MEMS transducers with recesses and projections

Description

Technical area

[0001] Embodiments according to the present disclosure relate to MEMS acoustic transducers with recesses and projections. Further embodiments relate to MEMS acoustic transducers with microstructures for air damping. Background of the Revelation

[0002] Like conventional loudspeakers, MEMS loudspeakers rely on the displacement of air through the reciprocating or bending motion of an actuator. The resulting sound level is proportional to the displaced air volume. A version of a MEMS loudspeaker with piezoelectrically driven, vertically moving microactuators is shown in Fig. 1(from F. Stoppel, A. Männchen, F. Niekiel, D. Beer, T. Giese, I. Pieper, D. Kaden, S. Grünzig, B. Wagner, Piezoelectric MEMS Loudspeakers for In-Ear Applications, MikroSystemTechnik Kongress 2019, Berlin, pp. 182-185; DE10 2017 208 911). Documents US 2011 / 182150, CN 103 922 271, and US 2013 / 121509 refer to a comb-drive MEMS acoustic transducer.

[0003] Fig. 1 shows a schematic representation of a MEMS loudspeaker 100 in the non-deflected (top) and deflected state (bottom). The MEMS loudspeaker has a chip frame 110, e.g., a substrate, and actuators 120 clamped to the chip frame 110. The actuators are two-layered, formed from a layer of piezoelectric PZT (lead zirconate titanate) 130 and a layer of polysilicon 140. Decoupling slots 150 are arranged between the actuators. During deflection (bottom), the actuators can move decoupled from each other through the decoupling slots 150.

[0004] In the case shown, the sound-generating actuator structure is not formed by a closed membrane, but by several actuators 120 separated by narrow slits 150. However, the moving MEMS actuator structures can have high resonance qualities (excessive vibration amplitudes) with values ​​in the range of 100. As a result, the generated sound pressure level can have sharp resonance peaks in the frequency response, which can lead to acoustic distortions (see Figure 2 and Figure 3 ).

[0005] Fig. 2Shows the sound pressure level (SPL) in dB of the MEMS loudspeaker, measured in an ear simulator at various drive voltages with and without an equalizer (EQ) filter versus frequency in Hz. The lower solid line represents a sound pressure level at one volt with an EQ filter, the dotted line represents a sound pressure level at one volt without an EQ filter, and the upper solid line represents a sound pressure level at ten volts with an EQ filter. The sound pressure level at one volt without an EQ filter shows a large peak at just over 8000 Hz. Fig. 2 shows that the sound pressure level can be smoothed by electronic filters. However, this measure cannot reduce the distortion, ie the rattling of the loudspeaker (see Figure 3 ).

[0006] Fig. 3 shows harmonic distortion in % at 1 V amplitude with EQ filter (corresponds to approx. 85 dB SPL) over the frequency in Hz. In Fig. 3The total harmonic distortion (THD) and the contributions of individual harmonics to the distortion factor (k2, k3, k5) are plotted. The plotted values ​​indicate the ratio of, for example, an undesired harmonic component to the signal. Fig. 3 shows high peaks of distortion and harmonic distortion in the range of just under 2000 Hz and in the range of just over 3000 Hz. Fig. 3 shows that EQ filters cannot smooth out these signal distortions.

[0007] Due to distortion, the full bandwidth of a corresponding MEMS transducer cannot be utilized. For example, applications in the ultrasound range require transducers with low Q, i.e., high bandwidth. This allows the transducer to generate short pulses using the pulse-echo method or to transmit or receive modulated signals using the continuous-wave method.

[0008] With existing MEMS sound transducers, the resonances of the actuators cannot be specifically damped. For example, it would be desirable to achieve Q-factors below 5 and / or completely suppress the resonance peak. Therefore, there is a need for an improved approach.

[0009] The object of the present disclosure is to create a concept which makes it possible to specifically dampen resonances of actuators of MEMS sound transducers. Summary of Revelation

[0010] Embodiments according to the present disclosure provide MEMS sound transducers for generating sound, comprising an actuator separated from a surrounding structure by one or more gaps and configured to perform a relative movement between the actuator and the surrounding structure. The MEMS sound transducer further comprises the surrounding structure, wherein the actuator and the surrounding structure have a plurality of recesses and projections, wherein the plurality of projections associated with the actuator are arranged to interlock with the plurality of recesses associated with the surrounding structure, and / or the plurality of projections associated with the surrounding structure are arranged to interlock with the plurality of recesses associated with the actuator, wherein the interlocking elements are separated by one or more gaps.

[0011] Embodiments according to the present disclosure are based on the core idea of ​​enabling frequency-dependent signal attenuation of a MEMS sound transducer through the arrangement of recesses and projections, e.g., in the form of interlocking meanders. The relative movement between the actuator and the surrounding structure displaces a gas, e.g., air (generally a medium), located in the gap between the actuator and the surrounding structure. This results in (air) friction, which in turn dampens the actuator. The velocity of the gas in the gap is dependent on the oscillation frequency of the actuator. By appropriately selecting the geometries of the actuator and the surrounding structure, the velocity-dependent and thus frequency-dependent attenuation can be utilized to attenuate specific frequencies of the MEMS sound transducer. This advantageously enables optimization of the sound transducer and its acoustic properties.

[0012] A MEMS loudspeaker according to the invention can produce distortion that cannot or can only be filtered electronically with difficulty (see e.g. Fig. 3 ). The damping depends on the overlapping surfaces of the actuator and the surrounding structure, which move past each other due to the relative movement, as well as on the distance between the overlapping surfaces of the actuator and the surrounding structure. In other words, the overlapping surfaces are the surfaces of the actuator or the surrounding structure that are directly opposite the surrounding structure or the actuator and which move past each other due to the relative movement. For example, these surfaces of the actuator and the surrounding structure can be designed parallel to each other and move past each other parallel or at least partially parallel due to the relative movement.

