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Piezoelectric Micromachined Ultrasound Transducer (PMUT) Devices: Sensing, Actuation Communication and Imaging in the µ-Scale

A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Physical Sensors".

Deadline for manuscript submissions: closed (15 November 2021) | Viewed by 28046

Special Issue Editors

Prof. Dr. Nuria Barniol Beumala

E-Mail Website
Guest Editor
Departament d'Enginyeria Electrònica, Universitat Autònoma de Barcelona, 08193 Barcelona, Spain
Interests: PMUT; PMUT-on-CMOS; CMOS-MEMS; mechanical resonators; non-linear resonators
Dr. Cristian Cassella

E-Mail Website
Guest Editor
Electrical and Computer Engineering, Northeastern University, Boston, MA, USA
Interests: acoustic resonators; PMUT; nonlinear dynamics; RF components and systems

Special Issue Information

Dear Colleague,

PMUTs, piezoelectrical micromachined ultrasound transducers, are becoming one of the more demanding ultrasonic systems thanks to their capabilities to generate and sense ultrasound signals in a very efficient and well-controlled way at the microscale. PMUTs systems benefits from the high-yield MEMS fabrication approach together with the thin-film piezolectrical materials (AlN, AlScN, PZT….). In addition, the capabilities to deposit thin film piezoelectric materials in a compatible way with CMOS opens the possibility for novel very compact systems using the same substrate for the sensor and the conditioning electronics. With this scenario, PMUTs transducers are pushing the applicability of ultrasound as the physical magnitude in a wide number of systems where size, power, sensitivity and cost play an important role (intravascular medical imaging, biometric identification, gesture recognition, rangefinder, proximity sensors, acoustic wireless communication systems, acoustophoresis, photoacoustics systems… among others).

The aim of this Special Issue is to present the most advanced research and latest achievements of PMUTs based systems and their application in any field. Reviews presenting a deep analysis of a specific problem and the use of ultrasound produced by PMUTs systems to address it would also be appropriate.

This Special Issue invites contributions in the following topics (but is not limited to them):

- Piezoelectric Materials and its application for PMUTs (AlN, AlScN, PZT, flexible materials…)

- PMUTs fabrication (including PMUTs-on-CMOS)

- Theoretical and modelization studies for PMUTs

- Novel PMUTs designs and exploitation of new functional modes: multifrequency, non-linearity,….

- PMUTs arrays and their management

- PMUT feeding schemes

- PMUTs for ultrasound biometrics (fingerprints)

- PMUTs for ultrasound range-finder and gesture recognition

- PMUTs for ultrasound communication links (in air, in water, intra-body….)

- PMUTs for acoustic wireless powering

- PMUTs for medical applications (ultrasound imaging for diagnosis, therapies, brain stimulation,…)

-PMUTs for contact less manipulation of particles in liquid

-PMUTs for sensory applications in any field

-PMUTs as acoustic source

-PMUTs for photoacoustics/optoacoustics imaging/interactions

-Others…

Prof. Dr. Núria Barniol
Dr. Cristian Cassella
Guest Editors

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Keywords

  • PMUT
  • AlN
  • AlScN
  • PZT
  • PMUT-on-CMOS
  • MEMS
  • ultrasound
  • ultrasound imaging
  • acoustic rangefinder
  • ultrasonic sensors
  • ultrasonic actuators
  • ultrasound transducers
  • piezoelectric materials

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Published Papers (5 papers)

