Enhanced performance MEMS loudspeaker

Abstract

The invention relates to an MEMS transducer that comprises a vibrating diaphragm (1) for producing or picking up pressure waves in a fluid in a vertical direction, wherein the vibrating diaphragm (1) is held by a support (4) and the vibrating diaphragm (1) has two or more vertical sections (2) that are formed parallel to the vertical direction and comprise at least one layer of an actuator material (11). The ends of the vibrating diaphragm (1) are in contact with an electrode (13), which means that actuation of the at least one electrode (13) allows the two or more vertical sections (2) to be excited to produce horizontal vibrations or which means that excitation of the two or more vertical sections (2) to produce horizontal vibrations results in an electrical signal being able to be generated at the at least one electrode (13).

Description

[0001] The invention relates to a MEMS transducer comprising a vibrating diaphragm for generating or receiving pressure waves of a fluid in a vertical direction, wherein the vibrating diaphragm is held by a support and the vibrating diaphragm has two or more vertical sections which are formed parallel to the vertical direction and comprise at least one layer of an actuator material. The vibrating diaphragm is preferably contacted at its end with an electrode, so that by actuating the at least one electrode the two or more vertical sections can be excited to horizontal vibrations, or so that when the two or more vertical sections are excited to horizontal vibrations, an electrical signal can be generated at the at least one electrode. Background and state of the art

[0002] Microsystems technology is now used in many application areas for the production of compact, mechanical-electronic devices. The microsystems that can be produced in this way (English: microsystems) are called microsystems or microcontrollers. microelectromechanical system, MEMS (short for MEMS) are very compact (micrometer range) while offering excellent functionality and ever-decreasing manufacturing costs.

[0003] MEMS transducers, such as MEMS loudspeakers or MEMS microphones, are also known from the prior art. Current MEMS loudspeakers are mostly designed as planar diaphragm systems with vertical actuation of a vibrating diaphragm in the emission direction. Excitation is achieved, for example, by means of piezoelectric, electromagnetic, or electrostatic actuators.

[0004] An electromagnetic MEMS loudspeaker for mobile devices is described in Shahosseini et al. 2015. The MEMS loudspeaker features a stiffening silicon microstructure as a sound radiator, with the moving part suspended on a support via silicon drive springs to enable large out-of-plane displacements by means of an electromagnetic motor.

[0005] Stoppel et al. (2017) describe a two-way loudspeaker whose concept is based on concentric piezoelectric actuators. A unique feature is that the diaphragm is not a closed unit, but rather comprises eight piezoelectric unimorphic actuators, each consisting of a piezoelectric and a passive layer. The outer woofers consist of four trapezoidal actuators mounted on one side, while the inner tweeters are formed by four triangular actuators connected to a rigid frame by a spring. This diaphragm separation is intended to allow for improved sound reproduction at higher power levels.

[0006] A disadvantage of such planar MEMS loudspeakers is their limitation in terms of sound power, especially at low frequencies. One reason for this is that the achievable sound pressure level is proportional to the square of the frequency for a given excursion. Therefore, sufficient sound power requires either excursions of at least 100 µm for the vibrating diaphragms or large diaphragms in the square centimeter range. Both conditions are difficult to achieve using MEMS technology.

[0007] In the prior art, it was therefore proposed to design MEMS loudspeakers that do not have a closed diaphragm vibrating in the vertical emission direction, but rather a multitude of movable elements that can be excited to lateral or horizontal vibrations. The advantage of this is that a larger volume flow can be moved within a smaller area, thus providing increased sound power.

[0008] A MEMS loudspeaker based on this principle is disclosed, for example, in US 2018 / 0179048 A1 and Kaiser et al. 2019.

[0009] The MEMS loudspeaker comprises multiple electrostatic bending actuators arranged as vertical lamellae between a top and bottom wafer. These lamellae can be driven into lateral vibrations by appropriate control. An inner lamella acts as an actuator electrode opposite two outer lamellae. Except for a connection point with galvanically isolated electrodes, an air gap exists between the three bent lamellae. When a potential is applied from the inside to the outside, the curvature of the design causes a bilateral attraction in a preferred direction, defined by an armature. The bulges of the outer lamellae allow for movement. A mechanical spring provides the restoring force. Therefore, a pull-push operation is not possible.

[0010] A further disadvantage is that gaps between the bending actuators and the top / bottom wafers, which are necessary for their movement, lead to ventilation between the two chambers. This limits the lower cutoff frequency. Furthermore, the lateral movement of the bending actuators, and thus the sound power, is restricted to prevent a pull-in effect and acoustic penetration.

[0011] An alternative MEMS-based air pulse or sound generation system is described in US 2019 / 011 64 17 A1. The device comprises a front and rear chamber and a plurality of valves, the front and rear chambers being separated by a folded diaphragm. In one embodiment, the folded diaphragm has a rectangular meandering cross-section with horizontal and vertical sections. Piezoelectric actuators are positioned on the respective horizontal sections to cause lateral movement of the vertical sections by synchronized stretching or compression of the horizontal sections. The proposed principle also allows for the generation of an increased volume flow and thus sound power on a small chip surface.

[0012] However, a disadvantage is the increased effort required for the synchronized drive of the piezo actuators.

[0013] There is also potential for improvement with regard to the volume displaced by the lateral vibrations, which is limited by the geometric arrangement of the unilaterally actuated horizontal sections.

[0014] From US 2002 / 006208 A1 and JP 3 919695 B2, a piezoelectric loudspeaker is known in which two piezoelectric films are formed into a diaphragm with an accordion shape. The diaphragm, in its folded form, is clamped laterally by a pair of corrugated plates, which are fixed, for example, by screws and form a composite side frame that stabilizes the vibrating diaphragm. Several electrodes are applied in a structured form to the crests and troughs of the diaphragm and are insulated from each other by strips of non-conductive material. Electrode leads are arranged in the plate pair or side frame to control the electrodes. Alternatively, the plate pair can also be formed, at least partially, from a conductive material.

[0015] The macroscopic piezoelectric loudspeaker US 2002 / 006208 A1 and JP 3 919695 B2 is obtained through an assembly process that cannot be readily miniaturized to create a MEMS loudspeaker. In particular, the clamping of the diaphragm in a two-part side frame, the structured application of multiple electrodes to the crests and troughs of the diaphragm, and the connection of the electrodes to electrode leads within the side frame are not transferable to a MEMS process.

[0016] In light of the disadvantages of the current state of the art, there is therefore a need for alternative or improved solutions for MEMS-based loudspeakers. Object of the invention

[0017] The object of the invention is to provide a MEMS transducer, in particular a MEMS loudspeaker or MEMS microphone, and a method for manufacturing the MEMS transducer, which do not exhibit the disadvantages of the prior art. In particular, it was an object of the invention to provide a high-performance MEMS loudspeaker or MEMS microphone with high sound quality or audio quality, which is simultaneously characterized by a simple, cost-effective and compact design. Summary of the invention

[0018] The problem is solved by the features of the independent claims. Preferred embodiments of the invention are described in the dependent claims.

[0019] The invention relates to a MEMS transducer for interacting with a volume flow of a fluid comprising a support, a vibrating membrane for generating or receiving pressure waves of the fluid in a vertical direction, wherein the vibrating membrane is held by the support and wherein the vibrating membrane has two or more vertical sections which are formed substantially parallel to the vertical direction and comprise at least one layer of an actuator material, wherein the vibrating membrane is contacted at its end with at least one electrode, such that by actuating the at least one electrode the two or more vertical sections can be excited to substantially horizontal vibrations or such that when the two or more vertical sections are excited to substantially horizontal vibrations an electrical signal can be generated at the at least one electrode.

[0020] Preferably, the MEMS transducer can be a MEMS loudspeaker. In a particularly preferred embodiment, the invention relates to a MEMS loudspeaker comprising a support, a vibrating membrane for generating sound waves in a vertical emission direction, wherein the vibrating membrane is held by the support, wherein the vibrating membrane has two or more vertical sections which are formed essentially parallel to the emission direction and comprise at least one layer of an actuator material, wherein the vibrating membrane is preferably contacted at its end with at least one electrode, so that by actuating the at least one electrode the two or more vertical sections can be excited to essentially horizontal vibrations.

[0021] The design of the MEMS loudspeaker allows for a MEMS loudspeaker with high sound power and simplified control.

[0022] Unlike conventional planar MEMS loudspeakers, the vibrating diaphragm itself does not need to cover a large area of ​​several square centimeters or be operated with a displacement exceeding 100 µm to generate sufficient sound pressure. Instead, the majority of the vertical sections of the vibrating diaphragm can move an increased total volume in the vertical emission direction with small horizontal or lateral movements of a few micrometers.

[0023] Compared to solutions according to US 2018 / 0179048 A1 or Kaiser et al. 2019, the claimed MEMS loudspeaker is characterized by a simplified design, control and manufacturing process.

[0024] In particular, the provision of the vertical lamellae or bending actuators for a MEMS loudspeaker according to Kaiser et al. 2019 is complex. Furthermore, sufficiently precise vertical etching is only possible for limited lamella heights, which limits the sound power.

[0025] Using the solution according to the invention, the vertical sections of the vibrating membrane, as explained in detail below, can instead be obtained in MEMS form through simple manufacturing steps. Furthermore, the actuator principle according to the invention avoids pull-in or adhesion of the vertical sections. In contrast to the solution by Kaiser et al. 2019, the single-sided electrodes prevent potential differences from forming in a gap between the vertical sections. Besides preventing overvoltage or pull-in, this also reduces dust accumulation, since, for example, an external electrode can be connected to a ground potential.

[0026] Another significant advantage of the described MEMS loudspeaker lies in its simplified control. While US 2019 / 011 64 17 A1 requires the contacting of numerous piezoelectric actuators on the horizontal sections, the proposed MEMS loudspeaker can be operated using at least one end electrode. This reduces manufacturing effort, minimizes potential sources of error, and inherently results in synchronous control of the vertical sections relative to the horizontal oscillations.

[0027] In this way, the air volumes between the vertical sections can be moved with extreme precision by the horizontal vibrations along the vertical emission direction. The result is improved sound quality, even at high sound power levels.