[0013] To increase the damping, this surface is therefore, according to the disclosure, enlarged by using interlocking projections and / or recesses, for example, with additional plate structures on the actuator and the surrounding structure. Additionally or alternatively, the damping can be increased by a small distance between the surfaces.

[0014] In other words, embodiments according to the present disclosure are based on the idea of ​​integrating additional fluid-mechanical structures, for example plate structures and / or projections and / or recesses, through which the MEMS sound transducer, for example designed as a loudspeaker, is damped by means of viscous gas flow or air flow.

[0015] In embodiments according to the present disclosure, the interlocking elements are separated by one or more gaps such that the interlocking elements have a damping function, for example the damping explained above, during a relative movement between the actuator and the surrounding structure.

[0016] In embodiments according to the present disclosure, the actuator comprises the plurality of recesses and projections associated with the actuator along at least 50%, or along at least 75%, or at least along 90%, or at least along 99%, or along 100% of the one or more columns. Alternatively or additionally, the surrounding structure may comprise the plurality of recesses and projections associated with the surrounding structure along at least 50%, or along at least 75%, or at least along 90%, or at least along 99%, or along 100% of the one or more columns.

[0017] In further embodiments according to the present disclosure, the surrounding structure is formed by a substrate. By forming projections and recesses directly on the substrate, a particularly simple and cost-effective implementation of a MEMS sound transducer according to the present disclosure can be achieved. The actuator can, for example, be etched directly from the substrate and provided with projections and recesses that interlock with corresponding structures of the substrate.

[0018] In embodiments according to the present disclosure, the plurality of recesses and projections are formed as microstructures with a height / width aspect ratio of more than 5, wherein the height is a height orthogonal to a surface of the actuator or the surrounding structure on which the projection is arranged. The width is a width parallel to the surface of the actuator or the surrounding structure on which the projection is arranged.

[0019] A high aspect ratio can increase viscous friction and thus damping. By designing the recesses and projections accordingly, the area between the actuator and the surrounding structure, which contributes to friction, e.g. for a desired frequency range, can be increased and, for example, a smaller distance between the elements can be achieved in order to further increase damping. It should be noted that the aspect ratio does not only apply to the heights of structures, but also to corresponding depths, e.g. in the case of recesses. Furthermore, recesses and / or projections can have corresponding heights or depths, e.g. in particular orthogonal to the direction of movement of the actuator, whereby the width of the recess or structure can be aligned parallel to the direction of movement.

[0020] In embodiments according to the present disclosure, the actuator has a piezoelectric, magnetic, or electrostatic drive. Alternatively or additionally, the actuator can be formed by a bending transducer. The piezoelectric drive can, for example, preferably be implemented by integrated piezoelectric layers, e.g. for applications as MEMS loudspeakers. Piezoelectric drives can have advantages with regard to short response times, high accelerations, and low energy requirements. Embodiments according to the present disclosure are not, however, limited to piezoelectric drives, but enable the use of drive concepts that are particularly advantageous for an application, e.g. optionally electrostatic or magnetic concepts or principles. The design of the actuator as, for example, a piezoelectric, bending transducer orBending actuators can have advantages in terms of travel and force, as well as reliability.

[0021] In embodiments according to the present disclosure, the projections of the plurality of projections have a height of more than 50 µm, wherein the height is a height orthogonal to a surface of the actuator or the surrounding structure on which the respective projection is arranged.

[0022] The disclosed design of the height of the projections allows for sufficient damping to at least partially suppress unwanted clanging (see Fig. 3 ). This allows, for example, an advantageous aspect ratio of projections and corresponding recesses to be achieved, so that the viscous gas friction enables the desired damping.

[0023] In embodiments according to the present disclosure, the plurality of projections is formed as columns and / or combs, and the plurality of recesses is formed as holes and / or slots. Columns and combs, as well as corresponding holes and slots, can be realized using cost-effective and sophisticated manufacturing processes, so that a corresponding MEMS sound transducer can be manufactured in large quantities and / or cost-effectively. Furthermore, corresponding structures such as columns or combs enable an advantageous aspect ratio in order to be able to adjust the damping sufficiently, for example, according to the requirements of an application. Furthermore, holes and slots corresponding to the columns and combs enable very small distances between the respective elements, which in turn can be advantageous for damping.

[0024] In embodiments according to the present disclosure, the plurality of recesses and projections consists of at least one of a semiconductor, such as silicon, silicon compounds, metals, or polymers. This enables easy manufacturability using conventional MEMS manufacturing technologies.

[0025] MEMS acoustic transducers according to the disclosure enable the use of readily available materials whose associated manufacturing processes are technically mature, so that a corresponding MEMS acoustic transducer can be manufactured at low cost and with high quality.

[0026] In embodiments according to the present disclosure, the MEMS sound transducer is configured to emit a sound signal when excited by an electrical signal. A disclosed embodiment of the MEMS sound transducer as a MEMS loudspeaker makes it possible to eliminate or at least mitigate problems of previous loudspeakers, e.g., with regard to distortion, through the plurality of recesses and projections.

[0027] In embodiments according to the present disclosure, the MEMS acoustic transducer is configured to generate signals in a frequency range of at least 20 Hz and / or up to 20 kHz. Alternatively or additionally, the MEMS acoustic transducer can be configured as a MEMS ultrasonic transducer. A MEMS ultrasonic transducer according to the disclosure can be configured to generate signals in a frequency range of at least 20 kHz and / or up to 100 MHz.

[0028] The design of the MEMS sound transducer for a frequency range of 20 Hz to 20 kHz, or in other words, the frequency range audible to humans, enables the use of the sound transducer in acoustic applications such as in-ear headphones, smartphones, or headsets. The use of recesses and projections according to the disclosure can, for example, achieve high audio quality. In particular, unwanted distortion can be suppressed, for example, even at high frequencies. A MEMS ultrasonic transducer according to the disclosure can also achieve a high bandwidth for high frequencies by attenuating harmonic distortions, allowing short pulses to be generated, for example, for measurement methods such as pulse-echo methods, or modulated signals to be transmitted for continuous-wave methods.

