Method for producing a MEMS converter using a stretching of an actuator material

Abstract

The invention relates to a method for producing a MEMS converter for interaction with a volume flow of a fluid. For this purpose, a shaping component for forming a vibration-capable membrane with an actuator layer in the form of a meandering structure and an actuator material comprising polymers are first provided, wherein the actuator material is present in the form of a polymer foil or a polymer liquid. To obtain the shape of the actuator layer of the vibration-capable membrane, the shaping component is brought into contact with the actuator material. Advantageously, when the shaping component is being brought into contact with the actuator material, the polymers of the actuator material are oriented and / or stretched, and therefore a dipole moment of the polymers and piezoelectric properties of the actuator material are increased. In a further aspect, the invention relates to a MEMS converter that can be produced by means of the method.

Description

[0001] Method for manufacturing a MEMS transducer using stretching of an actuator material

[0002] DESCRIPTION

[0003] The invention relates to a method for producing a MEMS transducer for interacting with a volume flow of a fluid. For this purpose, a shaping component for forming an oscillating membrane with an actuator layer in the form of a meander structure and an actuator material comprising polymers are first provided, wherein the actuator material is in the form of a polymer film or a polymer liquid. To obtain the shape of the actuator layer of the oscillating membrane, the shaping component is contacted with the actuator material. Advantageously, during the contacting of the shaping component with the actuator material, the polymers of the actuator material are aligned and / or stretched, so that a dipole moment of the polymers and piezoelectric properties of the actuator material are enhanced.

[0004] In a further aspect, the invention relates to a MEMS converter which can be produced by means of the method.

[0005] Background and state of the art

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

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

[0008] An electromagnetic MEMS loudspeaker for mobile devices is described in Shahosseini et al. (2015). The MEMS loudspeaker features a stiffening silicon microstructure as a sound radiator, with the movable part suspended from a support via silicon drive springs to enable large out-of-plane displacements using an electromagnetic motor.

[0009] Stoppel et al. (2017) discloses a two-way loudspeaker concept based on concentric piezoelectric actuators. A special feature is that the vibration membrane is not closed, but rather 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 connected to a rigid frame by one or more springs. The separation of the membrane is intended to enable an improved sound image at higher power levels.

[0010] A disadvantage of such planar MEMS loudspeakers is their limitations in terms of sound power, especially at low frequencies. One reason for this is that the achievable sound pressure level is proportional to the square of the frequency for a given displacement. To achieve sufficient sound power, either displacements of at least 100 pm for the vibrating membranes or large-area membranes in the square centimeter range are necessary. Both conditions are difficult to achieve using MEMS technology.

[0011] The prior art has therefore proposed designing MEMS loudspeakers that do not have a closed membrane for vibrations in the vertical emission direction, but rather a multitude of movable elements that can be excited to lateral or horizontal vibrations. The advantage of this is that a larger volume flow can be moved within a small area, thus providing increased sound power.

[0012] A MEMS loudspeaker based on this principle is disclosed, for example, in US 2018 / 0179048 A1 and Kaiser et al. 2019. The MEMS loudspeaker comprises a plurality of electrostatic bending actuators arranged as vertical fins between a top and bottom wafer and can be excited to lateral vibrations by appropriate control. An inner fin forms an actuator electrode opposite two outer fins. Except for a connecting node of still galvanically isolated electrodes, an air gap exists between the three curved fins. If a potential is applied inside to outside, this leads to a bilateral attraction due to the curvature of the design in a preferred direction, which is predetermined by an armature. The bulges of the outer fins serve to facilitate mobility. The restoring force is provided by a mechanical spring force. Pull-push operation is therefore not possible.

[0013] Another disadvantage is that gaps between the bending actuators and the lid / bottom wafers, which are necessary for their mobility, lead to ventilation between the two chambers. This limits the lower frequency limit. Furthermore, the lateral movement of the bending actuators and thus the sound power are restricted to avoid a pull-in effect and acoustic breakdown.

[0014] DE 10 2017 115 923 A11 discloses a method for producing a MEMS transducer that can be used in microphones or loudspeakers. For the production of the MEMS transducer, a negative mold is provided by a substrate and optionally a sacrificial layer, which can be used to define the structure of the membrane. The substrate or the negative mold has recesses that correspond to wave crests and troughs of the membrane. The negative mold is then coated with an electrically conductive layer and a piezoelectric layer. To expose the membrane, the negative mold or the substrate is partially removed, so that a holder for the membrane is also provided by the partial removal of the substrate. US 2018 / 0035229 A1 also relates to a MEMS transducer, in particular a capacitive MEMS microphone or MEMS loudspeaker.Here, a pair of electrodes is applied to the membrane itself to reduce measurement noise in MEMS transducers with a rigid backplate. The electrode pair comprises a first conductive element and a second conductive element, which experience distance variations due to the deflection of the membrane, whereby a capacitance can be measured. To achieve a distance variation between the electrodes, the membrane can have corrugations. To produce the MEMS transducer with a membrane comprising a corrugation, a plurality of layers are coated onto a substrate provided with a recess. To expose the membrane, the substrate is etched from the back.

[0015] WO 2021 / 144400 A1 discloses a MEMS transducer that can be used both as a MEMS loudspeaker and as a MEMS microphone. The MEMS transducer described therein has an oscillating membrane constructed in such a way that it comprises two or more vertical sections that are formed substantially parallel to the vertical direction. Furthermore, the oscillating membrane comprises at least one layer of an actuator material and is contacted at at least one end by an electrode. This allows the vertical sections to be excited to horizontal oscillations by controlling the electrode. Conversely, an electrical signal can also be generated at the electrode when the vertical sections are excited to horizontal oscillations.

[0016] The MEMS transducer disclosed in WO 2021 / 144400 A1 offers significant improvements over the prior art. The design of the vibrating membrane, including vertical sections, advantageously results in higher sound output in the case of a MEMS loudspeaker, while the contacting simultaneously ensures simplified controllability. In the case of a MEMS microphone, higher performance and audio quality with a suitable sound image are also advantageously enabled. Furthermore, proven semiconductor processing techniques can be used to manufacture the MEMS transducer, enabling cost-efficient production.

[0017] The MEMS converter disclosed in WO 2021 / 144400 A1 is preferably manufactured by etching a substrate, preferably from a front side, to form a meandering structure. Subsequently, at least two layers are applied, wherein at least a first layer comprises an actuator material and a second layer comprises a mechanical support material, or at least two layers are coated comprising an actuator material. Subsequently, the first and / or second layer are contacted with an electrode.

[0018] There is potential for optimization, particularly with regard to the manufacturing process of the MEMS transducer disclosed in WO 2021 / 144400 A1. For example, applying the actuator material to the meander structure formed in the substrate is complex to ensure a homogeneous coating. However, a uniform design of the vibratable membrane is of great importance for acoustic performance.

[0019] All MEMS transducers known in the prior art, such as MEMS loudspeakers or MEMS microphones, have in common that the vibrating membrane plays a particularly important role. Only the deflection of the membrane allows the detection or generation of a signal. Particular importance is attached to the material selection itself, in particular to the material selection of the actuator material, which is used in the manufacturing process of the MEMS transducer disclosed in WO 2021 / 144400 A1 for application to the meander structure of the substrate. On the one hand, the desired acoustic, mechanical, and electrical properties must be met to enable suitable functional suitability of the MEMS transducer. On the other hand, the material must also be easy to process in order to optimally manufacture the membrane and thus also the MEMS transducer.

[0020] In light of the state of the art, there is therefore a need to provide improved or alternative methods for manufacturing a MEMS converter.

[0021] Object of the invention

[0022] The object of the invention was to eliminate the disadvantages of the prior art. In particular, it was an object of the invention to provide a method for manufacturing MEMS transducers that is characterized by high process efficiency and reliably leads to a high-performance MEMS transducer with desired acoustic properties.

[0023] Summary of the invention

[0024] The object of the invention is achieved by the independent claims. Advantageous embodiments of the invention are disclosed in the dependent claims.

[0025] In a first aspect, the invention relates to a method for producing a MEMS transducer for interacting with a volume flow of a fluid, comprising a carrier, an oscillating membrane for generating or receiving pressure waves of the fluid in a vertical direction, wherein the oscillating membrane is held by the carrier, the oscillating membrane has a meander structure with vertical sections and horizontal sections, wherein the vertical sections are formed substantially parallel to the vertical direction and the horizontal sections connect the vertical sections to one another, and wherein the oscillating membrane comprises at least one actuator layer made of an actuator material and is contacted with at least one electrode,so that by controlling the at least one electrode, the vertical sections can be excited to horizontal vibrations or so that upon excitation of the vertical sections to horizontal vibrations, an electrical signal can be generated at the at least one electrode, wherein the method comprises the following steps: a) providing at least one shaping component for forming the vibratable membrane with the actuator layer in the form of a meander structure, b) providing an actuator material comprising polymers, wherein the actuator material is in the form of a polymer film or a polymer liquid, c) contacting the shaping component with the actuator material for a shape design of the actuator layer, wherein during the contacting of the shaping component with the actuator material, the polymers of the actuator material are aligned and / or stretched,so that a dipole moment of the polymers is increased and piezoelectric properties of the actuator material are enhanced.

[0026] The preferred method for manufacturing a MEMS converter has proven advantageous in a number of aspects.

[0027] A particular advantage is that the piezoelectric properties of the actuator material can be enhanced, particularly through the use of an actuator material comprising polymers and the alignment and / or stretching of the polymers. Enhancement of the piezoelectric properties preferably means that physical parameters relating to the piezoelectric effect can be advantageously increased. Relevant physical parameters preferably relate to piezoelectric charge coefficients, piezoelectric voltage coefficients, and / or piezoelectric coupling coefficients.

