EP3852391A1 - Enhanced performance mems loudspeaker - Google Patents

Abstract

The invention relates to a MEMS converter which comprises an oscillatable membrane (1) for generating or absorbing pressure waves of a fluid in a vertical direction, the oscillatable membrane (1) being held by a support (4) and the oscillatable membrane (1 ) has two or more vertical sections (2) which are formed parallel to the vertical direction and comprise at least one layer of an actuator material (11). The vibratable membrane (1) is preferably at the end in contact with an electrode (13) so that the two or more vertical sections (2) can be excited to horizontal vibrations by controlling the at least one electrode (13) or so that when the two or more vertical sections (2) to horizontal oscillations at the at least one electrode (13) an electrical signal can be generated.

Description

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

Background and prior art

For the production of compact, mechanical-electronic devices, microsystem technology is used in many fields of application today. The microsystems ( microelectromechanical system, abbreviated to MEMS) that can be produced in this way are very compact (micrometer range) with excellent functionality and ever lower production costs.

MEMS converters such as MEMS loudspeakers or MEMS microphones are also known from the prior art. Current MEMS loudspeakers are mostly designed as planar membrane systems with a vertical actuation of a vibratable membrane in the direction of emission. The excitation takes place, for example, by means of piezoelectric, electromagnetic or electrostatic actuators.

A MEMS electromagnetic speaker for mobile devices is described in Shahosseini et al. Described in 2015. The MEMS loudspeaker has a stiffening silicon microstructure as a sound emitter, with the movable part being suspended from a carrier via silicon mainsprings in order to enable large displacements out of the plane by means of an electromagnetic motor.

Stoppel et al. 2017 reveals a two-way loudspeaker whose concept is based on concentric piezoelectric actuators. As a special feature, the vibration diaphragm is not designed to be closed, but rather includes eight piezoelectric unimorph actuators, each of which consists 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, which are connected to a rigid frame by means of a spring. The separation of the membrane should allow an improved sound image with higher power.

A disadvantage of such planar MEMS loudspeakers is their limitation with regard to the sound power, in particular 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. For sufficient sound power, either deflections for the vibration diaphragms of at least 100 µm or large-area diaphragms in the square centimeter range are necessary. Both conditions are difficult to implement using MEMS technology.

In the prior art, it has therefore been proposed to design MEMS loudspeakers which 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. It is advantageous here that an increased volume flow can be moved over a small area and thus an increased sound power 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 disclosed.

The MEMS loudspeaker comprises a plurality of electrostatic bending actuators, which are arranged between a top and bottom wafer as vertical lamellas and can be excited to lateral vibrations by appropriate control. Here, an inner lamella forms an actuator electrode opposite two outer lamellae. With the exception of a connection node between the electrodes, which are still galvanically separated, there is an air gap between the three curved lamellae. If there is a potential inside against outside, this leads to a mutual attraction due to the curvature of the design in the direction of a preferred direction, which is specified by an anchor. The bulges of the outer lamellae are used for mobility. The restoring force is given by a mechanical spring force. A 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 therefore the sound power are restricted in order to avoid a pull-in effect and acoustic breakdown.

An alternative air pulse or sound generation system based on MEMS is shown in US 2019/011 64 17 A1 described. The device comprises a front and rear chamber and a plurality of valves, the front and rear chambers being separated from one another by means of a folded membrane. In one embodiment, the folded membrane has a rectangular meandering structure with horizontal and vertical sections in cross section. Piezo actuators are positioned on the respective horizontal sections in order to bring about a lateral movement of the vertical sections by synchronized expansion 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.

The disadvantage, however, is the increased effort for the synchronized drive of the piezo actuators. There is also potential for improvement with regard to the volume displaced by the lateral vibrations, which is limited by the geometric arrangement of the horizontal sections actuated on one side.

In light of the disadvantages of the prior art, there is thus 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, and 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 is characterized at the same time by a simple, inexpensive and compact structure.

Summary of the invention

The object is achieved 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

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 preferably relates to a MEMS converter for interaction with a volume flow of a fluid

• a carrier,
• a vibratable membrane for generating or absorbing pressure waves of the fluid in a vertical direction, wherein the vibratable membrane is held by the carrier

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 made of an actuator material, the oscillatable membrane being in contact with at least one electrode at the end,
so that the two or more vertical sections can be excited to horizontal oscillations by controlling the at least one electrode or so that an electrical signal can be generated at the at least one electrode when the two or more vertical sections are excited to horizontal oscillations.