[0029] In embodiments according to the present disclosure, the one or more gaps have a width of less than 20 µm, less than 10 µm, or less than 5 µm, or generally have a width in the range of 0.1 µm to 20 µm. The width of the gap can, for example, be a width in the lateral direction or horizontal direction of the component or MEMS acoustic transducer.

[0030] The widths in the µm range allow corresponding MEMS sound transducers to be built with minimal space requirements, while also enabling sufficient decoupling of the sound pressures upstream and downstream of the actuator, allowing a defined acoustic sound pressure to be generated. Furthermore, appropriately dimensioning the gap can be advantageous for frequency-dependent damping, for example, to suppress distortion.

[0031] In embodiments according to the present disclosure, the actuator is designed as a bending actuator, and the bending actuator and the surrounding structure are laterally opposite one another in a plane. The bending actuator is clamped at least on one side relative to the surrounding structure and is designed to execute the relative movement between the bending actuator and the surrounding structure, at least partially perpendicular to the plane, with one end of the bending actuator. At the moving end of the bending actuator, a plurality of recesses and / or projections in the form of a first comb structure are formed in the common plane of the bending actuator and the surrounding structure. The surrounding structure has, on a side facing the moving end of the bending actuator, a plurality of recesses and / or projections in the form of a second comb structure, wherein the first and second comb structures are designed such that they interlock.

[0032] By arranging the actuator and surrounding structure laterally in a plane, a corresponding MEMS sound transducer according to the disclosure can be designed perpendicular to the plane with little installation space required. By using a bending actuator, high sound pressures can also be generated, for example for certain applications, which are advantageous. The lever movement can mean that the relative movement of the actuator can be partially perpendicular to the surrounding structure, so that, for example, the overlapping surfaces are also moved partially perpendicular to one another. Furthermore, the bending actuator can be surrounded by the surrounding structure at several ends, so that, for example, recesses and projections can be arranged on several sides of the actuator that perform a relative movement with regard to the surrounding structure, for example in the form of a comb structure. Analogously, projections and recesses, for example, can be arranged additionally or alternatively on the corresponding sides of the surrounding structure.in the form of the second comb structure, so that the recesses and projections of the actuator and the projections and recesses of the surrounding structure interlock.

[0033] In embodiments according to the present disclosure, the actuator is designed as a lifting actuator, and the lifting actuator and the surrounding structure are arranged in a plane. The lifting actuator is designed to execute the relative movement between the lifting actuator and the surrounding structure perpendicular to the plane and has a plurality of recesses and / or projections in the form of a first comb structure along its circumference in the plane. Furthermore, the surrounding structure has, on a side facing the first comb structure, a plurality of recesses and / or projections in the form of a second comb structure, wherein the first and second comb structures are designed such that they interlock.

[0034] Such a MEMS sound transducer according to the disclosure can have a small installation space requirement in the direction of the plane in which the actuator and surrounding structure are arranged, or in other words, orthogonal to the direction of movement of the actuator. The stroke actuator can also be designed, for example, as a piston-shaped actuator.

[0035] In embodiments according to the present disclosure, the actuator is arranged in a first plane and the surrounding structure is arranged in a second plane, wherein the first and second planes are parallel to one another and wherein the actuator is designed to execute the relative movement between the actuator and the surrounding structure perpendicular to the first and second planes. The actuator has a plurality of projections in the form of columns and / or combs, wherein the columns and / or combs are arranged perpendicular to the parallel planes on a surface of the actuator facing the surrounding structure. The surrounding structure has a plurality of recesses in the form of holes and / or slots, wherein the columns and / or combs of the actuator and the holes and / or slots of the surrounding structure are designed such that they engage with one another.

[0036] The formation of the surrounding structure with holes and / or slots enables a shape of the recess to be produced, for example, simply and cost-effectively, since in this case, e.g., through an etching process, attention need not be paid to a specific depth of the etching. Furthermore, such a MEMS sound transducer according to the disclosure can be designed with a small installation space requirement, e.g., through the interlocking of the pillars and / or combs with the slots and / or holes, since these can slide past one another due to the relative movement, e.g., in a quasi-positive manner, separated by a gap. Additionally or alternatively, further recesses and / or projections can be arranged in the plane of the actuator around the actuator, which in turn are arranged in an interlocking manner with corresponding projections and / or recesses in the surrounding structure or another surrounding structure.

[0037] In embodiments according to the present disclosure, the surrounding structure is arranged in a first plane and the actuator in a second plane, wherein the first and second planes are parallel to one another. The actuator is designed to execute the relative movement between the actuator and the surrounding structure perpendicular to the first and second planes. The surrounding structure has a plurality of projections in the form of columns and / or combs, wherein the columns and / or combs are arranged perpendicular to the parallel planes on a surface of the surrounding structure facing the actuator. The actuator has a plurality of recesses in the form of holes and / or slots, wherein the columns and / or combs of the surrounding structure and the holes and / or slots of the actuator are designed such that they engage with one another.

[0038] The actuator can, for example, be partially formed as a perforated and / or slotted plate. This can, for example, offer advantages with regard to the achievable sound pressure. Furthermore, etching columns and / or combs out of a stationary substrate, for example, which forms the surrounding structure, can offer manufacturing advantages.

[0039] Further embodiments according to the present disclosure provide MEMS sound transducers for generating sound, comprising an actuator separated from a surrounding structure by one or more gaps. Furthermore, the MEMS sound transducer includes the surrounding structure. The actuator is configured to perform a relative movement between the actuator and the surrounding structure.The structures of the actuator and / or surrounding structure have the plurality of recesses and projections, wherein the plurality of projections belonging to the actuator and / or belonging to the plate structures of the actuator are arranged in an interlocking manner in the plurality of recesses belonging to the surrounding structure and / or belonging to the plate structures of the surrounding structure and / or the plurality of projections belonging to the surrounding structure and / or belonging to the plate structures of the surrounding structure are arranged in an interlocking manner in the plurality of recesses belonging to the actuator and / or belonging to the plate structures of the actuator, wherein the interlocking elements are separated by one or more gaps.

