EP3852391B1 - Enhanced performance mems loudspeaker - Google Patents

Description

The invention relates to a MEMS transducer which comprises an oscillating membrane for generating or receiving pressure waves of a fluid in a vertical direction, wherein the oscillating membrane is held by a carrier and the oscillating membrane has two or more vertical sections which are formed parallel to the vertical direction and comprise at least one layer of an actuator material. The oscillating membrane is preferably contacted at the end with an electrode, so that by controlling the at least one electrode the two or more vertical sections can be excited to horizontal oscillations or so that when the two or more vertical sections are excited to horizontal oscillations an electrical signal can be generated at the at least one electrode.

Background and state of the art

Microsystem technology is now used in many areas of application to produce compact, mechanical-electronic devices. The microsystems ( microelectromechanical systems , MEMS) produced in this way are very compact (micrometer range) while at the same time offering excellent functionality and ever lower production costs.

MEMS transducers, such as MEMS loudspeakers or MEMS microphones, are also known from the state of the art. Current MEMS loudspeakers are usually designed as planar membrane systems with a vertical actuation of an oscillating membrane in the emission direction. The excitation takes place, for example, using piezoelectric, electromagnetic or electrostatic actuators.

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

Stoppel et al. 2017 revealed a two-way loudspeaker whose concept is based on concentric piezoelectric actuators. As a special feature, the vibration membrane is not closed, but comprises eight piezoelectric unimorph actuators, each consisting of a piezoelectric and a passive layer. The outer woofers consist of four trapezoidal actuators clamped on one side, while the inner tweeters are formed by four triangular actuators that are connected to a rigid frame by means of a spring. The separation of the membrane is intended to allow an improved sound image with higher performance.

The disadvantage of such planar MEMS loudspeakers is their limitation in terms of sound output, especially at low frequencies. One reason for this is that the sound pressure level that can be generated is proportional to the square of the frequency for a given deflection. To achieve sufficient sound output, either deflections for the vibration membranes of at least 100 µm or large-area membranes in the square centimeter range are necessary. Both conditions are difficult to achieve using MEMS technology.

In the prior art, it was therefore proposed to design MEMS loudspeakers that do not have a closed membrane for vibrations in the vertical emission direction, but rather a large number of movable elements that can be excited to lateral or horizontal vibrations. The advantage of this is that an increased volume flow can be moved over a small area and thus an increased sound output can be provided.

A MEMS loudspeaker based on this principle is used, for example, in the US 2018 / 0179048 A1 and Kaiser et al. 2019, respectively.

The MEMS loudspeaker comprises a plurality of electrostatic bending actuators, which are arranged as vertical lamellae between a cover and a base wafer and can be excited to lateral vibrations by appropriate control. An inner lamella forms an actuator electrode opposite two outer lamellae. Except for a connecting node of electrodes that are still galvanically separated, there is an air gap between the three curved lamellae. If a potential is applied inside to outside, this leads to a bilateral attraction due to the curvature of the design in the direction of a preferred direction, which is specified by an anchor. The bulges in the outer lamellae serve to facilitate mobility. The restoring force is provided by a mechanical spring force. Pull-push operation is therefore not possible.

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

An alternative MEMS-based air pulse or sound generation system is being developed in the US 2019 / 011 64 17 A1 described. The device comprises a front and rear chamber and a plurality of valves, wherein the front and rear chambers are separated from one another by means of a folded membrane. In one embodiment, the folded membrane has a rectangular meander structure with horizontal and vertical sections in cross section. Piezo actuators are positioned on the respective horizontal sections in order to cause a lateral movement of the vertical sections by a synchronized stretching or compression of the horizontal sections. With the proposed principle, an increased volume flow and thus sound power can also be generated on a small chip surface.

However, the disadvantage is the increased effort required for the synchronized drive of the piezo actuators. There is also potential for improvement in terms of the volume displaced by the lateral vibrations, which is limited by the geometric arrangement of the one-sidedly actuated horizontal sections.

From the US 2002/006208 A1 and JP3 919695 B2 A piezoelectric loudspeaker is known in which two piezoelectric films are formed into a diaphragm with an accordion shape. The diaphragm is folded and clamped laterally by a wave-shaped pair of plates, which are fixed, for example, by means of screw connections and stabilize the vibrating diaphragm as a composite side frame. Several electrodes are applied in a structured form to the wave crests and troughs of the diaphragm and are insulated from one another by strips of non-conductive material. Electrode lines are arranged in the plate pair or side frame to control the electrodes. Alternatively, the plate pair can also be formed at least partially from a conductive material.

The macroscopic piezoelectric loudspeaker US 2002/006208 A1 and JP3 919695 B2 is 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 diaphragm in a two-part side frame, the structured application of several electrodes on wave crests and troughs of the diaphragm or the connection of the electrodes with electrode lines in the side frame cannot be transferred to a MEMS process.

In light of the disadvantages of the state of the art, there is a need for alternative or improved solutions for MEMS-based loudspeakers.

Object of the invention

The object of the invention is to provide a MEMS converter, in particular a MEMS loudspeaker or MEMS microphone, as well as a method for producing the MEMS converter, which do not have the disadvantages of the prior art. In particular, it was an object of the invention to provide a powerful MEMS loudspeaker or MEMS microphone with high sound quality or audio quality, which are also characterized by a simple, cost-effective and compact design.

Summary of the invention

The object is solved by the features of the independent claims. Preferred embodiments of the invention are described in the dependent claims.

• einen Träger,
• eine schwingfähige Membran zur Erzeugung oder Aufnahme von Druckwellen des Fluids in einer vertikalen Richtung, wobei die schwingfähige Membran von dem Träger gehalten wird, wobei die schwingfähige Membran zusammen mit dem Träger in einem Halbleiterprozess hergestellt wird

• und wobei die schwingfähige Membran zwei oder mehr vertikale Abschnitte aufweist, welche parallel zur vertikalen Richtung ausgebildet sind und mindestens eine Lage aus einem Aktuatormaterial umfassen, wobei die schwingfähige Membran endseitig mit mindestens einer Elektrode kontaktiert vorliegt,
• sodass durch Ansteuerung der mindestens einen Elektrode die zwei oder mehr vertikalen Abschnitte zu horizontalen Schwingungen angeregt werden können oder sodass bei Anregung der zwei oder mehr vertikalen Abschnitte zu horizontalen Schwingungen an der mindestens einen Elektrode ein elektrisches Signal erzeugt werden kann.

