MEMS transducers with improved performance

Abstract

The invention relates to a MEMS transducer, comprising a vibrating membrane (1) for generating or picking up pressure waves in a fluid in a vertical direction, wherein the vibrating membrane (1) is supported by a carrier (4) and has two or more vertical parts (2) formed parallel to the vertical direction and comprising at least one layer (11) of actuator material. The ends of the vibrating membrane (1) are in contact with electrodes (13), which means that actuation of at least one electrode (13) allows the two or more vertical parts (2) to be excited to produce horizontal vibrations, or means that the two or more vertical parts (2) are excited to produce horizontal vibrations so that an electrical signal can be generated at at least one electrode (13).

Description

[0001] manual

[0002] The present invention relates to a MEMS transducer, which includes a vibrating membrane for generating or receiving pressure waves of a fluid in a vertical direction, wherein the vibrating membrane is supported by a carrier and has two or more vertical parts, the two or more vertical parts are formed parallel to the vertical direction and include at least one layer of actuator material. At least one end of the vibrating membrane is preferably connected to an electrode, so that the two or more vertical parts can be induced to vibrate horizontally by driving at least one electrode, or when the two or more vertical parts are induced to vibrate horizontally, an electrical signal can be generated at at least one electrode. Background Art

[0003] Today, microsystem technology is used in many fields of application to produce compact, mechatronic devices. The microsystems that can be produced in this way (microelectromechanical systems, MEMS for short) are extremely compact (micrometer range), have excellent functionality and are manufactured at low cost.

[0004] MEMS transducers, such as MEMS loudspeakers or MEMS microphones, are also known in the prior art. Current MEMS loudspeakers are mostly designed as planar membrane systems, which drive a vibrating membrane vertically in the emission direction. For example, the vibration is induced by a piezoelectric actuator, an electromagnetic actuator or an electrostatic actuator.

[0005] Shahosseini et al. described an electromagnetic MEMS speaker for mobile devices in 2015. The MEMS speaker uses a hardened silicon microstructure as a sound radiator, where the moving part is suspended from a carrier via silicon drive springs to achieve large out-of-plane displacements via electromagnetic motors.

[0006] Stoppel et al. disclosed in 2017 a two-way loudspeaker, the concept of which is based on concentric piezoelectric actuators. As a special feature, the vibrating membrane is not a closed design, but includes eight piezoelectric unimorph actuators, each of which includes a piezoelectric layer and a passive layer. The external woofer includes four unilaterally clamped trapezoidal actuators, while the internal tweeter includes four triangular actuators connected to a rigid frame by springs. The separation of the membranes should allow improved sound at higher outputs.

[0007] A disadvantage of such planar MEMS loudspeakers is their limitation in terms of acoustic power, especially at low frequencies. One reason for this is that for a given displacement, the sound pressure level that can be generated is proportional to the square of the frequency. Therefore, in order to obtain sufficient acoustic power, a displacement of the diaphragm of at least 100 μm or a large membrane area in the range of square centimeters is necessary. Both conditions are difficult to achieve with MEMS technology.

[0008] Therefore, in the prior art, it is proposed to design a MEMS loudspeaker that does not have a closed membrane for vibrating in the vertical emission direction, but has a large number of movable elements that can be driven to produce lateral or horizontal vibrations. This has the advantage that an increased volume flow can be moved over a small surface and thus an increased sound power can be provided.

[0009] For example, US2018 / 0179048A1 or Kaiser et al. disclosed a MEMS speaker based on this principle in 2019.

[0010] The MEMS loudspeaker comprises a plurality of electrostatic bending actuators which are arranged as vertical sheets between the top and bottom wafers and which can be driven by appropriate control to produce lateral vibrations. Here, the inner sheet forms the actuator electrode opposite to the two outer sheets. In addition to the connection nodes of the electrodes which are still galvanically separated, there are air gaps between the three bending sheets. If a potential is applied inside to the outside, this results in an attractive force on both sides due to the designed curvature in the direction of the preferred direction predefined by the anchor. The protrusions of the outer sheets are used for mobility. The restoring force is provided by a mechanical spring force. Therefore, push-pull operations are not possible.

[0011] Another disadvantage is the gap between the bending actuators and the cover / bottom wafer, which is necessary for their mobility, resulting in ventilation between the two chambers. This limits the lower cut-off frequency. In addition, the lateral movement of the bending actuators and therefore the acoustic power is limited to avoid pull-in effects and acoustic breakdown.

[0012] An alternative MEMS-based air pulse or sound generating system is described in US2019 / 0116417A1. The device includes a front chamber and a rear chamber and a plurality of valves, wherein the front chamber and the rear chamber are separated from each other by a folded membrane. In one embodiment, the folded membrane has a rectangular meander structure in a cross section having a horizontal portion and a vertical portion. The piezoelectric actuator is located on the corresponding horizontal portion to cause lateral movement of the vertical portion by synchronous stretching or compression of the horizontal portion. Using the proposed principle, it is also possible to generate an increased volume flow and thus acoustic power on the surface of a small chip.

[0013] However, one disadvantage is the increased effort required for the synchronous drive of the piezoelectric actuators. There is also potential for improvement in the volume displaced by lateral vibrations, which is limited by the geometric arrangement of the horizontal parts of the unidirectional drive.

[0014] A piezoelectric loudspeaker is known from US 2002 / 006208 A1 and JP 3919695 B2 in which two piezoelectric thin films are formed as membranes with an accordion shape. In folded form, the membranes are each clamped laterally by pairs of corrugated plates, which are fixed, for example, by screw connections and stabilize the vibrating membrane as a composite side frame. A plurality of electrodes are applied in a structured form to the peaks and valleys of the membrane and are insulated from one another by strips of non-conductive material. Electrode cables are arranged in the paired plates or side frames to drive the electrodes. Alternatively, the paired plates can also be formed at least partially of a conductive material.

[0015] Macroscopic piezoelectric loudspeakers US2002 / 006208A1 and JP3919695B2 are obtained in an assembly process that cannot be miniaturized in an obvious way to obtain a MEMS loudspeaker. In particular, the intended clamping of the membrane in a two-part side frame, the structured attachment of multiple electrodes to the peaks and valleys of the membrane, or the connection of the electrodes to the electrode cables in the side frame cannot be transferred to a MEMS process.

[0016] Therefore, in view of the shortcomings of the prior art, there is a need for alternative or improved solutions for MEMS based speakers.

[0017] Purpose of the Invention

[0018] The object of the present invention is to provide a MEMS transducer, in particular a MEMS loudspeaker or a MEMS microphone, and a method for manufacturing a MEMS transducer, which do not have the disadvantages of the prior art. In particular, it is an object of the present invention to provide a high-performance MEMS loudspeaker or a MEMS microphone having a high sound quality or audio quality, while being characterized by a simple, inexpensive and compact design. Summary of the invention

[0019] This object is solved by a MEMS transducer for interacting with a volume flow of a fluid and a method for manufacturing a MEMS transducer according to the present application.Preferred embodiments of the present invention are described below.

[0020] The present invention preferably relates to a MEMS transducer for interacting with a volume flow of a fluid, comprising:

[0021] - a carrier,

[0022] - a vibratable membrane for generating or receiving pressure waves of a fluid in a vertical direction, the vibratable membrane being supported by a carrier

[0023] and wherein the vibratable membrane has two or more vertical portions, the two or more vertical portions being formed substantially parallel to the vertical direction and comprising at least one layer of actuator material, at least one end of the vibratable membrane being connected to at least one electrode,

[0024] Such that by driving at least one electrode, two or more vertical portions can be induced to vibrate substantially horizontally, or such that when two or more vertical portions are induced to vibrate substantially horizontally, an electrical signal can be generated at at least one electrode.

[0025] Particularly preferably, the MEMS transducer may be a MEMS speaker. In a particularly preferred embodiment, the present invention relates to a MEMS speaker comprising

[0026] - a carrier,

[0027] - a vibratable membrane for generating sound waves in a vertical emission direction, the vibratable membrane being supported by a carrier,

[0028] The vibrating membrane has two or more vertical parts, which are formed substantially parallel to the emission direction and include at least one layer of actuator material, and at least one end of the vibrating membrane is preferably connected to at least one electrode so that the two or more vertical parts can be induced to produce substantially horizontal vibrations by driving the at least one electrode.

[0029] This design of the MEMS speaker can realize a MEMS speaker with high acoustic power and simplified control.

[0030] Unlike known planar MEMS loudspeakers, the vibratable membrane itself does not need to operate over a large area of ​​several square centimeters or with a displacement greater than 100 μm to generate sufficient sound pressure. Instead, multiple vertical sections of the vibratable membrane can move the enlarged total volume with small horizontal or lateral movements of a few microns in the vertical emission direction.

[0031] Compared to the solution according to US 2018 / 0179048 A1 or Kaiser et al. from 2009, the claimed MEMS loudspeaker is characterized by a simplified structure, control and manufacturing process.

[0032] In particular, vertical foils or bending actuators are complex for MEMS loudspeakers according to Kaiser et al., 2009. Furthermore, sufficiently precise vertical etching is only possible for limited foil heights, which limits the acoustic power.

[0033] By means of the solution according to the invention, the vertical parts of the vibrating membrane can be realized in a MEMS design alternatively by simple manufacturing steps, as will be explained in detail below. Furthermore, the actuator principle according to the invention avoids the pulling in or sticking of the vertical parts. In contrast to the solution of Kaiser et al. in 2009, the one-sided electrodes do not obtain a potential difference in the gap between the vertical parts. In addition to avoiding overvoltages or pull-in, this can also reduce dust accumulation, since, for example, the outer electrodes can be placed at ground potential.

[0034] Another particular advantage of the MEMS loudspeaker is the simplified drive. While in US 2019 / 0116417A1 multiple piezoelectric actuators must be connected at the horizontal part, the proposed MEMS loudspeaker can be driven by at least one end-side electrode. This reduces manufacturing costs, minimizes error sources, and also inherently leads to synchronous control of the vertical part to produce horizontal vibrations.

[0035] In this way, the air volume present between the vertical parts can be moved very precisely by horizontal vibrations in the vertical emission direction. This results in improved sound, even at high sound power levels.

[0036] A "MEMS loudspeaker" preferably refers to a loudspeaker that is based on MEMS technology and whose sound generating structure at least partially has dimensions in the micrometer range (1 μm to 1000 μm). Preferably, for example, the vertical part of the vibrating membrane can have dimensions in the range of less than 1000 μm in terms of width, height and / or thickness. Here, it can also be preferred that, for example, only the height of the vertical part has a dimension in the micrometer range, while for example the length can have a larger dimension and / or the thickness can have a smaller dimension.