[0040] The inventive design of recesses and projections, i.e., for example, the integration of additional recesses and projections on plate structures, which in turn can themselves form a projection or part of a projection or analogous recess, enables improved damping properties, for example to dampen undesired distortion at high frequencies. Short character description

[0041] Examples according to the present disclosure are explained in more detail below with reference to the accompanying figures. With regard to the schematic figures shown, it should be noted that the illustrated functional blocks are to be understood both as elements or features of the device according to the disclosure and as corresponding method steps of the method according to the disclosure, and corresponding method steps of the method according to the disclosure can also be derived therefrom. They show: Fig. 1 shows a schematic representation of a MEMS loudspeaker in the non-deflected (top) and deflected state (bottom); Fig. 2 shows the sound pressure level (SPL) in dB of the MEMS loudspeaker, measured in an ear simulator at various drive voltages with and without an equalizer (EQ) filter versus frequency in Hz; Fig. 3 shows the harmonic distortion in % at 1 V amplitude with an EQ filter (corresponds to approximately 85 dB SPL) versus frequency in Hz; Fig. 4 shows an example of viscous air damping of a plate during parallel movement close to a stationary plate element to explain the physical principle in embodiments; Fig. 5 shows a schematic top view of a MEMS sound transducer according to an embodiment of the present disclosure; Fig. 6 shows a schematic representation of a MEMS sound transducer according to an embodiment of the present disclosure with comb-shaped recesses and projections at the edge of the actuator and surrounding structure, which has a fixed element; Fig.7a modification of the MEMS sound transducer from . Fig. 6 according to an embodiment of the present disclosure with plate structures with projections and recesses; Fig. 8 shows a schematic side view of a MEMS sound transducer according to an embodiment of the present disclosure with columns or vertical comb structures on the actuator and a perforated or slotted plate as a fixed element; and Fig. 9 shows a schematic side view of a MEMS sound transducer according to an embodiment of the present disclosure with an actuator with a perforated plate and columns and / or combs on a fixed element. Detailed description of the examples according to the figures

[0042] Before exemplary embodiments of the present disclosure are explained in more detail below with reference to the drawings, it is pointed out that identical, functionally equivalent or equivalent elements, objects and / or structures in the different figures are provided with the same or similar reference numerals, so that the description of these elements shown in different exemplary embodiments is interchangeable or can be applied to one another.

[0043] Fig. 5 shows a schematic top view of a MEMS acoustic transducer according to an embodiment of the present disclosure. Fig. 5shows the MEMS sound transducer 500 with an actuator 510 separated from a surrounding structure 530 (e.g., the substrate) by a gap 520. The actuator 510 and the surrounding structure 530 have a plurality of projections 510-1, 530-1 and recesses 510-2, 530-2, wherein the plurality of projections 510-1 associated with the actuator are arranged to interlock with the plurality of recesses 530-2 associated with the surrounding structure and / or the plurality of projections 530-1 associated with the surrounding structure are arranged to interlock with the plurality of recesses 510-2 associated with the actuator, the interlocking elements being separated by the gap 520.

[0044] The actuator 510 is configured to perform a relative movement between the actuator 510 and the surrounding structure 530, perpendicular to the image plane. This relative movement enables the actuator 510 to generate an acoustic signal from an electrical excitation. Due to the projections 510-1, 530-1 and recesses 510-2, 530-2, the MEMS sound transducer has large surfaces between the moving actuator 510 and the surrounding structure 530, which enable frequency-dependent damping through viscous gas damping. This arrangement allows the gap 520 to be selected to be very narrow, which in turn can have a positive effect on the desired damping. This allows certain frequency ranges, which, for example, exhibit high distortion, to be damped.

[0045] The projections 510-1, 530-1 and recesses 510-2, 530-2 can be formed in a variety of variations. Embodiments according to the present disclosure include trigonometric shapes of the projections 510-1 and recesses 510-2 or of the projections 530-1 and recesses 530-2 as shown in Fig. 5shown. Furthermore, embodiments also include MEMS sound transducers with projections and recesses with ridges, columns, meanders, pegs, or triangles. Projections and recesses according to the disclosure are designed, for example, such that the length of the gap 520 and the area between the actuator 510 and the surrounding structure 530 are as large as possible to increase the damping. Furthermore, the actuator 510 can be designed as a multi-part actuator, or in other words, have a multi-part membrane. Furthermore, the actuator 510 can be formed in two layers, from a layer of piezoelectric PZT (lead zirconate titanate) and a layer of polysilicon.^

[0046] Figure 4shows an example of viscous air damping of a plate during parallel movement close to a stationary plate element, e.g., with respect to the distance between the plates relative to the plate surface, and illustrates the cross-sectional view through the actuator and the surrounding structure. The surface area of ​​the elements dictated here as a plate—the actuator—and the opposing structure are maximized according to the exemplary embodiments by meandering structures or, more generally, recesses and projections. Figure 4shows a schematic sectional view of a plate 410 of the surrounding structure, which has a fixed element, and a plate 420 of the actuator. In general, the fixed element can be, for example, an immovable part of the surrounding structure, or the surrounding structure itself. The fixed element can be, for example, a substrate. The two plates are arranged at a distance d 430 from each other. The plate 420 of the actuator has a relative speed v plate 440, so that it moves past the plate 410 of the surrounding structure parallel to it. Between the plates 410, 420, a speed distribution 450 of the air speed v air of the space between the two plates 410, 420 is plotted.

[0047] If the distance d 430 between the plates is small compared to the plate dimensions, the air velocity from the stationary plate 410 to the moving plate 420 can increase linearly from zero to the value v. The air layers between the plates can therefore slide past each other at different speeds. This can result in a frictional force F r , which can be calculated using Newton's law of friction. F r = ηAv / d .

