Micromechanical acoustic transducer

Abstract

According to a first aspect, a micromechanical sound transducer comprises a first bending transducer with a free end and a second bending transducer with a free end, arranged in a common plane, the free end of the first bending transducer being separated from the free end of the second bending transducer by a gap. The second bending transducer is excited in phase with the vertical vibration of the first bending transducer. According to a second aspect, a micromechanical sound transducer comprises a first bending transducer, which is excited vertically with respect to the vibration, and an aperture element extending vertically to the first bending transducer, which is separated from a free end of the first bending transducer by a gap.

Description

[0001] Exemplary embodiments of the present invention relate to a micromechanical sound transducer with at least one bending actuator (generally a bending transducer) and a miniaturized gap, as well as to a miniaturized sound transducer with a cascaded bending transducer. Further exemplary embodiments relate to corresponding manufacturing processes.

[0002] While MEMS have found their way into almost every field, miniaturized transducers are still manufactured using precision engineering techniques. These so-called "microspeakers" are based on the electrodynamic drive system, in which a moving coil within a permanent magnetic field deflects a diaphragm. A significant disadvantage of these conventional electrodynamic transducers is their low efficiency and the resulting high power consumption, often exceeding one watt. Furthermore, such transducers lack any position sensors, meaning the diaphragm movement is uncontrolled, leading to high distortion at higher sound pressure levels. Additional drawbacks include significant manufacturing tolerances and relatively large heights, typically exceeding 3 mm.

[0003] Due to high-precision manufacturing processes and energy-efficient drive principles, MEMS have the potential to overcome these disadvantages and enable a new generation of transducers. However, a fundamental problem to date is the insufficient sound pressure level of MEMS transducers. The primary reason for this lies in the difficulty of generating sufficiently large excursion movements within the smallest possible dimensions. A further complication is that a diaphragm is required to prevent acoustic short circuits, and its additional spring stiffness negatively impacts the overall excursion. The latter can be minimized by using very soft and three-dimensionally shaped diaphragms (e.g., with a torus), which, however, cannot currently be manufactured using MEMS technology and must therefore be integrated in a complex and costly hybrid manner.

[0004] Publications and patents describe MEMS transducers of various designs, but due to the aforementioned problems, no market-ready products have yet emerged. These concepts are based on closed membranes that are set into vibration and generate sound. For example, [Hou13, US2013 / 156253A1] describes an electrodynamic MEMS transducer that requires the hybrid integration of a polymer membrane and a permanent magnet ring. The concept of piezoelectric MEMS transducers was presented in [Yi09, Dej12, US7003125, US8280079, US2013 / 0294636A1]. Here, piezoelectric materials such as PZT, AIN, or ZnO were applied directly to silicon-based transducer membranes, which, however, do not allow sufficiently large excursions due to their low elasticity.Another piezoelectric MEMS transducer with a plate-shaped body that is deflected out of the plane in a piston-like manner via a diaphragm or several actuators is described in [US 20110051985A1]. Digital MEMS transducers based on arrays with electrostatically driven diaphragms, which, however, can only generate sufficiently high sound pressures at high frequencies, are described in [Gla13, US7089069, US20100316242A1]. Therefore, there is a need for a better approach. Furthermore, DE 102006005048 A1 and EP 2 254 353 A3 represent further prior art. DE 102006005048 A1 describes an ultrasonic sensor, e.g., for a motor vehicle. EP 2 254 353 A3 describes a hearing device with a transducer and a method for manufacturing a transducer.

[0005] The object of the present invention is to create a micromechanical sound transducer that represents an improved compromise between sound pressure, frequency response and manufacturing effort.

[0006] The problem is solved by the independent patent claims.

[0007] Exemplary embodiments provide a micromechanical sound transducer (e.g., built into a substrate) with a first bending transducer or bending actuator and a second bending transducer or bending actuator. The first bending actuator has a free end and, for example, at least one or two free sides and is designed to be excited to vertical vibration by an audio signal, for instance, and to emit (or receive) sound. The second bending actuator also has a free end and is arranged relative to the first bending actuator such that the first and second bending actuators lie in or are suspended in a common plane. Furthermore, the arrangement is designed such that a gap (e.g., in the micrometer range) is formed between the first and second bending actuators, separating them from each other.The second bending actuator is always excited to vibrate in phase with the first bending actuator, which has the consequence that the gap remains essentially constant over the entire deflection of the bending actuators.

[0008] Exemplary embodiments of this aspect of the invention are based on the understanding that by using several separated bending transducers or actuators, separated from each other by a minimal (separation) gap, it is possible to achieve an almost constant, small gap (in the micrometer range) between the two actuators when the two transducers or actuators are deflected identically from the plane. This results in consistently high viscosity losses in the gap, which ultimately prevent an acoustic short circuit between the rear volume and the front volume (of the bending actuator). Compared to previous MEMS systems, which are mostly based on closed membranes, the present concept enables a significant increase in performance.The primary reason is that, due to actuator decoupling, no energy is required for the deformation of additional mechanical membrane elements, thus enabling significantly higher deflections and forces. Furthermore, nonlinearities only occur at considerably larger amplitudes of movement. While conventional systems sometimes require complexly shaped membranes or magnets that cannot yet be realized using MEMS technology, but can only be integrated hybridly with considerable effort, the present concept can be implemented using standard silicon technology methods. This offers significant advantages in manufacturing and cost. Due to the inherently low oscillating mass, both in terms of the design and the materials used, systems with an exceptionally wide frequency range and simultaneously high amplitudes of movement can be realized.

[0009] In accordance with another aspect, a micromechanical sound transducer is created with a first bending transducer or bending actuator (designed to be excited to vertical vibration) and an aperture element extending vertically (i.e., from the plane of the substrate and thus also from the plane of extension of the bending transducer) to the first bending transducer or bending actuator. The aperture element is separated from the free end of the first bending actuator by a gap.

[0010] The key insight here is that the aperture element, across the entire range of motion of the transducer or actuator (due to vibration), ensures that the distance between the aperture element and the free end of the actuator remains approximately constant. This achieves the same effect as described above, namely that an acoustic short circuit is prevented due to the high viscous losses at the free end (and possibly also the free sides) or in the gap. As a result, the same advantages are realized, particularly regarding the efficiency of the transducer, its bandwidth, and manufacturing costs.

[0011] Regarding the variant with at least two bending actuators, it should be noted that, according to the exemplary embodiment, the first and second bending actuators are identical. These can be, for example, planar, rectangular, trapezoidal, or generally polygonal bending actuators. According to another exemplary embodiment, these bending actuators can each have a triangular or circular segment shape. The triangular or circular segment shape is frequently used in micromechanical transducers that include more than two bending actuators. Therefore, according to another exemplary embodiment, the micromechanical transducer includes one or more additional bending actuators, such as three or four bending actuators.

[0012] As explained above, either the simultaneous or phase-coherent control of the two bending actuators or the provision of the aperture element allows the gap to remain small over the entire range of movement, starting from a gap that (in the rest state) is less than 10% or even less than 5%; 2.5%, 1%, 0.1% or 0.01% of the area of ​​the first bending actuator, i.e. that even when deflected it makes up a maximum of 15% or even only 10% (or 1% or 0.1% or 0.01%) of the area of ​​the first bending actuator. Regarding the variant with the aperture element, it should be noted that the height of the aperture element is dimensioned such that it is at least 30% or 50% or preferably 90% or even 100% or more of the maximum deflection of the first bending actuator in linear operation (i.e. linear mechano-elastic range) or the maximum elastic deflection of the first bending transducer (generally 5-100%).Alternatively, the height can be defined depending on the gap width (at least 0.5, 1, 3, or 5 times the gap width) or depending on the thickness of the bending transducer (at least 0.1, 0.5, 1, 3, or 5 times the thickness). These dimensioning specifications for the two variants enable the functionality described above / prevention of acoustic short circuits across the entire deflection range and thus also across the entire sound level range. According to another embodiment, a baffle element can be arranged not only opposite the free end but also, for example, on the unclamped sides around the bending actuator. This is particularly useful if the bending actuator is a single-sided clamped actuator.