[0037] Advantageously, the design of the vibratable membrane can not only be used to form a MEMS loudspeaker with high acoustic power and simplified control, but also, for example, makes it possible to provide a particularly powerful MEMS microphone with high audio quality.

[0038] Therefore, in a preferred embodiment, the present invention also relates to a MEMS microphone, comprising

[0039] - a carrier,

[0040] - a vibratable membrane for receiving sound waves in a vertical emission direction, the vibratable membrane being supported by a carrier,

[0041] And wherein the vibrating membrane has two or more vertical portions, the two or more vertical portions are formed parallel to the vertical direction and include at least one layer of actuator material, wherein at least one end of the vibrating membrane is preferably connected to at least one electrode so that an electrical signal can be generated at the at least one electrode when the two or more vertical portions are induced to vibrate horizontally.

[0042] The design of a MEMS microphone is structurally similar to that of a MEMS loudspeaker, particularly in terms of the design of the vibrating membrane. Instead of driving electrodes to produce horizontal vibrations and thus sound pressure waves, a MEMS microphone is designed to receive sound pressure waves in the same vertical direction. Preferably, there is an air volume between the vertical parts, which moves in the vertical detection direction when sound waves are received. The sound pressure waves induce horizontal vibrations in the vertical parts, causing the actuator material to generate a corresponding periodic electrical signal.

[0043] A "MEMS microphone" preferably refers to a microphone that is based on MEMS technology and whose sound receiving structure at least partially has dimensions in the micrometer range (1 μm to 1000 μm). Preferably, for example, the vertical part of the vibrating membrane can have dimensions in the range of less than 1000 μm in terms of width, height and / or thickness. Here, it can also be preferred that, for example, only the height of the vertical part has a dimension in the micrometer range, while for example the length can have a larger dimension and / or the thickness can have a smaller dimension.

[0044] Therefore, the term MEMS transducer refers to MEMS microphones and MEMS speakers. In general, a MEMS transducer refers to a transducer for interacting with a volume flow of a fluid, the transducer being based on MEMS technology and having a structure having dimensions in the micrometer range (1 μm to 1000 μm) for interacting with the volume flow or for receiving or generating pressure waves of the fluid. The fluid can be a gaseous fluid as well as a liquid fluid. The structure of the MEMS transducer, in particular the vibrating membrane, is designed to generate or receive pressure waves of the fluid.

[0045] For example, in the case of a MEMS loudspeaker or a MEMS microphone, this may be related to acoustic pressure waves. However, a MEMS transducer may be equally suitable as an actuator or sensor for other pressure waves. Thus, a MEMS transducer is preferably a device that converts pressure waves (e.g., an acoustic signal as an acoustic pressure wave) into an electrical signal or vice versa (converts an electrical signal into a pressure wave, such as an acoustic signal).

[0046] It is also possible to apply MEMS transducers as energy harvesters using pneumatic or hydraulic alternating pressure. In these cases, the electrical signal can be dissipated, stored or provided to other (consuming) devices as recovered electrical energy.

[0047] The end side preferably refers to an end of a vibrating membrane at which at least one electrode is located so that a connection can be established with an electronic system, for example, in the case of a MEMS loudspeaker, to a current source or a voltage source, preferably at one end of the membrane suspended from a carrier. An electrode preferably refers to an area made of a conductive material, preferably a metal, which is suitable for establishing a connection with an electronic system, for example, a current source and / or a voltage source in the case of a MEMS loudspeaker. Preferably, the material may be an electrode pad. Particularly preferably, the electrode pad is used to establish a connection with the electronic system and is itself connected to a conductive metal layer, which conductive metal layer may extend over the entire surface of the vibrating membrane. In the following, the conductive layer is referred to as an electrode together with the electrode pad to a certain extent, for example as a top electrode or a bottom electrode.

[0048] Particularly preferably, the layer of conductive material, preferably metal, is present as a continuous or full-surface or coherent layer of the vibrating membrane in the sense of the top or bottom electrode, which forms a substantially uniform surface and is in particular unstructured. Instead, two or more vertical sections are connected to the end electrodes or electrode pads, preferably via a layer of unstructured conductive material, preferably metal.

[0049] Advantageously, in particular, it is not necessary to create separate connection areas for different vertical sections of the vibratable membrane. In contrast to the methods for macroscopic piezoelectric loudspeakers according to US 2002 / 006208 A1 and JP 3919695 B2, the attachment of a structured top or bottom electrode is not necessary. Instead, the top or bottom electrode can be applied in each case as a continuous layer of conductive material, which is connected via at least one end-side electrode or electrode pad. The manufacturing process is thus significantly simplified and allows miniaturized MEMS transducers to be provided in large quantities by a batch process.

[0050] In a preferred embodiment, the MEMS transducer comprises two end side electrodes. Preferably, by connecting to an electronic system, for example, a current source or a voltage source can be established with electrodes at opposite ends of the vibratable membrane, between which there are two or more vertical sections, so that the (one or more) actuator layers in the vertical sections can be driven by the end side electrodes.

[0051] The end-side arrangement of electrodes is therefore preferably distinguished from the means of connection which actuate the respective vertical part with the respective independent electrode or, in the case of a MEMS microphone, receives the generated electrical signal. Preferably, the MEMS transducer therefore comprises exactly one or exactly two electrodes for the end-side connection and no further electrodes / electrode pads for connecting the central vertical part.

[0052] Preferably, the layer of actuator material in the vertical portion is used as a mechanical biomorphic component, wherein the lateral curvature of the vertical portion is induced by driving the actuator layer via electrodes, or wherein a corresponding electrical signal is generated by the induced lateral curvature.

[0053] In a preferred embodiment, two or more vertical sections have at least two layers, one of which comprises an actuator material and a second layer comprises a mechanical support material, and wherein at least the layer comprising the actuator material is connected to the end-side electrodes, so that horizontal vibrations 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., piezoelectric material) and a passive layer serving as a mechanical support layer. Both transverse and longitudinal piezoelectric effects can be used for bending.

[0054] When the actuator layer is driven, it can, for example, experience lateral or longitudinal tension or compression. This creates a stress gradient relative to the mechanical support layer, resulting in lateral curvature or vibration. Figure 1 As shown, alternating polarity at the electrodes can preferably result in a push-pull operation, whereby, alternately, almost the entire air volume between the vertical sections can be moved in the vertical emission direction.

[0055] The advantage of the actuator principle is therefore the efficient conversion of horizontal vibrations of the vertical part into vertical volume movement or sound generation.

[0056] Since the actuator principle is not based on electrostatic attraction, but on a relative change of shape of the actuator layer relative to the supporting layer (e.g. compression, tension, shear), adhesion of the membrane parts can be excluded. Instead, the vertical parts can be in contact with each other, so their displacement is not restricted.

[0057] In a further preferred embodiment, the two or more vertical sections comprise at least two layers, wherein both layers comprise actuator material and are connected to respective end-side electrodes, and horizontal vibrations can be generated by changing the shape of one layer relative to the other layer. In this embodiment, the horizontal vibrations of the vertical sections are therefore not generated by a stress gradient between the active actuator layer and the passive support layer, but by a relative change in the shape of the two active actuator layers.

[0058] The actuator layers can be made of the same actuator material and can be driven differently. The actuator layers can also be made of different actuator materials, for example of piezoelectric materials with different deformation coefficients.

[0059] Within the meaning of the present invention, a "layer comprising actuator material" is preferably also referred to as actuator layer. An actuator material preferably refers to a material which undergoes a shape change, such as stretching, compression or shearing, when a voltage is applied, or conversely generates a voltage when its shape changes.

[0060] Preferred materials are those having an electric dipole which undergoes a shape change upon application of a voltage, wherein the orientation of the dipole and / or the electric field may determine the preferred direction of the shape change.

[0061] Preferably, the actuator material may be a piezoelectric material, a polymer piezoelectric material and / or an electroactive polymer (EAP).

[0062] Particularly preferably, the piezoelectric material is selected from the group consisting of lead zirconate titanate (PZT), aluminum nitride (AlN), aluminum scandium nitride (AlScN) and zinc oxide (ZnO).

[0063] The polymer piezoelectric material preferably comprises a polymer having an internal dipole and thus imparting piezoelectric properties. This means that when an external voltage is applied, the piezoelectric polymer material (in a manner similar to the classical piezoelectric materials described above) undergoes a change in shape (e.g. compression, stretching or shearing). An example of a preferred piezoelectric polymer material is polyvinylidene fluoride.

[0064] Thus, a macroscopic solution can be achieved, in which a polymer piezoelectric material layer is arranged on a mechanical support layer and is wound on an upper comb part and a lower comb part. Preferably, a polymer piezoelectric material layer (including electrodes) is first provided on a support layer (possibly including a counter electrode). Subsequently, the upper comb part and the lower comb part (preferably a MEMS structure) are moved against each other so that a folded membrane with an actuable vertical part is formed.

[0065] Within the meaning of the present invention, a "layer comprising a mechanical support material" is preferably also referred to as a support layer. The mechanical support material or support layer preferably serves as a passive layer that can resist shape changes of the actuator layer. Unlike the actuator layer, the mechanical support material preferably does not change shape when a voltage is applied. Preferably, the mechanical support material is electrically conductive, so that it can also be used directly to contact the actuator layer. However, in some embodiments, it can also be non-conductive and, for example, coated with an electrically conductive layer.

[0066] Particularly preferably, the mechanical support material is monocrystalline silicon, polycrystalline silicon or doped polycrystalline silicon.

[0067] While the actuator layer changes shape when a voltage is applied, the layer of mechanical support material remains essentially unchanged. The stress gradient generated between the two layers (mechanical bimorph) preferably results in a horizontal curvature. For this purpose, the thickness of the support layer is preferably selected in such a way that a sufficiently large stress gradient is generated for the curvature compared to the thickness of the actuator layer. For doped polysilicon and piezoelectric materials such as PZT or AlN as mechanical support material, for example, substantially equal thicknesses (preferably between 0.5 μm and 2 μm) have proven to be particularly suitable.

[0068] 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 in particular less than ±1%. The indications of substantially, approximately, about, etc. also always disclose and include the exact value mentioned.

[0069] By driving the actuator layer periodically, for example by an AC voltage, horizontal vibrations can be generated quickly and precisely for sound emission.

