Cantilever beam-based piezoelectric micromachined ultrasonic transducer with post processing soft interconnecting strategy for in-air rangefinding

Despite of good performance immunity to stress and high transmitting/receiving sensitivity advantages, the fabrication imperfection induced asynchronous vibration and the resultant prolonged ring-down tail severely limit the potential of the cantilever beam-based piezoelectric micromachined ultrasonic transducer (PMUT) in pulse-echo applications as transceiver. To address this issue, a novel post processing soft interconnecting strategy is presented. In this case, specific reservoir structure is intentionally integrated into the cantilever-beam based PMUT design, under the assistance of which the liquid PDMS can be accurately applied and spontaneously driven to seal the air gaps between the already released cantilever beams via the capillary effect. After curing, the PDMS will be transformed from liquid to solid and serve as soft interconnecting spring between adjacent cantilever beams so as to force them to vibrate in synchronous mode. At the same time, this treatment does not change the existing fabrication process and has little effect on the original PMUT performance. From both of the mechanical and acoustic response measurement results, effective suppression for the asynchronous vibration and significant reduction of the ring-down tail have been successfully demonstrated for the treated PMUT device. In the subsequent pulse-echo rangefinding experiment, a distance detection range covering from 270.8 mm to 3.8 m with a divergence angle close to 170° has been achieved when it is driven at resonant frequency of 69.2 kHz with 40 V_pp, 40-cycles sinusoidal signal. Given the simple yet effective treatment, the proposed strategy shows great prospective in developing high performance PMUT for in-air rangefinding applications.