Corrugations or weakened regions on armature structures of vertical MEMS converter membranes

Abstract

One aspect of the invention relates to a MEMS converter which comprises a vibratable membrane for generating or receiving pressure waves in a vertical emission direction. The vibratable membrane is held by a support and has vertical sections which are formed substantially parallel to the emission direction or the receiving direction and which comprise at least one layer made of an actuator material. The vibratable membrane is preferably in contact with an electrode at the end face such that by controlling the electrode, horizontal vibrations can be excited in the vertical sections or such that upon exciting horizontal vibrations in the vertical sections, an electric signal can be generated on the electrode. The vertical sections and / or the horizontal sections have one or more corrugations and / or weakened regions. Another aspect of the invention relates to a method for producing the MEMS converter according to the invention.

Description

[0001] Corrugations or weakened areas on anchor structures of vertical MEMS transducer membranes

[0002] DESCRIPTION

[0003] In a first aspect, the invention relates to a MEMS transducer comprising an oscillating membrane for generating or receiving pressure waves in a vertical emission direction, wherein the oscillating membrane is held by a support and the oscillating membrane has vertical sections which are formed substantially parallel to the emission direction or reception direction and comprise at least one layer of an actuator material. The oscillating membrane is preferably contacted at its end with an electrode such that by controlling the electrode, the vertical sections can be excited to horizontal oscillations or such that upon excitation of the vertical sections to horizontal oscillations, an electrical signal can be generated at the electrode. The vertical sections and / or the horizontal sections have one or more corrugations and / or weakened regions.

[0004] In a further aspect, the invention relates to a method for producing the MEMS converter according to the invention.

[0005] Background and state of the art

[0006] Microsystems technology is now used in many applications to manufacture compact, mechanical-electronic devices. The resulting microsystems (microelectromechanical systems, or MEMS) are extremely compact (approximately in the micrometer range) while simultaneously offering excellent functionality and ever-decreasing manufacturing costs.

[0007] MEMS transducers, such as MEMS loudspeakers or MEMS microphones, are also known from the state of the art. Current MEMS loudspeakers are usually designed as planar membrane systems with vertical actuation of an oscillating membrane in the emission direction. Excitation is achieved, for example, by means of piezoelectric, electromagnetic, or electrostatic actuators.

[0008] Zou, Zhijian & Litian (1996) disclose a capacitive MEMS microphone comprising a thin, flexible diaphragm as the active electrode and a rigid backplate as the stationary electrode. To optimize the mechanical sensitivity of the diaphragm, corrugations are applied, which are connected by flat sections (bridges). The introduction of the corrugations is intended, in particular, to reduce intrinsic stress in the diaphragm. CN 112492487 also discloses a capacitive MEMS microphone. This is intended to prevent unwanted adhesion between the diaphragm and a backplate. For this purpose, a section of the diaphragm comprising protrusions is provided to prevent adhesion and thus ensure long-term functionality. 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 movable part suspended from a support via silicon drive springs to enable large out-of-plane displacements using an electromagnetic motor.

[0009] Stoppel et al. (2017) discloses a two-way loudspeaker based on concentric piezoelectric actuators. A special feature is that the vibration membrane is not closed, but rather comprises eight unimorph piezoelectric actuators, each consisting of a piezoelectric and a passive layer. The outer woofers consist of four trapezoidal actuators clamped on one side, while the inner tweeters are formed by four triangular actuators connected to a rigid frame by springs. The separation of the membrane is intended to enable an improved sound image at higher power levels.

[0010] A disadvantage of such planar MEMS loudspeakers is their limitations in terms of possible 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 displacement. To achieve sufficient sound power, either displacements of at least 100 pm for the vibrating membranes or large-area membranes in the square centimeter range are necessary. Both conditions are difficult to achieve using MEMS technology.

[0011] The prior art has therefore proposed designing MEMS loudspeakers that do not have a closed membrane for vibrations 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 small area, thus providing increased sound power.

[0012] A MEMS loudspeaker based on this principle is disclosed, for example, in US 2018 / 0179048 A1 or Kaiser et al. 2019.

[0013] The MEMS loudspeaker comprises a plurality of electrostatic bending actuators arranged as vertical fins between a top and bottom wafer. These can be excited to lateral vibrations by appropriate control. An inner fin forms an actuator electrode opposite two outer fins. An air gap exists between the three curved fins, except for a connecting node of still galvanically isolated electrodes. If a potential is applied inside to outside, this leads to a two-way attraction due to the curvature of the design in a preferred direction, which is predetermined by an armature. The bulges in the outer fins provide mobility. The restoring force is provided by a mechanical spring force. Pull-push operation is therefore not possible.

[0014] Another disadvantage is that gaps between the bending actuators and the lid / bottom wafers, which are necessary for their mobility, lead to ventilation between the two chambers. This limits the lower frequency limit. Furthermore, the lateral movement of the bending actuators and thus the sound power are restricted to avoid a pull-in effect and acoustic breakdown.

[0015] US 2017 / 0006381 A1 discloses a MEMS sound transducer comprising a multilayer piezoelectric membrane suspended between a carrier substrate. By providing an intermediate layer between two piezoelectric layers, the piezoelectric effect and thus the performance of the transducer as a microphone or loudspeaker are to be enhanced. The membrane is structured in such a way that several recesses are present where no piezoelectric layer is located. Furthermore, the membrane has indentations of varying depths so that the piezoelectric layers can be excited via a respective upper and lower electrode layer and / or electronic signals can be tapped.

[0016] The recesses are intended to enable a greater stroke in the z-direction and thus a higher sound pressure. The diaphragm is structured in such a way that, in a top view, a meandering pattern with active piezoelectric regions and passive piezoelectric regions is present. The active piezoelectric regions (25a-d) preferably have an anchor to the support at the outer end of the diaphragm and a free end toward the center of the diaphragm, thus enabling mobility or curvature of the diaphragm in an out-of-plane or z-direction.

[0017] 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, wherein the front and rear chambers are separated from each other by a folded membrane. In one embodiment, the folded membrane has a rectangular meandering structure with horizontal and vertical sections in cross-section. Piezo actuators are positioned on the respective horizontal sections to cause lateral movement of the vertical sections through synchronized expansion or compression of the horizontal sections. With the proposed principle, an increased volume flow and thus a higher sound power can be generated on a small chip surface.

[0018] A disadvantage, however, is the increased effort required for the synchronized drive of the piezo actuators. 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 one-sidedly actuated horizontal sections.

[0019] WO 2021 / 144400 A1 discloses a MEMS transducer that can be used both as a MEMS loudspeaker and as a MEMS microphone. The MEMS transducer described therein has an oscillating membrane constructed in such a way that it comprises two or more vertical sections that are formed substantially parallel to the vertical direction. Furthermore, the oscillating membrane comprises at least one layer of an actuator material and is contacted at at least one end by an electrode. This allows the vertical sections to be excited to horizontal oscillations by controlling the electrode. Conversely, an electrical signal can also be generated at the electrode when the vertical sections are excited to horizontal oscillations.

[0020] The MEMS transducer disclosed in WO 2021 / 144400 A1 offers significant improvements over the prior art. The design of the vibrating membrane, including vertical sections, advantageously results in higher sound output in the case of a MEMS loudspeaker, while the contacting simultaneously ensures simplified controllability. In the case of a MEMS microphone, higher performance and audio quality with a suitable sound image are also advantageously enabled. Furthermore, proven semiconductor processing techniques can be used to manufacture the MEMS transducer, enabling cost-efficient production.

[0021] Even though the MEMS converter disclosed in WO 2021 / 144400 A1 represents an advanced development of the state of the art, there is potential for optimization in terms of performance and sound behavior.

[0022] In light of the state of the art, there is therefore still a need to provide improved MEMS converters and methods for their manufacture.

[0023] Object of the invention

[0024] The object of the invention is to provide a MEMS converter and a method for manufacturing the MEMS converter that eliminate the disadvantages of the prior art. In particular, the object of the invention was to provide a MEMS converter with high performance and sound quality, which is simultaneously characterized by a simple, cost-effective, and compact design.

[0025] Summary of the invention

[0026] The object of the invention is achieved by the features of the independent claims. Preferred embodiments of the invention are described in the dependent claims.

[0027] In a first aspect, the invention preferably relates to a MEMS transducer for interacting with a volume flow of a fluid, comprising a carrier and an oscillating membrane for generating or receiving pressure waves of the fluid in a vertical direction, which membrane is attached to the carrier and contacted with at least one electrode, wherein the oscillating membrane has vertical sections and horizontal sections, wherein the vertical sections are formed substantially parallel to the vertical direction and the horizontal sections connect the vertical sections to one another, so that by controlling the at least one electrode, the vertical sections can be excited to horizontal oscillations or so that upon excitation of the vertical sections to horizontal oscillations, an electrical signal can be generated at the electrode, characterized in thatthat the vertical sections and / or the horizontal sections have one or more corrugations and / or weakened areas.,

[0028] In preferred embodiments, the MEMS transducer can be a MEMS loudspeaker or a MEMS microphone. The design of the MEMS transducer allows for a number of advantages for use as both a MEMS loudspeaker and a MEMS microphone.

[0029] In particular, a MEMS loudspeaker with high sound power and simplified control can be achieved. Unlike conventional planar MEMS loudspeakers, the vibrating membrane itself does not need to be driven over a large area of ​​several square centimeters or with a high excursion to generate sufficient sound pressure. Instead, the majority of the vertical sections of the vibrating membrane can move an increased total volume in the vertical emission direction with small horizontal or lateral movements of a few micrometers.

[0030] At the same time, simplified control can be achieved. While in the prior art, such as in US 2019 / 011 64 17 A1, a large number of piezoelectric actuators must be contacted at the horizontal sections, the MEMS loudspeaker described here can be operated using at least one electrode, preferably at the end. This reduces manufacturing costs, minimizes sources of error, and also inherently leads to synchronous control of the vertical sections to horizontal vibrations.

[0031] In this way, the air volumes present between the vertical sections can be moved extremely precisely by the horizontal vibrations along the vertical emission direction.

