Piezoelectric Micromachined Ultrasonic Transducers (PMUTs): Performance Metrics, Advancements, and Applications

Abstract

With the development of technology, systems gravitate towards increasing in their complexity, miniaturization, and level of automation. Amongst these systems, ultrasonic devices have adhered to this trend of advancement. Ultrasonic systems require transducers to generate and sense ultrasonic signals. These transducers heavily impact the system’s performance. Advancements in microelectromechanical systems have led to the development of micromachined ultrasonic transducers (MUTs), which are utilized in miniaturized ultrasound systems. Piezoelectric micromachined ultrasonic transducers (PMUTs) exhibit higher capacitance and lower electrical impedance, which enhances the transducer’s sensitivity by minimizing the effect of parasitic capacitance and facilitating their integration with low-voltage electronics. PMUTs utilize high-yield batch microfabrication with the use of thin piezoelectric films. The deposition of thin piezoelectric material compatible with complementary metal-oxide semiconductors (CMOS) has opened novel avenues for the development of miniaturized compact systems with the same substrate for application and control electronics. PMUTs offer a wide variety of applications, including medical imaging, fingerprint sensing, range-finding, energy harvesting, and intrabody and underwater communication links. This paper reviews the current research and recent advancements on PMUTs and their applications. This paper investigates in detail the important transduction metrics and critical design parameters for high-performance PMUTs. Piezoelectric materials and microfabrication processes utilized to manufacture PMUTs are discussed. Promising PMUT applications and outlook on future advancements are presented.

Membrane-Based NEMS/MEMS Biosensors

“…104 The resonant frequency of a PMUT depends on the shape and dimensions of the membrane, the boundary conditions, and the material properties. 1,105 PMUTs have unique advantages over CMUT biosensors. First, PMUTs operate at lower voltages than CMUTs and do not require a dc bias between the electrodes.…”

“…When operated at the resonant frequency, PMUTs can be used as mass-sensitive biosensors, where the change in mass of the membrane, e.g., due to adsorption of analyte molecules, changes the resonant frequency . The resonant frequency of a PMUT depends on the shape and dimensions of the membrane, the boundary conditions, and the material properties. , PMUTs have unique advantages over CMUT biosensors. First, PMUTs operate at lower voltages than CMUTs and do not require a dc bias between the electrodes. , Second, the membrane deformation of PMUT sensors is not limited by a gap through which they can transmit a relatively high sound pressure …”

Review of Piezoelectric Micromachined Ultrasonic Transducers for Rangefinders

“…Furthermore, the small size of pMUTs not only enables pMUT rangefinders to be integrated with electronics, which saves space and energy for mobile use but also enables the fabrication of large ultrasonic transducer arrays, helping to realize more complicated systems [ 26 , 27 , 28 ]. Compared to ultrasonic rangefinders based on capacitive micromachined ultrasonic transducers (cMUTs) [ 29 , 30 ], pMUT rangefinders have a larger ultrasound output, lower bias voltage, and larger detectable range [ 31 , 32 ]. Hence, the low power consumption, relatively high output pressure, and integrated property of pMUT rangefinders make them promising for implementation into mobile devices for range-finding.…”

Bottom-up micromachined PZT film-based ultrasonic microphone with compressible parylene tube

“…Thus, PMUTs do not require a DC bias and are relatively easy to fabricate, with the advantages of low power consumption, high sensitivity, and low cost [14]. These advantages allow PMUTs to supersede conventional transducers in diverse applications such as range finding, gesture recognition, and ultrasonic radar [15,16].…”