[0070] To ensure horizontal vibration, the piezoelectric material may preferably have a c-axis orientation perpendicular to the surface of the vertical portion, thereby utilizing the transverse piezoelectric effect. Other orientations, for example, use the longitudinal piezoelectric effect to create horizontal curvature or vibration (see Figure 1 ) may also be preferred.

[0071] The electrical connection of the actuator layer and / or the layer of mechanical support material and thus the application of the voltage can take place directly via the end-side electrodes or with the aid of a layer of conductive material.

[0072] Therefore, in a preferred embodiment, the vibratable membrane comprises at least one layer of conductive material.

[0073] In a preferred embodiment, the conductive material is selected from the group consisting of platinum, tungsten, (doped) tin oxide, single crystal silicon, polycrystalline silicon, molybdenum, titanium, tantalum, titanium-tungsten alloys, metal silicides, aluminum, graphite and copper.

[0074] The vertical and horizontal (or lateral) directional indications preferably refer to the preferred directions in which the vibratable membrane is oriented for generating or receiving pressure waves of a fluid. Preferably, the vibratable membrane is suspended horizontally between at least two side regions of the carrier, and the vertical direction (direction of interaction with the fluid) for generating or receiving pressure waves is orthogonal thereto. In the case of a MEMS speaker, the (interaction) vertical direction corresponds to the vertical sound emission direction of the MEMS speaker. In this case, vertical preferably refers to the direction of sound emission, while horizontal refers to the direction orthogonal thereto. In the case of a MEMS microphone, the (interaction) vertical direction corresponds to the vertical direction of sound detection by the MEMS microphone. In this case, vertical preferably refers to the direction of sound detection or recording, while horizontal refers to the direction orthogonal thereto.

[0075] Therefore, the vertical portion of the vibratable membrane preferably refers to the portion of the vibratable membrane that is substantially oriented in the emission direction of the MEMS speaker or the detection direction of the MEMS microphone. A person skilled in the art understands that it does not need to be an exact vertical alignment, but preferably, the vertical portion of the vibratable membrane is substantially aligned in the emission direction of the MEMS speaker or the detection direction of the MEMS microphone.

[0076] In a preferred embodiment, the vertical portion is oriented substantially parallel to the vertical direction, wherein substantially parallel refers to a tolerance range of ±30°, preferably ±20°, more preferably ±10° with respect to the vertical direction.

[0077] Therefore, the vibratable membrane may preferably have not only a rectangular meander-shaped cross section but also a curved or wavy or sawtooth (zigzag) shape.

[0078] Preferably, the vertical and / or horizontal sections are straight at least partially or over their entire length, but the vertical and / or horizontal sections may also be curved at least partially or over their entire length. In case the cross section of the vibratable membrane is curved or wavy, the alignment preferably refers to the tangent of the curved vertical and / or horizontal sections at their respective midpoints.

[0079] Although the vibratable membrane is preferably horizontal to the direction of sound emission or sound detection, sound waves are generated by driving the vertical part (or detected vice versa).

[0080] In a preferred embodiment of the invention, the carrier comprises two side regions, between which the diaphragm is arranged in horizontal direction.

[0081] The carrier is preferably a frame structure, which is essentially formed by a continuous outer boundary in the form of a side wall of the area remaining free. The frame structure is preferably stable and resistant to bending. In the case of an angular frame shape (triangular, quadrilateral, hexagonal or generally polygonal profile), the individual side areas that preferably essentially form the frame structure are particularly referred to as side walls.

[0082] The vibratable membrane is preferably held by at least two side walls of the carrier. Figure 1-Figure 9 In the example above, you can see cross sections of the two side walls.

[0083] However, preferably, the preferred carrier comprises four side regions, wherein the additional end faces are generally parallel to the drawn cross-section. These additional two side walls span the frame structure.

[0084] The vibratable membrane is preferably suspended in a planar manner within the free area. The planar extension of the vibratable membrane represents the horizontal direction, while the vertical part is substantially orthogonal thereto. With respect to the end faces, the membrane can be bonded to these side walls or slotted there to obtain greater mobility. Advantageously, the slot can represent a dynamic high-pass filter, which for example couples the front volume and the rear volume.

[0085] In a preferred embodiment of the invention, the carrier is formed by a substrate, which is preferably selected from single crystal silicon, polycrystalline silicon, silicon dioxide, silicon carbide, silicon germanium, silicon nitride, nitride, germanium, carbon, gallium arsenide, gallium nitride, indium phosphide and glass.

[0086] These materials are easy and inexpensive to process in semiconductor and / or microsystem manufacturing and are suitable for large-scale manufacturing. The carrier structure can be flexibly manufactured based on the material and / or manufacturing method. In particular, the MEMS transducer including the vibrating membrane and the carrier can preferably be manufactured in one (semiconductor) process, preferably on a wafer. This further simplifies the manufacturing process and reduces costs, so that a compact and robust MEMS transducer can be provided at low cost.

[0087] In a preferred embodiment, the vibratable membrane is formed of a layered structure or a meandering structure. Preferably, the specification of the layered or meandering structure refers to the shape of the cross section of the vibratable membrane.

[0088] The layered structure preferably refers to an arrangement similar to parallel layers, which preferably form a vertical section. The individual sheets are preferably oriented so that their surfaces are substantially parallel to the vertical direction, preferably parallel to the direction of emission or detection. Preferably, the sheets are multilayered and form a mechanical biomorphology. For example, the sheets can each include an actuator layer and a passive layer made of a supporting material and / or two differently controllable actuator layers.

[0089] Those skilled in the art understand that the sheet does not have to be aligned exactly parallel to the vertical direction, but the sheet is preferably aligned substantially in the emission direction of the MEMS speaker or the detection direction of the MEMS.

[0090] In a preferred embodiment, the vertical sections or lamellae are oriented substantially parallel to the vertical direction, wherein substantially parallel means a tolerance range of ±30°, preferably ±20°, particularly preferably ±10° with respect to the vertical direction.

[0091] It may be preferred that the flakes are planar, which means in particular that they extend in each of the two dimensions of their plane (height, width) greater than in the dimension perpendicular to said dimensions (thickness). For example, a size ratio of at least 2:1, preferably at least 5:1, 10:1 or more may be preferred.

[0092] Preferably, the vibratable membrane has a plurality of lamellae forming a vertical portion. For example, 2, 3, 4, 5, 10, 15, 20, 30, 40, 50 or more lamellae may be preferred. This achieves a high degree of efficiency in sound emission or sound detection required in confined spaces.

[0093] In an embodiment, preferably, the vibratable membrane is formed of a sheet as vertical parts, which are connected to each other via conductive bridges or horizontal parts. Suitable bridges are, for example, metal bridges (see Fig.10 ) or a bridge made of other conductive materials. The conductive bridge ensures the mechanical integrity of the vibrating membrane on the one hand. On the other hand, the conductive bridge advantageously allows all the sheets to be connected via the end electrodes. Advantageously, the sheets can thus be driven synchronously to generate horizontal vibrations or to detect horizontal vibrations with minimal control and manufacturing complexity.

[0094] A meandering structure preferably refers to a structure formed by a series of parts whose cross sections are essentially orthogonal to each other. The mutually orthogonal parts are preferably vertical parts and horizontal parts of the vibrating membrane. Particularly preferably, the cross section of the meandering structure is rectangular. However, it may also be preferred that the cross section of the meandering structure is sawtooth-shaped (zigzag) or curved or wavy. This is especially true if the vertical part is not aligned completely parallel to the vertical direction of emission or detection, but forms an angle of, for example, ±30°, preferably ±20°, particularly preferably ±10° with the vertical direction.

[0095] In a preferred embodiment, the horizontal portion may also be completely orthogonal to the vertical direction of emission or detection at an angle of 90°, but may, for example, form an angle with the vertical direction between 60° and 120°, preferably between 70° and 110°, particularly preferably between 80° and 100°.

[0096] In case the vertical and / or horizontal portions of the vibratable membrane are curved or wavy in cross-section, alignment preferably means being tangential to the vertical and / or horizontal portions at their respective midpoints.

[0097] The meandering structure thus preferably corresponds to a membrane that is folded along its width. Within the meaning of the present invention, the vibrating membrane can therefore also preferably be referred to as a bellows. The parallel folds of the bellows preferably form vertical sections. The connecting sections between the folds preferably form horizontal sections. Preferably, the vertical sections are longer than the horizontal sections, for example 1.5, 2, 3, 4 or more times longer.

[0098] The vertical parts are decisive for the function of the vibratable membrane in a meandering form for generating or receiving sound waves, in a manner similar to the above-described thin sheets. Preferably, the vertical parts are multilayered and form a mechanical biomorphic form. For example, the vertical parts can each comprise an actuator layer and a passive layer made of a supporting material and / or two differently controllable actuator layers. Preferably, the horizontal parts of the folded membrane can be constructed identically to the vertical parts (see in particular Figure 3-Figure 7 ). However, it is also preferred that the horizontal part - in contrast to the vertical part - has no actuator layer, but only a mechanical support layer and / or an electrically conductive layer.

[0099] In a preferred embodiment, the at least one layer of actuator material of the vibratable membrane is a continuous layer. Continuous preferably means without interruptions in the cross-sectional profile. It is therefore preferred in the described embodiment that a continuous layer of actuator material is present in both the vertical and horizontal parts. Advantageously, no structuring is required. A continuous layer is particularly easy to manufacture and ensures synchronous driving during operation of the MEMS loudspeaker.

[0100] The performance of a MEMS transducer, in particular a MEMS loudspeaker or a MEMS microphone, may be significantly determined by the number and / or size of the vertical sections.

[0101] In preferred embodiments, the vibratable membrane comprises more than 3, 4, 5, 10, 15, 20, 30, 40, 50, 100 or more vertical portions.

[0102] In preferred embodiments, the vibratable membrane comprises less than 10,000, 5,000, 2,000 or 1,000 or fewer vertical sections.

[0103] The preferred number of vertical sections produces high acoustic power on a minimal chip surface without sacrificing sound quality or audio quality.

[0104] Preferably, the vertical portions are planar, in particular meaning that they extend in each of the two dimensions of their plane (height, width) greater than in the dimension perpendicular to said dimensions (thickness). For example, a size ratio of at least 2:1, preferably at least 5:1, 10:1 or more may be preferred.

[0105] Within the meaning of the invention, the height of the vertical portion preferably corresponds to a dimension along the direction of sound emission or sound detection, while the thickness of the vertical portion preferably corresponds to the sum of the layer thicknesses of one or more layers forming the vertical portion. The length of the vertical portion preferably corresponds to a dimension orthogonal to the height or thickness. In the cross-sectional views of the accompanying drawings of the following figures, the height and thickness are shown schematically (not necessarily to scale), while the length dimension corresponds to the (invisible) drawing depth of the accompanying drawings.

