MEMS-SCHALLWANDLER

Description

[0001] Embodiments of the present invention relate to a MEMS sound transducer. Preferred embodiments describe a microspeaker using MEMS technology.

[0002] As a further development of conventional loudspeakers, microspeakers emerged from the miniaturization of the established electrodynamic drive. In the most common moving-coil arrangement, a coil is attached to the back of the diaphragm. When a current signal is applied, the coil moves in the magnetic field of a fixed permanent magnet, thus deflecting the diaphragm.

[0003] A development from hearing aid applications are so-called balanced armature transducers (BA transducers). A coil-wound rod is located in the gap of a ring-shaped permanent magnet and connected to a diaphragm. A current signal applied to the coil magnetizes the rod, which is then subjected to a torque by the permanent magnet's magnetic field. The rotation is transmitted to the diaphragm via a rigid connection. In its basic state, the rod is in an unstable equilibrium of magnetic attraction forces. This unstable state allows for greater excursions to be achieved with little effort (drive forces, energy). BA transducers are therefore characterized by higher achievable sound pressure levels and, due to their size, are preferred for in-ear applications.

[0004] Driven by the need for miniaturization and spurred by successes in the field of microphones, microsystems technology has taken on the topic of microspeakers. A development by Fraunhofer ISIT together with the company USound resulted in a MEMS speaker based on piezoelectric bending actuators that deflect a hybrid membrane [1]. A speaker module measuring 5.4 mm x 3.4 mm x 1.6 mm achieves a sound pressure level of 100 kΩ over a frequency range of 20 Hz - 20 kHz in a sealed volume. SPL 1.4 cm 3 of at least 106 dB (approx. 116 dB at 1 kHz) [2].

[0005] A further development of this approach is MEMS loudspeakers based on piezoelectric bending actuators, which operate without an additional membrane, developed at Fraunhofer ISIT. Here, the actuators themselves form the acoustically radiating membrane. A loudspeaker chip with an active area of ​​4 mm x 4 mm achieves a sound pressure level in a closed room. SPL 1.26 cm 3 of at least 105 dB (approx. 110 dB at 1 kHz) [3].

[0006] Various concepts for electrodynamically actuated MEMS loudspeakers are also known. Of particular note are the works at the Université Paris-Sud and the Université du Maine [4,5]. A stiffened Si membrane suspended by Si springs forms a piston-type oscillator. The coil is applied as a planar coil directly to the Si membrane and moves the membrane in the magnetic field of a hybrid permanent magnet. A related approach, pursued by several groups [6,7,8,9,10,11], involves applying the planar coil to a soft polymer membrane instead of the stiffened Si membrane. Furthermore, some prior art exists in the patent literature.

[0007] US 10,567,883 B2 discloses MEMS sound transducers. Other relevant documents include US 2011 / 182150 A1, US 2016 / 211439 A1, and DE 10 2013 013 402 A1.

[0008] The concept of a magnetostrictively driven micro loudspeaker is pursued by Albach et al.

[12] . The sound transducer consists of a two-part structure. The first part is a micro loudspeaker chip that supports the magnetostrictive diaphragm of the loudspeaker. The diaphragm itself consists of many individual bending beams. Their layered structure consists of a magnetostrictive (active) layer and further passive layers. When a magnetic field is applied, these micro actuators bend out of the plane of the chip and thus displace air, generating sound pressure. The second part of the micro loudspeaker is a current-carrying coil that generates the magnetic field required for operation. The concept proposed here envisions a second chip carrying corresponding micro flat coils.

[0009] Another microspeaker concept is based on the nanoscopic electrostatic drive (NED)

[13] . The device comprises clamped electrostatic bending actuators arranged in pairs in rows and columns within the device layer of a silicon-on-insulator (SOI) wafer and covered by another wafer bonded to the SOI wafer with a tiny gap. Between each adjacent row of actuators, acoustically effective openings are integrated alternately into the top and bottom of the wafer to enable sound radiation from the device without acoustic short circuiting.

[0010] Another piezoelectrically driven microspeaker was introduced by xMEMS. Here, a silicon membrane is piezoelectrically driven and set into vibration

[14] .

[0011] The best results so far have been observed for microspeakers with piezoelectric actuators. For MEMS loudspeakers, such as those featuring a piezoelectrically driven bending actuator, the limiting factor is the radiating area of ​​the bending actuator. Therefore, there is a need for an improved approach.

[0012] The object of the present invention is to create a concept that has an improved compromise between manufacturability, radiation characteristics and radiation area (achievable sound pressure).

[0013] The problem is solved by the subject matter of the independent patent claims.