[0013] According to one embodiment, the aperture element can have a varying cross-sectional geometry (e.g., a geometry curved / inclined towards the actuator) so that the slot has a largely constant cross-section along the actuator's movement. According to other embodiments, the aperture can form a mechanical stop to prevent mechanical overload.

[0014] According to another embodiment, a micromechanical sound transducer is created that includes a control unit which drives the second bending actuator so that it is excited to vibrate in phase with the first bending actuator. Furthermore, according to another embodiment, it can be advantageous to provide sensors that detect the vibration and / or the position of the first and / or the second bending actuator, enabling the control unit to drive the two bending actuators in phase. In contrast to previous systems, which usually lack sensors or only detect the displacement of the drive (not just the diaphragm), this principle allows the actual position of the sound-generating element to be determined using the easily integrated sensors. This is a significant advantage and enables considerably more accurate and reliable detection.This forms the basis for a controlled excitation (closed-loop), which allows external influences, aging effects and nonlinearities to be electronically compensated.

[0015] According to the invention, the bending actuators feature a so-called "cascading".

[0016] This means that the first and / or second bending actuator each comprise at least one first and one second bending element. These elements are connected in series. According to exemplary embodiments, "connected in series" means that the first and second bending elements each have a clamped end and a free end, and that the clamped end of the second bending element engages the free end of the first bending actuator, while its free end forms the free end of the entire bending actuator. The connection between the two bending elements can, for example, be formed by a flexible element. Optionally, the micromechanical transducer can have an additional frame, which is provided, for example, in the area of ​​the transition between the first and second bending elements. This frame serves for stiffening and mode decoupling.Regarding the two bending elements, it should be noted that, according to a preferred embodiment, these are controlled with different control signals, so that, for example, the inner bending element(s) are used for higher frequencies, while the outermost bending elements are driven to vibrate in a lower frequency range.

[0017] According to another aspect, a micromechanical sound transducer is created with at least one, preferably two, bending actuators, each bending actuator comprising a first and a second bending element connected in series. According to a further embodiment, such bending actuators can also have a flexible connection instead of a separation gap.

[0018] Exemplary embodiments of this aspect of the invention are based on the understanding that by connecting several bending elements of a bending actuator in series, it is possible to have different bending actuators responsible for different frequency ranges. For example, the innermost bending actuator can be designed for a high-frequency range, while the outermost actuator is used for the low-frequency range. In contrast to conventional diaphragm approaches, the described concept allows for cascading with several individually controllable actuator stages. Furthermore, the frequency-separated control in combination with the piezoelectric drives enables significant improvements in energy efficiency. The good mode decoupling also offers advantages in terms of sound reproduction quality. Additional advantages include, for example, the realization of particularly space-saving multi-way transducers.

[0019] In this embodiment of the bending actuator with cascading, the further developments described above are also applicable to additional embodiments. Of particular importance here are the features relating to the precise design of the cascading, e.g., the connecting element or the frames. Furthermore, the sub-aspects relating to the planar, rectangular, trapezoidal, or triangular (generally polygonal) bending actuator geometry are relevant for cascaded transducer configurations.

[0020] Another embodiment relates to a method for manufacturing a micromechanical sound transducer with cascaded bending actuators. The method comprises the steps of: providing a first layer that forms the first (and the second) bending actuator with the (respective) first and second bending element, and connecting the (respective) first and second bending elements.

[0021] According to one embodiment, it would be conceivable to nest actuators within each other and / or to make them of different sizes, e.g. to cover different frequency ranges.

[0022] Further developments are defined in the dependent claims. Exemplary embodiments of the present invention are explained in the accompanying figures. These show: Fig. 1a a schematic representation of a micromechanical transducer with two bending actuators according to a basic embodiment; Fig. 1b a schematic representation of a micromechanical transducer with one bending actuator and a vertical aperture element according to a further basic embodiment; Fig. 1c a schematic representation of a bending actuator with an arbitrarily adjacent structure to illustrate the improvement of the concepts from the Fig. 1a and 1bcompared to the prior art; Figs. 2a-c schematic cross-sections of possible actuator elements according to exemplary embodiments; Figs. 3a-d schematic top views of bending actuator configurations according to exemplary embodiments; Fig. 4 a schematic diagram illustrating a simulated sound pressure level for different exemplary embodiments; Fig. 5 a schematic representation of a micromechanical sound transducer with two bending actuators, each comprising a cascade, according to exemplary embodiments; Figs. 6a-c schematic top views of bending actuator configurations with cascade according to exemplary embodiments; Fig. 7 a schematic diagram illustrating a simulated sound pressure level with a bending actuator configuration with cascade; Figs. 8a,b schematic views or partial views of a top view of a bending actuator configuration with cascade according to a further exemplary embodiment; Fig.9. A schematic diagram illustrating the FEM-simulated displacement of a cascaded micromechanical transducer according to an embodiment; Fig. 10a-c: schematic top views of bending actuators with laterally arranged aperture elements according to embodiments; Fig. 11a-d: schematic representations illustrating a process flow in the manufacture of a micromechanical transducer according to embodiments; Fig. 12: a schematic representation of an array with a plurality of micromechanical transducers according to an embodiment; Fig. 13a: schematic representations of different implementations of the in . Fig. 1bExplained aperture structures according to exemplary embodiments; Figs. 14a-c schematic representations of micromechanical sound transducers with a cover according to additional exemplary embodiments; Figs. 15a-h schematic representations of top views of micromechanical sound transducers according to exemplary embodiments; and Fig. 16 a schematic representation of a double-sided clamped micromechanical sound transducer according to exemplary embodiments.

[0023] Before exemplary embodiments of the present invention are explained in detail below with reference to the accompanying drawings, it should be noted that equivalent elements and structures are provided with the same reference numerals, so that their descriptions are applicable to each other or interchangeable.

[0024] Fig. 1aFigure 1 shows a sound transducer 1 with a first bending actuator 10 and a second bending actuator 12. Both are arranged or clamped in a plane E1, as can be seen from the clamping points 10e and 12e. The clamping can be achieved by etching the bending actuators 10 and 12 from a common substrate (not shown), so that the bending actuators 10 and 12 are connected to the substrate on one side and a (common) cavity (not shown) is formed under the actuators 10 and 12. It should be noted that the bending actuators 10 and 12 shown here can, for example, be pre-stressed, so that the illustration either shows a rest state or a deflected moment (in this case, the rest state is shown by the dashed line).As can be seen, the two actuators 10 and 12 are arranged horizontally next to each other, so that the actuators 10 and 12, or at least the clamping points 10e and 12e, lie in a common plane E1. This statement refers primarily to the rest state, whereas in the prestressed case, the plane E1 mainly refers to the common clamping areas 10e and 12e.

[0025] The two actuators 10 and 12 are arranged opposite each other, so that a gap 14 of, for example, 5 µm, 25 µm, or 50 µm (generally in the range between 1 µm and 90 µm, preferably less than 50 µm or less than 20 µm) exists between them. This gap 14, which separates the two bending actuators 12 and 14 clamped at one end, can be referred to as the decoupling gap. The decoupling gap 14 varies only minimally over the entire deflection range of the actuators 10 and 12, e.g., by a factor of 1, 1.5, or 4 (generally in the range of 0.5–5), i.e., a variation of less than +500%, +300%, +100%, +75%, or less than +50% of the gap width (at rest), thus eliminating the need for additional sealing, as will be explained below.

