Resonant MEMS transducers for use at low frequencies

Abstract

This disclosure provides a resonant MEMS transducer. The resonant MEMS transducer includes a support structure, at least one anchor, at least one rigid plate, at least one clamped-clamped beam, a through hole and at least one electrode. Each respective clamped-clamped beam from the at least one clamped-clamped beam is anchored at a first point to a first respective anchor from the at least one anchor, anchored at a second point to a second respective anchor from the at least one anchor, and connected at a third point to a first respective rigid plate from the at least one rigid plate. The resonant MEMS transducer is configured to operate at a low resonance frequency and be exposed to the surrounding environment.

Description

Resonant MEMS Transducers for Use at Low Frequencies

[0001] The present application claims priority from U.S. provisional patent application No. 63 / 480,069 filed on January 16, 2023, incorporated herein by reference.TECHNICAL FIELD

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

[0003] Microelectromechanical systems (MEMS) are integrated devices that combine mechanical and electrical components. Because of their extensive optical, electrical and mechanical functionalities, MEMS devices are suitable for use in many different fields of science and engineering depending on their design. In this disclosure, resonant MEMS transducers are provided.SUMMARY

[0004] A MEMS resonator designed to operate at a relatively low frequency (32 kHz) is described in Serrano et al. “Electrostatically Tunable Piezoelectric-on-Silicon Micromechanical Resonator for Real-Time Clock” Vol. 59, No. 3, comprising a support structure, at least one anchor, a rigid plate, at least one clamped-clamped beam and at least one electrode. This MEMS resonator is a piezoelectric-on-silicon MEMS resonator. The support structure doubles as a tuning electrode for electrostatic de tuning. The rigid plate further includes multiple etch holes which are necessary to release the rigid plate from the handle layer and reduce squeeze film damping induced by the large area of the rigid plate.

[0005] A resonant MEMS transducer with at least one rigid plate may be advantageous for sensing applications. In particular, it may be advantageous if the resonant MEMS transducer is configured to operate without the need for a de tuning electrode. Furthermore, it may be advantageous if the resonant MEMS transducer is configured to operate and perform well when exposed to a surrounding environment (i.e. operation even in the absence of low vacuum, including conditions from above atmospheric pressures to much lower pressures) with reduced squeeze film damping or with control over the region or the rigid plate subject to squeeze film damping. It may also be advantageous if a differential mode of operations was enabled, or if switching between a differential mode of operation and a single-ended mode of operation was enabled.

[0006] As such, the present disclosure describes several resonant MEMS transducers for use atlow frequency, which do not require a de tuning electrode. Furthermore, the resonant MEMS transducers as described herein may perform well while exposed to the surrounding environment with reduced squeeze film damping or with control over the region or the rigid plate subject to squeeze film damping. The resonant MEMS transducers as described herein include a through hole defined by at least one rigid plate and a support structure that exposes the at least one rigid plate to pressure variations in the surrounding environment. Additionally, the resonant MEMS transducers as described herein may be joined to a substrate, which may provide control over the region or the rigid plate subject to squeeze film damping. Several resonant MEMS transducers for use in a differential mode of operation are provided. Finally, resonant MEMS transducers which may switch between differential and single-ended modes of operation are provided.

[0007] A resonant MEMS transducer for photoacoustic sensing is provided. The resonant MEMS transducer includes a support structure, at least one anchor, joined to the support structure, at least one rigid plate, at least one clamped-clamped beam, wherein each respective clamped-clamped beam from the at least one clamped-clamped beam is anchored at a first point to a first respective anchor from the at least one anchor, anchored at a second point to a second respective anchor from the at least one anchor, and connected at a third point to a first respective rigid plate from 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. The resonant MEMS transducer is configured to operate at a low resonance frequency, and wherein the through hole is configured to expose the at least one rigid plate to a surrounding environment.

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

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

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

[0011] In some embodiments, the support structure is further joined to the substrate, and the substrate further includes a substrate through hole.

[0012] In some further embodiments, the substrate through hole is of approximately the same size as the at least one rigid plate and aligned with the at least one rigid plate, such that each respective rigid plate from the at least one rigid plate resonates with reduced squeeze film damping.

[0013] In some embodiments, each respective clamped-clamped beam from the at least oneclamped-clamped beam is at least partially patterned near the first point with a first respective electrode from the at least one electrode, and wherein each respective clamped-clamped beam from the at least one clamped-clamped beam is at least partially patterned near the second point with a second respective electrode from the at least one electrode.

[0014] In some embodiments, each respective electrode from the at least one electrode is configured to operate as a sensing electrode.

[0015] In some embodiments, the resonant MEMS transducer further includes at least one long clamped-clamped beam and at least one internal beam.

[0016] In some further embodiments, each respective long clamped-clamped beam from the at least one long clamped-clamped beam is anchored at a fourth point to a first respective anchor from the at least one anchor, anchored at a fifth point to a second respective anchor from the at least one anchor, connected at a sixth point to a first respective rigid plate from the at least one rigid plate, connected at a seventh point to a second respective rigid plate from the at least one rigid plate, connected at a eighth point to a first respective internal beam from the at least one internal beam and connected at a ninth point to a second respective internal beam from the at least one internal beam.

[0017] In some further embodiments, each respective internal beam from the at least one internal beam is connected at a tenth point to a first respective long clamped-clamped beam from the at least one long clamped-clamped beam, connected at an eleventh point to a second respective long clamped-clamped beam from the at least one long clamped-clamped beam, and connected at a twelfth point to a first respective rigid plate from the at least one rigid plate.

[0018] In some further embodiments, the at least one rigid plate further includes a first rigid plate and a second rigid plate.

[0019] In some further embodiments, the substrate through hole is of approximately the same size as the first rigid plate and aligned with the first rigid plate, such that the substrate through hole enables differential operation.

[0020] In some embodiments, a PAS transducer including the resonant MEMS transducer 200 as defined is provided.

[0021] In some embodiments, a method of manufacturing a photoacoustic system 210 by joining a PAS transducer to an acoustic cell 200 is provided.

[0022] A further resonant MEMS transducer for photoacoustic sensing is provided. The resonantMEMS transducer includes a support structure, at least one anchor, joined to the support structure, a rigid plate, at least one serpentine beam, wherein each respective serpentine beam from the at least one serpentine beam is anchored at a first point to a first respective anchor from the at least one anchor and is connected at a second point to the rigid plate, a through hole defined by the support structure and the rigid plate, at least one electrode. The resonant MEMS transducer is configured to operate at a low resonance frequency, and wherein the through hole is configured to expose the rigid plate to a surrounding environment.

[0023] In some embodiments the low resonance frequency includes 100 kHz or less.

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

[0025] In some embodiments, the resonant MEMS transducer is configured to operate in one or a combination of (i) the out-of-plane eigenmode, (ii) the first teeter-totter eigenmode and (iii) the second teeter-totter eigenmode.