[0028] The preferred contacting of the shaping component with the actuator material for shaping the actuator layer serves in particular to provide the vibrating membrane of the MEMS transducer. By enhancing the piezoelectric properties, it is advantageously possible to provide a vibrating membrane that generates a correspondingly higher electrical measurement signal upon deflection of the vertical sections. Conversely, applying an electrical voltage can generate a greater deflection of the vertical sections, allowing a higher volume flow to be emitted. Consequently, the preferred method is ideally suited for providing a high-performance MEMS microphone or a MEMS loudspeaker as a MEMS transducer with desired acoustic properties.

[0029] According to the invention, it was recognized that an actuator material comprising polymers with the property of acquiring enhanced piezoelectric properties upon alignment and / or stretching of the polymers is ideally suited for use in a process for manufacturing a MEMS transducer. This allows for a particularly high-performance actuator layer to be achieved with minimal material expenditure and efficient process control, resulting in high sensitivity in the case of a MEMS microphone or high performance in the case of a MEMS loudspeaker.

[0030] The advantageous effect of increasing the piezoelectric properties is preferably based on an increase in the dipole moment of the polymers of the actuator material. In the context of the invention, the dipole moment preferably refers to an electric dipole moment, which serves as a measure of the spatial charge separation, thus preferably a measure of the strength of the dipole character of the polymers of the actuator material.

[0031] Without wishing to be limited to theory, it is preferred in the context of the invention that the piezoelectric properties of the formed actuator layer are enhanced by aligning and / or stretching the polymers of the actuator material. The molecular and / or submolecular structure of the polymers is relevant for achieving optimized piezoelectric properties. Stretching preferably means that, due to the contacting of the shaping component with the actuator material, the atoms and / or molecules of a polymer achieve a greater distance from one another, which preferably increases the spatial separation of the partial charges of the atoms and / or molecules. Accordingly, polarization occurs, and the piezoelectric properties are enhanced.

[0032] Alignment preferably means that the molecules and / or atoms of the polymers of the actuator material are arranged in such a way that an oriented charge distribution occurs in order to enhance the piezoelectric properties. Thus, alignment preferably comprises an arrangement of atoms and / or molecules with different electronegativities in order to increase the dipole moment. In particular, atoms and / or molecules with a high electronegativity and a low electronegativity are aligned in such a way that the polarization and thus the piezoelectric properties are increased. It may be preferred that certain material phases are achieved by aligning the atoms and / or molecules. For example, in the case of polyvinyl difluoride (PVDF), a β-phase can be achieved by aligning the polymers, which has proven particularly advantageous in the context of the invention.

[0033] The preferred process steps are particularly well suited for providing a high-performance actuator layer (i.e., the actuator material after contact with the molding component) as a component of an oscillating membrane, which exhibits outstanding performance due to its enhanced piezoelectric properties. A number of advantages also arise with regard to processing.

[0034] MEMS transducers can advantageously be manufactured in a hybrid manner by using an actuator material comprising polymers. This can advantageously result in cost-effective scaling of production. In particular, costs for equipment and manufacturing infrastructure can be lower compared to CMOS (complementary metal-oxide-semiconductor) manufacturing, depending on the application. The use of an actuator material comprising polymers facilitates production because polymers are inexpensive to acquire, easy to process, and exhibit high mechanical flexibility. Both in liquid form and as a polymer film, the actuator layer can advantageously be applied particularly homogenously to the molding component, with simultaneous enhanced piezoelectric properties of the actuator material being ensured by stretching and / or alignment.

[0035] At the same time, an additional material, e.g., a mechanical support material and / or an electrically conductive material, can be easily applied to the actuator layer. Accordingly, it is possible to provide mechanical stability, a protective function, and / or contact for the actuator layer on a front and back side of the actuator layer. The additional layer (e.g., a mechanical support material and / or an electrically conductive material) can be applied both before and after contact with the forming component, thus providing a high degree of flexibility in terms of process control. The preferred method also advantageously allows the vibratable membrane to be formed with particular precision.Thus, by contacting the shaping component with the actuator material, particularly fine dimensions of the vertical and / or horizontal sections of the oscillating membrane can be advantageously achieved, while at the same time ensuring a uniform design of the actuator layer.

[0036] The preferred method is also simple and quick to carry out, requires comparatively inexpensive materials, components and / or equipment and is characterized by high process efficiency.

[0037] Preferably, a shaping component is first provided. The shaping component preferably serves to contact the actuator material to form the actuator layer.

[0038] The actuator material comprising polymers is preferably in the form of a polymer film or a polymer liquid. Preferably, the shaping component is contacted with the actuator material to shape the actuator layer. Shape shaping preferably refers to establishing the shape or structure of the oscillatable membrane. In particular, the shape shaping relates to maintaining the actuator layer after the shaping component is contacted with the actuator material. Preferably, the shape shaping relates to the formation of a meandering structure having vertical sections and horizontal sections.

[0039] During contact between the shaping component and the actuator material, the polymers of the actuator material are aligned and / or stretched, increasing the dipole moment of the polymers and enhancing the piezoelectric properties of the actuator material. The prior art describes materials that gain polarization and thus acquire pronounced piezoelectric properties. These are described, for example, in Da Silva et al. (2010) and Gade, Bokka & Chase (2021). Da Silva et al. (2010) shows that the ß-phase of PVDF can be obtained by crystallizing N,N-dimethylformamide solution. Gade, Bokka & Chase (2021) discusses the production of PVDF fiber mats and fiber yarns and the measurement of their charge using a special Faraday cage design. The skilled person is not provided with any indications of applicability for the production of a MEMS converter.However, the inventors have recognized that materials comprising polymers that achieve increased polarization upon stretching and / or alignment are particularly well suited for providing an actuator layer for a MEMS transducer. In addition to high process efficiency, the increased performance of the actuator layer due to the adjustable polarization, coupled with excellent sound performance, is particularly important.

[0040] Advantageously, the preferred method can therefore provide a MEMS transducer that is particularly suitable with regard to its acoustic properties.

[0041] The design of the MEMS transducer advantageously combines the possibility of high sound power with simplified control. Unlike conventional planar MEMS loudspeakers, for example, the vibrating membrane itself does not need to be driven over a large area of ​​several square centimeters or with displacements of more than 100 pm 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.

[0042] At the same time, simplified control can be achieved. While in the prior art, such as in US 2019 / 011 64 17 A1, a large number of piezoelectric actuators must be contacted at the horizontal sections, the MEMS loudspeaker described here can be operated using at least one electrode, preferably at the end. This reduces manufacturing costs, minimizes sources of error, and also inherently leads to synchronous control of the vertical sections to horizontal vibrations.

[0043] In this way, the air volumes present between the vertical sections can be moved extremely precisely by the horizontal vibrations along the vertical emission direction.

[0044] This also enables the provision of a particularly powerful MEMS microphone with high audio quality. The structure of the MEMS microphone is structurally similar to that of the MEMS loudspeaker, particularly with regard to the design of the vibrating membrane. However, instead of controlling the electrodes to generate horizontal vibrations and thus sound pressure waves, the MEMS microphone is designed to record sound pressure waves in the same vertical direction. Preferably, air volumes are therefore present between the vertical sections, which are moved along a vertical detection direction when sound waves are recorded. The sound pressure waves excite the vertical sections to horizontal vibrations, so that the actuator material generates a corresponding periodic electrical signal.

[0045] The resulting actuator layers with enhanced polarization properties have proven to be extremely advantageous for the performance and vibration behavior of the membrane, both with regard to applications as MEMS loudspeakers and as MEMS microphones.

[0046] The manufacturable MEMS converter also has a low complexity and allows for the easy implementation of further processing steps, for example the suitable placement of a top and / or bottom electrode on the oscillating membrane.

[0047] The preferred method is used in particular for the production of a MEMS transducer. The term MEMS transducer refers to both a MEMS microphone and a MEMS loudspeaker. In general, a MEMS transducer is a transducer for interacting with a volume flow of a fluid, which is based on MEMS technology and whose structures for interacting with the volume flow or for recording or generating pressure waves of the fluid have dimensions in the micrometer range (1 pm to 1,000 pm). The fluid can be either a gaseous or a liquid fluid. The structures of the MEMS transducer, in particular the vibrating membrane, are designed to generate or record pressure waves of the fluid. For example, as in the case of a MEMS loudspeaker or MEMS microphone, these can be sound pressure waves. However, the MEMS transducer can also be suitable as an actuator or sensor for other pressure waves.The MEMS transducer is therefore preferably a device or 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).

[0048] 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 into other (consumer) devices.

[0049] A MEMS loudspeaker preferably refers to a loudspeaker based on MEMS technology, whose sound-generating structures are at least partially dimensioned in the micrometer range (1 pm to 1000 pm). For example, the vertical sections of the vibratable membrane can preferably have a width, height, and / or thickness dimension in the range of less than 1000 pm. It may also be preferred, for example, that only the height of the vertical sections is dimensioned in the micrometer range, while, for example, the length can have a larger dimension and / or the thickness can have a smaller size.

[0050] A MEMS microphone preferably refers to a microphone based on MEMS technology, whose sound-recording structures are at least partially dimensioned in the micrometer range (1 pm to 1000 pm). For example, the vertical sections of the vibratable membrane can preferably have a dimension in the range of less than 1000 pm in terms of width, height, and / or thickness. It may also be preferred, for example, that only the height of the vertical sections is dimensioned in the micrometer range, while, for example, the length can have a larger dimension and / or the thickness can have a smaller size.