[0026] The actuators 10 and 12 are preferably driven piezoelectrically. Each of these actuators 10 and 12 can, for example, have a layered structure and, in addition to the piezoelectric active layers, have one or more passive functional layers. Alternatively, electrostatic, thermal, or magnetic drive principles are also possible. When a voltage is applied to the actuators 12, they deform, or in the piezoelectric case, the piezoelectric material of the actuators 10 and 12 deforms, causing the actuators 10 and 12 to bend out of the plane. This bending results in the displacement of air. With a cyclic control signal, the respective actuator 10 and 12 is then excited to vibrate in order to emit a sound signal (or, in the case of a microphone, to record it). The actuators 10 and 12, or the corresponding control signal, are designed such that adjacent actuator edges or...The free ends of actuators 10 and 12 experience an almost identical displacement from the plane E1. The free ends are labeled 10f and 12f. Since actuators 10 and 12, or rather their free ends 10f and 12f, move parallel to each other, they are in phase. Therefore, the displacement of actuators 10 and 12 is described as being in phase.

[0027] Consequently, a continuous deflection profile forms in the overall structure of all actuators 10 and 12 when driven, interrupted only by the narrow decoupling slots 14. Since the gap width of the decoupling slots is in the micrometer range, high viscous losses occur at the slot sidewalls 10w and 12w, significantly restricting the airflow passing through. This prevents the dynamic pressure equalization between the front and back of the actuators 10 and 12 from occurring quickly enough, thus reducing the acoustic short circuit regardless of the actuator frequency. This means that, in the considered acoustic frequency range, a narrowly slotted actuator structure behaves fluidically like a closed diaphragm.

[0028] Fig. 1bThis shows another variant of how an actuator of a micromechanical sound transducer can achieve good sound pressure performance without a seal. The embodiment shown in Fig. 1bFigure 1 shows the sound transducer 1' encompassing the actuator 10, which is fixedly clamped at point 10e. The bending actuator 10 can be etched from a substrate (not shown) so that a cavity (not shown) is formed beneath it. The free end 10f can be excited to vibrate over a region B. Opposite the free end 10f, a vertically arranged aperture element 22 is provided. This aperture element is preferably at least as large as or larger than the range of motion B of the free end 10f. The aperture elements 22 preferably extend on the front and / or back of the actuator, i.e., viewed from the plane E1 (substrate plane), into a lower plane and a higher plane (e.g., perpendicular to the substrate). Between the aperture element 22 and the free end 10f, there is a gap 14' comparable to the gap 14 from Fig. 1a planned.

[0029] The aperture element 22 enables the width of the intended decoupling gap 14' to remain approximately constant even in the deflected state (see B). Thus, in this configuration, no significant openings arise at the adjacent edges as a result of the deflection, as is the case, for example, in Fig. 1c depicted.

[0030] Fig. 1c Figure 1 shows an actuator 10, which is also clamped at point 10e. Opposite it, an arbitrarily adjacent structure 23 without vertical extension and without movement is provided. As a result of a deflection of the actuator 10, an opening forms in the region of the free end 10f of the actuator. This opening is designated with the reference symbol "o". Depending on the deflection, these opening cross-sections 14o can be significantly larger than the decoupling slots (cf. Figure 10). Fig. 1a and 1b) or, more generally, a coupling slot in the resting state. An airflow between the front and back can occur through this opening, leading to an acoustic short circuit.

[0031] According to exemplary embodiments, the side surface of the aperture element 22 or the aperture element 22 itself can be adapted to the movement of the actuator 10 in the deflection range B. Specifically, a concave shape would be conceivable.

[0032] Both structure 1 from Fig. 1a as well as structure 1' from Fig. 1b This enables the acoustic short circuit to be prevented by providing means that keep the decoupling gap 14 or 14' approximately constant over the entire range of motion.

[0033] As explained above, a piezoelectric material can be used according to one embodiment. Fig. 2 Figure ac shows three different cross-sections of possible actuator elements. Fig. 2aA unimorphic structure is shown. A passive layer 10p, 12p and a piezoelectric layer 10pe or 12pe are also applied.

[0034] Fig. 2b The diagram shows a bimorphic structure. It includes two piezoelectric layers 10pe_1 or 12pe_1 and 10pe_2 or 12pe_2, as well as a passive intermediate layer 10p or 12p.

[0035] In Fig. 2c A piezoelectric layer stack is shown, each with two piezoelectric layers 10pe_1 or 12pe_1 and 10pe_2 and 12pe_2.

[0036] All piezo actuators shown from the Figs. 2a to 2cThey all have in common that they are formed from at least two layers: a piezoelectric layer 10pe or 12pe and another layer, such as a passive layer 10p, 12p or another piezoelectric layer 10pe_2, 12pe_2. The piezoelectric layers 10pe, 12pe, 10pe_1, 12pe_1, 10pe_2, 12pe_2 can be designed as multilayer systems with additional separating layers (see layers 10p, 12p) and / or can themselves be formed from any number of sublayers (see dashed lines). Contact is achieved, for example, by planar or interdigital electrodes.

[0037] According to an alternative embodiment, a thermal drive can also be used, which, analogous to piezoelectric actuators, can have a multilayer structure. In principle, the structure of a thermal drive then corresponds to the structure described in relation to... Fig. 2a-cexplained for piezoelectric layers, where thermally active layers are used instead of piezoelectric layers.

[0038] Referring to Fig. 3a-c Various actuator arrangements are used, comprising at least two opposing actuators (see below). Fig. 3b ) explained.

[0039] Fig. 3a Figure 1 shows an actuator arrangement with four actuators 10', 11', 12', and 13'. Each of these actuators 10' to 13' is triangular and clamped on one side along the hypotenuse. According to one embodiment, the triangles are right-angled triangles, so that the right-angled vertices of the actuators 10' to 13' all meet at a single point. Consequently, the feedback columns 14 extend between the legs of each actuator.

[0040] Depending on the embodiment, the individual actuators 10' to 13' can be further subdivided, as indicated by the dashed lines. With subdivision, the clamping is then no longer along the hypotenuse, but along one of the legs, while the decoupling gaps then extend along the hypotenuse and along the other leg.

[0041] Regardless of whether there are four or eight actuators, the triangular design allows the adjacent free ends (separated by the respective column 14) to experience the most equal deflection possible.

[0042] Fig. 3b In principle, it shows the top view of the embodiment. Fig. 1a , where it is just indicated here that both actuator 10 and actuator 12 can be subdivided, e.g. along the axes of symmetry (see dashed line).

[0043] Fig. 3cFigure 1 shows another embodiment in which the entire transducer is arranged in a circular segment and comprises a total of four 90° segments as actuators 10" to 13", which are in turn separated from each other by the separating gap 14. In this circular transducer, the individual actuators 10" to 13" can be further subdivided, as indicated by the dashed lines.

[0044] All examples of implementation from the Figures 3a to 3c They have in common that they are clamped at the edge, as indicated by the respective range 10e' to 13e' or 10e and 12e or 10e" to 13e" respectively.

[0045] Furthermore, it should be noted at this point that, as can be seen from the examples of implementation from Fig. 3a-3cAs shown, the separation gaps 14 preferably extend along the lines of symmetry. In embodiments with more than two actuators, this means that, according to a preferred embodiment, the separation gaps meet at the centroid of the total area of ​​the transducer.

[0046] Fig. 3d Figure 1 shows (in top view) another version of a micromechanical sound transducer with four (here rectangular or square) actuators 10‴, 11‴, 12‴ and 13‴, arranged in the form of four quadrants of a rectangle or square. The four actuators 10‴ to 13‴ are separated from each other by two intersecting separating slits 14. Each of the actuators 10‴ to 13‴ is clamped diagonally, i.e., on two sides at the outer edge.

