High-uniformity miniaturized PMUT array with broadband and high-sensitivity for wearable ultrasound imaging

Among the diverse ultrasound transducers deployed in wearable continuous imaging applications, piezoelectric micromachined ultrasonic transducer (PMUT), developed via microelectromechanical system (MEMS) technology, exhibit significant potential for wearable use, owing to their device miniaturization and low power consumption. However, PMUT arrays often suffer from poor imaging performance and no efficient method exists to evaluate large-scale arrays' performance other than post-fabrication measurement. This study proposes a mathematical model of mutual radiation impedance to predict the vibration amplitude of each cell in a PMUT array, thereby guiding optimal cell arrangement for simultaneous enhancement of sensitivity, bandwidth, and acoustic uniformity. The elevation aperture of linear PMUT arrays is reduced based on the beam-formed acoustic output, improving the integration and wearability of rigid silicon-based transducers. An ultra-narrow 64-element linear AlN PMUT array with a 7:1 aspect ratio (1 cm × 0.15 cm, aperture area 0.15 cm²) was fabricated for experimental validation. The device demonstrates a pulse-echo fractional bandwidth exceeding 60% at a center frequency of 7 MHz, along with an image contrast of ~50 dB. Its lateral and axial resolutions are measured to be ~0.26 mm and ~0.25 mm, respectively. Continuous and real-time clear phased-array imaging of multiple superficial organs in volunteers, including carotid artery, thyroid gland, and dorsalis pedis artery, demonstrates the qualified ultrasound performance of our designed PMUT array. Our work establishes a systematic framework for developing large-scale PMUT arrays enabling the realization of wearable ultrasound patch with compact form factor, high fidelity imaging quality, superior spatial resolution and low power consumption.