[0051] The MEMS transducer preferably comprises the oscillating membrane for generating or recording pressure waves of the fluid in a vertical direction. Thus, the oscillating membrane refers to the structure that enables the generation of an electrical signal after recording pressure waves or the generation of pressure waves by applying an electrical signal. For this purpose, it is preferred that the oscillating membrane has at least one actuator layer made of an actuator material. The oscillating membrane is preferably structured in such a way that it has a meandering structure comprising vertical and horizontal sections.

[0052] A meander structure preferably refers to a structure formed from a sequence of sections that are essentially orthogonal to one another in cross-section. The mutually orthogonal sections are preferably vertical and horizontal sections of the oscillatable membrane. The meander structure is particularly preferably rectangular in cross-section. However, it can also be preferred for the meander structure to have a sawtooth shape (zigzag shape) or to be curved or wave-shaped in cross-section. This is particularly the case if the vertical sections are not aligned exactly parallel to the vertical emission or detection direction, but rather enclose an angle of, for example, ± 30°, preferably ± 20°, particularly preferably ± 10° with the vertical direction.

[0053] In preferred embodiments, the horizontal sections may also not be exactly at an orthogonal angle of 90° to the vertical emission or detection direction, but may, for example, enclose an angle between 60° and 120°, preferably between 70° and 110°, particularly preferably between 80° and 100° with the vertical direction.

[0054] Preferably, the vertical and / or horizontal sections are straight, at least in sections or over their entire length; however, the vertical and / or horizontal sections can also be curved, at least in sections or over their entire length. In the case of a curved or undulating shape of the vertical and / or horizontal sections of the oscillatable membrane in cross-section, the alignment preferably refers to a tangent to the vertical and / or horizontal sections at their respective centers.

[0055] 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.

[0056] Preferably, the layer of actuator material in the vertical sections serves as a component of a mechanical biomorph, wherein 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. A bimorph preferably refers to a structure comprising two layers, wherein the interaction of the two layers enables displacement and / or curvature.

[0057] In a preferred embodiment, the 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 oscillations can be generated by a change in shape of the actuator material relative to the mechanical support material. Thus, in the aforementioned preferred embodiment, a vertical section is present as a mechanical bimorph. In this embodiment, the mechanical bimorph is formed by a layer of actuator material (e.g., a piezoelectric material) and a passive layer that acts as a mechanical support layer. In the mechanical bimorph, the actuator material is preferably already present as an actuator layer.

[0058] By providing the actuator layer by aligning and / or stretching the polymers of the actuator material, the piezoelectric properties can be advantageously adjusted particularly well. For example, greater stretching and / or alignment of the actuator material can generate a greater distance between partial charges of atoms and / or molecules of the polymers of the actuator material. This increases the dipole moment, thus enhancing the piezoelectric properties. Conversely, by less stretching and / or aligning the actuator material, the distance between partial charges of atoms and / or molecules of the polymers of the actuator material can be adjusted to be smaller. This increases the dipole moment to a lesser extent, so that the piezoelectric properties are less pronounced.By appropriately stretching and / or aligning the actuator material, the sensitivity of the actuator layer can be precisely adjusted for use as a bimorph. Adjusting the orientation and / or stretching of the polymers in the actuator material, and thus the piezoelectric properties, can be achieved, for example, by selecting stretching factors, which will be described in more detail below.

[0059] Both a transverse and a longitudinal piezoelectric effect can be used to bend the bimorph. In the direct longitudinal piezoelectric effect, the force is applied and thus the resulting stress gradient is created by the pressure waves along polar axes. In the inverse longitudinal piezoelectric effect, the voltage is applied along a non-polar axis, which leads to the expansion of the unit cell along a polar axis of the actuator layer. A polar axis preferably means an axis that runs between two charge centers, preferably between two unlike charge centers. In the direct transverse piezoelectric effect, the force is applied along a non-polar axis by emerging pressure waves, so that an electrical signal can be measured at the electrode. The non-polar axis preferably means an axis that does not run along two charge centers.In the inverse transverse piezoelectric effect, the voltage is applied along a polar axis, resulting in the expansion of the unit cell along a non-polar axis of the actuator layer. A transverse piezoelectric effect can be advantageously utilized by orienting the actuator layer along the C-axis.

[0060] When the actuator layer is controlled, it can, for example, experience transverse or longitudinal stretching or compression. This creates a stress gradient relative to the mechanical support layer, leading to lateral curvature or vibration. By alternating polarity at the electrodes, push-pull operation can be achieved, allowing almost the entire air volume to be moved alternately between the vertical sections in the vertical emission direction. The stretching and / or alignment of the polymers of the actuator material and the associated increase in the dipole moment and strengthening of the piezoelectric properties of the actuator layer result in particularly high performance. In particular, the performance of push-pull operation can be precisely adjusted during production depending on the application.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.

[0061] Since the actuator principle is not based on electrostatic attraction, but rather on a relative deformation (e.g., compression, stretching, shearing) of the actuator layer relative to a support layer, adhesion of the membrane sections can be ruled out. Instead, the vertical sections can touch each other and are thus not restricted in their deflection.

[0062] In a further preferred embodiment, the vertical sections comprise at least two layers, wherein both layers comprise an actuator material and are preferably contacted with electrodes at their ends, and the horizontal oscillations can be generated by a change in the shape of one layer relative to the other. In this embodiment, the horizontal oscillation of the vertical sections is therefore not generated by a stress gradient between an active actuator layer and a passive support layer, but rather by a relative change in the shape of two active actuator layers. In this embodiment, one vertical section is also bimorph.

[0063] 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. The actuator layers are preferably formed, as described, by stretching and / or aligning the polymers of an actuator material, whereby the extent of the stretching and / or alignment can also advantageously be used to adjust the deformation coefficients. Deformation coefficients preferably refer to material variables that can be used to quantify a deflection and / or vibration capability. For example, two different actuator materials can be provided that jointly undergo alignment and / or stretching of their different polymers.Consequently, by aligning and / or stretching the polymers of the two actuator materials, different deformation coefficients can be used to regulate the deflectability of the vertical sections.

[0064] For the purposes of the invention, the “layer comprising an actuator material” is preferably also referred to as actuator layer.

[0065] For the purposes of the invention, the "layer comprising a mechanical support material" is preferably also referred to as a support layer or support layer. The mechanical support material or support layer preferably serves as a passive layer that can resist a change in shape of the actuator layer. In contrast to an actuator layer, the mechanical support material preferably does not change its shape when an electrical voltage is applied. The mechanical support material is preferably electrically conductive, so that it can also be used directly for contacting the actuator layer. However, in some embodiments, it can also be non-conductive and, for example, be coated with an electrically conductive layer.

[0066] The mechanical support material is particularly preferably monocrystalline silicon, a polysilicon or a doped polysilicon.

[0067] While the actuator layer undergoes a deformation when subjected to an electrical voltage, the layer of the mechanical support material remains essentially unchanged. The resulting stress gradient between the two layers (mechanical bimorph) preferably causes a horizontal curvature. For this purpose, the thickness of the support layer relative to the thickness of the actuator layer should preferably be selected such that a sufficiently large stress gradient is generated for the curvature.

[0068] The meander structure preferably corresponds to a membrane folded across 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. The horizontal sections preferably refer to those structures that enable connections between two or more vertical sections.

[0069] The performance of the MEMS transducer, especially of a MEMS loudspeaker or MEMS microphone, can be significantly determined by the number and / or dimensioning of the vertical sections.

[0070] In preferred embodiments, the vibratable membrane comprises more than 3, 4, 5, 10, 15, 20, 30, 40, 50, 100 or more vertical sections.

[0071] In further preferred embodiments, the vibratable membrane comprises less than 10,000, 5,000, 2,000, or 1,000 or fewer vertical sections.

[0072] The preferred number of vertical sections results in high sound power levels on the smallest chip surfaces without compromising the sound image or audio quality.

[0073] Preferably, the vertical sections are planar, meaning in particular that their extension in each of the two dimensions (height, width) of their surface is greater than in a perpendicular dimension (thickness). For example, size ratios of at least 2:1, preferably at least 5:1, 10:1, or more may be preferred.

[0074] For the purposes of the invention, the height of the vertical sections preferably corresponds to the dimension along the direction of sound emission or sound detection, while the thickness of the vertical sections preferably corresponds to the sum of the layer thicknesses of the one or more layers forming 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.

[0075] In a preferred embodiment, the height of the vertical sections is between 1 pm and 1000 pm, preferably between 10 pm and 500 pm. Intermediate ranges from the aforementioned ranges can also be preferred, such as, for example, 1 pm to 10 pm, 10 pm to 50 pm, 50 pm to 100 pm, 100 pm to 200 pm, 200 pm to 300 pm, 300 pm to 400 pm, 400 pm to 500 pm, 600 pm to 700 pm, 700 pm to 800 pm, 800 pm to 900 pm or even 900 pm to 1000 pm. A person skilled in the art will recognize that the above range limits can also be combined to obtain further preferred ranges, such as 10 pm to 200 pm, 50 pm to 300 pm or even 100 pm to 600 pm.

[0076] In a preferred embodiment, the thickness of the vertical sections is between 100 nm and 10 pm, preferably between 500 nm and 5 pm. Intermediate ranges from the aforementioned ranges can also be preferred, such as, for example, 100 nm to 500 nm, 500 nm to 1 pm, 1 pm to 1.5 pm, 1.5 pm to 2 pm, 2 pm to 3 pm, 3 pm to 4 pm, 4 pm to 5 pm, 5 pm to 6 pm, 6 pm to 7 pm, 7 pm to 8 pm, 8 pm to 9 pm or even 9 pm to 10 pm. A person skilled in the art will recognize that the aforementioned range limits can also be combined to obtain further preferred ranges, such as, for example, 500 nm to 3 pm, 1 pm to 5 pm or even 1500 nm to 6 pm.

