Novel Analysis of a Micropillar Coupled Acoustic Wave Sensor

ABSTRACT Acoustic wave sensors are being developed for many emerging applications such as in semiconductor fabrication, biological diagnostics and polymer characterization. Traditional acoustic wave sensing devices such as quartz crystal microbalance (QCM) rely on polymer thin films coated on quartz plates to detect chemical and biological agents. It has been found that significant sensitivity enhancement of QCM devices can be achieved by simply attaching a polymer micropillar film onto the QCM substrate (QCM-P) to enable a unique coupled resonance between the micropillars and quartz substrate. In the present work, an equivalent circuit model integrating mechanical vibration of micropillars and electrical load impedance of piezoelectric substrate was developed to predict the frequency shift and Q-factor of the QCM-P devices when operating in air and liquid environments. In the model, the vibration of micropillars was solved simultaneously with the liquid loading on the pillar surface. The resultant hydraulic force was integrated into the circuit model to predict the load impedance on the sensor surface. The developed model was validated by experimental results for QCM-P devices operating in air and water with different micropillar heights. It will serve as a powerful tool to predict the performance of the QCM-P devices for different applications.