The invention relates to a MEMS converter for interaction with a volume flow of a fluid comprising

• a carrier,
• a vibratable membrane for generating or receiving pressure waves of the fluid in a vertical direction, wherein the vibratable membrane is held by the carrier, wherein the vibratable membrane is manufactured together with the carrier in a semiconductor process

• and wherein the vibratable membrane has two or more vertical sections which are formed parallel to the vertical direction and comprise at least one layer of an actuator material, wherein the vibratable membrane is contacted at the end with at least one electrode,
• so that by controlling the at least one electrode, the two or more vertical sections can be excited to horizontal oscillations or so that when the two or more vertical sections are excited to horizontal oscillations, an electrical signal can be generated at the at least one electrode.

• einen Träger,
• eine schwingfähige Membran zur Erzeugung von Schallwellen in eine vertikale Emissionsrichtung, wobei die schwingfähige Membran von dem Träger gehalten wird,

wobei die schwingfähige Membran zwei oder mehr vertikale Abschnitte aufweist, welche parallel zur Emissionsrichtung ausgebildet sind und mindestens eine Lage aus einem Aktuatormaterial umfassen, wobei die schwingfähige Membran bevorzugt endseitig mit mindestens einer Elektrode kontaktiert vorliegt, sodass durch Ansteuerung der mindestens einen Elektrode die zwei oder mehr vertikalen Abschnitte zu horizontalen Schwingungen angeregt werden können.Particularly preferably, the MEMS converter can be a MEMS loudspeaker. In a particularly preferred embodiment, the invention relates to a MEMS loudspeaker comprising

• a carrier,
• a vibratable membrane for generating sound waves in a vertical emission direction, the vibratable membrane being held by the carrier,

wherein the oscillatable membrane has two or more vertical sections which are formed parallel to the emission direction and comprise at least one layer of an actuator material, wherein the oscillatable membrane is preferably contacted at the end with at least one electrode, so that by controlling the at least one electrode the two or more vertical sections can be excited to horizontal oscillations.

The design of the MEMS loudspeaker makes it possible to obtain a MEMS loudspeaker with high sound power and simplified control.

In contrast to known planar MEMS loudspeakers, the vibrating membrane itself does not have to be operated over a large area of several square centimeters or with a deflection of more than 100 µm to generate sufficient sound pressure. Instead, the majority of the vertical sections of the vibrating membrane can move an increased total volume in the vertical emission direction with small horizontal or lateral movements of a few micrometers.

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

In particular, the provision of the vertical fins or bending actuators for a MEMS loudspeaker according to Kaiser et al. 2019 is complex. In addition, sufficiently precise vertical etchings are only possible for limited fin heights, which limits the sound power.

By means of the solution according to the invention, the vertical sections of the oscillating membrane can instead be obtained in MEMS design using simple manufacturing steps, as explained in more detail below. In addition, the actuator principle according to the invention avoids pull-in or gluing of the vertical sections. In contrast to the solution by Kaiser et al. 2019, the one-sided electrodes do not result in any potential differences in a gap between the vertical sections. In addition to avoiding overvoltage or pull-in, this can also reduce dust accumulation, since, for example, an external electrode can be set to a ground potential.

Another special advantage of the MEMS loudspeaker described is the simplified control. While in the US 2019 / 011 64 17 A1 a large number of piezoelectric actuators must be contacted at the horizontal sections, the proposed MEMS loudspeaker can be operated using at least one end electrode. This reduces the manufacturing effort, minimizes sources of error and also inherently leads to a synchronous control of the vertical sections to horizontal vibrations.

In this way, the air volumes between the vertical sections can be moved extremely precisely by the horizontal vibrations along the vertical emission direction. The result is an improved sound image, even at high sound power levels.

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

The design of the vibrating membrane can be used advantageously not only to create a MEMS loudspeaker with high sound output and simplified control, but also to provide a particularly powerful MEMS microphone with high audio quality.

• einen Träger,
• eine schwingfähige Membran zur Aufnahme von Schallwellen in einer vertikalen Richtung, wobei die schwingfähige Membran von dem Träger gehalten wird,

und wobei die schwingfähige Membran zwei oder mehr vertikale Abschnitte aufweist, welche parallel zur vertikalen Richtung ausgebildet sind und mindestens eine Lage aus einem Aktuatormaterial umfassen, wobei die schwingfähige Membran bevorzugt endseitig mit mindestens einer Elektrode kontaktiert vorliegt, sodass bei Anregung der zwei oder mehr vertikalen Abschnitte zu horizontalen Schwingungen an der mindestens einen Elektrode ein elektrisches Signal erzeugt werden kann.In a preferred embodiment, the invention thus also relates to a MEMS microphone comprising

• a carrier,
• a vibratable membrane for receiving sound waves in a vertical direction, the vibratable membrane being held by the support,

and wherein the oscillatable membrane has two or more vertical sections which are formed parallel to the vertical direction and comprise at least one layer of an actuator material, wherein the oscillatable membrane is preferably contacted at the end with at least one electrode, so that when the two or more vertical sections are excited to horizontal oscillations, an electrical signal can be generated at the at least one electrode.

The structure of the MEMS microphone is structurally similar to that of the MEMS loudspeaker, particularly with regard to the design of the vibrating membrane. Instead of controlling the electrodes to generate horizontal vibrations and thus sound pressure waves, the MEMS microphone is designed to record sound pressure waves in the same vertical direction. Preferably, there are therefore air volumes between the vertical sections, which are moved along a vertical detection direction when sound waves are recorded. The sound pressure waves excite the vertical sections to horizontal vibrations, so that the actuator material generates a corresponding periodic electrical signal.

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

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

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

Applications of the MEMS converter as an energy harvester are also possible, using pneumatic or hydraulic alternating pressures. In these cases, the electrical signal can be dissipated as generated electrical energy, stored or fed to other (consumer) devices.

End preferably means a positioning of the at least one electrode so that contact can be made with electronics, e.g. with a current or voltage source in the case of a MEMS loudspeaker, at one end of the vibratable membrane, preferably at an end at which the membrane is suspended from the carrier. Electrode preferably means an area made of a conductive material (preferably a metal) which is set up for such contact with electronics, e.g. with a current and/or voltage source in the case of a MEMS loudspeaker. It can preferably be an electrode pad. The electrode pad is particularly preferably used for contacting electronics and is itself connected to a conductive metal layer which can extend over the entire surface of the vibratable membrane. In some cases, the conductive layer together with an electrode pad is referred to below as an electrode, for example as a top electrode or bottom electrode.

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

The end-side provision of the electrodes is therefore preferably distinguished from a contact which controls the respective vertical sections with respective separate electrodes or, in the case of a MEMS microphone, picks up electrical signals generated. The MEMS converter therefore preferably comprises exactly one or exactly two electrodes for end-side contact and no further electrodes (pads) for contacting central vertical sections.

Preferably, the layer of actuator material in the vertical sections serves as a component of a mechanical biomorph, wherein a lateral curvature of the vertical sections is caused by controlling the actuator layer via the electrode or wherein a corresponding electrical signal is generated by an induced lateral curvature.