[0026] In some further embodiments, the resonant MEMS transducer is configured to switch between two or more of (i) the out-of-plane eigenmode, (ii) the first teeter-totter eigenmode and (iii) the second teeter-totter eigenmode.

[0027] In some embodiments, each respective serpentine beam from the at least one serpentine beam is at least partially patterned near the first point with a first respective electrode from the set of the at least one electrode.

[0028] In some embodiments, the support structure is further joined to the substrate, and wherein the substrate further includes the substrate through hole.

[0029] In some embodiments, the substrate through hole is of approximately the same size as the rigid plate and aligned with the rigid plate.

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

[0031] In some embodiments, a photoacoustic system including the resonant MEMS transducer is defined, including the acoustic cell filled with a sample gas operatively connected to the rigid plate, wherein the acoustic cell is configured to produce an acoustic wave within the acoustic cell when the sample gas is exposed to an electromagnetic radiation source, and wherein the rigid plate is configured to be excited by the acoustic wave.

[0032] In some further embodiments, the first half of the rigid plate is operatively connected tothe acoustic cell filled with the sample gas, and wherein the rigid plate is adapted to be excited at the first half of the rigid plate when exposed to the acoustic wave, for enabling differential operation.

[0033] In some further embodiments, a central region of the rigid plate is operatively connected to the acoustic cell filled with the sample gas, and wherein the rigid plate is adapted to be excited at the central region of the rigid plate when exposed to the acoustic wave, for enabling single- ended operation.

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

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

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

[0037] In some further embodiments, the first acoustic cell is filled with the sample gas, wherein the second acoustic cell is filled with an inert gas, wherein only the first acoustic cell is configured to produce a first acoustic wave within the first acoustic cell when the sample gas of the first acoustic cell and the inert gas of the second acoustic cell are exposed to the electromagnetic radiation source, the first acoustic wave exciting the first half of the rigid plate, enabling differential operation. Herein and throughput this disclosure, inert gas refers to a gas which exhibits minimal response to exposure to the electromagnetic radiation source.

[0038] In some embodiments, the at least one electrode is further connected to an electronic circuit capable of switching the electrode polarity, such that switching between differential and single- ended operation is enabled.

[0039] Another broad aspect is a resonant MEMS transducer for photoacoustic sensing comprising a support structure; at least two anchors, joined to the support structure; at least one rigid plate; at least one clamped-clamped beam, wherein each respective clamped-clamped beam from the at least one clamped-clamped beam is anchored at a first point to a first respective anchor from the at least two anchors, anchored at a second point to a second respective anchor from the at least two anchors, and connected at a third point to a first respective rigid plate from the at least one rigid plate; a through hole defined by the support structure and the at least one rigid plate; and at least one electrode configured for piezoelectric transduction; and wherein the resonant MEMS transducer is configured to operate at a low resonance frequency, and wherein the through hole is configured to expose the at least one rigid plate to a surrounding environment.

[0040] In some embodiments, the low resonance frequency may include 100 kHz or less.

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

[0042] In some embodiments, the resonant MEMS transducer may be configured to operate in an out-of-plane eigenmode.

[0043] In some embodiments, the support structure may be further joined to a substrate, and wherein the substrate further comprises a substrate through hole.

[0044] In some embodiments, the substrate through hole may be of approximately the same size as the at least one rigid plate and aligned with the at least one rigid plate, such that each respective rigid plate from the at least one rigid plate resonates with reduced squeeze film damping.

[0045] In some embodiments, each respective clamped-clamped beam from the at least one clamped-clamped beam may be at least partially patterned near the first point with a first respective electrode from the at least one electrode, and wherein each respective clamped-clamped beam from the at least one clamped-clamped beam may be at least partially patterned near the second point with a second respective electrode from the at least one electrode.

[0046] In some embodiments, each respective electrode from the at least one electrode may be configured to operate as a sensing electrode.

[0047] In some embodiments, the resonant MEMS transducer may include at least one longclamped-clamped beam and at least one internal beam.

[0048] In some embodiments, each respective long clamped-clamped beam from the at least one long clamped-clamped beam may be anchored at a fourth point to a first respective anchor from the at least two anchors, anchored at a fifth point to a second respective anchor from the at least two anchors, connected at a sixth point to a first respective rigid plate from the at least one rigid plate, connected at a seventh point to a second respective rigid plate from the at least one rigid plate, connected at an eighth point to a first respective internal beam from the at least one internal beam and connected at a ninth point to a second respective internal beam from the at least one internal beam.

[0049] In some embodiments, each respective internal beam from the at least one internal beam may be connected at a tenth point to a first respective long clamped-clamped beam from the at least one long clamped-clamped beam, connected at an eleventh point to a second respective long clamped-clamped beam from the at least one long clamped-clamped beam, and connected at a twelfth point to a first respective rigid plate from the at least one rigid plate.

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

[0051] In some embodiments, the substrate through hole may be of approximately the same size as the first rigid plate and aligned with the first rigid plate, such that the substrate through hole may enable differential operation.

[0052] Another broad aspect is a PAS transducer comprising the resonant MEMS transducer as defined herein.

[0053] Another broad aspect is a method of manufacturing a photoacoustic system comprising joining a PAS transducer to an acoustic cell as defined in claim herein.

[0054] Another broad aspect is a resonant MEMS transducer for photoacoustic sensing, including a support structure; at least one anchor, joined to the support structure; a rigid plate; at least one cantilever beam, wherein each respective cantilever beam from the at least one cantilever beam is anchored at a first point to a first respective anchor from the at least one anchor and is connected at a second point to the rigid plate; a through hole defined by the support structure and the rigid plate; and at least one electrode configured for piezoelectric transduction; and wherein the resonant MEMS transducer is configured to operate at a low resonance frequency, and wherein the through hole is configured to expose the rigid plate to a surrounding environment.

[0055] In some embodiments, the resonant MEMS transducer may be configured to operate in one or a combination of (i) an out-of-plane eigenmode, (ii) a first teeter-totter eigenmode and (iii) a second teeter-totter eigenmode.

[0056] In some embodiments, each respective cantilever beam from the at least one cantilever beam may be at least partially patterned near the first point with a first respective electrode from the set of the at least one electrode.

[0057] In some embodiments, the support structure may be further joined to a substrate, and wherein the substrate may include a substrate through hole.

[0058] In some embodiments, the at least one cantilever beam may be a serpentine beam.

[0059] In some embodiments, the cantilever beam may be a curved beam.

[0060] Another broad aspect is a photoacoustic system including the transducer as defined herein, comprising an acoustic cell filled with a sample gas operatively connected to the rigid plate, wherein the acoustic cell is configured to produce an acoustic wave within the acoustic cell when the sample gas is exposed to an electromagnetic radiation source, and wherein the rigid plate is configured to be excited by the acoustic wave.BRIEF DESCRIPTION OF THE DRAWINGS

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

[0062] Figure 1 A depicts a perspective view of an example acoustic cell.

[0063] Figure IB depicts a cross-sectional view of an example acoustic cell.