[0077] In a preferred embodiment, the length of the vertical sections is between 10 pm and 10 mm, preferably between 100 pm and 1 mm. Intermediate ranges from the aforementioned ranges can also be preferred, such as, for example, 10 pm to 100 pm, 100 pm to 200 pm, 200 pm to 300 pm, 300 pm to 400 pm, 400 pm to 500 pm, 500 pm to 1000 pm, 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, for example, 10 pm to 500 pm, 500 pm to 5 pm or even 1 mm to 5 mm.

[0078] With the aforementioned preferred dimensions of the oscillating membrane or the vertical sections, a particularly compact MEMS transducer, in particular a MEMS loudspeaker or MEMS microphone, can be provided, which simultaneously combines high performance with excellent sound or audio quality. Advantageously, the aforementioned dimensions can be achieved particularly easily by appropriately designing the shaping component. The structure of the shaping component preferably determines the structure of the oscillating membrane, comprising vertical and horizontal sections.

[0079] The directions vertical and horizontal (or lateral) preferably refer to a preferred direction in which the vibratable membrane is oriented to generate or receive pressure waves from the fluid. The vibratable membrane is preferably suspended horizontally between at least two side regions of a support, while the vertical direction (interaction direction with the fluid) for generating or receiving pressure waves is orthogonal to 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 orshot, while horizontal means an orthogonal direction.

[0080] The oscillating membrane of the MEMS transducer is of particular importance, as a measurement signal can only be generated or recorded through horizontal deflection of the vertical sections caused by pressure waves. Accordingly, the material selection for the oscillating membrane is relevant to the performance of the MEMS transducer. According to the invention, it was recognized that an actuator material comprising polymers, which causes an increase in the dipole moment of the polymer through alignment and / or stretching, delivers particularly good results.

[0081] In a further preferred embodiment, the actuator material is selected from a group comprising a piezoelectric material, a piezoelectric polymer material and / or electroactive polymers (EAP), wherein preferably the actuator material is a piezoelectric polymer material, wherein particularly preferably the piezoelectric polymer material is selected from a group comprising polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) and / or poly-L-lactic acid (PLLA).

[0082] An actuator material preferably means a material which undergoes a change in shape, for example stretching, compression or shearing, when an electrical voltage is applied, or conversely which generates an electrical voltage when changing shape.

[0083] Preferred materials are those with electric dipoles which undergo a change in shape when an electric voltage is applied, whereby the orientation of the dipoles and / or the electric field can determine the preferred direction of the shape changes.

[0084] Preferably, the actuator material can be a piezoelectric material, a piezoelectric polymer material (also piezoelectric material) and / or electroactive polymers (EAP).

[0085] Piezoelectric polymer materials preferably include polymers that exhibit internal dipoles and thus impart piezoelectric properties. This means that when an external electrical voltage is applied, the piezoelectric polymer materials (analogous to the aforementioned classical piezoelectric materials) undergo a change in shape (e.g., compression, stretching, or shearing). An example of a preferred piezoelectric polymer material is polyvinylidene fluoride (PVDF).

[0086] Electroactive polymers (EAPs) are polymers that change their shape when an electrical voltage is applied. A distinction is usually made between ionic EAPs and electronic EAPs. The mechanism of action of ionic EAPs is based on mass transport (diffusion) of ions. Subgroups of such EAPs include conductive polymers, ionic metal-polymer composites, and ionic gels. Electronic EAPs, on the other hand, are based on electronic charge transport. This group includes electrostrictive and ferroelectric polymers, as well as dielectric elastomers.

[0087] A piezoelectric polymer material is preferably used as the actuator material, with the piezoelectric polymer material particularly preferably being selected from a group comprising polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-trifluoroethylene (PVDF-TrFE), and / or poly-L-lactic acid (PLLA). These materials have proven advantageous for their ease of processing and for generating desired piezoelectric properties through alignment and / or stretching.

[0088] Piezoelectric polymer materials are advantageously particularly easy to deform, i.e. particularly easy to process, advantageously have a low dielectric constant and are particularly well suited for the provision and functional suitability of the vibrating membrane.

[0089] Particularly suitable piezoelectric polymer materials are those that exhibit a dipole moment essentially perpendicular to the main chain. This phenomenon is particularly evident in fluorinated polymers, such as PVDF, in which two fluorine atoms are bonded to every other carbon atom along the vinyl chain. By aligning and / or stretching, the fluorine atoms can be arranged to form a dipole, thereby increasing the dipole moment and thus the piezoelectric properties. Fluorine has a high electronegativity, while hydrogen has a significantly lower electronegativity. By aligning the fluorine and hydrogen atoms according to the ß-phase, taking into account the electronegativities of the atom types, a particularly strong dipole moment is advantageously generated, thus enhancing the piezoelectric properties.

[0090] Of particular importance for increasing the dipole moment can be the conversion of the actuator material into a so-called ß-phase. The ß-phase is preferably characterized by an all-trans planar zigzag conformation of the atoms, which induces a significant dipole moment (also known as the TTTT configuration or conformation). In the case of PVDF, the ß-phase is characterized by the separation of most of the fluorine atoms from the hydrogen atoms, creating a dipole moment perpendicular to the main chain. Because hydrogen and fluorine have different electronegativities, a strong dipole is generated, which accordingly exhibits enhanced piezoelectric properties. In PVDF in particular, the CH2-CF2 dipoles are aligned strictly perpendicular to the chain axis (carbon chain). The all-trans molecules are essentially packed in parallel, thus forming a crystalline structure, the ß-phase.Since dipoles in the ß-phase are essentially completely aligned in one direction, a particularly pronounced polarization is present, which results from summing the CH2-CF2 dipole moments over a unit volume.

[0091] By aligning and / or stretching the polymers, the actuator material, preferably PVDF, can preferably be converted into a β-phase. The β-phase can preferably be reliably stabilized and / or made more pronounced to optimize the piezoelectric properties. When using PVDF as a piezoelectric polymer material, it is in the β-phase after the preferred steps for producing a MEMS transducer as an actuator layer. The inventors have recognized that the β-phase of actuator materials is particularly well suited for utilizing it to improve the performance of MEMS transducers.

[0092] In a preferred embodiment, the actuator layer has a relative permittivity e r from 1 - 15, preferably from 5 - 15, particularly preferably from 7 - 12.

[0093] In a preferred embodiment, the actuator layer has piezoelectric charge coefficients of 1 - 50 pC / N (picocoulombs per Newton), preferably between 1 - 5 pC / N, particularly preferably 5 - 30 pC / N, most particularly preferably 30 - 50 pC / N.

[0094] The aforementioned parameter ranges regarding the relative permittivity and / or the piezoelectric charge coefficients preferably relate to the actuator layer, i.e., the layer of actuator material formed after stretching and / or aligning the polymers. These parameter ranges lead, in particular, to high performance of the actuator layer and thus improved functionality of the MEMS converter.

[0095] By stretching and / or aligning the polymers of the actuator material through contact with the molding component, the aforementioned parameter ranges can advantageously be achieved reliably and repeatably. Preferably, the stretching and / or aligning of the polymers leads to an enhancement of the piezoelectric properties, such as the piezoelectric charge coefficient, the piezoelectric voltage coefficient, and the piezoelectric coupling coefficient.

[0096] The piezoelectric charge coefficient preferably relates the electric charge generated per unit area to the applied mechanical force and is expressed in units of coulomb / newton (C / N). This parameter is often used to evaluate the performance of a piezoelectric material.

[0097] The piezoelectric stress coefficient is also referred to as the stress output constant. It is preferably defined as the ratio between the generated electric field and the applied mechanical stress and is expressed in voltmeters / Newton.

[0098] The piezoelectric coupling coefficient (less commonly referred to as the electromechanical coupling coefficient) is preferably defined as the ratio between the mechanical energy accumulated in response to an electrical input and the inverse ratio. It also corresponds to the fraction of electrical energy that can be converted into mechanical energy and vice versa.

[0099] Furthermore, it is preferred that the actuator material has a modulus of elasticity between approximately 1-5 GPa (gigapascals), preferably between approximately 2-4 GPa, and most preferably between approximately 2-3 GPa. These ranges of elasticity have proven advantageous in enabling simple shaping of the forming component, so that the meander structure can be achieved with high precision.

[0100] In a further preferred embodiment, the method is characterized in that the actuator material is provided in the form of the polymer film, wherein by means of the shaping component a mechanical stretching of the polymer film is carried out to form an actuator layer in the meander structure comprising the vertical sections and the horizontal sections.

[0101] The polymer film is advantageously easy to process, particularly by mechanical stretching, to create the meandering structure comprising the vertical and horizontal sections. The polymer film is characterized by a film comprising the polymers that are aligned and / or stretched after mechanical stretching of the polymer film. The polymer film is preferably provided as a sheet-like structure. A sheet-like structure preferably means a structure whose extension in a surface (length or width) is many times greater than orthogonal to the surface (thickness). Thus, the length or width can be greater than the thickness of a polymer film by a factor of approximately 2, 3, 10, 20, 50, 100, or more.

[0102] In a preferred embodiment, the thickness of the polymer film is between 100 nm and 50 pm, preferably between 500 nm and 10 pm. Intermediate ranges from the above-mentioned ranges can also be preferred, such as, for example, 100 nm to 500 nm, 500 nm to 1 pm, 1 pm to 1.5 pm, 1.5 pm to 2 pm, 2 pm to 3 pm, 3 pm to 4 pm, 4 pm to 5 pm, 5 pm to 6 pm, 6 pm to 7 pm, 7 pm to 8 pm, 8 pm to 9 pm, 9 pm to 10 pm, 10 pm to 20 pm, 20 pm to 30 pm, 30 pm to 40 or even 40 pm to 50 pm. A person skilled in the art will recognize that the above-mentioned range limits can also be combined to obtain further preferred ranges, such as, for example, 500 nm to 5 pm, 1 pm to 20 pm or even 1500 nm to 10 pm.