[0048] Where A is the overlap of the plate surfaces, d is the plate spacing 430, v is the speed 440 of the moving plate (v plate ), and η is the viscosity of the air. The friction force is proportional to the speed 440 of the moving plate and forms a damping element in the differential equation of plate motion or oscillation.

[0049] Accordingly, by designing the actuator and surrounding structure with recesses and / or projections or with plate structures, e.g. as projections, as disclosed, a MEMS sound transducer can be created which enables a desired attenuation of certain frequencies by adjusting the overlapping surface and the distance between the relatively moving surfaces of the actuator and surrounding structure.

[0050] Fig. 6 shows schematic views of a MEMS acoustic transducer according to an embodiment of the present disclosure with projections and recesses. Fig. 6 above shows a schematic sectional view of a MEMS transducer 800 and Fig. 6 Below is a schematic top view of the MEMS transducer 800.

[0051] Figure 6The figure above shows the MEMS sound transducer 800 with an actuator 810 separated from a surrounding structure 530 by one or more gaps 520, wherein the surrounding structure 530 comprises a fixed element. The actuator 810 is configured to perform a relative movement 620 between the actuator 810 and the surrounding structure 530. The actuator 810 and the surrounding structure 530, which can be configured as comb structures so that the gap 520 also follows the comb structure, are shown in the top view in the lower part of the figure.

[0052] Figure 6 The bottom view shows recesses and projections 820 between the lifting actuator 810 and the surrounding structure 530, which has a fixed element. The recesses and projections 820 can be designed as comb structures and thus, for example, can be arranged in an interlocking manner (continuously along the mutually facing edge surfaces of the lifting actuator 810 and the surrounding structure 530). Figure 6shows a possible combination of projections and recesses according to the disclosure. Figure 6It should also be clarified that, according to the disclosure, a multitude of possible arrangements are possible which enable a desired damping, for example of certain frequencies, for MEMS sound transducers. Furthermore, it should be noted that plate structures (not shown) or optional plates or diaphragms, which can be arranged, for example, perpendicular to the actuator 610 at the edge of the surrounding structure 530 (cf. edge facing the actuator 610) or of the actuator. The diaphragms / plates extend substantially parallel to the direction of movement 630 (e.g. out of the substrate) and prevent the gap from widening along the movement. The plate structures can also be used to increase the overlapping area between the actuator 610 and the surrounding structure 530 in order to increase viscous gas friction and accordingly damping of certain resonant frequencies.The plate structures can be designed as projections, whereby the actuator can be designed as a recess or vice versa.

[0053] By combining it with the example from Fig. 6For example, strong damping can be achieved by enlarging the overlapping surfaces. For the technological implementation of the previously explained damping, the actuator 810 of the MEMS sound transducer, e.g., a loudspeaker, is arranged on the vertically moving actuator 810 and on an opposite, surrounding structure 530, e.g., an opposite stationary element or fixed element with recesses and projections 820. These fluid-mechanical structures can dampen the actuator movement by the viscous gas flow, e.g., air flow. The equation for the friction force shows that damping is maximized when the largest possible surfaces are arranged as closely as possible. This means that damping structures with recesses and projections 820 with a high aspect ratio can be advantageous.The overlapping area of ​​the elements 610 can also be increased by forming the elements as interlocking comb structures with a plurality of fingers or by forming the recesses and projections 820 as interlocking comb structures with a plurality of fingers.

[0054] The actuator 810 can be used as in Fig. 6 As shown, it can optionally be designed as a lifting actuator. However, further embodiments also include corresponding bending actuators with associated plate structures with recesses and projections.

[0055] Fig. 7 shows a schematic top view of a MEMS sound transducer according to an embodiment of the present disclosure with comb-shaped recesses and projections at the edge of the actuator and surrounding structure, which has a fixed element. Fig. 7shows a MEMS sound transducer 700 with a bending actuator 710, which is laterally opposite a surrounding structure 530, which has a fixed element, in a plane. The bending actuator 710 is clamped at least on one side relative to the surrounding structure 530 and is designed to achieve a relative movement between the bending actuator 710 and the surrounding structure 530 at least partially perpendicular to the plane, i.e. at least partially perpendicular to the image plane of Fig. 7 , to execute.

[0056] At the moving end of the bending actuator 710, a plurality of recesses 710-1 and projections 710-2 in the form of a first comb structure 710-3 are formed in the common plane of the bending actuator 710 and the surrounding structure 530. On a side facing the moving end of the bending actuator, the surrounding structure has a plurality of recesses 530-2 and projections 530-1 in the form of a second comb structure 530-3, wherein the first and second comb structures are configured to interlock. The two comb structures are separated from each other by a gap 520.

[0057] In other words, Fig. 7 Comb structures at the edge of the actuator and the surrounding structure, which has a fixed element. As mentioned above, the overlapping area, e.g. of the damping plate structures, can be increased by forming them as combs. In the Fig. 7In the illustrated embodiment, comb structures 710-3, for example, with a high aspect ratio, are arranged at the moving end of a bending actuator 710. These move into each other with closely spaced comb structures 530-3 on the surrounding structure 530, for example, a fixed, laterally opposing element. In the same way, damping comb structures can also be used for piston-shaped stroke actuators (for example, analogous to Fig. 6 ). In this case, the comb structures can be arranged along the entire circumference of the actuator.