[0032] This also enables the provision of a particularly powerful MEMS microphone with high audio quality. The structure of the MEMS microphone is structurally similar to that of the MEMS loudspeaker, particularly with regard to the design of the vibrating membrane. However, instead of controlling the electrodes to generate horizontal vibrations and thus sound pressure waves, the MEMS microphone is designed to record sound pressure waves in the same vertical direction. Preferably, air volumes are therefore present between the vertical sections, which are moved along a vertical detection direction when sound waves are recorded. The sound pressure waves excite the vertical sections to horizontal vibrations, so that the actuator material generates a corresponding periodic electrical signal.

[0033] The MEMS transducer preferably comprises a substantially continuous actuator layer comprising an actuator material. In particular, the actuator layer runs along the vertical sections and the horizontal sections of the membrane. Therefore, it is preferred that the vertical and horizontal sections comprise an actuator material. A substantially continuous actuator layer preferably means that the actuator layer is only interrupted by corrugation and / or weakened regions, but otherwise extends over the entire surface of the oscillatable membrane. As explained in detail herein, the actuator layer preferably serves to excite the membrane to oscillate (in the case of a loudspeaker) or to detect oscillations of the membrane (in the case of a microphone), whereby the excitation or measurement principle differs significantly from capacitive MEMS transducers.For the vibration behavior of the membrane, the application of corrugations and / or weakened regions to the vertical and / or horizontal sections has proven to be extremely advantageous, both with regard to applications as MEMS loudspeakers and as MEMS microphones.

[0034] According to the invention, it was recognized that corrugations and / or weakened regions enable a higher degree of rotation of the vertical sections, thereby ensuring a particularly efficient deflection of the membrane during the generation or absorption of pressure waves of the fluid. In particular, the corrugations and / or weakened regions lead to the vertical sections experiencing a particularly defined curvature during the generation or absorption of pressure waves and potentially irregular kinks (, buckling 1 ) can be particularly effectively prevented.

[0035] When generating or recording pressure waves, the vertical sections can therefore be controlled or excited even more effectively to horizontal oscillations in order to optimize the performance of the MEMS converter.

[0036] In this regard, it is further advantageous that the corrugations and / or weakened areas allow higher amplitudes of the horizontal vibrations of the vertical sections.

[0037] In the case of a MEMS loudspeaker, for example, this results in a greater displacement of the fluid volume between the vertical sections, enabling an increase in the generated sound pressure level. This further improves the sound power, particularly the sound pressure level, compared to previous approaches. Accordingly, in the case of a MEMS microphone, more fluid volume can be captured between the vertical sections, increasing the sensitivity of the sound detector.

[0038] Another advantage is that it allows for a particularly uniform curvature of the vertical sections in both directions of horizontal vibration. This reduces harmonic distortion, particularly THD (total harmonic disorder). THD preferably indicates the ratio of the sum of the power of all harmonics to the power of the fundamental vibration of a vibrating membrane. Consequently, reducing THD reduces the sum of the harmonics and thus distortions of the measured signal or the generated signal. A particularly good sound image results both in the recording and in the generation of pressure waves of the fluid.

[0039] By introducing irregularities in the form of corrugations and / or weakened areas into the vibrating membrane, its vibration behavior is surprisingly not distorted but rather harmonized.

[0040] The advantageous effects can be attributed in part to the fact that the stiffness of the respective sections of the oscillating membrane can be adjusted using the corrugations and / or weakened areas. For example, the invention has recognized that overly rigid horizontal sections can adversely impede the mobility of the vertical sections and lead to irregularities in their deflection or curvature during horizontal oscillations. Through targeted positioning of corrugations and / or weakened areas, particularly in the horizontal sections, their stiffness is reduced and the deflectability or rotational freedom of the vertical sections is increased.

[0041] Thus, by designing the corrugations and / or the weakened areas, in particular with regard to geometry, width and / or depth, the stiffness and thus the deflectability can be advantageously adjusted and adapted depending on the application.

[0042] It was found that both corrugations and weakened regions result in the advantageous technical effects described above. Therefore, in addition to the design of the corrugations, the vibration behavior of the vibrating membrane of the MEMS transducer can also be optimized by preferred embodiments of the weakened regions, for example, by varying the layer thickness, number, or positioning.

[0043] Furthermore, the provision of corrugations and / or weakened areas is possible using known techniques, process steps, and / or methods in semiconductor and microsystem technology that have proven particularly effective in the state of the art. This advantageously enables the application of corrugations and / or weakened areas to the vertical and / or horizontal sections in a process-efficient manner.

[0044] A corrugation preferably denotes a deviation from the course of a partial section of the oscillatable membrane, wherein it is preferably a depression or elevation in an otherwise substantially planar course of the partial section. In a cross-sectional view of the oscillatable membrane, a corrugation preferably denotes a deviation from a continuous, preferably rectilinear course of a partial area (e.g. a horizontal and / or vertical partial area). For example, a corrugation can mean a groove or furrow or a web, ie in particular a depression or elevation in the vertical and / or horizontal sections. These corrugations can have a variety of designs with regard to geometry, depth, width and / or aspect ratio.

[0045] A weakened region preferably refers to a reduction in the thickness of a layer of the oscillating membrane. Weakened regions preferably refer to the thickness of the layers that provide the vertical and / or horizontal sections. For example, the horizontal and / or vertical sections can be formed in multiple layers, and one or more weakened regions can be created by varying the layer thickness of at least one layer. Preferably, the layer thickness of the at least one layer (e.g., an actuator layer, the layer of an electrically conductive layer, a top or bottom electrode, or a mechanical support layer) is reduced to less than 70%, preferably less than 60%, 50%, 40%, or less of an initial layer thickness. A weakened region can also refer to a reduction in the layer thickness of at least one layer to 30%, 20%, or 10% or less of an initial layer thickness.The terms "layer" and "ply" can be used synonymously in the context of the invention. A corrugation and / or a weakened area is preferably present in the vertical and / or horizontal sections, although preferably, multiple corrugations and / or weakened areas can also be present along a section.

[0046] It may also be preferred for a weakened region to correspond to a reduction in the layer thickness of at least one layer to 0% of an initial layer thickness. For example, it may be preferred for a weakened region to be characterized by the absence of at least one layer in a partial region of the membrane. Preferably, a weakened region is characterized by a reduction in the layer thickness of at least one layer (in some embodiments to 0%), wherein at least one other layer in the weakened region has no reduction in layer thickness compared to an initial layer thickness. In some embodiments, however, a weakened region can also be characterized by a reduction in the layer thickness of all layers of the membrane, up to and including the absence of all layers in a partial region. In the latter case, a weakened region is preferably formed by an opening in the membrane.

[0047] Furthermore, it may also be preferred for a weakened region to be characterized by an exchange of the at least one layer for another layer (i.e. a layer comprising a different material). For example, a weakened region can be formed by exchanging an actuator material in a partial region for a non-actuator material or insulation material, preferably an insulation layer or insulation layer. As shown in more detail below, a weakened region can therefore be created both by a weakening of the mechanical properties of a partial region (e.g. reduction in stiffness) and by a weakening of a functional property, e.g. the ability to be stimulated to change shape by applying a signal.

[0048] Preferably, weakened regions and corrugations can be present in combination with one another on the membrane. For example, it can be preferred that a weakened region is present along a partial section of the membrane to which a corrugation is also attached, wherein the partial section is, for example, a vertical and / or a horizontal section of the membrane. It can also be preferred that a weakened region is present on or within a corrugation. This means that it can be preferred that a weakened region is present within a corrugation, for example in the form of a reduction in the layer thickness of at least one layer compared to an initial layer thickness (in some cases to 0%). It can also be preferred that a corrugation is present within a weakened region. This means thatThe weakened area can, for example, extend over a partial section of the membrane, with a corrugation, as described above, additionally being introduced within the weakened partial section.

[0049] Both weakened areas and corrugations are preferably characterized by the fact that they represent a deviation or inhomogeneity with regard to the functional and / or mechanical properties of the subsections of the oscillating membrane, which, however, is deliberately introduced. The inventors have recognized that by deliberately introducing corrugations and / or weakened areas into horizontal and / or vertical sections, the deflectability of the vertical sections and thus the vibration behavior of the oscillating membrane can be significantly improved. A weakened area is therefore preferably characterized by a change in the functional and / or mechanical properties of a subsection or subregion of the membrane.

[0050] A functional property can preferably mean an adaptation of the actuation capability of the subsection, so that, in particular, a weaker actuation occurs in the weakened region than in subsections of the membrane that do not have a weakened region. For this purpose, it may be preferred that the layer thickness of the actuator layer be reduced or completely absent in the weakened region. Likewise, it may be preferred that a layer necessary for controlling the actuator layer, such as a layer of a conductive material, be partially absent or present only in a reduced form.

[0051] In the case of an actuator layer made of a piezoelectric material, weaker actuation can be ensured, for example, by reducing the occurrence of a piezoelectric effect in a partial section of the membrane. For example, it may be preferable to introduce a dielectric insulation layer in the partial section between a piezoelectric actuator layer or to omit a controlling top or bottom electrode in certain areas. During the excitation of the membrane to oscillate, the actuator layer will therefore experience no or only a reduced change in stress or shape in the weakened area. By deliberately introducing such irregularity in the actuation of the areas, the occurrence of buckling or other distortions can be surprisingly effectively prevented. In particular, the vertical sections can exhibit increased mobility and oscillate harmoniously—without distortion.

[0052] A weakened area can also be characterized by a change, in particular a reduction, in the mechanical properties of the membrane in the relevant section. Mechanical properties can, for example, mean stiffness, i.e. a property to mechanically resist a change in shape. Preferably, mechanical properties of a weakened area can, for example, be brought about by a reduction in the layer thickness of a mechanical support layer or by replacing a layer of mechanical support material with a material with lower stiffness (or a higher modulus of elasticity). The regional weakening of the mechanical properties, such as the stiffness of the membrane, advantageously also leads to an optimization of the deflection behavior of the membrane by increasing the mobility of the vertical sections and avoiding undesirable effects such as buckling.

[0053] The vertical and horizontal directions with respect to the MEMS transducer and the membrane, respectively, preferably refer to a preferred direction in which the oscillating membrane is oriented to generate or absorb pressure waves from the fluid. Preferably, the oscillating membrane is suspended horizontally between at least two side regions of a support, while the vertical direction (direction of interaction with the fluid) for generating or absorbing pressure waves is orthogonal to it.