[0103] The polymer film can advantageously be stretched mechanically particularly easily, i.e., particularly with minimal mechanical resistance, to create the meander structure for the oscillating membrane. The polymer film advantageously adapts to the shape of the forming component with the highest precision, so that a precisely desired meander structure can be achieved. At the same time, the polymer film is advantageously crack-resistant, so that implementation reliability is ensured during the preferred process. Thus, the polymer film preferably has a high tensile strength, although this can depend on the specific material selection of the actuator material. Depending on the material, the tensile strength can preferably be between 20 N / mm 2 and 300 N / mm 2 , preferably between 50 N / mm 2 - 250 N / mm 2 , particularly preferably between 100 N / mm 2 - 200 N / mm 2 , most preferably between 120 N / mm 2- 180 N / mm 2 be.

[0104] The temperature used during mechanical stretching can also be relevant for the resulting vibrating membrane. In preferred embodiments, for example, the temperature can be selected above or below the glass transition temperature of the material used. Therefore, within the context of the invention, the temperature during stretching and / or alignment of the actuator material can also be considered a factor for the orientation of the polymers (or stretching factor).

[0105] Mechanical stretching preferably means stretching such that the polymers of the actuator material are aligned and / or stretched through mechanical action principles in order to increase the dipole moment of the polymers and thus generate enhanced piezoelectric properties. Mechanical stretching preferably occurs when a polymer film is provided. Mechanical stretching includes, for example, the application of low pressure to convert the polymer film into the meandering structure. Likewise, mechanical stretching preferably includes the interaction of two shaping components to obtain the meandering structure of the vibratable membrane.

[0106] Stretching the polymer film preferably results in an increase in area and / or length along one dimension. An increase in area and / or length can preferably be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 200%, 300%, 400%, or more relative to an initial area and / or initial length, with an increase of 100%, 200%, 300%, 400% meaning an increase by a factor of 2, 3, or 4. In particular, this achieves that the polymers of the actuator material are stretched along the vertical direction by mechanical stretching in order to increase the piezoelectric properties.

[0107] Advantageously, mechanical stretching allows the actuator layer comprising the actuator material to achieve a particularly precise C-axis orientation, which is perpendicular to the surface of the vertical sections of the resulting meander structure. A C-axis orientation, for example, can utilize a transverse piezoelectric effect to oscillate the vertical sections of the resulting oscillatory membrane. Other orientations may also be preferred, for example, involving the utilization of a longitudinal piezoelectric effect to form the horizontal curvatures or oscillations.

[0108] In a further preferred embodiment, the method is characterized in that the shaping component has a comb structure comprising comb fingers.

[0109] A comb structure is preferably a structure that has a plurality of comb fingers, which are preferably arranged regularly, i.e., in particular, the comb fingers are substantially identical in terms of shape, length, width, and thickness. The comb structure preferably also comprises empty regions. A empty region preferably refers to a region of the comb structure where the material of the comb structure is not present. A comb structure preferably comprises a regularly alternating sequence of a comb finger and an empty region.

[0110] The comb structure can advantageously be created using common methods in semiconductor microsystem technology, for example, by etching a substrate. The etched areas of the substrate are referred to as empty areas, while the remaining areas represent the comb fingers. Since the comb structure is particularly easy to create, the meander structure can advantageously be optimized in terms of design depending on the application. Thus, the length of the comb fingers preferably corresponds to the length of the vertical sections, with the width of the empty areas corresponding to the width of the horizontal sections.

[0111] In a further preferred embodiment, the method is characterized in that the shaping component comprises a comb structure comprising comb fingers and the comb structure has openings, wherein the actuator material is applied as a polymer film to the comb fingers of the comb structure and a low pressure, preferably a vacuum, is applied via the openings so that partial regions of the polymer film are mechanically stretched in the direction of the openings so that a meander structure is formed.

[0112] The openings are preferably provided on a main strand of the comb structure. The main strand of the comb structure preferably refers to the section on which the comb fingers are provided. The openings can be provided by known prior art methods, for example, by known etching methods. The openings are preferably introduced into the main strand of the comb structure such that they are positioned between the comb fingers. By applying low pressure, regions of the polymer film are mechanically stretched in the direction of the openings, i.e., in particular, in the direction of the main strand of the comb structure.

[0113] The polymer film is preferably fixed to the comb structure at its end regions, so that fixing the polymer film after application of the low pressure results in a correspondingly stretched polymer film. In this case, the entire polymer film is preferably stretched along one dimension of the comb fingers arranged one behind the other, whereby the degree of stretching or elongation can be adjusted by the level and / or duration of the applied low pressure. By adjusting the strength of the end-side fixation, a mechanical resistance of the polymer film to the application of the low pressure can also be preferably adjusted, which leads to varying degrees of stretching or elongation of the polymer film. In the case of end-side fixation, which does not allow any relative movement of the polymer film, the increase in length of the polymer film due to the formation of the vertical sections will fully contribute to the elongation of the polymer film.With less pronounced end-side fixation, the formation of vertical sections by applying low pressure to the opening may only partially result in the stretching or extension of the polymer film, since the feed of polymer film from areas outside the comb structure is not completely prevented. Advantageously, the desired height of the vertical sections and the stretching or extension of the polymer film can be adjusted independently of each other by adjusting the end-side fixation.

[0114] In further embodiments, it may also be preferred for the polymer film to be fixed to the contact surfaces of the comb fingers, so that these areas are not stretched when low pressure is applied. Those areas of the polymer film that are stretched toward the openings form the vertical sections after stretching, while those areas that are not stretched form the horizontal sections.

[0115] The application of a low pressure preferably means the effect of a pressure that is lower than the pressure present between the comb fingers of the comb structure. The low pressure is particularly preferably a vacuum. The low pressure can preferably be lower than the ambient pressure. The low pressure is preferably selected from a range comprising approximately 0-100,000 Pa (Pascals), preferably between approximately 0-50,000 Pa, particularly preferably between approximately 0-20,000 Pa, very particularly preferably between approximately 0-10,000 Pa, and particularly strongly preferably between approximately 0-5,000 Pa. The low pressure can preferably be adapted to the mechanical properties, e.g., to the elasticity of a polymer film.

[0116] In the context of the invention, the low pressure can be understood as a stretching factor. The level of the low pressure can be used, among other things, to regulate the stretching of the polymer film to provide the actuator layer. For example, the stretching itself can be regulated by adjusting the low pressure, since the height of the resulting vertical sections (and, in the case of end-side fixation, a longitudinal expansion of the polymer film) can be adjusted with the value and / or the duration of the low pressure. Thus, the duration of the action, i.e. the time during which the low pressure is effective, can also be understood as a stretching factor. Thus, the shape of the oscillating membrane can be advantageously adjusted particularly easily using the low pressure.

[0117] Preferably, the application of low pressure through the openings of the comb structure occurs at a temperature between approximately 180°C and 220°C. The temperature used can promote the stretching of the polymer film in the direction of the openings, enabling, in particular, faster stretching in the direction of the openings. This is due, among other things, without being limited to theory, to the fact that at an elevated temperature, the mechanical stress of the polymer film is reduced, thereby enabling stretching with reduced mechanical resistance. The temperature during the preferred application of the low pressure preferably also represents a stretching factor.

[0118] The shape of the comb structure, to whose comb fingers the polymer film is preferentially applied when applying low pressure, can also be considered a stretching factor. For example, the height and width of the comb fingers approximately determine the height of the vertical sections and width of the horizontal sections of the resulting vibratable membrane, provided a low pressure is applied, which completely conforms the polymer film to the comb structure.

[0119] Preferably, a substantially identical low pressure is applied across each opening to achieve the most uniform mechanical stretching of the polymer film possible. The mechanical stretching effect achieved through the use of low pressure can be influenced by the size of the openings and / or the value of the low pressure. The lower the pressure and / or the larger the opening, the faster the mechanical stretching of the polymer film occurs to create the meander structure. The application of low pressure advantageously leads to particularly uniform stretching and thus excellent results in terms of the power and sound performance of the formed actuator layers. Potential damage to the actuator layer is also effectively avoided.

[0120] In a further preferred embodiment, the method is characterized in that the actuator material is applied as a polymer film on a first comb structure, wherein a second comb structure is guided in the direction of the polymer film and respective comb fingers of the first comb structure and the second comb structure are guided into empty areas, so that in an interaction of the first comb structure substrate and the second comb structure substrate, the meander structure comprising the vertical sections and the horizontal sections is formed.

[0121] Preferably, the polymer film is applied to the first comb structure such that the polymer film lies along the longitudinal axis of the comb fingers. The meander structure is provided by the interaction of the first comb structure and the second comb structure. The interaction preferably means that the first comb structure and the second comb structure are guided against one another such that the respective longitudinal axes of the comb fingers are inserted into the empty areas of the other comb structure. Thus, the insertion of the comb fingers of the first comb structure into the empty areas of the second comb structure results in a membrane with a meander structure comprising vertical and horizontal sections.

[0122] Preferably, the first comb structure and the second comb structure are guided together in such a way that the comb fingers of the two comb structures are substantially perpendicular to the vertical direction and a horizontal direction of the subsequently provided actuator layer or oscillatable membrane. In particular, the comb fingers of the two comb structures are guided together in such a way that the comb fingers are oriented in a sagittal direction. The length of the vertical sections can preferably be determined by the final distance between the first comb structure and the second comb structure. The final distance between the first comb structure and the second comb structure preferably refers to the distance that exists after the mechanical stretching has taken place. The greater the final distance, the longer the vertical section.Preferably, the final distance between the first comb structure and the second comb structure refers to the final distance between the tips of the comb fingers. Thus, in this embodiment, the final distance is also a stretching factor with which the shape and stretching of the actuator layer can be optimized. The shape and stretching of the actuator layer, and thus of the oscillatable membrane, can also be regulated by the shape of the two comb structures, for example, the length and / or width, for example, the length of the vertical sections and / or the shape in a sagittal direction.

