Low-frequency resonant MEMS transducer

Abstract

The present disclosure provides a resonant MEMS transducer including a support structure, at least one anchor, at least one rigid plate, at least one doubly-supported beam, a through-hole, and at least one electrode. Each doubly-supported beam of the at least one doubly-supported beam is fixed at a first point to a first corresponding one of the at least one anchor, at a second point to a second corresponding one of the at least two anchors, and at a third point to a first corresponding one of the at least one rigid plate. The resonant MEMS transducer operates at a low resonant frequency and is configured to be exposed to an ambient environment.

Description

[Technical Field]

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 480,069, filed January 16, 2023, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to the field of MEMS transducers. [Background technology]

[0003] Microelectromechanical systems (MEMS) are integrated devices that combine mechanical and electrical elements. Due to their wide range of optical, electrical, and mechanical functions, MEMS devices can be used in diverse fields of science and engineering depending on their design. In this disclosure, a resonant MEMS transducer is provided. Summary of the Invention

[0004] The MEMS resonator described in Serrano et al.'s "Electrostatically Tunable Piezoelectric-on-Silicon Micromechanical Resonator for Real-Time Clock," Vol. 59, No. 3, is designed to operate at a relatively low frequency (32 kHz) and includes a support structure, at least one anchor, a rigid plate, at least one doubly supported beam, and at least one electrode. This MEMS resonator includes a thin-film element on silicon. The support structure also functions as a tuning electrode for electrostatic detuning. The rigid plate has multiple etched holes necessary to release the rigid plate from the handle layer and reduce squeeze-film damping due to the large area of ​​the rigid plate.

[0005] A resonant MEMS transducer having at least one rigid plate may be advantageous in sensing applications, particularly if the resonant MEMS transducer is configured to operate without the need for detuning electrodes. Furthermore, it may be advantageous if the resonant MEMS transducer is configured to operate and perform well when exposed to the ambient environment by reducing squeeze-film damping or controlling the areas or rigid plates that experience squeeze-film damping (e.g., operating in a rough vacuum, including above atmospheric pressure to well below atmospheric pressure). It may also be advantageous to configure the resonant MEMS transducer to enable a differential mode of operation or to switch between differential and single-ended modes of operation.

[0006] Accordingly, the present disclosure describes several resonant MEMS transducers for low frequencies that do not require detuning electrodes. Furthermore, the resonant MEMS transducers described herein operate well in ambient environments with reduced squeeze film damping or controlled regions or rigid plates experiencing squeeze film damping. The resonant MEMS transducers described herein include a through-hole defined by at least one rigid plate and a support structure that exposes the rigid plate to pressure fluctuations in the ambient environment. Furthermore, the resonant MEMS transducers described herein can be bonded to a substrate, with the substrate providing the ability to control the regions or rigid plates experiencing squeeze film damping. Several resonant MEMS transducers are provided for use in a differential mode of operation. Finally, a resonant MEMS transducer is provided that can be switched between differential and single-ended modes of operation.

[0007] A resonant MEMS transducer for photoacoustic detection is provided. The resonant MEMS transducer includes a support structure, at least one anchor bonded to the support structure, at least one rigid plate, and at least one doubly-supported beam. Each doubly-supported beam of the at least one doubly-supported beam is fixed at a first point to a corresponding first one of the at least one anchor, at a second point to a corresponding second one of the at least one anchor, and at a third point to a corresponding first one of the at least one rigid plate. The resonant MEMS transducer includes a through-hole defined by the support structure and the at least one rigid plate, and at least one electrode. The resonant MEMS transducer is configured to operate at a low resonant frequency, and the through-hole is configured to expose the at least one rigid plate to the surrounding environment.

[0008] In some embodiments, the low resonant frequency includes 100 kHz or less.

[0009] In one embodiment, the resonant MEMS transducer is configured to operate in one or a combination of: (i) a single-ended mode; and (ii) a differential mode.

[0010] In one embodiment, the resonant MEMS transducer is configured to operate in an out-of-plane eigenmode.

[0011] In some embodiments, the support structure is further bonded to the substrate, and the substrate further comprises a substrate through-hole.

[0012] In a further embodiment, the substrate through-hole is approximately the same size as and aligned with the at least one rigid plate, and each rigid plate of the at least one rigid plate resonates with reduced squeeze film damping.

[0013] In one embodiment, each of the at least one doubly-supported beams has a first corresponding electrode of the at least one electrode patterned in the vicinity of a first point on at least a portion thereof, and each of the at least one doubly-supported beams has a second corresponding electrode of the at least one electrode patterned in the vicinity of a second point on at least a portion thereof.

[0014] In one embodiment, each electrode of the at least one electrode is configured to function as a detection electrode.

[0015] In one embodiment, the resonating MEMS transducer further includes at least one elongated, doubly supported beam and at least one internal beam.

[0016] In a further embodiment, each long-length doubly-supported beam of the at least one long-length doubly-supported beam is fixed to a first corresponding anchor of the at least one anchor at a fourth point, fixed to a second corresponding anchor of the at least one anchor at a fifth point, connected to a first corresponding rigid plate of the at least one rigid plate at a sixth point, connected to a second corresponding rigid plate of the at least one rigid plate at a seventh point, connected to a first corresponding internal beam of the at least one internal beam at an eighth point, and connected to a second corresponding internal beam of the at least one internal beam at a ninth point.

[0017] In a further embodiment, each internal beam of the at least one internal beam is connected at a tenth point to a first corresponding long-length doubly-supported beam of the at least one long-length doubly-supported beam, at an eleventh point to a second corresponding long-length doubly-supported beam of the at least one long-length doubly-supported beam, and at a twelfth point to a first corresponding rigid plate of the at least one rigid plate.

[0018] In a further embodiment, the at least one rigid plate further comprises a first rigid plate and a second rigid plate.

[0019] In a further embodiment, the substrate through-hole is approximately the same size as and aligned with the first rigid plate, the substrate through-hole allowing differential movement.

[0020] In one embodiment, a PAS transducer is provided that includes the resonant MEMS transducer 200 as defined above.

[0021] In one embodiment, a method is provided for bonding a PAS transducer to an acoustic cell 200 to produce an optoacoustic system 210.

[0022]

[0010] Yet another resonant MEMS transducer for optical acoustic detection is provided, the resonant MEMS transducer including a support structure, at least one anchor bonded to the support structure, a rigid plate, and at least one serpentine beam. Each serpentine beam of the at least one serpentine beam is fixed to a first one of the at least one anchor at a first point and connected to the rigid plate at a second point, and includes a through-hole defined by the support structure and the rigid plate and at least one electrode. The resonant MEMS transducer is configured to operate at a low resonant frequency, and the through-hole is configured to expose the rigid plate to the surrounding environment.

[0023] In one embodiment, the low resonant frequency includes 100 kHz or less.

[0024] In one embodiment, the resonant MEMS transducer is configured to operate in one or a combination of (i) a single-ended mode and (ii) a differential mode.

[0025] In one embodiment, the resonant MEMS transducer is configured to operate in one or a combination of: (i) an out-of-plane eigenmode; (ii) a first seesaw eigenmode; and (iii) a second seesaw eigenmode.

[0026] In a further embodiment, the resonant MEMS transducer is configured to switch between two or more modes: (i) the out-of-plane eigenmode, (ii) the first seesaw eigenmode, and (iii) the second seesaw eigenmode.

[0027] In one embodiment, each serpentine beam of the at least one serpentine beam is patterned, over at least a portion thereof, with a first corresponding electrode of the at least one set of electrodes near the first point.

[0028] In one embodiment, the support structure is further bonded to the substrate, and the substrate further comprises the substrate through-hole.