[0014] Embodiments of the present invention provide a MEMS sound transducer with at least one actuator (e.g., a piezo-based bending actuator), a radiating structure (e.g., in the form of a rigid plate), and a structure surrounding the radiating structure. The radiating structure is coupled to the actuator as a separate element and is configured to emit sound when actuated by the actuator. The structure surrounding the radiating structure is separated from the surrounding structure by one or more gaps. Furthermore, the MEMS sound transducer comprises at least one aperture arranged or extending along at least one of the one or more gaps.

[0015] Embodiments of the present invention are based on the realization that speaker performance can be optimized by separating the drive function and the air displacement function. The separation of the drive functionality (at least one actuator) and the air displacement functionality (radiating structure) is achieved by using separate components that can be optimized independently of each other. The active surface used for air displacement can, for example, be optimized toward a rigid platform with a uniform stroke, whereby the maximum deflection of the drive can be better converted into displaced volume. Furthermore, the active surface used for the drive can be optimized to the specific conditions of the drive concept used. This allows microspeakers to be designed using MEMS technology, which, depending on the design, offers the following advantages: ▪ Higher sound pressure level due to better air displacement ▪ Lower energy consumption due to optimized active area of ​​the actuator ▪ Lower distortion due to better linearity of the optimized actuator ▪ Lower drive voltage due to longer bending actuators

[0016] In this way, higher sound pressure levels can be achieved with micro loudspeakers with less energy consumption or with the same or smaller dimensions.

[0017] According to one embodiment, the radiation structure can be designed to perform a lifting movement in a direction out of the substrate plane when actuated by the actuator. In this case, the radiation structure is then arranged in one plane together with the surrounding structure. For example, the surrounding structure can be formed by a substrate, and the radiation structure can extend in or parallel to the substrate plane and / or be arranged in a cavity of the substrate. The separation between the radiation structure and the surrounding structure can, as already mentioned, be provided by one or more gaps. These can be circumferential. This circumferential characteristic enables the lifting movement, which is not possible with conventional bending actuators. A lifting movement is significantly more efficient because it allows more air to be displaced across the entire bending actuator surface.

[0018] According to embodiments, the radiating structure can be configured to be at rest relative to the surrounding structure. According to embodiments, the surrounding structure can be at rest, meaning that it is not actively stimulated to vibrate. The radiating structure, however, moves relative to the surrounding (stationary / immobile) structure. The sound transducer can be connected to a support component (circuit board, electrical component, etc.) via the immobile surrounding structure.

[0019] With regard to the acoustic separation of the surrounding structure and the radiating structure, it should be noted that one or more apertures are used, which enable acoustic decoupling of the rear volume of the radiating structure. According to embodiments, at least one aperture is formed as part of the radiating structure. Additionally or alternatively, the at least one aperture can extend into the substrate plane, e.g., vertically. Alternatively or additionally, the aperture can be formed as part of the surrounding structure. In this case, for example, the aperture can extend out of the substrate plane, e.g., vertically. According to embodiments, the aperture can be formed by a cavity of the surrounding structure.

[0020] As already explained above, the gap is preferably circumferential. According to a further embodiment, the aperture can also be arranged circumferentially around the radiating structure or along one or more gaps.

[0021] Regarding the actuator, it should be noted that, according to a preferred embodiment, it is provided as a bending actuator, a longitudinal bending actuator, or a bending actuator with a high aspect ratio. Such a bending actuator enables high stroke movements, at least of the front end. For example, with piezoelectric bending actuators, longer actuators can be used to achieve higher maximum deflection. Limiting the width ensures a lower capacitive load.

[0022] Bending actuators are typically provided with (for example) a free end and have (e.g. opposite) a clamped end. According to one embodiment, the radiating structure is coupled to the free end of the bending actuator. This can be achieved, for example, by providing a coupling of the radiating structure in the region of the free end. Viewed in the longitudinal direction, the bending actuator can, for example, be coupled in the front third (i.e. in the third in the longitudinal direction) closer to the free end than to the clamped end. This advantageously enables the maximum stroke to be transferred to the radiating structure. The actuator or bending actuator can, for example, be a piezoelectrically driven bending actuator. Alternatively, an electrodynamically or electrostatically driven actuator would of course also be conceivable.The bending actuator usually has both a suspension function and a drive function with respect to the radiating structure.

[0023] According to one embodiment, the radiating structure can be mounted above the surrounding structure by further elements, such as spring elements or springs.

