Mass-loaded suspended piezoelectric micromachined ultrasonic transducer array towards flexible stretchable electronics evaluation

We introduce a novel piezoelectric micromachined ultrasonic transducer (PMUT) with a mass-loaded suspended (MLSP) design, fabricated using sacrificial technique to advance the non-destructive testing (NDT) of flexible electronics. The MLSP features four trenches uniformly distributed at the membrane's edge and a mass load atop the membrane. These trenches transform the PMUT into a suspended membrane, significantly enhancing its sensitivity and effective vibrational area. The mass load is strategically added to tune the frequency and further boost sensitivity, while maintaining the same size and frequency as traditional clamped PMUTs (CP). In practice, we designed and fabricated 11 MHz PMUT arrays with a cell diameter of 40 mu m. Experiments demonstrated that MLSP's displacement is 2.2 times that of CP, and its pulse-echo sensitivity is 2.1 times higher. Mechanical scanning-based imaging of internal electrodes in stretchable electronic models revealed that MLSP provides better image contrast, clarity, and more accurate defect detection compared to CP. These findings underscore the potential of this innovative PMUT design for advancing compact, low-power handheld ultrasound systems in the flexible electronics sector. This approach offers a viable solution to meet the escalating demands for nondestructive testing (NDT).