• 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.The MEMS converter can particularly preferably be a MEMS loudspeaker. In a particularly preferred embodiment, the invention relates to a MEMS loudspeaker comprising

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

wherein the vibratory 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 vibratable membrane is preferably in contact with at least one electrode at the end, so that the two or more electrodes are triggered by the at least one electrode vertical sections can be excited to horizontal oscillations.

Due to the construction of the MEMS loudspeaker, a MEMS loudspeaker with high sound power and simplified control can be obtained.

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 in order to generate sufficient sound pressure. Instead, the majority of the vertical sections of the vibratable 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 and 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 lamellae 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 lamella heights, which limits the sound power.

By means of the solution according to the invention, the vertical sections of the oscillatable membrane can instead be obtained in MEMS design by means of simple manufacturing steps, as explained in detail below. In addition, the actuator principle according to the invention avoids pull-in or sticking of the vertical sections. In contrast to the solution by Kaiser et al. In 2019, no potential differences are obtained in a gap between the vertical sections due to the one-sided electrodes. In addition to avoiding an overvoltage or a pull-in, this can also reduce the accumulation of dust, since, for example, an external electrode can be connected to a ground potential.

Another particular advantage of the MEMS loudspeaker described is the simplified control. While in the US 2019/011 64 17 A1 a plurality of piezoelectric actuators must be contacted on the horizontal sections, the proposed MEMS loudspeaker can be operated by means of 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 oscillations.

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

A “MEMS loudspeaker” preferably denotes a loudspeaker which is based on MEMS technology and whose sound-generating structures are at least partially dimensioned in the micrometer range (1 μm to 1000 μm). For example, the vertical sections of the vibratable membrane can preferably have a dimension in the range of less than 1000 μm in width, height and / or thickness. It can also be preferred here 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 vibratory membrane can advantageously not only be used to form a MEMS loudspeaker with high sound power and simplified control. It is also possible, for example, 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 carrier,

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, the oscillatable membrane preferably being in contact at the end with at least one electrode, so that when the two or more vertical sections are excited an electrical signal can be generated for horizontal vibrations 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 vibratable membrane. Instead of controlling the electrodes to generate horizontal vibrations and therefore sound pressure waves, the MEMS microphone is designed to pick up sound pressure waves in the same vertical direction. Thus, there are preferably air volumes between the vertical sections which are moved along a vertical detection direction when sound waves are picked up. The vertical sections are excited to vibrate horizontally by the sound pressure waves, so that the actuator material generates a corresponding periodic electrical signal.

A “MEMS microphone” preferably denotes a microphone which is based on MEMS technology and whose sound-picking structures are at least partially dimensioned in the micrometer range (1 μm to 1000 μm). For example, the vertical sections of the vibratable membrane can preferably have a dimension in the range of less than 1000 μm in width, height and / or thickness. It can also be preferred here 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 is therefore to be understood as meaning both a MEMS microphone and a MEMS loudspeaker. In general, the MEMS converter refers to a converter for interaction with a volume flow of a fluid, which is based on MEMS technology and whose structures for interaction with the volume flow or for absorbing or generating pressure waves of the fluid are dimensioned in the micrometer range (1 µm to 1000 µm ) exhibit. The fluid can be either a gaseous or a liquid fluid. The structures of the MEMS transducer, in particular the vibratory membrane, are designed to generate or absorb pressure waves from the fluid.

For example, as in the case of a MEMS loudspeaker or MEMS microphone, they can be sound pressure waves. The MEMS converter can, however, 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 sound pressure) into electrical signals or vice versa (conversion of electrical signals into pressure waves, e.g. acoustic signals).

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

At the end, preferably means a positioning of the at least one electrode so that contact with electronics, for example a current or voltage source in the case of a MEMS loudspeaker, can take place at one end of the vibratable membrane, preferably at one end at which the membrane is attached The carrier is suspended. Electrode preferably means an area made of a conductive material (preferably a metal), which is set up for such contact with electronics, e.g. 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 to make contact with electronics and is itself connected to a conductive metal layer which can extend over the entire surface of the vibratory membrane. In the following, the conductive layer is sometimes referred to together with an electrode pad as an electrode, for example as a top electrode or bottom electrode.

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

The end-side provision of the electrodes is thus 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 thus preferably comprises exactly one or exactly two electrodes for contacting the end and no further electrodes (pads) for contacting central vertical sections.

The layer made of an actuator material in the vertical sections is preferably used as part of a mechanical biomorph, with a lateral curvature of the vertical sections being caused by controlling the actuator layer via the electrode or a corresponding electrical signal being generated by an induced lateral curvature.