[0123] Preferably, the final distance between the first comb structure and the second comb structure is determined by a guide path of the first comb structure and the second comb structure.

[0124] Preferably, the polymer film is fixed to the first comb structure at its end regions, so that the meandering structure of the vibratable membrane results from the fixation of the polymer film after the interaction of the first comb structure with the second comb structure. The strength of the fixation can preferably be adjusted to adjust the mechanical resistance of the polymer film, so that with a particularly strong fixation, a higher mechanical resistance can be generated than with a weaker fixation. Thus, the fixation of the polymer film at the end regions of the first comb structure is preferably also a stretching factor.

[0125] By combining the strength of the polymer film fixation at the end regions of the first comb structure with the guide path, a particularly precise adjustment can be made for the shape of the meander structure. For example, the length, width, shape, and / or stiffness of the vertical and / or horizontal sections can be optimized by selecting the strength of the polymer film fixation, the shape of the comb structure, and / or the length of the guide path.

[0126] Preferably, the temperature is below 180°C, while mechanical stretching occurs through the interaction of the first and second comb structures. Depending on the temperature, this can also facilitate stretching, reducing the mechanical stress of the polymer film through the temperature effect. The temperature during the interaction of the first comb structure with the second comb structure can also be considered a stretching factor.

[0127] In preferred embodiments, stretching occurs by applying low pressure or by the interaction of the first comb structure and the second comb structure at a temperature that is above or below the glass transition temperature of the polymer film. By adjusting the temperature, both the process of forming the meander structure and the stretching or orientation of the polymers can be advantageously influenced. At a temperature above the glass transition temperature, the formability of the polymer film is increased, so that a particularly stable meander structure of the membrane can be obtained. At a temperature below the glass transition temperature of the polymers, in contrast, a particularly pronounced orientation of the polymers can advantageously be achieved.

[0128] The temperature used during forming of the polymer film is therefore another relevant factor that can be optimized to maintain the meander structure and the piezoelectric properties of the vibrating membrane.

[0129] In the context of the invention, stretching factors refer to factors that can be used to regulate the stretching of the polymers of the actuator material. These can be different factors or parameters depending on the embodiment. For example, stretching factors include the low pressure, the shape of the comb structure(s), the fixation of the polymer film to the comb structure, the guide path of the comb structures, temperatures used during stretching and / or aligning the polymers, etc.

[0130] In a further preferred embodiment, the method is characterized in that the actuator material is provided in the form of the polymer film, on which at least one layer comprising a mechanical support material and / or a conductive material is additionally applied, wherein the layer comprising the mechanical support material and / or the layer comprising a conductive material also undergoes mechanical stretching upon contact with the shaping component.

[0131] Advantageously, mechanical stretching of the polymer film in combination with stretching of the mechanical support layer eliminates the need for further processing steps, enabling faster preparation of the meander structure. Thus, by mechanically stretching the mechanical support material in combination with stretching the polymer film, coating a mechanical support material is no longer necessary.

[0132] Thus, it may be preferable to provide the polymer film together with a mechanical support material, wherein the polymer film and the mechanical support material are preferably applied to one another, and the polymer film and the mechanical support material are arranged in combination on the comb fingers of a comb structure. Openings are preferably present on the main strand of the comb structure, which can be formed, for example, by etching processes. By applying low pressure, preferably a vacuum, the polymer film in combination with the mechanical support material is transferred towards the main strand and thus towards the openings. In particular, those regions positioned over the empty regions of the comb structure are transferred towards the main strand.In areas where the polymer film and the mechanical support material are placed on the comb fingers, no stretching occurs in the direction of the main strand or the openings. Thus, a meander structure can be provided which stretches the polymer film and the mechanical support material together. The mechanical stretching of the polymer film in combination with the mechanical support material can preferably also be achieved through the use of a first and second comb structure. The polymer film and the mechanical support material can preferably be provided arranged on top of one another and arranged on the first comb structure such that they are applied along the longitudinal axis of the comb fingers. The meander structure is preferably provided by an interaction of the first comb structure and the second comb structure.Preferably, the first comb structure and the second comb structure are guided toward each other in such a way that the comb fingers are brought into the empty areas of the other comb structure. Thus, through the interaction of the first comb structure with the second comb structure, the meander structure can be provided for both the actuator layer and the mechanical support layer. It may also be preferable to first provide the meander structure for the polymer film to form an actuator layer and then to coat the mechanical support material.

[0133] In preferred embodiments, conductive material is applied on and / or beneath the actuator material. By stretching and / or aligning the actuator material in combination with the conductive material, a top electrode (on the actuator material) and / or bottom electrode (beneath the actuator material) can advantageously be provided after stretching in addition to the actuator layer.

[0134] In further preferred embodiments, a conductive material may be identical to the support material, so that, for example, a bottom and / or top electrode is simultaneously a mechanical support layer.

[0135] The preferred additional application of at least one further layer comprising a mechanical support material and / or a conductive material to the polymer film, which together undergoes mechanical stretching upon contact with the shaping component, is particularly preferred if the at least one further layer is stretchable, i.e. mechanically deformable without sustaining damage or cracks. A stretchable, electrically conductive material can preferably be a lacquer which, for example, comprises carbon nanotubes. If the at least one further layer comprising a mechanical support material and / or a conductive material does not have sufficient stretchability for mechanical stretching, it is preferred that the at least one further layer is applied by means of a coating only after the shape of the polymer film has been shaped.

[0136] In a further preferred embodiment, the method is characterized in that, after mechanical stretching, the actuator material in the form of the polymer film is additionally coated with at least one layer comprising a mechanical support material and / or a conductive material. This results in a support layer and / or a layer comprising an electrically conductive material which has the meander structure according to the stretched polymer film, without the support material or the electrically conductive material itself having to be stretched. The application of the at least one layer comprising the mechanical support material and / or the conductive material preferably takes place using a coating process within a coating system. The coating process can, for example, be selected from a group comprising spray coating, mist coating and / or vapor coating.The coating processes mentioned are known to the person skilled in the art and can be carried out easily and advantageously.

[0137] Preferably, the coating takes place within a coating system, which can be a physical coating system or chemical coating system, preferably a plasma-assisted chemical coating system, low-pressure chemical and / or epitaxial coating system.

[0138] Preferably, the coating takes place within a temperature range in which there is no change in the already aligned polymers of the actuator material, so that the enhanced piezoelectric properties are retained particularly reliably.

[0139] In particular, it is preferred that all steps of the method for providing a MEMS transducer, which occur after stretching / or aligning the polymers of the actuator material, take place at a temperature at which the enhanced piezoelectric properties of the actuator layer are not compromised. Particularly preferably, temperatures of more than 300°C, preferably more than 200°C or more than 150°C, are avoided for method steps for providing a MEMS transducer after stretching / or aligning the polymers of the actuator material.

[0140] In a further preferred embodiment, the method is characterized in that the oscillatable membrane comprises a layer comprising a conductive material, which functions as a top and / or bottom electrode.

[0141] The top and / or bottom electrode preferably refers to a layer comprising an electrically conductive material that extends over the entire surface of the oscillating membrane. Preferably, the layer is contacted with an electrode pad as the electrode, whereby the conductive material in combination with the electrode can also be referred to as the top and / or bottom electrode. Preferably, the electrode is provided with electronics for providing an electrical voltage and / or an electrical current. Preferably, the electrode is attached to the end so that actuation of the actuator layer is possible from the electrode, or an electrical signal can be read at the electrode by a corresponding change in the shape of the actuator layer.

[0142] Particularly preferably, the layer of a conductive material, preferably a metal, in the sense of a top or bottom electrode is present as a continuous, full-surface, or continuous layer of the oscillating membrane, which forms a substantially homogeneous surface. The terms "top" and "bottom" preferably refer to the layer of the conductive material, so that in a cross-section, it can be said that the top electrode comprises a conductive material above the actuator layer, and the bottom electrode comprises a conductive material below the actuator layer. By means of the layer of a conductive material, preferably a metal, the two or more vertical sections can advantageously be contacted with an end electrode or an electrode pad.

[0143] End-side preferably means a positioning of the at least one electrode so that contact can be made to a current or voltage source at one end of the oscillatable membrane, preferably at an end at which the membrane is suspended from the support.

[0144] In preferred embodiments, the MEMS converter comprises two end electrodes. Contacting with electronics, e.g., a current or voltage source, can preferably be made with the electrodes at opposite ends of the oscillating membrane, between which the two or more vertical sections are located, so that the actuator layer(s) in the vertical sections can be controlled by means of the end electrodes.

[0145] The end-side provision of the electrodes is thus preferably distinguished from a contact arrangement that controls the respective vertical sections with separate electrodes or, in the case of a MEMS microphone, taps generated electrical signals. The MEMS converter thus preferably comprises exactly one or exactly two electrodes for end-side contact and no additional electrodes (pads) for contacting central vertical sections.

[0146] 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.

[0147] In a further preferred embodiment, the method is characterized in that the oscillatable membrane comprises a layer comprising a conductive material, wherein 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, copper, wherein preferably the conductive material is a superelastic metal, wherein particularly preferably the conductive material has a fiber reinforcement, wherein for the fiber reinforcement the conductive material has fibers, wherein very particularly preferably the fibers comprise carbon.