[0028] A "MEMS loudspeaker" preferably refers to a loudspeaker based on MEMS technology whose sound-generating structures have dimensions in the micrometer range (1 µm to 1000 µm), at least partially. Preferably, for example, the vertical sections of the vibrating diaphragm can have dimensions of less than 1000 µm in width, height, and / or thickness. It may also be preferred that, for example, only the height of the vertical sections is dimensioned in the micrometer range, while the length can be larger and / or the thickness smaller.

[0029] The design of the vibrating membrane can advantageously be used not only to create a MEMS loudspeaker with high sound power and simplified control. It also enables, for example, the provision of a particularly powerful MEMS microphone with high audio quality.

[0030] In a preferred embodiment, the invention also relates to a MEMS microphone comprising a support, a vibrating membrane for receiving sound waves in a vertical direction, wherein the vibrating membrane is held by the support, and wherein the vibrating membrane has two or more vertical sections which are formed parallel to the vertical direction and comprise at least one layer of an actuator material, wherein the vibrating membrane is preferably contacted at its end with at least one electrode, so that when the two or more vertical sections are excited to horizontal vibrations, an electrical signal can be generated at the at least one electrode.

[0031] The structure of the MEMS microphone is structurally similar to that of the MEMS loudspeaker, particularly with regard to the design of the vibrating diaphragm. However, instead of driving the electrodes to generate horizontal vibrations and thus sound pressure waves, the MEMS microphone is designed to detect sound pressure waves in the same vertical direction. Preferably, air volumes are located between the vertical sections, which are moved along a vertical detection direction when sound waves are detected. The sound pressure waves excite the vertical sections to horizontal vibrations, causing the actuator material to generate a corresponding periodic electrical signal.

[0032] A "MEMS microphone" preferably refers to a microphone based on MEMS technology whose sound-receiving structures have dimensions in the micrometer range (1 µm to 1000 µm), at least partially. Preferably, for example, the vertical sections of the vibrating diaphragm can have dimensions of less than 1000 µm in width, height, and / or thickness. It may also be preferred that, for example, only the height of the vertical sections is dimensioned in the micrometer range, while the length can be larger and / or the thickness smaller.

[0033] The term MEMS transducer encompasses both MEMS microphones and MEMS loudspeakers. Generally, a MEMS transducer is a device that interacts with a fluid flow, is based on MEMS technology, and whose structures for interacting with the fluid flow, or for capturing or generating pressure waves from the fluid, have dimensions in the micrometer range (1 µm to 1000 µm). The fluid can be either gaseous or liquid. The structures of the MEMS transducer, particularly the vibrating diaphragm, are designed to generate or capture pressure waves from the fluid.

[0034] For example, as in the case of a MEMS loudspeaker or MEMS microphone, the sound pressure waves can be sound waves. However, the MEMS transducer can also function as an actuator or sensor for other pressure waves. Thus, the MEMS transducer is preferably a device that converts pressure waves (e.g., acoustic signals as alternating sound pressures) into electrical signals or vice versa (conversion of electrical signals into pressure waves, for example, acoustic signals).

[0035] MEMS transducers can also be used as energy harvesters, utilizing pneumatic or hydraulic pressure changes. In these cases, the electrical signal can be extracted, stored, or supplied to other (consumer) devices as recovered electrical energy.

[0036] The term "end-side" preferably refers to the positioning of at least one electrode such that contact with electronics, e.g., a current or voltage source in the case of a MEMS loudspeaker, can be made at one end of the vibrating diaphragm, preferably at the end where the diaphragm is suspended from the support. "Electrode" preferably refers to an area made of a conductive material (preferably a metal) that is designed for such contact with electronics, e.g., a current and / or voltage source in the case of a MEMS loudspeaker. Preferably, this can be an electrode pad. Particularly preferably, the electrode pad serves for contact with electronics and is itself connected to a conductive metal layer that can extend over the entire surface of the vibrating diaphragm.In some instances, the conductive layer together with an electrode pad is referred to as the electrode, for example as the top electrode or bottom electrode.

[0037] Particularly preferably, the layer of a conductive material, preferably metal, is arranged as a top or bottom electrode, forming a continuous or entire or continuous layer of the vibrating membrane, which constitutes a substantially homogeneous surface and is, in particular, unstructured. Instead, the two or more vertical sections are preferably contacted with the end electrodes or electrode pad by means of an unstructured layer of a conductive material, preferably metal.

[0038] A particular advantage is that separate contact areas are not required for different vertical sections of the vibrating membrane. In contrast to the approach for a macroscopic piezoelectric loudspeaker according to US 2002 / 006208 A1 and JP 3 919695 B2, the application of a structured top or bottom electrode is unnecessary. Instead, a top or bottom electrode can be applied as a single, continuous layer of conductive material, which is contacted by at least one end electrode or electrode pad. This significantly simplifies the manufacturing process and allows for the mass production of miniaturized MEMS transducers using a batch process.

[0039] In preferred embodiments, the MEMS transducer comprises two end-face electrodes. Preferably, contact with electronics, e.g., a current or voltage source, can be made via the electrodes at opposite ends of the vibrating membrane, between which the two or more vertical sections are located, so that the actuator position(s) in the vertical sections can be controlled by means of the end-face electrodes.

[0040] The end-side provision of the electrodes is thus preferably distinct from a contacting arrangement that controls the respective vertical sections with separate electrodes or, in the case of a MEMS microphone, taps into generated electrical signals. Preferably, the MEMS transducer comprises exactly one or exactly two electrodes for end-side contacting and no further electrode pads for contacting central vertical sections. Preferably, the layer of actuator material in the vertical sections serves as part of a mechanical biomorph, wherein controlling the actuator layer via the electrode causes a lateral curvature of the vertical sections, or wherein an induced lateral curvature generates a corresponding electrical signal.

[0041] The two or more vertical sections have at least two layers, one comprising an actuator material and a second comprising a mechanical support material. At least the layer comprising the actuator material is contacted with an end electrode, such that horizontal vibrations can be generated by a deformation of the actuator material relative to the mechanical support material. In this embodiment, the mechanical bimorph is formed by a layer of actuator material (e.g., a piezoelectric material) and a passive layer that acts as a mechanical support. Both a transverse and a longitudinal piezoelectric effect can be used for bending.

[0042] When the actuator position is controlled, it can, for example, undergo transverse or longitudinal stretching or compression. This creates a stress gradient relative to the mechanical support layer, leading to lateral bulging or vibration. As in the Fig. 1 As illustrated, by changing the polarity at the electrodes, a push-pull operation can preferably be achieved, whereby almost the entire air volume between the vertical sections can be moved alternately in the vertical emission direction.

[0043] The advantage of the actuator principle is its highly efficient conversion of horizontal vibrations of vertical sections into vertical volume movement and sound generation. Since the actuator principle is not based on electrostatic attraction, but rather on a relative change in shape (e.g., compression, stretching, shearing) of the actuator layer relative to a support layer, adhesion of the membrane sections is prevented. Instead, the vertical sections can finally touch and are therefore not restricted in their deflection.

[0044] In an embodiment not covered by the scope of the claims, the two or more vertical sections comprise at least two layers, each layer comprising an actuator material and contacted at its end by electrodes, and the horizontal vibrations can be generated by a deformation of one layer relative to the other. In this embodiment, the horizontal vibration of the vertical sections is thus not generated by a stress gradient between an active actuator layer and a passive support layer, but by a relative deformation of two active actuator layers.

[0045] The actuator layers can be made of the same actuator material and controlled differently. Alternatively, the actuator layers can be made of different actuator materials, for example, piezoelectric materials with different deformation coefficients.

[0046] For the purposes of the invention, the "layer comprising an actuator material" is preferably also referred to as the actuator layer. An actuator material preferably means a material which, when an electrical voltage is applied, undergoes a change in shape, for example, elongation, compression, or shearing, or conversely, generates an electrical voltage when its shape changes.

[0047] Materials with electric dipoles are preferred, which undergo a change in shape when an electric voltage is applied, whereby the orientation of the dipoles and / or the electric field can determine the preferred direction of the shape changes.

[0048] Preferably, the actuator material can be a piezoelectric material, a polymer piezoelectrical material and / or electroactive polymers (EAP).

[0049] The piezoelectric material is particularly preferred if it is selected from a group comprising lead zirconate titanate (PZT), aluminum nitride (AIN), aluminum scandium nitride (AIScN) and zinc oxide (ZnO).

[0050] Polymer piezoelectric materials preferably include polymers that possess internal dipoles and thus exhibit piezoelectric properties. This means that when an external electrical voltage is applied, the piezoelectric polymer materials (analogous to the aforementioned classical piezoelectric materials) undergo a change in shape (e.g., compression, stretching, or shearing). An example of a preferred piezoelectric polymer material is polyvinylidene fluoride.

[0051] This allows for a macroscopic solution in which a polymer piezoelectric material layer is applied to a mechanical support layer and wound over an upper and lower comb. Preferably, a polymer piezoelectric material layer (including an electrode) is first provided on a support layer (optionally including a counter electrode). Subsequently, an upper and lower comb (preferably a MEMS structure) are moved against each other in such a way that a folded membrane with actuable vertical sections is formed.

[0052] For the purposes of the invention, the "layer comprising a mechanical support material" is preferably also referred to as a support layer or support layer. The mechanical support material or support layer preferably serves as a passive layer that can resist deformation of the actuator layer. In contrast to an actuator layer, the mechanical support material preferably does not change its shape when an electrical voltage is applied. Preferably, the mechanical support material is electrically conductive so that it can also be used directly for contacting the actuator layer. However, in some embodiments, it can also be non-conductive and, for example, coated with an electrically conductive layer.

[0053] The mechanical support material is preferably monocrystalline silicon, polysilicon or doped polysilicon.

[0054] While the actuator layer undergoes a deformation under electrical voltage, the position of the mechanical support material remains essentially unchanged. The resulting stress gradient between the two layers (mechanical bimorphism) preferably causes a horizontal warping. For this purpose, the thickness of the support layer is preferably selected relative to the thickness of the actuator layer such that a sufficiently large stress gradient is generated for the warping to occur. For example, for doped polysilicon as the mechanical support material and a piezoelectric material such as PZT or AIN, essentially equal thicknesses, preferably between 0.5 µm and 2 µm, have proven particularly suitable.

