Research

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15 pages, 883 KiB

Open AccessArticle

Modeling of MEMS Transducers with Perforated Moving Electrodes

by Karina Šimonová and Petr Honzík

Micromachines 2023, 14(5), 921; https://doi.org/10.3390/mi14050921 - 24 Apr 2023

Viewed by 868

Microfabricated electroacoustic transducers with perforated moving plates used as microphones or acoustic sources have appeared in the literature in recent years. However, optimization of the parameters of such transducers for use in the audio frequency range requires high-precision theoretical modeling. The main objective [...] Read more.

Microfabricated electroacoustic transducers with perforated moving plates used as microphones or acoustic sources have appeared in the literature in recent years. However, optimization of the parameters of such transducers for use in the audio frequency range requires high-precision theoretical modeling. The main objective of the paper is to provide such an analytical model of a miniature transducer with a moving electrode in the form of a perforated plate (rigid elastically supported or elastic clamped at all boundaries) loaded by an air gap surrounded by a small cavity. The formulation for the acoustic pressure field inside the air gap enables expression of the coupling of this field to the displacement field of the moving plate and to the incident acoustic pressure through the holes in the plate. The damping effects of the thermal and viscous boundary layers originating inside the air gap, the cavity, and the holes in the moving plate are also taken into account. The analytical results, namely, the acoustic pressure sensitivity of the transducer used as a microphone, are presented and compared to the numerical (FEM) results. Full article

(This article belongs to the Special Issue Micromachined Acoustic Transducers for Audio-Frequency Range)

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9 pages, 2470 KiB

Open AccessArticle

Temperature Stable Piezoelectric Imprint of Epitaxial Grown PZT for Zero-Bias Driving MEMS Actuator Operation

by Marco Teuschel, Paul Heyes, Samu Horvath, Christian Novotny and Andrea Rusconi Clerici

Micromachines 2022, 13(10), 1705; https://doi.org/10.3390/mi13101705 - 10 Oct 2022

Cited by 3 | Viewed by 1477

Abstract

In piezoelectric transducer applications, it is common to use a unipolar operation signal to avoid switching of the polarisation and the resulting nonlinearities of micro-electromechanical systems. However, semi-bipolar or bipolar operation signals have the advantages of less leakage current, lower power consumption and [...] Read more.

In piezoelectric transducer applications, it is common to use a unipolar operation signal to avoid switching of the polarisation and the resulting nonlinearities of micro-electromechanical systems. However, semi-bipolar or bipolar operation signals have the advantages of less leakage current, lower power consumption and no additional need of a DC−DC converter for low AC driving voltages. This study investigates the potential of using piezoelectric layers with an imprint for stable bipolar operation on the basis of epitaxially grown lead zirconate titanate cantilevers with electrodes made of a metal and metal oxide stack. Due to the manufacturing process, the samples exhibit high crystallinity, rectangular shaped hysteresis and a high piezoelectric response. Furthermore, the piezoelectric layers have an imprint, indicating a strong built-in field, which shifts the polarisation versus electric field hysteresis. To obtain the stability of the imprint, laser doppler vibrometry and switching current measurements were performed at different temperatures, yielding a stable imprinted electric field of −1.83 MV/m up to at least 100 °C. The deflection of the cantilevers was measured with a constant AC driving voltage while varying the DC bias voltage to examine the influence of the imprint under operation, revealing that the same high deflection and low nonlinearities, quantified by the total harmonic distortion, can be maintained down to low bias voltages compared to unipolar operation. These findings demonstrate that a piezoelectric layer with a strong imprint makes it possible to operate with low DC or even zero DC bias, while still providing strong piezoelectric response and linear behaviour. Full article

(This article belongs to the Special Issue Micromachined Acoustic Transducers for Audio-Frequency Range)

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17 pages, 8002 KiB

Open AccessArticle

Piezoelectric MEMS Acoustic Transducer with Electrically-Tunable Resonant Frequency

by Alessandro Nastro, Marco Ferrari, Libor Rufer, Skandar Basrour and Vittorio Ferrari

Micromachines 2022, 13(1), 96; https://doi.org/10.3390/mi13010096 - 08 Jan 2022

Cited by 7 | Viewed by 2446

Abstract

The paper presents a technique to obtain an electrically-tunable matching between the series and parallel resonant frequencies of a piezoelectric MEMS acoustic transducer to increase the effectiveness of acoustic emission/detection in voltage-mode driving and sensing. The piezoelectric MEMS transducer has been fabricated using [...] Read more.