[0064] Figure 2A depicts a top view of a resonant MEMS transducer operated via a single-ended mode.

[0065] Figure 2B depicts a cross-sectional view of a resonant MEMS transducer operated via a single-ended mode.

[0066] Figure 2C depicts a phase image of an out-of-plane eigenmode of a resonant MEMS transducer operated via a single-ended mode.

[0067] Figure 2D depicts a cross-sectional view of an example photoacoustic system operated via a single-ended mode.

[0068] Figure 3A depicts a top view of a resonant MEMS transducer operated via a differential mode.

[0069] Figure 3B depicts a cross-sectional view of a resonant MEMS transducer for enabling adifferential mode.

[0070] Figure 3C depicts a phase image of an out-of-plane eigenmode of a resonant MEMS transducer operated via a differential mode.

[0071] Figure 3D depicts a cross-sectional view of an example photoacoustic system operated via a differential mode.

[0072] Figure 4A depicts a top view of a resonant MEMS transducer operated via either or both a single-ended and a differential mode.

[0073] Figure 4B depicts a phase image of three eigenmodes of a resonant MEMS transducer operated via either or both a single-ended and a differential mode.

[0074] Figure 4C depicts a cross-sectional view of a photoacoustic system for enabling either a single-ended and a differential mode.

[0075] Figure 4D depicts a cross-sectional view of a photoacoustic system for enabling switching between a single-ended and a differential mode.

[0076] Figure 5A depicts a top view of a resonant MEMS transducer operated via a differential mode.

[0077] Figure 5B depicts a phase image of an out-of-plane eigenmode of a resonant MEMS transducer operated via a differential mode.

[0078] Figure 6A depicts a perspective view of a resonant MEMS transducer with cantilever beams.

[0079] Figure 6B depicts a top view of a resonant MEMS transducer with cantilever beams.

[0080] Figure 6C depicts a cross-sectional view of a resonant MEMS transducer with cantilever beams.DETAILED DESCRIPTION

[0081] This disclosure provides resonant MEMS transducers which are configured to operate at a low resonance frequency, while exposed to the surrounding environment. To provide context, information on applications which may utilize such attributes, specifically photoacoustic spectroscopy (PAS) is provided. This information is provided for the purpose of illustrating the general principles of the present disclosure and is not meant to limit the inventive concepts claimed herein. In some embodiments, “low resonance frequency” may involve operating a resonant MEMS transducer at a frequency below approximately 300 kHz. In other embodiments, “low resonance frequency” may involve operating the resonant MEMS transducer at a frequency belowapproximately 100 kHz. Still in other embodiments, “low resonance frequency” may involve operating the resonant MEMS transducer at a frequency below approximately 10 kHz.I. Overview of PAS

[0082] This disclosure provides resonant MEMS transducers which are configured to operate at a low resonance frequency, while exposed to the surrounding environment. Resonant MEMS transducers with these attributes may be of use in a variety of applications, including for photoacoustic spectroscopy (PAS). PAS is well suited for use in continuous monitoring applications or large-scale applications (medical, military, pollution monitoring, manufacturing etc.) which may require high throughput and accurate detection of trace amounts of a target analyte molecule in environments with variable temperature, humidity and background molecules found within a sample gas. PAS utilizes an electromagnetic radiation source to excite any target analyte molecules within the sample gas, thus generating pressure waves (also known as acoustic waves) to sense and convert (i.e. transduce) into electrical signals. Furthermore, PAS-based systems can be adapted to detect virtually any molecule by changing the output of the electromagnetic radiation source (for example, by tuning a laser wavelength), while retaining a high specificity.

[0083] In PAS, electromagnetic radiation of wavenumber u [cm'1] is absorbed by any target analyte molecules in the sample gas as it traverses at a rate proportional to the molar density p [mol cm'3] of the target analyte molecules, the absorption cross-section c(u) [cm2mol'1] at wavenumber u, and the electromagnetic radiation source intensity I [W cm'2] at wavenumber u. The subsequent relaxation of the target analyte molecules to the molecular ground state can occur through a number of processes: radiation (stimulated or spontaneous emission of a photon), chemical reactions, non-radiative relaxation, or a combination of these processes. Non-radiative relaxation can lead to an increase in the kinetic energy of the surrounding molecules, creating local heating and a corresponding increase in pressure. If the absorption process is periodically modulated either by the electromagnetic radiation source (intensity or frequency), or by shifting the absorption lines, then the induced periodic heating will produce a pressure wave (also known as an acoustic wave) at the same frequency. This periodic thermal excitation drives an acoustic resonance in the acoustic cell that is measured as pressure by a transducer. Several types of transducers may be suitable for PAS, including both resonant transducers and non-resonant transducers. Suitable resonant transducers may include resonant microelectromechanical system (MEMS) transducers and quartz tuning forks (QTFs). Additionally, non-resonant transducers suchas non-resonant broadband MEMS microphones, condenser microphones and electrets may be used. The pressure p [Pa] at the transducer location is proportional to the density, absorption crosssection and electromagnetic radiation source intensity, such that: p oc p a(v) I

[0084] Ideally, the transducer is suitable for low frequency applications, such that it can be strongly coupled to the acoustic wave. Furthermore, transducers suitable for low frequency resonance modes may be preferable because the photoacoustic signal is inversely proportional to the resonance frequency of the transducer, meaning that operating at a lower modulation frequency may result in a higher photoacoustic signal intensity even for fast-relaxing energy states.

[0085] Herein and throughout this disclosure, “sample gas” refers to a gas which may or may not have a sufficient quantity of the target analyte molecules within it to be detectable by PAS.

[0086] Figure 1 A depicts a perspective view of an example acoustic cell 100, which may be found in the prior art. Acoustic cell 100 includes a central resonator cavity 102 and an acoustic port 106. In this example, the central resonator cavity 102 is an open-ended cylindrical tube into which the sample gas may be introduced, and electromagnetic radiation may pass through. Figure 1A is provided for context, though many other designs may be possible for the acoustic cell 100, such as acoustic cells with a central resonator cavity and multiple buffer volumes, Helmholtz type acoustic cells, and acoustic cells for asymmetric excitation, among others whether now known or later developed may be utilized.

[0087] Figure IB depicts a cross-sectional view of the example acoustic cell 100.II. Resonant MEMS Transducer Designs

[0088] Figures 2A-C depict a resonant MEMS transducer 200. The resonant MEMS transducer 200 is a thin-film piezoelectric-on-silicon resonator. Piezoelectric transduction is chosen for its ease of fabrication and performance in the absence of low vacuum (i.e. resonant MEMS transducer may be exposed to the surrounding environment in atmospheric or near-atmospheric pressure). Furthermore, as compared to capacitive transduction, piezoelectric transducers can provide larger displacements at low voltage, thereby improving signal to noise ratio.