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Research

12 pages, 5122 KiB  
Article
Enhancing AlN PMUTs’ Acoustic Responsivity within a MEMS-on-CMOS Process
by Eyglis Ledesma, Ivan Zamora, Arantxa Uranga, Francesc Torres and Núria Barniol
Sensors 2021, 21(24), 8447; https://doi.org/10.3390/s21248447 - 17 Dec 2021
Cited by 14 | Viewed by 4066
Abstract
In this paper, guidelines for the optimization of piezoelectrical micromachined ultrasound transducers (PMUTs) monolithically integrated over a CMOS technology are developed. Higher acoustic pressure is produced by PMUTs with a thin layer of AlN piezoelectrical material and Si3N4 as a [...] Read more.
In this paper, guidelines for the optimization of piezoelectrical micromachined ultrasound transducers (PMUTs) monolithically integrated over a CMOS technology are developed. Higher acoustic pressure is produced by PMUTs with a thin layer of AlN piezoelectrical material and Si3N4 as a passive layer, as is studied here with finite element modeling (FEM) simulations and experimental characterization. Due to the thin layers used, parameters such as residual stress become relevant as they produce a buckled structure. It has been reported that the buckling of the membrane due to residual stress, in general, reduces the coupling factor and consequently degrades the efficiency of the acoustic pressure production. In this paper, we show that this buckling can be beneficial and that the fabricated PMUTs exhibit enhanced performance depending on the placement of the electrodes. This behavior was demonstrated experimentally and through FEM. The acoustic characterization of the fabricated PMUTs shows the enhancement of the PMUT performance as a transmitter (with 5 kPa V−1 surface pressure for a single PMUT) and as a receiver (12.5 V MPa−1) in comparison with previously reported devices using the same MEMS-on-CMOS technology as well as state-of-the-art devices. Full article
(This article belongs to the Special Issue Piezoelectric Micromachined Ultrasound Transducer (PMUT) Devices: Sensing, Actuation Communication and Imaging in the µ-Scale)
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18 pages, 6352 KiB  
Article
Multielement Ring Array Based on Minute Size PMUTs for High Acoustic Pressure and Tunable Focus Depth
by Eyglis Ledesma, Iván Zamora, Arantxa Uranga and Núria Barniol
Sensors 2021, 21(14), 4786; https://doi.org/10.3390/s21144786 - 13 Jul 2021
Cited by 5 | Viewed by 3913
Abstract
This paper presents a multielement annular ring ultrasound transducer formed by individual high-frequency PMUTs (17.5 MHz in air and 8.7 MHz in liquid) intended for high-precision axial focalization and high-performance ultrasound imaging. The prototype has five independent multielement rings fabricated by a monolithic [...] Read more.
This paper presents a multielement annular ring ultrasound transducer formed by individual high-frequency PMUTs (17.5 MHz in air and 8.7 MHz in liquid) intended for high-precision axial focalization and high-performance ultrasound imaging. The prototype has five independent multielement rings fabricated by a monolithic process over CMOS, allowing for a very compact and robust design. Crosstalk between rings is under 56 dB, which guarantees an efficient beam focusing on a range between 1.4 mm and 67 µm. The presented PMUT-on-CMOS annular array with an overall diameter down to 669 µm achieves an output pressure in liquid of 4.84 kPa/V/mm2 at 1.5 mm away from the array when the five channels are excited together, which is the largest reported for PMUTs. Pulse-echo experiments towards high-resolution imaging are demonstrated using the central ring as a receiver. With an equivalent diameter of 149 µm, this central ring provides high receiving sensitivity, 441.6 nV/Pa, higher than that of commercial hydrophones with equivalent size. A 1D ultrasound image using two channels is demonstrated, with maximum received signals of 7 mVpp when a nonintegrated amplifier is used, demonstrating the ultrasound imaging capabilities. Full article
(This article belongs to the Special Issue Piezoelectric Micromachined Ultrasound Transducer (PMUT) Devices: Sensing, Actuation Communication and Imaging in the µ-Scale)
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11 pages, 3021 KiB  
Article
High Accuracy Ultrasound Micro-Distance Measurements with PMUTs under Liquid Operation
by Iván Zamora, Eyglis Ledesma, Arantxa Uranga and Núria Barniol
Sensors 2021, 21(13), 4524; https://doi.org/10.3390/s21134524 - 1 Jul 2021
Cited by 4 | Viewed by 5104
Abstract
Ultrasonic systems driven by multi-frequency continuous waves (MFCW) have been used for range distance measurement, offering high accuracy in long and medium range distance estimation. However, the use of continuous waves in very short-distance measurements causes large errors due to multipath reflections. This [...] Read more.