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

When the actuator position is activated, it can experience, for example, 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 oscillation. Like in the Fig. 1 As illustrated, a push-pull operation can preferably take place by changing polarity on the electrodes, whereby almost the entire volume of air between the vertical sections can alternately be moved in the vertical emission direction.

The advantage of the actuator principle is therefore 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, shear) of the actuator layer in relation to a support layer, sticking of the membrane sections can be excluded. Instead, the vertical sections can finally touch and are therefore not restricted in their deflection.

In a further preferred embodiment, the two or more vertical sections comprise at least two layers, both layers comprising an actuator material and being in contact with electrodes at each end and the horizontal vibrations being able to be generated by changing the shape of one layer compared to the other layer. In the embodiment, the horizontal oscillation of the vertical sections is therefore not generated by a stress gradient between an active actuator layer and a passive support layer, but rather by a relative change in shape of two active actuator layers.

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

In the context 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 its shape, for example an expansion, Undergoes compression or shear or, conversely, generates an electrical voltage with a change in shape.

Preference is given to materials with electric dipoles which experience a change in shape when an electric voltage is applied, the orientation of the dipoles and / or the electric field being able to determine the preferred direction of the changes in shape.

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

The piezoelectric material is particularly preferably selected from a group comprising lead zirconate titanate (PZT), aluminum nitride (AlN) and zinc oxide (ZnO).

The polymer piezoelectric materials preferably include polymers which 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) experience a change in shape (e.g. compression, stretching or shear). An example of a preferred piezoelectric polymer material is polyvinylidene fluoride.

This enables a macroscopic solution to be implemented in which a polymer piezoelectrical material layer is applied to a mechanical support layer and is wound over an upper and lower comb. A polymer piezoelectrical material layer (including electrode) is preferably first provided on a support layer (possibly including a counter electrode). Subsequently, an upper and a lower comb (preferably a MEMS structure) are moved against one another in such a way that a folded membrane with actuatable vertical sections is created.

In the context 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 shape of the actuator layer. In contrast to an actuator layer, the mechanical support material preferably does not change its shape when an electrical voltage is applied. The mechanical support material is preferably electrically conductive, so that it can also be used directly for contacting the actuator layer. However, in some embodiments it can also be non-conductive and, for example, be coated with an electrically conductive layer.

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

While the actuator position 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 a piezoelectric material such as PZT or AlN, for example, a thickness of essentially the same size, preferably between 0.5 μm and 2 μm, has proven to be particularly suitable.

Terms such as essentially, 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%. Details of essentially, approximately, approximately, etc. disclose and always also include the exact stated value.

With periodic control of 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 oscillation, 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 arches or vibrations (cf. Fig. 1 ) can be preferred.

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

In a preferred embodiment, the vibratory membrane therefore comprises at least one layer made 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 directional information vertical and horizontal (or lateral) preferably relate to a preferred direction in which the oscillatable membrane is oriented for generating or absorbing pressure waves of the fluid. The vibratory membrane is preferably suspended horizontally between at least two side regions of a carrier, while the vertical direction (direction of interaction with the fluid) for generating or absorbing pressure waves is orthogonal thereto. 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 the sound emission, while horizontal means a direction orthogonal to it. In the case of a MEMS microphone, the vertical (interaction) direction corresponds to the vertical sound detection direction of the MEMS microphone. In this case, vertical preferably means the direction of sound detection or recording, while horizontal means a direction orthogonal thereto.

The vertical sections of the vibratable membrane thus preferably designate 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 vibratable membrane is preferably oriented horizontally to the direction of sound emission or sound detection, the sound waves are generated by actuation of the vertical sections or vice versa.

In a preferred embodiment of the invention, the carrier comprises two side areas between which the vibratable membrane is arranged in the 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 flat area that remains free. 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 regions, which preferably essentially form the frame structure, are called in particular side walls.

The oscillatable 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 carrier preferably comprises four side areas, with additional end faces, as a rule parallel to the cross-section shown. These other two side walls span the frame structure.

The oscillatable membrane is preferably hung flat within the area that remains free. The areal expansion of the vibrating membrane characterizes a horizontal direction, while the vertical sections are orthogonal to it. With regard to the end faces, the membrane can be adhered to these side walls or be slotted there for the purpose of greater mobility. The slot can advantageously represent a dynamic high-pass filter which, for example, couples a front volume and a rear volume to 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. In particular, it is preferably possible to manufacture the MEMS transducer comprising an oscillatable membrane together with a carrier in a (semiconductor) process, preferably on a wafer. This further simplifies and makes production cheaper, so that a compact and robust MEMS converter can be provided at low cost.