[0089] In Figures 2A-B, the resonant MEMS transducer 200 includes a support structure 209, at least one anchor 208, at least one rigid plate 206, at least one clamped-clamped beam 204, a through hole 205 and at least one electrode 210. The at least one anchor 208 is joined to the support structure 209. Each respective clamped-clamped beam from the at least one clamped-clampedbeam 204 is anchored at a first point 2 aO4A to a first respective anchor from the at least one anchor 208, anchored at a second point 204B to a second respective anchor from the at least one anchor 208, and connected at a third point 204C to a first respective rigid plate from the at least one rigid plate 206. The through hole 205 is defined 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 resonance frequency. The through hole 205 is configured to expose the at least one rigid plate 206 to a surrounding environment.

[0090] For clarity, only a single example of the first point 204 A, the second point 204B and the third point 204C are only shown in Figure 2 A. It is important to note that each respective clampedclamped beam from the at least one clamped-clamped beam 204 is anchored / connected in this manner.

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

[0092] The at least one anchor 208 joins the at least one clamped-clamped beam 204 to the support structure 209.

[0093] Each respective clamped-clamped beam from the at least one clamped-clamped beam 204 is mechanically coupled through the at least one rigid plate 206. The at least one clamped-clamped beam 204 serves two purposes (i) providing control over the resonance frequency of the resonant MEMS transducer 200 via the beam dimensions and (ii) providing a piezoelectric transduction region, such that high mechanical stress can be isolated 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 may be used to sense pressure waves.

[0094] The through hole 205 is configured to expose the at least one rigid plate 206 to the surrounding environment. Herein and throughout this disclosure, the surrounding environment includes the volume within and beyond that typically encompassed by a MEMS package (i.e. beyond ~2 mm x ~2 mm x ~2 mm). The through hole 205 is approximately the same size as the at least one rigid plate 206. Herein and throughout this disclosure “the through hole is approximately the same size as the at least one rigid plate 206” will be understood to mean that the through hole 205 has an area sufficiently large to encompass at least the at least one rigid plate 206 and the at least one clamped-clamped beam 204. Additionally, it can be seen that the through hole 205 is aligned with the at least one rigid plate 206, such that there is no support structure 209below the at least one rigid plate 206. Thus, the at least one rigid plate 206 may resonate freely and squeeze film damping is reduced (reduced with respect to the squeeze film damping of a MEMS transducer with an identical design except that the through hole has been removed such that there is a solid support structure).

[0095] Each electrode from the at least one electrode 210 is a piezoelectric electrode. A piezoelectric material layer is patterned, at least partly, over each respective clamped-clamped beam from the at least one clamped-clamped beam 204 and each respective anchor from the at least one anchor 208. A metal layer is patterned, at least partly, over the piezoelectric material layer, to form a single electrode. In the examples described herein, the piezoelectric material layer may include AIN, ZnO, PZT, ScAlN or other piezoelectric materials. Additionally, in the examples described herein, the metal layer may include molybdenum, platinum, or aluminum or other metals. A common ground reference may also be connected to the at least one electrode 210.

[0096] In some embodiments, the low resonance frequency includes 100 kHz or less.

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

[0098] In some embodiments, the resonant MEMS transducer 200 is configured to operate in an out-of-plane eigenmode. It will be understood that the out-of-plane eigenmode will also include substantially out-of-plane eigenmodes.

[0099] In some embodiments, the support structure 209 is further joined to the substrate 112, and the substrate 112 further includes a substrate through hole 113.

[0100] In some further embodiments, the substrate through hole 113 is of approximately the same size as the at least one rigid plate 206 and aligned with the at least one rigid plate 206, such that each respective rigid plate from the at least one rigid plate 206 resonates with reduced squeeze film damping. Herein and throughout this disclosure “the substrate through hole is of approximately the same size as the at least one rigid plate” will be understood to mean that the substrate through hole 113 has an area sufficiently large to encompass at least the at least one rigid plate 206 and the at least one clamped-clamped beam 204.

[0101] In some embodiments, each respective clamped-clamped beam from the at least one clamped-clamped beam is at least partially patterned near the first point 204A with a first respective electrode from the at least one electrode 210, and wherein each respective clampedclamped beam from the at least one clamped-clamped beam 204 is at least partially patterned nearthe second point 204B with a second respective electrode from the at least one electrode 210. It will be understood that because a pattern covers a set of points, the pattern located near the first point 204A may also cover (i) the first point 204A, (ii) the anchor adjacent to the first point 204A and (iii) a segment of length L on each of the two clamped-clamped beams adjacent to the first point 204A (where length L is approximately 14 of the length of a respective clamped-clamped beam). Similarly, the pattern near the second point 204B may also cover (i) the second point 204B, (ii) the anchor adjacent to the second point 204B and (iii) a segment of length L on each of the two clamped-clamped beams adjacent to the second point 204B.

[0102] In some embodiments, each respective electrode from the at least one electrode 210 is configured to operate as a sensing electrode.

[0103] Figure 2C depicts a single phase of a preferred eigenmode of the resonant MEMS transducer 200, an out-of-plane eigenmode.

[0104] The resonant MEMS transducer 200 is configured to operate in an out-of-plane eigenmode. As the resonant MEMS transducer 200 is single-ended, the signal generated by the at least one electrode 210 will be in-phase and may be summed to produce a larger signal output. Additionally, due to the uniform displacement of the at least one rigid plate 206, the resonant MEMS transducer 200 is straightforward to join to another structure via the support structure 209.

[0105] In some examples, the resonant MEMS transducer 200 has a resonance frequency of approximately 15 kHz. In this example, the dimensions of the proof mass (i.e. all rigid plates and clamped-clamped beams combined) of the resonant MEMS transducer 200 is relatively large, approximately 1050 pm by 1050 pm. Based on finite element model (FEM) simulations, in this example, the resonant MEMS transducer 200 has QroT(piezo) ~ 10k, where QroT(piezo) is the total quality factor with the piezoelectric material layer included, in vacuum.

[0106] In some examples, the resonant MEMS transducer 200 has a resonance frequency of approximately 32 kHz. In this example, the proof mass of the resonant MEMS transducer 200 is relatively small, approximately 770 pm by 770 pm. Based on FEM simulations, in this example, the resonant MEMS transducer 200 has QTOT(piezo) ~ 10k.

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

[0108] The substrate through hole 113 is at least partly aligned with the through hole 205, Thus, the at least one rigid plate 206 is operatively connected to the acoustic cell 100. The alignment of the substrate through hole 113 is configured to enable single-ended operation of the resonant MEMS transducer 200, as it enables the at least one rigid plate 206 to be operatively connected to the acoustic cell 100. Herein and throughout this disclosure, ‘operatively connected’ means that acoustic waves produced in an acoustic cell excite at least a portion of a resonant MEMS transducer.

[0109] The substrate 112 may be formed from a printed circuit board, plastic, metal or other substantially planar materials. The resonant MEMS transducer 200 may be joined to the substrate 112 with epoxy, solder, wirebonding or other methods known in the art. The substrate 112 may be joined to the acoustic cell 100 with epoxy, structural elements or other methods known in the art.