[0024] A preferred embodiment is as follows. The radiating structure comprises two or more, for example four, regions. A further central region is provided between the two or more regions. According to one embodiment, the at least one actuator or multiple actuators can be coupled to the radiating structure in the central region or act on it. If, according to further embodiments, it is assumed that four regions arranged as quadrants are provided, then, according to embodiments, the four regions arranged as quadrants can be interrupted by four suspension elements or four actuators / bending transducers (as part of the suspension and as a drive). The suspension elements or actuators are coupled to a central region between the four quadrants. This arrangement concentrates the force of four actuators and maximizes the area of ​​four quadrants.The central attack results in a lifting movement, which is advantageous from an efficiency point of view.

[0025] Further developments are defined in the subclaims. Embodiments of the present invention are explained with reference to the accompanying drawings. They show: Fig. 1 a schematic representation of a MEMS sound transducer according to a basic embodiment; Fig. 2a, 2b schematic representations of a MEMS sound transducer to illustrate apertures between platform and substrate as well as platform and actuator according to embodiments; Fig. 3a, 3b schematic representations for the illustration of apertures between platform and actuator as well as substrate and actuator according to embodiments; and Fig. 4a, 4b schematic representations of actuators below the platform with apertures between actuator and substrate according to further embodiments.

[0026] Before exemplary embodiments of the present invention are explained below with reference to the accompanying drawings, it should be noted that elements and structures with the same function are provided with the same reference numerals, so that the description of them is applicable to one another or interchangeable.

[0027] Fig. 1 shows a MEMS sound transducer 10, which is, for example, incorporated into a substrate 12. The substrate 12 has a cavity 12k. A sound-radiating surface 14 is provided in this cavity 12k. The sound-radiating surface is separated from the structure 12s surrounding the sound-radiating surface 14 by a gap 14s, which here, as an example, is arranged circumferentially around the sound-radiating surface 14. The structure 12s surrounding the sound-radiating surface is essentially formed by the substrate 12 or the walls of the cavity 12k.

[0028] The sound-emitting surface 14 is mounted relative to the surrounding structure 12s by a bending actuator 16, or generally an actuator 16. The mounting is such that the sound-emitting structure 14 is located approximately in the substrate plane or can move out of the substrate plane (as illustrated by the arrow marked with the reference symbol B). For this purpose, the actuator 16 protrudes from the edge of the cavity 12k into the cavity 12k, with the sound-emitting surface 14 being connected to the actuator 16 in the region 16b. The region 16b is provided, for example, in the front third of the bending actuator 16.

[0029] In this exemplary embodiment, the sound-radiating surface 14 is shaped as a flat element, such as a flat rectangle or flat disk. The gap 14s is as small as possible in order to effectively separate the back volume due to laminar flow at a very small gap. To improve this effect, a baffle 18 is provided, for example, in the edge region of the sound-radiating surface 14. The baffle extends, for example, perpendicular to the sound-radiating surface 14, e.g., into the substrate plane. According to exemplary embodiments, this baffle 18 can be circumferential around the radiating surface 14. It should be noted at this point that different shapes of the baffle 18 would be conceivable, e.g., on the underside of the sound-radiating surface 14, on the top side, or in the region of the surrounding structure.

[0030] In general, according to embodiments, the aperture is arranged in the area of ​​or along the gap 14s, since this is responsible for an acoustic short circuit or, if correctly dimensioned, can prevent an acoustic short circuit. The technical effect of the aperture is that the gap 14s varies along the direction of movement B even during a stroke, in this case a piston stroke, of the sound-emitting surface 14. By providing the aperture, it can be ensured that this gap remains as constant as possible. The piston stroke also makes it possible for the gap 14s to be very small, since apart from the vertical movement out of the substrate plane (cf. B), there is hardly any significant movement. The reason for this is that the bending actuator 16 typically performs a translational deformation. However, since the sound-emitting surface 14 is attached in the front third (cf.Reference numeral 16b) transfers, in particular, the stroke component of the movement to the sound-emitting surface. This effect can be further improved if, for example, two bending actuators are arranged opposite one another, so that the radial movement component is further reduced. This can, of course, also be achieved by three actuators arranged at a 120-degree angle, for example, or by another actuator arrangement that allows all movement components except the stroke component to be reduced.

[0031] In particular, the coupling of the radiating surface 14 or air-displacing surface 14 and the surface of the drive 16 enables optimization of the average deflection of the active surface 14 and thus the achievement of higher sound pressure levels with constant or smaller dimensions. The acoustic function of the air-displacing surface 14 is ideally / optionally designed as a rigid plate according to embodiments, which executes a uniform vertical stroke B. In detail, this means that the deflection of every point on the air-displacing surface 14 is the same at all times. For the bending actuators 16, a possible elongated design is optimal, as this maximizes the achieved deflections and achieves better linearity. The elongated actuator, for example, has an aspect ratio of 5:1.Since the maximum deflection of the actuator 16 occurs at its tip, the coupling to the rigid plate 14 at this point 16b must be achieved using a suitable structure, such as a flexible structure. An optimized geometry would therefore be a rigid plate 14 suspended from the longest possible bending actuators 16, which performs a lifting movement B. The gain arises from the decoupling of the area used for both functions. The average deflection of the air-displacing surface utilizes the maximum deflection of the bending actuators 16. In addition, the ratio of the area used for air displacement to the area used for the bending actuators can be freely selected and thus optimized.