[0148] The conductive materials selected from a group comprising platinum, tungsten, (doped) tin oxide, monocrystalline silicon, polysilicon, molybdenum, titanium, tantalum, titanium-tungsten alloy, metal silicide, aluminum, graphite, copper are particularly well suited to be applied to the actuator layer in a coating process, in particular after the polymer film has been mechanically stretched.

[0149] Conductive materials such as superelastic metals or conductive materials with fiber reinforcement are particularly well-suited for mechanical stretching in combination with the polymer film. Superelastic metals preferably refer to metals that belong to the superelastic class and exhibit so-called pseudoelastic or superelastic behavior. Under heavy load, they can reversibly deform to a high degree of elongation. This "elastic" deformation can exceed the elasticity of the metals by up to twenty times. The cause of this behavior is a phase transformation within the material. Various metal alloys can be used for this purpose, e.g., alloys comprising copper, zinc, and aluminum, or copper, aluminum, and nickel, or nickel and titanium.

[0150] Fiber-reinforced materials, such as those reinforced with fibers containing carbon, can have beneficial effects on both support function and electrical conductivity. Fiber reinforcement can advantageously generate higher mechanical resistance, thus increasing the stress gradient generated during deformation of a vertical section. At the same time, electrical conductivity can be increased by selecting the appropriate crystal structure of the fibers, e.g., the carbon.

[0151] In a further preferred embodiment, the method is characterized in that the oscillatable membrane comprises a layer comprising a mechanical support material, wherein the mechanical support material is selected from a group comprising monocrystalline silicon, polycrystalline silicon and / or doped polycrystalline silicon.

[0152] The materials mentioned have proven particularly advantageous for serving as a support layer. Furthermore, they are particularly well-suited for application to the actuator layer as part of a coating process, e.g., after mechanical stretching.

[0153] In a further preferred embodiment, the method is characterized in that the actuator material is provided as a polymer liquid and the shaping component is immersed in the polymer liquid, wherein after contacting the shaping component with the polymer liquid, the polymers of the actuator material undergo such an alignment that a dipole moment of the polymers is increased and piezoelectric properties of the actuator material are enhanced, wherein preferably the shaping component comprises a comb structure comprising comb fingers.

[0154] The polymers of the polymer liquid are aligned by immersing the shaping component in the polymer liquid. In preferred forms, the shaping component can be provided with an intermediate coating for this purpose, which effects alignment of the polymers. It may also be preferred for the shaping component to be formed from a semiconductor material, whereby a crystal orientation is utilized to align the growing polymer layer. By appropriately selecting or designing the shaping component, a desired alignment of the polymers of the polymer liquid can be advantageously achieved and the piezoelectric properties of the resulting actuator layer can be enhanced.

[0155] Preferably, the shaping component is immersed in the polymer liquid at a temperature above the glass transition temperature of the polymer liquid, so that the alignment of the polymers can advantageously be provided more easily. In a further preferred embodiment, the method is characterized in that after contacting the shaping component with the polymer liquid, the polymer liquid adheres to the shaping component and hardens to form the actuator layer comprising vertical and horizontal sections. Preferably, after the formation of the actuator layer, the actuator layer is coated with a layer comprising a conductive material and / or a mechanical support material.

[0156] The alignment of the polymers of the polymer liquid can occur particularly (in the viscous state) if the alignment is frozen or maintained after immersion of the shaping component.

[0157] In a further preferred embodiment, the method is characterized in that at least a partial section of the shaping component, preferably an entire section, is removed after contacting with the actuator material, preferably by an etching process and / or by a thermal treatment.

[0158] The etching process and / or the thermal treatment can advantageously expose the meander structure comprising vertical and horizontal sections, so that the vibration capability is provided.

[0159] An etching process preferably refers to a process for etching, i.e., for removing material to remove the shaping component. The etching process is preferably selected from a group comprising wet-chemical etching processes and / or dry etching processes, preferably physical and / or chemical dry etching processes, particularly preferably by reactive ion etching and / or reactive ion deep etching (Bosch process), or by a combination of the aforementioned etching processes.

[0160] The aforementioned etching processes are known to the person skilled in the art and can be selected accordingly to ensure efficient removal of the shaping component.

[0161] Preferably, removal of the shaping component can also be achieved by thermal treatment. Thermal treatment preferably refers to a process for removing the shaping component by applying heat. The choice of temperature depends on the material comprising the shaping component.

[0162] After exposing the meander structure and providing the oscillating membrane, it is contacted with the support. Preferably, the oscillating membrane is contacted with the support at its ends, so that the membrane extends in a horizontal direction.

[0163] In a further preferred embodiment, the method is characterized in that the shaping component and / or the carrier comprises a material selected from a group comprising monocrystalline silicon, polysilicon, silicon dioxide, silicon carbide, silicon germanium, silicon nitride, nitride, germanium, carbon, gallium arsenide, gallium nitride, indium phosphide and / or glass. These materials are easy and cost-effective to process in semiconductor and / or microsystem production and are suitable for large-scale applications. In particular, the carrier and / or the housing can be manufactured flexibly due to the materials and / or manufacturing methods. In particular, production of the MEMS converter comprising an oscillatable membrane together with a carrier in one (semiconductor) process, preferably on a wafer, is preferably possible.This further simplifies and reduces the cost of manufacturing, allowing a compact and robust MEMS converter to be manufactured cost-effectively.

[0164] In a preferred embodiment of the invention, the carrier comprises two side regions, preferably four side regions, between which the vibratable membrane is arranged in the horizontal direction.

[0165] The support is preferably a frame structure, which is essentially formed by a continuous outer border in the form of side walls of a free, flat area. The frame structure is preferably stable and rigid. In the case of an angular frame shape (triangular, square, hexagonal, or generally polygonal outline), the individual side areas, which preferably essentially form the frame structure, are particularly referred to as side walls. The vibratable membrane is preferably held by at least two side walls of the support.

[0166] The support preferably comprises four side areas, preferably with additional end faces that are generally parallel to the drawn cross-section. These two additional side walls span the frame structure.

[0167] Preferably, the carrier can be provided by the forming component, for example, in embodiments where mechanical stretching is preferred. For example, in the case of mechanical stretching, it may be preferred that the housing of the MEMS converter be provided by the interaction of two forming components.

[0168] In a further aspect, the invention relates to a MEMS converter for interacting with a volume flow of a fluid, which can be produced according to a method as described above.

[0169] The average person skilled in the art recognizes that technical features, definitions and advantages of preferred embodiments of the described method for manufacturing a MEMS converter also apply to the MEMS converter and vice versa.

[0170] It was surprising that preferred process steps for manufacturing the MEMS transducer resulted in a MEMS transducer characterized by excellent acoustic, electrical, and mechanical properties, particularly with regard to the oscillating membrane. The shape of the meander structure could be adjusted particularly precisely, for example, by selecting stretching factors. In particular, the shape of the vertical and / or horizontal sections can be advantageously determined particularly easily. The deflectability of the vertical sections can advantageously be regulated by stretching and / or aligning the polymers of the actuator material, so that the manufactured MEMS transducer can be used efficiently in a variety of applications. Thus, preferred embodiments of the process affect the structural and thus also the functional properties of the MEMS transducer.

[0171] The improved properties of the MEMS transducer are particularly evident during operation. The enhanced piezoelectric properties advantageously result in a vibrating membrane, which generates a correspondingly higher electrical measurement signal when the vertical sections are deflected. Conversely, applying an electrical voltage can generate a greater deflection of the vertical sections, allowing a higher volume flow of a fluid (especially air) to be expelled. Thus, the MEMS transducer is characterized by particularly high performance with the desired acoustic properties.

[0172] Advantageously, the MEMS transducer has an actuator layer with excellent piezoelectric properties, resulting in improved performance for the vibrating membrane in particular. This allows for higher deflections of the vertical sections to be achieved when sound pressure waves are to be detected (in the case of a MEMS microphone) or sound pressure waves are to be emitted (in the case of a MEMS loudspeaker).

[0173] The invention will be explained below with reference to figures and examples. The examples and figures serve to illustrate preferred embodiments of the invention without limiting it.

[0174] FIGURES

[0175] Short description of the characters

[0176] Fig. 1 Schematic representation of preferred process steps for producing a MEMS converter

[0177] Fig. 2 Further schematic representation of preferred process steps for producing a MEMS converter

[0178] Fig. 3 Further schematic representation of preferred process steps for producing a MEMS converter

[0179] Detailed description of the characters

[0180] Fig. 1 shows a schematic representation of preferred process steps.

[0181] Fig. 1 a shows a first shaping component 13 and a second shaping component 15. The first shaping component or first comb structure 13 and the second shaping component or second comb structure 15 are designed as comb structures, ie, they comprise comb fingers 9, which, however, point out of or into the plane of the sheet in the illustration.

[0182] Furthermore, the actuator material is shown in the form of a polymer film 3 and a layer comprising a mechanical support material 11. The polymer film 3 is applied to the mechanical support material 11. Fig. 1b shows that the polymer film 3 and the layer comprising a mechanical support material 11 are applied to the comb fingers of the second comb structure 15.

[0183] Fig. 1c shows that the first comb structure 13 is guided toward the polymer film 3 and the layer comprising the mechanical support material 11. In this process, respective comb fingers of the first comb structure 13 are guided into empty areas of the second comb structure 15. Thus, the interaction of the first comb structure 13 and the second comb structure 15 forms the meander structure for an actuator layer 6, wherein the meander structure has vertical sections and horizontal sections.

[0184] The final distance between the first comb structure 13 and the second comb structure 15, particularly between the tips of the comb fingers, can advantageously determine the length of the vertical sections of the oscillating membrane. The shape of the two comb structures 13, 15 also regulates the shape of the actuator layer and thus of the oscillating membrane. The final distance between the first comb structure 13 and the second comb structure 15 is determined by a guide path of the comb structures 13, 15.