In a preferred embodiment, the two or more vertical sections have at least two layers, wherein one layer comprises an actuator material and a second layer comprises a mechanical support material, and wherein at least the layer comprises the actuator material and is contacted with an end electrode, so that the horizontal vibrations can be generated by a change in shape of the actuator material relative to the mechanical support material. In the embodiment, the mechanical bimorph is formed by a layer of actuator material (e.g. a piezoelectric material) and a passive layer, which acts as a mechanical support layer. Both a transverse and a longitudinal piezo effect can be used for the bending.

When the actuator layer is activated, it can, for example, experience a transverse or longitudinal stretching or compression. This creates a stress gradient in relation to the mechanical support layer, which leads to a lateral curvature or vibration. As shown in the Fig.1 As illustrated, by alternating polarity at the electrodes, a push-pull operation can preferably be achieved, whereby almost the entire air volume can be moved alternately between the vertical sections in the vertical emission direction.

The advantage of the actuator principle is a highly efficient translation of the horizontal vibrations of vertical sections into a vertical volume movement or sound generation.

Since the actuator principle is not based on electrostatic attraction, but on a relative change in shape (e.g. compression, stretching, shearing) of the actuator layer compared to a support layer, sticking of the membrane sections can be ruled out. Instead, the vertical sections can finally touch each other and are therefore not restricted in their deflection.

In a further preferred embodiment, the two or more vertical sections comprise at least two layers, wherein both layers comprise an actuator material and are contacted with electrodes at each end, and the horizontal vibrations can be generated by a change in shape of one layer relative to the other layer. In the embodiment, the horizontal vibration of the vertical sections is therefore not generated by a stress gradient between an active actuator layer and a passive support layer, but by a relative change in shape of two active actuator layers.

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

In the sense of the invention, the "layer comprising an actuator material" is preferably also referred to as an actuator layer. An actuator material preferably means a material which, when an electrical voltage is applied, changes shape, for example stretches. undergoes compression or shearing or, conversely, generates an electrical voltage under deformation.

Preferred are materials with electrical dipoles which undergo a change in shape when an electrical voltage is applied, whereby the orientation of the dipoles and/or the electrical field can determine the preferred direction of the change in shape.

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

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

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

This makes it possible to implement a macroscopic solution in which a polymer piezoelectrical material layer is applied to a mechanical support layer and wound over an upper and lower comb. Preferably, a polymer piezoelectrical material layer (including electrode) is first provided on a support layer (possibly including a counter electrode). An upper and lower comb (preferably a MEMS structure) are then moved against each other in such a way that a folded membrane with actuatable vertical sections is created.

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

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

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

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

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

To ensure horizontal vibration, the piezoelectric material can preferably have a C-axis orientation perpendicular to the surface of the vertical sections, so that a transverse piezoelectric effect is used. Other orientations and, for example, the use of a longitudinal piezoelectric effect to form the horizontal curvatures or vibrations (see. Fig.1 ) may be preferred.

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

In a preferred embodiment, the vibratable membrane therefore comprises at least one layer of a conductive material.

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

The direction specifications vertical and horizontal (or lateral) preferably refer to a preferred direction in which the vibratable membrane is aligned to generate or record pressure waves of the fluid. Preferably, the vibratable membrane is suspended horizontally between at least two side regions of a support, while the vertical direction (interaction direction with the fluid) for generating or recording pressure waves is orthogonal to it. In the case of a MEMS loudspeaker, the vertical (interaction) direction corresponds to the vertical sound emission direction of the MEMS loudspeaker. In this case, vertical preferably means the direction of sound emission, while horizontal means a direction orthogonal to this. In the case of a MEMS microphone, the vertical (interaction) direction corresponds to the vertical sound detection direction of the MEMS microphone. In this case, vertical preferably means the direction of sound detection or recording, while horizontal means a direction orthogonal to this.

The vertical sections of the vibratable membrane thus preferably refer to sections of the vibratable membrane which are aligned in the emission direction of a MEMS loudspeaker or the detection direction of a MEMS microphone.

While the vibrating membrane is preferably aligned horizontally to the sound emission direction or sound detection direction, the sound waves are generated by actuating the vertical sections or vice versa detected.

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

The carrier is preferably a frame structure which is essentially formed by a continuous outer border in the form of side walls of a free flat area. The frame structure is preferably stable and rigid. In the case of an angular frame shape (triangular, square, hexagonal or generally polygonal outline), the individual side areas which preferably essentially form the frame structure are called side walls in particular.

The oscillating membrane is preferably held by at least two side walls of the carrier. In the exemplary Fig. 1-9 the two side walls can be seen in cross-section. Preferably, however, the support comprises four side areas, with additional end faces usually parallel to the drawn cross-section. These two additional side walls span the frame structure.

The oscillating membrane is preferably suspended flat within the free surface. The flat spread of the oscillating membrane characterizes a horizontal direction, while the vertical sections are orthogonal to this. In relation to the front surfaces, the membrane can be attached to these side walls or slit there for greater mobility. The slit can advantageously represent a dynamic high-pass filter, which, for example, couples a front volume and a rear volume with one another.

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

These materials are easy and inexpensive to process in semiconductor and/or microsystem production and are suitable for large-scale production. The carrier structure can be manufactured flexibly due to the materials and/or manufacturing methods. The MEMS converter comprising an oscillating membrane together with a carrier is manufactured in a semiconductor process, preferably on a wafer. This further simplifies and reduces the cost of production, so that a compact and robust MEMS converter can be provided cost-effectively.

In a preferred embodiment, the oscillating membrane is formed by a lamellar structure or meander structure. Preferably, the specification of a lamellar or meander structure refers to the shape of the oscillating membrane in cross section. A lamellar structure preferably refers to an arrangement of similar, parallel layers, which preferably form the vertical sections. The individual lamellae are preferably arranged with their surface parallel to the vertical direction, preferably an emission or Detection direction. Preferably, the lamellae are constructed in multiple layers and form a mechanical biomorph. For example, the lamellae can each comprise an actuator layer and a passive layer made of a support material and/or two differently controllable actuator layers.

It may be preferred that the lamellae are flat, which means in particular that their extension in each of the two dimensions (height, width) of their surface is greater than in a dimension perpendicular to this (the thickness). For example, size ratios of at least 2:1, preferably at least 5:1, 10:1 or more may be preferred.

The vibratable membrane preferably has a plurality of lamellae which form the vertical sections. For example, 2, 3, 4, 5, 10, 15, 20, 30, 40, 50 or more lamellae may be preferred. This achieves a high level of efficiency for a desired sound emission or sound detection in a very small space.