[0055] Terms such as "essentially", "approximately", "about", "approximately", etc. preferably describe a tolerance range of less than ± 20%, preferably less than ± 10%, even more preferably less than ± 5%, and particularly less than ± 1%. Statements using "essentially", "approximately", "about", etc., always disclose and include the exact value stated.

[0056] By periodically controlling the actuator position, e.g. by means of an alternating voltage, horizontal vibrations can thus be generated quickly and precisely for sound emission.

[0057] To ensure horizontal vibration, the piezoelectric material can preferably have a C-axis orientation perpendicular to the surface of the vertical sections, thus utilizing a transverse piezoelectric effect. Other orientations and, for example, the use of a longitudinal piezoelectric effect to form the horizontal bulges or vibrations are also possible (see [reference]). Fig. 1 ) may be given preference.

[0058] Contacting the actuator layer and / or the layer made of a mechanical support material, and thus applying an electrical voltage, can be done directly via the end electrodes or supported by a layer made of a conductive material.

[0059] In a preferred embodiment, the vibrating membrane therefore comprises at least one layer of a conductive material.

[0060] In preferred embodiments, the conductive material is selected from a group comprising platinum, tungsten, (doped) tin oxide, monocrystalline silicon, polysilicon, molybdenum, titanium, tantalum, titanium-tungsten alloy, metal silicide, aluminum, graphite and copper.

[0061] The directional terms vertical and horizontal (or lateral) preferably refer to a preferred direction in which the vibrating diaphragm is oriented to generate or receive pressure waves from the fluid. Preferably, the vibrating diaphragm is suspended horizontally between at least two side regions of a support, while the vertical direction (interaction direction with the fluid) for generating or receiving pressure waves is orthogonal to this. In the case of a MEMS loudspeaker, the vertical (interaction) direction corresponds to the vertical sound emission direction of the MEMS loudspeaker. In this case, "vertical" preferably refers to the direction of sound emission, while "horizontal" refers to a direction orthogonal to it. In the case of a MEMS microphone, the vertical (interaction) direction corresponds to the vertical sound detection direction of the MEMS microphone. In this case, "vertical" preferably refers to the direction of sound detection.Intake, while horizontal refers to a direction orthogonal to it.

[0062] The vertical sections of the vibrating membrane thus preferably denote sections of the vibrating membrane which are oriented essentially in the emission direction of a MEMS loudspeaker or the detection direction of a MEMS microphone. Those skilled in the art understand that this does not necessarily have to be an exact vertical alignment, but rather that the vertical sections of the vibrating membrane are preferably oriented essentially in the emission direction of a MEMS loudspeaker or the detection direction of a MEMS microphone.

[0063] In a preferred embodiment, the vertical sections are aligned substantially parallel to the vertical direction, wherein substantially parallel means a tolerance range of ± 30°, preferably ± 20°, particularly preferably ± 10° around the vertical direction.

[0064] The vibrating membrane can therefore preferably have not only a rectangular meander shape in cross-section, but also a curved or wavy shape or a sawtooth shape (zigzag shape).

[0065] Preferably, the vertical and / or horizontal sections are straight at least partially or along their entire length; however, the vertical and / or horizontal sections may also be curved at least partially or along their entire length. In the case of a curved or wavy cross-section of the vibrating membrane, the orientation preferably refers to a tangent to the curved vertical and / or horizontal sections at their respective midpoints.

[0066] While the vibrating membrane is preferably oriented horizontally to the direction of sound emission or sound detection, the sound waves are generated by an actuation of the vertical sections or, conversely, detected.

[0067] In a preferred embodiment of the invention, the support comprises two side regions between which the vibrating membrane is arranged in a horizontal direction.

[0068] The support structure is preferably a frame structure, which is essentially formed by a continuous outer boundary in the form of side walls of a free, planar area. The frame structure is preferably stable and rigid. In the case of an angular frame shape (triangular, square, hexagonal, or generally polygonal outline), the individual side areas that preferably constitute the frame structure are specifically referred to as side walls.

[0069] The vibrating membrane is preferably held by at least two side walls of the support. In the exemplary Figs. 1-9 The two side walls are shown in cross-section. Preferably, however, the support comprises four side sections, with additional end faces generally parallel to the drawn cross-section. These two additional side walls span the frame structure.

[0070] The vibrating membrane is preferably suspended across its entire surface within the remaining free area. The planar spread of the vibrating membrane is characterized by a horizontal direction, while the vertical sections are essentially orthogonal to it. With respect to the end faces, the membrane can be attached to these side walls or slotted there for greater mobility. Advantageously, the slot can represent a dynamic high-pass filter, which, for example, couples a front volume and a rear volume.

[0071] In a preferred embodiment of the invention, the support is formed from a substrate, preferably selected from the group consisting of monocrystalline silicon, polysilicon, silicon dioxide, silicon carbide, silicon germanium, silicon nitride, nitride, germanium, carbon, gallium arsenide, gallium nitride, indium phosphide and glass.

[0072] These materials are easy and cost-effective to process in semiconductor and / or microsystem manufacturing and are suitable for large-scale production. The support structure can be flexibly manufactured due to the materials and / or manufacturing methods. In particular, it is preferable to manufacture the MEMS transducer comprising a vibrating membrane together with a support in a single (semiconductor) process, preferably on a wafer. This further simplifies and reduces the manufacturing cost, enabling the cost-effective provision of a compact and robust MEMS transducer.

[0073] In a preferred embodiment, the vibrating membrane is formed by a lamellar or meandering structure. Preferably, the designation of a lamellar or meandering structure refers to the cross-sectional shape of the vibrating membrane. A lamellar structure preferably denotes an arrangement of similar, parallel layers, which preferably form the vertical sections. The individual lamellae are preferably oriented with their surface substantially parallel to the vertical direction, more preferably to an emission or detection direction. The lamellae are multilayered and form a mechanical biomorph. Each lamellae comprises an actuator layer and a passive layer made of a support material.

[0074] The person skilled in the art understands that the lamellae do not necessarily have to be aligned exactly parallel to the vertical direction, but rather that the lamellae are preferably aligned essentially in the emission direction of a MEMS loudspeaker or the detection direction of a MEMS microphone.

[0075] In a preferred embodiment, the vertical sections or lamellae are aligned substantially parallel to the vertical direction, wherein substantially parallel means a tolerance range of ± 30°, preferably ± 20°, particularly preferably ± 10° around the vertical direction.

[0076] It may be preferred that the lamellae are planar, meaning in particular that their extent in each of the two dimensions (height, width) of their surface is greater than in a dimension perpendicular to these (thickness). For example, size ratios of at least 2:1, preferably at least 5:1, 10:1 or more, may be preferred.

[0077] Preferably, the vibrating membrane has a plurality of lamellae forming the vertical sections. For example, 2, 3, 4, 5, 10, 15, 20, 30, 40, 50 or more lamellae may be preferred. This achieves a high efficiency for the desired sound emission or sound detection in a very small space.

[0078] In this embodiment, the vibrating membrane is preferably formed by the lamellae as vertical sections, which are connected to each other via conductive bridges or horizontal sections. Suitable bridges include, for example, metal bridges (see...). Fig. 10) or bridges made of other conductive materials. These conductive bridges ensure the mechanical integrity of the vibrating membrane. Furthermore, they advantageously allow all lamellae to be contacted via end-contact electrodes. This allows the lamellae to be synchronously excited to horizontal vibrations or to detect them with minimal control and manufacturing effort.

[0079] A meandering structure preferably refers to a structure formed from a sequence of essentially orthogonal sections in cross-section. These orthogonal sections are preferably vertical and horizontal sections of the vibrating membrane. A rectangular cross-section of the meandering structure is particularly preferred. However, it may also be preferred that the meandering structure has a sawtooth (zigzag) cross-section or is curved or wave-shaped. This is particularly the case if the vertical sections are not aligned exactly parallel to the vertical emission or detection direction, but rather form an angle, for example, of ± 30°, preferably ± 20°, and particularly preferably ± 10° with the vertical direction.

[0080] In preferred embodiments, the horizontal sections may also not be positioned at an exact orthogonal angle of 90° to the vertical emission or detection direction, but may, for example, form an angle between 60° and 120°, preferably between 70° and 110°, and particularly preferably between 80° and 100° with the vertical direction. In the case of a curved or wavy shape of the vertical and / or horizontal sections of the vibrating membrane in cross-section, the orientation preferably refers to a tangent to the vertical and / or horizontal sections at their respective midpoints.

[0081] The meandering structure thus preferably corresponds to a membrane folded along its width. In accordance with the invention, a vibrating membrane can therefore preferably also be referred to as a bellows. The parallel folds of the bellows preferably form the vertical sections. The connecting sections between the folds preferably form the horizontal sections. Preferably, the vertical sections are longer than the horizontal sections, for example by a factor of 1.5, 2, 3, 4 or more.

[0082] Regarding the function of a vibrating, meandering membrane for generating or receiving sound waves, the vertical sections are crucial, analogous to the lamellae described above. Preferably, the vertical sections are multilayered and form a mechanical biomorph. Each vertical section comprises an actuator layer and a passive layer made of a support material. The horizontal sections of the folded membrane can preferably be structured identically to the vertical sections (see, among others, [reference]). Fig. 3-7 However, it may also be preferred that the horizontal sections – in contrast to the vertical sections – do not have an actuator layer, but merely a mechanical support layer and / or an electrically conductive layer.

[0083] In a preferred embodiment, the at least one layer of actuator material in the vibrating diaphragm is a continuous layer. "Continuous" preferably means that there are no breaks in the cross-sectional profile. Accordingly, in this embodiment, it is preferred that a continuous layer of actuator material exists in both the vertical and horizontal sections. Advantageously, no structuring is necessary. A continuous layer is particularly easy to manufacture and ensures synchronous actuation during the operation of a MEMS loudspeaker.

[0084] The performance of the MEMS transducer, especially of a MEMS loudspeaker or MEMS microphone, can be significantly determined by the number and / or dimensions of the vertical sections.

[0085] In preferred embodiments, the vibrating membrane comprises more than 3, 4, 5, 10, 15, 20, 30, 40, 50, 100 or more vertical sections.