[0110] In some embodiments, a PAS transducer including the resonant MEMS transducer 200 as defined is provided.

[0111] In some embodiments, a method of manufacturing a photoacoustic system 210 by joining a PAS transducer to an acoustic cell 200 is provided.

[0112] Figures 3 A-B depict a differential resonant MEMS transducer 300. The resonant MEMS transducer 300 is a thin-film piezoelectric-on-silicon resonator.

[0113] The resonant MEMS transducer 300 includes a support structure 309, at least one anchor 308, at least one clamped-clamped beam 304, at least one rigid plate 306, at least one long clamped-clamped 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 joined to the support structure 309. Each respective clamped-clamped beam from the at least one clamped-clamped beam 304 is anchored at a first point 304 A to a first respective anchor from the at least one anchor 308, anchored at a second point 304B to a second respective anchor from the at least one anchor 308, and connected at a third point 304C to a first respective rigid plate from the at least one rigid plate 306. Each respective long clamped-clamped beam from the at least one long clamped-clamped beam 305 is anchored at a fourth point 305 A to a first respective anchor from the at least one anchor 308, anchored at a fifth point 305B to a second respective anchor from the at least one anchor 308, connected at a sixth point 305C to a first respective rigid plate from the at least one rigid plate 308, connected at a seventh point 305D to a second respective rigid plate from the at least one rigid plate 306, connected at a eighth point 305E to a first respective internal beam from the at least one internalbeam 307 and connected at a ninth point 305F to a second respective internal beam from the at least one internal beam 307. Each respective internal beam from the at least one internal beam 307 is connected at a tenth point 307A to a first respective long clamped-clamped beam from the at least one long clamped-clamped beam 305, connected at a eleventh point 307B to a second respective long clamped-clamped beam from the at least one long clamped-clamped beam 305, and connected at a twelfth point 307C to a first respective rigid plate from the at least one rigid plate 306. A 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 resonance frequency. The through hole 301 is configured to expose the at least one rigid plate 306 to the surrounding environment.

[0114] For clarity, only a single example of the first point 304A, the second point 304B, the third point 304C, the fourth point 305A, the fifth point 305B, the sixth point 305C, the seventh point 305D, the eighth point 305E, the ninth point 305F, the tenth point 307 A, the eleventh point 307B and the twelfth point 307C are shown in Figure 3A. It is important to note that each respective clamped-clamped beam, long clamped-clamped beam or internal beam can be defined in this manner. It will be understood that as a result of the multiple ways that the points may be defined, points may overlap. For example, eighth point 305E is identical to tenth point 307A in Figure 3A.

[0115] The support structure 309 allows the joining of the resonant MEMS transducer 300 to another structure, such as the acoustic port 106 or the substrate 112 (not shown in this figure).

[0116] The at least one anchor 308 joins the at least one clamped-clamped beam 304 and the at least one long clamped-clamped beam 305 to the support structure 309.

[0117] Each respective clamped-clamped beam from the at least one clamped-clamped beam 304 and each respective long clamped-clamped beam from the at least one long clamped-clamped beam 305 is mechanically through the at least one rigid plate 306. The clamped-clamped beams 304 and the long clamped-clamped beams 305 serve two purposes, (i) providing control over the resonance frequency of the resonant MEMS transducer 300 via the beam dimensions and (ii) providing a piezoelectric transduction region, such that high mechanical stress can be isolated 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 may be used to sense pressure waves.

[0118] The through hole 301 is configured to expose the at least one rigid plate 306 to the surrounding environment. It can be seen that the through hole 301 in the support structure 309 isapproximately the same size of as the at least one rigid plate 306. Additionally, it can be seen that the through hole 301 in the support structure 309 is aligned with the at least one the rigid plate 306, such that there is no support structure 309 below the at least one the rigid plate 306. Thus, the at least one rigid plate 306 may resonate freely and squeeze film damping is reduced (reduced with respect to the squeeze film damping of a MEMS transducer with an identical design except that the through hole has been removed such that there is a solid support structure).

[0119] Each electrode from the at least one electrode 310 is a piezoelectric electrode. A piezoelectric material layer is patterned, at least partly, over each respective clamped-clamped beam from the at least one clamped-clamped beam 304 and each respective anchor from the at least one anchor 308. A metal layer is patterned, at least partly, over the piezoelectric material layer, to form a single electrode. The same is true for the at least one long clamped-clamped beam 305. In the examples described herein, the piezoelectric material layer may include AIN, ZnO, PZT, ScAlN or other piezoelectric materials. Additionally, in the examples described herein, the metal layer may include molybdenum, platinum, or aluminum or other metals. A common ground reference may also be connected to the at least one electrode 310.

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

[0121] In some embodiments, the resonant MEMS transducer 300 is configured to operate in a differential mode. When resonant MEMS transducer 300 operates in a differential mode, the at least one rigid plate 306 move out of phase with each other, thus the strain in the anchor elements and the generated voltage are of opposite sign. Thus, subtracting voltage signals will allow for cancellation of common-mode noise.

[0122] In some embodiments, the resonant MEMS transducer 300 is configured to operate in an out-of-plane eigenmode. It will be understood that the out-of-plane eigenmode will also cover substantially out-of-plane eigenmodes.

[0123] In some embodiments, the support structure 309 is further joined to the substrate 112, and the substrate further includes a substrate through hole 113.

[0124] In some embodiments, the substrate through hole 113 is of approximately the same size as the at least one rigid plate 306 and aligned with the at least one rigid plate 306, such that each respective rigid plate from the at least one rigid plate 306 resonates with reduced squeeze film damping.

[0125] In some embodiments, each respective clamped-clamped beam from the at least oneclamped-clamped beam 304 is at least partially patterned near the first point 304A with a first respective electrode from the at least one electrode 310, and wherein each respective clampedclamped beam from the at least one clamped-clamped beam 304 is at least partially patterned near the second point 304B with a second respective electrode from the at least one electrode 310. It will be understood that because a pattern covers a set of points, the pattern near the first point 304 A may also cover (i) the first point 304 A, (ii) the anchor adjacent to the first point 304 A, (iii) a segment of length L on the respective clamped-clamped beam (where length L is equivalent to approximately 14 of the length of the respective clamped-clamped beam) and (iv) a segment of length L on the long clamped-clamped beam adjacent to the first point 304 A. Similarly, the pattern near the second point 304B may also cover (i) the second point 304B, (ii) the anchor adjacent to the second point 304B, (iii) a segment of length L on the respective clamped-clamped beams and (iv) a segment of length L on the long clamped-clamped beams adjacent to the second point 304B.

[0126] In some embodiments, each respective electrode from the at least one electrode 310 is configured to operate as a sensing electrode.

[0127] In some embodiments, the resonant MEMS transducer further includes at least one long clamped-clamped beam 305 and at least one internal beam 307.