In a preferred embodiment, the vibratory membrane is formed by a lamellar structure or a meandering structure. The specification of a lamellar or meandering structure preferably relates to the shape of the oscillatable membrane in cross section.

A lamellar structure preferably denotes an arrangement of similar, parallel layers, which preferably form the vertical sections. The individual lamellae are preferably with their surface parallel to the vertical direction, preferably an emission or Direction of detection aligned. The lamellae are preferably constructed in several layers and form a mechanical biomorph. For example, the slats can each include an actuator layer and a passive layer made of a support material and / or two differently controllable actuator layers.

It can be preferred here that the lamellae are flat, which means in particular that their extension in each of the two dimensions (height, width) of their area 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 can be preferred.

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

In the embodiment, the vibratory 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 vibrating membrane. On the other hand, the conductive bridges advantageously allow contact to be made with all of the lamellae by means of electrodes at the end. Advantageously, the lamellas can be excited synchronously with horizontal vibrations or detect the same with little control and manufacturing effort.

A meandering structure preferably denotes 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 oscillatable membrane. The meandering structure is particularly preferably rectangular in cross section. The meander structure thus preferably corresponds to a membrane folded along its width. For the purposes of the invention, an oscillatable 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.

With regard to the function of a vibrating membrane in a meandering shape for generating or absorbing sound waves, the vertical sections are decisive, analogously to the lamellae described above. The vertical sections are preferably constructed in several layers and form a mechanical biomorph. For example, the vertical sections can each include 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. inter alia Fig. 3-7 ). However, it can 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 made of an actuator material of the vibratable membrane is a continuous layer. Continuous preferably means that there are no interruptions 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 converter, in particular a MEMS loudspeaker or MEMS microphone, can be determined essentially by the number and / or dimensioning 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 fewer than 10,000, 5,000, 2,000 or 1,000 or fewer vertical sections.

The preferred number of vertical sections leads to high sound power on the smallest chip surfaces without the sound image or audio quality suffering.

The vertical sections are preferably flat, which means in particular that their extension in each of the two dimensions (height, width) of their area 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 can be preferred.

According to the invention, the height of the vertical sections preferably corresponds to the dimension along the direction of the 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, the height and thickness are shown schematically (not necessarily true to scale), while the dimension of the length corresponds to a (not 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, for example, 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 µm, 600 µm to 700 µm, 700 µm to 800 µm, 800 µm to 900 µm or 900 µm to 1000 µm. A person skilled in the art recognizes that the aforementioned range limits can also be combined in order to obtain further preferred ranges, such as, for example, 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, for example 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 9 µm to 10 µm. A person skilled in the art recognizes that the aforementioned range limits can also be combined in order to obtain further preferred ranges, such as, for example, 500 nm to 3 μm, 1 μm to 5 μm or also 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 areas from the aforementioned ranges can also be preferred, such as, for example, 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 also 8 mm to 10 mm. A person skilled in the art recognizes that the aforementioned range limits can also be combined in order to obtain further preferred ranges, such as, for example, 10 μm to 500 μm, 500 μm to 5 μm or also 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 at the same time combines high performance with excellent sound image or audio quality.

In a preferred embodiment of the invention, the oscillatable membrane is formed by a meandering structure with alternating vertical and horizontal sections, with holding structures attached to at least two of the horizontal sections, which are connected directly or indirectly to the carrier. The holding structures can be provided, for example, by the 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 holding structures can preferably be present on one and / or two sides of the oscillatable membrane, i.e. preferably attached to upper and / or lower horizontal sections.

In particular when a larger-sized vibratory membrane is suspended between the side walls of a carrier, the use of holding structures advantageously allows stabilization without negatively affecting the generation or absorption of sound.

Since the horizontal sections in a meandering 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 carrier.

Various layers can be provided for the construction of the vibratable membrane in order to ensure the described actuation and excitation of horizontal vibrations or their detection.

Contacting one or more actuator layer (s) and / or one or more layers made of a mechanical support material and thus the application or detection of an electrical one Voltage can take place directly via the electrodes at the end or be supported by a layer made of a conductive material,

In a preferred embodiment, the vibratory membrane therefore comprises at least one layer made 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 vibratory membrane comprises three layers, an upper layer being formed from a conductive material and connected to an upper electrode, a middle layer being formed from the actuator material and a lower layer being formed from a conductive material.

The conductive material of the upper and / or lower layer can preferably be a mechanical support material, so that this layer has a double function. On the one hand, the location ensures that the actuator layer is contacted with an electrical potential that can be applied to the electrodes at the end. On the other hand, it functions as a mechanical support layer in the manner described for generating horizontal curvatures or vibrations when the actuator position is actuated accordingly.