[0058] Fig. 8 shows a schematic side view of a MEMS sound transducer according to an embodiment of the present disclosure with columns or vertical comb structures on the actuator and a perforated or slotted plate as a fixed element, which forms the surrounding structure or part of the surrounding structure. Fig. 8shows a MEMS sound transducer 900 with an actuator 510 in a first plane and a surrounding structure 530 in a second plane, wherein the surrounding structure 530 has a fixed element which is designed as a perforated or slotted plate and wherein the first and second planes are parallel to one another. The actuator is designed to execute a relative movement 620 between the actuator 510 and the surrounding structure 530 perpendicular to the first and second planes. The actuator has a plurality of projections in the form of columns and / or combs 510-4, wherein the columns and / or combs 510-4 are arranged perpendicular to the parallel planes on a surface of the actuator facing the surrounding structure 530.The surrounding structure 530 has a plurality of recesses in the form of holes and / or slots 530-4, and the columns and / or combs 510-4 of the actuator and the holes and / or slots 530-4 of the surrounding structure are configured to interlock and are separated by a gap 520.

[0059] In other words, Fig. 8 Columns or vertical comb structures on the actuator 510 and a perforated or slotted plate as a fixed element, which forms the surrounding structure or part of the surrounding structure. In this embodiment, the damping structures are arranged over the entire surface of the actuator 510. They can be designed as columns and / or combs 510-4. The fixed element 530 is arranged vertically above the actuator 510 and is designed as a perforated and / or slotted plate. Similarly, the damping structures could be arranged below the actuator 510 or on both sides of the actuator.

[0060] A MEMS transducer according to Fig. 8 can be manufactured easily and thus at low cost by using a perforated or slotted plate, since, for example, no defined etching depths for the recesses need to be observed. Furthermore, the arrangement of a large number of columns and / or combs 510-4 and associated holes and / or slots 530-4 enables a significant increase in the overlapping area, allowing for high attenuation.

[0061] Fig. 9 shows a schematic side view of a MEMS sound transducer according to an embodiment of the present disclosure with an actuator with a perforated plate and columns and / or combs on a solid element which forms the surrounding structure or a part of the surrounding structure. Fig. 9shows a MEMS sound transducer 1000 with a surrounding structure 530 arranged in a first plane and an actuator 510 arranged in a second plane, wherein the first and second planes are parallel to one another. The actuator 510 is designed to perform a relative movement 620 between the actuator 510 and the surrounding structure 530 perpendicular to the first and second planes. The surrounding structure 530 has a plurality of projections in the form of columns and / or combs 530-5, wherein the columns and / or combs 530-5 are arranged perpendicular to the parallel planes on a surface of the surrounding structure facing the actuator 510. The actuator 510 has a plurality of recesses in the form of holes and / or slots 510-5, wherein the actuator 510 is, however, only partially designed as a hole or slotted plate.The columns and / or combs 530-5 of the surrounding structure and the holes and / or slots 510-5 of the actuator are designed such that they interlock and are separated by a gap 520.

[0062] In other words, Fig. 9 an actuator with a perforated plate and columns and / or combs 530-5 on a surrounding structure 530 having a fixed element. In this embodiment, the surrounding structure 530 or the fixed element supports columns or combs 530-5 into which the actuator 510 moves. For this purpose, the actuator 510 is at least partially designed as a perforated and / or slotted plate.

[0063] A MEMS transducer according to Fig. 9 enables the already Fig. 8explained advantages regarding manufacturing. Only partially forming the actuator 510 as a hole or slotted plate can be advantageous with regard to the possible sound pressure level and lead to better decoupling between the radiated air volume and the sound pressure behind the actuator, opposite to the radiation direction. Conclusions and further remarks

[0064] Embodiments according to the present disclosure provide MEMS loudspeakers or MEMS ultrasonic transducers with viscous air damping, characterized in that high aspect ratio microstructures are arranged on a vertically moving actuator and on a vertically or laterally opposing fixed element or surrounding structure, which microstructures move at a close distance relative to each other, whereby the actuator movement is viscously damped by the air flow.

[0065] Further embodiments according to the present disclosure provide MEMS loudspeakers with piezoelectric or magnetic or electrostatic drive.

[0066] Further embodiments according to the present disclosure have an aspect ratio of the microstructures height / width > 10 and / or height of the microstructures > 50 µm.

[0067] Further embodiments according to the present disclosure have damping structures, for example recesses and projections on the edge of the actuator and the surrounding structure and / or the fixed element, for example in the form of plates or comb structures.

[0068] Further embodiments according to the present disclosure have column or comb structures on the actuator surface, hole or slot structures on the surrounding structure, e.g. the fixed element.

[0069] Further embodiments according to the present disclosure have hole or slot structures in the actuator surface, columns or comb structures on the surrounding structure, for example the fixed element.

[0070] Further embodiments according to the present disclosure include damping structures made of silicon, Si compounds, metals or polymers.

[0071] Further embodiments according to the present disclosure provide MEMS speakers with a frequency range of 20 Hz - 20 kHz.

[0072] Further embodiments according to the present disclosure provide MEMS ultrasonic transducers with a frequency range of 20 kHz to 100 MHz.

[0073] Embodiments according to the present disclosure provide MEMS sound transducers or speakers for in-ear headphones and / or free-field speakers for near-ear applications.

[0074] In general, embodiments according to the present disclosure allow the loudspeaker damping to be integrated directly into the MEMS structure, e.g., the MEMS sound transducer, and to be adjusted by the arrangement and dimensioning of the microstructures. This can constitute a decisive advantage of MEMS sound transducers according to the disclosure, e.g., with regard to installation space and functionality, e.g., for mobile applications.

[0075] All lists of materials, environmental influences, electrical properties and optical properties listed herein are to be considered exemplary and not exhaustive.

[0076] Although some aspects have been described in connection with a device, it is understood that these aspects also represent a description of the corresponding method, so that a block or component of a device can also be understood as a corresponding method step or as a feature of a method step. Similarly, aspects described in connection with or as a method step also represent a description of a corresponding block, detail, or feature of a corresponding device.

[0077] The above-described embodiments are merely illustrative of the principles of the present disclosure. It is understood that modifications and variations of the arrangements and details described herein will be apparent to others skilled in the art. Therefore, it is intended that the disclosure be limited only by the scope of the following claims and not by the specific details presented in the description and explanation of the embodiments herein.

