Method for producing MEMS transducers using tension of actuator material

Abstract

The invention relates to a method for producing a MEMS transducer that interacts with the volume flow of a fluid. For this purpose, first, a shaped part for forming a vibratable film having an actuator layer in the form of a serpentine structure and an actuator material are provided, the actuator material comprising a polymer, the actuator material being present in the form of a polymer foil or a polymer liquid. In order to obtain the shape of the actuator layer of the membrane that can vibrate, a shaped part is brought into contact with the actuator material. Advantageously, when the shaped part is brought into contact with the actuator material, the polymer of the actuator material is oriented and / or stretched, and thus the dipole moment of the polymer and the piezoelectric properties of the actuator material are increased. In another aspect, the invention relates to a MEMS transducer that can be produced by this method.

Description

[0001] The invention relates to a method for producing a MEMS transducer that interacts with a volume flow of a fluid. For this purpose, firstly a shaped part and an actuator material are provided, the shaped part being used to form a vibratable membrane having an actuator layer in the form of a serpentine structure, and the actuator material comprising a polymer, wherein the actuator material is in the form of a polymer foil or a polymer liquid. In order to obtain the shape of the actuator layer of the vibratable membrane, the shaped part is placed in contact with the actuator material. Advantageously, when the shaped part and the actuator material are in contact, the polymer of the actuator material is oriented and / or stretched, so that the dipole moment of the polymer and the piezoelectric properties of the actuator material are enhanced.

[0002] In a further aspect, the invention relates to a MEMS transducer which can be produced using the method. Background Art

[0003] Today, microsystem technology is used in many areas of application to produce compact electromechanical devices. The microelectromechanical systems (MEMS for short) that can be produced in this way are extremely compact (micrometer range), have outstanding functionality and are increasingly cost-effective to produce.

[0004] MEMS transducers, such as MEMS loudspeakers or MEMS microphones, are also known from the prior art. Current MEMS loudspeakers are usually designed as planar membrane systems, in which a vibratable membrane is actuated vertically in the emission direction. The membrane vibration is caused, for example, by means of a piezoelectric, electromagnetic or electrostatic actuator.

[0005] An electromagnetic MEMS speaker for mobile devices is described in Shahosseini et al. 2015. The MEMS speaker uses a reinforced silicon microstructure as a sound radiator, where the moving part is suspended on a carrier by a silicon driver to achieve large out-of-plane displacements with the help of an electromagnetic motor.

[0006] Stoppel et al. 2017 disclose a two-way loudspeaker, the concept of which is based on concentric piezoelectric actuators. As a special feature, the diaphragm is not closed, but comprises eight piezoelectric monolithic actuators, each consisting of a piezoelectric layer and a passive layer. The outer woofer consists of four trapezoidal actuators clamped on one side, while the inner tweeter is formed by four triangular actuators connected to a rigid frame by one or more springs. The separation of the membranes is intended to achieve an improved sound mode with a higher output.

[0007] One disadvantage of such planar MEMS loudspeakers is that they are limited in terms of sound power, especially at low frequencies. One reason for this is that for a given displacement, the sound pressure level that can be generated is proportional to the square of the frequency. Sufficient sound power therefore requires a displacement of at least 100 μm for the diaphragm, or a displacement in the square centimeter range for large-area membranes. Both conditions are difficult to achieve using MEMS technology.

[0008] Therefore, in the prior art, it is proposed to design a MEMS speaker that does not use a closed membrane for vibrating in the vertical emitting direction, but uses multiple movable elements that can cause lateral or horizontal vibrations. The advantage of this design is that an increased volume flow can be moved to a small surface area, thereby providing increased sound power.

[0009] For example, in US2018 / 0179048 A1, and Kaiser et al. 2019 disclose MEMS speakers based on this principle. The MEMS speaker includes a plurality of electrostatic bending actuators, which are arranged as vertical thin layers between the top wafer and the bottom wafer, and can induce lateral vibrations by appropriate control. The inner thin layer forms an actuator electrode opposite to the two outer thin layers. In addition to the connection nodes of the electrodes, which are still galvanically isolated, there is an air gap between the three bending thin layers. If an electric potential is applied to the inside to the outside, this will result in an attractive force on both sides due to the design of the bending in the preferred direction specified by the armature. The bending of the outer thin layer promotes mobility. The restoring force is provided by a mechanical spring force. Therefore, push-pull operations are impossible.

[0010] Another disadvantage is that the gap between the bending actuators and the top / bottom wafers (which is necessary for their mobility) leads to ventilation between the two chambers. This limits the lower cut-off frequency. In addition, the lateral movement of the bending actuators and the sound power are limited to avoid pull-in effects and acoustic failures.

[0011] DE 10 2017 115 923 A11 discloses a method for producing a MEMS transducer that can be used in a microphone or loudspeaker. To produce the MEMS transducer, a negative form is provided by means of a substrate and optionally a sacrificial layer, with the aid of which the structure of the membrane can be predetermined. The substrate or negative form has recesses corresponding to the peaks or troughs of the membrane. The negative form is then coated with a conductive layer and a piezoelectric layer. To expose the membrane, the negative form or substrate is partially removed, so that a support for the membrane is also provided by partially removing the substrate.

[0012] US2018 / 0035229 A1 also relates to a MEMS transducer, in particular a capacitive MEMS microphone or MEMS speaker. Here, a pair of electrodes is attached to the membrane itself to reduce the measurement noise in a MEMS transducer with a rigid backplate. The pair of electrodes includes a first conductive element and a second conductive element, and the distance between the first conductive element and the second conductive element changes due to the displacement of the membrane, so that the capacitance can be measured. In order to achieve the distance change between the electrodes, the membrane can adopt corrugation. In order to produce a MEMS transducer with a membrane including corrugations, a coating of multiple layers is applied to a substrate provided with a recess. In order to expose the membrane, the back side of the substrate is etched.

[0013] WO 2021 / 144400 A1 discloses a MEMS transducer that can be used as both a MEMS speaker and a MEMS microphone. The MEMS transducer described therein uses a vibrating membrane that is configured so that it includes two or more vertical segments that are substantially parallel to the vertical direction. In addition, the vibrating membrane includes at least one layer of actuator material and is in contact with at least one electrode at its end. This allows the vertical segment to be caused to vibrate horizontally by driving the electrode. Conversely, when the vertical segment is caused to vibrate horizontally, an electrical signal is also generated at the electrode.

[0014] The MEMS transducer disclosed in WO 2021 / 144400 A1 represents a significant improvement over the prior art. In the case of a MEMS loudspeaker, the configuration of a vibrating membrane comprising vertical sections advantageously results in a higher sound power, wherein the contact simultaneously ensures simplified controllability. In the case of a MEMS microphone, a higher performance and audio quality with a suitable sound mode can also be advantageously achieved. In addition, the MEMS transducer can be produced using mature semiconductor processing methods, thereby enabling cost-effective production.

[0015] The MEMS transducer disclosed in WO 2021 / 144400 A1 is preferably produced by etching a substrate (preferably from the front side) to form a serpentine structure. At least two layers are then applied, wherein at least the first layer comprises an actuator material and the second layer comprises a mechanical support material, or at least two layers comprising an actuator material are applied. The first layer and / or the second layer are then placed in contact with the electrode.