Such an embodiment can be obtained by means of simple manufacturing steps, as exemplified in FIG Figure 2 illustrated. In the in Figure 2G , Figs. 3 and 4 In the preferred embodiment shown, the vibratory membrane has a meandering structure with a continuous upper layer made of a conductive material (metal), a continuous middle layer made of an actuator material and a lower layer made of a conductive mechanical support material. A reverse sequence 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 vibratory membrane comprises two layers made of an actuator material, which are separated by a middle layer made of a conductive material, preferably metal, the middle layer being connected to a first electrode and at least one of the two layers made of an actuator material be in contact with a second electrode via a further layer made of a conductive material, preferably a metal.

As explained above, in a preferred embodiment, two actuator positions can also be used in order, for example, to set the vertical sections into horizontal oscillations by means of different actuation. 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, in this case preferably serve exclusively for contacting and not as a mechanical support layer. The voltage required in the sense of a bimorph for a MEMS loudspeaker for bulging or oscillation is induced by a different control of the actuator positions themselves.

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

In the in Fig. 5 such a preferred embodiment is shown by way of example. This has an oscillatable membrane as a meandering structure with two layers made of an actuator material, which are separated by a middle layer made of a conductive material (metal). The middle layer is connected to a first electrode pad at the end, while the upper actuator layer is in contact with a second electrode at the end via a further layer made of a conductive material. A lower layer made of a conductive material is not in contact with any of the electrodes. A reverse order of the layers or a waiver of the lower layer made of conductive material, which is in no contact with the electrodes, can also be provided.

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

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

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

A preferred manufacturing method for an embodiment with a discontinuous actuator layer is shown in FIG Figure 7 illustrated. Here, a targeted spacer etching of the actuator layer can take place in horizontal sections, so that only the vertical sections of the membrane still have a layer made of an actuator material. A continuous layer made of a mechanical support material can at the same time be dielectric in order to avoid a short circuit between an upper and lower conductive layer (also referred to as top and bottom electrodes).

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

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

Alternatively, a vibratory membrane can also be produced by providing vertical sections and connecting them by means of metal bridges.

In a preferred embodiment, the vertical sections of the vibratable membrane comprise two layers, a first layer consisting of an actuator material, a second layer consisting of a conductive support material, and the vertical sections being connected via horizontal metal bridges.

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

In the embodiment, a continuous, homogeneous conductive layer is not 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 vibratable membrane is coated with a layer made of a non-stick material. With non-stick materials are meant, in particular, materials with low surface energies, which are largely inert to the environment and thus avoid 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 also 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. The control unit is preferably 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 converter, 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 oscillations of the two or more vertical sections. The control unit of a MEMS microphone is preferably configured for picking up and processing an electrical signal which corresponds to a frequency of the horizontal oscillations between 10 Hz and 20 kHz and is therefore set up for sound detection in the audible range.

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

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

In the context of the invention, a data processing unit preferably denotes a unit which is suitable and configured for receiving, sending, storing and / or processing data, preferably with a view 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 a flash memory for storing the data.

In preferred embodiments, the control unit is integrated in addition to further components of the MEMS transducer (carrier, vibratable membrane) on a printed circuit board or printed circuit board. 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 system, can also be installed on one and the same printed circuit board.

A compact overall solution is advantageously 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 inexpensive 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-side resonance volume. The sound emission of such a MEMS loudspeaker therefore preferably takes place towards the open front side ( sound port ), the sound image being improved in particular for lower frequencies by the resonance volume on the back.

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 converter, preferably a MEMS loudspeaker or MEMS microphone, as described above, comprising the following steps:

• Etching of a substrate, preferably from a front side, to form a structure, preferably a meander structure
• Optional application of an etch stop
• Application of at least two layers, wherein at least 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), the oscillatable membrane (1) for generating or absorbing pressure waves of the fluid in a vertical direction at least two or more comprises vertical sections (2) which are formed parallel to the vertical direction and so that the two or more vertical sections can be excited to horizontal oscillations by controlling the at least one electrode
so that when the two or more vertical sections are excited into horizontal oscillations at the at least one electrode, an electrical signal can be generated.

The average person skilled in the art recognizes that technical features, definitions and advantages of preferred embodiments of the described MEMS converter, preferably MEMS loudspeaker or MEMS microphone, also apply to the described manufacturing method. The production method described is preferably used to provide a MEMS transducer with a folded, oscillatable membrane with a meander structure. Examples of preferred manufacturing steps are given in Figures 2A-G or Figures 8A-J described.