[0047] Referring to Fig. 4 The influence of the gap width is shown. Fig. 4The figure shows the resulting sound pressure level (SPL) over a frequency range of 500 Hz to 20 kHz for four different gap widths (5 µm, 10 µm, 25 µm, and 50 µm). In the depicted frequency range, the reduction in the sound pressure level (SPL) (acoustic short circuit) for gap widths below 10 µm becomes negligible, and the structure behaves acoustically like a closed diaphragm. As can be further seen, in the higher frequency range (e.g., above 6000 Hz), the influence of the gap width decreases significantly. Compared to closed diaphragm systems, the present systems are characterized by significantly higher efficiency due to the decoupling of the individual actuators. This is reflected in very high excursions and sound pressure levels. Furthermore, there are additional advantages regarding linearity.

[0048] Referring to Fig. 5 An example implementation will now be explained using a corresponding further aspect. Fig. 5 Figure 1 shows the setup of a 1" micromechanical transducer with two actuators, 10* and 12*. Each actuator, 10* and 12*, comprises an inner and an outer stage. This means that actuator 10* includes a first actuator element, 10a* (outer stage), and a second actuator element, 10i* (inner stage). Similarly, actuator 12* includes actuator element 12a* and actuator element 12i*.

[0049] As shown here, the outer stages 10a* and 12a* are always clamped, specifically via sections 10e* and 12e*. The opposite end of the actuators 10a* and 12a* is referred to as the free end. The inner stages 10i* and 12i* are coupled to this free end by means of optional connecting elements 17. The coupling is implemented such that, for example, the connection is again made via one end of the inner actuator elements 10i* or 12i*, namely in such a way that the opposite ends of the inner actuators 10i* or 12i* serve as free ends. In other words, this means that the actuator 10* or 12* is constructed such that the inner stage 10i* (or 12i*) is connected in series with the outer stage 10a* (12a*).

[0050] As shown here, a decoupling gap 14* is formed between the free ends of elements 10i* and 12i*. This gap is not necessarily designed in the same way as the decoupling gap described in the above embodiments (see Figure 1). Fig. 1a ) was explained. This means that, analogous to the embodiments described above, the actuators 10* and 12* are separated from each other only by a decoupling gap 14 a few micrometers wide and are preferably designed such that adjacent structural edges (free edges of the inner elements 10e* and 12e*) experience the same deflection (synchronous or in phase) from the plane E1 (in which the actuators 10* and 12* or the clamping area 10e* and 12e* are arranged) during operation. Alternatively, the inner elements 10i* and 12i* could be connected in the area of ​​the gap shown, e.g., by means of a flexible material.

[0051] According to optional embodiments, the individual cascaded stages can rest on a frame 19. In this embodiment, the frame 19 is arranged such that the clamped ends of the inner stages 10i* and 12i* rest on the same frame 19. Generally, however, it is preferred that the frame 19 is arranged so that it is located in the area of ​​the connection points (see connecting elements 17). The frame makes it possible to suppress parasitic vibration modes as well as unwanted mechanical deformations.

[0052] Although the above embodiments assume that two actuators 10* and 12*, each with an inner and outer actuator stage comprising actuator elements 10a*, 10i*, 12a*, and 12i*, are provided, it should be noted here that, according to further embodiments, a micromechanical transducer with only one actuator (e.g., actuator 10*) is created, which has the first stage 10a* and the second stage 10i* in a corresponding series arrangement. This actuator can, for example, oscillate freely relative to a fixed end, so that a gap is formed between them, or it can be flexibly connected to a fixed end. According to another embodiment, an aperture, such as that found, for example, in Fig. 1b As explained, it is conceivable.

[0053] Referring to Figs. 6a to 6c Three implemented sound transducers are explained in a schematic top view, where the configurations consist of Figs. 3a to 3cis extended by cascading (two-stage cascading configurations).

[0054] Fig. 6a Figure 1 shows a micromechanical sound transducer with four actuators 10*' to 13*', each actuator 10*' to 13*' comprising two actuator elements 10a*', 10i*' to 13i*', and 13a*', respectively. The inner elements 10i*' to 13i*' are triangular in shape (with respect to their area), while the outer elements 10a*' to 13a*' are trapezoidal in shape (with respect to their area). The smaller leg of the trapezoidal actuator 10a*' to 13a*' is connected to the hypotenuse leg of the triangular actuator 10i*' to 13i*' via connecting elements 17. In this embodiment, the optional connecting elements are preferably arranged at the corners of the trapezoid and the triangle, respectively.

[0055] Fig. 6b The top view essentially shows the electromechanical sound transducer made of Fig. 5with the inner actuators 10i* and 12i* and the outer actuators 10a* and 12a*. Connecting elements 17 are also provided at the corners of the rectangular inner and outer elements 10i*, 10a*, 12i* and 12a*.

[0056] Fig. 6c Starting from the circular segment-shaped micromechanical transducer, the cascaded actuators 10*" to 13*" are shown, each actuator having an inner actuator element and an outer actuator element. The inner actuator elements 10i*" to 13i*" are designed as circular segment-shaped elements, while the outer elements 10a*" to 13a*" are designed as circular disk segments. The connection is made via connecting elements 17.

[0057] All examples of implementation from the Figs. 6a to 6cThey have in common that, according to preferred embodiments, the actuators 10*' to 13*' or 10* to 12* or 10*" to 13*" are separated from each other by separating gaps 14. Additional separating gaps 15 can also be provided between the inner actuators (for example, 10i*' and 10a*'), which are bridged only by the connecting elements 17. In other words, this means that the outer stages (for example, 10a* and 12a* in Fig. 6b ) are connected to the second inner stages 10i* and 12i* respectively via at least one connecting element, but preferably via two or more spaced-apart connecting elements 17. The connecting elements can be designed as mechanical spring elements or joints.

[0058] As in connection with Fig. 3a-cAs explained, the actuators can also be further subdivided, so that any number of actuators can be created per actuator element 10* or 12* (see dashed line).

[0059] Now that the structure of the transducers has been explained, their function will be discussed below: In the driven state, the actuators of the outer stage deflect the inner stage out of the plane, with the actuators of the inner stage exerting a further deflection. This results in a deflected structure which, due to the high viscous losses in the decoupling slots, behaves acoustically like a closed diaphragm.

[0060] Alternatively, the cascaded overall structure can also have three or more stages. The different stages can be driven with either identical or different drive signals. In the case of different drive signals, the stages can be operated in different frequency ranges and, for example, form a multi-way transducer with a particularly small footprint.

[0061] It should be noted at this point that this relates to Fig. 1b The principle of flow baffles explained can also be extended to multi-part cascaded systems, e.g. to minimize acoustic losses between connecting elements and actuators or intermediate stages.

[0062] With reference to the above examples, it should be noted that the ones in the Figs. 6a to 6cThe described variants can be combined as desired according to additional embodiments. For example, it is possible that instead of the four inner actuator elements 10a*' to 13a*', the following can be used: Fig. 6a only two internal actuator elements 10i* and 12i*, as they are in Fig. 6b shown, are provided for. Furthermore, it is also conceivable that only an inner actuator element, e.g. also in combination with an aperture (see embodiment from Fig. 1b ) is planned.

[0063] Fig. 7The diagram shows the simulated sound pressure across the frequency range, broken down by inner and outer stages. As can be seen, the outer stage is particularly suited to the lower frequency range (maximum sound pressure at approximately 1500 Hz), while the inner stage serves the higher frequency range (maximum sound pressure at approximately 10000 Hz). In this particular case, a MEMS transducer with a chip size of 1x1 cm was used, and measurements were taken at a distance of 10 cm.

[0064] Fig. 8 The concept of cascading is illustrated using the example of a specific two-stage design. Fig. 8a The top view is shown, with in Fig. 8b A close-up of the connection area is shown.