[0106] In a preferred embodiment, the height of the vertical portion is between 1 μm and 1000 μm, preferably between 10 μm and 500 μm. Intermediate ranges of the above ranges may also be preferred, such as 1 μm to 10 μm, 1 μm to 50 μm, 50 μm to 100 μm, 100 μm to 200 μm, 200 μm to 300 μm, 300 μm to 400 μm, 400 μm to 500 μm, 600 μm to 700 μm, 700 μm to 800 μm, 800 μm to 900 μm, or even 900 μm to 1000 μm. Those skilled in the art will recognize that the above range limits may also be combined to obtain other preferred ranges, such as 10 μm to 200 μm, 50 μm to 300 μm, or even 100 μm to 600 μm.

[0107] In a preferred embodiment, the thickness of the vertical portion is between 100 nm and 10 μm, preferably between 500 nm and 5 μm. Intermediate ranges of the above ranges may also be preferred, such as 100 nm to 500 nm, 500 nm to 1 μm, 1 μm to 1.5 μm, 1.5 μm to 2 μm, 2 μm to 3 μm, 3 μm to 4 μm, 4 μm to 5 μm, 5 μm to 6 μm, 6 μm to 7 μm, 7 μm to 8 μm, 8 μm to 9 μm, or even 9 μm to 10 μm. Those skilled in the art will recognize that the above range limits may also be combined to obtain other preferred ranges, such as 500 nm to 3 μm, 1 μm to 5 μm, or even 1500 nm to 6 μm.

[0108] In a preferred embodiment, the length of the vertical portion is between 10 μm and 10 mm, preferably between 100 μm and 1 mm. Intermediate ranges of the above ranges may also be preferred, such as 10 μm to 100 μm, 100 μm to 200 μm, 200 μm to 300 μm, 300 μm to 400 μm, 400 μm to 500 μm, 500 μm to 1000 μm, 1 mm to 2 mm, 3 mm to 4 mm, 4 mm to 5 mm, 5 mm to 8 mm, or even 8 mm to 10 mm. Those skilled in the art will recognize that the above range limits may also be combined to obtain other preferred ranges, such as 10 μm to 500 μm, 500 μm to 5 μm, or even 1 mm to 5 mm.

[0109] By means of the above-mentioned preferred dimensions of the vibratable membrane and the vertical part, a particularly compact MEMS transducer, in particular a MEMS loudspeaker or a MEMS microphone, may be provided which combines high performance with excellent sound quality or audio quality.

[0110] In a preferred embodiment of the invention, the vibratable membrane is formed by a meandering structure having alternating vertical and horizontal sections, wherein a retaining structure is attached to at least two of the horizontal sections, the retaining structure being directly or indirectly connected to the carrier. For example, the retaining structure may be provided by the substrate material of the carrier, i.e. the retaining structure may be formed directly by the substrate of the bottom wafer. Alternatively, the retaining structure may also be connected to the horizontal sections as a separate ridge or ridge of the top wafer.

[0111] The holding structure may preferably be present on one and / or both sides of the vibratable membrane, ie preferably on the upper horizontal part and / or on the lower horizontal part.

[0112] Particularly when suspending a larger vibratable membrane between the side walls of a carrier, the use of a retaining structure advantageously allows stabilization without negatively affecting sound generation or sound capture.

[0113] Since the horizontal parts of the meandering shape are at least substantially mechanically neutral, locking them by means of the retaining structure advantageously does not lead to any undesired stresses between the membrane and the retaining structure or the carrier.

[0114] Different layers may be provided for the structure of the vibratable membrane to ensure said driving and sensing of horizontal vibrations or detection thereof.

[0115] The connection of one or more actuator layers and / or one or more layers of mechanical support material, and thus the application or detection of voltage, can be effected directly via end-side electrodes or assisted by a layer of conductive material.

[0116] Therefore, in a preferred embodiment, the vibratable membrane comprises at least one layer of conductive material.

[0117] In a preferred embodiment, the conductive material is selected from the group consisting of platinum, tungsten, (doped) tin oxide, single crystal silicon, polycrystalline silicon, molybdenum, titanium, tantalum, titanium-tungsten alloys, metal silicides, aluminum, graphite and copper.

[0118] In a preferred embodiment, the vibratable membrane comprises three layers, an upper layer formed of a conductive material and connected to an upper electrode, a middle layer formed of an actuator material, and a lower layer formed of a conductive material.

[0119] Preferably, the conductive material of the upper and / or lower layer can be a mechanical support material, so that this layer has a dual function. On the one hand, this layer ensures that the actuator layer is connected to the potential that can be applied to the end-side electrodes. On the other hand, it acts as a mechanical support layer in the manner described to generate horizontal curvature or vibrations when the actuator layer is driven accordingly.

[0120] Such an embodiment can be realized by simple manufacturing steps, such as Figure 2 The example in Figure 2 Part G, Figure 3 and Figure 4 In the preferred embodiment shown, the vibratable membrane has a meandering structure with a continuous top layer of conductive material (metal), a continuous middle layer of actuator material and a bottom layer of conductive mechanical support material. It is also possible to provide a reverse order of layers or another additional conductive layer in contact with the mechanical support layer and / or the actuator layer to improve the connection.

[0121] In another preferred embodiment, the vibrating membrane comprises two layers of actuator material, which are separated by an intermediate layer of conductive material (preferably metal), wherein the intermediate layer is connected to the first electrode and at least one of the two layers of actuator material is connected to the second electrode via another layer of conductive material (preferably metal).

[0122] As described above, in a preferred embodiment, two actuator layers can also be used, for example to move the vertical part in a horizontal vibration by different drivers. In order to transmit the potential changes from the end-side electrodes to the corresponding actuator layer, two or more intermediate layers of conductive material can preferably be provided. Preferably, the layer of conductive material, for example a metal, is in this case preferably used exclusively for connection and does not serve as a mechanical support layer. The stresses required to induce the curvature or vibration in the sense of the bimorph of the MEMS loudspeaker are themselves induced by different control of the actuator layers themselves.

[0123] Preferably, the layer of conductive material such as metal can thus be made particularly thin (less than 500 nm, preferably less than 200 nm).

[0124] Figure 5An example of such a preferred embodiment is shown. This example has a vibrating membrane as a meandering structure with two layers of actuator material separated by an intermediate layer of conductive material (metal). The intermediate layer is connected to a first end-side electrode pad, while the upper actuator layer is connected to a second end-side electrode via a further layer of conductive material. The layer of lower conductive material is not connected to any of the electrodes. It is also possible to provide the layers in the opposite order or to omit the layer of lower conductive material which is not in contact with the electrodes.

[0125] In the above embodiment, it is preferred that the (one or more) actuator layers and (if applicable) the mechanical support layer are continuous, that is, the cross-section extends from one end of the membrane (where the first electrode is preferably present) through several alternating horizontal and vertical parts to the second end of the membrane (where the second electrode is preferably present).

[0126] The inventors have realised that for the working principle of a MEMS transducer, preferably a MEMS loudspeaker, it is sufficient to provide a mechanical biomorphic form in a vertical cross section.

[0127] In a preferred embodiment, at least one actuator layer is not continuous but is present only in the vertical parts and not in the horizontal parts. In this case, it is preferred for the mechanical support layer, if present, to extend continuously or discontinuously and, for example, to be arranged only in the vertical parts. In order to be able to connect the vertical parts by end-side electrodes, one or more continuous layers of conductive material, preferably metal, are preferably applied.

[0128] Figure 7 A preferred manufacturing process for an embodiment with a non-continuous actuator layer is shown. Here, a selective spacer etching of the actuator layer can be performed in the horizontal parts so that only the vertical parts of the membrane have a layer of actuator material. The continuous layer of mechanical support material can be a dielectric at the same time to avoid short circuits between the upper and lower conductive layers (also called top and bottom electrodes).

[0129] This embodiment is characterized by particularly efficient actuation and high performance, wherein only the vertical sections are induced to undergo alternating bending or vibrations, while the horizontal sections remain mechanically neutral. Advantageously, the displacement volume can be further increased in each actuation phase.

[0130] In the above-described embodiments, the vibratable membrane in the form of a meander is preferably realized by applying or etching a suitable functional layer.

[0131] Alternatively, the vibratable membrane can also be manufactured by providing vertical parts and connecting them using metal bridges.

[0132] In a preferred embodiment, the vertical portions of the vibratable membrane comprise two layers, wherein a first layer comprises the actuator material and a second layer comprises the flexible support material, and wherein the vertical portions are connected by horizontal metal bridges.

[0133] like Fig.10 As shown, several individual piezoceramic elements can be preferably provided for this purpose, the piezoceramic elements comprising a layer of mechanical support material and a layer of piezoelectric material as well as a sacrificial layer. Through a plurality of process steps including interlayer connection and metal filling as well as stacking and cutting of the piezoceramic elements, a membrane with high efficiency can advantageously be obtained in a robust and process-efficient manner.

[0134] In this embodiment, no continuous, uniform conductive layer is required. Instead, the connection of the actuator layer in the vertical sections is ensured by metal bridges and conductive mechanical support material.

[0135] In a preferred embodiment, the vibratable membrane is coated with a layer of non-adhesive material. Non-adhesive materials are in particular materials with low surface energy, which are largely inert to the environment and thus prevent the deposition of dust or other undesirable particles. For example, the non-adhesive material can be formed by a carbon layer, such as a diamond-like carbon (DLC) layer or a layer comprising perfluorocarbons (PFCs), such as polytetrafluoroethylene (PTFT).

[0136] In a preferred embodiment of the present invention, the MEMS transducer (preferably a MEMS speaker) comprises a control unit configured to drive at least one electrode so that two or more vertical portions are induced to produce horizontal vibrations. Preferably, the control unit is configured to drive the electrodes to ensure that the frequency of the horizontal vibrations is between 10 Hz and 20 kHz.

[0137] In a preferred embodiment of the invention, the MEMS transducer, preferably a MEMS microphone, comprises a control unit configured to detect an electrical signal provided by at least one electrode, said electrical signal having been generated by horizontal vibrations of two or more vertical portions. Preferably, the control unit of the MEMS microphone is configured to receive and process electrical signals corresponding to frequencies of horizontal vibrations between 10 Hz and 20 kHz, and is therefore suitable for sound detection in the audible range.