[0128] In some further embodiments, each respective long clamped-clamped beam from the at least one long clamped-clamped beam 305 is anchored at a fourth point 305A to a first respective anchor from the at least one anchor 308, anchored at a fifth point 305B to a second respective anchor from the at least one anchor 308, connected at a sixth point 305C to a first respective rigid plate from the at least one rigid plate 308, connected at a seventh point 305D to a second respective rigid plate from the at least one rigid plate 308, connected at a eighth point 305E to a first respective internal beam from the at least one internal beam 307 and connected at a ninth point 305F to a second respective internal beam from the at least one internal beam 307.

[0129] In some further embodiments, each respective internal beam from the at least one internal beam 307 is connected at the tenth point 307A to the first respective long clamped-clamped beam from the at least one long clamped-clamped beam 305, connected at the eleventh point 307B to the second respective long clamped-clamped beam from the at least one long clamped-clamped beam 305, and connected at the twelfth point 307C to the first respective rigid plate from the at least one rigid plate 306.

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

[0131] In some further embodiments, the substrate through hole 113 is of approximately the same size as the first rigid plate 306 A and aligned with the first rigid plate 306 A, such that the substrate through hole 113 enables differential operation.

[0132] Figure 3C depicts a single phase of a preferred eigenmode of resonant MEMS transducer 300, an out-of-plane mode.

[0133] In some examples, the resonant MEMS transducer 300 has a resonance frequency of approximately 15 kHz. In this example, the dimension of the proof mass is relatively large, approximately 1000 pm by 2100 pm. Based on FEM simulations, in this example, the resonant MEMS transducer 300 has a QroT(piezo) ~ 10k.

[0134] In some examples, the resonant MEMS transducer 300 has a resonance frequency of approximately 32 kHz. In this example, the dimension of the proof mass is relatively small, approximately 710 pm by 1600 pm. Based on FEM simulations, in this example, the resonant MEMS transducer 300 has a QroT(piezo) ~ 10k.

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

[0136] The substrate through hole 113 is at least partly aligned with the through hole 301. Thus, the at least one rigid plate 306 is operatively connected to the acoustic cell 100. The alignment of the substrate through hole 113 is configured to enable differential operation of the resonant MEMS transducer 300, by determining which region(s) of the at least one rigid plate 306 is operatively connected to the acoustic cell 100.

[0137] In some embodiments, a PAS transducer including the resonant MEMS transducer 300 as defined is provided.

[0138] In some embodiments, a method of manufacturing the photoacoustic system 310 by joining a PAS transducer to the acoustic cell 100 is provided.

[0139] Figure 4A depicts a resonant MEMS transducer 400. The resonant MEMS transducer 400 is a thin-film piezoelectric-on-silicon resonator.

[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 beam404 (as an exemplary embodiment, the cantilever beam 404 of Figure 4A is a serpentine beam) and at least one electrode 410. The at least one anchor 408 is joined to the support structure 409. Each respective serpentine beam from the at least one serpentine beam 404 is anchored at a first point 404A to a first respective anchor from the at least one anchor 408 and is connected at a second point 404B to the rigid plate 406. 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 resonance frequency. The through hole 401 is configured to expose the rigid plate 406 to a surrounding environment.

[0141] For clarity, only a single example of the first point 404 A and the second point 404B are only shown in Figure 4A. It is important to note that each respective serpentine beam from the at least one serpentine beam 404 is anchored / connected in this manner.

[0142] The support structure 409 allows the joining of the resonant MEMS transducer 400 to another structure, such as the acoustic port 106 or the substrate 112 (not shown in this figure).

[0143] The at least one anchor 408 joins the at least one serpentine beam 404 to the support structure 409.

[0144] Each respective serpentine beam from the at least one serpentine beam 404 is mechanically coupled through the rigid plate 406. The at least one serpentine beam 404 serve two purposes, (i) providing control over the resonance frequency of the resonant MEMS transducer 400 via the beam dimensions and (ii) providing a piezoelectric transduction region, such that high mechanical stress can be isolated from the rigid plate 406. By isolating the high stress piezoelectric transduction region from the rigid plate 406, the rigid plate 406 may be used to sense pressure waves.

[0145] The through hole 401 is configured to expose the rigid plate 406 to the surrounding environment, which may allow the rigid plate 406 to be excited by pressure waves in the surrounding environment. The through hole 401 in the support structure 409 is approximately the same size of as the rigid plate 406. Additionally, the through hole 401 in the support structure 409 is aligned with the rigid plate 406, such that there is no support structure 409 below the rigid plate 306. Thus, the rigid plate 406 may resonate freely and squeeze film damping is reduced (reduced with respect to the squeeze film damping of a MEMS transducer with an identical design except that the through hole has been removed such that there is a solid support structure).

[0146] Each electrode from the at least one electrode 410 is a piezoelectric electrode. Apiezoelectric material layer is patterned, at least partly, over each respective serpentine beam from the at least one serpentine beam 404 and each respective anchor from the at least one anchor 408. A metal layer is patterned, at least partly, over the piezoelectric material layer, to form a single electrode. In the examples described herein, the piezoelectric material layer may include AIN, ZnO, PZT, ScAlN or other piezoelectric materials. Additionally, in the examples described herein, the metal layer may include molybdenum, platinum, or aluminum or other metals. A common ground reference may also be connected to the at least one electrode 410.

[0147] Figure 4B depicts a single phase of a preferred eigenmodes of operation of resonant MEMS transducer 400. Resonant MEMS transducer 400 is configured to operate in one or a combination of (i) an out-of-plane eigenmode, (ii) a first teeter-totter eigenmode and (iii) a second teeter-totter eigenmode. Phase image 412 depicts a single phase of the out-of-plane eigenmode. In the out-of-plane eigenmode, which corresponds to the lowest resonance frequency, the rigid plate 406 moves uniformly out of plane. Phase image 418 depicts a single phase of the first teeter-totter eigenmode. In the first teeter-totter eigenmode, which corresponds to the intermediate resonance frequency, the rigid plate 406 moves in a teeter-totter motion orthogonal to a long axis extending between a first end 421 and a second end 423 of the rigid plate 406. Phase image 416 depicts a single phase of the second teeter-totter eigenmode. In the second teeter-totter eigenmode, which corresponds to the highest resonance frequency, the rigid plate 406 moves in a teeter-totter motion along the long axis of the rigid plate 406.

[0148] Figure 4C depict a cross-sectional view of a photoacoustic system 450. Photoacoustic system 450 includes the resonant MEMS transducer 400, the substrate 112 and the acoustic cell 100. The substrate 112 further includes the substrate through hole 113. The resonant MEMS transducer 400 is joined to the substrate 112. The substrate 112 is joined to the acoustic port 106. The substrate through hole 113 is at least partly aligned with the through hole 401. Thus, the resonant MEMS transducer 400 is operatively connected to the acoustic cell 100. The alignment 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, to excite the out-of-plane eigenmode, the central region of the rigid plate 406 may be operatively connected to the acoustic cell 100. Herein and throughout this disclosure, central region means the region near the center of mass of the rigid plate 406. Additionally, to excite the first teeter-tottereigenmode, the first end 421 of the rigid plate 406 or the second end 423 of the rigid plate 406 may be operatively connected to the acoustic cell 100. Finally, to excite the second teeter-totter eigenmode, a point away from the long axis may be operatively connected to the acoustic cell 100.

