Piezoelectric Microcantilevered Plate Resonators Utilizing Flexural-Based 2-D Modes for Individually Sensing Density and Viscosity in Liquids

This article investigates a piezoelectric microcantilevered wide-plate resonator for liquid sensing. The higher order flexural mode featuring 2-D vibration of the resonator is exploited to enable precise measurements under viscous liquid conditions. The analytical model based on fluid-structure interaction successfully explains this nonconventional flexural mode and resonance characteristics, which provides an optimization design method for the resonator. For on-chip fully electrical interfaces, the piezoelectric aluminum nitride (AlN) film is employed in combination with tailored electrode design to allow self-actuation and self-sensing capabilities when submerged in liquid media. The experiments demonstrated that the density and dynamic viscosity of various liquids can be individually determined from their high-linear relationships with the resonant frequency and quality factor of the resonator. The proposed piezoelectric resonator exhibited excellent sensing characteristics, resulting in accuracies of 0.48% for density with a sensitivity of 27.94 kHz/(g<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula>cm−3) and 3.37% for viscosity. In addition, the minimum detectable changes were evaluated to be <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.79\times 10^{-4}$ </tex-math></inline-formula> g<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula>cm−3 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$9.29~\mu $ </tex-math></inline-formula>Pa<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula>s for the liquid density and viscosity, respectively. The results presented here show the outstanding potential of 2-D vibrational modes using microplate resonators for achieving high accuracy and compact design in liquid monitoring applications.