As a substrate, for. B. one of the preferred materials mentioned above can be used. During the etching, a blank, for example a wafer, can be brought into the desired basic shape of the meander structure. In a next step, the layers for the vibratable membrane are preferably applied.

Applying the at least one layer of a conductive material preferably also 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 that are systematically applied to one another. The application of a layer or a layer system preferably serves to define the vibratable membrane comprising vertical sections which can be excited to horizontal vibrations.

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, for example, a deposition, z. B. 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).

Should a further structuring of the vibratable membrane be desired, this can be done, for. B. be made by further etching processes. Additional material can also be deposited or doping can be carried out using conventional methods.

For contacting the layers, suitable material, such as. B. copper, gold and / or platinum can be deposited by common processes. Physical vapor deposition (PVD), chemical vapor deposition (CVD) or electrochemical deposition can preferably be used for this purpose.

By means of the process steps, a finely structured vibratory membrane with a desired definition of vertical and horizontal sections can be provided, which are preferably suspended between two side areas of a stable carrier and have dimensions in the micrometer range. The manufacturing steps are part of standard method steps in semiconductor processing, so that 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.In a further aspect, the invention relates to a manufacturing method for a MEMS converter as described above, comprising the following steps:

• Providing a plurality of individual piezoceramic elements, comprising a sacrificial layer, a layer made of a conductive material and a layer made of a piezoelectric material
• Definition of holes for through-contacts in the piezoceramic elements and metal filling
• Stacking the piezoceramic elements and optional cutting (dicing) so that a stack of piezoceramic elements is obtained, which is connected by metal bridges
• Removal of the sacrificial layer and introduction of the stack of piezoceramic elements into a carrier, the first and last piezoceramic elements being contacted with one electrode each,

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

The average person skilled in the art recognizes that technical features, definitions and advantages of preferred embodiments of the described MEMS converter, preferably a MEMS loudspeaker or MEMS microphone, also apply to the described manufacturing method. The production method described is preferably used to provide a MEMS transducer with an oscillatable membrane with a lamellar structure, the lamellae being mechanical bimorphs and being connected by metal bridges. Examples of preferred manufacturing steps are shown in Fig. 9 AF illustrated.

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

Piezoceramics are preferably ceramic materials which, when deformed by an external force, show charge separation or 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, and also a sacrificial layer.

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

The sacrificial layer can preferably be a photoresist or photoresist, for example. These materials change their solubility when exposed to light, especially UV light. In particular, it can be a so-called positive varnish, the solubility of which increases as a result of UV irradiation. In this way, the sacrificial layer can be removed in a targeted manner after a metal filling to provide the metal bridges.

Detailed description

The invention is to be explained below with reference to further figures and examples. The examples and figures serve to illustrate preferred embodiment of the invention without restricting it.

Brief description of the images

Fig. 1

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

Fig. 2

Schematic representation of a preferred manufacturing method for a MEMS loudspeaker with an oscillatable membrane which has a meandering shape in cross section.

Fig. 3, 4

Schematic representation of preferred embodiments of a MEMS loudspeaker with an oscillatable membrane in a 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, which are 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 housing with a resonance volume on the rear.

Fig. 8

Schematic representation of a preferred manufacturing method for a MEMS loudspeaker with an oscillatable membrane which has a meandering shape in cross section, only the vertical sections having a layer made of an actuator material.

Fig. 9

Schematic representation of a preferred manufacturing method for a MEMS loudspeaker with an oscillatable membrane based on individual piezoceramic elements.

Detailed description of the images

Figure 1 illustrates a preferred embodiment of a MEMS loudspeaker according to the invention. Fig 1A indicates a hibernation while Figure 1B illustrates two phases during the actuation of the MEMS loudspeaker.

The MEMS loudspeaker comprises an oscillatable membrane 1 for generating sound waves in a vertical emission direction, the oscillatable membrane 1 being held in a horizontal position by a support 4. The oscillatable 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 vibratable membrane 1 and the actuator layer are preferably contacted by means of electrodes at the end. In addition, an electrode pad (not shown) can 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 made of an actuator material and a second layer made of a mechanical support material. By controlling the actuator position, a stress gradient and consequently a curvature or oscillation can be generated. Likewise, it can also be preferred that the vertical sections 2 comprise two actuator layers which are activated in opposite directions in order to bring about a curvature of the vertical sections 2 by means of a corresponding relative change in shape.

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

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

Figure 2A shows an etching of the substrate 8 from a top or front side to form a structure. In the method 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 an etch stop 9 ( Figure 2B ) applied, which can be, for example, TEOS or PECVD. On the etch stop 9 is a layer of a mechanical support material 10 ( Figure 2C ) and a layer of an actuator material 11 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. For example, 1 μm may be preferred as layer thicknesses. 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.