[0029] In one embodiment, the substrate through-hole is approximately the same size as the rigid plate and is aligned with the rigid plate.

[0030] In one embodiment, the substrate through-hole is approximately half the size of the rigid plate and is aligned with a first half of the rigid plate.

[0031] In one embodiment, a photoacoustic system is defined that includes the resonant MEMS transducer, the system including a sample gas filled configuration in operative communication with the rigid plate, the acoustic cell configured to generate acoustic waves within the acoustic cell when the sample gas is exposed to an electromagnetic radiation source, and the rigid plate configured to be excited by the acoustic waves.

[0032] In a further embodiment, the first half of the rigid plate is functionally connected to the acoustic cell filled with the sample gas, and the rigid plate is configured to be excited at the first half of the rigid plate when exposed to the acoustic wave, allowing differential movement.

[0033] In a further embodiment, a central region of the rigid plate is functionally connected to the acoustic cell filled with the sample gas, and the rigid plate is configured such that the central region of the rigid plate is excited when exposed to the acoustic waves, thereby enabling single-ended operation.

[0034] In one embodiment, an optoacoustic system is defined that includes the resonant MEMS transducer, the system including a first acoustic cell operatively connected to the first half of the rigid plate and a second acoustic cell operatively connected to a second half of the rigid plate, the optoacoustic system configured to enable switching between differential and single-ended operation by controlling the electromagnetic radiation source and gas type within the first and second acoustic cells.

[0035] In a further embodiment, the first acoustic cell is further filled with the sample gas, the second acoustic cell is further filled with the sample gas, the first acoustic cell is configured to generate the first acoustic wave within the first acoustic cell when the sample gas is exposed to the electromagnetic radiation source, and the first half of the rigid plate is configured to be excited by the first acoustic wave, enabling differential movement.

[0036] In a further embodiment, both the first acoustic cell and the second acoustic cell are configured to generate the first acoustic wave in the first acoustic cell when the sample gas is exposed to the electromagnetic radiation source and to generate a second acoustic wave in the second acoustic cell when exposed to the electromagnetic radiation source, the first acoustic wave exciting a first half of the rigid plate and the second acoustic wave simultaneously exciting a second half of the rigid plate 406, thereby enabling the single-ended operation.

[0037] In a further embodiment, the first acoustic cell is filled with the sample gas and the second acoustic cell is filled with an inert gas, wherein only the first acoustic cell is configured to generate a first acoustic wave therein when the sample gas in the first acoustic cell and the inert gas in the second acoustic cell are exposed to the electromagnetic radiation source, the first acoustic wave exciting a first half of the rigid plate and enabling differential motion. In this specification and throughout this disclosure, an inert gas refers to a gas that exhibits minimal response when exposed to the electromagnetic radiation source.

[0038] In a further embodiment, the at least one electrode is further connected to an electronic circuit capable of switching the polarity of the electrodes, thereby allowing switching between differential and single-ended operation.

[0039] In another broad aspect, a resonant MEMS transducer for optical acoustic detection includes a support structure, at least two anchors connected to the support structure, at least one rigid plate, at least one doubly-supported beam, a through hole defined by the support structure and the at least one rigid plate, and at least one electrode configured for piezoelectric transduction, wherein each doubly-supported beam of the at least one doubly-supported beam is anchored at a first point to a corresponding first one of the at least two anchors, at a second point to a corresponding second one of the at least two anchors, and at a third point to a corresponding first one of the at least one rigid plate, wherein the resonant MEMS transducer is configured to operate at a low resonant frequency, and wherein the through hole is configured to expose the at least one rigid plate to an ambient environment.

[0040] In one embodiment, the low resonant frequency includes 100 kHz or less.

[0041] In one embodiment, the resonant MEMS transducer is configured to operate in one or a combination of (i) a single-ended mode and (ii) a differential mode.

[0042] In one embodiment, the resonant MEMS transducer is configured to operate in an out-of-plane eigenmode.

[0043] In some embodiments, the support structure is further bonded to a substrate, and the substrate further comprises a substrate through-hole.

[0044] In one embodiment, the substrate through-holes are approximately the same size as the at least one rigid plate and are aligned with the at least one rigid plate, such that each rigid plate of the at least one rigid plate resonates with reduced squeeze film damping.

[0045] In one embodiment, each of the at least one doubly-supported beams has a first corresponding electrode of the at least one electrode patterned in the vicinity of the first point, at least in a portion thereof, and each of the at least one doubly-supported beams has a second corresponding electrode of the at least one electrode patterned in the vicinity of the second point, at least in a portion thereof.

[0046] In one embodiment, each electrode of the at least one electrode is configured to function as a detection electrode.

[0047] In one embodiment, the resonant MEMS transducer includes at least one elongated, doubly supported beam and at least one internal beam.

[0048] In one embodiment, each of the at least one long, double-supported beams is fixed to a first corresponding anchor of the at least two anchors at a fourth point, fixed to a second corresponding anchor of the at least two anchors at a fifth point, connected to a first corresponding rigid plate of the at least one rigid plate at a sixth point, connected to a second corresponding rigid plate of the at least one rigid plate at a seventh point, connected to a first corresponding internal beam of the at least one internal beam at an eighth point, and connected to a second corresponding internal beam of the at least one internal beam at a ninth point.

[0049] In one embodiment, each internal beam of the at least one internal beam is connected at a tenth point to a first corresponding long-length doubly-supported beam of the at least one long-length doubly-supported beam, at an eleventh point to a second corresponding long-length doubly-supported beam of the at least one long-length doubly-supported beam, and at a twelfth point to a first corresponding rigid plate of the at least one rigid plate.

[0050] In one embodiment, the at least one rigid plate may further include a first rigid plate and a second rigid plate.

[0051] In one embodiment, the substrate through-hole is approximately the same size as the first rigid plate and is aligned with the first rigid plate, allowing for differential movement.

[0052] In another broad aspect, a PAS transducer includes a resonant MEMS transducer as defined herein.

[0053] In another broad aspect, a method of manufacturing an optoacoustic system includes bonding a PAS transducer to an acoustic cell as defined herein.

[0054] In another broad aspect, a resonant MEMS transducer for optical acoustic detection includes a support structure, at least one anchor bonded to the support structure, a rigid plate, at least one cantilever beam, a through-hole defined by the support structure and the rigid plate, and at least one electrode configured for piezoelectric transduction, wherein each cantilever beam of the at least one cantilever beam is fixed at a first point to a corresponding first one of the at least one anchor and connected to the rigid plate at a second point, the resonant MEMS transducer is configured to operate at a low resonant frequency, and the through-hole is configured to expose the rigid plate to an ambient environment.

[0055] In one embodiment, the resonant MEMS transducer is configured to operate according to one or a combination of: (i) an out-of-plane eigenmode; (ii) a first seesaw eigenmode; and (iii) a second seesaw eigenmode.

[0056] In one embodiment, each cantilever beam of the at least one cantilever beam is patterned on at least a portion thereof, near the first point, with a first corresponding electrode of the at least one set of electrodes.

[0057] In some embodiments, the support structure is further bonded to a substrate, and the substrate may include a substrate through-hole.

[0058] In one embodiment, the at least one cantilever beam is a serpentine beam.

[0059] In one embodiment, the cantilever beam is a bending beam.

[0060] In another broad aspect, an optoacoustic system includes the transducer as defined herein, and includes an acoustic cell filled with a sample gas and operatively connected to the rigid plate, the acoustic cell configured to generate acoustic waves within the acoustic cell when the sample gas is exposed to a source of electromagnetic radiation, and the rigid plate configured to be excited by the acoustic waves. [Brief explanation of the drawings]

[0061] Embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0062] [Figure 1A] FIG. 1A is a perspective view of an exemplary acoustic cell.