[0054] In preferred embodiments, the MEMS transducer is a MEMS loudspeaker or a MEMS microphone. The term MEMS transducer therefore refers to both a MEMS microphone and a MEMS loudspeaker. In general, a MEMS transducer is a transducer for interacting with a volume flow of a fluid, which is based on MEMS technology and whose structures for interacting with the volume flow or for absorbing or generating pressure waves of the fluid have dimensions in the micrometer range (1 pm to 1000 pm). The fluid can be either a gaseous or a liquid fluid. The structures of the MEMS transducer, in particular the oscillating membrane, are designed to generate or absorb pressure waves of the fluid.

[0055] For example, as in the case of a MEMS loudspeaker or MEMS microphone, these can be sound pressure waves. However, the MEMS transducer can also be suitable as an actuator or sensor for other pressure waves. The MEMS transducer is therefore 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, e.g., acoustic signals).

[0056] In the case of a MEMS loudspeaker, the vertical (interaction) direction corresponds to the vertical sound emission direction of the MEMS loudspeaker. Vertical in this case refers primarily to the direction of sound emission, while horizontal refers to a direction orthogonal to it.

[0057] In the case of a MEMS microphone, the vertical (interaction) direction corresponds to the vertical sound detection direction of the MEMS microphone. Vertical in this case preferably refers to the direction of sound detection or recording, while horizontal refers to a direction orthogonal to this.

[0058] The vertical sections of the oscillatable membrane thus preferably refer to sections of the oscillatable membrane that are substantially aligned in the emission direction of a MEMS loudspeaker or the detection direction of a MEMS microphone. Those skilled in the art will understand that this does not have to be an exact vertical alignment, but rather the vertical sections of the oscillatable membrane are preferably substantially aligned in the emission direction of a MEMS loudspeaker or the detection direction of a MEMS microphone.

[0059] 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.

[0060] The oscillating 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).

[0061] Preferably, the vertical and / or horizontal sections are rectilinear at least in sections or over their entire length; however, the vertical and / or horizontal sections can also be curved at least in sections or over their entire length. In the case of a curved shape of the oscillating membrane in cross-section, the orientation preferably relates to a tangent to the curved vertical and / or horizontal sections at their respective centers. While the oscillating membrane is preferably aligned horizontally to the sound emission direction or sound detection direction, the sound waves are generated by actuating the vertical sections or, conversely, detected. Therefore, at least the vertical sections preferably comprise a layer comprising an actuator material.

[0062] For the purposes of the invention, the vertical and / or horizontal sections of the membrane preferably refer to sections of a membrane (surface) that have different orientations. While the vertical sections of the membrane are oriented substantially in the direction of sound emission or sound detection, the horizontal sections of the membrane are oriented substantially orthogonally thereto. The membrane can thus also be understood as a folded membrane, the folding of which preferably occurs along a width. While the vertical and horizontal sections have different orientations, they are preferably characterized by a similar layer structure and by substantially equal layer thicknesses.Preferably, functional layers of the membrane, such as an actuator layer, mechanical support layer, and / or a layer comprising an electrically conductive material, also extend along both the horizontal and vertical sections. In this respect, the membrane according to the invention with horizontal and / or vertical sections differs significantly from the membrane disclosed in US 2017 / 0006381 A1. Instead, the membrane disclosed in US 2017 / 0006381 A1 for the MEMS transducer is a planar membrane that exists in one plane and does not have any folding into vertical or horizontal sections. Accordingly, when configured as a loudspeaker, the membrane of US 2017 / 0006381 A1 is excited to vertical vibrations along the emission direction by exciting the piezoelectric layers.In the case of a microphone design, sound waves are translated into vertical (out-of-plane) vibrations of the membrane along a detection direction, which can be read out using the piezoelectric layers. A folded membrane with vertical and horizontal sections, in which the vertical sections are excited to horizontal vibrations, i.e., orthogonal to the emission or detection direction, is not disclosed. In contrast to the planar membrane of US 2017 / 0006381 A1, in a membrane according to the invention, the vertical sections are excited to a horizontal vibration, whereby in particular fluid volumes located between the vertical sections are set into flow. As explained at the beginning, in the case of a MEMS loudspeaker, an increase in the generated sound pressure level can be achieved compared to planar membranes due to a greater displacement of the fluid volume.In the case of a MEMS microphone, the folded design of the membrane allows more fluid volume to be accommodated between the vertical sections and the sensitivity of the sound detector to be increased.

[0063] In a preferred embodiment of the invention, the carrier comprises two side regions between which the vibratable membrane is arranged in the horizontal direction.

[0064] The support is preferably a frame structure, which is essentially formed by a continuous outer border in the form of side walls of a free, flat 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, which preferably essentially form the frame structure, are particularly referred to as side walls.

[0065] The oscillating membrane is preferably held by at least two side walls of the support. In the exemplary Fig. 2h, the two side walls are shown in cross-section. However, the support preferably comprises four side regions, preferably with additional end faces generally parallel to the cross-section shown. These two additional side walls span the frame structure.

[0066] The oscillating membrane is preferably suspended flat within the remaining free area. The flat extension of the oscillating membrane characterizes a horizontal direction, while the vertical sections are essentially orthogonal to it. With respect to the end surfaces, the membrane can be attached to these side walls or slit there for greater mobility. Advantageously, the slit can represent a dynamic high-pass filter, which, for example, couples a front volume and a rear volume.

[0067] In a preferred embodiment of the invention, the carrier is formed from a substrate, preferably selected from a group comprising monocrystalline silicon, polysilicon, silicon dioxide, silicon carbide, silicon germanium, silicon nitride, nitride, germanium, carbon, gallium arsenide, gallium nitride, indium phosphide and / or glass.

[0068] 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 manufactured flexibly depending on the materials and / or manufacturing methods. In particular, it is preferable to manufacture the MEMS converter comprising an oscillating membrane together with a support in a single (semiconductor) process, preferably on a wafer. This further simplifies and reduces the cost of manufacturing, allowing a compact and robust MEMS converter to be provided cost-effectively.

[0069] Preferably, the at least one electrode is positioned at the end so that contact can be made with electronics, e.g., a current or voltage source in the case of a MEMS loudspeaker, at one end of the vibratable membrane, preferably at an end at which the membrane is suspended from the support. Electrode preferably means an area made of a conductive material (preferably a metal) which is designed for such contact with electronics, e.g., a current and / or voltage source in the case of a MEMS loudspeaker. This can preferably be an electrode pad. Particularly preferably, the electrode pad serves to make contact with electronics and is itself connected to a conductive metal layer, which can extend over the entire surface of the vibratable membrane.In some cases, the conductive layer together with an electrode pad is referred to as an electrode, for example as a top electrode or bottom electrode.

[0070] Particularly preferably, the layer of a conductive material, preferably metal, in the sense of a top or bottom electrode, is present as a continuous, full-surface, or continuous layer of the oscillating membrane, which forms a substantially homogeneous surface and, in particular, is not structured. Instead, the two or more vertical sections are preferably contacted with the end electrode or electrode pad by means of an unstructured layer of a conductive material, preferably metal.

[0071] In preferred embodiments, the MEMS converter comprises two end electrodes. Contact with electronics, e.g., a current or voltage source, can preferably be made with the electrodes at opposite ends of the vibratable membrane, between which the vertical sections are located, so that the actuator position(s) in the vertical sections can be controlled by means of the end electrodes.

[0072] The end-side provision of the electrodes is thus preferably distinguished from a contact arrangement that controls the respective vertical sections with separate electrodes or, in the case of a MEMS microphone, taps generated electrical signals. The MEMS converter thus preferably comprises exactly one or exactly two electrodes for end-side contact and no additional electrodes (pads) for contacting central vertical sections.

[0073] Preferably, the layer of actuator material in the vertical sections serves as a component of a mechanical bimorph, 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. It has proven extremely beneficial for the performance of the mechanical bimorph to have corrugations and / or weakened areas in vertical, horizontal, and / or at the junctions between vertical and horizontal sections.

[0074] In a preferred embodiment, the two or more vertical sections comprise at least two layers, wherein one layer comprises an actuator material and a second layer comprises a mechanical support material. At least the layer comprises the actuator material and is contacted with an end electrode, so that the horizontal oscillations can be generated by a change in shape 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 layer. Both a transverse and a longitudinal piezoelectric effect can be used for bending.

[0075] When the actuator layer is activated, it can, for example, experience transverse or longitudinal stretching or compression. This creates a stress gradient relative to the mechanical support layer, leading to lateral curvature or vibration. By alternating polarity at the electrodes, push-pull operation can be achieved, whereby almost the entire air volume between the vertical sections can be moved alternately in the vertical emission direction. The corrugations and / or weakened areas allow for particularly high deflection of the vertical sections and thus increase the displacement volume. The advantage of the actuator principle is therefore a highly efficient translation of the horizontal vibrations of vertical sections into vertical volume movement or sound generation.By applying corrugations and / or weakened areas, this can be particularly optimized, since both the flexural rigidity of the vertical sections and their freedom of rotation can be adjusted.

[0076] Since the actuator principle is not based on electrostatic attraction, but rather on a relative deformation (e.g., compression, stretching, and / or shear) of the actuator layer relative to a support layer, adhesion of the membrane sections can be ruled out. Instead, the vertical sections can touch each other and are thus not restricted in their deflection.

[0077] In a further preferred embodiment, the two or more vertical sections comprise at least two layers, wherein both layers comprise an actuator material and are preferably contacted with electrodes at the ends, and the horizontal oscillations can be generated by a change in the shape of one layer relative to the other layer. In this embodiment, the horizontal oscillation of the vertical sections is therefore not generated by a stress gradient between an active actuator layer and a passive support layer, but rather by a relative change in the shape of two active actuator layers.

[0078] The actuator layers can be made of the same actuator material and controlled differently. The actuator layers can also be made of different actuator materials, for example, piezoelectric materials with different deformation coefficients.

[0079] For the purposes of the invention, the "layer comprising an actuator material" is preferably also referred to as an actuator layer. An actuator material preferably means a material that undergoes a change in shape, for example, stretching, compressing, or shearing, upon application of an electrical voltage, or conversely, generates an electrical voltage upon change in shape.