[0016] There is also potential for optimization, in particular for the production method of the MEMS transducer disclosed in WO 2021 / 144400 A1. In particular, the application of the actuator material to the serpentine structure formed in the substrate is complicated in order to ensure a homogeneous coating. However, a uniform configuration of the vibrating membrane is very important for the acoustic performance.

[0017] All MEMS transducers known from the prior art, such as MEMS loudspeakers or MEMS microphones, have in common that a vibrating membrane is particularly important. Only the displacement of the membrane allows the detection or generation of a signal. The material selection itself is particularly important, in particular the material selection of the actuator material for the serpentine structure applied to the substrate in the MEMS transducer production method disclosed in WO 2021 / 144400 A1. On the one hand, in order for the MEMS transducer to function properly, the desired acoustic, mechanical and electrical properties must be met. On the other hand, in order to optimize the production of the membrane and therefore also the production of the MEMS transducer, the material must also be easy to process.

[0018] Therefore, in view of the prior art, there is a need to provide improved or alternative methods for producing MEMS transducers.

[0019] Purpose of the Invention

[0020] The object of the present invention is to eliminate the disadvantages of the prior art. In particular, one object of the present invention is to provide a method for producing a MEMS transducer, which method is characterized by high process efficiency and reliably obtains a high-performance MEMS transducer with desired acoustic properties. Summary of the invention

[0021] The objects of the invention are achieved by the independent claims. Advantageous embodiments of the invention are disclosed in the dependent claims.

[0022] In a first aspect, the invention relates to a method for producing a MEMS transducer for interacting with a volume flow of a fluid, the MEMS transducer comprising:

[0023] -Carrying parts

[0024] - a vibratable membrane for generating or receiving fluid pressure waves in a vertical direction, wherein the vibratable membrane is supported by a carrier,

[0025] The vibratable membrane adopts a serpentine structure having vertical segments and horizontal segments, wherein the vertical segments are formed substantially parallel to the vertical direction and the horizontal segments connect the vertical segments to each other, and wherein the vibratable membrane includes at least one actuator layer made of an actuator material and is in contact with at least one electrode, so that the vertical segments can be caused to vibrate horizontally by driving the at least one electrode, or so that when the vertical segments are caused to vibrate horizontally, an electrical signal can be generated at the at least one electrode, wherein the method comprises the following steps:

[0026] a) providing at least one shaped part for forming a vibratable membrane having an actuator layer in the form of a serpentine structure;

[0027] b) providing an actuator material comprising a polymer, wherein the actuator material is in the form of a polymer foil or a polymer liquid;

[0028] c) placing a shaped part in contact with the actuator material to shape the actuator layer, wherein during contact between the shaped part and the actuator material, a polymer of the actuator material is oriented and / or stretched such that a dipole moment of the polymer is increased and the piezoelectric properties of the actuator material are enhanced.

[0029] The preferred method for producing MEMS transducers has proven to be advantageous in several respects.

[0030] A particular advantage is that the piezoelectric properties of the actuator material can be enhanced, in particular by using an actuator material comprising a polymer and aligning and / or stretching the polymer. The enhancement of the piezoelectric properties preferably means that the physical parameters related to the piezoelectric effect can be advantageously increased. The relevant physical parameters preferably relate to the piezoelectric charge coefficient, the piezoelectric voltage coefficient and / or the piezoelectric coupling coefficient.

[0031] The preferred contact of the shaped part for shaping the actuator layer with the actuator material is particularly useful for providing a vibratable membrane of a MEMS transducer. By enhancing the piezoelectric properties, a vibratable membrane can advantageously be provided which generates a correspondingly higher electrical measurement signal when the vertical segment is displaced. Conversely, by applying a voltage, a greater displacement of the vertical segment can be generated, so that a higher volume flow can be emitted. The preferred method is therefore ideally suitable for providing a high-performance MEMS microphone or MEMS loudspeaker as a MEMS transducer with desired acoustic properties.

[0032] According to the invention, it was recognized that an actuator material comprising a polymer is ideally suitable for a method for producing a MEMS transducer, wherein the actuator material has the characteristic of obtaining enhanced piezoelectric properties in the case of oriented alignment and / or stretching of the polymer. Here, a particularly powerful actuator layer can be ensured with low material costs and efficient process control, which enables high sensitivity in the case of a MEMS microphone or high power in the case of a MEMS loudspeaker.

[0033] The advantageous effect of increasing the piezoelectric properties is preferably based on an increase in the dipole moment of the polymer of the actuator material. In the context of the present invention, dipole moment preferably refers to the electric dipole moment, which is a measure of the spatial charge separation and thus preferably a measure of the strength of the dipole character of the polymer of the actuator material.

[0034] Without wishing to be bound by theory, in the context of the present invention, it is preferred that the piezoelectric properties of the formed actuator layer are enhanced by aligning and / or stretching the polymer of the actuator material. The molecular and / or submolecular structure of the polymer is associated with the tuning of the optimized piezoelectric properties.

[0035] Stretching preferably means that the contact between the shaped part and the actuator material causes the atoms and / or molecules of the polymer to be spaced further apart, which preferably increases the spatial separation of the partial charges of the atoms and / or molecules. Thus, polarization occurs and the piezoelectric properties are enhanced.

[0036] Directed arrangement preferably means that the molecules and / or atoms of the polymer of the actuator material are arranged so that a directed charge distribution occurs, thereby enhancing the piezoelectric properties. Therefore, the directed arrangement preferably includes the arrangement of atoms and / or molecules with different electronegativity to increase the dipole moment. In particular, atoms and / or molecules with high electronegativity and low electronegativity are directed so that the polarization increases and thus the piezoelectric properties increase. It may be preferred that certain material phases are obtained by directing the arrangement of atoms and / or molecules. For example, in the case of polyvinylidene fluoride (PVDF, polyvinyl difluoride), the β phase can be achieved by directing the arrangement of the polymer, which has been shown to be particularly advantageous in the context of the present invention.

[0037] The preferred method steps are particularly suitable for providing a high performance actuator layer (ie the actuator material after contact with the shaped part) as part of a vibratable membrane, which actuator layer exhibits excellent performance due to enhanced piezoelectric properties. There are also a number of resulting advantages in terms of processing.

[0038] Thus, MEMS transducers can be advantageously produced in a hybrid manner by using an actuator material comprising a polymer. Thus, scaling up production can advantageously be cost-effective. In particular, depending on the application, the costs for equipment and manufacturing infrastructure can be lower compared to CMOS (complementary metal oxide semiconductor) manufacturing. The use of an actuator material comprising a polymer facilitates production, since polymers are inexpensive to purchase, easy to process and have a high degree of mechanical flexibility. Whether in liquid form or as a polymer foil, the actuator layer can advantageously be applied particularly uniformly to the shaped part, wherein enhanced piezoelectric properties of the actuator material are simultaneously ensured by stretching and / or oriented alignment.

[0039] At the same time, further materials (e.g. mechanical support material and / or conductive material) can also be applied to the actuator layer in a simple manner. Thus, mechanical stability, protective functions and / or contact can be provided to the actuator layer on the front side and the back side of the actuator layer. Another layer (e.g. mechanical support material and / or conductive material) can be applied before and after contact with the shaped part, allowing a high degree of flexibility in process control.