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

Figures 2F and 2G illustrate a further etching of the substrate 8 from the rear side or underside, and the removal of the etch stop.

The manufacturing steps 2A-G thus obtain an oscillatable membrane 1 which has a meandering structure in cross section. A continuous actuator layer 11 and the provision of end-side contacts 13 advantageously allow the vertical sections 2 to be efficiently actuated to produce horizontal vibrations (cf. Fig. 1 ). As in Figure 2G carried apparent preferably a drive means of two electrodes, the Aktuatorlage 12 is preferably both from a front side (top electrode, conductive layer 12) and from a rear side (bottom electrode on leifähiges mechanical support material 10) contacted (see FIG. Figure 6A ).

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

Fig. 5 illustrates a preferred alternative embodiment of a MEMS loudspeaker, the vibratable membrane 1 comprising 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 electrode pad 13 at the end, while in the embodiment shown the upper actuator layer 11 is present in contact with a second electrode pad 13 at the end via a further layer made of a conductive material 12.

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

In Figure 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 electrode pads 13 at one end, so that the horizontal vibrations can be generated by changing the shape of the actuator material in relation 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, for example, be applied to the front-side electrode pad 13 (left), while the rear-side electrode pad 13 (right) is grounded.

In Figure 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 one for the top and bottom electrode pads 13 (left), while the middle layer 12 is grounded via a further electrode pad 13 (right).

Fig. 7 shows an example of a preferred integration of a MEMS loudspeaker according to the invention in a housing 15. The vibratable membrane 1 held by the carrier 4 is preferably arranged in a front side or front side 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 production method for providing a MEMS loudspeaker with an oscillatable membrane 1 according to the invention Figures 8A-D The process steps shown are analogous to Fig. 2 .

Figure 8A shows an etching of the substrate 8 from an upper or front side to form a structure, preferably a meander structure. In the method 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 an etch stop 9 ( Figure 2B ) applied, which can be, for example, TEOS or PECVD. On the etch stop 9 is a layer of a mechanical support material 10 ( Figure 2C ) and an actuator material 11 applied to the mechanical support material 10 can be doped polysilicon, for example, while a piezoelectric material is preferably used for the actuator material 12.

In contrast to the in Fig. 2 The embodiment shown, the actuator layer 11 is not contacted as a continuous layer with an upper conductive layer. Instead, a spacer etch takes place ( Figure 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 made of an actuator material 11 .

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

Figures 8I and 8J illustrate a further etching of the substrate 8 from the rear side or underside and optionally the application of a continuous conductive layer 12 as a rear side electrode.

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

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

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

After removing the sacrificial layer 20 ( Figure 9F ) the stacked piezoceramic elements 19 are introduced into a carrier 4, the first and last piezoceramic elements preferably being contacted with one electrode 13 each ( Figure 9G ).

In this way, an oscillatable 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 oscillations.

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. The metal bridges 23 ensure that all vertical sections 2 are contacted by end-side control.

REFERENCE LIST

1

Vibrating membrane

2

Vertical sections of the vibratable membrane

3

Horizontal sections of the vibratable membrane

4th

carrier

5

Air volumes between the vertical sections

8th

Substrate

9

Etch stop

10

Layer made of a mechanical support material, preferably doped polysilicon

11

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

12th

Layer made of a conductive material, preferably made of metal

13th

Contacting the electrode, preferably an electrode pad

14th

Holding structures

15th

casing

16

rear resonance volume

17th

Ventilation opening

18th

Layer made of a dielectric material

19th

Piezoceramic element (s)

20th

Sacrifice

21

Defined holes for a through-hole with metal filling

22nd

Cutting (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 (15)