[0086] In preferred embodiments, the vibrating membrane comprises fewer than 10000, 5000, 2000 or 1000 or fewer vertical sections.

[0087] The preferred number of vertical sections results in high sound power on the smallest chip surfaces, without compromising the sound image or audio quality.

[0088] Preferably, the vertical sections are planar, meaning in particular that their extent in each of the two dimensions (height, width) of their surface is greater than in a dimension perpendicular to these (thickness). For example, size ratios of at least 2:1, preferably at least 5:1, 10:1 or more, may be preferred.

[0089] In accordance with the invention, the height of the vertical sections preferably corresponds to the dimension along the direction of sound emission or sound detection, while the thickness of the vertical sections preferably corresponds to the sum of the layer thicknesses of the one or more layers that form the vertical sections. The length of the vertical sections preferably corresponds to a dimension orthogonal to the height or thickness. In the cross-sectional views of the figures shown below, the height and thickness are represented schematically (not necessarily to scale), while the length dimension corresponds to a (non-visible) drawing depth of the figures.

[0090] In a preferred embodiment, the height of the vertical sections is between 1 µm and 1000 µm, preferably between 10 µm and 500 µm. Intermediate ranges from the aforementioned ranges may also be preferred, such as 1 µm to 10 µm, 10 µm to 50 µm, 50 µm to 100 µm, 100 µm to 200 µm, 200 µm to 300 µm, 300 µm to 400 µm, 400 µm to 500 µm, 600 µm to 700 µm, 700 µm to 800 µm, 800 µm to 900 µm or even 900 µm to 1000 µm. A person skilled in the art will recognize that the aforementioned range limits can also be combined to obtain further preferred ranges, such as 10 µm to 200 µm, 50 µm to 300 µm or 100 µm to 600 µm.

[0091] In a preferred embodiment, the thickness of the vertical sections is between 100 nm and 10 µm, preferably between 500 nm and 5 µm. Intermediate ranges from the aforementioned ranges are also preferred, such as 100 nm to 500 nm, 500 nm to 1 µm, 1 µm to 1.5 µm, 1.5 µm to 2 µm, 2 µm to 3 µm, 3 µm to 4 µm, 4 µm to 5 µm, 5 µm to 6 µm, 6 µm to 7 µm, 7 µm to 8 µm, 8 µm to 9 µm, or even 9 µm to 10 µm. A person skilled in the art will recognize that the aforementioned range limits can also be combined to obtain further preferred ranges, such as 500 nm to 3 µm, 1 µm to 5 µm or 1500 nm to 6 µm.

[0092] In a preferred embodiment, the length of the vertical sections is between 10 µm and 10 mm, preferably between 100 µm and 1 mm. Intermediate ranges from the aforementioned ranges are also preferred, such as 10 µm to 100 µm, 100 µm to 200 µm, 200 µm to 300 µm, 300 µm to 400 µm, 400 µm to 500 µm, 500 µm to 1000 µm, 1 mm to 2 mm, 3 mm to 4 mm, 4 mm to 5 mm, 5 mm to 8 mm, or even 8 mm to 10 mm. A person skilled in the art will recognize that the aforementioned range limits can also be combined to obtain further preferred ranges, such as 10 µm to 500 µm, 500 µm to 5 µm or 1 mm to 5 mm.

[0093] With the aforementioned preferred dimensions of the vibrating membrane or the vertical sections, a particularly compact MEMS transducer, especially MEMS loudspeaker or MEMS microphone, can be provided, which simultaneously combines high performance with excellent sound image or audio quality.

[0094] In a preferred embodiment of the invention, the vibrating membrane is formed by a meandering structure with alternating vertical and horizontal sections, wherein support structures are attached to at least two of the horizontal sections, which are connected directly or indirectly to the support. The support structures can, for example, be provided by substrate material of the support; that is, the support structures can be formed directly from the substrate of a bottom wafers can be formed. Alternatively, it is also possible for the holding structures to be formed as separate ridges or elevations of a top waferto be connected to the horizontal sections.

[0095] The support structures can preferably be attached to the vibrating membrane on one and / or both sides, i.e., preferably to the upper and / or lower horizontal sections. Particularly when a larger vibrating membrane is suspended between the side walls of a support, the use of support structures advantageously allows for stabilization without negatively affecting sound generation or reception.

[0096] Since the horizontal sections in a meander shape are at least essentially mechanically neutral, locking them in place by means of the holding structure advantageously does not lead to any undesirable stresses between the membrane and the holding structure or support.

[0097] The construction of the vibrating membrane incorporates various layers to ensure the described actuation and excitation of horizontal vibrations or their detection.

[0098] Contacting one or more actuator layers and / or one or more layers of a mechanical support material, and thus applying or detecting an electrical voltage, can be done directly via the end-side electrodes or supported by a layer of a conductive material.

[0099] In a preferred embodiment, the vibrating membrane therefore comprises at least one layer of a conductive material.

[0100] In preferred embodiments, the conductive material is selected from a group comprising platinum, tungsten, (doped) tin oxide, monocrystalline silicon, polysilicon, molybdenum, titanium, tantalum, titanium-tungsten alloy, metal silicide, aluminum, graphite and copper.

[0101] In a preferred embodiment, the vibrating membrane comprises three layers, wherein an upper layer is formed from a conductive material and is connected to an upper electrode, a middle layer is formed from the actuator material, and a lower layer is formed from a conductive material.

[0102] Preferably, the conductive material of the upper and / or lower layer can be a mechanical support material, giving this layer a dual function. Firstly, it ensures contact between the actuator layer and an electrical potential that can be applied to the end electrodes. Secondly, it acts as a mechanical support layer, as described, to generate horizontal bulges or vibrations when the actuator layer is actuated accordingly.

[0103] Such an embodiment can be obtained by means of simple manufacturing steps, as exemplified in the Figure 2 illustrated. In the Fig. 2G , Figs. 3 and 4 In the preferred embodiment shown, the vibrating membrane has a meandering structure with a continuous upper layer made of a conductive material (metal), a continuous middle layer made of an actuator material, and a lower layer made of a conductive mechanical support material. A reversed order of the layers or an additional conductive layer in contact with the mechanical support layer and / or actuator layer for improved contact can also be provided.

[0104] In an embodiment which is not covered by the scope of protection of the claims, the vibrating membrane comprises two layers of an actuator material, which are separated by a middle layer of a conductive material, preferably metal, wherein the middle layer is connected to a first electrode and at least one of the two layers of an actuator material is contacted with a second electrode via a further layer of a conductive material, preferably a metal.

[0105] As explained above, in an embodiment not covered by the scope of the claims, two actuator layers can also be used, for example, to set the vertical sections into horizontal oscillations by means of different control signals. To transmit the electrical potential changes from the end electrodes to the respective actuator layer, two or more intermediate layers made of a conductive material can preferably be provided. Preferably, the layers made of conductive material, for example, a metal, serve exclusively for contact purposes and not as a mechanical support layer. The voltage required for the curvature or oscillation of a MEMS loudspeaker, in the sense of a bimorph, is induced by the different control signals of the actuator layers themselves.Preferably, the layers made of a conductive material, such as metal, can therefore be made particularly thin (less than 500 nm, preferably less than 200 nm).

[0106] In the Fig. 5 An exemplary embodiment of this type is shown. This embodiment features a vibrating membrane in a meandering structure with two layers of an actuator material, separated by a middle layer of a conductive material (metal). The middle layer is connected to a first end electrode pad, while the upper actuator layer is contacted via another layer of conductive material with a second end electrode. A lower layer of conductive material is not in contact with either electrode. A reversed layer order or the omission of the lower conductive layer, which is not in contact with the electrodes, is also possible.

[0107] In the embodiment described above, it is preferred that the actuator layer(s) and, if applicable, the mechanical support layers are continuous, i.e., extend in cross-section from one end of the membrane (where a first electrode is preferably located) through several alternating horizontal and vertical sections to a second end of the membrane (where a second electrode is preferably located).

[0108] The inventors recognized that for the operating principle of the MEMS transducer, preferably a MEMS loudspeaker, the provision of a mechanical biomorph in the vertical sections is sufficient.

[0109] In a preferred embodiment, the at least one actuator layer is not continuous, but is only present in the vertical sections, not in the horizontal sections. It may be preferred that any mechanical support layer, if present, runs continuously, or that it does not run continuously and is, for example, only provided in vertical sections. In order to still be able to contact the vertical sections by means of end electrodes, it is preferred to apply one or more continuous layers of a conductive material (preferably metal).

[0110] A preferred manufacturing method for an embodiment with a non-continuous actuator layer is described in the Figure 7This is illustrated. Here, targeted spacer etching of the actuator layer can be performed in horizontal sections, so that only the vertical sections of the membrane contain a layer of actuator material. A continuous layer of mechanical support material can simultaneously be dielectric to prevent a short circuit between an upper and lower conductive layer (also known as the top and bottom electrodes).

[0111] This embodiment is characterized by particularly effective actuation and high performance, in which only the vertical sections are selectively excited to alternately warp or oscillate, while the horizontal sections remain mechanically neutral. Advantageously, the displaced volume per actuation phase can be further increased.

[0112] In the embodiments described above, a vibrating membrane in a meandering shape is preferably obtained by applying or etching appropriately functional layers.

[0113] Alternatively, a vibrating membrane can also be produced by providing vertical sections and connecting them using metal bridges.

[0114] In a preferred embodiment, the vertical sections of the vibrating membrane comprise two layers, wherein a first layer consists of an actuator material, a second layer consists of a conductive support material, and wherein the vertical sections are connected via horizontal metal bridges.

[0115] As in the Fig. 10As illustrated, several individual piezoceramic elements, each comprising a layer of mechanical support material, a layer of piezoelectric material, and a sacrificial layer, can preferably be provided for this purpose. Through several process steps, including through-hole plating and metal filling, as well as stacking and dicing of the piezoceramic elements, a membrane with high efficiency can advantageously be obtained in a robust and process-efficient manner.

[0116] In this embodiment, a continuous, homogeneous conductive layer is not necessary. Instead, contact with the actuator layer in the vertical sections is ensured by the metal bridges and a conductive mechanical support material.