[0138] Therefore, the control unit is preferably configured and adapted to drive the vibratory membrane (or (one or more) actuator layers in the vertical part) by electrical signals to produce horizontal vibrations and sound emissions in the audible frequency range, or to receive and process the corresponding electrical signals when the vibratory membrane is driven.

[0139] Preferably, in the case of a MEMS speaker, the vertical part of the membrane is driven directly by the audio signal. Compared to the combined drive separation membrane unit and multiple valves according to US2019 / 0116417A1, the drive for sound generation is thus significantly simplified.

[0140] For generating or receiving electrical signals, the control unit may preferably comprise a data processing unit.

[0141] Within the meaning of the present invention, a data processing unit preferably refers to a unit adapted and configured for receiving, transmitting, storing and / or processing data (preferably in terms of driving electrodes or receiving electrical signals provided at electrodes). The data processing unit preferably comprises: an integrated circuit for processing data, and for example an application specific integrated circuit, a processor, a processor chip, a microprocessor or a microcontroller; and optionally a data memory, a random access memory (RAM), a read-only memory (ROM) or a flash memory for storing data.

[0142] In a preferred embodiment, the control unit is integrated with the other components of the MEMS transducer (carrier, vibrating membrane) on a printed circuit board or circuit board. This means that there is preferably a seamless integration of the MEMS transducer with the electronic systems necessary for driving or detecting. In addition to the control unit, other electronic components, such as communication interfaces (preferably wireless, such as Bluetooth), amplifiers, filters or sensor systems, can also be mounted on the same printed circuit board.

[0143] Advantageously, a compact overall solution is achieved, wherein a MEMS transducer, preferably a MEMS speaker or a MEMS microphone, and the desired electronic system can be provided in a confined space, and preferably with low-cost CMOS processing suitable for mass production.

[0144] In a further preferred embodiment, the vibratable membrane held by the carrier is arranged on the front side of a housing which surrounds the rear resonance volume. Thus, the sound emission of such a MEMS loudspeaker is preferably directed towards the open front side (sound port), thereby improving the sound, in particular for lower frequencies, through the rear resonance volume.

[0145] In a further preferred embodiment, a vent is present in the housing for preventing acoustic short circuits and / or for supporting the sound. Compared to the sound port, the vent is preferably smaller and may, for example, have a maximum dimension of less than 100 μm, preferably less than 50 μm.

[0146] In another aspect, the present invention relates to a method for manufacturing a MEMS transducer as described above, preferably a MEMS loudspeaker or a MEMS microphone, the method comprising the following steps:

[0147] - etching the substrate preferably from the front side to form a structuring, the structuring preferably being a meandering structure

[0148] -Optionally apply etch stop

[0149] - applying at least two layers, wherein at least the first layer comprises the actuator material and the second layer comprises the mechanical support material, or at least two layers comprise the actuator material

[0150] - Connect the first layer and / or the second layer to the electrodes

[0151] - etching preferably from the back side and optionally removing the etch stop,

[0152] A vibratable membrane (preferably in the form of a meandering structure) is held by a carrier (4) formed by a substrate (8), the vibratable membrane (1) comprising at least two or more vertical portions (2) for generating or receiving pressure waves of a fluid in a vertical direction, the vertical portions being formed parallel to the vertical direction, and the two or more vertical portions being induced to generate horizontal vibrations by driving at least one electrode, or

[0153] Such that when the two or more vertical portions are induced to vibrate horizontally, an electrical signal may be generated at at least one electrode.

[0154] A person skilled in the art will recognize that the technical features, limitations and advantages of the preferred embodiments of the MEMS transducer (preferably a MEMS speaker or a MEMS microphone) are also applicable to the manufacturing process, and vice versa. Preferably, the manufacturing method is used to provide a MEMS transducer having a folded vibratable membrane with a curved structure. Figure 2 Section A to Figure 2 Part G, Figure 8 Section A to Figure 8 Part J or Fig. 9 Examples of preferred manufacturing steps are described in .

[0155] For example, one of the preferred materials mentioned above can be used as substrate. During etching, a blank (eg a wafer) can be formed into the desired basic shape of the meandering structure. In a next step, a layer for a vibratable membrane is preferably applied.

[0156] Applying at least one layer of conductive material preferably comprises applying several layers, in particular applying a layer system, in addition to applying one layer. The layer system comprises at least two layers applied relative to each other in a planned manner. The applied layer or layer system is preferably used to define a vibratable membrane comprising a vertical portion that can be induced to produce horizontal vibrations.

[0157] Preferably, the deposition can be selected from physical vapor deposition (PVD), in particular thermal evaporation, laser beam evaporation, arc evaporation, molecular beam epitaxy, sputtering, chemical vapor deposition (CVD) and / or atomic layer deposition (ALD). In particular, the deposition can include, for example, electroplating, for example in the case of a substrate made of polycrystalline silicon.

[0158] The etching and / or structuring can preferably be selected from the group of dry etching, wet chemical etching and / or plasma etching, in particular reactive ion etching, reactive ion deep etching (Bosch process).

[0159] In a preferred embodiment, the substrate is etched, preferably from the front side, to form the structured feature in that the substrate has a crystal structure and a plurality of grooves are formed by etching along the lattice vectors of the crystal structure. Preferably, the grooves are defined as parallel slits from the front side of the substrate. After application of the functional layer and appropriate backside treatment, the vibrating membrane is formed as a bellows having a meandering structure in cross section (see Figure 2 and Figure 8 wait).

[0160] Etching preferably along the orientation of the crystalline substrate can advantageously obtain smooth quasi-crystalline trenches with large depths greater than 200 μm, 300 μm, 400 μm, 500 μm or more with high precision orientation and negligible roughness.

[0161] It is also advantageous if the surface normals of the side faces of the trenches are also aligned with the crystal structure, preferably with orthogonal lattice vectors.

[0162] When a layer of actuator material, preferably piezoelectric material, is applied to such a structured substrate, the orientation of the actuator material can also be quasi-crystalline. In particular, piezoelectric materials such as AlN, AlScN or PZT advantageously exhibit columnar growth on the sidewalls of the trenches oriented in this way, which can ensure that the piezoelectric layer has a particularly precise c-axis orientation perpendicular to the surface of the vertical part of the resulting membrane.

[0163] Horizontal vibrations created by the transverse piezoelectric effect can therefore be particularly efficient and precise, and can provide improved sound in the case of a MEMS speaker, or detection capabilities in the case of a MEMS microphone.

[0164] In a preferred embodiment, the substrate is preferably etched from the front side to form a structured (preferably a meandering structure) characterized in that the substrate has a crystalline structure and the plurality of grooves along the lattice vectors are at least partially achieved by wet chemical etching, preferably performing anisotropic etching that depends on the crystal orientation.

[0165] Preferably, an etchant is used for this purpose which has significantly different etching rates in two orthorhombic crystal orientations relative to the crystal orientation of the substrate. For example, the etching rate for a substrate selected in a first crystal orientation may be 50, 10, 150, 200 or more times higher than the etching rate in a second crystal orientation orthogonal thereto.

[0166] Preferably, the substrate is oriented in such a way that the first crystal orientation in which the etching rate increases is aligned with the surface normal of the substrate surface. An etching mask can be used to define areas on the substrate surface that are not etched. Preferably, the etching mask can define a frame in which the grooves or strips for forming the grooves remain free. The remaining area between the parallel grooves to be formed can be used as a substrate for the horizontal portion of the membrane.

[0167] After anisotropic wet chemical etching, etching is preferentially performed perpendicular to the substrate surface to form deep vertical trenches. Etching in the orthogonal (horizontal) direction is thus reduced. The larger the anisotropy factor of the etching, which depends on the crystal orientation, the less pronounced the undercut.

[0168] For example, particularly good results can be obtained using potassium hydroxide (KOH) as an etchant for silicon crystal substrates. <110> Orientation and <111> The etching of orientation shows a clear preference for orientation. As shown by Sato et al. in 1988, KOH on silicon single crystals <110> The etching rate in the direction can be 1.455μm / min, which is higher than that in the orthogonal direction. <111> orientation (etching rate 0.005 μm / min) is 291 times higher.

[0169] Fig. 9 It is shown how proper alignment of silicon crystals can reliably produce almost perfectly smooth and deep trenches whose sides are crystallographically oriented to ensure c-axis-oriented growth of the piezoelectric material.

[0170] Those skilled in the art will appreciate that alternative crystal orientation dependent etchants, such as tetramethylammonium hydroxide (TMAH) (see, for example, Seidel et al., 1990), may be used equally.

[0171] Advantageously, the method is not only suitable for upscaling of mass production. Furthermore, the meander-shaped vibratable membranes that can be produced in this way are also characterized by a particularly precise alignment of the vertical sections, which leads to an improved vibration behavior and thus to an improved sound generation or sound detection.

[0172] If further structuring of the vibratable membrane is required, this can be carried out, for example, by further etching processes. Likewise, additional materials can be deposited or doped by conventional processes.

[0173] For connecting these layers, suitable materials such as copper, gold and / or platinum can be additionally deposited by conventional processes. Preferably, physical vapor deposition (PVD), chemical vapor deposition (CVD) or electrochemical deposition can be used for this purpose.

[0174] By these process steps, a finely structured vibratable membrane with the desired definition of vertical and horizontal parts can be provided, which is preferably suspended between two side areas of a stable carrier and has dimensions in the micrometer range. The manufacturing steps belong to standard process steps of semiconductor processes, so they are proven and more suitable for large-scale production.

[0175] In a further aspect, the invention therefore also relates to a MEMS transducer which can be manufactured by a manufacturing process as described above.

[0176] The person skilled in the art realizes that special features of the manufacturing steps, such as performing a crystal orientation-dependent etching to form deep grooves with quasi-crystalline smooth surfaces, are directly transferred to the structural features of the MEMS transducer. In the case of quasi-crystalline smooth surfaces on the sides of the grooves, a vibratable membrane with a plurality of vertical portions in the shape of meanders can be formed in a particularly precise manner, as described above. The c-axis orientation of the actuator material, preferably a piezoelectric material, can also result directly from the application of the preferred manufacturing steps.