[0063] [Figure 1B] FIG. 1B is a cross-sectional view of an exemplary acoustic cell.

[0064] [Figure 2A] FIG. 2A is a plan view of a resonant MEMS transducer operating in single-ended mode.

[0065] [Figure 2B] FIG. 2B is a cross-sectional view of a resonant MEMS transducer operating in single-ended mode.

[0066] [Figure 2C] Figure 2C is a phase image of the out-of-plane eigenmodes of a resonant MEMS transducer operating in single-ended mode.

[0067] [Figure 2D] FIG. 2D is a cross-sectional view illustrating an example of an optoacoustic system operating in single-ended mode.

[0068] [Figure 3A] FIG. 3A is a plan view of a resonant MEMS transducer operating in a differential mode.

[0069] [Figure 3B] FIG. 3B is a cross-sectional view of a resonant MEMS transducer that allows for differential modes.

[0070] [Figure 3C] FIG. 3C is a phase image of the out-of-plane eigenmode of a resonant MEMS transducer operating in differential mode.

[0071] [Figure 3D] FIG. 3D is a cross-sectional view illustrating an example of an optoacoustic system operating in differential mode.

[0072] [Figure 4A] FIG. 4A is a plan view of a resonating MEMS transducer operating in either single-ended or differential mode, or both.

[0073] [Figure 4B] FIG. 4B is a phase image of the three eigenmodes of a resonant MEMS transducer operating in either single-ended or differential mode or both.

[0074] [Figure 4C] FIG. 4C is a cross-sectional view of an optoacoustic system that allows either single-ended or differential mode operation.

[0075] [Figure 4D] FIG. 4D is a cross-sectional view of an optoacoustic system that allows switching between single-ended and differential modes.

[0076] [Figure 5A] FIG. 5A is a plan view of a resonating MEMS transducer operating in a differential mode.

[0077] [Figure 5B] FIG. 5B is a phase image of the out-of-plane eigenmode of a resonant MEMS transducer operating in differential mode.

[0078] [Figure 6A] FIG. 6A shows a perspective view of a resonant MEMS transducer with a cantilever beam.

[0079] [Figure 6B] FIG. 6B is a plan view of a resonating MEMS transducer with a cantilever beam.

[0080] [Figure 6C] FIG. 6C is a cross-sectional view of a resonating MEMS transducer with a cantilever beam. DETAILED DESCRIPTION OF THE INVENTION

[0081] The present disclosure provides a resonant MEMS transducer configured to operate at a low resonant frequency when exposed to an ambient environment. For background purposes, information is provided regarding photoacoustic spectroscopy (PAS), among other applications that utilize such characteristics. This information is provided to illustrate the general principles of the present disclosure and is not intended to limit the inventive concepts claimed in the present disclosure. In certain embodiments, a "low resonant frequency" may include operating the resonant MEMS transducer at a frequency less than about 300 kHz. In other examples, a "low resonant frequency" may include operating the resonant MEMS transducer at a frequency less than about 100 kHz. In yet other embodiments, a "low resonant frequency" may include operating the resonant MEMS transducer at a frequency less than about 10 kHz. [Overview of I.PAS]

[0082] This disclosure provides a resonant MEMS transducer configured to operate at a low resonant frequency while exposed to the ambient environment. These properties make the resonant MEMS transducer useful in a variety of applications, including photoacoustic spectroscopy (PAS). PAS is ideal for use in continuous monitoring and large-scale applications (e.g., medical, military, pollution monitoring, manufacturing) that require accurate and high-yield detection of minute amounts of target analytes in environments with fluctuating temperature, humidity, and background molecules in the sample gas. PAS uses an electromagnetic radiation source to excite any target analyte molecules in the sample gas, generating pressure waves (also known as acoustic waves) that are then detected and transduced (i.e., converted into an electrical signal). Furthermore, PAS-based systems can be adapted to detect nearly any molecule while maintaining specificity by varying the output power of the electromagnetic radiation source (e.g., tuning the laser wavelength).

[0083] In PAS, the wave number υ [cm -1 ] passes through the target analyte molecules in the sample gas, the molar density ρ [mol cm -3 ], the absorption cross section σ(υ) [cm 2 mol -1 ], and the intensity I [W cm ] of the electromagnetic radiation source at wavenumber υ -2[The term "absorption" refers to the rate at which the energy of the target analyte is absorbed. The target analyte molecules can then undergo multiple processes, such as radiation (induced or spontaneous photon emission), chemical reaction, nonradiative relaxation, or a combination of these, resulting in relaxation to the molecular ground state. Nonradiative relaxation increases the kinetic energy of surrounding molecules, causing local heating and a corresponding increase in pressure. If the absorption process is cyclically modulated by an electromagnetic radiation source (intensity or frequency) or absorption line shifts, the induced cyclic heating generates pressure waves (also known as acoustic waves) at the same frequency. This cyclic thermal excitation causes acoustic resonance within the acoustic cell, which is measured as pressure by the transducer. Several types of resonant transducers are suitable for PAS, including both resonant and nonresonant transducers. Suitable resonant transducers include resonant microelectromechanical system (MEMS) transducers and quartz tuning forks (QTFs). Furthermore, non-resonant transducers can be used such as non-resonant wideband MEMS microphones, condenser microphones, electrets, etc. The pressure p [Pa] at the transducer position is proportional to the density, absorption cross section, and strength of the electromagnetic radiation source, and is expressed by the following equation:

number

[0084] In theory, transducers may be suitable for low-frequency applications and may be able to couple strongly to acoustic waves. Furthermore, transducers suitable for low-frequency resonant modes may be preferred because the photoacoustic signal is inversely proportional to the resonant frequency of the transducer, and therefore operating at lower modulation frequencies may result in higher photoacoustic signal strength for faster relaxation of energy states.

[0085] Herein and throughout this disclosure, "sample gas" refers to gas whether or not it contains PAS-detectable amounts of target analyte molecules.

[0086] FIG. 1A is a perspective view of an exemplary prior art acoustic cell 100. Acoustic cell 100 includes a central resonant cavity 102 and an acoustic port 106. In this example, central resonant cavity 102 is an open-ended cylindrical tube through which sample gas can be introduced and electromagnetic radiation can pass. While FIG. 1A is shown for reference purposes, it should be noted that many other designs for acoustic cell 100 can be used, including acoustic cells with a central resonant cavity and multiple buffer volumes, Helmholtz-type acoustic cells, acoustic cells for asymmetric excitation, and other designs now known or later developed.

[0087] FIG. 1B shows a cross-sectional view of an exemplary acoustic cell 100. [II. Design of Resonant MEMS Transducer]

[0088] 2A-C show a resonating MEMS transducer 200. The resonating MEMS transducer 200 is a resonator that includes a thin-film piezoelectric element on silicon. Piezoelectric transduction was chosen because of its ease of fabrication and its performance in low vacuum (i.e., when the resonating MEMS transducer is exposed to the ambient environment at atmospheric or near-atmospheric pressure). Furthermore, compared to capacitive transduction, piezoelectric transducers can provide larger displacements at lower voltages, which improves the signal-to-noise ratio.

