Role of Mass Accumulation and Viscoelastic Film Properties for the Response of Acoustic-Wave-Based Chemical Sensors

TLDR

The acoustic load at the interface between the device and viscoelastic coating encodes surface mass and film modulus, allowing analysis across any thickness and revealing gravimetric and nongravimetric response regimes. The study examines how acoustic‑wave microsensors coated with viscoelastic films respond to mass changes and film modulus variations, aiming to assign sensor signals to gravimetric or nongravimetric regimes. The authors develop a method that assigns the sensor signal to either a gravimetric or a nongravimetric response based on oscillator measurements. They determine a critical value from oscillator measurements that delineates the transition between regimes, show that coating‑thickness limits differ between fabrication and sensing, and demonstrate the method on a 10 MHz quartz crystal resonator.

Abstract

The sensitivity of acoustic-wave microsensors coated with a viscoelastic film to mass changes and film modulus (changes) is examined. The study analyzes the acoustic load at the interface between the acoustic device and the coating. The acoustic load carries information about surface mass and film modulus; its determination has no restrictions in film thickness. Two regimes of film behavior can be distinguished: the gravimetric regime, where the sensor response is mainly mass sensitive, and the nongravimetric regime, where viscoelasticity gains influence on the sensor response. We develop a method, which allows the assignment of the sensor signal to a gravimetric or a nongravimetric response. The critical value can be determined from oscillator measurements. The related limits for the coating thickness are not the same for the coating procedure and mass accumulation during chemical sensing. As an example, we present results from a 10 MHz quartz crystal resonator.