[0032] In the piezoelectric bending actuators used in this embodiment, other drive types, such as mechanical or electromagnetic drives, are also conceivable. In these cases, the requirements for the surface 16 required for the drive are different. Connecting the air-displacing surface, optionally designed as a rigid plate, to the substrate via a spring suspension would be one alternative. This spring suspension is similar to the piezoelectric bending actuators described above.

[0033] In the concept described above, strong relative movements occur between the air-displacing plate 14, the bending actuators 16 or the spring suspension and a substrate 12 to which the plate is suspended via the bending actuators 16 or springs.

[0034] At the edges of plate 14, deflection can cause gaps 14s to open, which can lead to an acoustic short circuit between the front and rear volumes of the microspeaker. These can be prevented or optimized by separating the elements as a narrow gap. To prevent these gaps from increasing even during large deflections, additional aperture structures 16b are used. The aperture structures can be applied to the substrate 12 as well as to the movable plate 14 or the deforming bending actuators 16 or spring structures. Depending on the design of the concept, the provision of apertures between platform 14 and substrate 12, between platform 14 and spring / actuator 16, and between spring / actuator 16 and substrate 12 is considered.It should be noted at this point that, by utilizing the cavity 12k in which the platform 14 and the actuators 16 / springs are suspended, the substrate itself can also function as a shutter. Depending on the direction of movement, the shutters 16b are configured, for example, to point upwards and / or downwards. Pre-deflection of the platform according to embodiments allows the shutters 14b to be configured in only one direction, e.g., upwards or downwards.

[0035] With such a pre-deflection, the mechanical stress on the springs / actuators 16 is taken into account. In particular, the shortening of the actuators / springs in the lateral direction, which is permitted by the suitable coupling structure, must be considered. In this respect, the coupling structure 16b prevents the slots from widening in the lateral direction.

[0036] Below is an extended embodiment with reference to Fig. 2 explained. Fig. 2 shows a MEMS sound transducer 10', which is undeflected in illustration A and deflected in illustration B. The MEMS sound transducer has a surrounding structure 12, a radiating surface 14', which has four quadrants 14a to 14d. In this exemplary embodiment, the surface 14' is driven by four actuators 16a to 16d. These are arranged between the quadrants 14a-14d as follows. In detail: 16a is provided between 14a and 14b, 16b between 14b and 14c, 16c between 14c and 14d, and 16d between 14d and 14a. For this purpose, a type of slot is provided between each of the quadrants 14a to 14d. This slot is designated purely by way of example with reference numeral 14f in Fig. 2b provided.

[0037] The bending actuators 16a to 16d act on a central point of the radiating surface. The central point or surface is designated by the reference symbol 14z and connects the four quadrants 14a to 14d. As shown in Fig. 2b As can be seen, the radiation structure 14' has one or more apertures 18. The apertures 18a, also referred to as external apertures, are arranged in the region of the gap 14s and extend downwards from the radiation surface 14' into the substrate 12, so that the gap width remains constant upon deflection in the stroke direction B. The plurality of apertures 18a are provided, for example, on the outer edges of each quadrant, i.e. on the side facing the substrate 12 (i.e. 4x2). Further apertures 18b, also referred to as internal apertures, are also provided on the inside in the region 14f, i.e. adjacent to the bending transducers 16a to 16d. According to exemplary embodiments, only the aperture 18a or 18b can be used.

[0038] As can be seen here, deflection results in a lifting movement of the radiating unit 14, which is caused by the fact that each bending actuator 16a to 16d leads to a deflection of the element 14z, whereby the longitudinal forces are balanced by the opposing arrangement of the actuators 16a and 16c or 16b and 16d.

