Response of piezoelectric circular microdiaphragm sensors in higher frequency modes

In this study we investigate two phenomena in the vibration of piezoelectric circular microdiaphragm (PCM) sensors, the non-degenerated vibration modes and increase of mass sensitivity with using higher modes. The investigated parameters can enhance the performance of PCM in mass sensing applications. In order to achieve the desired goals, we used reflection digital holography microscope (RDHM) to visualize different frequency modes of the fabricated PCM. It was found that the degeneracy of the modes with at least one nodal diameter is broken, even though it was expected that these orthogonal modes are degenerated in frequency. These non degenerated modes are correlated to the lack of symmetry of the PCM, mainly imposed by the top electrode configuration. These modes may be applied as an alternative way for temperature and humidity compensation in the mass sensing resonators as a dual mode resonant sensor. Moreover, it was demonstrated that the frequency shift of PCM to mass loading increases in higher frequency modes. This shift is almost 8.5 times higher in mode (0,3) than mode (0,1).