[0065] As shown by the Fig. 8a As can be seen, the two-part design features outer actuators 10a*' and inner actuators 10i*'. In terms of configuration, this is shown here in Fig. 8aThe design shown is from the design Fig. 8a comparable. In the embodiment shown here, the decoupling slots 14 are indicated by solid lines. As can be seen particularly in the enlargement from Fig. 8b As can be seen, decoupling slots 14 are also provided between the individual stages.

[0066] As opposed to Fig. 6a is the design made of Fig. 8a also additionally illustrates the frame structure 19*', which is smaller in lateral dimensions than the lateral dimensions of all internal steps 10e*'.

[0067] As demonstrated by Fig. 8b As can be seen, folded springs 17*' serve as connecting elements, the spaces between which are provided with decoupled filling structures 17f*', e.g. made of a material from the spring or actuator. Analogously, the spaces 14 between the actuators of both stages also have such filling structures 17f*'.

[0068] In Fig. 9 is a deflection profile of the example design obtained by means of FEM simulation. Fig. 8a and b shown in the three-dimensional cross-section. As illustrated by the deflection values ​​shown by hatching, an almost continuous deflection profile is formed despite the decoupling slots, which is only interrupted by the narrow decoupling slots 14.

[0069] Referring to Fig. 10 will be an extension of the design Fig. 1a as well as the design from Fig. 1b explained. The configuration from Fig. 10a is comparable to the configuration from Fig. 1b, wherein the aperture element 22 provided opposite the actuator 10 clamped on one side (see clamping 10e) is not only provided in the area of ​​the free end 10f, but also extends along the sides of the actuator, i.e. along the entire decoupling slot 14'. The laterally arranged aperture elements are marked with the reference numerals 22s.

[0070] Fig. 10b assumes a sound transducer configuration with two opposing actuators 10 and 12, as used, for example, in Fig. 3b This is shown. These are again actuators clamped on one side (see clamping 10e or 12e). In this embodiment, a vertically arranged aperture element 22s extends along the lateral decoupling slots 14.

[0071] Both the exemplary embodiment from Fig. 10a as well as the exemplary embodiment from Fig. 10bThe use of the laterally arranged aperture elements 22s enables good fluidic separation of the front and back sides in the structures with discontinuous deflection profiles shown here.

[0072] Fig. 10cFigure 1 shows another variant in which four actuators 10ʺʺ, 11ʺʺ, 12ʺʺ, and 13ʺʺ extend from a central surface 16. The four actuators 10ʺʺ to 13ʺʺ are each trapezoidal and are clamped against the surface 16 on one side via their short side. The four actuators 10ʺʺ to 13ʺʺ are separated from each other by four diagonally arranged separating slits 14 (which extend as an extension of the diagonals of the surface 16), so that the long side of the actuators 10ʺʺ to 13ʺʺ can oscillate freely. To provide a seal against the edge regions, a (circumferential) vertically formed aperture element 22s is provided along the long side of the trapezoidal actuators 10ʺʺ to 13ʺʺ.

[0073] Fig. 12 Figure 1 shows a micromechanical sound transducer in array form. The micromechanical sound transducer shown here has eight sound transducers 1, as they are described, for example, in relation to… Fig. 1aThese eight transducers 1 are arranged in two rows and four columns. This allows for a large surface area and thus a high sound pressure level. Assuming that each actuator of the transducers 1 has a base area of ​​5 x 5 mm, this effectively creates a diaphragm area of ​​200 mm². In general, the transducer depicted in this way is arbitrarily scalable, so that transducer sizes of, for example, 1 cm in length or more (generally in the range of 1 mm to 50 cm) can be achieved.

[0074] Even though in the example shown here Fig. 12 For example, the micromechanical sound transducer 1 from Fig. 1a As explained above, it should be noted here that any other sound transducers, such as the 1' transducer from Fig. 1b or the cascaded transducers from Fig. 5can be used. Other forms and arrangements are also conceivable.

[0075] In further embodiments, the individual actuators described above can be equipped with sensors. These sensors enable the actual displacement of the actuators to be determined. Typically, these sensors are connected to the actuator control system, so that the control signal for each individual actuator is adjusted via a feedback loop to ensure that the actuators oscillate in phase. The sensors can also be used to detect non-linearities and, during control, to distort the signal in such a way that these non-linearities can be compensated for or reduced.

[0076] Background: Since the actuators also form the sound-generating element, aging effects and nonlinearities during operation can be directly measured and, if necessary, electronically compensated. This represents a significant advantage over conventional membrane-based systems, where either no sensors are present or only the behavior of the actuators, but not of the sound-generating membrane element, can be detected.

[0077] Position detection is preferably achieved via the piezoelectric effect. For this purpose, one or more areas of the piezoelectric layer on the actuators can be equipped with separate sensor electrodes, from which a voltage or charge signal approximately proportional to the displacement can be detected. Furthermore, multiple piezoelectric layers can be implemented, with at least one layer being partially used for position detection. A combination of different piezoelectric materials is also possible, arranged either on top of or next to each other (e.g., PZT for actuators, AIN for sensors).

[0078] As an alternative to piezoelectric sensor elements, the integration of thin-film strain gauges or additional electrodes for capacitive position detection is also possible. If the actuator structures are made of silicon, piezoresistive silicon resistors can also be integrated directly.

[0079] All of the above-mentioned aspects have in common that a membrane-free concept, fully compatible with MEMS manufacturing processes, is created for generating high sound pressure levels. All embodiments enable a particularly compact design. Optional cascading allows for the realization of integrated multi-path transducers. Depending on further developments, the control system can be designed with integrated position sensors to minimize distortion of the emitted sound.

[0080] The following table lists possible materials for the individual functional elements. function materials Piezoelectric layer PZT, PNZT, AIN, AlScN, ZnO, BCZT, KNN Passive layer Si, poly-Si, SiN, SiNO, SiO 2 , AIN, metals Frame Si, metals, glass, [piezoelectric layer], [passive layer] Aperture Si, metals, glass, polymers, [piezoelectric layer], [passive layer] Connecting elements [passive layer], [piezoelectric layer]

[0081] Possible dimensions are as follows: - Actuator surface 50x50µm 2< - 5x5cm 2< - Decoupling slot 0,1µm - 40µm - Auslenkungsamplitude 0.01µm - 3mm

[0082] Such transducers can be operated, for example, with a first eigenmode from 10 Hz to 300 kHz. The excitation frequency is, for example, statically selected up to 300 kHz.

[0083] The described actuator structures are suitable for applications where sound needs to be generated in a frequency range between 10 Hz and 300 kHz with the smallest possible component volume (< 10 cm³). This applies primarily to miniaturized sound transducers for wearables, smartphones, tablets, laptops, headphones, hearing aids, and also ultrasound transducers. Other applications involving fluid displacement are also possible (e.g., fluid-mechanical and aerodynamic drive and guide structures, inkjet printing).

[0084] Exemplary embodiments provide a miniaturized device for displacing gases and liquids with at least one bending actuator that can be deflected out of the plane, characterized in that the device contains narrow opening slots with such high flow resistance that the device behaves fluid-technically in the acoustic and ultrasonic frequency range (20 Hz to 300 kHz) approximately like a closed membrane.

[0085] According to further embodiments, the device can include the following features: decoupling slots in the actuator materials, the total length of which is a maximum of 5% of the total actuator area and which have an average length-to-width ratio of over 10. Additionally, according to further embodiments, the device can be designed such that openings created in the deflected state constitute less than 10% of the total actuator area, so that a high fluidic separation between the front and back sides is achieved even without a closed diaphragm.

[0086] According to another embodiment, the device can have two or more opposing, separate actuators.

[0087] According to another embodiment, the actuators can be driven piezoelectrically, electrostatically, thermally, electromagnetically, or by a combination of several principles. According to a further embodiment, it would also be conceivable for the device to be designed with two or more actuator stages coupled via connecting elements.