[0040] The preferred method also advantageously allows forming the vibratable membrane in a particularly precise manner. Thus, by placing the shaped part in contact with the actuator material, particularly fine dimensions of the vertical and / or horizontal sections of the vibratable membrane can advantageously be achieved, wherein at the same time a uniform configuration of the actuator layer is ensured.

[0041] Preferred methods are also quick and easy to perform, require relatively inexpensive materials, components and / or equipment, and are characterized by high process efficiency.

[0042] Preferably, a shaped part is provided first. The shaped part is preferably used to contact with the actuator material to form the actuator layer.

[0043] The actuator material comprising a polymer is preferably in the form of a polymer foil or a polymer liquid. Preferably, a shaping part is placed in contact with the actuator material to shape the actuator layer. Shaping preferably means establishing the form or structure of the vibratable membrane. In particular, shaping involves obtaining the actuator layer after placing a shaping part in contact with the actuator material. Preferably, shaping involves the formation of a serpentine structure having vertical sections and horizontal sections.

[0044] During the contact between the formed part and the actuator material, the polymer of the actuator material is oriented and / or stretched so that the dipole moment of the polymer increases and the piezoelectric properties of the actuator material are enhanced. The prior art describes materials that obtain polarization and thus achieve significant piezoelectric properties. For example, these cases are described in Da Silva et al. (2010) and Gade, Bokka & Chase (2021). Da Silva et al. (2010) shows that the β phase of PVDF can be obtained by crystallization of 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 construction. The skilled person does not receive any indication of the suitability for producing MEMS transducers. However, the inventors have recognized that materials including polymers that achieve increased polarization when the polymer is stretched and / or oriented are particularly suitable for providing actuator layers for MEMS transducers. In addition to the high process efficiency, the increased performance of the actuator layer due to adjustable polarization combined with excellent acoustic characteristics is particularly beneficial.

[0045] Advantageously, the preferred method may thus provide a MEMS transducer that is particularly adapted with regard to its acoustic properties.

[0046] The design of the MEMS transducer advantageously combines the possibility of high sound power with simplified control. Compared to known planar MEMS loudspeakers, for example, the vibrating membrane itself does not have to operate over a large area of ​​several square centimeters or with a displacement of more than 100 μm to generate sufficient sound pressure. Instead, the most vertical sections of the vibrating membrane can move an enlarged total volume in the vertical emission direction, while the horizontal or lateral movement is only a few micrometers.

[0047] At the same time, simplified control can be achieved. Whereas in the prior art, such as in US 2019 / 011 64 17 A1, multiple piezoelectric actuators must be in contact with the horizontal segment, the MEMS loudspeaker described here can be operated by at least one electrode, preferably at the end. This reduces the complexity of production, minimizes sources of error, and at the same time also essentially results in synchronous control of the vertical segments to vibrate horizontally.

[0048] In this way, the air volume present between the vertical sections can be moved extremely precisely in the vertical emission direction by means of the horizontal vibrations.

[0049] This also makes it possible to provide a particularly powerful MEMS microphone with high audio quality. The structure of a MEMS microphone is similar to that of a MEMS loudspeaker, in particular with regard to the configuration of the vibrating membrane. However, instead of driving electrodes to generate horizontal vibrations and thus sound pressure waves, the MEMS microphone is configured to receive sound pressure waves in the same vertical direction. Preferably, there is a certain amount of air between the vertical segments, which moves in the vertical detection direction when sound waves are received. The sound pressure waves cause the vertical segments to vibrate horizontally, so that the actuator material generates a corresponding periodic electrical signal.

[0050] The obtained actuator layer with enhanced polarization properties has been shown to be extremely beneficial for the performance and vibration behavior of the membrane, both for application as a MEMS loudspeaker and a MEMS microphone.

[0051] Producible MEMS transducers are also less complex and allow additional processing steps to be easily performed, such as appropriate placement of top and / or bottom electrodes on the vibratable membrane.

[0052] The preferred method is particularly used for producing MEMS transducers. The term MEMS transducer refers to both MEMS microphones and MEMS loudspeakers. In general, a MEMS transducer refers to a transducer for interacting with a volume flow of a fluid, which is based on MEMS technology and whose structure for interacting with the volume flow or for receiving or generating pressure waves of the fluid has dimensions in the micrometer range (1 μm to 1,000 μm). The fluid can be a gaseous fluid or a liquid fluid. The structure of the MEMS transducer, in particular the vibrating membrane, is configured to generate or receive pressure waves of the fluid.

[0053] For example, in the case of a MEMS loudspeaker or a MEMS microphone, these may be sound pressure waves. However, a MEMS transducer may also be suitable as an actuator or sensor for other pressure waves. Thus, a MEMS transducer is preferably a device or apparatus that converts pressure waves (e.g., an acoustic signal being a sound pressure wave) into an electrical signal or vice versa (converts an electrical signal into a pressure wave, e.g., an acoustic signal).

[0054] Applications of MEMS transducers as energy harvesters are also possible, where pneumatic or hydraulic alternating pressure is used. In these cases, the electrical signal can be released, stored or fed to other (consumer) devices as recovered electrical energy.

[0055] A MEMS loudspeaker preferably refers to a loudspeaker based on MEMS technology and whose sound generating structure at least partially has dimensions in the micrometer range (1 μm to 1000 μm). Preferably, for example, a vertical segment of the vibrating membrane may have dimensions in the range of less than 1000 μm in width, height and / or thickness. For example, it is also preferred that only the dimension of the height of the vertical segment is set in the micrometer range, while for example the length may have a larger dimension and / or the thickness has a smaller magnitude.

[0056] A MEMS microphone preferably refers to a microphone based on MEMS technology and whose sound receiving structure at least partially has dimensions in the micrometer range (1 μm to 1000 μm). Preferably, for example, a vertical segment of the vibrating membrane can have dimensions in the range of less than 1000 μm in width, height and / or thickness. For example, it is also preferred that only the dimension of the height of the vertical segment is set in the micrometer range, while for example the length can have a larger dimension and / or the thickness has a smaller magnitude.

[0057] Preferably, the MEMS transducer comprises a vibrating membrane for generating or receiving pressure waves of a fluid in a vertical direction. Thus, a vibrating membrane refers to a structure that can generate an electrical signal after receiving a pressure wave or generate a pressure wave by applying an electrical signal. For this purpose, preferably, the vibrating membrane has at least one actuator layer made of an actuator material. Preferably, the structure of the vibrating membrane is arranged so that it has a serpentine structure including a vertical section and a horizontal section.

[0058] A serpentine structure preferably refers to a structure formed by a series of segments that are substantially orthogonal in cross section. The mutually orthogonal segments are preferably vertical segments and horizontal segments of the vibrating membrane. It is particularly preferred that the serpentine structure is rectangular in cross section. However, it may also be preferred that the serpentine structure has a sawtooth shape (zigzag shape) in cross section, or is curved or wavy. This is especially true if the vertical segments are not oriented completely parallel to the vertical emission or detection direction, but form an angle of ±30°, preferably ±20°, and particularly preferably ±10° with the vertical direction.

