Abstract
We present a 5.41 MHz square-extensional (SE) mode resonator in closed-loop oscillation for resonant mass sensing in the liquid phase. The resonator has been fabricated in piezoelectric thin film aluminum nitride (AlN) on silicon (Si). The strain profile of the SE mode allows for higher electromechanical coupling efficiency using piezoelectric transduction to lower the motional resistance (Rm) given the expected low quality factors (Q) in liquid (136 compared to 942 in air). By locking the device into self-sustained oscillation, the minimum detectable frequency shift is reduced from 3680 ppm (open-loop in water) to 8.76 ppm (closed-loop in air).
Highlights
The development of biochemical mass sensors has been interest due to their wide scope of applications that cover clinical diagnosis, agriculture & food quality control, the automotive industry, and contamination detection in polluted water
Systems (MEMS) resonators designed to interact with fluids are of interest for sensing the physical properties of liquids [1] and biosensing [2] as they allow for high throughput, real-time monitoring, and require low sample volumes
As the quality factor (Q) determines the minimum resolvable frequency, it should be as high as possible when the resonator is covered in fluid
Summary
The development of biochemical mass sensors has been interest due to their wide scope of applications that cover clinical diagnosis, agriculture & food quality control, the automotive industry, and contamination detection in polluted water. Systems (MEMS) resonators designed to interact with fluids are of interest for sensing the physical properties of liquids [1] and biosensing [2] as they allow for high throughput, real-time monitoring, and require low sample volumes. Such a resonator should deliver a workable signal-to-noise ratio. By exploiting the enhanced transduction efficiency using piezoelectric transduction, the circuit design is greatly simplified compared to the capacitive resonators described in [7,8], which is critical in the context of applying MEMS resonators as mass sensors in fluids.
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