required in many biological detection applications) continues to remain a challenge.When immersed in liquid, the strong vibrations in air are heavily damped by the surroundingfluid. Since the goal is to interface these devices with integrated electronics, it is important todrive and detect mechanical oscillations electrically. For example, electrolysis of liquid is acommon problem in conventional capacitive transducers, which makes efficient transductionhighly difficult. In response to these problems, some researchers have taken the approach ofconfining liquid in channels embedded on the resonator. For low-cost disposable biologicaldetection applications, the complex fabrication of such a device would have an undesirablyhigh price tag.The aim of this project is to implement a novel resonator design that ismore robust to fluiddampingand hashigher transduction efficiency. The novelty lies in realizing anunreleasedsilicon resonator designed to vibrate in thethickness shear mode(TSM) in liquid. The TSMreduces damping and increases energy storage, each contributing to higher quality factor (Q).Efficient transduction will be achieved through using piezoelectric Aluminum Nitride (AlN)for a fully electrical interface. We aim to empirically demonstrate 100MHz AlN-on-Si TSMresonators measurable when immersed in liquid with Q>250 –– much higher than the typicalQs of 10-90 reported in literature. Finally, we apply this breakthrough technology to singlecell-mass measurements in a rare and milestone demonstration of capability for bio-detection.We have formed a cross-disciplinary team that fuses expertise in designing and characterizingmicroelectromechanical resonators with that of biomedical instrumentation and cell biology.Based on our initial results from simulations as well as our combination of expertise, we arein a strong position to lead the proposed research and confident of achieving all the researchobjectives. The outcomes of this project will initiate breakthrough advancements not only inmicrotechnology for resonant sensing but also in biomedical instrumentation and cell biology.?