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Piezoelectric micromachined ultrasonic transducer (pMUT) is a promising candidate for the next-generation 3-D diagnostic ultrasonic imaging. However, the transmitting sensitivity of reported pMUT is not satisfied so far. Enhancement of the transmitting sensitivity hence is always desirable. In this letter, we report a piston-like pMUT. With the help of etching holes in the membrane, the mode shape becomes from Gaussian-like to piston-like, which enables higher transmitted acoustic pressure. In addition, frequency of such pMUT does not decrease after etching holes are fabricated, but slightly increases. Higher frequency for ultrasonic imaging thus is practical, and the frequency can be predicted by well-established methods. Sensitivity of 73 nm/V at 2.31 MHz is achieved for the piston-like pMUT with three rows of etching holes. Benefited from the piston-like membrane motion, the space pressure level is 5.3 dB higher than the classical pMUT.
Wang et al. (Tue,) studied this question.