[0177] In another aspect, the present invention relates to a method for manufacturing a MEMS transducer as described above, the method comprising the following steps:

[0178] - providing a plurality of individual piezoelectric ceramic elements, the piezoelectric ceramic elements comprising a sacrificial layer, a layer of conductive material, and a layer of piezoelectric material

[0179] -Define holes for interlayer connection and metal filling in piezoelectric ceramic elements

[0180] - stacking and optionally cutting the piezoelectric ceramic elements to obtain a stack of piezoelectric ceramic elements connected by metal bridges

[0181] - removing the sacrificial layer and inserting the stack of piezoceramic elements into a carrier, whereby the piezoceramic elements are each connected to one electrode,

[0182] A vibrating membrane, preferably in the form of a layered structure, is held by a carrier formed by a substrate, the vibrating membrane comprising at least two or more vertical portions to generate or receive pressure waves of a fluid in a vertical direction, the vertical portions being formed parallel to the vertical direction, and such that the two or more vertical portions can be induced to vibrate horizontally by driving at least one electrode, or such that an electrical signal can be generated at at least one electrode when the two or more vertical portions are induced to vibrate horizontally.

[0183] A person skilled in the art will recognize that the technical features, limitations and advantages of the preferred embodiments of the MEMS transducer (preferably a MEMS speaker or a MEMS microphone) are also applicable to the manufacturing process, and vice versa. Preferably, the manufacturing method is used to provide a MEMS transducer having a vibrating membrane of a layered structure, wherein the thin sheets are mechanical bimorphs and are bridged by metal. An example of a preferred manufacturing step is Fig.10 Sections A to F and Fig.11 Shown in.

[0184] In an alternative manufacturing process, several individual piezoelectric ceramic elements may advantageously be used, by defining holes, metal filling and stacking and cutting, to obtain a vibratable membrane with thin sheets as vertical parts connected by metal bridges.

[0185] A piezoelectric ceramic is preferably a ceramic material that exhibits charge separation under deformation by an external force or undergoes a change of shape when a voltage is applied. As described above, a piezoelectric ceramic element preferably comprises a piezoelectric layer and a layer of mechanical support material and further comprises a sacrificial layer.

[0186] The sacrificial layer is used to process and provide the metal bridge and will not itself be part of the vibratable membrane.

[0187] Preferably, the sacrificial layer can be, for example, a photoresist. These materials change their solubility when irradiated with light, in particular UV light. In particular, it can be a so-called positive resist, the solubility of which increases due to UV irradiation. This allows the sacrificial layer to be removed in a targeted manner after the metal filling to provide the metal bridge.

[0188] In another aspect, the present invention relates to a method for manufacturing a MEMS transducer, the method comprising the following steps:

[0189] - providing a plurality of individual piezoceramic elements, said piezoceramic elements comprising a layer of electrically conductive mechanical support material and a layer of piezoelectric material

[0190] - providing an upper frame and a lower frame with recesses for a plurality of individual piezoelectric ceramic elements

[0191] - Fix the piezoelectric ceramic elements in the recesses of the upper and lower frames (preferably by adhesive)

[0192] - applying at least one continuous electrically conductive layer to connect the piezoelectric ceramic element via at least one electrode

[0193] A vibratable membrane, preferably in the form of a layered structure, is held by a carrier formed by an upper frame and a lower frame, and wherein the vibratable membrane for generating and receiving pressure waves of a fluid in a vertical direction comprises two or more vertical parts formed at least parallel to the vertical direction, so that by driving at least one electrode, the two or more vertical parts can be induced to vibrate horizontally, or when the two or more vertical parts are induced to vibrate horizontally, an electrical signal can be generated at at least one electrode.

[0194] The preferred embodiment is Fig.12 Advantageously, in this embodiment, the structured connection is omitted. Instead, the connection is made through a continuous conductive surface from the front side and / or the back side of the MEMS transducer.

[0195] In a preferred embodiment, the upper and lower frames are formed from a non-electrically conductive material, such as a polymer. Preferably, a 3D printing process may be used to form the frames.

[0196] In order to connect the individual sheets or piezoceramic elements, a continuous layer of a conductive material, preferably a metal, is preferably applied from the front (front electrode) or from the back (back electrode). For example, the application can be carried out by a sputtering process.

[0197] A person skilled in the art will recognize that the technical features, limitations and advantages of the preferred embodiments of the MEMS transducer (preferably a MEMS speaker or a MEMS microphone) also apply to the manufacturing process, and vice versa. Preferably, the manufacturing method is used to provide a MEMS transducer having a vibratable membrane of a layered structure, wherein the thin sheets are mechanical bimorphs and are connected by continuous layers of conductive material (preferably metal).

[0198] Specific description

[0199] The invention will be explained below with reference to further figures and examples. The examples and figures serve to illustrate preferred embodiments of the invention without limiting them. BRIEF DESCRIPTION OF THE DRAWINGS

[0200] Figure 1 2 are cross sections of a preferred embodiment of a MEMS speaker according to the present invention, A: at rest; and B: during driving.

[0201] Figure 2 is a diagram of a preferred manufacturing method for a MEMS speaker having a vibratable membrane having a meandering shape in cross-section.

[0202] Figure 3 , Figure 4is a diagram of a preferred embodiment of a MEMS loudspeaker having a vibratable membrane of a meandering shape, the horizontal portion of which is supported by a holding structure.

[0203] Figure 5 is a diagram of a preferred embodiment of a MEMS speaker having two actuator layers separated by an intermediate layer of conductive material.

[0204] Figure 6 A diagram of a preferred drive system for operating a MEMS speaker.

[0205] Figure 7 Diagram of a preferred integration of a MEMS loudspeaker in the front of an enclosure with a rear resonant volume.

[0206] Figure 8 is a diagram of a preferred method of manufacturing a MEMS loudspeaker having a vibratable membrane whose cross section has a meandering shape, with only the vertical portions having a layer of actuator material.

[0207] Fig. 9 The substrate is preferably structured in crystalline form to form deep trenches by an etching process that depends on the crystal orientation.

[0208] Fig.10 is a diagram of a preferred manufacturing method for a MEMS loudspeaker having a vibratable membrane based on a single piezoelectric ceramic element.

[0209] Fig.11 FIG. 1 is a diagram of preferred electrical connections for a MEMS loudspeaker having a vibratable membrane based on a single piezoelectric ceramic.

[0210] Fig.12 is a diagram of a preferred manufacturing method for a MEMS loudspeaker having a vibratable membrane based on a single piezoelectric ceramic element. DETAILED DESCRIPTION

[0211] Figure 1 A preferred embodiment of the MEMS speaker according to the present invention is shown. Figure 1 Part A shows the idle state, while Figure 1 Part B of FIG. 1 shows two phases during driving the MEMS speaker.

[0212] The MEMS loudspeaker comprises a vibrating membrane 1 for generating sound waves in a vertical emission direction, the vibrating membrane 1 being held in a horizontal position by a carrier 4. In cross section, the vibrating membrane 1 has a meandering structure having a horizontal portion 3 and a vertical portion 2. The vertical portion is formed parallel to the emission direction and has at least one actuator layer, for example a layer made of a piezoelectric material. The connection between the vibrating membrane 1 and the actuator layer is preferably achieved by electrodes at the ends. To this end, for example, an electrode pad (not shown) can be located on the carrier 4.

[0213] Preferably, the vertical part is a mechanical bimorph that can be induced to produce horizontal vibrations due to appropriate driving. To this end, the vertical part 2 can include, for example, a first layer of actuator material and a second layer of mechanical support material. By driving the actuator layer, a stress gradient can be generated and thus bending or vibration. Likewise, it can also be preferred that the vertical part 2 includes two actuator layers that are driven in opposite directions so as to cause bending of the vertical part 2 due to corresponding relative changes in shape.

[0214] Figure 1 Part B shows by way of example two phases during actuation. Advantageously, due to the plurality of vertical sections 2 of the vibratable membrane 1, the increased total volume can be moved with small horizontal movements (bendings) of a few micrometers in the vertical emission direction and thus used for sound generation. Actuation here allows a particularly efficient implementation, since during one phase almost the entire air volume between the vertical sections can be moved upwards or downwards in the emission direction.

[0215] Figure 2 Schematically shown is a preferred manufacturing method for providing a MEMS loudspeaker having a vibratable membrane 1, the cross section of which has a meandering shape. A vibratable membrane having a meandering shape in cross section may also preferably be referred to as a folded membrane or bellows.

[0216] Figure 2 Part A of 2000 shows etching of substrate 8 from the top or front side to form the structuring. In this process step, parallel deep trenches are etched into substrate 8. The structure formed represents a bellows, or a meander in cross section.

[0217] Subsequently, a layer of etch stop 9 is applied ( Figure 2 The layer of mechanical support material 10 ( Figure 2C) and a layer of actuator material 11 is applied to the etch stop 9. The mechanical support material 10 can be, for example, doped polysilicon, while a piezoelectric material can be used for the actuator material 11. As a layer thickness, for example, 1 μm may be preferred. Preferably, the piezoelectric material can have a C-axis orientation perpendicular to the surface, so that the transverse piezoelectric effect is used. Other orientations, and for example the use of longitudinal effects, may also be preferred.

[0218] Figure 2 Part E of FIG. 1 shows that a full-surface top electrode is preferably used as a layer of conductive material 12. The end-side connection can be achieved, for example, by electrode pads 13 ( Figure 2 part F) to achieve this.

[0219] Figure 2 Part F and Figure 2 Part G of Graph 1 shows further etching of the substrate 8 from the back side and bottom side, respectively, and removal of the etch stop.

[0220] Manufacturing step 2, part A to Figure 2 The portion G thus results in a vibrating membrane 1 which exhibits a meandering structure in cross section. Advantageously, the continuous actuator layer 11 and the provision of the end-side connection 13 allow the vertical portion 2 to be effectively driven to produce horizontal vibrations (see Figure 1 ).like Figure 2 As shown in part G of FIG. 1 , the actuation is preferably achieved via two electrodes, so that the actuator layer 12 is preferably connected from the front side (top electrode, conductive layer 12) and from the back side (bottom electrode, via conductive mechanical support material 10) (see FIG. Figure 6 Part A).

[0221] A retaining structure 14 may be provided to stabilize the membrane 1 suspended between the side walls of the carrier 4. Figure 3 and Figure 4 As shown, these holding structures 14 can preferably support the horizontal portion 3 of the vibratable membrane 1. Advantageously, the horizontal portion 3 is mechanically neutral (see Figure 1 B) so that no undesirable stresses are induced between the membrane 1 and the retaining structure 14 or the carrier 4 during actuation.

[0222] Figure 5 A preferred alternative embodiment of a MEMS loudspeaker is shown, in which the vibratable membrane 1 comprises two actuator layers separated by an intermediate layer of conductive material 12, preferably metal. The intermediate layer is connected to a first end-side electrode pad 13, while in the embodiment shown, the upper actuator layer 11 is connected to a second end-side electrode pad 13 via a further layer of conductive material 12.