In a non-claimed embodiment, the vibrating membrane is preferably formed by the lamellae as vertical sections, which are connected to one another via conductive bridges or horizontal sections. Metal bridges, for example, are suitable as bridges (cf. Fig.9 ) or bridges made of other conductive materials. On the one hand, the conductive bridges ensure the mechanical integrity of the oscillating membrane. On the other hand, the conductive bridges advantageously allow all lamellae to be contacted using electrodes at the end. The lamellae can thus be excited synchronously with horizontal vibrations or detect them with little control and manufacturing effort.

A meander structure preferably refers to a structure formed from a sequence of mutually orthogonal sections in cross-section. The mutually orthogonal sections are preferably vertical and horizontal sections of the vibratable membrane. The meander structure is particularly preferably rectangular in cross-section. The meander structure thus preferably corresponds to a membrane folded along the width. In the sense of the invention, a vibratable membrane can therefore preferably also be referred to as a bellows. The parallel folds of the bellows preferably form the vertical sections. The connecting sections between the folds preferably form the horizontal sections. The vertical sections are preferably longer than the horizontal sections, for example by a factor of 1.5, 2, 3, 4 or more.

In relation to the function of an oscillating membrane in meander form for generating or receiving sound waves, the vertical sections are decisive, analogous to the lamellae described above. The vertical sections are preferably constructed in multiple layers and form a mechanical biomorph. For example, the vertical sections can each comprise an actuator layer and a passive layer made of a support material and/or two differently controllable actuator layers. The horizontal sections of the folded membrane can preferably be constructed identically to the vertical sections (cf. among others Fig. 3-7 ). However, it may also be preferred that the horizontal sections - in contrast to the vertical sections - do not have an actuator layer, but only a mechanical support layer and/or an electrically conductive layer.

In a preferred embodiment, the at least one layer of actuator material of the oscillatable membrane is a continuous layer. Continuous preferably means that there is no interruption in the cross-sectional profile. Accordingly, in the embodiment mentioned, it is preferred that there is a continuous layer of actuator material in both the vertical and horizontal sections. A continuous layer is particularly easy to manufacture and ensures synchronous actuation when operating a MEMS loudspeaker.

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

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

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

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

Preferably, the vertical sections are flat, which means in particular that their extension in each of the two dimensions (height, width) of their surface is greater than in a dimension perpendicular thereto (the thickness). For example, size ratios of at least 2:1, preferably at least 5:1, 10:1 or more may be preferred.

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

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

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

In a preferred embodiment, the length of the vertical sections is between 10 µm and 10 mm, preferably between 100 µm and 1 mm. Intermediate ranges from the aforementioned ranges can 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. A person skilled in the art will recognize that the aforementioned range limits can also be combined to obtain further preferred ranges, such as 10 µm to 500 µm, 500 µm to 5 µm or even 1 mm to 5 mm.

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

In a preferred embodiment of the invention, the oscillatable membrane is formed by a meander structure with alternating vertical and horizontal sections, with holding structures attached to at least two of the horizontal sections, which are directly or indirectly connected to the carrier. The holding structures can be provided, for example, by substrate material of the carrier, ie the holding structures can be formed directly from the substrate of a bottom wafer . Alternatively, it is also possible for the holding structures to be connected to the horizontal sections as separate ridges or elevations of a top wafer .

The support structures can preferably be attached to one and/or two sides of the vibratable membrane, i.e. preferably to upper and/or lower horizontal sections.

Particularly when a larger dimensioned vibrating membrane is suspended between the side walls of a support, the use of support structures advantageously allows stabilization without negatively affecting sound generation or sound absorption.

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

Different layers can be provided for the construction of the oscillating membrane in order to ensure the described actuation and excitation of horizontal oscillations or their detection.

Contacting one or more actuator layers and/or one or more layers of a mechanical support material and thus applying or detecting an electrical Voltage can be applied directly via the end electrodes or supported by a layer of conductive material,

In a preferred embodiment, the vibratable membrane therefore comprises at least one layer of a conductive material.

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

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

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, the layer ensures contact between the actuator layer and an electrical potential that can be applied to the end electrodes. On the other hand, it functions as a mechanical support layer in the manner described to generate horizontal curvatures or vibrations when the actuator layer is actuated accordingly.

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

In a further preferred embodiment, the oscillatable membrane comprises two layers of an actuator material, which are separated by a middle layer of a conductive material, preferably metal, wherein the middle layer is connected to a first electrode and at least one of the two layers of an actuator material is contacted with a second electrode via a further layer of a conductive material, preferably a metal.

As explained above, in a preferred embodiment, two actuator layers can also be used, for example to cause the vertical sections to vibrate horizontally by means of different controls. In order to transfer the electrical potential changes from the end electrodes to the respective actuator layer, two or more intermediate layers made of a conductive material can preferably be provided. The layers made of conductive material, for example made of a metal, preferably serve exclusively for contacting and not as a mechanical support layer. The voltage required for curvature or vibration in the sense of a bimorph for a MEMS loudspeaker is induced by a different control of the actuator layers themselves.

Preferably, the layers made of a conductive material, such as metal, can therefore be made particularly thin (less than 500 nm, preferably less than 200 nm).

In the Fig.5 One such preferred embodiment is shown as an example. This has an oscillating membrane as a meander structure with two layers of an actuator material, which are separated by a middle layer of a conductive material (metal). The middle layer is connected to a first end electrode pad, while the upper actuator layer is in contact with a second end electrode via a further layer of a conductive material. A lower layer of a conductive material is not in contact with any of the electrodes. A reverse order of the layers or omission of the lower layer of conductive material, which is not in contact with the electrodes, can also be provided.

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

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

In a preferred embodiment, the at least one actuator layer is not continuous, but is only present in the vertical sections, but not in the horizontal sections. In this case, it can be preferred that a mechanical support layer, if present, runs continuously, or not runs continuously and is only provided in vertical sections, for example. In order to still be able to contact the vertical sections using end-side electrodes, it is preferred to apply one or more continuous layers made of a conductive material (preferably metal).

A preferred manufacturing process for an embodiment with a non-continuous actuator layer is described in the Figure 7 illustrated. Here, a targeted spacer etching of the actuator layer can be carried out in horizontal sections, so that only the vertical sections of the membrane have a layer of an actuator material. A continuous layer of a mechanical support material can also be dielectric in order to avoid a short circuit between an upper and lower conductive layer (also known as top and bottom electrode).

The design is characterized by a particularly effective actuation and high performance, in which only the vertical sections are specifically stimulated to alternately arch or oscillate, while the horizontal sections remain mechanically neutral. The displaced volume per phase of the actuation can advantageously be increased again.

In the embodiments described above, a vibratable membrane in meander shape is preferably obtained by applying or etching correspondingly functional layers.

Alternatively, a vibrating membrane can also be manufactured by providing vertical sections and connecting them using metal bridges.

In a non-claimed embodiment, the vertical sections of the vibratable membrane comprise two layers, wherein a first layer consists of an actuator material, a second layer consists of a conductive support material and wherein the vertical sections are connected via horizontal metal bridges.