[0088] According to another embodiment, it would also be conceivable that the device has two or more actuator stages that are controlled with separate signals and thus form a two-way or multi-way sound transducer.

[0089] Referring to the exemplary embodiment from Fig. 5 or 6a bis c It should be noted that each actuator element 10a*, 12a*, 10i* and 12i* is an active, individually controllable element. This can be actuated, for example, piezoelectrically or by another principle explained here.

[0090] According to another embodiment, the device has a frame structure for stiffening and mode decoupling.

[0091] In the above examples, the actuators were specifically described as single-sided clamped actuators. It should be noted here that double-sided clamping is also possible (see...). Fig. 3d ) or, more generally, multi-sided clamping devices would be conceivable.

[0092] Further embodiments provide a device with flow baffles to reduce the opening cross-sections between the front and back sides in the deflected state. According to another embodiment, the device can include sensor elements for position detection and control.

[0093] According to further embodiments, the device can be designed to generate sound or ultrasound in air (a gaseous medium), i.e., in the range of 20 Hz to 300 kHz. Other areas of application include the generation and control of airflow, e.g., for cooling.

[0094] The following refers to Fig. 11 A possible manufacturing process for the above-mentioned transducers is explained. The embodiment shown here is from the Fig. 11a-d This enables the production of the embodiment as it is found, for example, in Fig. 1b As shown. However, with slight modifications, the embodiments shown in the further figures, in particular from, can also be achieved using the method presented here. Fig. 1a detectable.

[0095] In the first in Fig. 11a In the step shown, a passive layer 50p is applied to a substrate 48, before a piezoelectric layer 50pe with two electrodes 50e is provided.

[0096] Substrate 48 can be an SOI wafer (silicon on insulator) comprising an SI substrate. SiO2 layers 50p are then deposited onto this with the material described in the following diagram: Fig. 1b The insulators 50pi and Si insulating layers, such as piezoelectric functional layers (PZT) 50pe, are deposited. The corresponding metal electrodes (Pt, Au, Mo, ...) 50e can then be deposited.

[0097] In the next step, which will take place in Fig. 11b As shown, the electrodes 50e, the PZT 50pe, and the insulating layer 50p are then structured. This creates, for example, the grooves 50g in the piezoelectric layer 50pe. The structuring can be done by wet or dry etching. Depending on the desired product design, the structuring step, or the creation of the groove 50g, is carried out in such a way that it has only minimal dimensions, in order to ensure that the product is made of Fig. 1a to produce or have larger dimensions, so that the intermediate product shown here is then developed in the direction of the product from 1b.

[0098] To remove the product from Fig. 1a To produce it, a small trench of 50g is applied and then the Fig. 11c The step shown was skipped, in order to then proceed as in Fig. 11d As shown, the back side is opened by a one- or multi-stage etching process and the movable structures are exposed. In this step, the substrate below the passivation layer 50p is removed, particularly in the area aligned with the structuring piezoelectric actuators 50pe. This creates the cavity 48c.

[0099] To create a product, as it is in relation to Fig. 1b As explained, the optional step, which is described in Fig. 11c As shown, it has been carried out. Fig. 11c Figure 75 illustrates the application of the vertically extending aperture elements 57. These are inserted into the grooves 50g of the piezoelectric layer 50pe. Optionally, the lateral position of the grooves 57 can be chosen such that they are aligned with areas of the structured passivation layer 50p, so that, for example, the vertical aperture element 75 extends the wall of a groove in the passive layer 50p. The aperture elements 57 can be applied, for example, by electroplating, and preferably such that the aperture elements 57 protrude from the layer of piezoelectric elements 50p.

[0100] After the aperture elements 57 have been applied, the following then takes place, as already mentioned above in relation to the exemplary embodiment. Fig. 1a The single- or multi-stage etching of the back side of the substrate 48 to produce the cavity 48c is explained. As illustrated here, individual areas of the substrate 48 can remain intact, so that the frame 48f is formed within the cavity 48c. This frame corresponds, for example, to the one shown in Fig. 5 explained framework 19.

[0101] MEMS technologies can be adopted in the manufacturing steps described, so that the product described above can be manufactured using conventional manufacturing methods.

[0102] Although some aspects have been described in connection with a device, it is understood that these aspects also constitute a description of the corresponding process, so that a block or component of a device is also to be understood as a corresponding process step or as a feature of a process step. Similarly, aspects described in connection with or as a process step also constitute a description of a corresponding block, detail, or feature of a corresponding device.

[0103] The following sections will start from the basic embodiment. Fig. 1b Different implementations of the aperture 22 are explained. In all subsequently discussed embodiments, it is assumed that the discussed aperture 22*, 22 etc< is separated from the bending actuator 10 (fixed at the reference point 10e) by a gap 14', so that the free end 10f of the bending actuator 10 can move along the vertical extent of the aperture element 22* or 22 etc<. It should be noted that aspects of the subsequently discussed embodiments, as well as those of the embodiments already discussed, can be combined arbitrarily (e.g., a cover with rounded / slanted sides (apertures) or an asymmetrical aperture with a cover and stop...).

[0104] Fig. 13a Figure 1 shows a schematic cross-section of an aperture structure. It can be seen that the aperture structure 22* consists of several segments 22a*, 22b*, and 22c*. Segment 22a* extends from the substrate plane (plane of reference point 10e), in which the bending actuator 10 is located, for example, in its rest position, out of the substrate, while segment 22b* lies in the same plane of reference point 10e. Segment 22c* lies within the substrate or extends from the substrate surface into the substrate. All the depicted segments 22a*, 22b*, and 22c* can have different geometries, i.e., different longitudinal and transverse dimensions, as well as variable cross-sections, depending on the embodiment. Furthermore, according to other embodiments, it would be conceivable that the individual segments 22a*, 22b*, and 22c* could also have different materials or material properties.For example, segments 22c* and 22b* may be formed by the substrate itself, while segment 22a* has grown.

[0105] According to further embodiments, it would of course also be conceivable that more than the three segments 22a*, 22b* and 22c* shown are provided.

[0106] It should be noted that in the above and following embodiments, the middle position does not necessarily have to correspond to the rest position, but can also be shifted upwards or downwards as desired (electrically or mechanically preloaded).

[0107] Fig. 13b Figure 1 shows another embodiment of the aperture structure, here aperture structure 22**. The aperture structure 22**, or in particular the segment extending out of the substrate plane, has an angled cross-section that extends towards the actuator 10. This ensures that the slit 14' has a relatively constant width regardless of the position of the actuator 10. The reason for this is that the side of the aperture structure 22** directly opposite the actuator 10 extends approximately along the path of movement (circular path around the fixed point 10e). As shown here in Fig. 13b As shown, the aperture 22** can be angled either only upwards and / or also downwards. The asymmetrical structure shown here is therefore only an example; naturally, the lower segment of the aperture structure 22** can also be angled in a similar way to achieve a symmetrical structure.

[0108] This embodiment of the aperture structure 22** with the beveled inner surface has the advantage that gap widening at larger amplitudes can be reduced or compensated for. From a manufacturing perspective, the beveling can be achieved, for example, by adjusting the lacquer profile or the etching process.

[0109] Fig. 13c shows a further development of the aperture structure 22** from Fig. 13b , namely the aperture structure 22***. The aperture structure 22*** has a curved / rounded inner surface. This curvature extends along the arc-shaped path of movement of the actuator 10 or the free end 10f of the actuator 10. Although the rounded inner surface is shown here only on the side extending out of the substrate, this rounded inner surface can of course also be present on the aperture structure side in the substrate plane. Analogous to the embodiment from Fig. 13b The aperture structure 22*** with its rounded inner surface reduces or compensates for gap widening at large amplitudes. From a manufacturing perspective, this rounding can be achieved, for example, by adjusting the paint profile or the etching profile.