The paper presents a technique to obtain an electrically-tunable matching between the series and parallel resonant frequencies of a piezoelectric MEMS acoustic transducer to increase the effectiveness of acoustic emission/detection in voltage-mode driving and sensing. The piezoelectric MEMS transducer has been fabricated using the PiezoMUMPs technology, and it operates in a plate flexural mode exploiting a 6 mm × 6 mm doped silicon diaphragm with an aluminum nitride (AlN) piezoelectric layer deposited on top. The piezoelectric layer can be actuated by means of electrodes placed at the edges of the diaphragm above the AlN film. By applying an adjustable bias voltage V_b between two properly-connected electrodes and the doped silicon, the d31 mode in the AlN film has been exploited to electrically induce a planar static compressive or tensile stress in the diaphragm, depending on the sign of V_b, thus shifting its resonant frequency. The working principle has been first validated through an eigenfrequency analysis with an electrically induced prestress by means of 3D finite element modelling in COMSOL Multiphysics^®. The first flexural mode of the unstressed diaphragm results at around 5.1 kHz. Then, the piezoelectric MEMS transducer has been experimentally tested in both receiver and transmitter modes. Experimental results have shown that the resonance can be electrically tuned in the range V_b = ±8 V with estimated tuning sensitivities of 8.7 ± 0.5 Hz/V and 7.8 ± 0.9 Hz/V in transmitter and receiver modes, respectively. A matching of the series and parallel resonant frequencies has been experimentally demonstrated in voltage-mode driving and sensing by applying V_b = 0 in transmission and V_b = −1.9 V in receiving, respectively, thereby obtaining the optimal acoustic emission and detection effectiveness at the same operating frequency. Full article

(This article belongs to the Special Issue Micromachined Acoustic Transducers for Audio-Frequency Range)

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20 pages, 8871 KiB

Open AccessArticle

Novel Fabrication Technology for Clamped Micron-Thick Titanium Diaphragms Used for the Packaging of an Implantable MEMS Acoustic Transducer

by Lukas Prochazka, Alexander Huber, Michael Schneider, Naureen Ghafoor, Jens Birch and Flurin Pfiffner

Micromachines 2022, 13(1), 74; https://doi.org/10.3390/mi13010074 - 31 Dec 2021

Cited by 1 | Viewed by 1873

Abstract

Micro-Electro-Mechanical Systems (MEMS) acoustic transducers are highly sophisticated devices with high sensing performance, small size, and low power consumption. To be applied in an implantable medical device, they require a customized packaging solution with a protecting shell, usually made from titanium (Ti), to [...] Read more.

Micro-Electro-Mechanical Systems (MEMS) acoustic transducers are highly sophisticated devices with high sensing performance, small size, and low power consumption. To be applied in an implantable medical device, they require a customized packaging solution with a protecting shell, usually made from titanium (Ti), to fulfill biocompatibility and hermeticity requirements. To allow acoustic sound to be transferred between the surroundings and the hermetically sealed MEMS transducer, a compliant diaphragm element needs to be integrated into the protecting enclosure. In this paper, we present a novel fabrication technology for clamped micron-thick Ti diaphragms that can be applied on arbitrary 3D substrate geometry and hence directly integrated into the packaging structure. Stiffness measurements on various diaphragm samples illustrate that the technology enables a significant reduction of residual stress in the diaphragm developed during its deposition on a polymer sacrificial material. Full article