[0223] Figure 6 A preferred drive system for operating the MEMS speaker is shown.

[0224] Figure 6 Part A of shows a preferred drive system for a MEMS loudspeaker with an actuator layer 11 and a passive mechanical support layer 10. Preferably, the drive is performed via two end-side electrode pads 13, so that horizontal vibrations can be generated by a change in shape of the actuator material relative to the mechanical support material. The actuator layer 11 is preferably connected both from the front side (top electrode 13, conductive layer 10) and from the back side (bottom electrode 13, conductive mechanical support material 10). For example, an AC voltage as an audio input signal can be applied to the front electrode pad 13 (left), while the back electrode pad 13 (right) is grounded.

[0225] Figure 6 Part B of illustrative embodiments shows a preferred drive system of a MEMS loudspeaker with two actuator layers 11 separated by an intermediate layer of conductive material 12, preferably metal.

[0226] The upper actuator layer 11 is preferably driven from the front side (top electrode 13 and upper conductive layer 12) and the middle conductive layer 12. The lower actuator layer 11 is preferably driven from the back side (bottom electrode 13 and lower conductive layer 12) and the middle conductive layer 12. In the embodiment shown, an AC voltage may be applied as an audio input signal, for example to the electrode pads 13 for the top and bottom (left), while the middle layer 12 is grounded via another electrode pad 13 (right).

[0227] Figure 7 An example of a preferred integration of a MEMS loudspeaker according to the invention in a housing 15 is shown. Preferably, a vibratable membrane 1 held by a carrier 4 is arranged on the front side of the housing (sound port). The housing also encloses a rear resonance volume (back volume 16). Vents 17 may be provided to prevent acoustic short circuits or to support the sound.

[0228] Figure 8 An alternative manufacturing method for providing a MEMS loudspeaker with a vibratable membrane 1 according to the invention is shown. Figure 8 Section A to Figure 8 The process steps shown in Section D are similar to Figure 2 .

[0229] Figure 8 Part A of 2000 shows etching of substrate 8 from the top or front side to form a structure, preferably a meander structure. In this process step, parallel deep trenches are etched into substrate 8. The structure formed represents a bellows, or a meander in cross section.

[0230] Subsequently, a layer of etch stop 9 is applied ( Figure 2 The mechanical support material 10 ( Figure 2C) and a layer of actuator material 11 are applied to the etch stop 9. The mechanical support material 10 may be, for example, doped polysilicon, while a piezoelectric material is preferably used for the actuator material 12.

[0231] and Figure 2 In contrast to the embodiment shown, the actuator layer 11 is not connected to the upper conductive layer as a continuous layer. Instead, the spacer etching ( Figure 8 Part F) is performed in the horizontal part of the membrane so that only the vertical part of the membrane still has the layer 11 of actuator material.

[0232] Then, a continuous dielectric layer 18 is preferably applied to prevent short circuits between the top and bottom electrodes to be applied later ( Figure 8 G). A continuous conductive layer as the top electrode 12 allows front-side connection ( Figure 8 part H).

[0233] Figure 8 Part I and Figure 8 Part J of FIG. 5 shows further etching of the substrate 8 from the back or bottom side and optionally applying a continuous conductive layer 12 as back electrode.

[0234] Fig. 9 A preferred way of providing a structured substrate 8 is shown. Figure 8 By means of the process steps shown in part A of , parallel deep trenches are etched into the substrate 8. The structure formed represents a bellows, or a meander in cross section, to which a vibratable membrane can be applied in a meandering form.

[0235] Fig. 9 A preferred arrangement of the structured substrate 8 in is characterized in that the crystal structure of the substrate 8 is utilized, wherein the grooves are formed along lattice vectors of the crystal structure.

[0236] In this way, particularly smooth quasi-crystalline grooves with high depths exceeding 200 μm, 400 μm or more can be obtained with high precision of orientation. It is also advantageous if the surface normals of the side surfaces of the grooves are aligned with lattice vectors which are orthogonal to the lattice vectors in the direction of which the etching process has been carried out.

[0237] For example, if silicon is used as the substrate, the silicon substrate 8 may be as follows: Fig. 9 The presence of a surface orientation preferably with the Miller index <110> Therefore, preferably, the lattice vectors of the crystal structure <110> Perpendicularly to the surface of the still unstructured substrate, by etching the mask 24 (eg a SiO2 hard mask), horizontal areas or strips which are not etched can be defined on the substrate surface.

[0238] Smooth and precisely oriented grooves are obtained by anisotropic etching, where the preferred direction is along the <110> orientation, rather than <111> For this purpose, wet chemical processes can be advantageously used, which are suitable for large-scale production in batch processes. For example, potassium hydroxide is used for <110> and <111> The etching of crystal orientation shows a clear directional preference. As shown by Sato et al. in 1988, KOH on single crystal silicon <110> The etching rate on is 1.455μm / min, while on <111> The etching rate in the orientation is only 0.005 μm / min. Due to the anisotropic etching rate, deep trenches with low underetch can be obtained using wet chemical processes.

[0239] For example, to form a 400 μm deep trench, KOH can be applied to <110> Oriented silicon substrate 275 minutes. Due to the orthogonal <111> The orientation etch rate is reduced by a factor of 291, with only 1.37 μm of underetching occurring during this period. Even variations in the local intensity of the underetching process will result in orientation variations of well below 1° for a large trench depth of 400 μm. Instead, the process can achieve nearly perfect vertical deep trenches with a high degree of accuracy, characterized by a smooth quasi-crystalline orientation.

[0240] As a further advantage, the side walls of the vertical portion of the trench thus obtained, on which the film is formed, are crystal-oriented (here: <111> ). This situation favours the columnar growth of piezoelectric material such as AlN or PZT: this ensures in a particularly precise manner that the piezoelectric material has a c-axis orientation perpendicular to the surface of the vertical portion, so that the transverse piezoelectric effect can be used to generate horizontal vibrations.

[0241] Fig.10 A preferred manufacturing method for providing a MEMS loudspeaker having a vibratable membrane based on a single piezoelectric ceramic is shown.

[0242] First, a plurality of individual piezoelectric ceramic elements 19 are provided, which comprise a layer of mechanical support material layer 10 (eg doped polysilicon) and a layer of piezoelectric material layer 11 as well as a sacrificial layer 20 (see Fig.10 Part A and Fig.10 Part B). The sacrificial layer 20 may be, for example, a photoresist. Preferably, the layer of mechanical support material 10 may be electrically conductive to ensure connection. One or two layers of conductive material 12 may also be applied to one layer of piezoelectric material 11, the one or two layers of conductive material 12 being used to make electrical connection with the piezoelectric material.

[0243] Subsequently, holes 21 for interlayer connection and metal filling are defined (see Fig.10 The piezoelectric ceramic element 19 is stacked ( Fig.10 D) and cutting (cutting 22, Fig.10 Part E), thereby obtaining a stack of two or more piezoelectric ceramic elements 19, which are connected by metal bridges 21 (see Fig.10 Part E).

[0244] After removing the sacrificial layer 20 ( Fig.10 After the stacked piezoelectric ceramic elements 19 are inserted into the carrier 4, preferably, the first and last piezoelectric ceramic elements are connected to the electrodes 13 ( Fig.10 Part E).

[0245] In this way, a vibratable membrane 1 is also obtained between the carriers 4, which vibratable membrane 1 comprises at least two or more vertical portions 2 for generating sound waves in a vertical emission direction, which vertical portions 2 are formed parallel to the emission direction and can be driven to vibrate horizontally.

[0246] The actuator principle is preferably also based here on a relative change of shape of the actuator layer 11 relative to the mechanical support layer 10. For this purpose, no continuous actuator layer is required. The connection of all vertical parts 2 by end-side drive is ensured by the bonding of metal bridges 23 to the conductive layer 12.

[0247] Fig.11 The preferred electrical connections of a MEMS loudspeaker having a vibratable membrane based on a separate piezoelectric ceramic are shown.

[0248] Fig.11 Part A is a top view of the MEMS speaker, and Fig.11 Part B is a side view thereof. The individual lamellae or vertical sections are driven in parallel via electrode pads 13, wherein u-shaped spacers are present on each side of the lamellae and create mechanical and electrical connections to the next lamellae.

[0249] Fig.12 An alternative manufacturing method for providing a MEMS loudspeaker with a vibratable membrane based on a separate piezoelectric ceramic is shown.

[0250] Advantageously, according to Fig.10 or Fig.11 In contrast to the embodiment of FIG. 1 , the structured connection can be omitted in the embodiment shown. Instead, the connection can be made via a continuous conductive surface from the front (front electrode) or the back (back electrode), as described below.

[0251] Similar to Fig.10By way of a manufacturing method of the invention, a plurality of individual piezoceramic elements 19 are provided, which comprise a layer of a mechanical support material 10 (eg doped polysilicon) and a layer of a piezoelectric material 11. Preferably, the layer of mechanical support material 10 is electrically conductive.

[0252] Furthermore, the upper frame 25 and the lower frame 26 are respectively provided with a recess or groove 27 for receiving the piezoelectric ceramic element 19. Preferably, the upper frame and the lower frame are made of a non-electrically conductive material, such as a polymer. Preferably, a 3D printing process can be used to form the frames.

[0253] In order to fix the piezoelectric ceramic element 19, an adhesive can preferably be used, preferably firstly applied to the recess 27 (see Fig.12 After the piezoceramic element 19 is fixed in the corresponding recess 27 of the lower frame 26, an adhesive can be applied to the piezoceramic element 19 so that the upper frame fixes the piezoceramic element 19 on the upper side (see Fig.12 Part B).

[0254] In order to connect the individual sheets or piezoceramic elements 19, a continuous layer of a (not visible) conductive material, preferably a metal, is preferably applied from the front (front electrode) or from the back (back electrode), for example by a sputtering process.

[0255] In this way, a vibratable membrane 1 is also obtained, which, in order to generate sound waves in a vertical emission direction, comprises at least two or more vertical parts 2, which are formed parallel to the emission direction and can be induced to vibrate horizontally. The composite frame 25, 26 can serve as a carrier for the vertical parts 2.