[0089] 2A-B includes a support structure 209, at least one anchor 208, at least one rigid plate 206, at least one doubly-supported beam 204, a through-hole 205, and at least one electrode 210. The at least one anchor 208 is bonded to the support structure 209. Each doubly-supported beam of the at least one doubly-supported beam 204 is fixed to a first corresponding anchor of the at least one anchor 208 at a first point 204A, fixed to a second corresponding anchor of the at least one anchor 208 at a second point 204B, and connected to a first corresponding rigid plate of the at least one rigid plate 206 at a third point 204C. The through-hole 205 is formed by the support structure 209 and the at least one rigid plate 206. The resonant MEMS transducer 200 is configured to operate at a low resonant frequency. The through-holes 205 are configured to expose at least one rigid plate 206 to the surrounding environment.

[0090] For simplicity of explanation, only a single example of first point 204A, second point 204B, and third point 204C is shown in Figure 2A. It is important to note that each doubly supported beam of the at least one doubly supported beam 204 is secured / connected in this manner.

[0091] The support structure 209 allows for bonding of the resonant MEMS transducer 200 to other structures, such as the acoustic port 106 or the substrate 112 (not shown in this figure).

[0092] At least one anchor 208 connects at least one cantilever beam 204 to a support structure 209 .

[0093] Each of the at least one doubly-supported beams 204 is mechanically coupled via at least one rigid plate 206. The at least one doubly-supported beam 204 serves two purposes: (i) to control the resonant frequency of the resonating MEMS transducer 200 by the beam dimensions, and (ii) to provide a piezoelectric transduction region, thereby isolating high mechanical stresses from the at least one rigid plate 206. By isolating the high-stress piezoelectric transduction region from the at least one rigid plate 206, the at least one rigid plate 206 can be used to detect pressure waves.

[0094] The through-hole 205 is configured to expose the at least one rigid plate 206 to the surrounding environment. In this specification and throughout this disclosure, the surrounding environment includes both the area typically enclosed by the MEMS package (e.g., greater than about 2 mm by about 2 mm by about 2 mm by about 2 mm) and the area outside the area. The through-hole 205 is approximately the same size as the at least one rigid plate 206. In this specification and throughout this disclosure, "the through-hole is approximately the same size as the at least one rigid plate 206" means that the area of ​​the through-hole 205 is large enough to cover the at least one rigid plate 206 and the at least one doubly supported beam 204. Furthermore, it can be seen that the through-hole 205 is aligned with the at least one rigid plate 206, and that there is no support structure 209 below the at least one rigid plate 206. This allows the at least one rigid plate 206 to resonate freely, resulting in reduced squeeze film damping (compared to the squeeze film damping of a MEMS transducer of the same design, except where the through-hole is removed and a solid support structure is present).

[0095] Each electrode of the at least one electrode 210 is a piezoelectric electrode. Each doubly supported beam of the at least one doubly supported beam 204 and each anchor of the at least one anchor 208 has a piezoelectric material layer patterned over at least a portion thereof. A metal layer on the piezoelectric material layer is patterned over at least a portion thereof to form a single electrode. In the examples described herein, the piezoelectric material layer may include AlN, ZnO, PZT, ScAlN, or other piezoelectric materials. Furthermore, in the examples described herein, the metal layer may include molybdenum, platinum, aluminum, or other metals. A common ground reference may be connected to the at least one electrode 210.

[0096] In one embodiment, the low resonant frequency is 100 kHz or less.

[0097] In one embodiment, the resonant MEMS transducer 200 is configured to operate in a single-ended mode.

[0098] In one embodiment, the resonant MEMS transducer 200 is configured to operate in an out-of-plane eigenmode, which is understood to include modes that can be considered substantially out-of-plane eigenmodes.

[0099] In one embodiment, the support structure 209 is further bonded to a substrate 112 , which further includes a substrate through-hole 113 .

[0100] In a further embodiment, the substrate through-hole 113 is approximately the same size as and aligned with the at least one rigid plate 206, such that each rigid plate of the at least one rigid plate 206 resonates with reduced squeeze film damping. Herein and throughout this disclosure, "the substrate through-hole is approximately the same size as the at least one rigid plate" means that the area of ​​the substrate through-hole 113 is large enough to completely encompass the at least one rigid plate 206 and the at least one doubly supported beam 204.

[0101] In one embodiment, each doubly-supported beam of the at least one doubly-supported beam is patterned over at least a portion thereof near a first point 204A with a first corresponding electrode of the at least one electrode 210. And each doubly-supported beam of the at least one doubly-supported beam 204 is patterned over at least a portion thereof near a second point 204B with a second corresponding electrode of the at least one electrode 210. To ensure that the patterning covers a set of points, it is understood that the patterning disposed near the first point 204A may cover (i) the first point 204A, (ii) an anchor adjacent to the first point 204A, and (iii) a segment of length L (where length L corresponds to approximately one-quarter of the length of each doubly-supported beam) of each of the two doubly-supported beams adjacent to the first point 204A. Similarly, patterning near the second point 204B may cover (i) the second point 204B, (ii) the anchor adjacent to the second point 204B, and (iii) a segment of length L present on each of the two cantilever beams adjacent to the second point 204B.

[0102] In an embodiment, each electrode of the at least one electrode 210 is configured to function as a detection electrode.

[0103] FIG. 2C shows the preferred eigenmode of the resonating MEMS transducer 200, namely, a single phase of the out-of-plane eigenmode.

[0104] The resonant MEMS transducer 200 is configured to operate in an out-of-plane eigenmode. Because the resonant MEMS transducer 200 is single-ended, signals generated by the at least one electrode 210 are in phase and can sum to generate a larger signal output. Furthermore, the uniform displacement of the at least one rigid plate 206 allows the resonant MEMS transducer 200 to be easily bonded to other structures via a support structure 209.

[0105] In some examples, the resonant frequency of the resonant MEMS transducer 200 is approximately 15 kHz. In this example, the dimensions of the proof mass (i.e., the combination of all rigid plates and doubly supported beams) of the resonant MEMS transducer 200 are relatively large, approximately 1050 pm x 1050 pm. Finite element method (FEM) simulations show that the Q of the resonant MEMS transducer 200 in this example is approximately 15 kHz. TOT(piezo) is about 10k in a vacuum, where Q TOT(piezo) is the total Q value including the piezoelectric material layer.

[0106] In some examples, the resonant frequency of the resonant MEMS transducer 200 is approximately 32 kHz. In this example, the proof mass of the resonant MEMS transducer 200 is relatively small, approximately 770 pm x 770 pm. FEM simulations have shown that in this example, the resonant MEMS transducer 200 has a Q of approximately 10 kΩ. TOT(piezo) It has.

[0107] 2D is a cross-sectional view of an optoacoustic system 210. The optoacoustic system 210 includes a resonant MEMS transducer 200, a substrate 112, and an acoustic cell 100. The resonant MEMS transducer 200 is bonded to the substrate 112. The substrate 112 is bonded to the acoustic port 106. The substrate 112 further includes a substrate through-hole 113.

[0108] Substrate through-holes 113 are positioned such that at least a portion of them is aligned with through-hole 205, thereby operatively connecting at least one rigid plate 206 to acoustic cell 100. The arrangement of substrate through-holes 113 is configured to allow at least one rigid plate 206 to be operatively connected to acoustic cell 100, thereby enabling single-ended operation of resonating MEMS transducer 200. Herein and throughout this disclosure, "operatively connected" means that acoustic waves generated in the acoustic cell excite at least a portion of the resonating MEMS transducer.

[0109] The substrate 112 may be formed from a printed circuit board, plastic, metal, or other substantially planar material. The resonating MEMS transducer 200 may be bonded to the substrate 112 with epoxy, solder, wire bonding, or other known methods. The substrate 112 is bonded to the acoustic cell 100 with epoxy, a structural element, or other known methods.

[0110] In one embodiment, a PAS transducer is provided that includes a resonant MEMS transducer 200 as defined herein.