[0039] As can be clearly seen here, the radiating surface 14 is significantly larger due to the four quadrants 14a, 14b, 14c and 14d, as well as the central element 14z, than a radiating surface resulting from the flexural sound transducers 16a to 16d. Furthermore, the flexural sound transducers 16a to 16d are designed to be long in order to achieve a sufficiently high stroke at the end of the flexural transducer, i.e. opposite the clamped end (transition 16a to 16d to 12). This arrangement means that the elements 14' and 16a to 16d can be optimized independently of one another. Depending on the exemplary embodiments, it would of course also be conceivable to use only two, three or even more flexural transducers instead of the four flexural transducers 16a to 16d. The geometry of the elements 14a to 14d then changes depending on this. It should be noted at this point that some components, such as the B. the outer panels 18a or the inner panels 18b can also be arranged differently.

[0040] It would be conceivable, for example, that instead of the (vertical) apertures 18a and 18b on the deflectable structure 14, apertures could alternatively or additionally be arranged in the substrate region 12, e.g., along the gap 14s surrounding the radiating structure 14'. The apertures can also extend not only into the substrate end, but also out of the substrate end. Such an arrangement is described in Fig. 3 shown.

[0041] Fig. 3 shows a MEMS sound transducer 10" with a radiating structure 14", which is provided here as a rectangular surface. The radiating structure 14" is mounted relative to the substrate 12 by four actuators 16a" to 16d". The actuators 16a" to 16d" extend along the outer edge of the radiating structure 14", thus being arranged in the gap 14s". All actuators 16a" to 16d" are in turn arranged longitudinally and are connected to the substrate 12 or the radiating structure 14" at the outermost ends of the elongated actuator. This in turn results in the advantage of a large radiating surface of the radiating structure 14" and long actuators or bending actuators 16a" to 16d", which ultimately have a large stroke. The arrangement of the actuators 16a" to 16d", which are oriented opposite each other (cf. 16a" and 16c" or 16b" and 16d"), not only results in a slight tilt of the radiating structure 14", but also, in particular, in a large stroke component of the deflection.

[0042] With regard to the apertures, it should be noted that these can be arranged both in the area of ​​the radiating structure 14" and in the area of ​​the substrate 12. Both variants are illustrated here as examples, although one variant would generally be sufficient. It should be noted that, according to exemplary embodiments, the design with both aperture variants would be preferred, since otherwise the gap between the actuator and the substrate as well as between the actuator and the radiating surface would widen.

[0043] As can be seen from the deflected version 3b, the baffles 18a" are located on the outside or surrounding the sound-radiating structure 14". In this case, with the square sound-radiating structure 14" with the four edges, four baffles 18a" are provided. These seal off the gap 14s", and here in particular the gap between the bending actuator 14a" / 14b" / 14c" / 14d" and the sound-radiating structure 14". In order to seal the area between the actuator 14a" / 14b" / 14c" / 14d" and the substrate 12, further apertures 18s" are provided. These apertures extend the edge of the cavity 12k in the substrate 12 out of the substrate plane. The elements 18s" interact, for example, with the side wall of the cavity 12k and thus enable, starting from the rest position in Fig. 3a as well as the upward and downward deflection of the radiating structure 14" the gap is kept constantly small.

[0044] The aperture 18s" can, as shown here, be interrupted in the area of ​​the firmly clamped ends of the bending actuators 16a", 16b", 16c" or 16d".

[0045] A slightly different configuration is in Fig. 4 where the outer aperture is uninterrupted, comparable to 18s", to further improve sealing.

[0046] Fig. 4 shows a MEMS sound transducer 10‴, in which a sound-emitting structure 14‴ is arranged in a cavity 12k of the substrate 12. The sound-emitting structure 14‴ is comparable in shape and position to the sound-emitting structure 14" and can also have apertures comparable to the aperture 18a". In this case, however, one or more bending actuators are provided below the sound-emitting structure 14‴. These are provided with the reference numerals 16a‴ to 16d‴. In contrast to the embodiment of Fig. 3 The elements are located below the sound-radiating structure 14‴, further optimizing the surface area of ​​the sound-radiating structure 14‴. This creates only a single gap 14s‴ around the sound-radiating structure 14‴. This gap is sealed, for example, using the cover 18s‴.

[0047] The embodiment from Fig. 4 This advantageously allows for a vertical arrangement of the springs / actuators 16a‴ to 16d‴ and the sound-radiating structure 14‴. The springs / actuators 16a‴ are connected to the platform above or below the platform level. This allows for the accommodation of the springs / actuators 16a‴ to 16d‴ without requiring additional space; sealing the gaps 14s‴ is therefore only necessary between the platform 14‴ and the substrate.

[0048] It should be noted here that the radiation structure described above does not necessarily have to be square or rectangular, but can also have any other shape, e.g., a round shape, a shape with 90° segments as quadrants, or even another shape. The radiation structure can also be curved or have a 3D structure.

[0049] Another embodiment provides a substrate having a plurality of radiating structures embedded in the substrate.

