Equidimensional Suspended Piezoelectric Micromachined Ultrasound Transducer Array with Various Mass Loads for High Ultrasound Sensitivity and Wide Bandwidth

For the first time, we develop piezoelectric micromachined ultrasound transducer (PMUT) array with the cells having suspended vibrational membranes and the array having the same-dimension cells in plane but with various mass loads for tuning their frequency range. The suspended membrane of PMUT, facilitated by four through-holes at the edge, offers distinct advantages of low constraint and high sensitivity. The resonant frequency of equidimensional suspended PMUT with the same diameter becomes adjustable through various mass loads. The suspended PMUT array containing same-dimension cells with different mass loads exhibits superior acoustic performance and broader bandwidth compared to traditional PMUT array. According to this strategy, this paper presents our PMUT array, with central frequency be in around 10MHz, has a 1.5X higher displacement and 1.8X higher bandwidth than traditional PMUT array. It promises significant advancements in PMUT-based ultrasound imaging.

INTRODUCTION

PMUTs represent a compelling solution for compact, low-power, and portable ultrasound systems, demonstrating suitability for diverse imaging applications [1]. Compared to conventional block ultrasonic transducers, PMUTs offer advantages such as scalability in production, cost-effectiveness, compactness, and compatibility with Complementary Metal Oxide Semiconductor (CMOS) technology. Their favorable acoustic impedance matching with human tissue further underscores their utility [2]. Compared to CMUT ultrasound imaging, PMUT arrays offer advantages by eliminating the need for applying DC bias voltages. Furthermore, PMUT fabrication is less complex due to the absence of stringent requirements for precise gaps of very small depth [3]. However, to achieve optimal performance, PMUTs demand higher pulse-echo sensitivity (equivalent to emission sensitivity × receiving sensitivity) and bandwidth (BW) for enhanced imaging depth, signal-to-noise ratio, and longitudinal resolution. Additionally, ensuring that the pitch of elements within the PMUT array meets the half wavelength rule is critical (for example, underwater frequency>7.5MHz, pitch<100µm) [4].