Ultrasonic systems driven by multi-frequency continuous waves (MFCW) have been used for range distance measurement, offering high accuracy in long and medium range distance estimation. However, the use of continuous waves in very short-distance measurements causes large errors due to multipath reflections. This paper presents a new strategy to estimate very short relative distances with high accuracy based on the use of multi-frequency pulsed waves (MFPW). The proposed strategy allows to avoid the multipath reflections that appear when continuous waves are used, and it improves the achieved accuracy compared to the original MFCW method. To validate it, an 80 µm square AlScN piezoelectric micromachined ultrasonic transducer (PMUT) was chosen as a transmitter while a hydrophone was utilized as a target and receiver, immersed in fluorinert (FC-70) as a propagation medium. Three independent and consecutive tone-burst signals were transmitted successively. The selected frequencies are f1 = 2.3962 MHz, f2 = 2.327 MHz and f3 = 2.1195 MHz, giving first and second-order resolutions of 6.88 and 0.79 µm/°, respectively. Experimental results show a ±6.2 μm measured range error in a range of 3.5 mm, and therefore it represents a good candidate for ultrasound micro-profilometer applications under liquid operation. Full article
(This article belongs to the Special Issue Piezoelectric Micromachined Ultrasound Transducer (PMUT) Devices: Sensing, Actuation Communication and Imaging in the µ-Scale)
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9 pages, 1288 KiB  
Communication
Flexible Thin-Film PZT Ultrasonic Transducers on Polyimide Substrates
by Tianning Liu, Ajay Dangi, Jeong Nyeon Kim, Sri-Rajasekhar Kothapalli, Kyusun Choi, Susan Trolier-McKinstry and Thomas Jackson
Sensors 2021, 21(3), 1014; https://doi.org/10.3390/s21031014 - 2 Feb 2021
Cited by 20 | Viewed by 7430
Abstract
We report flexible thin-film lead zirconate titanate (PZT)-based ultrasonic transducers on polyimide substrates. The transducers are bar resonators designed to operate in the width extension mode. The active elements are 1 µm thick PZT films that were crystallized on Si substrates at 700 [...] Read more.
We report flexible thin-film lead zirconate titanate (PZT)-based ultrasonic transducers on polyimide substrates. The transducers are bar resonators designed to operate in the width extension mode. The active elements are 1 µm thick PZT films that were crystallized on Si substrates at 700 °C and transferred to 5 µm thick solution-cast polyimide via dissolution of an underlying release layer. Underwater pitch–catch testing between two neighboring 100 µm × 1000 µm elements showed a 0.2 mV signal at a 1.5 cm distance for a driving voltage of 5 V peak at 9.5 MHz. With the same excitation, a 33 kPa sound pressure output at a 6 mm distance and a 32% bandwidth at −6 dB were measured by hydrophone. Full article
(This article belongs to the Special Issue Piezoelectric Micromachined Ultrasound Transducer (PMUT) Devices: Sensing, Actuation Communication and Imaging in the µ-Scale)
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18 pages, 12088 KiB  
Article
Modeling and Optimization of Directly Modulated Piezoelectric Micromachined Ultrasonic Transducers
by Flavius Pop, Bernard Herrera, Cristian Cassella and Matteo Rinaldi
Sensors 2021, 21(1), 157; https://doi.org/10.3390/s21010157 - 29 Dec 2020
Cited by 9 | Viewed by 4480
Abstract
The present work details a novel approach to increase the transmitting sensitivity of piezoelectric micromachined ultrasonic transducer arrays and performing the direct modulation of digital information on the same device. The direct modulation system can reach 3× higher signal-to-noise ratio level and 3× [...] Read more.
The present work details a novel approach to increase the transmitting sensitivity of piezoelectric micromachined ultrasonic transducer arrays and performing the direct modulation of digital information on the same device. The direct modulation system can reach 3× higher signal-to-noise ratio level and 3× higher communication range (from 6.2 cm boosted to 18.6 cm) when compared to more traditional continuous wave drive at the same energy consumption levels. When compared for the same transmission performance, the direct modulation consumes 80% less energy compared to the continues wave. The increased performance is achieved with a switching circuit that allows to generate a short high-AC voltage on the ultrasonic array, by using an LC tank and a bipolar junction transistor, starting with a low-DC voltage, making it CMOS-compatible. Since the modulation signal can directly be formed by the transmitted bits (on/off keying encoding) this also serve as the modulation for the data itself, hence direct modulation. The working principle of the circuit is described, optimization is performed relative to several circuital parameters and a high-performance experimental application is demonstrated. Full article
(This article belongs to the Special Issue Piezoelectric Micromachined Ultrasound Transducer (PMUT) Devices: Sensing, Actuation Communication and Imaging in the µ-Scale)
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