Like in the Fig.9 As illustrated, several individual piezoceramic elements comprising a layer of a mechanical support material and a layer of a piezoelectric material, as well as a sacrificial layer, can preferably be provided for this purpose. Through several process steps comprising through-plating and metal filling as well as stacking and dicing of the piezoceramic elements, a membrane with high efficiency can advantageously be obtained in a robust and process-efficient manner.

In this embodiment, no continuous, homogeneous conductive layer is necessary. Instead, the contacting of the actuator layer in the vertical sections is ensured by the metal bridges and a conductive mechanical support material.

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

In a preferred embodiment of the invention, the MEMS converter, preferably a MEMS loudspeaker, comprises a control unit which is configured to control the at least one electrode so that the two or more vertical sections are excited to horizontal oscillations. Preferably, the control unit is configured to control the electrodes, which ensures a frequency of the horizontal oscillations between 10 Hz and 20 kHz.

In a preferred embodiment of the invention, the MEMS transducer, preferably a MEMS microphone, comprises a control unit which is configured to detect an electrical signal provided by the at least one electrode, which was generated by horizontal vibrations of the two or more vertical sections. The control unit of a MEMS microphone is preferably configured to receive and process an electrical signal which corresponds to a frequency of the horizontal vibrations between 10 Hz and 20 kHz and is thus set up for sound detection in the audible range.

The control unit is therefore preferably configured and set up to use electrical signals to control the vibrating membrane (or the actuator position(s) in the vertical sections) to horizontal vibrations and a sound emission in the audible frequency range or to record and process a corresponding electrical signal when the vibrating membrane is excited.

For this purpose, the control unit may preferably comprise a data processing unit.

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

In preferred embodiments, the control unit is integrated on a circuit board or circuit board alongside other components of the MEMS converter (carrier, oscillating membrane). This means that the MEMS converter is preferably seamlessly integrated with the electronics required for control or detection. In addition to the control unit, other electronic components such as a communication interface (preferably wireless, e.g. Bluetooth), an amplifier, a filter or a sensor can also be installed on one and the same circuit board.

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

In a further preferred embodiment, the vibratable membrane held by the carrier is arranged in a front side of a housing which encloses a rear resonance volume. The sound emission of such a MEMS loudspeaker thus preferably occurs towards the open front side ( sound port ), whereby the sound image is improved, particularly for lower frequencies, by the rear resonance volume.

In a further preferred embodiment, there is a ventilation opening in the housing to avoid acoustic short circuits and/or to support the sound image. The ventilation opening is preferably small compared to the sound port and can, for example, have a maximum dimension of less than 100 µm, preferably less than 50 µm.

• Ätzen eines Substrats, vorzugsweise von einer Vorderseite, zur Ausbildung einer Strukturierung, vorzugsweise einer Mäanderstruktur
• Optionales Auftragen eines Ätzstops
• Aufbringen mindestens zweier Lagen, wobei mindestens erste Lage ein Aktuatormaterial und eine zweite Lage ein mechanischen Stützmaterial umfassen oder mindestens zwei Lagen ein Aktuatormaterial umfassen
• Kontaktieren der ersten und/oder zweiten Lage mit einer Elektrode
• Ätzen, vorzugsweise von der Rückseite, und optionale Entfernung des Ätzstops,

• sodass eine schwingfähige Membran, vorzugsweise in Form einer Mäanderstruktur, von einem durch das Substrat (8) gebildeten Träger (4) gehalten wird, wobei die schwingfähige Membran (1) zur Erzeugung oder Aufnahme von Druckwellen des Fluids in einer vertikalen Richtung mindestens zwei oder mehr vertikale Abschnitte (2) umfasst, welche parallel zur vertikalen Richtung ausgebildet sind und sodass durch Ansteuerung der mindestens einen Elektrode die zwei oder mehr vertikalen Abschnitte zu horizontalen Schwingungen angeregt werden können oder
• sodass bei Anregung der zwei oder mehr vertikalen Abschnitte zu horizontalen Schwingungen an der mindestens einen Elektrode ein elektrisches Signal erzeugt werden kann.

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

• Etching a substrate, preferably from a front side, to form a structure, preferably a meander structure
• Optional application of an etch stop
• Applying at least two layers, wherein at least the first layer comprises an actuator material and a second layer comprises a mechanical support material or at least two layers comprise an actuator material
• Contacting the first and/or second layer with an electrode
• Etching, preferably from the back, and optional removal of the etch stop,

• so that an oscillatable membrane, preferably in the form of a meander structure, is held by a carrier (4) formed by the substrate (8), wherein the oscillatable membrane (1) comprises at least two or more vertical sections (2) for generating or receiving pressure waves of the fluid in a vertical direction, which are formed parallel to the vertical direction and so that by controlling the at least one electrode, the two or more vertical sections can be excited to horizontal oscillations or
• such that when the two or more vertical sections are excited to horizontal oscillations, an electrical signal can be generated at the at least one electrode.

The average person skilled in the art will recognize that technical features, definitions and advantages of preferred embodiments of the described MEMS transducer, preferably MEMS loudspeaker or MEMS microphone, also apply to the described manufacturing method. Preferably, the described manufacturing method serves to provide a MEMS transducer with a folded oscillatable membrane with a meander structure. Examples of preferred manufacturing steps are described in the Fig. 2A-G or Fig. 8A-J described.

One of the preferred materials mentioned above can be used as a substrate. During etching, a blank, such as a wafer, can be brought into the desired basic shape of the meander structure. In a next step, the layers for the vibrating membrane are preferably applied.

Applying at least one layer of a conductive material preferably includes applying a plurality of layers and in particular a layer system in addition to applying one layer. A layer system comprises at least two layers applied in a planned manner to one another. Applying a layer or a layer system preferably serves to define the oscillatable membrane comprising vertical sections which can be excited to horizontal oscillations.

The application can preferably be selected from the group comprising physical vapor deposition (PVD), in particular thermal evaporation, laser beam evaporation, arc evaporation, molecular beam epitaxy, sputtering, chemical vapor deposition (CVD) and/or atomic layer deposition (ALD). In particular, the application can comprise, for example, deposition, e.g. in the case of a substrate made of polysilicon.

Etching and/or structuring can preferably be selected from the group comprising dry etching, wet chemical etching and/or plasma etching, in particular reactive ion etching, reactive ion deep etching (Bosch process).

If further structuring of the vibrating membrane is desired, this can be done using additional etching processes, for example. Additional material can also be deposited or doped using conventional methods.

To contact the layers, suitable material such as copper, gold and/or platinum can also be deposited using common processes. Physical vapor deposition (PVD), chemical vapor deposition (CVD) or electrochemical deposition are preferably used for this.