[0059] In a preferred embodiment, the horizontal segment may not be at a strictly 90° perpendicular angle to the vertical emission or detection direction, but may include, for example, an angle between 60° and 120° to the vertical direction, preferably between 70° and 110°, and particularly preferably between 80° and 100°.

[0060] Preferably, the vertical and / or horizontal sections are at least partially or over their entire length straight, however the vertical and / or horizontal sections may also be curved at least partially or over their entire length. In case the vertical and / or horizontal sections of the vibratable membrane are curved or wavy in cross section, the alignment preferably refers to the tangent of the vertical and / or horizontal sections at their respective centers.

[0061] Although the vibratable membrane is preferably oriented horizontally to the sound emission direction or the sound detection direction, sound waves are generated or detected by actuation of the vertical segments.

[0062] Preferably, the layer of actuator material in the vertical section is used as a component of a mechanical bimorph, wherein lateral bending of the vertical section is caused by driving the actuator layer via electrodes, or wherein a corresponding electrical signal is generated by the induced lateral bending. A bimorph preferably refers to a structure comprising two layers, wherein a displacement and / or bending can be achieved by the interaction of the two layers.

[0063] In a preferred embodiment, the vertical section has at least two layers, wherein one layer comprises the actuator material and the second layer comprises the mechanical support material, and wherein at least the layer comprising the actuator material is in contact with the end-side electrodes, so that horizontal vibrations can be generated by a change in shape of the actuator material relative to the mechanical support material. Therefore, in the preferred embodiment, the vertical section is present in the form of a mechanical bimorph. In this embodiment, the mechanical bimorph is formed by a layer of actuator material (e.g. piezoelectric material) and a passive layer as a mechanical support layer. In the mechanical bimorph, the actuator material is preferably already present as an actuator layer.

[0064] Advantageously, the piezoelectric properties can be particularly well adjusted by providing the actuator layer by aligning and / or stretching the polymer of the actuator material. For example, a high degree of stretching and / or aligning of the actuator material can generate a greater distance of partial charges of the polymer atoms and / or molecules of the actuator material. This will increase the dipole moment, so that the piezoelectric properties are enhanced. Conversely, by reducing the stretching and / or aligning of the actuator material, the distance of partial charges of the polymer atoms and / or molecules of the actuator material can be reduced. Therefore, the increase in the dipole moment is less, making the piezoelectric properties less obvious. By stretching and / or aligning the actuator material accordingly, the sensitivity of the actuator layer can be precisely adjusted in the context of use as a bimorph. For example, the piezoelectric properties can be adjusted by adjusting the aligning and / or stretching of the polymer of the actuator material by selecting a stretching factor, which will be described in more detail below.

[0065] Both transverse and longitudinal piezoelectric effects can be used to bend bimorphs. For the positive longitudinal piezoelectric effect, the application of force and the resulting stress gradient are caused by a pressure wave along the polar axis. In the inverse longitudinal piezoelectric effect, stress is applied along a non-polar axis, which causes the unit lattice to expand along the polar axis of the actuator layer. The polar axis preferably means an axis extending between two charge centers, preferably an axis extending between two unequal charge centers. For the positive transverse piezoelectric effect, the pressure wave applies a force along a non-polar axis so that an electrical signal can be measured at the electrode. The non-polar axis is preferably an axis that does not extend along two charge centers. In the inverse transverse piezoelectric effect, stress is applied along a polar axis, which causes the unit lattice to expand along the non-polar axis of the actuator layer. The transverse piezoelectric effect can be used to take full advantage of the C-axis orientation of the actuator layer.

[0066] For example, when the actuator layer is driven, it can undergo lateral or longitudinal stretching or compression. This generates a stress gradient in relation to the mechanical support layer, which results in lateral bending or vibration. By alternating the polarity of the electrodes, a push-pull operation can be achieved, so that almost the entire air volume can be moved in an alternating manner between the vertical segments in the vertical emission direction. The stretching and / or directional arrangement of the polymer of the actuator material and the associated increase in the dipole moment and the enhancement of the piezoelectric properties of the actuator layer lead to particularly high performance. In particular, the performance of the push-pull operation can be precisely adjusted during the production process depending on the application. The advantage of the actuator principle is therefore that the horizontal vibrations of the vertical segments can be efficiently converted into vertical volume motion or sound generation.

[0067] Since the actuator principle is not based on electrostatic attraction, but on the relative shape change (e.g. compression, tension, shear) of the actuator layer relative to the support layer, the possibility of the membrane segments sticking together can be ruled out. Instead, the vertical segments can touch each other at their ends and are therefore not limited in their displacement.

[0068] In a further preferred embodiment, the vertical segment comprises at least two layers, wherein both layers comprise actuator material and are preferably in contact with electrodes at their ends, and horizontal vibrations can be generated by a shape change of one layer relative to the other. Thus, in this embodiment, the horizontal vibrations of the vertical segment are not generated by a stress gradient between the active actuator layer and the passive support layer, but by a relative shape change of the two active actuator layers. Thus, in this embodiment, the vertical segment also exists as a bimorph.

[0069] The actuator layers may consist of the same actuator material and be driven differently. The actuator layers may also consist of different actuator materials, for example of piezoelectric materials with different deformation coefficients. The actuator layers are preferably formed as described by stretching and / or orienting a polymer of the actuator material, wherein the degree of stretching and / or orientation may also advantageously be used to adjust the deformation coefficient. The deformation coefficient preferably refers to a material variable that can be used to quantify displacement and / or vibration capacity. For example, two different actuator materials may be provided which together undergo orientation and / or stretching of their different polymers. Thus, by orienting and / or stretching the polymers of the two actuator materials, different deformation coefficients may be used to adjust the displacement capacity of the vertical segment.

[0070] In the context of the present invention, a "layer comprising an actuator material" is preferably also called an actuator layer.

[0071] In the context of the present invention, a "layer comprising a mechanical support material" is preferably also referred to as a support layer. The mechanical support material or support layer preferably acts as a passive layer that can resist changes in shape of the actuator layer. In contrast to the actuator layer, the mechanical support material preferably does not change its shape when a voltage is applied. Preferably, the mechanical support material is electrically conductive, so that it can also be used directly to establish contact with the actuator layer. However, in some embodiments, it can also be non-conductive and, for example, coated with a conductive layer.

[0072] The mechanical support material is preferably single crystal silicon, polycrystalline silicon or doped polycrystalline silicon.

[0073] While the actuator layer undergoes a change in shape when subjected to a voltage, the position of the mechanical support material remains essentially unchanged. The stress gradient generated between the two layers (mechanical bimorph) preferably causes horizontal bending. For this purpose, the thickness of the support layer should preferably be selected relative to the thickness of the actuator layer so that a sufficiently large stress gradient is generated for bending.

[0074] The serpentine structure preferably corresponds to a membrane that is folded along its width. In the context of the present invention, the vibrating membrane may therefore also preferably be referred to as a bellows. The parallel folds of the bellows preferably form vertical segments. The connecting segments between the folds preferably form horizontal segments. Preferably, the vertical segments are longer than the horizontal segments, for example 1.5, 2, 3, 4 or more times longer. Horizontal segments preferably denote those structures that enable a connection between two or more vertical segments.