[0050] In all of the above embodiments, it would be conceivable for the aperture to be integrated into the substrate. For example, the walls of the cavity could form the aperture if the radiating structure is located primarily within the substrate cavity, i.e., below the surface of the substrate, during its stroke. This could be achieved, for example, by prestressing the radiating structure.

[0051] Another embodiment creates a micro loudspeaker in MEMS technology with the following features: (rigid) platform that performs a lifting movement Platform suspended from a substrate Separation of the moving parts by narrow gaps Aperture structure to maintain the narrow gap even during deflection,

[0052] According to embodiments, the platform can be driven, for example, by piezoelectric bending actuators, which simultaneously form the suspension of the platform.

[0053] According to embodiments, aperture structures may be formed on the substrate and / or the moving platform.

[0054] According to embodiments, aperture structures can be formed upwards, downwards or in both directions.

[0055] In corresponding embodiments, the platform is suspended inside as well as above or below the platform.

[0056] Another embodiment provides a manufacturing method for manufacturing the micro loudspeaker.

[0057] All of the above-mentioned and explained embodiments have the advantage that the decoupling of the drive and air distribution functions allows separate optimization of the individual components.

[0058] The general area of ​​application is micro sound transducers, i.e., micro loudspeakers and microphones. In addition to applications in the audible range (e.g., micro loudspeakers for consumer electronics, telecommunications, and medical technology), applications in the ultrasonic range are also conceivable. Literaturverzeichnis

[0059] [1] Patentanmeldung DE 10 2014 217 798, "Mikromechanische piezoelektrische Aktuatoren zur Realisierung hoher Kräfte und Auslenkungen" [2] "Data Sheet Achelous, MEMS-based microspeaker for headphones, wearables and array applications", USound GmbH, 2018 [3] F. Stoppel, A. Männchen, F. Niekiel, D. Beer, T. Giese, B. Wagner, "New integrated full-range MEMS speaker for in-ear applications", IEEE Micro Electro Mechanical Systems (MEMS), 2018 [4] Patentschrift US 9 237 961 B2 [5] I. Shahosseini, E. Lefeuvre, J. Moulin, E. Martincic, M. Woytasik, G. Lemarquand, IEEE Sens. J. 13 (2013), pp. 273-284 [6] F. L. Ayatollahi, B. Y. Majlis, "Materials Design and Analysis of Low-Power MEMS Microspeaker Using Magnetic Actuation Technology", Adv. Mater. Res. 74 (2009), pp. 243-246 [7] Y. C. Chen, Y. T. Cheng, "A low-power milliwatt electromagnetic microspeaker using a PDMS membrane for hearing aids application", IEEE Int. Conf. Micro Electro Mech. Syst., 24th (2011), pp. 1213-1216 [8] M.-C. Cheng, W.-S.Huang, S. R.-S. Huang, "A silicon microspeaker for hearing instruments", J. Micromech. Microeng. 14 (2004), pp. 859-866 [9] S.-S. Je, F. Rivas, R. E. Diaz, J. Kwon, J. Kim, B. Bakkaloglu, S. Kiaei, J. Chae, "A Compact and Low-Cost MEMS Loudspeaker for Digital Hearing Aids", IEEE Trans. Biomed. Circ. Sys. 3 (2009), pp. 348-358

[10] B. Y. Majlis, G. Sugandi, M. M. Noor, "Compact electrodynamics MEMSspeaker", China Semiconductor Technology International Conference (CSTIC), 2017

[11] P. R. Jadhav, Y. T. Cheng, S. K. Fan, C. Y. Liang, "A sub-mW Electromagnetic Microspeaker with Bass Enhancement using Parylene / Graphene / Parylene Composite Membrane", IEEE Micro Electro Mechanical Systems (MEMS), 2018

[12] Albach, T. S., Horn, P., Sutor, A. & Lerch, R. Sound Generation Using a Magnetostrictive, Micro Actuator. J. Appl. Phys. 109(7), (2011)

[13] B. Kaiser, S. Langa, L. Ehrig, M. Stolz, H. Schenk, H. Conrad, H. Schenk, K Schimmanz, D.Schuffenhauer, Concept and proof for an all-silicon MEMS micro speaker utilizing air chambers, Microsystems & Nanoengineering (2019)

[14] Patentschrift US 10327060, "Air Pulse Generating Element and Sound Producing Device".