[0149] Figure 4D depicts a cross-sectional view of a photoacoustic system 460, which is configured to enable switching between single-ended and differential operation. The photoacoustic system 460 includes the resonant MEMS transducer 400, the substrate 112, a first acoustic cell 492 and a second acoustic cell 494. The substrate 112 is joined resonant MEMS transducer 400. The substrate 112 further includes the substrate through hole 113. The substrate through hole 113 is at least partly aligned with the through hole 401. Thus, the resonant MEMS transducer 400 is operatively connected to either one or both of the first acoustic cell 492 and the second acoustic cell 494, depending on the alignment of the substrate through hole 113. The first acoustic cell 492 and the second acoustic cell 494 may be independently or simultaneously excited, and thus enable either (i) single-ended or (ii) differential operation, or allowing switching between both.

[0150] The first acoustic cell 492 and the second acoustic cell 494 may be any acoustic cell design now known or later discovered, including acoustic cells with a central resonator cavity and multiple buffer volumes, Helmholtz type acoustic cells, and acoustic cells for asymmetric excitation, among others.

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

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

[0153] In some embodiments, the resonant MEMS transducer 400 is configured to operate in one or a combination of (i) the out-of-plane eigenmode, (ii) the first teeter-totter eigenmode and (iii) the second teeter-totter eigenmode.

[0154] In some further embodiments, the resonant MEMS transducer 400 is configured to switch between two or more of (i) the out-of-plane eigenmode, (ii) the first teeter-totter eigenmode and (iii) the second teeter-totter eigenmode.

[0155] In some embodiments, each respective serpentine beam from the at least one serpentine beam 404 is at least partially patterned near the first point 404A with a first respective electrode from the set of the at least one electrode 410.

[0156] In some embodiments, the support structure 409 is further joined to the substrate 112, and wherein the substrate 112 further includes the substrate through hole 113.

[0157] In some embodiments, the substrate through hole 113 is of approximately the same size as the rigid plate 406 and aligned with the rigid plate 406.

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

[0159] In some embodiments, a photoacoustic system including the resonant MEMS transducer 400 is defined, including the acoustic cell 100 filled with a sample gas operatively connected to the rigid plate 406, wherein the acoustic cell 100 is configured to produce an acoustic wave within the acoustic cell 100 when the sample gas is exposed to a electromagnetic radiation source, and wherein the rigid plate 406 is configured to be excited by the acoustic wave.

[0160] In some further embodiments, the first half of the rigid plate 406 is operatively connected to the acoustic cell 100 filled with the sample gas, and wherein the rigid plate 406 is adapted to be excited at the first half of the rigid plate when exposed to the acoustic wave, for enabling differential operation.

[0161] In some further embodiments, a central region of the rigid plate 406 is operatively connected to the acoustic cell 100 filled with the sample gas, and wherein the rigid plate 406 is adapted to be excited at the central region of the rigid plate 406 when exposed to the acoustic wave, for enabling single-ended operation.

[0162] In some embodiments, a photoacoustic system including the resonant MEMS transducer 400 is defined, including a first acoustic cell 492 operatively connected to the first half of the rigid plate 406, and a second acoustic cell 494 operatively connected to the second half of the rigid plate 406, and wherein the photoacoustic system is configured to enable switching between differential and single-ended operation by controlling the electromagnetic radiation source and type of gas within the first acoustic cell 492 and the second acoustic cell 494.

[0163] In some further embodiments, the first acoustic cell 492 is further filled with the sample gas, wherein the second acoustic cell 494 is filled with the sample gas, wherein the first acoustic cell 492 is configured to produce a first acoustic wave within the first acoustic cell 492 when the sample gas is exposed to the electromagnetic radiation source, and wherein the first half of the rigid plate 406 is configured to be excited by the first acoustic wave for enabling differential operation.

[0164] In some further embodiments, both of the first acoustic cell 492 and the second acoustic cell 494 are configured to produce the first acoustic wave within the first acoustic cell 492 whenthe sample gas is exposed to the electromagnetic radiation source and to produce a second acoustic wave within the second acoustic cell 494 when exposed to the electromagnetic radiation source, the first acoustic wave exciting the first half of the rigid plate 406 and the second acoustic wave exciting the second half of the rigid plate 406 simultaneously, enabling single-ended operation.

[0165] In some further embodiments, the first acoustic cell 492 is filled with the sample gas, wherein the second acoustic cell 494 is filled with an inert gas, wherein only the first acoustic cell 492 is configured to produce a first acoustic wave within the first acoustic cell 492 when the sample gas of the first acoustic cell 492 and the inert gas of the second acoustic cell 494 are exposed to the electromagnetic radiation source, the first acoustic wave exciting the first half of the rigid plate 406, enabling differential operation. Herein and throughput this disclosure, inert gas refers to a gas which exhibits minimal response to exposure to the electromagnetic radiation source.

[0166] In some embodiments, the at least one electrode 410 is further connected to an electronic circuit capable of switching the electrode polarity, such that switching between differential and single-ended operation is enabled.

[0167] In some examples, the resonant MEMS transducer 400 has a resonance frequency of approximately 15 kHz in the out-of-plane eigenmode, a resonance frequency of approximately 19 kHz in the first teeter-totter mode and a resonance frequency of approximately 32 kHz in the second teeter-totter mode. Based on FEM simulations, in the out-of-plane eigenmode, the resonant MEMS transducer 400 has QroT(piezo) ~ 5k. In the out-of-plane eigenmode the QTOT(piezo) predicted by FEM simulations is limited by piezoelectric film losses due to the high energy dissipation over the length of the serpentine clamped-clamped beams 404. However, the quality of the piezoelectric layer and metal layer will also affect the real-world QroT(piezo). Based on FEM simulations, in the first teeter-totter mode, the resonant MEMS transducer 400 has Qroixpiezo) ~ 10k. Based on FEM simulations, in the second teeter-totter mode, the resonant MEMS transducer 400 has QTOT(piezo) ~ 10k.

[0168] In an example where the resonant MEMS transducer 400 is used for PAS, the single- ended the out-of-plane eigenmode may be easiest to couple to the acoustic pressure wave. In a PAS system with an acoustic cell, for example the acoustic cell 100, the resonant MEMS transducer 400 (and the through hole 405) could be placed directly over the acoustic port 106 to (i) maximize the coupling between the acoustic pressure wave and the rigid plate 406 and (ii) reduce squeeze film damping.