[0075] The performance of a MEMS transducer, in particular a MEMS loudspeaker or a MEMS microphone, can be determined significantly by the number and / or the dimensions of the vertical segments.

[0076] In preferred embodiments, the vibratable membrane comprises more than 3, 4, 5, 10, 15, 20, 30, 40, 50, 100 or more vertical segments.

[0077] In further preferred embodiments, the vibratable membrane comprises less than 10,000, 5,000, 2,000 or 1,000 or fewer vertical segments.

[0078] The preferred number of vertical sections is required to achieve high sound power levels on a minimal chip surface without compromising the sound pattern or audio quality.

[0079] Preferably, the vertical sections are planar, which means in particular that they extend in each of the two dimensions of their surface (height, width) greater than in the dimension perpendicular thereto (thickness). For example, a size ratio of at least 2:1, preferably at least 5:1, 10:1 or more may be preferred.

[0080] In the context of the present invention, the height of a vertical segment preferably corresponds to the dimension along the direction of sound emission or sound detection, while the thickness of a vertical segment preferably corresponds to the sum of the layer thicknesses of one or more layers forming the vertical segment. The length of a vertical segment preferably corresponds to a dimension orthogonal to the height or thickness. In the cross-sectional views of the accompanying drawings shown below, the height and thickness are shown schematically (not necessarily to scale), while the dimension of length corresponds to the (invisible) drawing depth of the figure.

[0081] In a preferred embodiment, the height of the vertical segment is between 1 μm and 1000 μm, preferably between 10 μm and 500 μm. Intermediate ranges of the above ranges may also be preferred, such as 1 μm to 10 μm, 10 μm to 50 μm, 50 μm to 100 μm, 100 μm to 200 μm, 200 μm to 300 μm, 300 μm to 400 μm, 400 μm to 500 μm, 600 μm to 700 μm, 700 μm to 800 μm, 800 μm to 900 μm or even 900 μm to 1000 μm. Those skilled in the art will recognize that the above range limits may also be combined to obtain additional preferred ranges, such as 10 μm to 200 μm, 50 μm to 300 μm or even 100 μm to 600 μm.

[0082] In a preferred embodiment, the thickness of the vertical segment is between 100 nm and 10 μm, preferably between 500 nm and 5 μm. Intermediate ranges of the above ranges may also be preferred, such as 100 nm to 500 nm, 500 nm to 1 μm, 1 μm to 1.5 μm, 1.5 μm to 2 μm, 2 μm to 3 μm, 3 μm to 4 μm, 4 μm to 5 μm, 5 μm to 6 μm, 6 μm to 7 μm, 7 μm to 8 μm, 8 μm to 9 μm or even 9 μm to 10 μm. Those skilled in the art will recognize that the above range limits may also be combined to obtain additional preferred ranges, such as 500 nm to 3 μm, 1 μm to 5 μm or even 1500 nm to 6 μm.

[0083] In a preferred embodiment, the length of the vertical segment is between 10 μm and 10 mm, preferably between 100 μm and 1 mm. Intermediate ranges of the above ranges may also be preferred, such as 10 μm to 100 μm, 100 μm to 200 μm, 200 μm to 300 μm, 300 μm to 400 μm, 400 μm to 500 μm, 500 μm to 1000 μm, 1 mm to 2 mm, 3 mm to 4 mm, 4 mm to 5 mm, 5 mm to 8 mm or even 8 mm to 10 mm. Those skilled in the art will recognize that the above range limits may also be combined to obtain additional preferred ranges, such as 10 μm to 500 μm, 500 μm to 5 μm or even 1 mm to 5 mm.

[0084] With the above preferred dimensions of the vibratable membrane or the vertical section, a particularly compact MEMS transducer, in particular a MEMS loudspeaker or a MEMS microphone, can be provided, which combines high performance with a good sound pattern or audio quality at the same time. Advantageously, the above dimensions can be achieved particularly easily by configuring the shaped part accordingly. Preferably, the structure of the shaped part determines the structure of the vibratable membrane comprising the vertical section and the horizontal section.

[0085] The vertical and horizontal (or lateral) direction indications preferably refer to the preferred directions in which the vibratable membrane is oriented for generating or receiving pressure waves of the fluid. Preferably, the vibratable membrane is suspended horizontally between at least two side regions of the carrier, and the vertical direction (direction of interaction with the fluid) for generating or receiving pressure waves is orthogonal thereto. In the case of a MEMS speaker, the vertical (interaction) direction corresponds to the vertical sound emission direction of the MEMS speaker. In this case, vertical preferably refers to the direction of sound emission, while horizontal means a direction orthogonal thereto. In the case of a MEMS microphone, the vertical (interaction) direction corresponds to the vertical sound detection direction of the MEMS microphone. In this case, vertical preferably means the direction of sound detection or reception, while horizontal means a direction orthogonal thereto.

[0086] The vibratable membrane of the MEMS transducer is particularly important, since a measurement signal can only be generated or received if the vertical section is displaced horizontally by a pressure wave. The choice of material used to arrange the vibratable membrane is therefore relevant to the performance of the MEMS transducer. According to the invention, it was recognized that an actuator material comprising a polymer provides particularly good results, wherein the actuator material comprising a polymer achieves an increase in the dipole moment of the polymer by aligning and / or stretching.

[0087] In another preferred embodiment, the actuator material is selected from the group including piezoelectric materials, piezoelectric polymer materials 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 the group including polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-trifluoroethylene (PVDF-TrFE) and / or poly-L-lactic acid (PLLA).

[0088] An actuator material preferably refers to a material that undergoes a change in shape, such as stretching, compression or shearing, when a voltage is applied, or conversely a material that generates a voltage when its shape changes.

[0089] Materials having an electric dipole are preferred, which undergo a change in shape when a voltage is applied, wherein the orientation of the dipole and / or the electric field may determine the preferred direction of the shape change.

[0090] Preferably, the actuator material may be a piezoelectric material, a piezoelectric polymer material (also called piezoelectric material) and / or an electroactive polymer (EAP).

[0091] The piezoelectric polymer material preferably comprises a polymer having an internal dipole and piezoelectric properties imparted thereto. This means that the piezoelectric polymer material (similar to the classical piezoelectric material described above) undergoes a shape change (e.g. compression, stretching or shearing) when an external voltage is applied. An example of a preferred piezoelectric polymer material is polyvinylidene fluoride (PVDF).

[0092] Electroactive polymers (EAPs) are polymers that change their shape when a voltage is applied. A distinction is usually made between ionic and electronic EAPs. The mechanism of action of ionic EAPs is based on mass transport (diffusion) of ions. Subclasses of this type of EAPs are conducting polymers, ion-metal polymer composites and ion gels. On the other hand, the mode of action of electronic EAPs is based on electronic charge transport. This group includes electrostrictive and ferroelectric polymers as well as dielectric elastomers.

[0093] Preferably, a piezoelectric polymer material is used as the actuator material, wherein, particularly preferably, the piezoelectric polymer material is selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-trifluoroethylene (PVDF-TrFE) and / or poly-L-lactic acid (PLLA). The above materials have been advantageously proven to be easy to process and to generate the desired piezoelectric properties by aligning and / or stretching.