[0111] In one embodiment, a method is provided for bonding a PAS transducer to an acoustic cell 200 to produce an optoacoustic system 210.

[0112] 3A-B show a differential resonating MEMS transducer 300. The resonating MEMS transducer 300 is a resonator that includes a thin film piezoelectric element on silicon.

[0113] The resonating MEMS transducer 300 includes a support structure 309, at least one anchor 308, at least one doubly-supported beam 304, at least one rigid plate 306, at least one long doubly-supported beam 305, at least one internal beam 307, a through-hole 301, and at least one electrode 310. The at least one anchor 308 is bonded to the support structure 309. Each doubly-supported beam of the at least one doubly-supported beam 304 is fixed to a first corresponding one of the at least one anchor 308 at a first point 304A, fixed to a second corresponding anchor of the at least one anchor 308 at a second point 304B, and connected to a first corresponding one of the at least one rigid plate 306 at a third point 304C. Each of the at least one long-length doubly supported beams 305 is fixed to a first corresponding anchor of the at least one anchor 308 at a fourth point 305A, fixed to a second corresponding anchor of the at least one anchor at a fifth point 305B, connected to a first corresponding rigid plate of the at least one rigid plate 308 at a sixth point 305C, connected to a second corresponding rigid plate of the at least one rigid plate 306 at a seventh point 305D, connected to a first corresponding internal beam of the at least one internal beam 307 at an eighth point 305E, and connected to a second corresponding internal beam of the at least one internal beam 307 at a ninth point 305F. Each internal beam of the at least one internal beam 307 is connected to a first corresponding long, doubly-supported beam of the at least one long, doubly-supported beam 305 at a tenth point 307A, to a second corresponding long, doubly-supported beam of the at least one long, doubly-supported beam 305 at an eleventh point 307B, and to a first corresponding rigid plate of the at least one rigid plate 306 at a twelfth point 307C. The through-hole 301 is defined by the support structure 309 and the at least one rigid plate 306. The resonant MEMS transducer 300 is configured to operate at a low resonant frequency. The through-hole 301 is configured to expose the at least one rigid plate 306 to the surrounding environment.

[0114] For clarity, Figure 3A shows only single examples of first point 304A, second point 304B, third point 304C, fourth point 305A, fifth point 305B, sixth point 305C, seventh point 305D, eighth point 305E, ninth point 305F, tenth point 307A, eleventh point 307B, and twelfth point 307C. Importantly, each of these points can be used to identify a double-supported beam, a long double-supported beam, or an interior beam. It will be understood that there are multiple ways to identify the points, and therefore, some overlapping points may occur. For example, eighth point 305E is the same as tenth point 307A in Figure 3A.

[0115] The support structure 309 allows the resonant MEMS transducer 300 to be bonded to other structures such as the acoustic port 106 or the substrate 112 (not shown in this figure).

[0116] At least one anchor 308 connects at least one cantilever beam 304 and at least one long cantilever beam 305 to a support structure 309 .

[0117] Each doubly-supported beam of the at least one doubly-supported beam 304 and each long doubly-supported beam of the at least one long doubly-supported beam 305 are mechanically connected via at least one rigid plate 306. The doubly-supported beam 304 and the long doubly-supported beam 305 are used for two purposes: (i) to control the resonant frequency of the resonating MEMS transducer 300 by the dimensions of the beams, and (ii) to provide a piezoelectric transduction region and thereby isolate high mechanical stress from the at least one rigid plate 306. By isolating the high-stress piezoelectric transduction region from the at least one rigid plate 306, the at least one rigid plate 306 can be used to detect pressure waves.

[0118] The through-holes 301 are configured to expose the at least one rigid plate 306 to the surrounding environment. It can be seen that the through-holes 301 in the support structure 309 are approximately the same size as the at least one rigid plate 306. It can further be seen that the through-holes 301 in the support structure 309 are aligned with the at least one rigid plate 306 such that there is no support structure 309 below the at least one rigid plate 306. Thus, the at least one rigid plate 306 is free to resonate, resulting in reduced squeeze film damping (compared to that of a MEMS transducer of the same design but with a solid support structure and no through-holes).

[0119] Each of the at least one electrode 310 is a piezoelectric electrode. Each of the at least one doubly-supported beam 304 and each of the at least one anchor 308 has a piezoelectric material layer patterned over at least a portion thereof. A metal layer is patterned over at least a portion of the piezoelectric material layer to form a single electrode. The same is true for the at least one long doubly-supported beam 305. In the examples described herein, the piezoelectric material layer may include AlN, ZnO, PZT, ScAlN, or other piezoelectric materials. Furthermore, in the examples described herein, the metal layer may include molybdenum, platinum, aluminum, or other metals. A common ground reference may be connected to the at least one electrode 310.

[0120] In some embodiments, the low resonant frequency includes 100 kHz or less.

[0121] In one embodiment, the resonating MEMS transducer 300 is configured to operate in a differential mode. When the resonating MEMS transducer 300 operates in a differential mode, the at least one rigid plate 306 moves out of phase with one another, causing the strains on the anchor elements and the voltages generated to be of opposite signs. Therefore, subtracting the voltage signals allows for cancellation of common-mode noise.

[0122] In one embodiment, the resonant MEMS transducer 300 is configured to operate in an out-of-plane eigenmode, which is understood to include modes that can be considered substantially out-of-plane eigenmodes.

[0123] In one embodiment, the support structure 309 is further bonded to a substrate 112 , which further includes a substrate through-hole 113 .

[0124] In one embodiment, the substrate through-holes 113 are approximately the same size as and aligned with the at least one rigid plate 306, such that each rigid plate of the at least one rigid plate 306 resonates with reduced squeeze film damping.

[0125] In one embodiment, at least a portion of each of the at least one doubly-supported beams 304 is patterned near a first point 304A with a first corresponding electrode of the at least one electrode 310. Also, at least a portion of each of the at least one doubly-supported beams 304 is patterned near a second point 304B with a second corresponding electrode of the at least one electrode 310. Because the patterning covers a set of points, the patterning near the first point 304A may cover (i) the first point 304A, (ii) an anchor adjacent to the first point 304A, (iii) a segment of length L on the corresponding doubly-supported beam (length L corresponds to approximately one-quarter of the length of the corresponding doubly-supported beam), and (iv) a segment of length L on the long doubly-supported beam adjacent to the first point 304A. Similarly, patterning near the second point 304B may cover (i) the second point 304B, (ii) an anchor adjacent to the second point 304B, (iii) a segment of length L on the corresponding doubly supported beam, and (iv) a segment of length L on the long doubly supported beam adjacent to the second point 304B.

[0126] In an embodiment, each electrode of the at least one electrode 310 is configured to function as a detection electrode.

[0127] In one embodiment, the resonating MEMS transducer further includes at least one elongated, doubly supported beam 305 and at least one internal beam 307 .

[0128] In a further embodiment, each long-length doubly-supported beam of the at least one long-length doubly-supported beam 305 is fixed to a first corresponding anchor of the at least one anchor 308 at a fourth point 305A, fixed to a second corresponding anchor of the at least one anchor 308 at a fifth point 305B, connected to a first corresponding rigid plate of the at least one rigid plate 308 at a sixth point 305C, connected to a second corresponding rigid plate of the at least one rigid plate 308 at a seventh point 305D, connected to a first corresponding internal beam of the at least one internal beam 307 at an eighth point 305E, and connected to a second corresponding internal beam of the at least one internal beam 307 at a ninth point 305F.

[0129] In a further embodiment, each internal beam of the at least one internal beam 307 is connected to a first corresponding long-length doubly supported beam of the at least one long-length doubly supported beam 305 at a tenth point 307A, to a second corresponding long-length doubly supported beam of the at least one long-length doubly supported beam 305 at an eleventh point 307B, and to a first corresponding rigid plate of the at least one rigid plate 306 at a twelfth point 307C.