Claims

1. An MEMS sound transducer (10, 10', 10", 10"') comprising: at least one actuator (16, 16a-16d, 16a"-16d", 16a‴-16d‴); a radiation structure (14, 14', 14a-14d, 14", 14"') coupled to the actuator (16, 16a-16d, 16a"-16d", 16a‴-16d‴) and configured as a separate element; a structure (12) surrounding the radiation structure (14, 14', 14a-14d, 14", 14‴), wherein the radiation structure (14, 14', 14a-14d, 14", 14"') is separated from the surrounding structure (12) by one or more gaps (14s, 14s", 14s‴); and at least one screen (18, 18s", 18a", 18a, 18b, 18s‴) arranged along at least one of the one or more gaps (14s, 14s", 14s‴), wherein the at least one screen (18, 18s", 18a", 18a, 18b, 18s"') is formed as part of the radiation structure (14, 14', 14a-14d, 14" 14"').

2. The MEMS sound transducer (10, 10', 10", 10‴) in accordance with claim 1, wherein the radiation structure (14, 14', 14a-14d, 14", 14"') and the surrounding structure (12) are arranged in one plane; and / or wherein the surrounding structure (12) is formed by a substrate and the radiation structure (14, 14', 14a-14d, 14", 14"') is located in or in parallel to a substrate plane or cavity (12k) of the substrate.

3. The MEMS sound transducer (10, 10', 10", 10‴) in accordance with any of the preceding claims, wherein the one or more gaps (14s, 14s", 14s‴) are provided circumferentially around the radiation structure (14, 14', 14a-14d, 14", 14‴).

4. The MEMS sound transducer (10, 10', 10", 10‴) in accordance with any of the preceding claims, wherein a further screen (18, 18s", 18a", 18a, 18b, 18s"') extends into a substrate plane or perpendicularly into a substrate plane; and / or wherein the further screen (18, 18s", 18a", 18a, 18b, 18s"') is formed as part of the surrounding structure (12); and wherein the further screen (18, 18s", 18a", 18a, 18b, 18s‴) extends out of the substrate plane or perpendicularly out of a substrate plane; or wherein the further screen (18, 18s", 18a", 18a, 18b, 18s"') is formed by a cavity (12k) of the surrounding structure (12).

5. The MEMS sound transducer (10, 10', 10", 10‴) in accordance with any of the preceding claims, wherein the radiation structure (14, 14', 14a-14d, 14" 14‴) is pre-deflected relative to the surrounding structure (12) in an idle state; and / or wherein the at least one screen (18, 18s", 18a", 18a, 18b, 18s"') is arranged to be circumferential around the radiation structure (14, 14', 14a-14d, 14", 14‴) or along the one or more gaps (14s, 14s", 14s"').

6. The MEMS sound transducer (10, 10', 10", 10‴) in accordance with any of the preceding claims, wherein the actuator (16, 16a-16d, 16a"-16d", 16a‴-16d‴) comprises a bending actuator or a longitudinal bending actuator or a bending actuator having an aspect ratio of at least 5:1; and / or wherein the actuator (16, 16a-16d, 16a"-16d", 16a‴-16d‴) comprises a clamped end or a free end.

7. The MEMS sound transducer (10, 10', 10", 10‴) in accordance with claim 6, wherein the radiation structure (14, 14', 14a-14d, 14" 14‴) is coupled to the free end of the bending transducer or coupled to the bending transducer in the region of the free end or coupled in the longitudinal direction of the bending transducer in the third closer to the free end than to the clamped end.

8. The MEMS sound transducer (10, 10', 10", 10‴) in accordance with any of the preceding claims, wherein the actuator (16, 16a-16d, 16a"-16d", 16a‴-16d‴) comprises a piezoelectric actuator, electrodynamic actuator (16, 16a-16d, 16a"-16d", 16a‴-16d‴) or electrostatic actuator (16, 16a-16d, 16a"-16d", 16a‴-16d‴); and / or wherein the radiation structure (14, 14', 14a-14d, 14" 14‴) is supported relative to the surrounding structure (12) by at least one actuator (16, 16a-16d, 16a"-16d", 16a‴-16d‴), bending actuator, spring elements or springs; and / or wherein the at least one actuator (16, 16a-16d, 16a"-16d", 16a‴-16d‴) connects the radiation structure (14, 14', 14a-14d, 14" 14"') by a partially flexible structure or several partially flexible structures; and / or wherein the radiation structure (14, 14', 14a-14d, 14" 14‴) is supported relative to the surrounding structure (12) by at least one actuator (16, 16a-16d, 16a"-16d", 16a‴-16d‴), bending actuators, spring elements or springs or is supported by several actuators (16, 16a-16d, 16a"-16d", 16a‴-16d‴), several bending actuators, several spring elements or several springs; and / or wherein the radiation structure (14, 14', 14a-14d, 14" 14‴) is supported relative to the surrounding structure (12) by at least one actuator (16, 16a-16d, 16a"-16d", 16a‴-16d‴), bending actuator, spring elements or springs or is supported by several actuators (16, 16a-16d, 16a"-16d", 16a‴-16d‴), several bending actuators, several spring elements or several springs which extend along the gap or in the gap.