[0110] Fig. 13d Figure 22**** shows another aperture structure. Here, the cross-section at the end of aperture structure 22**** has a widening or overhang, which serves as a mechanical stop for actuator 10 or the free end 10f of the actuator. This stop advantageously provides mechanical overload protection.

[0111] Fig. 13e Figure 1 shows another aperture structure 22*****, in which the aperture structure 22***** is asymmetrically constructed. The reason for this is that there are actuators 10 that are primarily deflected in one direction, so that the vertical extension of the aperture 22***** extends in one direction, here out of the substrate plane. Although the deflection of the actuator 10 and the extension of the aperture structure 22***** are shown here upwards (out of the substrate plane), this can, of course, also be reversed according to exemplary embodiments, i.e., that both elements extend into the substrate. It should be noted that the displacement of the actuator's rest position can be achieved by an electrical offset in the control signal or a mechanical protrusion (e.g., layer stress in actuator layers).

[0112] Fig. 13f Figure 1 shows an example of an aperture structure 22****** with a small extent. The aperture structure 22****** can be implemented so flat when the deflection of the actuator (10) is small. For example, the height of the aperture 22****** is within the range of the actuator thickness. This variant has advantages in terms of manufacturing, as additionally applied aperture structure areas can be omitted.

[0113] Fig. 13g Figure 1 shows an example of an aperture structure 22*******, which consists of a substrate region 23s and the actual aperture element 22*******. The upper aperture structure 22******* can be made, for example, of an electroplated metal or a polymer (SU8, BCB, ...), or even of glass or silicon. The lower aperture structure 23s consists primarily of the substrate (e.g., silicon or glass) itself and can be provided with additional layers according to further embodiments.

[0114] Fig. 13h Figure 1 shows another aperture structure without an additional applied element. It is assumed that the bending actuator 10 oscillates primarily into the substrate plane, thus eliminating the need for an aperture element protruding from the substrate plane. Here, the aperture element consists of the substrate element 23s, which forms the lower aperture structure. It should be noted that, as explained above, the rest position of the actuator 10 can be shifted downwards via mechanical preload or an electrical offset, making the aperture element 23s sufficient. In operation, the actuator can simply be deflected downwards, eliminating the need for an upward aperture and thus reducing manufacturing effort.

[0115] Fig. 13i Figure 22******** shows another aperture structure, which essentially consists of a thin layer applied to the substrate element 23s. Depending on the desired actuator deflection, the layer thickness of the aperture element 22******** can be in the range of the actuator thickness. The substrate 23s can (but does not have to) also act as an aperture structure and be flush with the aperture structure 22******** or have an offset.

[0116] Referring to Fig. 14a bis 14c Further embodiments are explained in which the micromechanical sound transducer is extended by an additional substrate 220a, 220b and 220c (cover). According to these embodiments, the additional substrate 220a, 220b, 220c forms the aperture structure.

[0117] Fig. 14a Figure 1 shows a substrate 220a designed as a cover, which is placed on a substrate 23s above a cavity 23k of the bending actuator 10, so that the bending actuator 10 can oscillate within the cover 220a, or within the space defined by the interior of the cover 220a and the cavity 23. The cover 220a is arranged on the side opposite the free end such that the inner wall of the cover 220a is separated from the end 10e by the gap 140. Since the cover 220a is completely closed in this embodiment, the bending actuator 10 emits sound, for example, through the cavity 23k.

[0118] In this embodiment, it should be noted that all the above embodiments and their explanations essentially assume that the sound is emitted from the substrate. Of course, depending on the embodiment, it is also conceivable that the sound is conducted through the substrate or through a cavity in the substrate.

[0119] It should be noted at this point that Fig. 14a a cross-section through the substrate 220a, wherein the further substrate extends, for example, in a circular or angular shape around the bending actuator 10 to create a (back) volume or, more generally, a cover for it. From a manufacturing perspective, it should be noted that the cover 220a can, for example, be made from a second structured substrate (i.e., a substrate with a cavity) (see reference numeral 221k). This second substrate is then applied to the substrate with the bending actuator 10, so that the cavity 221k is aligned with the cavity 23, at least partially (in the area of ​​the gap 140).

[0120] Fig. 14b Figure 2 shows another embodiment with a modified cover 220b, where the remaining structure is based on the same actuator 10 and substrate 23s. Cover 220b differs from cover 220a in that it has optional sound openings 222o and 222s. The sound opening 222o, or the multiple sound openings 222o, are located on the main surface of cover 220b, while the opening 222s is provided laterally. It should be noted that, according to other embodiments, it is sufficient to provide only one opening, either 222o or 222s. The enclosed air volume in the cavity 221k can be ventilated through these openings 222o and 222s. The openings can serve for sound emission or for pressure equalization. Several openings can together form one or more grid structures that protect the actuator from mechanical impacts and dust.

[0121] Fig. 14c Figure 1 shows another sound transducer with a cover 220c having an opening 222o. The bending actuator is mounted on another substrate 230s, which has a lateral opening 232s. The substrate 230s is mounted on another substrate 233s or a cover 233s, thus closing the cavity 230k. This further substrate 233s may also have optional sound openings 233o. This forms a closed volume or a volume ventilated via at least one of the optional openings 232s, 233o, or 222o. The volume is essentially formed by the cavities 221k and 230k and is opened via at least one or more openings. The openings can serve for sound emission or to allow pressure equalization. Several openings can interact to form one or more grid structures that protect the actuator 10 from mechanical impact and dust.

[0122] The following refers to the Figuren 15a bis 15h Different actuator geometries are explained, which differ from the geometries from Fig. 10 are extended. In illustrations, the actuator is designated with reference numeral 100 or 100_1 to 100_4, while the aperture is designated with reference numeral 225. A coupling slot, designated with reference numeral 140, always extends between the actuator and the aperture.

[0123] It should be mentioned that in exemplary embodiments, the actuator geometry can be combined arbitrarily (e.g. Fig 15f with rounded or triangular actuators).

[0124] Fig. 15a shows a top view of a rounded actuator 100, while Fig. 15b This shows a top view of a triangular actuator 100. Identical or different actuators 100 can be combined with each other as desired, for example, by means of Fig. 15c, 15d and 15eis shown.

[0125] Fig. 15c Figure 1 shows triangular actuators 100_1 to 100_4, which together describe a quadrilateral area. A cross-shaped aperture structure 225 separates the four actuators 100_1 to 100_4 from one another. A slot 145 is provided between the actuators 100_1 to 100_4 and the aperture structure 225. Alternatively, arrangements with 3, 5, 6, ... actuators would also be conceivable. It should also be noted that the overall area does not necessarily have to be quadrilateral, but can also be polygonal.

[0126] Fig. 15d Figure 1 shows two opposing rectangular actuators 100_5 and 100_6, which describe a quadrilateral. The rectangular actuators 100_5 and 100_6 each form three free corners, which are bounded by the H-shaped aperture 225 with associated slot 140.

[0127] Fig. 15e shows four circular segment-shaped actuators 100_7 to 100_10, which are similar to those in Fig. 15c are separated from each other by a cross-shaped aperture 225 with a slot 140.

[0128] In the variant of Fig. 15c The hypotenuse of each triangular actuator 100_1 to 100_4 is clamped, whereas in the embodiment from Fig. 15e The circular segment arcs 100_7 to 100_10 are firmly clamped in place. Alternatively, arrangements with 3, 5, 6... actuators would also be conceivable. It should also be noted that the overall surface does not necessarily have to be rectangular, but can also be polygonal.

[0129] By combining different actuators, reusable systems can be implemented, as demonstrated by the following: Fig. 15f, Fig. 15g und Fig. 15h shown.