[0130] In a further embodiment, the at least one rigid plate 306 includes a first rigid plate 306A and a second rigid plate 306B.

[0131] In a further embodiment, the substrate through-holes 113 are approximately the same size as and aligned with the first rigid plate 306A, thereby allowing the substrate through-holes 113 to provide differential movement.

[0132] FIG. 3C shows a single phase of the preferred eigenmode of the resonant MEMS transducer 300, the out-of-plane mode.

[0133] In some examples, the resonant frequency of the resonant MEMS transducer 300 is approximately 15 kHz. In this example, the dimensions of the proof mass are relatively large, approximately 1000 μm×2100 μm. FEM simulations show that the Q of the resonant MEMS transducer 300 in this example is approximately TOT(piezo) is about 10k.

[0134] In some examples, the resonant frequency of the resonant MEMS transducer 300 is approximately 32 kHz. In this example, the dimensions of the proof mass are relatively small, approximately 710 μm×1600 μm. FEM simulations show that in this example, the Q of the resonant MEMS transducer 300 is TOT(piezo) is about 10k.

[0135] The photoacoustic system 310 includes a resonant MEMS transducer 300, a substrate 112, and an acoustic cell 100. The resonant MEMS transducer 300 is bonded to the substrate 112. The substrate 112 is bonded to the acoustic port 106. The substrate 112 further includes a substrate through-hole 113.

[0136] The substrate through-holes 113 are positioned such that at least a portion of the through-holes 113 is aligned with the through-holes 301, thereby operatively connecting the at least one rigid plate 306 to the acoustic cell 100. The placement of the substrate through-holes 113 is configured to enable differential operation of the resonating MEMS transducer 300 by determining which regions of the at least one rigid plate 306 are operatively connected to the acoustic cell 100.

[0137] In some embodiments, a PAS transducer is provided that includes a resonant MEMS transducer 300 as defined herein.

[0138] In one embodiment, a method is provided for bonding a PAS transducer to an acoustic cell 100 to produce an optoacoustic system 310.

[0139] 4A shows a resonating MEMS transducer 400. The resonating MEMS transducer 400 is a resonator made of a thin film piezoelectric element on silicon.

[0140] The resonant MEMS transducer 400 includes a support structure 409 (not shown), at least one anchor 408, a rigid plate 406, a through-hole 401 (not shown), at least one cantilever beam 404 (as an illustrative example, the cantilever beam 404 in FIG. 4A is a serpentine beam), and at least one electrode 410. The at least one anchor 408 is bonded to the support structure 409. Each serpentine beam of the at least one serpentine beam 404 is fixed to a first corresponding anchor of the at least one anchor 408 at a first point 404A and connected to the rigid plate 406 at a second point 404B. The through-hole 401 is defined by the support structure 409 and the rigid plate 406. The resonant MEMS transducer 400 is configured to operate at a low resonant frequency. The through-hole 401 is configured to expose the rigid plate 406 to the surrounding environment.

[0141] For clarity, only a single example of first point 404A and second point 404B is shown in Figure 4A. What is important is that each serpentine beam of the at least one serpentine beam 404 is secured / joined in this manner.

[0142] Support structure 409 allows for bonding of resonant MEMS transducer 400 to other structures, such as acoustic port 106 or substrate 112 (not shown in this figure).

[0143] At least one anchor 408 connects at least one serpentine beam 404 to a support structure 409 .

[0144] Each serpentine beam of the at least one serpentine beam 404 is mechanically coupled via a rigid plate 406. The at least one serpentine beam 404 serves two purposes: (i) to control the resonant frequency of the resonating MEMS transducer 400 via the beam dimensions, and (ii) to provide a piezoelectric transducer region, thereby isolating high mechanical stresses from the rigid plate 406. By isolating the high stress piezoelectric transducer region from the rigid plate 406, the rigid plate 406 can be used to detect pressure waves.

[0145] The through-holes 401 are configured to expose the rigid plate 406 to the surrounding environment, allowing the rigid plate 406 to be excited by pressure waves in the surrounding environment. The through-holes 401 in the support structure 409 are approximately the same size as the rigid plate 406. Furthermore, the through-holes 401 in the support structure 409 are aligned with the rigid plate 406, such that there is no support structure 409 below the rigid plate 406. This allows the rigid plate 406 to resonate freely, resulting in reduced squeeze film damping (compared to that of a MEMS transducer of the same design but with a solid support structure and no through-holes).

[0146] Each electrode of the at least one electrode 410 is a piezoelectric electrode. Each serpentine beam of the at least one serpentine beam 404 and each anchor of the at least one anchor 408 has a piezoelectric material layer patterned over at least a portion thereof. The piezoelectric material layer has a metal layer patterned over at least a portion thereof to form a single electrode. In the examples described herein, the piezoelectric material layer may include AlN, ZnO, PZT, ScAlN, or other piezoelectric materials. Furthermore, in the examples described herein, the metal layer may include molybdenum, platinum, aluminum, or other metals. A common ground reference may be connected to the at least one electrode 410.

[0147] FIG. 4B illustrates a single phase of a preferred eigenmode of the resonating MEMS transducer 400. The resonating MEMS transducer 400 is configured to operate in one or a combination of (i) an out-of-plane eigenmode, (ii) a first seesaw eigenmode, and (iii) a second seesaw eigenmode. Phase image 412 illustrates a single phase of the out-of-plane eigenmode. The out-of-plane eigenmode corresponds to the lowest resonant frequency, in which the rigid plate 406 moves uniformly out-of-plane. Phase image 418 illustrates a single phase of the first seesaw eigenmode. In the first seesaw eigenmode (corresponding to the intermediate resonant frequency), the rigid plate 406 seesaws in a direction perpendicular to the long axis extending between the first end 421 and the second end 423 of the rigid plate 406. Phase image 416 illustrates a single phase of the second seesaw eigenmode. In the second seesaw eigenmode (corresponding to the highest resonant frequency), the rigid plate 406 seesaws along the long axis of the rigid plate 406 .

[0148] FIG. 4C is a cross-sectional view of an optoacoustic system 450. The optoacoustic system 450 includes a resonant MEMS transducer 400, a substrate 112, and an acoustic cell 100. The substrate 112 further includes a substrate through-hole 113. The resonant MEMS transducer 400 is bonded to the substrate 112. The substrate 112 is bonded to the acoustic port 106. The substrate through-hole 113 is positioned such that at least a portion of the substrate through-hole 113 is aligned with the through-hole 401, thereby operatively connecting the resonant MEMS transducer 400 to the acoustic cell 100. The placement of the substrate through-hole 113 is configured to enable either (i) single-ended operation or (ii) differential operation of the resonant MEMS transducer 400 by determining which portion of the resonant MEMS transducer 400 is operatively connected to the acoustic cell 100. For example, a central region of the rigid plate 406 can be operatively connected to the acoustic cell 100 to excite an out-of-plane eigenmode. Herein and throughout this disclosure, central region refers to the region near the center of mass of rigid plate 406. Additionally, the first end 421 or the second end 423 of rigid plate 406 may be operatively connected to acoustic cell 100 to excite the first seesaw eigenmode. Finally, a point away from the major axis may be operatively connected to acoustic cell 100 to excite the second seesaw eigenmode.