[0094] Piezoelectric polymer materials are advantageously particularly easy to form, ie particularly easy to process, have an advantageously low dielectric constant and are particularly suitable for the provision and functional suitability of a vibratable membrane.

[0095] In particular, piezoelectric polymer materials that have a dipole moment that is substantially perpendicular to the main chain are suitable. 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. The fluorine atoms can be oriented and / or stretched to produce a dipole, which increases the dipole moment and thus the piezoelectric properties. Fluorine exhibits a high electronegativity, while hydrogen exhibits a significantly lower electronegativity. By oriented fluorine and hydrogen atoms in a β phase, a particularly strong dipole moment is advantageously generated, taking into account the electronegativity of the atomic species, thereby enhancing the piezoelectric properties.

[0096] The transformation of the actuator material into the so-called β can be particularly important with respect to increasing the dipole moment. Preferably, the β phase is characterized by an all-trans planar zigzag conformation of atoms, which results in a significant dipole moment (also called TTTT configuration or conformation). In the case of PVDF, the β phase is characterized by the separation of most fluorine atoms from hydrogen atoms and the generation of a dipole moment perpendicular to the main chain. Due to the fact that hydrogen and fluorine exhibit different electronegativity, a strong dipole is generated, which correspondingly exhibits enhanced piezoelectric properties. In particular, in PVDF, the CH2-CF2 dipole is strictly perpendicular to the chain axis (carbon chain). The all-trans molecules are essentially stacked in parallel, thereby forming a crystal structure, i.e., the β phase. Since the dipoles in the β phase are essentially completely oriented in one direction, there is a particularly pronounced polarization, which is due to the sum of the CH2-CF2 dipole moments per unit volume.

[0097] The alignment and / or stretching of the polymer may preferably cause the actuator material (preferably PVDF) to transform into the β phase. Preferably, the β phase may be reliably stabilized and / or made more pronounced to optimize the piezoelectric properties. When PVDF is used as the 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 the actuator material is particularly well suited for the improved performance of the MEMS transducer.

[0098] In a preferred embodiment, the actuator layer has a relative dielectric constant ε of 1-15 r , preferably 5-15, particularly preferably 7-12.

[0099] In a preferred embodiment, the actuator layer has a piezoelectric charge coefficient of 1-50 pC / N (picocoulombs per Newton), preferably between 1-5 pC / N, particularly preferably between 5-30 pC / N, most preferably between 30-50 pC / N.

[0100] The parameter ranges mentioned for the relative dielectric constant and / or the piezoelectric charge coefficient preferably relate to the actuator layer, i.e. the layer formed from the actuator material after stretching and / or alignment of the polymer. The above parameter ranges lead in particular to high actuator layer performance and thus to improved functionality of the MEMS transducer.

[0101] By stretching and / or orienting the polymers of the actuator material, as they are in contact with the shaped part, the above parameter ranges can advantageously be achieved reliably and repeatably. Preferably, the stretching and / or orienting of the polymers results in an enhancement of the piezoelectric properties, such as those related to the piezoelectric charge coefficient, the piezoelectric voltage coefficient, and the piezoelectric coupling coefficient.

[0102] The piezoelectric charge coefficient preferably describes the relationship between the charge generated per unit area and the applied mechanical force and is expressed in units of coulombs / newton (C / N).This parameter is often used to assess the quality of piezoelectric materials.

[0103] The piezoelectric voltage coefficient is also called the voltage output constant. It is preferably defined as the ratio between the generated electric field and the applied mechanical stress and is expressed in units of voltage meters per newton.

[0104] The piezoelectric coupling coefficient (less frequently 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 ratio in which electrical energy can be converted into mechanical energy and vice versa.

[0105] Furthermore, it is preferred that the actuator material has an elastic modulus between about 1-5 GPa (Gigapascal), preferably between about 2-4 GPa, and most preferably between about 2-3 GPa. The above elastic modulus range has proven to be advantageous in facilitating forming on the formed part, so that the serpentine structure can be achieved with high precision.

[0106] In a further preferred embodiment the method is characterized in that the actuator material is provided in the form of a polymer foil, wherein the polymer foil is mechanically stretched by means of a forming part to form the actuator layer into a serpentine structure comprising vertical and horizontal sections.

[0107] Advantageously, the polymer foil can be easily processed, particularly by mechanical stretching, to be shaped into a serpentine structure comprising a vertical section and a horizontal section. The polymer foil is characterized in that the foil comprises a polymer that is oriented and / or stretched after the mechanical stretching of the polymer foil. The polymer foil is preferably provided in a planar form. The planar form preferably means a structure that is many times larger than the extension of the plane (length or width) orthogonal to the extension of the plane (thickness). For example, the length or width can be about 2 times, 3 times, 10 times, 20 times, 50 times, 100 times or more than the thickness of the polymer foil.

[0108] In a preferred embodiment, the thickness of the polymer foil is between 100 nm and 50 μm, preferably between 500 nm and 10 μm. Intermediate ranges of the above ranges may also be preferred, such as 100 nm to 500 nm, 500 nm to 1 μm, 1 μm to 1.5 μm, 1.5 μm to 2 μm, 2 μm to 3 μm, 3 μm to 4 μm, 4 μm to 5 μm, 5 μm to 6 μm, 6 μm to 7 μm, 7 μm to 8 μm, 8 μm to 9 μm, 9 μm to 10 μm, 10 μm to 20 μm, 20 μm to 30 μm, 30 μm to 40 μm or even 40 μm to 50 μm. Those skilled in the art will recognize that the above range limits may also be combined to obtain additional preferred ranges, such as 500 nm to 5 μm, 1 μm to 20 μm or even 1500 nm to 10 μm.

[0109] Advantageously, the polymer foil can be mechanically stretched particularly easily, i.e. in particular with little mechanical resistance, in order to produce a serpentine structure for the vibratable membrane. Advantageously, the polymer foil adapts to the shape of the shaped part with the greatest accuracy, so that the desired serpentine structure can be obtained precisely. At the same time, the polymer foil is advantageously resistant to cracking, so that the reliability of the implementation during the preferred process is ensured. Therefore, the polymer foil preferably exhibits a high tensile strength, wherein this can depend on the specific material choice of the actuator material. Depending on the material, the tensile strength is preferably in the range of 20 N / mm 2 Up to 300N / mm 2 Between, preferably 50N / mm 2 -250 N / mm 2 between 100 N / mm and 100 N / mm 2 -200N / mm 2 Between, most preferably 120N / mm 2 -180 N / mm 2 between.

[0110] The temperature used during mechanical stretching can also be related to the resulting vibratable membrane. In a preferred embodiment, for example, a temperature above or below the glass transition temperature of the material used can be selected. In the context of the present invention, the temperature during stretching and / or alignment of the actuator material can therefore also be understood as a factor (or stretching factor) for the alignment of the polymer.

[0111] Mechanical stretching preferably means stretching in such a way that the polymer of the actuator material is oriented and / or stretched by mechanical action principles to increase the dipole moment of the polymer and thus generate enhanced piezoelectric properties. When a polymer foil is provided, mechanical stretching is preferably performed. Mechanical stretching includes, for example, applying a low pressure to convert the polymer foil into a serpentine structure. Mechanical stretching also preferably involves the interaction of two shaped parts to obtain a serpentine structure that can vibrate the membrane.

