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Effects of flexural vibration and thickness vibration on receiving characteristics of a diaphragm-type PZT resonator

The piezoelectric micromachined ultrasonic transducer (PMUT) is increasingly being used in medical applications with the development of microelectromechanical system technology. The PMUT generates flexural vibration depending on its structure, but there is also thickness vibration depending on the film thickness of the resonator. This paper clarifies the effect of each vibration on the PMUT reception characteristics. Two approaches that may weaken flexural vibration are investigated in finite element simulation. One is thickening the support layer to increase the damping function. The other is increasing the thickness vibration by thickening the lead zirconate titanate (PZT) layer. Results reveal that flexural vibration is strongly related to ringing in the received waveform, owing to flexural vibration generating rapid phase changes in the frequency domain. Meanwhile, thickness vibration, the degree of which depends on the thickness of the PZT layer, is confirmed to affect the pulse width but be less relevant to ringing.