(This article belongs to the Special Issue Micromachined Acoustic Transducers for Audio-Frequency Range)

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23 pages, 43500 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Novel MEMS Capacitive Microphone with Semiconstrained Diaphragm Supported with Center and Peripheral Backplate Protrusions

by Shubham Shubham, Yoonho Seo, Vahid Naderyan, Xin Song, Anthony J. Frank, Jeremy Thomas Morley Greenham Johnson, Mark da Silva and Michael Pedersen

Micromachines 2022, 13(1), 22; https://doi.org/10.3390/mi13010022 - 25 Dec 2021

Cited by 17 | Viewed by 10143

Abstract

Audio applications such as mobile phones, hearing aids, true wireless stereo earphones, and Internet of Things devices demand small size, high performance, and reduced cost. Microelectromechanical system (MEMS) capacitive microphones fulfill these requirements with improved reliability and specifications related to sensitivity, signal-to-noise ratio [...] Read more.

Audio applications such as mobile phones, hearing aids, true wireless stereo earphones, and Internet of Things devices demand small size, high performance, and reduced cost. Microelectromechanical system (MEMS) capacitive microphones fulfill these requirements with improved reliability and specifications related to sensitivity, signal-to-noise ratio (SNR), distortion, and dynamic range when compared to their electret condenser microphone counterparts. We present the design and modeling of a semiconstrained polysilicon diaphragm with flexible springs that are simply supported under bias voltage with a center and eight peripheral protrusions extending from the backplate. The flexible springs attached to the diaphragm reduce the residual film stress effect more effectively compared to constrained diaphragms. The center and peripheral protrusions from the backplate further increase the effective area, linearity, and sensitivity of the diaphragm when the diaphragm engages with these protrusions under an applied bias voltage. Finite element modeling approaches have been implemented to estimate deflection, compliance, and resonance. We report an 85% increase in the effective area of the diaphragm in this configuration with respect to a constrained diaphragm and a 48% increase with respect to a simply supported diaphragm without the center protrusion. Under the applied bias, the effective area further increases by an additional 15% as compared to the unbiased diaphragm effective area. A lumped element model has been also developed to predict the mechanical and electrical behavior of the microphone. With an applied bias, the microphone has a sensitivity of −38 dB (ref. 1 V/Pa at 1 kHz) and an SNR of 67 dBA measured in a 3.25 mm × 1.9 mm × 0.9 mm package including an analog ASIC. Full article

(This article belongs to the Special Issue Micromachined Acoustic Transducers for Audio-Frequency Range)

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14 pages, 937 KiB

Open AccessArticle

Total Harmonic Distortion of a Piezoelectric MEMS Loudspeaker in an IEC 60318-4 Coupler Estimation Using Static Measurements and a Nonlinear State Space Model

by Romain Liechti, Stéphane Durand, Thierry Hilt, Fabrice Casset, Christophe Poulain, Gwenaël Le Rhun, Franklin Pavageau, Hugo Kuentz and Mikaël Colin

Micromachines 2021, 12(12), 1437; https://doi.org/10.3390/mi12121437 - 24 Nov 2021

Cited by 7 | Viewed by 2586

Abstract

We propose a method to evaluate the Total Harmonic Distortion generated by a cantilever-based PZT loudspeaker inside an IEC 60318-4 coupler. The model is validated using experimental data of a commercial loudspeaker. Using the time domain equations of the equivalent electrical circuit of [...] Read more.