[0117] In a preferred embodiment, the vibrating membrane is coated with a layer of a non-stick material. Non-stick materials are, in particular, materials with low surface energies that are largely inert to the environment and thus prevent the deposition of dust or other unwanted particles. For example, the non-stick materials can be formed by carbon layers, e.g., diamond-like carbon (DLC) layers, or by layers comprising perfluorocarbons (PFCs), such as polytetrafluoroethylene (PTFT).

[0118] In a preferred embodiment of the invention, the MEMS transducer, preferably a MEMS loudspeaker, comprises a control unit configured to drive the at least one electrode such that the two or more vertical sections are excited to horizontal oscillations. Preferably, the control unit is configured to drive the electrodes in a way that ensures a frequency of the horizontal oscillations between 10 Hz and 20 kHz.

[0119] In a preferred embodiment of the invention, the MEMS transducer, preferably a MEMS microphone, comprises a control unit configured for detecting an electrical signal provided by the at least one electrode, which is generated by horizontal vibrations of the two or more vertical sections. Preferably, the control unit of a MEMS microphone is configured for receiving and processing an electrical signal corresponding to a frequency of the horizontal vibrations between 10 Hz and 20 kHz and is thus set up for sound detection in the audible range.

[0120] The control unit is therefore preferably configured and set up to drive the vibrating membrane (or the actuator position(s) in the vertical sections) to horizontal vibrations and sound emission in the audible frequency range by means of electrical signals, or to receive and process a corresponding electrical signal when the vibrating membrane is excited.

[0121] Preferably, the vertical sections of the diaphragm in the MEMS loudspeaker are directly controlled with audio signals. In contrast to the combined control of separate diaphragm units and a plurality of valves according to US 2019 / 011 64 17 A1, the control for sound generation is thus significantly simplified.

[0122] For the purpose of generating or receiving electrical signals, the control unit may preferably include a data processing unit.

[0123] For the purposes of the invention, a data processing unit preferably refers to a unit that is suitable and configured for receiving, sending, storing, and / or processing data, preferably with regard to controlling the electrodes or receiving an electrical signal provided at the electrodes. The data processing unit preferably comprises an integrated circuit, for example, also an application-specific integrated circuit, a processor, a processor chip, a microprocessor, or a microcontroller for processing data, and optionally a data storage device. random access memory (RAM), a read-only memory (ROM) or also a flash memory for storing the data.

[0124] In preferred embodiments, the control unit is integrated on a printed circuit board (PCB) alongside other components of the MEMS transducer (carrier, vibrating membrane). This preferably involves seamless integration of the MEMS transducer with the electronics required for control or detection. In addition to the control unit, other electronic components, such as a communication interface (preferably wireless, e.g., Bluetooth), an amplifier, a filter, or sensors, can also be installed on the same PCB.

[0125] Advantageously, a compact overall solution is obtained in which a MEMS converter, preferably a MEMS loudspeaker or MEMS microphone, together with desired electronics, can be provided in a very small space and preferably with cost-effective CMOS processing suitable for mass production.

[0126] In another preferred embodiment, the vibrating diaphragm held by the support is arranged in the front of a housing which encloses a rear resonance volume. The sound emission of such a MEMS loudspeaker thus preferably occurs towards the open front ( sound port ) whereby the sound image is improved, especially for lower frequencies, by the rear resonance volume.

[0127] In another preferred embodiment, the housing includes a ventilation opening to prevent acoustic short circuits and / or to enhance the sound. The ventilation opening is preferably small compared to the housing. Sound port and can, for example, have a maximum dimension of less than 100 µm, preferably less than 50 µm.

[0128] In another aspect, the invention relates to a manufacturing method for a MEMS transducer, preferably a MEMS loudspeaker or MEMS microphone, as described above, comprising the following steps: Etching of a substrate, preferably from a front side, to form a structure, preferably a meandering structure. Optional application of an etch stop. Application of at least two layers, wherein at least the first layer comprises an actuator material and the second layer a mechanical support material. Contacting the first and / or second layer with an electrode. Etching, preferably from the back side, and optional removal of the etch stop. such that a vibrating membrane, preferably in the form of a meander structure, is held by a support (4) formed by the substrate (8), wherein the vibrating membrane (1) comprises at least two or more vertical sections (2) for generating or receiving pressure waves of the fluid in a vertical direction, which are formed parallel to the vertical direction, and such that by actuating the at least one electrode the two or more vertical sections can be excited to horizontal vibrations, or such that when the two or more vertical sections are excited to horizontal vibrations an electrical signal can be generated at the at least one electrode.

[0129] The average person skilled in the art recognizes that the technical features, definitions, and advantages of preferred embodiments of the described MEMS transducer, preferably a MEMS loudspeaker or MEMS microphone, also apply to the described manufacturing process, and vice versa. Preferably, the described manufacturing process serves to provide a MEMS transducer with a folded, vibrating diaphragm having a meandering structure. Examples of preferred manufacturing steps are given in the Fig. 2A-G , Fig. 8A-J or Fig. 9 described.

[0130] One of the preferred materials mentioned above can be used as a substrate. During etching, a blank, for example a wafer, can be formed into the desired basic shape of the meander structure. In a subsequent step, the layers for the vibrating membrane are preferably applied.

[0131] Applying at least one layer of a conductive material preferably includes not only applying a single layer but also applying multiple layers, and in particular, a layer system. A layer system comprises at least two layers applied in a planar arrangement relative to each other. Applying a layer or a layer system preferably serves to define the vibrating membrane, which includes vertical sections that can be excited to horizontal vibrations.

[0132] Preferably, the deposition process may be selected from the group comprising physical vapor deposition (PVD), in particular thermal evaporation, laser beam evaporation, arc evaporation, molecular beam epitaxy, sputtering, chemical vapor deposition (CVD) and / or atomic layer deposition (ALD). In particular, the deposition process may, for example, include deposition, e.g., in the case of a polysilicon substrate.

[0133] An etching and / or structuring process may preferably be selected from the group comprising dry etching, wet chemical etching and / or plasma etching, in particular reactive ion etching, reactive ion deep etching (Bosch process).

[0134] In a preferred embodiment, the etching of a substrate, preferably from a front side, to create a structure is characterized in that the substrate has a crystal structure and a plurality of trenches are created by etching along a lattice vector of the crystal structure. Preferably, the trenches are defined as parallel slots from the front side of the substrate. After the application of the functional layers and corresponding back-side processing, a vibrating membrane is formed in the form of a bellows with a meandering cross-section (see, among others, [reference]). Fig. 2 and 8 ).

[0135] By preferentially etching along the orientation of a crystal substrate, advantageously smooth, quasi-crystalline pockets with a large depth of more than 200 µm, 300 µm, 400 µm, 500 µm or more can be obtained with high-precision orientation and negligible roughness.

[0136] It is also advantageous that the surface normal of the side faces of the pockets is also aligned with the crystal structure, preferably with an orthogonal lattice vector.

[0137] When applying a layer of actuator material, preferably a piezoelectric material, to such a structured substrate, the actuator material can also be oriented in a quasi-crystalline manner. In particular, piezoelectric materials such as AIN, AIScN, or PZT advantageously exhibit columnar growth on the oriented sidewalls of the pockets, thereby ensuring that the piezoelectric layer has a particularly precise c-axis orientation, which is perpendicular to the surface of the vertical sections of the resulting membrane.

[0138] The generation of horizontal vibrations through the transverse piezoelectric effect can therefore be particularly effective and precise, resulting in improved sound quality in the case of a MEMS loudspeaker or detection capability in the case of a MEMS microphone.

[0139] In a preferred embodiment, the etching of a substrate, preferably from a front side, to form a structuring, preferably a meandering structure, is characterized in that the substrate has a crystal structure and a plurality of pockets (trenches) along a lattice vector are at least partially carried out by wet chemical etching, preferably crystal orientation-dependent, anisotropic etching.

[0140] Preferably, an etchant is used which exhibits a significantly different etch rate with respect to the crystal orientation of the substrate in two orthogonal crystal orientations. For example, an etch rate for the selected substrate can be 50, 10, 150, 200 or more higher in a first crystal orientation than in a second orthogonal crystal orientation.

[0141] Preferably, the substrate is oriented such that the first crystal orientation, for which an increased etch rate is present, is aligned with the surface normal of the substrate surface. Areas on the substrate surface that are not to be etched can be defined using an etching mask. Preferably, the etching mask can define a frame in which slots or strips remain free for the formation of the pockets. Areas remaining between the parallel pockets to be formed can serve as substrate for the horizontal sections of the membrane.

[0142] The anisotropic wet chemical etching process then preferably results in etching perpendicular to the substrate surface to form deep vertical pockets. Etching in an orthogonal (horizontal) direction is therefore reduced. The greater the anisotropy factor of the crystal orientation-dependent etching, the less undercutting will occur.

[0143] Particularly good results can be achieved, for example, with potassium hydroxide (KOH) as an etchant for a silicon crystal substrate. Potassium hydroxide, for instance, exhibits a clear preference for etching along a [missing information]. <110> Orientation of a silicon crystal versus a <111> Orientation. As shown in Sato et al. 1988, the etch rate for KOH on a silicon monocrystal can be determined in a <110> The velocity in the direction is 1.455 µm / min, a factor of 291 higher than in an orthogonal direction. <111> Orientation (etch rate 0.005 µm / min).

[0144] Fig. 9 illustrates how, by appropriately aligning a silicon crystal, almost perfectly smooth and deep pockets can be produced in a robust manner, the side surfaces of which are crystal-oriented to ensure c-axis oriented growth of piezoelectric materials.

[0145] The person skilled in the art understands that alternative crystal orientation-dependent etchants, such as tetramethylammonium hydroxide (TMAH), can be used equally well (see, among others, Seidel et al. 1990).

[0146] The process is not only advantageous for scaling up to mass production. Furthermore, the resulting meandering, vibrating membranes are also characterized by a particularly precise alignment of the vertical sections, leading to improved vibration behavior and thus sound generation or detection.

[0147] Should further structuring of the vibrating membrane be desired, this can be achieved, for example, through further etching processes. Similarly, additional material can be deposited or doping can be carried out using conventional methods.