[0185] The polymer film 3 is preferably fixed to the end regions of the chamber structure 13 and / or 15, so that the polymer film 3 is stretched or extended by the interaction of the first comb structure 13 with the second comb structure 15 in order to obtain a corresponding meander structure.

[0186] Fig. 2 shows further preferred process steps for forming the meander structure.

[0187] Fig. 2a shows a shaping component 7 in the form of a comb structure 7 having comb fingers 9. The structure of the comb fingers 9 advantageously allows the meander structure for the structure of the oscillating membrane to be achieved particularly easily.

[0188] In Fig. 2b, the actuator material in the form of a polymer film 3 as well as the layer comprising the mechanical support material 11 are provided, which are applied to the comb fingers 9 of the comb structure 7.

[0189] In Fig. 2c, it can be seen that the comb structure has openings formed on a main strand 8 of the comb structure 7, on which the comb fingers 9 are arranged. The arrows indicate the application of low pressure, so that partial regions of the polymer film 3 and the layer comprising the mechanical support material 11 are stretched.

[0190] During the application of the low pressure, the polymer film 3 is fixed to the end regions of the chamber structure 7, causing a corresponding stretching of the polymer film 3. Preferably, the entire polymer film is stretched along one dimension of the comb fingers 9 arranged one behind the other, whereby the degree of stretching or elongation can be adjusted by the level and / or duration of the applied low pressure.

[0191] In particular, a substantially identical low pressure is applied across each opening to achieve the most uniform mechanical stretching of the polymer film 3 possible. The mechanical stretching achieved through the use of low pressure can be influenced by the size of the openings and / or the value of the low pressure. The lower the pressure and / or the larger the opening, the faster the mechanical stretching of the polymer film 3 occurs to create the meandering structure.

[0192] Fig. 3 shows a further schematic representation of preferred process steps. In Fig. 3a, a polymer liquid 3 and the shaping component 7 are provided, wherein the shaping component 7 is present as a comb structure 7 comprising comb fingers 9.

[0193] Fig. 3b shows that the comb structure 7 is immersed in the polymer liquid 5. After contacting or immersing the comb structure 7 in the polymer liquid 5, the polymers of the actuator material or polymer liquid 5 will undergo an alignment such that a dipole moment of the polymers is increased and the piezoelectric properties of the actuator material are enhanced. The alignment of the polymers of the polymer liquid 5 is achieved by immersing the shaping component 7 in the polymer liquid 5.

[0194] In Fig. 3c it is shown that the polymer liquid 5 adheres to the comb structure 7 and hardens to form the actuator layer 6 as a meander structure comprising vertical and horizontal sections.

[0195] After formation of the actuator layer 6, the comb structure 7 is removed, which can be done, for example, by an etching process and / or a thermal treatment (see Fig. 3d).

[0196] LITERATURE

[0197] 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>

[0198] 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.

[0199] Bert Kaiser, Sergiu Langa, Lutz Ehrig, Michael Stolz, Hermann Schenk, Holger Conrad, Harald Schenk, Klaus Schimmanz und David Schuffenhauer, Concept and proof for an all-silicon MEMS microspeaker utilizing air chambers Microsystems & Nanoengineering volume 5, Article number: 43 (2019).

[0200] Da Silva, Aline Bruna, et al. Effect of drawing on the dielectric properties and polarization of pressed solution cast ß-PVDF films. Journal of materials science 45.15 (2010): 4206-4215.

[0201] Gade, Harshal, Sreevalli Bokka, and George G. Chase. Polarization treatments of electrospun PVDF fiber mats. Polymer 212 (2021 ): 123152.

[0202] BEZUGSZEICHENLISTE

[0203] I Oscillating membrane

[0204] 3 polymer film

[0205] 5 Polymer liquid

[0206] 6 Actuator position

[0207] 7 Shaping component, preferably as comb structure

[0208] 8 Main strand

[0209] 9 comb fingers

[0210] II layer comprising a mechanical support material, support layer

[0211] 13 First shaping component, preferably as first comb structure

[0212] 15 Second shaping component, preferably as a second comb structure

Claims

PATENT CLAIMS 1. Method for manufacturing a MEMS transducer for interacting with a volume flow of a fluid, comprising a support and a vibrating membrane (1) for generating or receiving pressure waves of the fluid in a vertical direction, wherein the vibrating membrane is held by the support, the vibrating membrane (1) has a meandering structure with vertical sections and horizontal sections, wherein the vertical sections are substantially parallel to the vertical direction and the horizontal sections connect the vertical sections together, and wherein the vibrating membrane (1) comprises at least one actuator layer (6) made of an actuator material and is contacted with at least one electrode.such that by controlling the at least one electrode, the vertical sections can be excited to horizontal vibrations, or such that when the vertical sections are excited to horizontal vibrations, an electrical signal can be generated at the at least one electrode, characterized in that the method comprises the following steps: a) providing at least one shaping component (7, 13, 15) for forming the vibrating membrane (1) with the actuator layer (6) in the form of a meandering structure, b) providing an actuator material comprising polymers, wherein the actuator material is in the form of a polymer film (3) or a polymer liquid (5), c) contacting the shaping component (7, 13, 15) with the actuator material for shaping the actuator layer (6), wherein during the contacting of the shaping component with the actuator material the polymers of the actuator material are aligned and / or stretched,so that the dipole moment of the polymers is increased and the piezoelectric properties of the actuator material are enhanced.

2. A method according to the preceding claim characterized in that the actuator material is selected from a group comprising a piezoelectric material, a piezoelectric polymer material and / or electroactive polymers (EAP), wherein preferably the actuator material is a piezoelectric polymer material, wherein the piezoelectric polymer material is particularly preferably selected from a group comprising polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-trifluoroethylene (PVDF-TrFE) and / or poly-L-lactic acid (PLLA).

3. Method according to one or more of the preceding claims characterized in that the actuator position (6) has a relative permittivity e ra method according to one or more of the preceding claims, characterized in that the actuator material is provided in the form of the polymer film (3), wherein the polymer film is mechanically stretched by means of the forming component (7, 13, 15) to form an actuator layer (6) in the meandering structure comprising the vertical sections and the horizontal sections. A method according to the preceding claim, characterized in that the forming component (7, 13, 15) has a comb structure (7, 13, 15) comprising comb fingers (9).A method according to one or more of the preceding claims characterized in that the shaping component (7, 13, 15) comprises a comb structure (7) including comb fingers (9) and the comb structure (7) has openings, wherein the actuator material is applied as a polymer film (3) to the comb fingers (9) of the comb structure (7) and a low pressure, preferably a vacuum, is applied via the openings, so that partial areas of the polymer film (3) are mechanically stretched in the direction of the openings, forming a meander structure.A method according to one or more of the preceding claims characterized in that the actuator material is applied as a polymer film (3) on a first comb structure (13), wherein a second comb structure (15) is guided in the direction of the polymer film (3) and respective comb fingers of the first comb structure (13) and the second comb structure (15) are guided into empty areas, so that in a combination of the first comb structure (13) and the second comb structure (15) the meander structure comprising the vertical sections and the horizontal sections is formed.A method according to one or more of the preceding claims characterized in that the actuator material is provided in the form of the polymer film (3) on which at least one additional layer comprising a mechanical support material (11) and / or a conductive material is applied, wherein the layer comprising the mechanical support material (11) and / or the layer comprising a conductive material. also undergoes mechanical stretching upon contact with the shaping component (7, 13, 15). A method according to one or more of the preceding claims, characterized in that, after mechanical stretching, the actuator material in the form of the polymer film (3) is additionally coated with at least one layer comprising a mechanical support material (11) and / or a conductive material.A method according to one or more of the preceding claims, characterized in that the vibrating membrane (1) comprises a layer comprising a conductive material, wherein the conductive material is selected from the group comprising platinum, tungsten, (doped) tin oxide, monocrystalline silicon, polysilicon, molybdenum, titanium, tantalum, titanium-tungsten alloy, metal silicide, aluminum, graphite, copper, wherein preferably the conductive material is a superelastic metal, wherein the conductive material particularly preferably has a fiber reinforcement, wherein for the fiber reinforcement the conductive material comprises fibers, wherein the fibers most preferably comprise carbon.Method according to one or more of the preceding claims characterized in that the vibrating membrane (1 ) comprises a layer comprising a mechanical support material (11 ), wherein the mechanical support material is selected from a group comprising monocrystalline silicon, polycrystalline silicon and / or doped polycrystalline silicon.A method according to one or more of the preceding claims, characterized in that the actuator material is provided as a polymer liquid (5) and the shaping component (7, 13, 15) is immersed in the polymer liquid (5), wherein, after contact of the shaping component (7, 13, 15) with the polymer liquid (5), the polymers of the actuator material undergo such an alignment that a dipole moment of the polymers is increased and piezoelectric properties of the actuator material are enhanced, wherein preferably the shaping component (7, 13, 15) comprises a comb structure (7) including comb fingers (9). A method according to one or more of the preceding claims, characterized in that, after contact of the shaping component (7, 13, 15) with the polymer liquid (5), the polymer liquid (5) adheres to the shaping component and hardens to form the actuator layer comprising vertical and horizontal sections. wherein, preferably after the formation of the actuator layer (6), the actuator layer (6) is coated with a layer comprising a conductive material and / or a mechanical support material (11). A method according to one or more of the preceding claims, characterized in that at least a partial section of the shaping component (7, 13, 15), preferably an entire section, is removed after contact with the actuator material (5), preferably by an etching process and / or by a thermal treatment. MEMS transducers for interaction with a volume flow of a fluid can be manufactured according to a method according to one or more of the preceding claims.

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