[0080] Preferred materials are those with electric dipoles 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.

[0081] Preferably, the actuator material can be a piezoelectric material, a polymer piezoelectric material and / or electroactive polymers (EAP).

[0082] Particularly preferably, the piezoelectric material is selected from a group comprising lead zirconate titanate (PZT), aluminum nitride (AIN), aluminum scandium nitride (AIScN) and zinc oxide (ZnO).

[0083] 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 a change in shape 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. The mechanical support material is preferably 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, be coated with an electrically conductive layer.

[0084] The mechanical support material is particularly preferably monocrystalline silicon, a polysilicon or a doped polysilicon.

[0085] While the actuator layer undergoes a deformation when subjected to an electrical voltage, the layer of the mechanical support material remains essentially unchanged. The resulting stress gradient between the two layers (mechanical bimorph) preferably causes a horizontal curvature. For this purpose, the thickness of the support layer relative to the thickness of the actuator layer should preferably be selected such that a sufficiently large stress gradient is generated for the curvature. For doped polysilicon as a mechanical support material and a piezoelectric material such as PZT or AIN, for example, essentially equal thicknesses, preferably between 0.5 pm and 2 pm, have proven particularly suitable.

[0086] Terms such as substantially, approximately, about, etc. preferably describe a tolerance range of less than ± 20%, preferably less than ± 10%, even more preferably less than ± 5%, and especially less than ± 1%. Terms such as substantially, approximately, about, about, etc. always disclose and include the exact value stated.

[0087] Contacting the actuator layer and / or the layer of a mechanical support material and thus the application of an electrical voltage can be done directly via end-side electrodes or supported by a layer of a conductive material.

[0088] In a preferred embodiment, the oscillatable membrane therefore comprises at least one layer of a conductive material.

[0089] 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 / or copper.

[0090] The introduction of corrugations and / or the weakened areas according to the invention can equally relate to layers of an actuator material, a mechanical support material and / or a conductive material.

[0091] In a preferred embodiment, the MEMS transducer is characterized in that the one or more corrugations and / or weakened regions are present along the horizontal sections, along the vertical sections and / or at junctions between vertical sections and horizontal sections.

[0092] Thus, it may be preferred to apply the corrugations and / or weakened regions only along the horizontal sections. It may also be preferred to apply corrugations and / or weakened regions only along the vertical sections. In further preferred embodiments, corrugations and / or weakened regions are applied to the vertical sections and the horizontal sections. Furthermore, it may be preferred for corrugations and / or weakened regions to be present at connection points, either alone or in combination with further corrugations and / or weakened regions on vertical and / or horizontal sections.

[0093] Corrugations and / or weakened areas on horizontal sections and at joints advantageously increase the rotational freedom of the vertical sections. Corrugations and / or weakened areas on vertical sections advantageously reduce the flexural rigidity, thus further increasing the deflection of the vertical sections. Both positionings can be used alone or in combination to generate high sound pressure levels without significant distortion.

[0094] In a further preferred embodiment, the MEMS converter is characterized in that at least 1, 2, 3, 4, 5 or more corrugations and / or weakened regions are provided along a vertical section and / or a horizontal section.

[0095] The number of corrugations and / or weakened areas advantageously represents a parameter whose selection can be used to optimize the vibration behavior of the vertical sections. A higher number of corrugations and / or weakened areas in vertical sections and / or connection points advantageously results in greater freedom of rotation. A higher number of corrugations and / or weakened areas in the vertical sections advantageously results in greater deflection of the vertical sections by significantly reducing the stiffness of the vertical sections.

[0096] In further applications, it may be preferable to provide a relatively small number of corrugations and / or weakened regions, for example, only one or two corrugations and / or weakened regions per vertical and / or horizontal section. Thus, the vibration behavior of the vibratable membrane can advantageously be optimized in a particularly simple manner by appropriate selection, particularly with regard to the number of corrugations and / or weakened regions.

[0097] In a further preferred embodiment, the MEMS converter is characterized in that the one or more corrugations have a rectangular, trapezoidal, square, triangular, part-circular and / or round cross-section.

[0098] The aforementioned geometric shapes can advantageously promote the optimization of vibration behavior by the corrugations. Furthermore, the production of these geometric configurations of the corrugations has proven particularly simple. The preferred cross-sections of the corrugations can be achieved, for example, by providing a correspondingly shaped forming component or a structured carrier substrate and a subsequent coating process.

[0099] Preferably, one or more corrugations have a rectangular cross-section. A rectangular cross-section is preferably characterized by a flat quadrilateral whose interior angles are all substantially right angles. It may also be preferred for one or more corrugations to have a trapezoidal cross-section. A trapezoidal cross-section is preferably characterized by a flat quadrilateral with two sides that are substantially parallel to one another. Furthermore, it may be preferred for one or more corrugations to have a square cross-section. A square cross-section is preferably characterized by four sides of substantially equal length and four substantially right angles. Furthermore, it may be preferred for one or more corrugations to have a triangular cross-section. A triangular cross-section is preferably characterized by three angles that are spanned by its sides.

[0100] It may also be preferred for one or more corrugations to have a partially circular cross-section. "Partially circular" preferably refers to a partial section of a circular shape. A partially circular cross-section may preferably also be in the form of a substantially semicircle. Furthermore, it may be preferred for one or more corrugations to have a round cross-section. A round cross-section preferably refers to a cross-section that dispenses with corners and / or edges within the corrugations and can, for example, be semicircular or have another shape (elliptical, etc.).

[0101] In a preferred embodiment, the MEMS converter is characterized in that the one or more corrugations have a depth of 1 pm - 100 pm, preferably 2 pm - 20 pm and / or a width between approximately 0.5 pm - 50 pm, preferably between 1 pm - 5 pm.

[0102] In a further preferred embodiment, the MEMS converter is characterized in that the one or more corrugations have a width-to-depth aspect ratio of 1:1 or more, preferably 1:2 or more. The aspect ratio is preferably the ratio of the depth or height to the (smallest) lateral dimension.

[0103] The aspect ratios mentioned are advantageous in that they lead to a particularly effective increase in the deflectability of the vertical sections and can also be manufactured simply and reliably using methods known in the state of the art.

[0104] In a preferred embodiment, the MEMS converter is characterized in that the horizontal sections and / or vertical sections are formed in multiple layers and wherein one or more weakened regions are caused by a variation of the layer thickness of at least one layer, wherein preferably the layer thickness of the at least one layer is reduced to less than 70%, preferably less than 60%, 50%, 40% or less of an initial layer thickness.

[0105] As described above, a weakened region preferably refers to a reduced layer thickness of a membrane layer compared to the average thickness of the membrane section. In the case of a multilayer membrane, varying the layer thicknesses in the weakened region can involve a reduction in the layer thickness of a selection of the layers, for example, one or two layers, or all layers of the multilayer membrane. In this case, weakened regions exhibit similar advantageous technical effects to the application of corrugations.

[0106] The aforementioned reductions in layer thickness have proven to be advantageous in that, on the one hand, they are particularly simple and quick to provide and, on the other hand, they enable a particularly efficient optimization of the vibration behavior of the vibrating membrane.

[0107] In a further preferred embodiment, the MEMS converter is characterized in that the horizontal sections and / or vertical sections are formed in multiple layers, and wherein one or more weakened regions are formed by a regional reduction of a layer thickness of at least one layer to 0%. This can preferably relate to a layer comprising a conductive material, a layer comprising a support material, and / or the actuator layer. In embodiments, it may be preferred that one or more weakened regions are provided by a regional reduction of a layer thickness of all layers of the membrane to 0% of an initial layer thickness, provided that these layers comprise an actuator material, a mechanical support material, or a conductive material.In these embodiments, however, it may be preferred to avoid the formation of through-openings by providing a cover layer, preferably a layer made of a polymer material, which extends at least over the weakened areas. Preferred embodiments of the cover layer, preferably in the form of a polymer layer, are disclosed elsewhere herein.

[0108] A reduction to 0% of the initial layer thickness preferably refers to the complete absence of a layer in at least a partial area of ​​the membrane, which thus defines the weakened area, so that in the context of the invention this can also be synonymously referred to as an absence or omission of a layer in the relevant (weakened) area.

[0109] For example, a weakened area, which is characterized by a partial absence of a layer, can result in reduced actuation.

[0110] For example, there may be a recess in a conductive material of the membrane - for example a top and / or bottom electrode.

[0111] Preferably, a top electrode can be left out in one or more weakened regions, for example in a horizontal section. In the region where the top electrode is missing, in contrast to the remaining horizontal section of the membrane, no or only a reduced electric field can be formed between the top and bottom electrodes. A piezoelectric actuator layer located between the top and bottom electrodes is therefore not excited or actuated to a shape change in the region of the top electrode recess, or is actuated to a lesser extent. In an analogous manner, it may be preferred for one or more weakened regions to be formed by partially recessing a bottom electrode.

[0112] The reduced or weaker actuation is based—without being limited to theory—on a weakened electric field. The reduced actuation therefore results from a preferential reduction or elimination of a piezoelectric effect at the relevant location. This can advantageously optimize the vibration behavior of the membrane by increasing the mobility of adjacent vertical sections and / or avoiding undesirable effects such as buckling. Such a regional reduction in the actuation capability of the membrane can also be achieved by a regional absence of the actuator layer—for example, a piezoelectric actuator layer.

[0113] It may also be preferable for the actuator layer, for example, in the weakened region, to be replaced by a material that is not an actuator material, such as a dielectric material. By partially replacing a functional layer (e.g., an actuator layer) with a non-functional layer (e.g., a dielectric material as insulation material), the effect of reduced actuation can be achieved while simultaneously maintaining a homogeneous overall layer thickness in the weakened region.

[0114] Furthermore, it may also be preferable to additionally introduce an insulating material as an insulating layer (e.g., a dielectric material) in a weakened region—for example, between a layer comprising a conductive material (top and / or bottom electrode) and the actuator layer. This also reduces the piezoelectric effect and thus the actuation capability of the multilayer membrane in the weakened region. In this case, the weakened region can preferably be achieved by varying the layer thickness of at least one layer, in which an additional layer is introduced, possibly even increasing the overall thickness of the membrane.