[0148] For contacting the layers, suitable material such as copper, gold, and / or platinum can be deposited using standard processes. Physical vapor deposition (PVD), chemical vapor deposition (CVD), or electrochemical deposition are preferred methods for this.

[0149] These process steps enable the production of a finely structured, vibrating membrane with a desired definition of vertical and horizontal sections, preferably suspended between two sides of a stable support and exhibiting dimensions in the micrometer range. The manufacturing steps are standard semiconductor processing procedures, thus proving their worth and making them suitable for mass production.

[0150] In another aspect, the invention also relates to a MEMS converter, which can be manufactured using the manufacturing process described above.

[0151] A person skilled in the art will recognize that specific features of the manufacturing steps, such as crystal orientation-dependent etching to form deep pockets with a quasi-crystalline smooth surface, are directly transferred to structural features of the MEMS transformation. In the case of a quasi-crystalline smooth surface on the side faces of the pockets, a vibrating membrane with a plurality of meandering vertical sections can be formed with particular precision, as explained above. A c-axis orientation of an actuator material, preferably a piezoelectric material, can also result directly from the application of the preferred manufacturing steps.

[0152] In another aspect, the invention relates to a manufacturing process for a MEMS transducer as described above, comprising the following steps: Providing several individual piezoceramic elements, comprising a sacrificial layer, a layer of a conductive material, and a layer of a piezoelectric material; defining holes for through-hole plating in the piezoceramic elements and metal filling; stacking the piezoceramic elements and optionally cutting (dicing) to obtain a stack of piezoceramic elements connected by metal bridges; removing the sacrificial layer and placing the stack of piezoceramic elements into a substrate, with each piezoceramic element being contacted with an electrode. such that a vibrating membrane, preferably in the form of a lamellar structure, is held by a support formed by the substrate, wherein the vibrating membrane comprises at least two or more vertical sections, which are formed parallel to the vertical direction, for generating or receiving pressure waves of the fluid in a vertical direction, and such that by actuating the at least one electrode the two or more vertical sections can be excited to horizontal vibrations, or such that when the two or more vertical sections are excited to horizontal vibrations an electrical signal can be generated at the at least one electrode.

[0153] The average person skilled in the art will recognize that the technical features, definitions, and advantages of preferred embodiments of the described MEMS transducer, preferably a MEMS loudspeaker or MEMS microphone, also apply to the described manufacturing process, and vice versa. Preferably, the described manufacturing process serves to provide a MEMS transducer with a vibrating diaphragm having a lamellar structure, wherein the lamellae are mechanical bimorphs and are connected by metal bridges. Examples of preferred manufacturing steps are given in the Fig. 10 AF and Fig. 11 illustrated.

[0154] In the alternative manufacturing process, several individual piezoceramic elements can be advantageously used to obtain a vibrating membrane with lamellae as vertical sections connected by metal bridges by defining holes, metal filling, and stacking and dicing.

[0155] Piezoceramics are preferably defined as ceramic materials that exhibit charge separation under the influence of deformation by an external force or undergo a change in shape when an electrical voltage is applied. The piezoceramic elements preferably comprise a piezoelectric layer, a layer of a mechanical support material as described above, and a sacrificial layer.

[0156] The sacrificial layer serves to process and provide the metal bridges and will not itself be part of the vibrating membrane.

[0157] The sacrificial layer can preferably be a photoresist or photoresist. These materials change their solubility when irradiated with light, especially UV light. In particular, it can be a so-called positive resist, whose solubility increases under UV irradiation. This allows the sacrificial layer to be selectively removed after metal filling to provide the metal bridges.

[0158] In another aspect, the invention relates to a manufacturing process for a MEMS converter comprising the following steps: Providing several individual piezoceramic elements, comprising a layer of a mechanical support material which is electrically conductive and a layer of a piezoelectric material; providing an upper and lower frame with recesses for the several individual piezoceramic elements; fixing the piezoceramic elements in the recesses of the upper and lower frame, preferably by means of an adhesive; applying at least one continuous electrically conductive layer for contacting the piezoceramic elements by means of at least one electrode such that a vibrating membrane, preferably in the form of a lamellar structure, is held by a support formed by the upper and lower frames, and wherein the vibrating membrane comprises at least two or more vertical sections, which are formed parallel to the vertical direction, for generating or receiving pressure waves of the fluid in a vertical direction, such that by actuating the at least one electrode the two or more vertical sections can be excited to horizontal vibrations, or such that when the two or more vertical sections are excited to horizontal vibrations an electrical signal can be generated at the at least one electrode.

[0159] The preferred embodiment is described in the Fig. 12Illustrated. Advantageously, in this embodiment, structured contacting is omitted. Instead, contact is achieved via a continuous conductive surface from a front and / or a rear side of the MEMS transducer.

[0160] In a preferred embodiment, the upper and lower frames are made of an electrically non-conductive material, for example, a polymer. A 3D printing process can preferably be used to form the frames.

[0161] The individual lamellae or piezoceramic elements are preferably contacted from the front ( front electrode) or from behind ( backside The electrode) has a continuous layer of a conductive material, preferably metal, applied to it. This application can be done, for example, by sputtering.

[0162] The average person skilled in the art will recognize that the technical features, definitions, and advantages of preferred embodiments of the described MEMS transducer, preferably a MEMS loudspeaker or MEMS microphone, also apply to the described manufacturing process, and vice versa. Preferably, the described manufacturing process serves to provide a MEMS transducer with a vibrating diaphragm having a lamellar structure, wherein the lamellae are mechanical bimorphs and are connected by a continuous layer of a conductive material, preferably metal. Detailed description

[0163] The invention will be explained below with reference to further figures and examples. The examples and figures serve to illustrate preferred embodiments of the invention without limiting them. Brief description of the images

[0164] Fig. 1Schematic representation of a cross-section of a preferred embodiment of a MEMS loudspeaker according to the invention A: at rest and B: during actuation. Fig. 2 Schematic representation of a preferred manufacturing process for a MEMS loudspeaker with a vibrating membrane which has a meandering shape in cross-section. Fig. 3, 4 Schematic representation of preferred embodiments of a MEMS loudspeaker with a vibrating diaphragm in meander shape, the horizontal sections of which are supported by retaining structures. Fig. 5 Schematic representation of an embodiment of a MEMS loudspeaker not covered by the scope of protection of the claims, with two actuator layers separated by a middle layer of a conductive material. Fig. 6 Schematic representation of preferred control methods for operating the MEMS loudspeakers Fig. 7Schematic representation of a preferred integration of a MEMS loudspeaker in the front of a housing with a rear resonance volume. Fig. 8 Schematic representation of a preferred manufacturing process for a MEMS loudspeaker with a vibrating membrane having a meandering cross-section, wherein only the vertical sections have a layer of actuator material. Fig. 9 Schematic representation of a preferred structuring of a substrate in crystalline form for the formation of deep trenches (pockets) using a crystal orientation-dependent etching process. Fig. 10 Schematic representation of a preferred manufacturing process for a MEMS loudspeaker with a vibrating membrane based on individual piezoceramic elements. Fig. 11 Schematic representation of a preferred electrical contacting of a MEMS loudspeaker with a vibrating membrane based on individual piezoceramics. Fig. 12 Schematic representation of a preferred manufacturing process for a MEMS loudspeaker with a vibrating membrane based on individual piezoceramic elements. Detailed description of the illustrations

[0165] Figure 1 Figure 1 illustrates a preferred embodiment of a MEMS loudspeaker according to the invention. Fig 1 A indicates a resting state, while Fig. 1B Two phases during the activation of the MEMS speaker are illustrated.

[0166] The MEMS loudspeaker includes a vibrating diaphragm. 1 for generating sound waves in a vertical emission direction, wherein the vibrating membrane 1 from a carrier 4 is held in a horizontal position. The vibrating membrane 1 It exhibits a meandering structure in cross-section with horizontal 3 and vertical sections 2.The vertical sections are parallel to the emission direction and have at least one actuator layer, for example, a layer of a piezoelectric material. A contact point for the vibrating membrane. 1 The actuator position is determined by means of electrodes at the end. Furthermore, the purpose can, for example, be on the carrier. 4 an electrode pad (not shown) is located.

[0167] The vertical sections are mechanical bimorphs that can be excited to horizontal vibrations by suitable control signals. For this purpose, the vertical sections comprise... 2A first layer of an actuator material and a second layer of a mechanical support material. By controlling the actuator layer, a stress gradient and thus a warping or vibration can be generated. Not covered by the scope of the claims is the fact that the vertical sections 2 comprise two actuator layers which are controlled in opposite directions in order to cause a warping of the vertical sections by means of a corresponding relative change in shape. 2 to effect.

[0168] Figure 1B This illustrates two phases during an actuation. The majority of vertical sections can be advantageously used. 2 the vibrating membrane 1With small horizontal movements (curvature) of just a few micrometers, an increased total volume is moved in the vertical emission direction and thus used to generate sound. The actuation allows for particularly efficient implementation, as almost the entire air volume between the vertical sections can be moved upwards or downwards along the emission direction during a single phase.

[0169] Figure 2 schematically shows a preferred manufacturing process for providing a MEMS loudspeaker with a vibrating membrane. 1, which has a meandering cross-section. A vibrating membrane with a meandering cross-section can also preferably be referred to as a folded membrane or bellows.

[0170] Fig. 2A shows an etching of the substrate. 8from a top or front surface to create a structure. In this process step, parallel deep trenches (pockets) are cut into the substrate. 8 etched. The molded structure represents a bellows or, in cross-section, a meander.

[0171] Next, a layer of etch stop is applied. 9 ( Fig. 2B ) applied, which could be, for example, TEOS or PECVD. On the etch stop 9 A layer of mechanical support material is used. 10 ( Fig. 2C ) and a layer of actuator material 11 applied to the mechanical support material 10 It could, for example, be doped polysilicon, while for the actuator material 10For example, a piezoelectric material can be used. Layer thicknesses of 1 µm, for instance, are preferred. Preferably, the piezoelectric material can have a C-axis orientation perpendicular to the surface, thus utilizing a transverse piezoelectric effect. Other orientations, such as the exploitation of a longitudinal effect, may also be preferred.