[0112] Stretching the polymer foil preferably achieves an increase in area and / or length along one dimension. The increase in area and / or length relative to the initial area and / or initial length may preferably be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 200%, 300%, 400% or more, an increase of 100%, 200%, 300%, 400% means an increase of 2, 3, 4 times. In particular, this results in the polymer of the actuator material being stretched in the vertical direction by mechanical stretching to increase the piezoelectric properties.

[0113] An advantage of mechanical stretching is that the actuator layer comprising the actuator material obtains a particularly precise C-axis orientation, which is perpendicular to the surface of the vertical segment of the generated serpentine structure. For example, the C-axis orientation allows the transverse piezoelectric effect (piezoelectric effect) to be used for the vibration of the vertical segment of the generated vibratable membrane. Other orientations may also be preferred, and other orientations may, for example, involve the use of the longitudinal piezoelectric effect to form horizontal bending or vibration.

[0114] In a further preferred embodiment, the method is characterized in that the shaped part has a comb-like structure with comb teeth.

[0115] The comb-like structure is preferably a structure with a plurality of teeth, which are preferably arranged regularly, i.e. in particular the teeth are substantially identical in shape, length, width and thickness. The comb-like structure preferably also comprises empty regions. Empty regions preferably refer to regions of the comb-like structure in which no material of the comb-like structure is present. Preferably, the comb-like structure comprises a regularly alternating sequence of teeth and empty regions.

[0116] The comb-like structure can advantageously be provided by conventional methods of semiconductor microsystem technology, for example by etching the substrate. The etched areas of the substrate are referred to as empty areas, while the remaining areas represent the comb teeth. Since the comb-like structure is particularly easy to provide, the serpentine structure can be optimized in terms of design depending on the intended use. For example, the length of the comb teeth preferably corresponds to the length of the vertical segments, wherein the width of the empty areas corresponds to the width of the horizontal segments.

[0117] In a further preferred embodiment, the method is characterized in that the forming part comprises a comb-like structure comprising comb teeth and having openings, wherein the actuator material is applied to the comb teeth of the comb-like structure as a polymer foil and a low pressure, preferably a vacuum, is applied through the openings so that a partial area of ​​the polymer foil is mechanically stretched in the direction of the opening so that a serpentine structure is formed.

[0118] Preferably, the opening is located on the trunk of the comb-like structure. The trunk of the comb-like structure preferably refers to the section to which the comb teeth are attached. The opening can be provided by known prior art methods, for example by known etching methods. Preferably, the openings are made in the trunk of the comb-like structure so that they are positioned between the comb teeth. By applying a low pressure, the area of ​​the polymer foil is mechanically stretched in the direction of the opening, i.e., in particular in the direction of the trunk of the comb-like structure.

[0119] Preferably, the polymer foil is fixed to the comb-like structure at its end regions, so that fixing the polymer foil after applying the low pressure causes a corresponding stretching of the polymer foil. In this case, the entire polymer foil is preferably stretched along one dimension of a row of comb teeth one after another, wherein the degree of stretching or elongation can be adjusted by the level and / or duration of the applied low pressure.

[0120] The mechanical resistance of the polymer foil to the application of low pressure can also be preferably adjusted by the strength with which it is fixed at its ends, which causes different degrees of stretching or elongation of the polymer foil. In the case where it is fixed at its ends in a way that does not allow any relative movement of the polymer foil, the increase in the length of the polymer foil due to the shaping of the vertical sections will fully contribute to the stretching of the polymer foil. If it is not fixed so firmly at its ends, the shaping of the vertical sections formed due to the application of low pressure at the opening may only be partially caused by the elongation or stretching of the polymer foil, because the supply of polymer foil from the area outside the comb-like structure cannot be completely prevented. Advantageously, by adjusting the strength with which the foil is fixed at its ends, the desired height of the vertical sections and the stretching or elongation of the polymer foil can be adjusted independently of each other.

[0121] In a further embodiment, the polymer foil may also be preferably fixed to the contact surface of the comb teeth so that these areas are not stretched when low pressure is applied. Those areas of the polymer foil that are stretched in the opening direction form vertical sections after stretching, while those areas that are not stretched form horizontal sections.

[0122] The application of low pressure preferably means the effect of a pressure lower than the pressure existing between the teeth of the comb-like structure. The low pressure is particularly preferably a vacuum. The low pressure can preferably be lower than the ambient pressure. Preferably, the low pressure is selected from a range including about 0-100000 Pa (Pascal), preferably between about 0-50000 Pa, particularly preferably between about 0-20000 Pa, particularly more preferably between about 0-10000 Pa, most preferably between about 0-5000 Pa. Preferably, the low pressure can be adapted to the mechanical properties, for example to the elasticity of the polymer foil.

[0123] In the context of the present invention, low pressure can be understood as a stretching factor. In addition, the stretching of the polymer foil to provide the actuator layer can be adjusted by the level of low pressure. For example, the stretching itself can be adjusted by adjusting the low pressure, because the height of the vertical section produced (and the longitudinal stretching of the polymer foil when its ends are fixed) can be adjusted by the value and / or effective duration of the low pressure. This means that the duration of the action, i.e. the time during which the low pressure plays a role, can also be regarded as a stretching factor. This means that the shape of the vibrating membrane can be adjusted particularly easily using low pressure.

[0124] Preferably, the low pressure is applied through the openings of the comb-like structure at a temperature between about 180° C. and 220° C. The temperature used can promote the stretching of the polymer foil in the direction of the opening, thereby in particular allowing faster stretching in the direction of the opening. This is partly due (without being limited by theory) to the fact that the mechanical tension of the polymer foil decreases when the temperature increases, so that stretching can be carried out under reduced mechanical resistance. The temperature during the preferred application of the low pressure preferably also represents a stretching factor.

[0125] The shape of the comb structure can also be understood as a stretching factor, and when low pressure is applied, the polymer foil is preferably applied to the teeth of the comb structure. For example, assuming that low pressure is applied to completely mold the polymer foil into the comb structure, the height and width of the teeth approximately determine the height of the vertical section and the width of the horizontal section of the resulting vibratable membrane.

[0126] Preferably, substantially the same low pressure is applied through each opening to achieve the most uniform possible mechanical stretching of the polymer foil. The mechanical stretching by means of the low pressure may be influenced by the size of the opening 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 foil occurs to provide the serpentine structure. Applying the low pressure advantageously results in a particularly uniform stretching, thus resulting in excellent results in terms of power and acoustic performance of the actuator layer formed. Potential damage to the actuator layer is also effectively avoided.

[0127] In a further preferred embodiment, the method is characterized in that the actuator material is applied as a polymer foil to a first comb structure, wherein the second comb structure is guided towards the polymer foil and the respective comb teeth of the first comb structure and the second comb structure are guided into empty areas, so that a serpentine structure comprising vertical segments and horizontal segments is formed in the interaction of the first comb structure base and the second comb structure base.