MEMS converter for interaction with a volume flow of a fluid comprising - a carrier (4), - an oscillatable membrane (1) for generating or absorbing pressure waves of the fluid in a vertical direction, the oscillatable membrane (1) being held by the carrier (4), characterized in that
the vibratable membrane (1) has two or more vertical sections (2) which are formed parallel to the vertical direction and comprise at least one layer made of an actuator material (11), the vibratable membrane (1) at the end with at least one electrode (13) contacted,
so that the two or more vertical sections (2) can be excited to horizontal vibrations by controlling the at least one electrode (13) or so that an electrical signal is generated at the at least one electrode when the two or more vertical sections (2) are excited to horizontal vibrations can be. MEMS converter according to the previous claim
characterized in that
the MEMS transducer is a MEMS loudspeaker, air volumes (5) preferably being present between the vertical sections (2), which are moved by the horizontal vibrations to generate sound waves along a vertical emission direction, 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 detection direction when sound waves are picked up. MEMS converter 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, at least the layer (11) comprising the actuator material with an electrode (13) contacted,
so that horizontal vibrations can be generated by changing the shape of the actuator material compared to the mechanical support material or
so that horizontal vibrations lead to a change in shape of the actuator material compared to the mechanical support material and generate an electrical signal MEMS converter 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 being in contact with one electrode (13) each, and
the horizontal vibrations can be generated by changing the shape of one position in relation to the other position or
horizontal vibrations lead to a change in shape of one layer compared to the other and generate an electrical signal. MEMS converter according to one of the preceding claims
characterized in that
the carrier (4) comprises two side areas between which the vibratable membrane (1) is arranged in the horizontal direction
and or
the carrier (4) is formed from 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. MEMS converter according to one of the preceding claims
characterized in that
the vibratory membrane (1) is formed by a lamellar structure or a meandering structure. MEMS converter according to one of the preceding claims
characterized in that
the vibratory membrane (1) is formed by a meander structure with alternating vertical (2) and horizontal (3) sections, with holding structures (14) attached to at least two of the horizontal sections (3), which are attached directly or indirectly to the carrier (4 ) are connected. MEMS converter 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). MEMS converter according to one of the preceding claims
characterized in that
the vibratory 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. MEMS converter according to one of the preceding claims
characterized in that
the vibratory membrane (1) comprises two layers (11) made of an actuator material, which are separated by a middle layer (12) made of a conductive material, preferably metal the middle layer (12) being connected to a first electrode (13) and at least one of the two layers (11) made of an actuator material via a further layer (12) made of a conductive material, preferably a metal, with a second electrode (13) have been contacted. MEMS converter according to one of the preceding claims
characterized in that
the vertical sections (2) of the vibratory membrane (1) comprise two layers, a first layer (11) consisting of an actuator material, a second layer (10) consisting of a conductive support material and the vertical sections (2) being over horizontal metal bridges (23) exist connected. MEMS converter according to one of the preceding claims
characterized in that
the vibratory membrane (1) is coated with a layer made of a non-stick material. MEMS converter according to one of the preceding claims
characterized in that
the vibratable membrane (1) held by the carrier (4) is arranged in a front side of a housing (15) which encloses a rear-side resonance volume (16), with a ventilation opening (17) preferably being present in the housing (15) to avoid acoustic noise Short circuits and / or to support the sound image. 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 structure, preferably a meander structure - Optional application of an etch stop - Application of at least two layers, at least one first layer (11) comprising an actuator material and a second layer (10) comprising a mechanical support material or at least two layers (11) comprising an actuator material - Contacting the first and / or second layer with an electrode (13) - Etching, preferably from the back, and optional removal of the etch stop, so that an oscillatable membrane (1), preferably in the form of a meander structure, is held by a carrier (4) formed by the substrate (8), the oscillatable membrane (1) for generating or absorbing pressure waves of the fluid in a vertical direction at least comprises two or more vertical sections (2) which are formed parallel to the vertical direction and so that the two or more vertical sections (2) can be excited to horizontal oscillations by controlling the at least one electrode (13) or
so that when the two or more vertical sections (2) are excited, they become horizontal Vibrations at the at least one electrode, an electrical signal can be generated. Manufacturing method for a MEMS transducer according to one of the preceding claims 1-13 comprising the following steps: - Provision of a plurality of individual piezoceramic elements (19), comprising a sacrificial layer (20), a layer (12) made of a conductive material and a layer (11) made of a piezoelectric material - Definition of holes (21) for a plated-through hole in the piezoceramic elements and metal filling - Stacking the piezoceramic elements (19) and optional cutting (dicing) (22), so that a stack of piezoceramic elements (19) is obtained, which is connected by metal bridges (23) - Removal of the sacrificial layer (29) and introduction of the stack of piezoceramic elements (19) in a carrier (4), the first and last piezoceramic elements (19) being contacted with one electrode (13) each, so that an oscillatable membrane (1), preferably in the form of a lamellar structure, is held by a carrier (4) formed by the substrate (8), the oscillatable membrane (1) for generating or absorbing pressure waves of the fluid in a vertical direction at least comprises two or more vertical sections (2) which are formed parallel to the vertical direction and so that the two or more vertical sections (2) can be excited to horizontal oscillations by controlling the at least one electrode (13) or
so that when the two or more vertical sections (2) are excited into horizontal oscillations at the at least one electrode, an electrical signal can be generated.

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