[0172] Fig. 2E shows the preferred application of a full-surface top electrode as a single layer of a conductive material. 12. End-side contact can be achieved, for example, by means of an electrode pad. 13 take place ( Fig. 2 F) .

[0173] Fig. 2F and 2G Illustrate further etching of substrate 8 from the back or underside, and the removal of the etching stop.

[0174] Manufacturing steps 2A-G thus produce a vibrating membrane. 1obtained, which exhibits a meandering structure in cross-section. Advantageously allows for a continuous actuator position. 11 and the provision of end-end contacts 13 efficient updating of the vertical sections 2 to horizontal vibrations (see Fig. 1 ). As in Fig. 2G It is evident that control is preferably achieved using two electrodes, thus determining the actuator position. 12 preferably from both a front side (top electrode, conductive layer) 12 ) as well as from a rear side (bottom electrode, via conductive mechanical support material 10) (see Fig. 6A ).

[0175] To stabilize the area between the side walls of the support 4 suspended membrane 1 can support structures 14 be planned. As in the Figs. 3 and 4 As shown, these preferably horizontal sections 3 the vibrating membrane 1Support. The horizontal sections are advantageous. 3 mechanically neutral (cf. Fig 1B ), so that no unwanted tensions occur between the membrane during actuation. 1 and support structure 14 or carrier 4 be induced.

[0176] Fig. 5 illustrates an embodiment of a MEMS loudspeaker not covered by the scope of protection of the claims, wherein the vibrating membrane 1 comprises two actuator layers, which are connected by a middle layer made of a conductive material 12, preferably metal, to be separated. The middle layer is equipped with a first end-side electrode pad. 13 connected, while in the illustrated embodiment the upper actuator position 11 via another layer of a conductive material 12 with a second end-side electrode pad 13 contacted is available.

[0177] Fig. 6illustrates preferred control methods for operating the described MEMS loudspeakers.

[0178] In Fig. 6A is a preferred control method for a MEMS loudspeaker with one actuator layer 11 and a passive mechanical support position 10 shown. Preferably, the control is achieved using two end-mounted electrode pads. 13, so that the horizontal vibrations can be generated by a change in the shape of the actuator material relative to the mechanical support material. The actuator position 11 is preferably from both a front side (top electrode) 13, conductive layer 10 ) as well as from a rear side (bottom electrode) 13, conductive mechanical support material 10 ) contacted. An alternating voltage as an audio input signal can, for example, be applied to the front electrode pad. 13 (left) applied, while the rear electrode pad 13 (right) is present.

[0179] In Fig. 6B is a preferred control method for a MEMS loudspeaker with two actuator layers 11 shown, which is achieved by a middle layer made of a conductive material 12, preferably metal, to be separated.

[0180] An upper actuator layer 11 is preferably from a front side (top electrode) 13 and upper conductive layer 12 ) as well as the middle conductive layer 12 controlled. A lower actuator position 11 is preferably from a back side (bottom electrode) 13 and lower conductive layer 12 ) as well as the middle conductive layer 12 is controlled. In the illustrated embodiment, an alternating voltage can be applied as an audio input signal, for example, to the pads for the top and bottom electrodes. 13 (left) are applied, while the middle position 12 is applied via another electrode pad. 13(right) is present.

[0181] Fig. 7 shows an exemplary preferred integration of a MEMS loudspeaker according to the invention in a housing. 15. The preferred location is that of the carrier 4 held vibrating membrane 1 in a front side or front of a housing ( sound port ) arranged. The housing also encloses a rear resonance volume ( back volume 16 A ventilation opening 17 It can be used to prevent acoustic short circuits or to support the sound image.

[0182] Fig. 8 illustrates an alternative manufacturing process for providing a MEMS loudspeaker with a vibrating membrane according to the invention. 1. The in Figures 8A-D The process steps shown are analogous to Fig. 2 .

[0183] Fig. 8A shows an etching of the substrate. 8from a top or front surface to create a structure, preferably a meandering structure. In this process step, parallel deep trenches (pockets) are cut into the substrate. 8 etched. The molded structure represents a bellows or, in cross-section, a meander.

[0184] Next, a layer of etch stop is applied. 9 ( Fig. 2B ) applied, which could be, for example, TEOS or PECVD. On the etch stop 9 A layer of mechanical support material is used. 10 ( Fig. 2C ) and an actuator material 11 applied to the mechanical support material 10 It could, for example, be doped polysilicon, while for the actuator material 12 A piezoelectric material is preferably used.

[0185] In contrast to the one in Fig. 2 In the embodiment shown, the actuator position 11not contacted as a continuous layer with an upper conductive layer. Instead, a spacer etching takes place ( Fig. 8F ) the actuator position 11 in the horizontal sections of the membrane, so that only the vertical sections of the membrane contain a layer of an actuator material. 11 exhibit.

[0186] Subsequently, a continuous dielectric layer 18 is preferably applied to prevent a short circuit between the upper and lower electrodes to be applied later ( Fig. 8G ). A continuous conductive layer as the top electrode 12 allows for front-side contact ( Fig. 8H ).

[0187] Fig. 8 I and 8 J Illustrate further etching of the substrate 8 from the back or underside and optionally the application of a continuous conductive layer 12 as a backside electrode.

[0188] Fig. 9 illustrates a preferred provision of a structured substrate 8.Analogous to the one in Fig. 8a In the process step shown, parallel deep trenches (pockets) are created in the substrate. 8 etched. The molded structure represents a bellows or, in cross-section, a meander, onto which a vibrating membrane in meander shape can be applied.

[0189] The preferred provision of the structured substrate 8 in the Fig. 9 is achieved by utilizing a crystal structure of the substrate 8 characterized, wherein the pockets are formed along a lattice vector of the crystal structure.

[0190] This allows for the creation of exceptionally smooth, quasi-crystalline pockets with great depths of more than 200 µm, 400 µm, or more, with highly precise orientation. A further advantage is that the surface normal of the pocket faces is aligned with a lattice vector that is orthogonal to the lattice vector in the direction of the etching process.

[0191] For example, if silicon is used as a substrate, the silicon substrate can 8 as in the Fig. 9 shown, preferably with a surface orientation of the Miller indices <110> The lattice vector of the crystal structure is therefore preferably aligned. <110> perpendicular to the surface of the still unstructured substrate. Using an etching mask 24, For example, with a SiO2 hard mask, horizontal areas or stripes can be defined on the substrate surface that should not be etched.

[0192] By anisotropic etching with a preferred direction along the <110> Orientation of the silicon crystal, versus a <111> Orientation ensures smooth and precisely oriented pockets. Wet chemical processes, suitable for batch mass production, can be advantageously employed for this purpose. For example, potassium hydroxide exhibits a clear preference for etching along the <110> versus a <111> Crystal orientation. As shown in Sato et al. 1988, the etch rate for KOH on a silicon monocrystal in <110> 1,455 µm / min, while the etching rate in the <111> The orientation rate is only 0.005 µm / min. Due to the anisotropic etching rates, deep pockets with minimal undercutting can be achieved using the wet chemical process.

[0193] For example, to form pockets 400 µm deep, KOH can be applied to a <110> The process is carried out on an oriented silicon substrate for 275 minutes. Due to the etch rate being reduced by a factor of 291 in the orthogonal <111> orientation, only an undercut of 1.37 µm will occur during this period. Even a variation in the local intensity of the undercut process results in orientation fluctuations of well under 1° with respect to the large pocket depth of 400 µm. Instead, the process can produce almost perfectly perpendicular deep pockets with high accuracy, characterized by a smooth, quasi-crisalline orientation.

[0194] Another advantage is that the resulting side walls of the pockets, onto which the vertical sections of the membrane are formed, are oriented in a crystal orientation (here: <111> ) before. This circumstance favors columnar growth of piezoelectric materials, such as AIN or PZT: This allows for a particularly precise assurance that the piezoelectric material has a c-axis orientation perpendicular to the surface of the vertical sections, so that a transverse piezoelectric effect can be used to generate the horizontal vibrations.

[0195] Fig. 10 illustrates a preferred manufacturing method for providing a MEMS loudspeaker with a vibrating membrane based on individual piezoceramics.

[0196] First, several individual piezoceramic elements are used. 19, comprising a layer of mechanical support material 10(e.g. doped polysilicon) and a layer of a piezoelectric material 11 as well as a victim situation 20 provided (see above). Fig. 10A and 10B Regarding the victim situation 20 This could, for example, be a photoresist (photolac). Preferably, the layer can consist of a mechanical support material. 10 It must be electrically conductive to ensure contact. It is also possible to use a piezoelectric material on one layer. 11 one or two layers of a conductive material 12 to apply which serve for the electrical contacting of the piezoelectric material.

[0197] This is followed by the definition of holes for through-hole plating and metal filling. 21 (cf.) Fig. 10 C) , The piezoceramic elements 19 are stacked ( Fig. 10 D) and cut (Dicing) 22 , Fig. 10E ), so that two or more stacks of piezoceramic elements19 to be obtained, which is achieved through metal bridges 21 are connected (cf. Fig. 10E ).

[0198] After removal of the victim's body 20 ( Fig. 10F ) the stacked piezoceramic elements are inserted. 19 into a carrier 4, wherein preferably the first and last piezoceramic element is contacted with an electrode each 13 is done ( Fig. 10E ).

[0199] In this way, a vibrating membrane 1 is also placed between a support. 4 obtained, which for the generation of sound waves in a vertical emission direction have at least two or more vertical sections 2 includes elements that are parallel to the direction of emission and can be excited to horizontal vibrations.

[0200] The actuator principle is preferably based here as well on a relative change in the shape of the actuator position. 11compared to the mechanical support layer 10. A continuous actuator layer is not necessary for this. Contacting all vertical sections is sufficient. 2 End-side control is achieved through the metal bridges 23 in combination with conductive layers 12 is ensured.

[0201] Fig. 11 illustrates a preferred electrical contacting of the MEMS loudspeaker with a vibrating membrane based on individual piezoceramics.

[0202] Fig. 11A is a top view and Fig. 11B A side view of a MEMS loudspeaker. Parallel control of individual lamellae or vertical sections is achieved via the electrode pads 13, with each section using U-shaped spacers ( spacer ) are present on each side of the lamellae and create a mechanical and electrical connection to the next lamella.