[0115] In further preferred embodiments, a weakened area can also be characterized by the partial absence or omission of a mechanical support layer. This reduces the stiffness of the relevant sub-area, thus also optimizing the deflectability of the membrane. It is understood that, likewise in the case of the mechanical support layer, the omitted support material can also be replaced with a material with lower mechanical stiffness (or a higher modulus of elasticity).

[0116] The recess in one or more layers can be formed during coating by a predetermined masking. It may also be preferable to create the recess after coating by structuring.

[0117] In preferred embodiments, a weakened region, characterized by the absence of at least one layer, is present in a horizontal section. It may also be preferred for such a weakened region to be located within a corrugation. This means, for example, that in a corrugation, which is characterized as a depression or elevation in an otherwise essentially planar profile of the partial section, at least one layer (e.g., a support layer, actuator layer, top and / or bottom electrode) is omitted.

[0118] In particularly preferred embodiments, the MEMS transducer is characterized in that the horizontal sections and / or vertical sections are formed in multiple layers, and wherein one or more weakened regions are brought about by varying the layer thickness of at least one layer (preferably exactly one layer), wherein the layer thickness of the at least one layer is preferably reduced to less than 70%, preferably less than 60%, 50%, 40% or 0% of an initial layer thickness, but wherein the layer thickness of at least one layer of the membrane (preferably all layers except one layer) is not reduced. As a result, the mechanical or functional properties of the membrane in the weakened region are specifically changed without compromising the integrity of the membrane. Any acoustic disadvantages caused by the provision of through-openings can thus be avoided.The preferred remaining layer can be, for example, an actuator layer, a mechanical support layer, or a layer comprising a conductive material. It may also be preferred for only a cover layer to remain, preferably comprising a polymer material. The cover layer preferably essentially serves to prevent a complete, continuous opening of the membrane in the weakened areas, wherein the cover layer is preferably non-conductive and / or impermeable to a fluid in which the sound waves propagate, preferably air.

[0119] In some embodiments, however, the weakened regions can also be provided as continuous openings, thus reducing the layer thickness of all layers to 0% in some areas. The provision of continuous openings can also reduce the mechanical stiffness of the horizontal and / or vertical sections, thus resulting in improved vibration behavior of the membrane.

[0120] This can be optimized in particular by the geometric shape of the openings and / or the number of openings. In preferred embodiments, there are 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 10, 30, 50, 100 or more openings on a horizontal and / or vertical section. The more openings there are, the more the mechanical resistance can be reduced during an oscillation. The openings can preferably be circular, elliptical, angular or applied as a slit. In a further preferred embodiment, the MEMS transducer is characterized in that by configuring the one or more corrugations and / or weakened regions, preferably with regard to a depth, width, layer thickness, geometry and / or number, a stiffness of the horizontal sections and / or vertical sections can be adjusted in order to optimize an oscillation behavior of the vertical sections.

[0121] Advantageously, the stiffness of the vertical sections can be optimized by designing and / or selecting parameters including depth, width, layer thickness, geometry, and / or number, in particular adapting it to the intended use of the MEMS transducer. In particular, the stiffness of the vertical sections includes the flexural stiffness, i.e., the resistance to bending during horizontal oscillation, for example to generate or record pressure waves. Reducing the flexural stiffness advantageously results in a higher maximum deflectability of the vertical sections, so that higher sound pressure levels with good sound quality can advantageously be generated by a preferred MEMS loudspeaker. With respect to a preferred provision of the MEMS transducer as a MEMS microphone, its sensitivity, recording quality, and / or signal-to-noise ratio can advantageously be improved.

[0122] In preferred embodiments, the membrane comprises a cover layer, preferably in the form of a polymer layer. A polymer layer preferably characterizes a layer made of a polymer material and is particularly preferred in embodiments in which the remaining functional layers of the membrane, such as the layers made of an actuator material, an electrically conductive material, and / or a mechanical support material, are omitted.

[0123] In the embodiment, it is therefore preferred that in a weakened region the layer thickness of all layers of the membrane is reduced to 0% of an initial layer thickness, except for the layer thickness of a cover layer, which is preferably a layer comprising a polymer material.

[0124] The provision of a cover layer is advantageous in these embodiments in that it reliably prevents acoustic short circuits, regardless of the size of the recesses or openings to be provided. Thus, in the case of continuous openings in the membrane with dimensions of approximately 5 μm or more, a so-called acoustic short circuit can occur. Acoustic short circuit preferably refers to a reduction in sound radiation in the case of a loudspeaker or a reduction in sound pickup in the case of a microphone due to undesired pressure equalization between a rear and a front side of the membrane. An acoustic short circuit can occur, in particular, during the emission or reception of sound in the low-frequency range. By selecting smaller dimensions for continuous openings, such pressure equalization can be avoided for frequencies of desired applications.

[0125] The use of a cover layer, for example a polymer layer, advantageously prevents the occurrence of an acoustic short circuit even for openings of any size.

[0126] Recesses are avoided. This advantageously increases design flexibility with regard to providing weakened areas as recesses in the layers comprising an actuator material, a support material, or an electrically conductive material.

[0127] In preferred embodiments, the cover layer can be located on a front side or a back side of the membrane. A front side preferably refers to the side of the membrane into which sound emission occurs or from which sound waves are detected.

[0128] In preferred embodiments, the cover layer extends substantially continuously over the entire surface of the membrane. This specifically means that the cover layer is substantially identical in design and dimensions to those of the underlying or overlying layers of the membrane. Therefore, it is preferred that the cover layer be present as a single, preferably continuous, layer on the membrane.

[0129] In further preferred embodiments, it may be preferred that the cover layer, preferably in the form of a polymer layer, is present only at least in the weakened regions where the prevention of acoustic short circuiting is desired, and is not present in other regions of the membrane where there are no weakened regions. Thus, it may be preferred that the cover layer does not extend entirely along the membrane, but is selectively applied to cover the weakened regions or openings. In this embodiment, an interrupted, discontinuous cover layer may thus preferably be present, although the cover layer is provided at least in the weakened regions of the membrane.

[0130] In preferred embodiments, the cover layer is provided as a polymer film, polymer liquid, or a polymer lacquer. Preferably, the cover layer is not permeable to a fluid in which the sound waves propagate, for example air. The cover layer is therefore preferably gas-impermeable in order to maintain the acoustic integrity of the membrane and avoid an acoustic short circuit. Furthermore, it is preferred that the cover layer is not electrically conductive. In particular, it is preferred that the cover layer comprises a dielectric material. For example, it may be preferred that the cover layer comprises a polymer material selected from a group comprising polyvinyl difluoride (PVDF), polymethyl methacrylate (PMMA), parylene, and / or SU-8 polyimide.

[0131] In preferred embodiments, the cover layer has a layer thickness between 5 - 100 nm, preferably between 10 - 80 nm, particularly preferably between 20 - 60 nm, most particularly preferably between 30 - 50 nm.

[0132] In a preferred embodiment, the MEMS transducer is characterized in that the introduction of one or more corrugations and / or weakened regions at the horizontal sections and / or vertical sections increases a rotational freedom of the vertical sections in order to optimize a vibration behavior of the vertical sections.

[0133] Advantageously, increasing the rotational freedom can increase the mobility starting from the connection point of the vertical sections to the horizontal sections. The increase in rotational freedom can thus preferably be understood as improved mobility at the suspension point on the horizontal section.

[0134] In a preferred embodiment, the vibratable membrane is designed as a meander structure, wherein the meander structure is formed by the vertical sections and horizontal sections.

[0135] A meander structure preferably refers to a structure formed from a sequence of sections that are essentially orthogonal to one another in cross-section. The mutually orthogonal sections are preferably vertical and horizontal sections of the oscillatable membrane. The meander structure is particularly preferably rectangular in cross-section. However, it can also be preferred for the meander structure to have a sawtooth shape (zigzag shape) or to be curved or wave-shaped in cross-section. This is particularly the case if the vertical sections are not aligned exactly parallel to the vertical emission or detection direction, but rather enclose an angle of, for example, ± 30°, preferably ± 20°, particularly preferably ± 10° with the vertical direction. The meander structure preferably comprises structural and / or functional irregularities or inhomogeneities in the form of corrugations and / or weakened regions.

[0136] In preferred embodiments, the horizontal sections may also not be exactly at an orthogonal angle of 90° to the vertical emission or detection direction, but may, for example, enclose an angle between 60° and 120°, preferably between 70° and 110°, particularly preferably between 80° and 100° with the vertical direction.

[0137] In the case of a curved shape of the vertical and / or horizontal sections of the oscillatable membrane in cross-section, the orientation preferably refers to a tangent to the vertical and / or horizontal sections at their respective centers.

[0138] In this case, too, the corrugations according to the invention preferably define a local deviation (depression or elevation) from an otherwise continuous course of the (curved) vertical and / or horizontal sections.

[0139] The meandering structure thus preferably corresponds to a membrane folded across its width. For the purposes of the invention, an oscillating 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. The vertical sections are preferably longer than the horizontal sections, for example by a factor of 1, 5, 2, 3, 4, or more.

[0140] With regard to the function of a vibrating membrane in a meander shape for generating or receiving sound waves, the vertical sections, which can also be referred to as lamellae, are crucial. The vertical sections are preferably constructed in multiple layers and form a mechanical bimorph. For example, the vertical sections can each comprise an actuator layer and a passive layer made of a support material and / or two differently controllable actuator layers. The horizontal sections of the folded membrane can preferably be constructed identically to the vertical sections. However, it can 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.

[0141] In a preferred embodiment, the at least one layer of actuator material of the oscillatable membrane is a continuous layer. Continuous preferably means that there are no interruptions in the cross-sectional profile. Accordingly, in the aforementioned embodiment, it is preferred that a continuous layer of actuator material is present in both the vertical and horizontal sections. Advantageously, no structuring is necessary. A continuous layer is particularly simple to manufacture and ensures synchronous actuation during operation of a MEMS loudspeaker. With regard to the formation of weakened areas, however, it may also be preferable to deliberately introduce interruptions or recesses in an actuator layer in order to optimize the vibration behavior.

