Vibration Analysis of MEMS Sensors for Detection of Ultrasound

The modal vibration characteristics of new MEMS (microelectromechanical systems) ultrasonic sensors have been studied theoretically and experimentally. Such studies are needed in order to design MEMS sensors with improved sensitivity for detection of ultrasound. The determination of vibration behavior of such sensors is critical for a successful design, and a validated vibration characterization strategy is therefore proposed. Modal analysis techniques using microscanning laser Doppler interferometry and finite element numerical analysis are employed to determine the mechanical resonance parameters of sensors based on both polyvinylidene fluoride (PVDF) -coated and aluminum nitride (AlN) -coated silicon MEMS devices, which lead to redesign strategies for improved ultrasound detection. The measurements and predictions of modal frequencies and mode shapes are seen to be in reasonable agreement, once the manufacturing imperfections are accounted for. The results also show that if the dimensions (particularly the thicknesses) of various layers in the laminated sensors are selected appropriately, ultrasonic signals of the desired frequencies can be detected.