We propose a method to evaluate the Total Harmonic Distortion generated by a cantilever-based PZT loudspeaker inside an IEC 60318-4 coupler. The model is validated using experimental data of a commercial loudspeaker. Using the time domain equations of the equivalent electrical circuit of the loudspeaker inside the coupler and a state space formulation, the acoustic pressure response is calculated and compared to the measurement of the manufacturer. Next, the stiffness, transduction and capacitance nonlinear functions are evaluated with a Double-Beam Laser Interferometer (DBLI) and a nanoindenter on test devices and on the commercial loudspeaker. By introducing the nonlinear functions into the model as amplitude-dependent parameters, the THD generated by the loudspeaker is calculated and compared to the value provided by the manufacturer. The good agreement between the measurement and the simulation could allow for a rather quick simulation of the performance of similarly designed loudspeakers at the early stage of the design, by only estimating the static linearity of the main nonlinearity sources. Full article

(This article belongs to the Special Issue Micromachined Acoustic Transducers for Audio-Frequency Range)

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23 pages, 23135 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Road to Acquisition: Preparing a MEMS Microphone Array for Measurement of Fuselage Surface Pressure Fluctuations

by Thomas Ahlefeldt, Stefan Haxter, Carsten Spehr, Daniel Ernst and Tobias Kleindienst

Micromachines 2021, 12(8), 961; https://doi.org/10.3390/mi12080961 - 14 Aug 2021

Cited by 11 | Viewed by 2661

Abstract

Preparing and pre-testing experimental setups for flight tests is a lengthy but necessary task. One part of this preparation is comparing newly available measurement technology with proven setups. In our case, we wanted to compare acoustic Micro-Electro-Mechanical Systems (MEMS) to large and proven [...] Read more.

Preparing and pre-testing experimental setups for flight tests is a lengthy but necessary task. One part of this preparation is comparing newly available measurement technology with proven setups. In our case, we wanted to compare acoustic Micro-Electro-Mechanical Systems (MEMS) to large and proven surface-mounted condenser microphones. The task started with the comparison of spectra in low-speed wind tunnel environments. After successful completion, the challenge was increased to similar comparisons in a transonic wind tunnel. The final goal of performing in-flight measurements on the outside fuselage of a twin-engine turboprop aircraft was eventually achieved using a slim array of 45 MEMS microphones with additional large microphones installed on the same carrier to drawn on for comparison. Finally, the array arrangement of MEMS microphones allowed for a complex study of fuselage surface pressure fluctuations in the wavenumber domain. The study indicates that MEMS microphones are an inexpensive alternative to conventional microphones with increased potential for spatially high-resolved measurements even at challenging experimental conditions during flight tests. Full article

(This article belongs to the Special Issue Micromachined Acoustic Transducers for Audio-Frequency Range)

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Review

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29 pages, 7653 KiB

Open AccessReview

Review of Recent Development of MEMS Speakers

by Haoran Wang, Yifei Ma, Qincheng Zheng, Ke Cao, Yao Lu and Huikai Xie

Micromachines 2021, 12(10), 1257; https://doi.org/10.3390/mi12101257 - 16 Oct 2021

Cited by 27 | Viewed by 10449

Abstract

Facilitated by microelectromechanical systems (MEMS) technology, MEMS speakers or microspeakers have been rapidly developed during the past decade to meet the requirements of the flourishing audio market. With advantages of a small footprint, low cost, and easy assembly, MEMS speakers are drawing extensive [...] Read more.

Facilitated by microelectromechanical systems (MEMS) technology, MEMS speakers or microspeakers have been rapidly developed during the past decade to meet the requirements of the flourishing audio market. With advantages of a small footprint, low cost, and easy assembly, MEMS speakers are drawing extensive attention for potential applications in hearing instruments, portable electronics, and the Internet of Things (IoT). MEMS speakers based on different transduction mechanisms, including piezoelectric, electrodynamic, electrostatic, and thermoacoustic actuation, have been developed and significant progresses have been made in commercialization in the last few years. In this article, the principle and modeling of each MEMS speaker type is briefly introduced first. Then, the development of MEMS speakers is reviewed with key specifications of state-of-the-art MEMS speakers summarized. The advantages and challenges of all four types of MEMS speakers are compared and discussed. New approaches to improve sound pressure levels (SPLs) of MEMS speakers are also proposed. Finally, the remaining challenges and outlook of MEMS speakers are given. Full article

(This article belongs to the Special Issue Micromachined Acoustic Transducers for Audio-Frequency Range)

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