[0130] Fig. 15f For example, three differently shaped, but each rectangular, actuators 100_11 to 100_13 are combined, each clamped on one of the four sides, with three of the four sides forming free ends. A labyrinthine aperture 225 is provided between the free ends, which, using the slots 140, separates the actuators 100_11 to 100_13. All actuators 100_11 to 100_13 have, for example, different sizes (areas) and can thus be designed for different frequency ranges.

[0131] Fig. 15g Figure 1 shows two actuators, 100_14 and 100_15, the first being a small, rectangular actuator, 100_14. The larger actuator, 100_15, is also rectangular but has a recess 100_15a for the other actuator, 100_14. The recess 100_15a is positioned so that both actuators are clamped on the same side. A slot 140 provided between the two actuators, 100_14 and 100_15, allows their movement to be decoupled. The larger actuator, 100_15, can be used, for example, for the low-frequency range, while the inner actuator, 100_14, can be used for the high-frequency range.

[0132] Fig. 15h Figure 1 shows a similar arrangement of the actuators 100_14 and 100_15, wherein, in addition to the separation of the two actuators 100_14 and 100_15 by means of the slot 140, a further aperture 225 is also provided. Both embodiments ( Fig. 15g und 15h The following features are common: at least along the free ends of the large actuator 100_15 with the recess 100_15a, in which the small actuator 100_14 is arranged, the apertures 225 and slot 140 are arranged. Such internal nesting or provision of larger and smaller actuators generally makes it possible to cover different frequency ranges with different actuators.

[0133] Fig. 16 Figure 1 shows a schematic top view of a bending actuator 10** clamped on two or more sides (see areas 10e1 and 10e2), which has at least one free side 10f** (here 2). This free side 10f** can be acoustically separated, as explained above, by an opposing aperture 22** (here 2, corresponding to the variants explained) with an intermediate gap 14**.

[0134] In the above embodiments, it was specifically assumed that a sound transducer for sound emission (loudspeaker) was to be created, which is why it was always referred to as a bending actuator. Of course, the principle is also reversible, so that, according to one embodiment, the sound transducer forms a microphone in which the bending transducer (see bending actuator) is designed to be excited, for example, by air, to vibrate (e.g., vertically) in order to output an electrical signal depending on this vibration (generally to detect acoustic waves from the environment). According to another embodiment, a component is created that incorporates both a loudspeaker and a microphone based on the concepts explained above. Here, the two components can be formed on the same substrate, which is advantageous from a manufacturing perspective. Quellenangaben

[0135] [Hou13] Houdouin et al., Acoustic vs electric power response of a high-performance MEMS microspeaker, IEEE SENSORS 2014 [Dej12] Dejaeger et al., Development and Characterization of a Piezoelectrically Actuated MEMS Digital Loudspeaker, Procedia Engineering 47 (2012) 184 - 187 [Gla13] Glacer et al., Reversible acoustical transducers in MEMS technology, Proc. DTIP 2013, [Yi09] Yi et al., Performance of packaged piezoelectric microspeakers depending on the material properties, Proc. MEMS 2009, 765-768

Claims

1. A micromechanical sound transducer (1, 1', 1") with a first bending transducer (10), having a free end (10f) or a free side and is configured to be excited to vibrate vertically in order to emit or receive sound; wherein the first bending transducer (10, 12) includes a first and a second bending element connected in series in order to form the first bending transducer, wherein the first bending element may be driven with a first control signal and the second bending element may be driven with a second control signal; wherein the first bending element comprises a clamped-in end and a free end, and the second element grips with its clamped-in end the free end of the first bending element (10) and forms with its free end the free end (10f, 12f) of the first bending transducer (10, 12), and wherein the first bending element is connected to the second bending element via a flexible element or a connection element (17).

2. The micromechanical sound transducer (1, 1', 1") according to claim 1, wherein the first control signal differs from the second control signal.

3. The micromechanical sound transducer (1, 1', 1") according to claim 2, wherein the first control signal and the second control signal are derived from a mutual original signal and wherein the first control signal is modified with respect to the second control signal.

4. The micromechanical sound transducer (1, 1', 1") according to claim 1 or 3, wherein the first control signal comprises a frequency range that differs from the second control signal or partially overlaps the same, and wherein the first control signal and the second control signal are derived from a mutual original signal and wherein the first control signal has experienced a different frequency filtering than the second control signal.

5. The micromechanical sound transducer (1, 1', 1") according to claim 4, wherein the first control signal comprises a lower frequency range than the second control signal.

6. The micromechanical sound transducer (1, 1', 1") according to any one of claims 1 to 5, including a second bending transducer (12) that comprises a free end (12f) and is arranged in a mutual plane (e1) with the first bending transducer (10), wherein the second bending transducer (10, 12) includes a first and a second bending element (10, 12) connected in series so as to form the second bending transducer.

7. The micromechanical sound transducer (1, 1', 1") according to any one of claims 1 to 6, wherein the micromechanical sound transducer comprises a frame; or wherein the micromechanical sound transducer comprises a frame and the frame is arranged in an area of transition between the first and the second bending element.

8. The micromechanical sound transducer (1, 1', 1") according to any one of claims 1 to 7, wherein the first bending element and the second bending element of the first bending transducer (10) are driven with different control signals.

9. The micromechanical sound transducer (1, 1', 1") according to any one of claims 1 to 8, wherein the first bending transducer (10, 12) is a planar, trapezoid-shaped or rectangular bending transducer; or wherein the first bending transducer (12) is a triangular or circular segment-shaped bending transducer.

10. The micromechanical sound transducer (1, 1', 1") according to any one of claims 1 to 9, including one or several further bending transducers that are arranged in a mutual plane so that their free ends are separated from the free ends (10f, 12f) of the first bending transducer (12) via a slit (14), wherein the at least one further bending transducer (12) is excited to vibrate vertically in-phase with the vertical vibration of the first bending transducer (10, 12).

11. The micromechanical sound transducer (1, 1', 1") according to claim 10, wherein the slit (14) is smaller than 10% or smaller than 5% or than 1% or than 0.1% or smaller than 0.01% of the surface of the first bending transducer (10); and / or wherein, upon deflection, the slit (14) is smaller than 15% or smaller than 10%, 5%, 1% or 0.1%, or smaller than 0.01% of the area of the first bending transducer (10).

12. A method for manufacturing a micromechanical sound transducer comprising a first bending transducer (10), the first bending transducer (10, 12) being configured to be excited to vibrate vertically in order to emit or receive sound, the method comprising: providing in a mutual plane (e1) a first layer that at least forms the first bending transducer (10) with a first and a second bending element each so that the first bending transducer (10) comprises a free end (10f); and connecting the respective first bending element to the second bending element of the respective first bending transducer; such that the first bending transducer (10, 12) includes a first and a second bending element connected in series in order to form the first bending transducer, wherein the first bending element may be driven with a first control signal and the second bending element may be driven with a second control signal; such that the first bending element comprises a clamped-in end and a free end, and the second element grips with its clamped-in end the free end of the first bending element (10) and forms with its free end the free end (10f, 12f) of the first bending transducer (10, 12), and wherein the first bending element is connected to the second bending element via a flexible element or a connection element (17).

13. The micromechanical sound transducer (1, 1', 1") according to any one of claims 1 to 11, wherein the first and a second bending transducer (10) are positioned with their clamped-in ends opposite to a substrate (23s), wherein the geometry of the first bending transducer is enclosed or surrounded by the geometry of the second bending transducer (10).

14. The micromechanical sound transducer (1, 1', 1") according to claim 13, wherein the second of the two bending transducers (10) comprises a recess for the first of the two bending transducers (10); and / or wherein the two bending transducers are separated by a slit or a slit with a diaphragm.

15. The micromechanical sound transducer (1, 1', 1") according to claim 13 or 14, wherein the two bending transducers may be driven with two different control signals or with two control signals for two different frequency ranges.

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