[0169] In some embodiments, as represented in Figures 6A-6C, the resonant MEMS transducer 400 may have a different shape. For instance, the cantilever beams 404 may have a curved shape (e.g. crableg beams), as shown in Figures 6A-6C. The electrodes 410 may be located at the tips of these cantilever beams 404. Each respective cantilever beam 404 from the set of at least one cantilever beam 404 is anchored at a first point to a first respective anchor from the set of at least one anchor 408 and is connected at a second point to the rigid plate 406. For purposes of illustration, the example of the MEMS transducer 400 of Figures 6A-6C shows four cantilevers beams 404, however, it will be understood that the number of cantilever beams 404 may vary without departing from the present teachings. As with the example of Figure 4A, it will be understood that there may be more than one rigid plate 406 (e.g. interconnected through the cantilever beams 404). Furthermore, as with the example of Figure 4A, each respective cantilever beam 404 from the at least one cantilever beam 404 is mechanically coupled through the rigid plate 406. The at least one cantilever beam 404 serve two purposes, (i) providing control over the resonance frequency of the resonant MEMS transducer 400 via the beam dimensions and (ii) providing a piezoelectric transduction region, such that high mechanical stress can be isolated from the rigid plate 406. Thus, it will be understood that the width, aspect ratio, angle or number of the curved shapes in the cantilever beams 404 may change in order to obtain a desired resonance frequency. Furthermore, by isolating the high stress piezoelectric transduction region from the rigid plate 406, the rigid plate 406 may be used to sense pressure waves.

[0170] Figure 6B depicts a single phase of a preferred eigenmodes of operation of resonant MEMS transducer 400, specifically an out-of-plane eigenmode.

[0171] Figure 6C depicts a cross-sectional view of the MEMS transducer 400 along crosssection A-A.

[0172] Figure 5A depicts a resonant MEMS transducer 500. The resonant MEMS transducer 500 is a thin-film piezoelectric-on-silicon resonator.

[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 clamped-clamped beam 504, a through hole 501 and at least one electrode 510. The at least one anchor 508 is joined to the support structure 509. Each respective clamped-clamped beam from the at least one clamped-clamped beam 504 is anchored at a first point to a first respective anchor from the at least one anchor 508, anchored at a second point to a second respective anchor from the at least one anchor 508, andconnected at a third point to a first respective rigid plate from 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 resonance frequency. The through hole 501 is configured to expose the at least one rigid plate 506 to the surrounding environment.

[0174] Figure 5B depicts a single phase of a preferred eigenmode of the resonant MEMS transducer 500, an out-of-plane mode.

[0175] In some examples, the resonant MEMS transducer 500 has a resonance frequency of approximately 15 kHz. In this example, the proof mass of the resonant MEMS transducer 500 is large. Based on FEM simulations, in this example, the resonant MEMS transducer 500 has QTOT(piezo) ~ 10k.

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

[0177] Although the invention has been described with reference to preferred embodiments, it is to be understood that modifications may be resorted to as will be apparent to those skilled in the art. Such modifications and variations are to be considered within the purview and scope of the present invention.

[0178] Representative, non-limiting examples of the present invention were described above in detail with reference to the attached drawing. This detailed description is merely intended to teach a person of skill in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention. Furthermore, each of the additional features and teachings disclosed above and below may be utilized separately or in conjunction with other features and teachings.

[0179] Moreover, combinations of features and steps disclosed in the above detailed description, as well as in the experimental examples, may not be necessary to practice the invention in the broadest sense, and are instead taught merely to particularly describe representative examples of the invention. Furthermore, various features of the above-described representative examples, as well as the various independent and dependent claims below, may be combined in ways that are not specifically and explicitly enumerated in order to provide additional useful embodiments of the present teachings.

Claims

WHAT IS CLAIMED IS:

1. A resonant MEMS transducer for photoacoustic sensing comprising: a support structure; at least two anchors, joined to the support structure; at least one rigid plate; at least one clamped-clamped beam, wherein each respective clamped-clamped beam from the at least one clamped-clamped beam is anchored at a first point to a first respective anchor from the at least two anchors, anchored at a second point to a second respective anchor from the at least two anchors, and connected at a third point to a first respective rigid plate from the at least one rigid plate; a through hole defined by the support structure and the at least one rigid plate; and at least one electrode configured for piezoelectric transduction; and wherein the resonant MEMS transducer is configured to operate at a low resonance frequency, and wherein the through hole is configured to expose the at least one rigid plate to a surrounding environment.

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

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

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

5. The transducer of any one of claims 1 to 4, wherein the support structure is further joined to a substrate, and wherein the substrate further comprises a substrate through hole.

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

7. The transducer of any one of claims 1 to 6, wherein each respective clamped-clamped beam from the at least one clamped-clamped beam is at least partially patterned near the first point with a first respective electrode from the at least one electrode, and wherein each respective clampedclamped beam from the at least one clamped-clamped beam is at least partially patterned near the second point with a second respective electrode from the at least one electrode.

8. The transducer of any one of claims 1 to 7, wherein each respective electrode from the at leastone electrode is configured to operate as a sensing electrode.

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

10. The transducer of claim 9, wherein each respective long clamped-clamped beam from the at least one long clamped-clamped beam is anchored at a fourth point to a first respective anchor from the at least two anchors, anchored at a fifth point to a second respective anchor from the at least two anchors, connected at a sixth point to a first respective rigid plate from the at least one rigid plate, connected at a seventh point to a second respective rigid plate from the at least one rigid plate, connected at an eighth point to a first respective internal beam from the at least one internal beam and connected at a ninth point to a second respective internal beam from the at least one internal beam.

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

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. The transducer of claim 12, wherein the substrate through hole is of approximately the same size as the first rigid plate and aligned with the first rigid plate, such that the substrate through hole enables differential operation.

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

15. A method of manufacturing a photoacoustic system comprising joining a PAS transducer to an acoustic cell as defined in claim 14.

16. A resonant MEMS transducer for photoacoustic sensing comprising: a support structure; at least one anchor, joined to the support structure; a rigid plate; at least one cantilever beam, wherein each respective cantilever beam from the at least one cantilever beam is anchored at a first point to a first respective anchor from the atleast one anchor and is connected at a second point to the rigid plate; a through hole defined by the support structure and the rigid plate; and at least one electrode configured for piezoelectric transduction; and wherein the resonant MEMS transducer is configured to operate at a low resonance frequency, and wherein the through hole is configured to expose the rigid plate to a surrounding environment.

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

18. The transducer of claim 16 or claim 17, wherein each respective cantilever beam from the at least one cantilever beam is at least partially patterned near the first point with a first respective electrode from the set of the at least one electrode.

19. The transducer of any one of claims 16 to 18, wherein the support structure is further joined to a substrate, and wherein the substrate further comprises a substrate through hole.

20. A photoacoustic system comprising the transducer as defined in any one of claims 16 to 19, comprising an acoustic cell filled with a sample gas operatively connected to the rigid plate, wherein the acoustic cell is configured to produce an acoustic wave within the acoustic cell when the sample gas is exposed to an electromagnetic radiation source, and wherein the rigid plate is configured to be excited by the acoustic wave.

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