[0149] 4D is a cross-sectional view of an optoacoustic system 460 configured to enable switching between single-ended and differential operation. The optoacoustic system 460 includes a resonant MEMS transducer 400, a substrate 112, a first acoustic cell 492, and a second acoustic cell 494. The substrate 112 is bonded to the resonant MEMS transducer 400. The substrate 112 further includes a substrate through-hole 113. The substrate through-hole 113 is positioned such that at least a portion of the substrate through-hole 113 is aligned with the through-hole 401. This allows the resonant MEMS transducer 400 to be operatively connected to either the first acoustic cell 492 or the second acoustic cell 494, or both, depending on the positioning of the substrate through-hole 113. The first acoustic cell 492 and the second acoustic cell 494 can be excited independently or simultaneously, thereby enabling switching between (i) single-ended operation or (ii) differential operation, or both.

[0150] First acoustic cell 492 and second acoustic cell 494 can include any acoustic cell design now known or hereafter discovered, including acoustic cells with a central resonant cavity and multiple buffer volumes, Helmholtz-type acoustic cells, acoustic cells for asymmetric excitation, and other designs.

[0151] In some embodiments, the low resonant frequency includes 100 kHz or less.

[0152] In one embodiment, the resonant MEMS transducer 400 is configured to operate in one or a combination of (i) a single-ended mode and (ii) a differential mode.

[0153] In one embodiment, the resonant MEMS transducer 400 is configured to operate according to one or a combination of: (i) an out-of-plane eigenmode, (ii) a first seesaw eigenmode, and (iii) a second seesaw eigenmode.

[0154] In a further embodiment, the resonating MEMS transducer 400 is configured to switch between two or more of: (i) an out-of-plane eigenmode, (ii) a first Theter-Totter eigenmode, and (iii) a second Theter-Totter eigenmode.

[0155] In one embodiment, each serpentine beam of the at least one serpentine beam 404 has a first corresponding electrode of the set of at least one electrode 410 patterned on at least a portion thereof near the first point 404A.

[0156] In one embodiment, the support structure 409 is further bonded to a substrate 112 , which further comprises a substrate through-hole 113 .

[0157] In one embodiment, the substrate through-holes 113 are approximately the same size as the rigid plate 406 and are aligned with the rigid plate 406 .

[0158] In one embodiment, the substrate through-hole 113 is approximately half the size of the rigid plate 406 and is aligned with a first half of the rigid plate 406 .

[0159] In one embodiment, an optoacoustic system is defined that includes a resonant MEMS transducer 400 and also includes an acoustic cell 100 filled with a sample gas and operatively connected to a rigid plate 406. The acoustic cell 100 is configured to generate acoustic waves within the acoustic cell 100 when the sample gas is exposed to a source of electromagnetic radiation, and the rigid plate 406 is configured to be excited by the acoustic waves.

[0160] In a further embodiment, a first half of the rigid plate 406 is operatively connected to the acoustic cell 100 filled with a sample gas, and the rigid plate 406 is configured such that when exposed to an acoustic wave, the first half of the rigid plate is excited to vibrate, enabling differential movement.

[0161] In a further embodiment, the central region of the rigid plate 406 is operatively connected to the acoustic cell 100 filled with sample gas, and the rigid plate 406 is configured to vibrate at the central region of the rigid plate 406 when exposed to acoustic waves, thereby enabling single-ended operation.

[0162] In some embodiments, an optoacoustic system is defined that includes the resonant MEMS transducer 400 and includes a first acoustic cell 492 operatively connected to a first half of the rigid plate 406 and a second acoustic cell 494 operatively connected to a second half of the rigid plate 406. The optoacoustic system is configured to allow switching between differential and single-ended operation by controlling the types of electromagnetic radiation sources and gases within the first acoustic cell 492 and the second acoustic cell 494.

[0163] In a further embodiment, the first acoustic cell 492 is further filled with a sample gas, the second acoustic cell 494 is filled with a sample gas, the first acoustic cell 492 is configured to generate a first acoustic wave within the first acoustic cell 492 when the sample gas is exposed to an electromagnetic radiation source, and the first half of the rigid plate 406 is configured to be excited by the first acoustic wave to enable differential movement.

[0164] In a further embodiment, the first acoustic cell 492 and the second acoustic cell 494 are both configured to generate a first acoustic wave in the first acoustic cell 492 when the sample gas is exposed to an electromagnetic radiation source, and to generate a second acoustic wave in the second acoustic cell 494 when exposed to the electromagnetic radiation source, the first acoustic wave exciting a first half of the rigid plate 406 and the second acoustic wave exciting a second half of the rigid plate 406 simultaneously, allowing single-ended operation.

[0165] In a further embodiment, first acoustic cell 492 is filled with a sample gas and second acoustic cell 494 is filled with an inert gas. In this case, only first acoustic cell 492 is configured to generate a first acoustic wave therein when the sample gas therein and the inert gas therein are exposed to an electromagnetic radiation source. The first acoustic wave excites a first half of rigid plate 406, enabling differential movement. Herein and throughout this disclosure, an inert gas refers to a gas that exhibits a minimal response to exposure to an electromagnetic radiation source.

[0166] In one embodiment, at least one electrode 410 is further connected to electronic circuitry capable of switching the polarity of the electrode, thereby allowing switching between differential and single-ended operation.

[0167] In some examples, the resonant MEMS transducer 400 has a resonant frequency of about 15 kHz in the out-of-plane eigenmode, a resonant frequency of about 19 kHz in the first see-saw mode, and a resonant frequency of about 32 kHz in the second see-saw mode. FEM simulations have shown that the Q of the resonant MEMS transducer 400 in the out-of-plane eigenmode is TOT(piezo) is about 5k. For the out-of-plane eigenmode, the Q predicted by the FEM simulation TOT(piezo) is limited by losses in the piezoelectric film due to high energy losses along the length of the serpentine beam 404. However, the quality of the piezoelectric and metal layers also affects the actual Q TOT(piezo) According to the FEM simulation, the Q of the resonant MEMS transducer 400 in the first seesaw mode is TOT(piezo) is approximately 10k. According to the FEM simulation, in the second seesaw mode, the Q TOT(piezo) is about 10k.

[0168] In an example where vibration resonating MEMS transducer 400 is used in a PAS, the single-ended out-of-plane eigenmodes are more likely to couple with acoustic pressure waves. In a PAS system having an acoustic cell such as acoustic cell 100, resonating MEMS transducer 400 (and through-hole 405) can be positioned directly over acoustic port 106 to (i) maximize coupling of acoustic pressure waves to rigid plate 406 and (ii) reduce squeeze film attenuation.

[0169] In some embodiments, as shown in FIGS. 6A-6C, the resonant MEMS transducer 400 may have a different shape. For example, the cantilever beams 404 may have a curved shape (e.g., crumbled beams) (see FIGS. 6A-6C). Electrodes 410 are disposed at the tips of the cantilever beams 404. Each cantilever beam 404 of a set of at least one cantilever beam 404 is anchored at a first point to a corresponding first anchor of a set of at least one anchor 408 and connected at a second point to a rigid plate 406. For clarity, the example MEMS transducer 400 of FIGS. 6A-6C shows four cantilever beams 404, but it will be understood that the number of cantilever beams 404 can vary without departing from the teachings of the present disclosure. As with the example of FIG. 4A, it will be understood that there may be one or more rigid plates 406 (e.g., interconnected via the cantilever beams 404). 4A , each of the at least one cantilever beams 404 is mechanically coupled via a rigid plate 406. The at least one cantilever beam 404 serves two purposes: (i) to control the resonant frequency of the resonant MEMS transducer 400 through the beam dimensions, and (ii) to provide a piezoelectric transduction area for isolating high mechanical stresses from the rigid plate 406. It is therefore understood that the width, aspect ratio, angle, or number of curved shapes of the cantilever beams 404 can be varied to achieve a desired resonant frequency. Furthermore, by isolating the high-stress piezoelectric transduction area from the rigid plate 406, the rigid plate 406 can be used to detect pressure waves.