Claims

1. A method for manufacturing an MEMS sound transducer (500, 700, 800, 900, 1000) for generating sound, comprising: providing an actuator (510, 710, 810) and a surrounding structure (530), wherein the actuator (510, 710, 810) is separated from the surrounding structure (530) by one or more gaps (520) and is configured to execute a relative movement (620) between the actuator (510, 710, 810) and the surrounding structure (530), and wherein the actuator (510, 710, 810) and the surrounding structure (530) comprise a plurality of recesses (510-2, 510-5, 530-2, 530-4, 710-2) and projections (510-1, 510-1-1, 510-4, 530-1, 530-1-1, 530-5, 710-1), wherein the plurality of projections (510-1, 510-1-1, 510-4, 710-1) belonging to the actuator (510, 710, 810) are arranged to interdigitate into the plurality of recesses (530-2) belonging to the surrounding structure (530), and / or the plurality of projections (530-1, 530-1-1, 530-5) belonging to the surrounding structure (530) to interdigitate into the plurality of recesses (510-2, 510-5, 710-2) belonging to the actuator (510, 710, 810), forming the interdigitating elements such that the interdigitating elements are thus separated by the one or more gaps (520), and such that overlapping areas of the plurality of recesses and projections are configured such that the interdigitating elements comprise a specific frequency-depending attenuation function with a relative movement between the actuator (510, 710, 810) and the surrounding structure (530) to suppress harmonic distortions; and wherein the overlapping areas are directly opposite areas moving past each other by the relative movement.

2. The method for manufacturing an MEMS sound transducer (500, 600, 700, 800, 900, 1000) in accordance with claim 1, wherein an aspect ratio of height / width of the plurality of recesses and projections, the overlapping areas of actuator and surrounding structure which move past each other by the relative movement, and the distance of the overlapping areas of actuator and surrounding structure are configured to adjust a frequency-dependent attenuation to suppress harmonic distortions, wherein the height is a height orthogonally to a surface of the actuator or the surrounding structure on which the projection is arranged, and wherein the width is a width in parallel to the surface of the actuator or the surrounding structure on which the projection is arranged.

3. The method for manufacturing an MEMS sound transducer (500, 700, 800, 900, 1000) in accordance with any of the preceding claims, wherein the surrounding structure (530) is formed by a substrate.

4. The method for manufacturing an MEMS sound transducer (500, 700, 800, 900, 1000) in accordance with any of the preceding claims, wherein the plurality of recesses (510-2, 510-5, 530-2, 530-4, 710-2) and projections (510-1, 510-1-1, 510-4, 530-1, 530-1-1, 530-5, 710-1) are implemented as microstructures having an aspect ratio between height / width of more than 5, wherein the height is a height orthogonally to a surface of the actuator or the surrounding structure (530) on which the projection is arranged; and wherein the width is a width in parallel to the surface of the actuator or the surrounding structure (530) on which the projection is arranged.

5. The method for manufacturing an MEMS sound transducer (500, 700, 800, 900, 1000) in accordance with any of the preceding claims, wherein the actuator (510, 710, 810) comprises a piezoelectric or magnetic or electrostatic drive; and / or wherein the actuator (510, 710, 810) is formed by a bending transducer (710).

6. The method for manufacturing an MEMS sound transducer (500, 700, 800, 900, 1000) in accordance with any of the preceding claims, wherein the projections (510-1, 510-1-1, 510-4, 530-1, 530-1-1, 530-5, 710-1) of the plurality of projections comprise a height of more than 50 µm, and wherein the height is a height orthogonally to a surface of the actuator or the surrounding structure (530) on which the respective projection is arranged.

7. The method for manufacturing an MEMS sound transducer (500, 700, 800, 900, 1000) in accordance with any of the preceding claims, wherein the plurality of projections are implemented as columns and / or combs (510-4, 530-5), and wherein the plurality of recesses are implemented as holes and / or slots (530-4, 510-5).

8. The method for manufacturing an MEMS sound transducer (500, 700, 800, 900, 1000) in accordance with any of the preceding claims, wherein the plurality of recesses (510-2, 510-5, 530-2, 530-4, 710-2) and projections (510-1, 510-1-1, 510-4, 530-1, 530-1-1, 530-5, 710-1) are made of at least one of silicon, silicon compounds, metals or polymers.

9. The method for manufacturing an MEMS sound transducer (500, 700, 800, 900, 1000) in accordance with any of the preceding claims, wherein the MEMS sound transducer (500, 700, 800, 900, 1000) is configured to generate signals in a frequency range of at least 20 Hz and / or up to 20 kHz; and / or wherein the MEMS sound transducer (500, 700, 800, 900, 1000) is an MEMS ultrasonic transducer, the MEMS ultrasonic transducer being configured to generate signals in a frequency range of at least 20 kHz and / or up to 100 MHz.

10. The method for manufacturing an MEMS sound transducer (500, 700, 800, 900, 1000) in accordance with any of the preceding claims, wherein the one or more gaps (520) comprise a width of less than 20 µm, less than 10 µm or less than 5 µm, or, generally, comprise a width in a range between 0.1 and 20 µm.

11. The method for manufacturing an MEMS sound transducer (500, 700, 800, 900, 1000) in accordance with any of the preceding claims, wherein the actuator (510, 710, 810) is implemented as a bending actuator (710), and wherein the bending actuator (710) and the surrounding structure (530) are laterally opposite each other in a plane; and wherein the bending actuator (710) is suspended relative to the surrounding structure (530) at least on one side; and wherein the bending actuator (710) is configured to execute, with an end of the bending actuator, the relative movement (620) between the bending actuator and the surrounding structure (530) at least partially perpendicularly to the plane; and wherein, at the moveable end of the bending actuator, a plurality of recesses (710-2) and / or projections (710-1) in the form of a first comb structure (710-3) are implemented, in the common plane of the bending actuator (710) and the surrounding structure (530); and wherein the surrounding structure (530) comprises a plurality of recesses (530-2) and / or projections (530-1) in the form of a second comb structure (530-3) on a side facing the movable end of the bending actuator, wherein the first and second comb structures are configured to interdigitate.