The process steps can be used to provide a finely structured vibratable membrane with a desired definition of vertical and horizontal sections, which is preferably suspended between two side areas of a stable support and has dimensions in the micrometer range. The manufacturing steps are standard process steps in semiconductor processing, so they have proven themselves and are also suitable for mass production.

• Bereitstellen mehrerer einzelner Piezokeramikelemente, umfassend eine Opferlage, eine Lage aus einem leitfähigen Material und eine Lage aus einem piezoelektrischen Material
• Definition von Löchern für eine Durchkontaktierung in den Piezokeramikelementen und Metallfüllung
• Stapeln der Piezokeramikelemente und optionales Schneiden (Dicing), sodass ein Stapel von Piezokeramikelementen erhalten wird, welcher durch Metallbrücken verbunden ist
• Entfernung der Opferlage und Einbringen des Stapels der Piezokeramikelemente in einen Träger, wobei eine Kontaktierung des ersten und letzten Piezokeramikelementes mit jeweils einer Elektrode erfolgt,

sodass eine schwingfähige Membran, vorzugsweise in Form einer Lamellenstruktur, von einem durch das Substrat gebildeten Träger gehalten wird, wobei die schwingfähige Membran zur Erzeugung oder Aufnahme von Druckwellen des Fluids in einer vertikalen Richtung mindestens zwei oder mehr vertikale Abschnitte umfasst, welche parallel zur vertikalen Richtung ausgebildet sind und sodass durch Ansteuerung der mindestens einen Elektrode die zwei oder mehr vertikalen Abschnitte zu horizontalen Schwingungen angeregt werden können oder sodass bei Anregung der zwei oder mehr vertikalen Abschnitte zu horizontalen Schwingungen an der mindestens einen Elektrode ein elektrisches Signal erzeugt werden kann.An unclaimed manufacturing method for a MEMS converter as described above comprises the following steps:

• Providing a plurality of individual piezoceramic elements comprising a sacrificial layer, a layer of a conductive material and a layer of a piezoelectric material
• Definition of holes for through-plating in the piezoceramic elements and metal filling
• Stacking of the piezoceramic elements and optionally dicing to obtain a stack of piezoceramic elements connected by metal bridges
• Removal of the sacrificial layer and insertion of the stack of piezoceramic elements into a carrier, whereby the first and last piezoceramic elements are each contacted with an electrode,

such that an oscillatable membrane, preferably in the form of a lamellar structure, is held by a carrier formed by the substrate, wherein the oscillatable membrane for generating or receiving pressure waves of the fluid in a vertical direction comprises at least two or more vertical sections which are formed parallel to the vertical direction and such that by controlling the at least one electrode the two or more vertical sections can be excited to horizontal oscillations or such that when the two or more vertical sections are excited to horizontal oscillations an electrical signal can be generated at the at least one electrode.

The average person skilled in the art will recognize that technical features, definitions and advantages of preferred embodiments of the described MEMS transducer, preferably a MEMS loudspeaker or MEMS microphone, also apply to the described manufacturing method. Preferably, the described manufacturing method serves to provide a MEMS transducer with an oscillatable membrane with a lamella structure, wherein the lamellae are mechanical bimorphs and are connected by metal bridges. Examples of unclaimed manufacturing steps are given in the Fig. 9 A-F illustrated.

In the alternative manufacturing process, several individual piezoceramic elements can advantageously be used to obtain an oscillating membrane with lamellae as vertical sections, which are connected to each other by metal bridges, by means of a definition of holes, metal filling as well as stacking and dicing.

Piezoceramics are preferably ceramic materials that show a charge separation when deformed by an external force or that undergo a change in shape when an electrical voltage is applied. The piezoceramic elements preferably comprise a piezoelectric layer and a layer made of a mechanical support material, as described above, as well as a sacrificial layer.

The sacrificial layer is used to process and provide the metal bridges and will not itself be part of the vibrating membrane.

Preferably, the sacrificial layer can be a photoresist or photo lacquer, for example. These materials change their solubility when exposed to light, particularly UV light. In particular, it can be a so-called positive lacquer, the solubility of which increases when exposed to UV light. This allows the sacrificial layer to be removed in a targeted manner after a metal filling to provide the metal bridges.

Detailed description

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 it.

Short description of the figures

Fig.1

Schematic representation of a cross section of a preferred embodiment of a MEMS loudspeaker according to the invention A: at rest and B: during actuation.

Fig.2

Schematic representation of a preferred manufacturing process for a MEMS loudspeaker with an oscillating membrane which has a meander shape in cross-section.

Fig. 3, 4

Schematic representation of preferred embodiments of a MEMS loudspeaker with an oscillating membrane in meander shape, the horizontal sections of which are supported by holding structures.

Fig.5

Schematic representation of a preferred embodiment of a MEMS loudspeaker with two actuator layers separated by a middle layer made of a conductive material.

Fig.6

Schematic representation of preferred controls for operating the MEMS loudspeakers

Fig.7

Schematic representation of a preferred integration of a MEMS loudspeaker in the front of a cabinet with rear resonance volume.

Fig.8

Schematic representation of a preferred manufacturing process for a MEMS loudspeaker with an oscillating membrane which has a meander shape in cross section, wherein only the vertical sections have a layer of an actuator material.

Fig.9

Schematic representation of a non-claimed manufacturing process for a MEMS loudspeaker with an oscillating membrane based on individual piezoceramic elements.

Detailed description of the figures

Figure 1 illustrates a preferred embodiment of a MEMS loudspeaker according to the invention. Fig. 1 A shows a resting state, while Fig. 1B Two phases during the actuation of the MEMS loudspeaker are illustrated.

The MEMS loudspeaker comprises a vibrating membrane 1 for generating sound waves in a vertical emission direction, wherein the vibrating membrane 1 is held in a horizontal position by a carrier 4. The vibrating membrane 1 has a meandering structure in cross section with horizontal 3 and vertical sections 2. The vertical sections are formed parallel to the emission direction and have at least one actuator layer, for example a layer made of a piezoelectric material. The vibrating membrane 1 and the actuator layer are contacted by means of electrodes at the end. For this purpose, an electrode pad (not shown) can also be located on the carrier 4 , for example.

The vertical sections are preferably mechanical bimorphs which can be excited to horizontal vibrations by suitable controls. For this purpose, the vertical sections 2 can comprise, for example, a first layer of an actuator material and a second layer of a mechanical support material. By controlling the actuator layer, a stress gradient and thus a curvature or vibration can be generated. It can also be preferred that the vertical sections 2 comprise two actuator layers which are controlled in opposite directions in order to cause a curvature of the vertical sections 2 by a corresponding relative change in shape.