9. The MEMS sound transducer (10, 10', 10", 10‴) in accordance with any of the preceding claims, wherein the at least one actuator (16, 16a-16d, 16a"-16d", 16a"'-16d‴) is arranged alongside or in parallel along an edge of the radiation structure (14, 14', 14a-14d, 14" 14"').

10. The MEMS sound transducer in accordance with any of the preceding claims, wherein the radiation structure (14, 14', 14a-14d, 14" 14"') comprises two or more regions, wherein a central region (14z) is arranged between the two or more regions.

11. The MEMS sound transducer (10, 10', 10", 10‴) in accordance with any of the preceding claims, wherein the at least one actuator (16, 16a-16d, 16a"-16d", 16a"'-16d‴) is coupled to the radiation structure (14, 14', 14a-14d, 14" 14"') in a central region (14z); and / or wherein the at least two actuators (16, 16a-16d, 16a"-16d", 16a‴-16d‴) are coupled to the radiation structure (14, 14', 14a-14d, 14" 14"'), and wherein the at least two actuators (16, 16a-16d, 16a"-16d", 16a‴-16d‴) are arranged to be opposite.

12. The MEMS sound transducer (10, 10', 10", 10‴) in accordance with any of the preceding claims, wherein at least one further additional screen (18, 18s", 18a", 18a, 18b, 18s"') extends along a gap between the at least one actuator (16, 16a-16d, 16a"-16d", 16a‴-16d‴) and an edge of the radiation structure (14, 14', 14a-14d, 14" 14‴); and / or wherein the radiation structure (14, 14', 14a-14d, 14" 14"') comprises four regions arranged as quadrants (14a-14d), wherein the four regions arranged as quadrants (14a-14d) are interrupted by four suspension elements or actuators (16, 16a-16d, 16a"-16d", 16a‴-16d‴), and / or wherein the suspension elements or actuators (16, 16a-16d, 16a"-16d", 16a"'-16d‴) are coupled to a central region (14z) between the four quadrants (14a-14d).

13. The MEMS sound transducer (10, 10', 10", 10‴) in accordance with any of the preceding claims, wherein the radiation structure (14, 14', 14a-14d, 14" 14"') is configured to perform, when actuated by the actuator (16, 16a-16d, 16a"-16d", 16a‴-16d‴), a stroke movement (B) in a direction out of the substrate plane.

14. A method for manufacturing an MEMS sound transducer (10, 10', 10", 10‴) in accordance with any of the preceding claims, comprising: providing at least one actuator (16, 16a-16d, 16a"-16d", 16a‴-16d‴) and a radiation structure (14, 14', 14a-14d, 14" 14‴) which is coupled to the actuator (16, 16a-16d, 16a"-16d", 16a‴-16d‴) and configured as a separate element, and a structure (12) surrounding the radiation structure (14, 14', 14a-14d, 14" 14‴), wherein the radiation structure (14, 14', 14a-14d, 14" 14‴) is separated from the surrounding structure (12) by one or more gaps (14s, 14s", 14s‴); and arranging at least one screen (18, 18s", 18a", 18a, 18b, 18s"') along at least one of the one or more gaps (14s, 14s", 14s"').

15. An MEMS sound transducer (10, 10', 10", 10"') comprising: at least one actuator (16, 16a-16d, 16a"-16d", 16a‴-16d‴); a radiation structure (14, 14', 14a-14d, 14", 14"') coupled to the actuator (16, 16a-16d, 16a"-16d", 16a‴-16d‴) and configured as a separate element; a structure (12) surrounding the radiation structure (14, 14', 14a-14d, 14", 14‴), wherein the radiation structure (14, 14', 14a-14d, 14", 14"') is separated from the surrounding structure (12) by one or more gaps (14s, 14s", 14s‴); and at least one screen (18, 18s", 18a", 18a, 18b, 18s‴) arranged along at least one of the one or more gaps (14s, 14s", 14s‴), wherein the at least one screen (18, 18s", 18a", 18a, 18b, 18s"') is formed as part of the surrounding structure (12) and by a cavity (12k) of the surrounding structure (12); and wherein the at least one screen (18, 18s", 18a", 18a, 18b, 18s"') extends out of a substrate plane or perpendicularly out of a substrate plane, and wherein the at least one screen (18, 18s", 18a", 18a, 18b, 18s"') extends an edge of the cavity (12k).