Squared PMUT with Enhanced Pressure Sensitivities

Abstract

This study presents a squared AlN piezoelectric micromachined ultrasonic transducer (PMUT). Using this PMUT greater level of output pressure and higher reception sensitivity has been achieved, compared with the state-of-the-art. Another outstanding characteristic for this PMUT is that it can be monolithically integrated on CMOS substrate, being remarkably advantageous in relation to the bonding method implemented until now.

Review of Piezoelectric Micromachined Ultrasonic Transducers for Rangefinders

“…In Equation (3), the amplitude of the term “ ” is equal to [ 41 ]. Equation (3) is usually used to calculate the sound pressure level [ 4 ] or the transmitting sensitivity [ 42 ] of a pMUT in its transmit mode since in Equation (2) is not directly measurable and must be derived using Equation (3). For the cases in which acoustic absorption is not neglectable (e.g., in-air range-finding) and the acoustic gain , which is related to the target geometry [ 31 ], must be considered, Equation (3) is changed to: where is the absorption coefficient, which is used to evaluate the energy losses along the acoustic propagation path in the medium.…”

“…The vibrational modes of a pMUT are determined by the shape of the piezoelectric membrane, as shown in Figure 9 . For the same device size, square-membrane pMUT units have a higher coverage area than circular ones [ 42 ], so the membrane vibration displacement of square-membrane pMUTs is largely higher than circular ones with the same driving voltage, which is proved by a comparison experiment in [ 71 ], as shown in Figure 10 . Therefore, square membrane pMUT rangefinders have the potential for higher sensitivities and than current circular ones and achieve a larger detection range and lower range error.…”

An Integrated 2D Ultrasound Phased Array Transmitter in CMOS With Pixel Pitch-Matched Beamforming

“…The transmitter is implemented as an integrated device with a 2D array of lead zirconate titanate (PZT) piezoelectric transducers directly microfabricated on top of a complementary metal-oxide-semiconductor (CMOS) integrated circuit (IC). PZT exhibits higher transmit electroacoustic sensitivity (Stx) than capacitive and piezoelectric micromachined ultrasound transducers (CMUT, PMUT, respectively) [27,28], which is critical for the applications targeted in this work. This direct integration leads to several orders of magnitude smaller form-factors when compared to commercially available transducers and a decrease of the parasitic capacitance for interconnection between transducer and transmitter circuits to only a few fF.…”

“…Since pMUT membranes are softer than bulk PZT, they inherently increase the acoustic matching with soft tissue without requiring acoustic matching layers. However, the Stx of pMUTs is still much lower than of bulk PZT transducers [28,34], making pMUTs more appropriate in sensing applications [35]. Similarly to pMUTs, cMUTs also operate with suspended flexural membranes, and have the advantage of using membrane materials compatible with the CMOS manufacturing process, such as silicon nitride.…”

Fabrication and characterization of annular-shaped piezoelectric micromachined ultrasonic transducer mounted with Pb(Zr,Ti)O3-based monocrystalline thin film

“…Thus far, most of the previously reported pMUTs have a design in which a transducer material and a driving electrode are formed at the center of a vibrating diaphragm [13][14][15]. However, it is questionable whether this design is optimal for improving both the resonance frequency and displacement sensitivity.…”