Figure 1B illustrates two phases during an actuation as an example. Advantageously, the majority of the vertical sections 2 of the vibrating membrane 1 can move an increased total volume in the vertical emission direction with small horizontal movements (curvature) of a few micrometers and thus be used to generate sound. The actuation allows a particularly efficient implementation, since during one phase almost the entire air volume between the vertical sections can be moved up or down along the emission direction.

Figure 2 shows schematically a preferred manufacturing method for providing a MEMS loudspeaker with an oscillating membrane 1 which has a meandering shape in cross section. An oscillating membrane with a meandering shape in cross section can also preferably be referred to as a folded membrane or bellows.

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

Then a layer of etch stop 9 ( Fig. 2B ), which can be TEOS or PECVD , for example. A layer of a mechanical support material 10 ( Fig. 2C ) and a layer of an actuator material 11 is applied. The mechanical support material 10 can be doped polysilicon, for example, while a piezoelectric material can be used for the actuator material 10 , for example. Layer thicknesses of 1 µm, for example, can be preferred. The piezoelectric material can preferably have a C-axis orientation perpendicular to the surface, so that a transverse piezoelectric effect is used. Other orientations and, for example, the use of a longitudinal effect can also be preferred.

Fig. 2E shows the preferred application of a full-surface top electrode as a layer of a conductive material 12 . End contact can be made, for example, by means of an electrode pad 13 ( Fig. 2 F) .

Fig. 2F and 2G illustrate a further etching of the substrate 8 from the back or bottom side, and the removal of the etch stop.

The manufacturing steps 2A-G thus produce an oscillating membrane 1 which has a meandering structure in cross section. Advantageously, a continuous actuator layer 11 and the provision of end-side contacts 13 allow efficient actuation of the vertical sections 2 to produce horizontal oscillations (cf. Fig.1 ). As in Fig. 2G As can be seen, control is preferably carried out by means of two electrodes, so the actuator layer 12 is preferably contacted both from a front side (top electrode, conductive layer 12) and from a rear side (bottom electrode, via conductive mechanical support material 10) (cf. Fig. 6A ).

To stabilize the membrane 1 suspended between the side walls of the carrier 4, holding structures 14 can be provided. As shown in the Fig. 3 and 4 shown, these can preferably support horizontal sections 3 of the vibrating membrane 1. The horizontal sections 3 are advantageously mechanically neutral (cf. Fig 1B ), so that no undesirable stresses are induced between the membrane 1 and the support structure 14 or carrier 4 during actuation.

Fig.5 illustrates a preferred alternative embodiment of a MEMS loudspeaker, wherein the vibratable membrane 1 comprises two actuator layers, which are separated by a middle layer made of a conductive material 12 , preferably metal. The middle layer is connected to a first end-side electrode pad 13 , while in the embodiment shown the upper actuator layer 11 is contacted with a second end electrode pad 13 via a further layer made of a conductive material 12 .

Fig.6 illustrates preferred controls for operating the described MEMS loudspeakers.

In Fig. 6A a preferred control for a MEMS loudspeaker with an actuator layer 11 and a passive mechanical support layer 10 is shown. The control is preferably carried out by means of two end-side electrode pads 13 , so that the horizontal vibrations can be generated by a change in the shape of the actuator material compared to the mechanical support material. The actuator layer 11 is preferably contacted both from a front side (top electrode 13 , conductive layer 10) and from a rear side (bottom electrode 13 , conductive mechanical support material 10) . An alternating voltage as an audio input signal can be applied, for example, to the front electrode pad 13 (left), while the rear electrode pad 13 (right) is grounded.

In Fig. 6B a preferred control for a MEMS loudspeaker with two actuator layers 11 is shown, which are separated by a middle layer made of a conductive material 12 , preferably metal.

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

Fig.7 shows, by way of example, a preferred integration of a MEMS loudspeaker according to the invention in a housing 15. Preferably, the vibrating membrane 1 held by the carrier 4 is arranged in a front side or front of a housing ( sound port ). The housing also encloses a rear resonance volume ( back volume 16 ). A ventilation opening 17 can be introduced to avoid acoustic short circuits or to support the sound image.

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

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

Then a layer of etch stop 9 ( Fig. 2B ), which can be TEOS or PECVD , for example. A layer of a mechanical support material 10 ( Fig. 2C ) and an actuator material 11. In the The mechanical support material 10 can be, for example, doped polysilicon, while a piezoelectric material is preferably used for the actuator material 12 .

In contrast to the Fig.2 In the embodiment shown, the actuator layer 11 is not contacted as a continuous layer with an upper conductive layer. Instead, a spacer etching is carried out ( Fig. 8F ) of the actuator layer 11 in the horizontal sections of the membrane, so that only the vertical sections of the membrane have a layer of an actuator material 11 .

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

Fig. 8 I and 8 J illustrate a further etching of the substrate 8 from the back or bottom side and optionally the application of a continuous conductive layer 12 as a back side electrode.

Fig.9 illustrates an unclaimed manufacturing method for providing a MEMS loudspeaker with an oscillating membrane based on individual piezoceramics.

First, several individual piezoceramic elements 19 are provided, comprising a layer of a mechanical support material 10 (e.g. doped polysilicon) and a layer of a piezoelectric material 11 as well as a sacrificial layer 20 (cf. Fig. 9A and 9B The sacrificial layer 20 can, for example, be a photoresist.

This is followed by a definition of holes for through-plating and metal filling 21 (cf. Fig. 9C) , The piezoceramic elements 19 are stacked ( Fig. 9 D) and cut (Dicing 22 , Fig. 9E ), so that two or more stacks of piezoceramic elements 19 are obtained, which are connected by metal bridges 21 (cf. Fig. 9E ).

After removal of the victim 20 ( Fig. 9F ), the stacked piezoceramic elements 19 are introduced into a carrier 4 , wherein preferably the first and last piezoceramic elements are each contacted with an electrode 13 ( Fig. 9G ).

In this way, a vibratable membrane 1 is also obtained between a carrier 4 , which comprises at least two or more vertical sections 2 for generating sound waves in a vertical emission direction, which are formed parallel to the emission direction and can be excited to horizontal vibrations.

Here too, the actuator principle is preferably based on a relative change in shape of the actuator layer 11 compared to the mechanical support layer 10. A continuous actuator layer is not necessary for this. Contacting of all vertical sections 2 by means of end-side control is ensured by the metal bridges 23 .