[0256] Reference numerals

[0257] 1 Vibrating membrane

[0258] 2 The vertical part of the vibrating membrane

[0259] 3 horizontal part of the vibrating membrane

[0260] 4 bearing parts

[0261] 5The volume of air between the vertical parts

[0262] 8 Substrate

[0263] 9 Etching stop

[0264] 10 Layer of mechanical support material, preferably doped polysilicon

[0265] 11 A layer of actuator material (actuator layer), preferably a piezoelectric material

[0266] 12 Layer of conductive material, preferably metal

[0267] 13. The connecting part of the electrode, preferably an electrode pad

[0268] 14. Maintain structure

[0269] 15 Shell

[0270] 16 Rear resonance volume

[0271] 17 Vents

[0272] 18 Layers of dielectric material

[0273] 19 piezoelectric ceramic element (one or more)

[0274] 20 Sacrificial Layer

[0275] 21 Defined holes for interlayer connection and metal filling

[0276] 22 Cutting (cutting)

[0277] 23 Metal Bridge

[0278] 24 Etching Mask

[0279] 25 Upper frame

[0280] 26 lower frame.

[0281] literature

[0282] F.Stoppel,C.Eisermann,S.Gu-Stoppel,D.Kaden,T.Giese and B.Wagner,NOVELMEMBRANE-LESS TWO-WAY MEMS LOUDSPEAKER BASED ON PIEZOELECTRIC DUAL-CONCENTRICACTUATORS,Transducers2017,Kaohsiung,TAIWAN,CHINA,June 18-22,2017.

[0283] 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>.

[0284] Bert Kaiser,Sergiu Langa,Lutz Ehrig,Michael Stolz,Hermann Schenk,Holger Conrad,Harald Schenk,Klaus Schimmanz and David Schuffenhauer,Conceptand proof for an all-silicon MEMS microspeaker utilizing air chambersMicrosystems&Nanoengineering volume 5,Article number:43(2019).Kazuo Sato,Mitsuhiro Shikida,Yoshihiro Matsushima,Takashi Yamashiro,Kazuo Asaumi,YasurohIriye,and Masaharu Yamamoto,Characterization of orientation-dependent etchingproperties of single-crystal silicon:effects of KOH concentration,SensorsandActuatorsA 64(1988)87-93).

[0285] Seidel,H.,Csepregi,L.,Heuberger,A.,and Baumgartel,H.(1990).Anisotropic etching of Crystalline Silicon in Alkaline Solutions.Journal ofThe Electrochemical Society 137.10.1149 / 1.2086277。

Claims

1. A MEMS transducer for interacting with a volume flow of a fluid, the MEMS transducer comprising: - a carrier (4), a vibratable membrane (1) for generating or receiving pressure waves of the fluid in a vertical direction, the vibratable membrane (1) being supported by the support (4), wherein the vibratable membrane (1) and the support (4) are manufactured together, It is characterized in that The vibratable membrane (1) has two or more vertical portions (2), the two or more vertical portions (2) are formed substantially parallel to the vertical direction, and the two or more vertical portions (2) include at least one layer containing an actuator material, wherein at least one end of the vibratable membrane (1) is connected to at least one electrode, It is possible to induce two or more of the vertical parts (2) to vibrate horizontally by driving the at least one electrode; or it is possible to generate an electrical signal at the at least one electrode when the two or more vertical parts (2) are induced to vibrate horizontally.

2. The MEMS transducer according to claim 1, It is characterized in that The MEMS transducer is a MEMS speaker, wherein an air volume (5) exists between the vertical parts (2), and due to the horizontal vibration, the air volume (5) moves in a vertical transmission direction to generate sound waves; or the MEMS transducer is a MEMS microphone, wherein an air volume (5) exists between the vertical parts (2), and when receiving sound waves, the air volume (5) moves in a vertical detection direction.

3. The MEMS transducer according to claim 1 or 2, It is characterized in that Two or more of the vertical portions (2) comprise at least two layers, a first layer of the at least two layers comprises an actuator material and a second layer of the at least two layers comprises a mechanical support material, wherein at least the first layer comprising the actuator material is connected to an electrode, enabling horizontal vibrations to be generated by a change in shape of the actuator material relative to the mechanical support material, or Such horizontal vibrations cause the actuator material to change shape relative to the mechanical support material and generate an electrical signal.

4. The MEMS transducer according to claim 1 or 2, It is characterized in that Two or more of the vertical portions (2) comprise at least two layers, both of the at least two layers comprise actuator material, and the two layers are each connected to an electrode, respectively, and The horizontal vibrations can be produced by a change in shape of one layer relative to another layer, or The horizontal vibrations cause the shape of one layer to change relative to the other and generate an electrical signal.

5. The MEMS transducer according to claim 1 or 2, It is characterized in that The carrier (4) comprises two side regions, the vibratable membrane (1) is arranged in the horizontal direction between the two side regions, and / or The carrier (4) is formed by a substrate (8).

6. The MEMS transducer according to claim 5, wherein: The substrate (8) is selected from the group consisting of single crystal silicon, polycrystalline silicon, silicon dioxide, silicon carbide, silicon germanium, nitride, germanium, carbon, gallium arsenide, gallium nitride, indium phosphide, and glass.

7. The MEMS transducer according to claim 1 or 2, It is characterized in that The vibratable membrane (1) is formed of a layered structure or a meandering structure.

8. The MEMS transducer according to claim 1 or 2, It is characterized in that The vibratable membrane (1) is formed by a meandering structure having alternating vertical parts (2) and horizontal parts (3), at least two of the horizontal parts (3) being attached with a retaining structure (14), which is directly or indirectly connected to the carrier (4).

9. The MEMS transducer according to claim 1 or 2, It is characterized in that The actuator material comprises a piezoelectric material, a polymer piezoelectric material and / or an electroactive polymer.

10. The MEMS transducer according to claim 9, characterized in that: The piezoelectric material is selected from the group consisting of lead zirconate titanate, aluminum nitride, scandium aluminum nitride, and zinc oxide.

11. The MEMS transducer according to claim 1 or 2, It is characterized in that The vibratable membrane (1) comprises three layers, an upper layer of the three layers is formed of a conductive material, a middle layer of the three layers is formed of an actuator material, and a lower layer of the three layers is formed of a conductive material.

12. The MEMS transducer according to claim 11, characterized in that: The conductive material of the upper layer and / or the lower layer is a mechanical support material.

13. The MEMS transducer according to claim 1 or 2, It is characterized in that The vibratable membrane (1) comprises two layers comprising actuator material, the two layers comprising actuator material being separated by an intermediate layer of conductive material, wherein the intermediate layer is connected to a first electrode and at least one of the two layers comprising actuator material is connected to a second electrode via a further layer of conductive material.

14. The MEMS transducer according to claim 1 or 2, It is characterized in that The vibratable membrane (1) is coated with a layer of non-stick material.

15. The MEMS transducer according to claim 1 or 2, It is characterized in that The vibratable membrane (1) supported by the carrier (4) is arranged on the front side of a housing (15) which surrounds a rear resonance volume (16).

16. The MEMS transducer according to claim 15, characterized in that: Ventilation openings (17) are present in the housing (15) for avoiding acoustic short circuits and / or for supporting sound.

17. A method for manufacturing a MEMS transducer according to one of claims 1 to 16, the method comprising the following steps: - etching the substrate (8) to form a structuring portion, - Applying an etch stop, - applying at least two layers, wherein at least a first layer of the at least two layers comprises an actuator material and a second layer comprises a mechanical support material, or at least two layers comprise an actuator material, - connecting the first layer and / or the second layer to an electrode (13), - performing etching and removing the etching stop, A vibratable membrane (1) is supported by a carrier (4) formed by a substrate (8), wherein the vibratable membrane (1) includes at least two or more vertical portions (2) to generate or receive pressure waves of the fluid in a vertical direction, wherein the vertical portions are formed parallel to the vertical direction, and wherein the two or more vertical portions (2) can be induced to vibrate horizontally by driving at least one of the electrodes, or When two or more of the vertical parts (2) are induced to vibrate horizontally, an electrical signal can be generated at at least one of the electrodes.

18. The method for manufacturing a MEMS transducer according to claim 17, characterized in that: The manufacturing method comprises etching the substrate (8) from the front side.

19. The method for manufacturing a MEMS transducer according to claim 17, characterized in that: The structured portion is a meandering structure.

20. The method for manufacturing a MEMS transducer according to claim 17, characterized in that: The vibratable membrane (1) is in the form of a meandering structure.

21. A MEMS transducer for interacting with a volume flow of a fluid, the MEMS transducer comprising: - a carrier (4), a vibratable membrane (1) for generating or receiving pressure waves of the fluid in a vertical direction, the vibratable membrane (1) being supported by the carrier (4), It is characterized in that The vibratable membrane (1) has two or more vertical portions (2), the two or more vertical portions (2) are formed substantially parallel to the vertical direction, and the two or more vertical portions (2) include at least one layer containing an actuator material, wherein at least one end of the vibratable membrane (1) is connected to at least one electrode, enabling the two or more vertical parts (2) to be induced to vibrate horizontally by driving the at least one electrode; or enabling an electrical signal to be generated at the at least one electrode when the two or more vertical parts (2) are induced to vibrate horizontally, And wherein the vertical parts (2) of the vibrating membrane (1) comprise two layers, wherein the first layer comprises actuator material and the second layer comprises conductive support material, and wherein the vertical parts (2) are connected via horizontal metal bridges (23), and wherein the vertical parts (2) are respectively connected to electrodes.

22. A method for manufacturing a MEMS transducer according to claim 21, the method comprising the following steps: - providing a plurality of individual piezoelectric ceramic elements (19), each of the plurality of individual piezoelectric ceramic elements (19) comprising a sacrificial layer (20), a layer (12) of conductive material, and a layer of piezoelectric material, - defining holes (21) for interlayer connection and metal filling in the piezoelectric ceramic element, - stacking the piezoelectric ceramic elements (19) and cutting the piezoelectric ceramic elements (19) to obtain a stack of piezoelectric ceramic elements connected by metal bridges (23), - removing the sacrificial layer (20) and inserting the stack of piezoceramic elements into a carrier (4), wherein the piezoceramic elements (19) are respectively connected to electrodes, The vibratable membrane (1) is supported by the support member (4), the vibratable membrane (1) comprising at least two or more vertical parts (2) to generate or receive pressure waves of the fluid in a vertical direction, the vertical parts being formed parallel to the vertical direction, and enabling the two or more vertical parts (2) to be induced to vibrate horizontally by driving the at least one electrode, or When two or more of the vertical parts (2) are induced to vibrate horizontally, an electrical signal can be generated at the at least one electrode.

23. The method for manufacturing a MEMS transducer according to claim 22, characterized in that: The vibratable membrane (1) is in the form of a layered structure.

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