[0142] The performance of the MEMS transducer, in particular of a MEMS loudspeaker or MEMS microphone, can be significantly determined by the number and / or dimensions of the vertical sections. Corrugations and / or weakened regions, as explained above, lead to a particularly defined curvature and deflectability of the vertical sections. In preferred embodiments, the vibratable membrane comprises more than 3, 4, 5, 10, 15, 20, 30, 40, 50, 100, or more vertical sections.

[0143] In preferred embodiments, the vibratable membrane comprises less than 10,000, 5,000, 2,000, or 1,000 or fewer vertical sections.

[0144] The preferred number of vertical sections results in high acoustic power on smallest chip surfaces, whereby an excellent sound image and outstanding audio quality are achieved, in particular by providing the corrugations and / or attenuation areas.

[0145] Preferably, the vertical and / or horizontal sections are substantially planar, meaning in particular that their extent in each of the two dimensions (height, width) of their surface is greater than in a perpendicular dimension (thickness). For example, size ratios of at least 2:1, preferably at least 5:1, 10:1, or more may be preferred. Corrugations and / or weakened areas, as explained above, preferably define deviations from a planar plane.

[0146] For the purposes of the invention, the height of the vertical sections preferably corresponds to the dimension along the direction of sound emission or sound detection. With regard to the horizontal sections, however, a width preferably refers to the dimension along the connecting line between two vertical sections.

[0147] A thickness of the vertical and / or horizontal sections preferably corresponds to a sum of the layer thicknesses of the one or more layers that form the vertical and / or horizontal sections. The length of the vertical and / or horizontal sections preferably corresponds to a dimension orthogonal to the height or width, as well as the thickness. In the cross-sectional views of the figures listed below, the height or width and thickness are shown schematically (not necessarily to scale), while the dimension of the length corresponds to a (non-visible) drawing depth of the figures.

[0148] In a preferred embodiment, a height of the vertical sections is between 10 pm and 1 000 pm, preferably between 50 pm and 500 pm, while a width of the horizontal sections is between 2 pm and 200 pm, preferably between 5 pm and 100 pm.

[0149] In a preferred embodiment, a thickness of the vertical and / or horizontal sections is between 100 nm and 10 pm, preferably between 500 nm and 5 pm and / or a length of the vertical and / or horizontal sections is between 10 pm and 10 mm, preferably between 100 pm and 1 mm.

[0150] In preferred embodiments, the corrugations or weakened areas have a constant cross-section or layer thickness variation in the dimension of length and can therefore also be referred to as grooves or webs.

[0151] In the case of the recess in layers made of a conductive material, i.e. preferably the top and / or bottom electrode, it is preferred that the weakened regions do not represent continuous interruptions in the dimension of the length of the flat membrane. Instead, it may be preferable, for example, to provide conductor tracks or remaining conductive regions which ensure end-side contact and continuous current flow in the top and / or bottom electrode. Thus, the recess of the top and / or bottom electrode can preferably be present essentially along the entire dimension of the length of the membrane, wherein the recess is interrupted by thin (e.g., less than 20 pm, preferably less than 10 pm) conductive regions or conductor tracks.

[0152] With the aforementioned preferred dimensions of the oscillating membrane or the vertical sections, a particularly compact MEMS transducer, in particular a MEMS loudspeaker or MEMS microphone, can be provided, which simultaneously combines high performance with excellent sound or audio quality.

[0153] In a further aspect, the invention relates to a manufacturing method for a MEMS transducer, preferably a MEMS loudspeaker or MEMS microphone, comprising the following steps:

[0154] Etching a substrate, preferably from a front side, to form a structure, preferably a meander structure, and preferably to form corrugations, optionally applying an etch stop,

[0155] Applying at least two layers, wherein at least a first layer comprises an actuator material and a second layer comprises a mechanical support material or at least two layers comprise an actuator material, wherein one or more weakened regions are preferably provided in the process of applying the at least two layers or by subsequent etching.

[0156] Contacting the first and / or second layer with an electrode,

[0157] Etching the substrate, preferably from the back, and optionally removing the etching stop, so that the oscillatable membrane is attached to the carrier for executing oscillations, wherein the oscillatable membrane has vertical sections and horizontal sections, wherein the vertical sections are formed substantially parallel to the vertical direction and the horizontal sections connect the vertical sections to one another, wherein the vertical sections and / or the horizontal sections have one or more corrugations and / or weakened regions, so that by controlling the electrode the vertical sections can be excited to horizontal oscillations or when the vertical sections are excited to horizontal oscillations an electrical signal can be generated at the electrode.

[0158] The average person skilled in the art will recognize that 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 method, and vice versa. The described manufacturing method preferably serves to provide a MEMS transducer with a folded, oscillatable membrane having a meandering structure. Examples of preferred manufacturing steps are shown in Fig. 2 ah.

[0159] Preferably, etching the substrate comprises applying a structure congruent to the meander structure for the membrane to provide vertical and horizontal sections as well as corrugations and / or areas of weakness after deposition.

[0160] Alternatively, corrugations and / or weakened areas can be created by structuring or coating through the use of a mask. It may also be preferable to create weakened areas, for example in the form of recesses in at least one layer, by subsequent structuring (etching) of the membrane.

[0161] For example, one of the preferred materials mentioned above can be used as the substrate. During etching, a blank, such as a wafer, can be formed into the desired basic shape of the meander structure. In a next step, the layers for the vibrating membrane are preferably applied.

[0162] Applying at least one layer of a conductive material preferably includes, in addition to applying one layer, the application of multiple layers, and in particular, a layer system. A layer system comprises at least two layers applied in a systematic manner relative to one another. The application of a layer or a layer system preferably serves to define the oscillatable membrane comprising vertical sections that can be excited to horizontal oscillations.

[0163] In preferred embodiments, after an optional application of an etch stop, a cover layer in the form of a polymer layer can be coated. It may then be preferable to apply the further preferred layers for the membrane and structure them accordingly to provide corrugations and / or weakened areas, in particular openings. This results in a membrane having a cover layer, preferably in the form of a polymer layer, as its bottom layer.

[0164] It may also be preferable to apply the cover layer as the last layer, i.e., as the topmost layer within a coating. The cover layer is preferably applied in the form of a polymer layer as the last layer after structuring layers to create corrugations and / or weakened areas, in particular openings, on the membrane. Thus, a membrane is obtained that has a polymer layer as its topmost layer.

[0165] As explained above, the use of a cover layer, particularly in the form of a polymer layer, has proven particularly advantageous for preventing acoustic short circuits. This is especially the case if it is preferable to omit all other layers of a membrane (e.g., actuator layer, mechanical support layer, and / or layer comprising a conductive material) in the relevant weakened areas.

[0166] Preferably, the application can 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).

[0167] Etching and / or structuring can 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).

[0168] If further structuring of the oscillating membrane is desired—for example, to create weakened areas as described—this can be achieved, for example, through further etching processes. Additional material can also be deposited or doped using conventional methods.

[0169] To connect the layers, suitable materials such as copper, gold, and / or platinum can be deposited using common processes. Physical vapor deposition (PVD), chemical vapor deposition (CVD), or electrochemical deposition are preferred.

[0170] Using these process steps, a finely structured, vibratable membrane with a desired definition of vertical and horizontal sections can be created, which is preferably suspended between two side regions of a stable support and has dimensions in the micrometer range. The manufacturing steps are standard steps in semiconductor processing, making them proven and suitable for mass production.

[0171] The invention will be explained below with reference to further figures and examples. The figures and examples serve to illustrate preferred embodiments of the invention without limiting it.

[0172] FIGURES

[0173] Short description of the characters

[0174] Fig. 1 Schematic representation of corrugations on vertical and horizontal

[0175] sections

[0176] Fig. 2 Schematic representation of preferred process steps for producing a MEMS converter

[0177] Fig. 3 Schematic representation of corrugations on vertical and horizontal sections

[0178] Fig. 4 Further schematic representation of corrugations on vertical sections

[0179] Fig. 5 Schematic representation of weakened areas on horizontal sections

[0180] Fig. 6 Simulation results for the vibration behavior of a vertical section in case of the introduction of corrugations in adjacent horizontal sections

[0181] Fig. 7 Schematic representation of weakened areas by providing recesses in the top or bottom electrode

[0182] Fig. 8 Schematic representation of weakened areas due to structuring of the actuator layer

[0183] Fig. 9 Schematic representation of weakened areas due to the formation of through openings

[0184] TI Fig. 10 Schematic representation of a preferred embodiment of a MEMS converter comprising a cover layer in the form of a polymer layer

[0185] Detailed description of the characters

[0186] Fig. 1 a, b illustrates an oscillatable membrane 1 of a MEMS transducer, which has corrugations 7 on its vertical sections 3 and horizontal sections 5.

[0187] In Fig. 1 a, a rectangular cross-section of the corrugations 7 is shown, while Fig. 1 b illustrates a trapezoidal cross-section.

[0188] Advantageously, the vibration behavior of the vibratable membrane 1 can be optimized by designing the geometric shape of one or more corrugations 7.

[0189] On the one hand, the corrugations 7 lead to a higher degree of rotation of the vertical sections 3, thereby ensuring a particularly efficient deflection of the oscillating membrane. On the other hand, the corrugations advantageously ensure that the vertical sections experience a particularly defined curvature when pressure waves are generated or absorbed (see Fig. 1 b). A potential occurrence of irregular buckling 1 is particularly effectively prevented.

[0190] Furthermore, a targeted introduction of corrugations 7 allows higher amplitudes of the horizontal vibrations.

[0191] In the case of a MEMS loudspeaker, for example, this results in a greater displacement of the fluid volume between the vertical sections 3, enabling an increase in the generated sound pressure level. Accordingly, in the case of a MEMS microphone, more fluid volume can be captured between the vertical sections, increasing the sensitivity of the sound detector. The particularly uniform curvature of the vertical sections 7 during horizontal vibrations also reduces the occurrence of harmonic distortion. This results in a particularly good sound image both when recording and when generating pressure waves from a fluid.

[0192] Fig. 2 shows preferred method steps for producing an embodiment of a MEMS converter according to the invention.