LIST OF REFERENCE SYMBOLS

1

Oscillating membrane

2

Vertical sections of the vibrating membrane

3

Horizontal sections of the vibrating membrane

4

carrier

5

Air volumes between the vertical sections

8th

Substrat

9

Etching stop

10

Layer of a mechanical support material, preferably doped polysilicon

11

Layer of an actuator material (actuator layer), preferably of a piezoelectric material

12

Layer of a conductive material, preferably metal

13

Contacting the electrode, preferably electrode pad

14

Support structures

15

Housing

16

rear resonance volume

17

Ventilation opening

18

Layer of a dielectric material

19

Piezoceramic element(s)

20

Victim situation

21

Defined holes for through-hole plating with metal filling

22

Dicing

23

Metal bridges

LITERATURE

• F. Stoppel, C. Eisermann, S. Gu-Stoppel, D. Kaden, T. Giese and B. Wagner, NOVEL MEMBRANE-LESS TWO-WAY MEMS LOUDSPEAKER BASED ON PIEZOELECTRIC DUAL-CONCENTRIC ACTUATORS, Transducers 2017, Kaohsiung, TAIWAN, June 18-22, 2017 .
• Iman Shahosseini, Elie LEFEUVRE, Johan Moulin, Marion Woytasik, Emile Martincic, et al. Electromagnetic MEMS Microspeaker for Portable Electronic Devices. Microsystem Technologies, Springer Verlag (Germany), 2013, pp.10. <hal-01103612> .
• Bert Kaiser, Sergiu Langa, Lutz Ehrig, Michael Stolz, Hermann Schenk, Holger Conrad, Harald Schenk, Klaus Schimmanz and David Schuffenhauer, Concept and proof for an all-silicon MEMS microspeaker utilizing air chambers .

Claims (13)

1. MEMS transducer for interacting with a volume flow of a fluid comprising

   - a carrier (4),

   - a vibratable membrane (1) for generating or receiving pressure waves of the fluid in a vertical direction, the vibratable membrane (1) being supported by the carrier (4), wherein the vibratable membrane (1) is manufactured together with the carrier (4) in a semiconductor process

   and wherein the vibratable membrane (1) exhibits two or more vertical sections (2) formed parallel to the vertical direction and comprising at least one layer of an actuator material (11), wherein at least one end of the vibratable membrane (1) is connected to at least one electrode (13),

   such that the two or more vertical sections (2) can be induced to vibrate horizontally by driving the at least one electrode (13) or such that an electrical signal can be generated at the at least one electrode when the two or more vertical sections (2) are induced to vibrate horizontally.
2. MEMS transducer according to the preceding claim
   characterized in that
   the MEMS transducer is a MEMS loudspeaker, wherein air volumes (5) are preferably present between the vertical sections (2), which, as a result of the horizontal vibrations, are moved along a vertical direction of emission to generate sound waves, or the MEMS transducer is a MEMS microphone, wherein air volumes (5) are preferably present between the vertical sections (2), which are moved along a vertical direction of detection when sound waves are received.
3. MEMS transducer according to one of the preceding claims
   characterized in that

   the two or more vertical sections (2) comprise at least two layers, one layer (11) comprising an actuator material and a second layer (10) comprising a mechanical support material, wherein at least the layer (11) comprising the actuator material is connected to an electrode (13),

   such that horizontal vibrations can be generated by a change in shape of the actuator material relative to the mechanical support material or

   such that horizontal vibrations cause a change in shape of the actuator material relative to the mechanical support material and generate an electrical signal.
4. MEMS transducer according to one of the preceding claims
   characterized in that

   the two or more vertical sections (2) comprise at least two layers, both layers (11) comprising an actuator material and each being connected respectively to an electrode (13), and

   the horizontal vibrations being able to be generated by a change in shape of one layer relative to the other layer, or

   the horizontal vibrations causing a change in shape of one layer relative to the other layer and generating an electrical signal.
5. MEMS transducer according to one of the preceding claims
   characterized in that

   the carrier (4) comprises two side regions between which the vibratable membrane (1) is arranged in a horizontal direction and/or

   the carrier (4) is formed of a substrate (8), preferably selected from the group consisting of monocrystalline silicon, polysilicon, silicon dioxide, silicon carbide, silicon germanium, silicon nitride, nitride, germanium, carbon, gallium arsenide, gallium nitride, indium phosphide and glass.
6. MEMS transducer according to one of the preceding claims
   characterized in that
   the vibratable membrane (1) is formed by a lamellar structure or meander structure.
7. MEMS transducer according to one of the preceding claims
   characterized in that
   the vibratable membrane (1) is formed by a meander structure with alternating vertical (2) and horizontal (3) sections, at least two of the horizontal sections (3) having attached to them retaining structures (14) which are connected directly or indirectly to the carrier (4).
8. MEMS transducer according to one of the preceding claims
   characterized in that
   the actuator material comprises a piezoelectric material, a polymer piezoelectrical material and/or electroactive polymers (EAP), wherein the piezoelectric material is preferably selected from a group comprising lead zirconate titanate (PZT), aluminum nitride (AIN) and zinc oxide (ZnO).
9. MEMS transducer according to one of the preceding claims
   characterized in that
   the vibratable membrane (1) comprises three layers, an upper layer (12) being formed by a conductive material, a middle layer (11) being formed by an actuator material, and a lower layer (12) being formed by a conductive material, wherein the conductive material of the upper and/or lower layer is preferably a mechanical support material.
10. MEMS transducer according to one of the preceding claims
    characterized in that
    the vibratable membrane (1) comprises two layers (11) of actuator material, which are separated by a middle layer (12) of conductive material, preferably metal, wherein the middle layer (12) is connected to a first electrode (13) and at least one of the two layers (11) of actuator material is connected to a second electrode (13) via a further layer (12) of conductive material, preferably metal.
11. MEMS transducer according to one of the preceding claims
    characterized in that
    the vibratable membrane (1) is coated with a layer of a non-stick material.
12. MEMS transducer according to one of the preceding claims
    characterized in that
    the vibratable membrane (1) supported by the carrier (4) is arranged in a front side of a housing (15) which encloses a rear resonant volume (16), wherein a ventilation opening (17) is preferably present in the housing (15) for avoiding acoustic short circuits and/or for supporting the sound.
13. Manufacturing method for a MEMS transducer according to one of the preceding claims comprising the following steps:

    - Etching of a substrate (8), preferably from a front side, to form a structuring, preferably a meandering structure

    - Optional application of an etch stop

    - Application of at least two layers, wherein at least a first layer (11) comprises an actuator material and a second layer (10) comprises a mechanical support material, or at least two layers (11) comprise an actuator material

    - Connection of the first and/or second layer to an electrode (13)

    - Etching, preferably from the rear side, and optional removal of the etch stop,

    such that a vibratable membrane (1), preferably in the form of a meander structure, is supported by a carrier (4) formed by the substrate (8), the vibratable membrane (1) comprising at least two or more vertical sections (2) for generating or receiving pressure waves of the fluid in a vertical direction, which sections are formed parallel to the vertical direction and such that the two or more vertical sections (2) can be induced to vibrate horizontally by driving the at least one electrode (13), or

    such that when the two or more vertical sections (2) are induced to vibrate horizontally, an electrical signal can be generated at the at least one electrode.

Images