12. The method for manufacturing an MEMS sound transducer (500, 700, 800, 900, 1000) in accordance with any of the preceding claims, wherein the actuator (510, 710, 810) is implemented as a lifting actuator (810), and wherein the lifting actuator (810) and the surrounding structure (530) are arranged in a plane; and wherein the lifting actuator (810) is configured to execute the relative movement (620) between the lifting actuator (810) and the surrounding structure (530) perpendicularly to the plane; and wherein the lifting actuator (810) comprises a plurality of recesses and / or projections (820) in the form of a first comb structure along its periphery in the plane; and wherein the surrounding structure (530) comprises a plurality of recesses and / or projections (820) in the form of a second comb structure on a side facing the first comb structure; and wherein the first and the second comb structures are configured to interdigitate.

13. The method for manufacturing an MEMS sound transducer (500, 700, 800, 900, 1000) in accordance with any of the preceding claims, wherein the actuator (510, 710, 810) is arranged in a first plane, and wherein the surrounding structure (530) is arranged in a second plane, the first and second planes being parallel to each other; and wherein the actuator (510, 710, 810) is configured to execute the relative movement (620) between the actuator (510, 710, 810) and the surrounding structure (530) perpendicularly to the first and second planes; and wherein the actuator (510, 710, 810) comprises a plurality of projections in the form of columns and / or combs (510-4), wherein the columns and / or combs (510-4) are arranged on a surface of the actuator facing the surrounding structure (530), perpendicularly to the parallel planes; and wherein the surrounding structure (530) comprises a plurality of recesses in the form of holes and / or slots (530-4); and wherein the columns and / or combs (510-4) of the actuator and the holes and / or slots (530-4) of the surrounding structure (530) are configured to interdigitate.

14. The method for manufacturing an MEMS sound transducer (500, 700, 800, 900, 1000) in accordance with any of the preceding claims, wherein the surrounding structure (530) is arranged in a first plane, and wherein the actuator (510, 710, 810) is arranged in a second plane, the first and second planes being parallel to each other; and wherein the actuator (510, 710, 810) is configured to execute the relative movement (620) between the actuator (510, 710, 810) and the surrounding structure (530) perpendicularly to the first and second planes; and wherein the surrounding structure (530) comprises a plurality of projections in the form of columns and / or combs (530-5), wherein the columns and / or combs (530-5) are arranged on a surface of the surrounding structure facing the actuator (510, 710, 810), perpendicularly to the parallel planes; and wherein the actuator (510, 710, 810) comprises a plurality of recesses in the form of holes and / or slots (510-5); and wherein the columns and / or combs (530-5) of the surrounding structure (530) and the holes and / or slots (510-5) of the actuator are configured to interdigitate.

15. An MEMS sound transducer (500, 700, 800, 900, 1000) for generating sound, comprising: an actuator (510, 710, 810), wherein the actuator (510, 710, 810) is separated from a surrounding structure (530) by one or more gaps (520) and is configured to execute a relative movement (620) between the actuator (510, 710, 810) and the surrounding structure (530), and the surrounding structure, wherein the actuator (510, 710, 810) and the surrounding structure (530) comprise a plurality of recesses (510-2, 510-5, 530-2, 530-4, 710-2) and projections (510-1, 510-1-1, 510-4, 530-1, 530-1-1, 530-5, 710-1), wherein the plurality of projections (510-1, 510-1-1, 510-4, 710-1) belonging to the actuator (510, 710, 810) are arranged to interdigitate into the plurality of recesses (530-2) belonging to the surrounding structure (530), and / or the plurality of projections (530-1, 530-1-1, 530-5) belonging to the surrounding structure (530) to interdigitate into the plurality of recesses (510-2, 510-5, 710-2) belonging to the actuator (510, 710, 810), wherein the interdigitating elements are separated by one or more gaps (520), and wherein the interdigitating elements are separated by one or more gaps (520) such that the interdigitating elements comprise an attenuation function with a relative movement between the actuator (510, 710, 810) and the surrounding structure (530); and wherein the actuator (510, 710, 810) is arranged in a first plane, and wherein the surrounding structure (530) is arranged in a second plane, the first and second planes being parallel to each other; and wherein the actuator (510, 710, 810) is configured to execute the relative movement (620) between the actuator (510, 710, 810) and the surrounding structure (530) perpendicularly to the first and second planes; and wherein the actuator (510, 710, 810) comprises a plurality of projections in the form of columns and / or combs (510-4), wherein the columns and / or combs (510-4) are arranged on a surface of the actuator facing the surrounding structure (530), perpendicularly to the parallel planes; and wherein the surrounding structure (530) comprises a plurality of recesses in the form of holes and / or slots (530-4); and wherein the columns and / or combs (510-4) of the actuator and the holes and / or slots (530-4) of the surrounding structure (530) are configured to interdigitate; and / or wherein the surrounding structure (530) is arranged in a first plane, and wherein the actuator (510, 710, 810) is arranged in a second plane, the first and second planes being parallel to each other; and wherein the actuator (510, 710, 810) is configured to execute the relative movement (620) between the actuator (510, 710, 810) and the surrounding structure (530) perpendicularly to the first and second planes; and wherein the surrounding structure (530) comprises a plurality of projections in the form of columns and / or combs (530-5), wherein the columns and / or combs (530-5) are arranged on a surface of the surrounding structure facing the actuator (510, 710, 810), perpendicularly to the parallel planes; and wherein the actuator (510, 710, 810) comprises a plurality of recesses in the form of holes and / or slots (510-5); and wherein the columns and / or combs (530-5) of the surrounding structure (530) and the holes and / or slots (510-5) of the actuator are configured to interdigitate.