[0193] Fig. 2a illustrates a substrate 9 that was previously etched from a front side to form a pattern. During the etching process, deep parallel trenches (pockets) were formed into the substrate 9, so that the formed structure represents a bellows or, in cross-section, a meander. Furthermore, the etching process provided elevations or depressions in sections of the substrate 9 that will form the horizontal sections to form the corrugation.

[0194] Fig. 2 b illustrates the application of an etch stop 11, which acts as a sacrificial layer and is intended to protect the vertical sections 3 and / or the horizontal sections 5 during the back-side etching to expose the membrane.

[0195] A layer of mechanical support material 17 is applied to the etch stop 9 (Fig. 2 c). The mechanical support material 17 can preferably also be a conductive material, e.g., polysilicon, so that the layer of mechanical support material 17 can simultaneously function as a bottom electrode.

[0196] In Fig. 2 d, a middle layer comprising an actuator material 15 is coated onto the layer of a mechanical support material 17. The actuator material 15 can preferably be a piezoelectric material, e.g., AlN.

[0197] Subsequently, Fig. 2 e shows that an upper layer comprising a conductive material 13 is coated, wherein the upper layer 13 will act as a top electrode.

[0198] Fig. 2 f shows the application of an electrode pad for contacting the upper layer of a conductive material 13, which acts as a top electrode, and the lower layer of a conductive, mechanical support material 17, which acts as a bottom electrode.

[0199] In Fig. 2g, the substrate 9 is etched from a rear side to expose the vibratable membrane 1 and form a carrier 2. The carrier 2 comprises two side regions, between which the vibratable membrane 1 is arranged horizontally. The vibratable membrane 1 is designed as a meander structure, wherein the meander structure is formed by the vertical sections 3 and horizontal sections 5. After etching the substrate, the horizontal sections 5 now have corrugations 7 according to the invention, which lead to a significant improvement in the vibration behavior of the vibratable membrane 1.

[0200] The arrows shown in Fig. 2 h serve to represent the horizontal vibrations of the vertical sections 3. In particular, the rotational freedom of the vertical sections 3 is increased by the application of corrugations 7, so that an optimization of the vibration behavior of the vibratable membrane 1 can be advantageously achieved.

[0201] Fig. 3 shows a further preferred embodiment of an oscillatable membrane 1 comprising corrugations 7. The corrugations 7 shown have a round, part-circular cross-section.

[0202] In Fig. 3 a, the corrugations 7 are attached to the vertical sections 3. By attaching corrugations 7 to the vertical sections 3, the flexural rigidity is advantageously reduced, so that a greater deflectability of the vertical sections 3 can be achieved.

[0203] Fig. 3 b shows the oscillating membrane 1 from Fig. 3 a. However, corrugations 7 are now also attached to the horizontal sections 5, which has a further advantageous effect on the freedom of rotation of the vertical sections 3.

[0204] Fig. 4 shows a schematic representation of corrugations 7 on vertical sections 3 and now additionally on the connection points between horizontal sections 5 and vertical sections 3.

[0205] While Fig. 4 a shows the initial position of the vertical sections 3, Fig. 4 b shows a deflection of the vertical sections 3, e.g., by controlling an electrode. The corrugations 7 ensure a uniform curvature, without the risk of irregular buckling.

[0206] Fig. 5 shows a preferred embodiment for forming weakened areas 19 on horizontal sections 5.

[0207] In the preferred embodiment, the membrane 1 is formed in multiple layers. A lower layer of mechanical support material 17 is formed from a conductive material (here: polysilicon), so that the lower layer of mechanical support material 17 simultaneously functions as both a bottom electrode and a carrier layer. On top of the layer of support material 17 is a middle layer comprising an actuator material 15 (here: aluminum nitride AIN as a piezoelectric layer) and an upper layer comprising conductive material 13 (here: aluminum), which functions as a top electrode.

[0208] In Fig. 5 a, the layer thickness of the middle actuator layer 15 is reduced in some areas compared to the initial layer thickness to form a weakened area 19.

[0209] In Fig. 5 b, in addition to the variation of the layer thickness of the middle actuator layer 15, the layer thickness of the lower support layer 17 is reduced in some areas compared to the initial layer thickness to form a weakened area 19.

[0210] Advantageously, weakened areas 19 can achieve similar effects with regard to optimizing the vibration behavior of the vertical sections 3 as by applying corrugations.

[0211] In particular, the introduction of weakened areas 19 allows a reduction in the stiffness of horizontal sections 5, thus increasing the deflectability of the vertical sections 3. The arrows in Figs. 5 a and b illustrate the resulting improved freedom of movement and rotation of the vertical sections 3.

[0212] Fig. 6 shows the results of a simulation of the vibration behavior of a vertical section 3 when corrugations 7 are applied to adjacent horizontal sections.

[0213] As can be seen in Fig. 6, the rotational freedom of the vertical sections 3 can be increased by attaching corrugations 7 to horizontal sections 5, resulting in a particularly uniform curvature of the vertical sections 3 without irregular buckling occurring.

[0214] Fig. 7 shows a schematic representation of a preferred provision of weakened regions 19 by providing recesses in the top or bottom electrode. The weakened regions 19 are thus characterized by a partial reduction of the thickness of the layer of conductive material 13 (top or bottom electrode) to 0%.

[0215] Fig. 7 a shows a section of a horizontal section 5 with a corrugation 7. The membrane 1 comprises an upper layer made of a conductive material 13, which functions as a top electrode, an actuator layer 15 comprising an actuator material, and a lower layer made of a conductive material 13, which simultaneously functions as a support layer 17 and bottom electrode. The weakened region 19 is such that the conductive material 13 or the top electrode is missing over the region of the corrugation 7. In the region where the top electrode is missing, in contrast to the remaining horizontal section 5 of the membrane, no or only a reduced electric field can be formed between the top and bottom electrodes.The actuator layer 15, preferably comprising a piezoelectric material located between the top and bottom electrodes, is therefore not stimulated or actuated to a change in shape in the region of the recess of the top electrode, or is only stimulated to a lesser extent.

[0216] The reduced actuation therefore results from a local reduction of the piezoelectric effect at the affected location. This can advantageously optimize the vibration behavior of the membrane by increasing the mobility of adjacent vertical sections and / or avoiding undesirable effects such as buckling.

[0217] Fig. 7 b shows a section of a membrane with a corrugation 7 along a horizontal section 5. The membrane comprises an actuator layer 15 comprising an actuator material, which is applied to a layer of a conductive material 13, which simultaneously functions as a support layer 17. This provides a weakened region 19 such that the conductive material 13 or the top electrode is missing not only in the region of the corrugation 7, but also in other regions of the horizontal section 5.

[0218] Fig. 7 c and 7 d show embodiments similar to Fig. 7 a and b, but the weakened region 19 is formed by recesses in the lower layer of a conductive material 13, which functions both as a bottom electrode and as a support layer 17. The weakened region 19 is thus present in such a way that the conductive material 13 or the bottom electrode is missing over the area of ​​the corrugation 7. In addition to the effect of reduced actuation of the actuator layer 15, the absence of the support layer 17 contributes to a reduction in the stiffness of the membrane 1 in this area and allows for an optimization of the vibration behavior.

[0219] In Fig. 7 c, the weakened region 19 is provided such that the conductive material 13 or the top electrode is missing in the region of the corrugation 7. In Fig. 7 d, a weakened region is provided such that the conductive material 13 or the bottom electrode is missing or omitted not only in the region of the corrugation 7, but also in other regions of the horizontal section 5.

[0220] Preferably, the recess in the layer of conductive material 13 extends substantially along the length of the planar membrane to a depth (not visible in the figures). However, it is preferred to provide conductor tracks or remaining conductive regions that ensure end-to-end contact and continuous current flow in the top and / or bottom electrode. Thus, the recess in the top and / or bottom electrode can preferably extend substantially along the entire length of the membrane, with the recess being interrupted by thin (less than 20 pm, preferably less than 10 pm) conductive regions or conductor tracks. To illustrate the formation of the weakened regions 19, the figures preferably show a cross-sectional plane along the length at which the recess is visible.

[0221] Fig. 8 shows a schematic representation for a preferred provision of weakened regions 19 by providing recesses in an actuator layer 15. The weakened regions 19 are thus characterized by a regional reduction of a layer thickness of at least the layer 15 of an actuator material to 0%.

[0222] In the embodiments shown, a regional reduction in the actuation capability is thus achieved by structuring the actuator layer 15 - for example, a piezoelectric actuator layer 15.

[0223] Fig. 8 a shows an embodiment in which the horizontal section 5 of the membrane has a weakened region 19 over the area of ​​the corrugation 7, in which an actuator layer 15 is missing along the corrugation 19. The upper layer of conductive material 13, which functions as a top electrode, is also recessed in this region.

[0224] Fig. 8 b shows a section of a membrane with a corrugation 7 along a horizontal section 5. In the weakened region 19, the membrane comprises only a support layer 17, which is conductive and simultaneously functions as a bottom electrode. This provides a weakened region 19 such that both the conductive material 13 or the top electrode and the actuator layer 15 are missing not only in the region of the corrugation 7, but also in other regions of the horizontal section 5.

[0225] Fig. 8 c shows a section of a membrane with a corrugation 7 along a horizontal section 5. The membrane comprises a lower layer made of a conductive material 13, which functions as a bottom electrode and support layer 17, and an upper layer made of a conductive material 13, which forms a top electrode. The actuator layer 15 is missing between the layers of electrically conductive material. Instead, an insulation layer 23 is introduced, which is formed by a dielectric material. In this embodiment, too, the actuation capability of the membrane 1 is reduced in the weakened region 19. Advantageously, replacing the actuator layer 15 with an insulation layer 23 makes it possible to maintain the overall thickness of the membrane 15. In addition, it may be preferable to ensure mechanical stability of the membrane even in the weakened region 19 through the dielectric layer.

[0226] Fig. 9 shows a schematic representation of weakened areas 19 by forming through openings 21.