[0170] FIG. 6B illustrates a single phase of operation of a preferred eigenmode of the resonating MEMS transducer 400, specifically the out-of-plane eigenmode.

[0171] FIG. 6C shows a cross-sectional view of the MEMS transducer 400 along section AA.

[0172] 5A shows a resonating MEMS transducer 500. The resonating MEMS transducer 500 is a resonator made of a thin film piezoelectric element on silicon.

[0173] The resonant MEMS transducer 500 includes a support structure 509 (not shown), at least one anchor 508, at least one rigid plate 506, at least one doubly-supported beam 504, a through-hole 501, and at least one electrode 510. The at least one anchor 508 is bonded to the support structure 509. Each doubly-supported beam of the at least one doubly-supported beam 504 is fixed at a first point to a first corresponding anchor of the at least one anchor 508, at a second point to a second corresponding anchor of the at least one anchor 508, and at a third point to a first corresponding rigid plate of the at least one rigid plate 506. The through-hole 501 is defined by the support structure 509 and the at least one rigid plate 506. The resonant MEMS transducer 500 is configured to operate at a low resonant frequency. The through-hole 501 is configured to expose the at least one rigid plate 506 to the surrounding environment.

[0174] FIG. 5B shows the preferred eigenmode of the resonating MEMS transducer 500, a single phase of the out-of-plane mode.

[0175] In some examples, the resonant frequency of the resonant MEMS transducer 500 is approximately 15 kHz. In this example, the proof mass of the resonant MEMS transducer 500 is large. FEM simulations show that in this example, the Q of the resonant MEMS transducer 500 is TOT(piezo) is about 10k.

[0176] Drawings are not to scale unless otherwise noted.

[0177] While the present disclosure has been described with reference to preferred embodiments, modifications may be made as will be understood by those skilled in the art, and such modifications and variations are deemed to be within the scope and scope of the present disclosure.

[0178] Representative, non-limiting examples of the present disclosure have been described in detail with reference to the accompanying drawings. This detailed description is intended to teach those skilled in the art additional details for implementing preferred embodiments of the present disclosure, and is not intended to limit the scope of the present disclosure. Furthermore, the additional features and teachings disclosed above and below can be used alone or in combination with other features and teachings.

[0179] Furthermore, the combinations of features and steps disclosed in the above detailed description and experimental examples are not necessarily required to practice the invention in its broadest sense, but are disclosed merely to specifically illustrate representative examples of the invention. Moreover, various features of the representative examples described above and the following independent and dependent claims can be combined in ways not specifically and explicitly described to provide other useful embodiments of the teachings of the present disclosure.

Claims

1. 1. A resonant MEMS transducer for photoacoustic detection, comprising: a support structure; at least two anchors joined to the support structure; at least one rigid plate; at least one doubly-supported beam, each doubly-supported beam of the at least one doubly-supported beam being fixed at a first point to a corresponding first anchor of the at least two anchors, at a second point to a corresponding second anchor of the at least two anchors, and at a third point to a corresponding first rigid plate of the at least one rigid plate; a through hole defined by the support structure and the at least one rigid plate; at least one electrode configured for piezoelectric transduction; The resonant MEMS transducer is configured to operate at a low resonant frequency, and the through-hole is configured to expose the at least one rigid plate to a surrounding environment.

2. 2. The transducer of claim 1, wherein the low resonant frequency is 100 kHz or less.

3. 3. The transducer of claim 1 or 2, wherein the resonant MEMS transducer is configured to operate in one or a combination of: (i) a single-ended mode; and (ii) a differential mode.

4. A transducer according to any one of claims 1 to 3, wherein the resonant MEMS transducer is configured to operate with an out-of-plane eigenmode.

5. The transducer of any one of claims 1 to 4, wherein the support structure is further bonded to a substrate, the substrate further comprising a substrate through-hole.

6. 6. The transducer of claim 5, wherein the substrate through-hole is approximately the same size as and aligned with the at least one rigid plate, and each rigid plate of the at least one rigid plate resonates with reduced squeeze film damping.

7. 7. A transducer as described in any one of claims 1 to 6, wherein each of the at least one doubly-supported beams has a first corresponding electrode of the at least one electrode patterned on at least a portion thereof near the first point, and each of the at least one doubly-supported beams has a second corresponding electrode of the at least one electrode patterned on at least a portion thereof near the second point.

8. A transducer according to any preceding claim, wherein each electrode of the at least one electrode is configured to operate as a detection electrode.

9. The transducer of any one of claims 1 to 8, wherein the resonant MEMS transducer further comprises at least one long, doubly supported beam and at least one internal beam.

10. 10. The transducer of claim 9, wherein each of the at least one elongated doubly-supported beams is fixed to a first corresponding anchor of the at least two anchors at a fourth point, fixed to a second corresponding anchor of the at least two anchors at a fifth point, connected to a first corresponding rigid plate of the at least one rigid plate at a sixth point, connected to a second corresponding rigid plate of the at least one rigid plate at a seventh point, connected to a first corresponding internal beam of the at least one internal beam at an eighth point, and connected to a second corresponding internal beam of the at least one internal beam at a ninth point.

11. 11. The transducer of claim 10, wherein each internal beam of the at least one internal beam is connected to a first corresponding long-length doubly-supported beam of the at least one long-length doubly-supported beam at a tenth point, connected to a second corresponding long-length doubly-supported beam of the at least one long-length doubly-supported beam at an eleventh point, and connected to a first corresponding long-length doubly-supported beam of the at least one rigid plate at a twelfth point.

12. The transducer of claim 11 , wherein the at least one rigid plate further comprises a first rigid plate and a second rigid plate.

13. 13. The transducer of claim 12, wherein the substrate through-hole is approximately the same size as the first rigid plate and is aligned with the first rigid plate to allow differential movement.

14. A PAS transducer comprising the resonant MEMS transducer according to any one of claims 1 to 13.

15. 15. A method for manufacturing an optoacoustic system, comprising bonding a PAS transducer according to claim 14 to an acoustic cell.

16. 1. A resonant MEMS transducer for photoacoustic detection, comprising: a support structure; at least one anchor joined to the support structure; A rigid plate; at least one cantilever beam, each cantilever beam of the at least one cantilever beam being fixed at a first point to a corresponding first one of the at least one anchor and connected to the rigid plate at a second point; a through hole defined by the support structure and the rigid plate; at least one electrode configured for piezoelectric transduction; The resonant MEMS transducer is configured to operate at a low resonant frequency, and the through-hole is configured to expose the rigid plate to a surrounding environment.

17. 17. The transducer of claim 16, wherein the resonating MEMS transducer is configured to operate according to one or a combination of: (i) an out-of-plane eigenmode, (ii) a first seesaw eigenmode, and (iii) a second seesaw eigenmode.

18. 18. The transducer of claim 16 or 17, wherein each cantilever beam of the at least one cantilever beam is patterned with a first corresponding electrode of the at least one electrode over at least a portion thereof, near the first point.

19. The transducer of any one of claims 16 to 18, wherein the support structure is further bonded to a substrate, the substrate further comprising a substrate through-hole.

20. An optoacoustic system including the transducer defined in any one of claims 16 to 19, an acoustic cell filled with a sample gas and operatively connected to said rigid plate; the acoustic cell is configured to generate acoustic waves within the acoustic cell when the sample gas is exposed to a source of electromagnetic radiation; the rigid plate is configured to be excited by the acoustic wave; Photoacoustic system.

Images