A CMOS Integrated PZT Piezoelectric Micromachined Ultrasound Transducer (PMUT) With Large Bandwidth

Conventional piezoelectric micromachined ultrasound transducers (PMUTs) operating at the fundamental flexural mode of a single square or circular membrane are typically limited by their inherently narrow bandwidth for use in imaging applications. Moreover, the integration of PMUTs based on lead zirconate titanate (PZT) with complementary metal-oxide-semiconductor (CMOS) technology has yet to be demonstrated. This article presents the design and characterization of a large bandwidth PZT PMUT bonded to a CMOS die utilizing a eutectic bonding process. Large bandwidth response is achieved at the single PMUT level by combining six rectangular membranes of different aspect ratios designed such that their resonant modes merge when the PMUT is coupled to a low acoustic impedance material such as polydimethylsiloxane or it is immersed in a liquid. The fabricated PMUT was characterized by electrical impedance measurements in air revealing the membrane modes and pulse-echo experiment in liquid demonstrating the large bandwidth frequency response. The characterized frequency response displays a center frequency of 3.11 MHz and a 65% fractional bandwidth appropriate for many imaging applications.