[0227] Fig. 9 a shows the cross-section of a MEMS transducer having a membrane 1 comprising vertical sections 3 and horizontal sections 5. The membrane 1 extends horizontally along a support 2 from which the membrane 1 is suspended. The membrane 1 comprises a conductive support layer 17, which simultaneously functions as a bottom electrode, an actuator layer 15, and, located thereon, an upper layer made of conductive material 13, which serves as a top electrode. In Fig. 9 a, dashed lines are also drawn on the horizontal sections 5, which are intended to symbolize that at these points in the horizontal sections 5 there are through-openings as weakened regions 19. The weakened regions 19 are thus provided by a regional reduction of the layer thickness of all layers to 0%.

[0228] Fig. 9 b shows a top view of the MEMS converter, wherein it can be seen that weakened regions 19 in the form of openings 21 are arranged in a row along the dimension of the length of the horizontal section 5. Despite the openings 21, the top and bottom electrodes remain continuously conductive across their surface. Thus, by providing openings 21, the stiffness of the horizontal sections and / or vertical sections can be locally reduced in order to optimize the vibration behavior of the membrane 1. The desired degree of stiffness reduction can be adjusted, in particular, by the geometric shape of the openings 21 and / or the number of openings 21.

[0229] Fig. 10 shows a schematic representation of a preferred embodiment of the MEMS converter. As in the embodiment shown in Fig. 9, the membrane 1 comprises a conductive support layer 17, which simultaneously functions as a bottom electrode, an actuator layer 15, and, located thereon, an upper layer of conductive material 13, which serves as a top electrode. In this embodiment, the weakened regions 19 are provided by a region-by-region reduction of the layer thickness of all layers comprising an actuator material, a conductive material, or a support material to 0% of an initial thickness. Thus, the weakened regions 19 are present as recesses in all layers 13, 15, and 17 of the membrane 1.

[0230] To avoid the formation of continuous openings through the membrane 1, it is preferred in the embodiment that the membrane 1 comprises a cover layer 25, preferably in the form of a polymer layer.

[0231] The provision of a cover layer 25, preferably in the form of a polymer layer, is advantageous in that it reliably prevents acoustic short circuits, regardless of the size of the recesses or openings to be provided. Thus, in the case of continuous openings in the membrane 1 with dimensions of approximately 5 μm or more, a so-called acoustic short circuit can occur. Acoustic short circuit preferably refers to a reduction in sound radiation in the case of a loudspeaker or sound reception in the case of a microphone due to undesired pressure equalization between a rear and a front side. An acoustic short circuit can occur, in particular, during the emission or reception of sound in the low-frequency range. By selecting small opening dimensions accordingly, such pressure equalization can be avoided for the frequencies of desired applications.

[0232] The use of a cover layer 25, for example in the form of a polymer layer, advantageously prevents the occurrence of an acoustic short circuit even for openings of any size. This increases design flexibility with regard to the provision of weakened areas, which are provided as openings through all layers comprising an actuator material, a support material, or an electrically conductive material.

[0233] Fig. 10 shows that the cover layer 25 is applied to a front side of the membrane 1. Analogously, the cover layer 25 could also be applied to a back side of the membrane 1. In this case, the cover layer 25 extends essentially completely along the membrane 1. Alternatively, the cover layer could also be present as an interrupted, discontinuous layer, which, however, ensures at least some coverage of the weakened areas 19.

[0234] LITERATURE

[0235] 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).

[0236] 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>.

[0237] 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.

[0238] Zou, Quanbo, Zhijian Li, and Litian Liu. "Design and fabrication of silicon condenser microphone using corrugated diaphragm technique." Journal of microelectromechanical systems 5.3 (1996): 197-204.

[0239] LIST OF REFERENCE SYMBOLS

[0240] 1 Oscillating membrane

[0241] 2 carriers

[0242] 3 Vertical section

[0243] 5 Horizontal section

[0244] 7 Corrugation

[0245] 9 Substrat

[0246] 11 Etching stop

[0247] 13 layers of conductive material

[0248] 15 layers of actuator material (actuator layer)

[0249] 17 layers of a mechanical support material (support layer or support layer)

[0250] 19 weak areas

[0251] 21 Opening

[0252] 23 Insulation layer

[0253] 25 Top layer, preferably in the form of a polymer layer

Claims

PATENT CLAIMS 1. MEMS transducer for interacting with a volume flow of a fluid comprising a support (2) and a vibrating diaphragm (1) for generating or receiving pressure waves of the fluid in a vertical direction, which is attached to the support (2) and contacted with at least one electrode, wherein the vibrating diaphragm (1) has vertical sections (3) and horizontal sections (5) having the vertical sections (3) being substantially parallel to the vertical direction and the horizontal sections (5) the vertical sections (3) connect to each other, such that by controlling the at least one electrode the vertical sections (3) can be excited to horizontal vibrations or such that when the vertical sections (3) are excited to horizontal vibrations an electrical signal can be generated at the electrode, characterized in that the vertical sections (3) and / or the horizontal sections (5) have one or more corrugations (7) and / or weakening areas (19).

2. MEMS transducer according to the previous claim characterized in that one or more corrugations (7) and / or weakening areas (19) are present along the horizontal sections (5), along the vertical sections (3) and / or at junctions between vertical sections (3) and horizontal sections (5).

3. MEMS transducer according to one or more of the preceding claims characterized in that at least 1, 2, 3, 4, 5 or more corrugations (7) and / or attenuation areas (19) are provided along a vertical section (3) and / or a horizontal section (5).

4. MEMS transducer according to one or more of the preceding claims, characterized in that the one or more corrugations (7) have a rectangular, trapezoidal, square, triangular, semicircular and / or round cross-section and / or the one or more corrugations (7) have a depth of 1 pm - 100 pm, preferably 2 pm - 20 pm, and / or a width between approximately 0.5 pm - 50 pm, preferably between 1 pm - 5 pm.

5. MEMS transducer according to one or more of the preceding claims characterized in that the one or more corrugations (7) have an aspect ratio of width to depth of 1 :1 or more, preferably of 1 :2 or more.A MEMS transducer according to one or more of the preceding claims, characterized in that the horizontal sections (5) and / or vertical sections (7) are formed in multiple layers, and wherein one or more weakening regions (19) are formed by varying the layer thickness of at least one layer, wherein the layer thickness of the at least one layer is preferably reduced to less than 70%, preferably less than 60%, 50%, 40% or less of an initial layer thickness. A MEMS transducer according to one or more of the preceding claims, characterized in that the horizontal sections and / or vertical sections are formed in multiple layers, and wherein one or more weakening regions are formed by selectively reducing the layer thickness of at least one layer to 0%, which is preferably a layer comprising a conductive material (13), a layer comprising a support material (17) and / or a layer comprising an actuator material (15).A MEMS transducer according to one or more of the preceding claims, characterized in that the stiffness of the horizontal sections (5) and / or vertical sections (7) can be adjusted by designing one or more corrugations (7) and / or weakening areas (19), preferably with respect to depth, width, layer thickness, geometry and / or number, in order to optimize the vibration behavior of the vertical sections (5). A MEMS transducer according to one or more of the preceding claims, characterized in that the introduction of one or more corrugations (7) and / or weakening areas (19) on the horizontal sections (5) and / or vertical sections (3) increases the rotational freedom of the vertical sections (3) in order to optimize the vibration behavior of the vertical sections (5).A MEMS transducer according to one or more of the preceding claims, characterized in that one or more corrugations (7) are present in vertical sections (7) and / or at junctions between vertical sections (3) and horizontal sections (5), wherein preferably the one or more corrugations (7) are provided by an etching process during the formation of vertical trenches for the vertical sections (3). A MEMS transducer according to one or more of the preceding claims, characterized in that the MEMS transducer is a MEMS loudspeaker, wherein preferably air volumes are present between the vertical sections (3), which are connected by the horizontal sections (5). Vibrations are used to generate sound waves along a vertical emission direction, or the MEMS transducer is a MEMS microphone, wherein preferably air volumes are present between the vertical sections (3) which are moved along a vertical detection direction when sound waves are received. A MEMS transducer according to one or more of the preceding claims is characterized in that the vibrating diaphragm (1) comprises at least two layers, each comprising an actuator material (15) and each being contacted with an electrode, and the horizontal vibrations can be generated by a change in shape of one layer relative to the other layer, or the horizontal vibrations lead to a change in shape of one layer relative to the other layer and generate an electrical signal.MEMS transducer according to one or more of the preceding claims characterized in that the vibrating membrane (1) comprises at least two layers, wherein a first layer comprising an actuator material (15) and a second layer comprising a mechanical support material (17), wherein at least the first layer comprising the actuator material (15) is in contact with the electrode, such that horizontal vibrations can be generated by a change in shape of the actuator material relative to the mechanical support material or such that horizontal vibrations lead to a change in shape of the actuator material relative to the mechanical support material and generate an electrical signal.A MEMS transducer according to one or more of the preceding claims, characterized in that the vibrating membrane (1) comprises three layers, wherein an upper layer is formed of a conductive material (13) and functions as the top electrode, a middle layer (15) is formed of an actuator material, and a lower layer is formed of a conductive material (13) and functions as the bottom electrode, wherein the conductive material of the upper and / or lower layer is preferably a mechanical support material (17). A method for manufacturing a MEMS transducer according to one or more of the preceding claims comprising the following steps: Etching of a substrate (9), preferably from a front side, to form a structuring, preferably a meandering structure, and to preferably form corrugations (7), optional application of an etch stop (11) , Applying at least two layers, wherein at least one first layer is an actuator material (15) and a second layer is a mechanical support material (17) comprising or comprising at least two layers of an actuator material (15), wherein preferably one or more weakening areas (19) are provided in the process of applying the at least two layers or by subsequent etching. Contacting the first and / or second layer with an electrode Etching of the substrate (9), preferably from the back, and optional removal of the etching stop (11), so that the vibrating membrane (1) is attached to the support (2) for performing vibrations, wherein the vibrating membrane (1) has vertical sections (3) and horizontal sections (5), wherein the vertical sections (3) are formed substantially parallel to the vertical direction and the horizontal sections (5) connect the vertical sections (3) to each other, wherein the vertical sections (3) and / or the horizontal sections (5) have one or more corrugations (7) and / or attenuation areas (19), so that by actuating the electrode the vertical sections (5) can be excited to horizontal vibrations or when the vertical sections (5) are excited to horizontal vibrations an electrical signal can be generated at the electrode.

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