[0203] Fig. 12illustrates an alternative manufacturing process for providing a MEMS loudspeaker with a vibrating membrane based on individual piezoceramics.

[0204] Advantageously, in contrast to the embodiment according to the Fig. 10 or 11 in the illustrated embodiment, structured contacting can be omitted. Instead, as explained below, contacting can be achieved by means of a continuous conductive surface from the front ( front electrode) or rear ( backside electrode).

[0205] Analogous to the manufacturing process according to the Fig. 10 Several individual piezoceramic elements are used 19, comprising a layer of mechanical support material 10 (e.g. doped polysilicon) and a layer of a piezoelectric material 11 Provided. Preferably, the layer consists of a mechanical support material. 10 electrically conductive.

[0206] Furthermore, an upper frame is added in each case. 25 and lower frame 26 provided, which recesses or grooves 27 to accommodate the piezoceramic elements 19 The upper and lower frames are preferably made of an electrically non-conductive material, for example, a polymer. A 3D printing process can preferably be used to form the frames.

[0207] For fixing the piezoceramic elements 19 It may be preferable to use an adhesive, which is preferably applied first to recesses. 27 is introduced (cf. Fig. 12A After attaching the piezoceramic elements 19 in the respective depths 27 of the lower frame 26, Can the adhesive be applied to the piezoceramic elements? 19 be brought so that the upper frame holds the piezoceramic elements 19 fixed at the top (see above). Fig. 12B ).

[0208] For contacting the individual lamellae or piezoceramic elements 19 A continuous layer of a conductive material, preferably metal, is preferably applied (not visible) from the front (front electrode) or from the back (backside electrode). For example, by means of a sputtering process.

[0209] In this way, a vibrating membrane can also be created. 1 obtained, which for the generation of sound waves in a vertical emission direction have at least two or more vertical sections 2 This includes elements that are parallel to the emission direction and can be excited to horizontal vibrations. These serve as supports for the vertical sections. 2 can the composite frame 25, 26 function. REFERENCE MARK LIST

[0210] 1 Vibrating membrane 2 Vertical sections of the vibrating membrane 3 Horizontal sections of the vibrating membrane 4 Support 5 Air volumes between the vertical sections 8 Substrate 9 Etching stop 10 Layer of a mechanical support material, preferably doped polysilicon 11 Layer of an actuator material (actuator layer), preferably of a piezoelectric material 12 Layer of a conductive material, preferably of metal 13 Contacting of the electrode, preferably electrode pad 14 Retaining structures 15 Housing 16 Rear resonance volume 17 Ventilation opening 18 Layer of a dielectric material 19 Piezoceramic element(s) 20 Sacrificial layer 21 Defined holes for through-hole plating with metal filling 22 Dicing 23 Metal bridges 24 Etching mask 25 Upper frame 26 Lower frame LITERATUR

[0211] F. Stoppel, C. Eisermann, S. Gu-Stoppel, D. Kaden, T. Giese and B. Wagner, NOVEL MEMBRANE-LESS TWO-WAY MEMS LOUDSPEAKER BASED ON PIEZOELECTRIC DUAL-CONCENTRIC ACTUATORS, Transducers 2017, Kaohsiung, TAIWAN, June 18-22, 2017. Iman Shahosseini, Elie LEFEUVRE, Johan Moulin, Marion Woytasik, Emile Martincic, et al. Electromagnetic MEMS Microspeaker for Portable Electronic Devices. Microsystem Technologies, Springer Verlag (Germany), 2013, pp.10. <hal-01103612> . Bert Kaiser, Sergiu Langa, Lutz Ehrig, Michael Stolz, Hermann Schenk, Holger Conrad, Harald Schenk, Klaus Schimmanz und David Schuffenhauer, Concept and proof for an all-silicon MEMS microspeaker utilizing air chambers Microsystems & Nanoengineering volume 5, Article number: 43 (2019). Kazuo Sato, Mitsuhiro Shikida, Yoshihiro Matsushima, Takashi Yamashiro, Kazuo Asaumi, Yasuroh Iriye, and Masaharu Yamamoto, Characterization of orientation-dependent etching properties of single-crystal silicon: effects of KOH concentration, Sensors and Actuators A 64 (1988) 87-93). Seidel, H., Csepregi, L., Heuberger, A. und Baumgartel, H. (1990). Anisotropic Etching of Crystalline Silicon in Alkaline Solutions. Journal of The Electrochemical Society 137. 10.1149 / 1.2086277< / hal-01103612>

Claims

1. MEMS transducer for interacting with a volume flow of a fluid comprising - a carrier (4), - a vibratable membrane (1) for generating or receiving pressure waves of the fluid in a vertical direction, the vibratable membrane (1) being supported by the carrier (4), and wherein the vibratable membrane (1) exhibits two or more vertical sections (2) formed substantially parallel to the vertical direction and comprising at least one layer of an actuator material (11), wherein at least one end of the vibratable membrane (1) is connected to at least one electrode (13), such that the two or more vertical sections (2) can be induced to vibrate horizontally by driving the at least one electrode (13) or such that an electrical signal can be generated at the at least one electrode (13) when the two or more vertical sections (2) are induced to vibrate horizontally, wherein the two or more vertical sections (2) comprise at least two layers, wherein one layer (11) comprises an actuator material and one layer (10) comprises a mechanical support material, wherein at least the layer (11) comprising the actuator material is in contact with an electrode (13) such that horizontal vibrations can be generated by a change in the shape of the actuator material relative to the mechanical support material or such that horizontal vibrations lead to a change in the shape of the actuator material relative to the mechanical support material and generate an electrical signal.

2. MEMS transducer according to the preceding claim characterized in that the MEMS transducer is a MEMS loudspeaker, wherein air volumes (5) are present preferably between the vertical sections (2), which, as a result of the horizontal vibrations, are moved along a vertical direction of emission to generate sound waves, or the MEMS transducer is a MEMS microphone, wherein air volumes (5) are present preferably between the vertical sections (2), which are moved along a vertical direction of detection when sound waves are received.

3. MEMS transducer according to one of the preceding claims characterized in that the carrier (4) comprises two side regions between which the vibratable membrane (1) is arranged in a horizontal direction and / or the carrier (4) is formed of a substrate (8) selected from the group consisting of monocrystalline silicon, polysilicon, silicon dioxide, silicon carbide, silicon germanium, silicon nitride, nitride, germanium, carbon, gallium arsenide, gallium nitride, indium phosphide and glass.

4. MEMS transducer according to one of the preceding claims characterized in that the vibratable membrane (1) is formed by a lamellar structure or meander structure.

5. MEMS transducer according to one of the preceding claims characterized in that the vibratable membrane (1) is formed by a meander structure with alternating vertical (2) and horizontal (3) sections, at least two of the horizontal sections (3) having attached to them retaining structures (14) which are connected directly or indirectly to the carrier (4).

6. MEMS transducer according to one of the preceding claims characterized in that the actuator material comprises a piezoelectric material, a polymer piezoelectrical material and / or electroactive polymers (EAP), wherein the piezoelectric material is preferably selected from a group comprising lead zirconate titanate (PZT), aluminum nitride (AIN), aluminum scandium nitride (AlScN) and zinc oxide (ZnO).

7. MEMS transducer according to one of the preceding claims characterized in that the vibratable membrane (1) comprises three layers, an upper layer (12) being formed by a conductive material, a middle layer (11) being formed by an actuator material, and a lower layer (10) being formed by a conductive material, wherein the conductive material of the upper and / or lower layer is preferably a mechanical support material.

8. MEMS transducer according to one of the preceding claims characterized in that the vibratable membrane (1) is coated with a layer of a non-stick material.

9. MEMS transducer according to one of the preceding claims characterized in that the vibratable membrane (1) supported by the carrier (4) is arranged in a front side of a housing (15) which encloses a rear resonant volume (16), wherein a ventilation opening (17) is preferably present in the housing (15) for avoiding acoustic short circuits and / or for supporting the sound.

10. Manufacturing method for a MEMS transducer according to one of the preceding claims comprising the following steps: - etching of a substrate (8), preferably from a front side, to form a structuring, preferably a meander structure - optional application of an etch stop - applying at least two layers, wherein at least a first layer (11) comprises an actuator material and a second layer (10) comprises a mechanical support material - connecting the first and / or second layer to an electrode (13) - etching, preferably from the rear side, and optional removal of the etch stop, such that a vibratable membrane (1), preferably in the form of a meander structure, is supported by a carrier (4) formed by the substrate (8), the vibratable membrane (1) comprising at least two or more vertical sections (2) for generating or receiving pressure waves of the fluid in a vertical direction, which sections are formed parallel to the vertical direction and such that the two or more vertical sections (2) can be induced to vibrate horizontally by driving the at least one electrode (13), or such that when the two or more vertical sections (2) are induced to vibrate horizontally, an electrical signal can be generated at the at least one electrode (13).

11. MEMS transducer according to one of the preceding claims 1-9 characterized in that the vertical sections (2) are connected via horizontal metal bridges (23) and wherein the vertical sections (2) are respectively connected to an electrode (13).

12. Manufacturing method for a MEMS transducer according to the preceding claim comprising the following steps: - obtaining a plurality of individual piezoceramic elements (19) comprising a sacrificial layer (20), a layer (12) of conductive material, and a layer (11) of piezoelectric material, - defining holes (21) for interlayer connection in the piezoceramic elements and metal filling, - stacking the piezoceramic elements (19) and optional dicing (22) to obtain a stack of piezoceramic elements (19) connected by metal bridges (23) - removing the sacrificial layer (20) and insertion of the stack of piezoceramic elements (19) into a carrier (4), wherein the piezoceramic elements (19) are respectively connected to an electrode (13), such that a vibratable membrane (1), preferably in the form of a lamellar structure, is supported by the carrier (4), the vibratable membrane (1) comprising at least two or more vertical sections (2) for generating or receiving pressure waves of the fluid in a vertical direction, which sections are formed parallel to the vertical direction and such that the two or more vertical sections (2) can be induced to vibrate horizontally by driving the at least one electrode (13), or such that when the two or more vertical sections (2) are induced to vibrate horizontally, an electrical signal can be generated at the at least one electrode (13).

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