[0128] Preferably, the polymer foil is applied to the first comb structure such that the polymer foil is placed along the longitudinal axis of the comb teeth. The serpentine structure is provided by the interaction of the first comb structure with the second comb structure. The interaction preferably means that the first comb structure and the second comb structure are guided together such that the respective longitudinal axis of the comb teeth is inserted into the empty area of ​​the other comb structure. Thus, the introduction of the comb teeth of the first comb structure into the empty area of ​​the second comb structure produces a membrane with a serpentine structure comprising vertical sections and horizontal sections.

[0129] Preferably, the first comb structure and the second comb structure are guided together so that the teeth of the two comb structures are substantially perpendicular to the vertical direction and the horizontal direction of the actuator layer or the diaphragm arranged thereon. In particular, the teeth of the two comb structures are guided together so that the teeth are oriented in the sagittal direction.

[0130] The length of the vertical segment 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 means the distance that exists after mechanical stretching occurs. The larger the final distance, the longer the vertical segment. 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 teeth. Therefore, the final distance in this embodiment is also a stretching factor, which can be used to optimize the shape and stretching of the actuator layer. The shape and stretching of the actuator layer and therefore the vibrating membrane can also be adjusted by the shape of the two comb structures, for example by length and / or width, for example the length and / or sagittal shape of the vertical segment.

[0131] Preferably, the final distance between the first comb structure and the second comb structure is determined by the displacement of the first comb structure from the second comb structure.

[0132] Preferably, the polymer foil is fixed to the first comb structure at its end region, so that the serpentine structure of the vibratable membrane is generated by fixing the polymer foil after the first comb structure interacts with the second comb structure. The mechanical resistance of the polymer foil can preferably be adjusted by the strength of its fixing, so that when it is particularly firmly fixed, a higher mechanical resistance can be generated than when it is less firmly fixed. Therefore, the fixing of the polymer foil at the end region of the first comb structure is preferably also a tensile factor.

[0133] By combining the selection of the strength of the fixing of the polymer foil at the end region of the first comb-like structure with the displacement, the shape of the serpentine structure can be adjusted particularly precisely. For example, the length, width, shape and / or stiffness of the vertical and / or horizontal segments can be optimized by selecting the strength of the fixing of the polymer foil, the shape of the comb-like structure and / or the distance of the displacement.

[0134] Preferably, the temperature is below 180° C. when mechanical stretching occurs by the interaction between the first comb structure and the second comb structure. Depending on the temperature level, this can also promote stretching so as to reduce the mechanical tension of the polymer foil by temperature effects. The temperature during the interaction of the first comb structure with the second comb structure can also be considered as a stretching factor.

[0135] In a preferred embodiment, the stretching is achieved by applying a low pressure or by the interaction of the first comb structure with the second comb structure at a temperature above or below the glass transition temperature of the polymer foil. By adjusting the temperature, the process of forming the serpentine structure and the stretching or alignment of the polymer can be favorably influenced.

[0136] At temperatures above the glass transition temperature, the ductility of the polymer foil increases, so that a particularly stable serpentine structure of the film can be obtained. On the other hand, at temperatures below the glass transition temperature of the polymer, a particularly pronounced orientation of the polymer can advantageously be achieved.

[0137] Therefore, the temperature used during the forming of the polymer foil is another relevant factor that can be optimized to obtain the piezoelectric properties of the serpentine structure and the vibratable membrane.

[0138] In the context of the present invention, stretching factors refer to factors that can be used to adjust the stretching of the polymer of the actuator material. These factors or parameters can vary depending on the implementation. For example, stretching factors include low pressure, the shape of one or more comb structures, the fixing of the polymer foil to the comb structure, the displacement of the comb structure, the temperature used for polymer stretching and / or alignment, etc.

[0139] In a further preferred embodiment, the method is characterized in that the actuator material is provided in the form of a polymer foil, to which at least one layer comprising a mechanical support material and / or an electrically conductive material is additionally applied, wherein the layer comprising the mechanical support material and / or the layer comprising the electrically conductive material also undergoes mechanical stretching when in contact with the shaped part.

[0140] Advantageously, the combination of mechanical stretching of the polymer foil and stretching of the mechanical support layer eliminates the need for additional processing steps, thereby enabling the serpentine structure to be provided more quickly. For example, mechanical stretching of the mechanical support material combined with stretching of the polymer foil means that coating of the mechanical support material is no longer required.

[0141] Therefore, polymer foil can be preferably provided together with mechanical support material, wherein, polymer foil and mechanical support material are preferably attached to each other, and polymer foil and mechanical support material combination are arranged on the comb teeth of comb-like structure. Preferably, the trunk of comb-like structure is provided with opening, for example, this opening can be formed by etching process. By applying low pressure, preferably vacuum, the combination of polymer foil and mechanical support material is displaced along the trunk direction accordingly, and therefore displaced along the opening. In particular, those regions above the empty area of ​​comb-like structure are displaced along the direction of the trunk. In the region where polymer foil and mechanical support material are positioned on the comb teeth, there is no stretching in the direction of the trunk or opening accordingly. Therefore, a serpentine structure in which polymer foil and mechanical support material are stretched together can be provided.

[0142] The mechanical stretching of the polymer foil in combination with the mechanical support material can also be preferably achieved by using the first comb-like structure and the second comb-like structure. The polymer foil and the mechanical support material can preferably be arranged on top of each other and arranged on the first comb-like structure so that they are applied along the longitudinal axis of the comb teeth. Preferably, the serpentine structure is provided by the interaction of the first comb-like structure with the second comb-like structure. Preferably, the first comb-like structure and the second comb-like structure are guided toward each other so that the comb teeth enter the empty area of ​​the other comb-like structure accordingly. Therefore, by the interaction of the first comb-like structure with the second comb-like structure, a serpentine structure can be provided for both the actuator layer and the mechanical support layer. It is also preferred that the serpentine structure is first provided for the polymer foil to form the actuator layer and then the mechanical support material is applied.

[0143] In a preferred embodiment, the conductive material is present above and / or below the actuator material. By stretching and / or orienting the combination of the actuator material and the conductive material, in addition to the actuator layer, a top electrode (above the actuator material) and / or a bottom electrode (below the actuator material) can advantageously be provided after stretching.

[0144] In a further preferred embodiment, the conductive material may be identical to the support material, so that, for example, the bottom electrode and / or the top electrode is at the same time the mechanical support layer.

[0145] If at least one further layer comprising mechanical support material and / or conductive material is stretchable, i.e. can be mechanically deformed without causing damage or cracks, it is particularly preferred to apply the at least one further layer preferably additionally on the polymer foil, which at least one further layer is also subjected to mechanical stretching when in contact with the shaped part. The stretchable conductive material can preferably be a coating comprising, for example, carbon nanotubes. If the at least one further layer comprising mechanical support material and / or conductive material does not have sufficient elasticity for mechanical stretching, it is preferred to apply the at least one further layer by coating only after the polymer foil has been shaped.

[0146] In a further preferred embodiment, the method is characterized in that, after the mechanical stretching, the actuator material in the form of a polymer foil is additionally coated with at least one layer comprising a mechanical support material and / or an electrically conductive material. In this way, a support layer and / or a layer comprising an electrically conductive material is obtained which has a serpentine structure according to the stretched polymer foil, without stretching the support material or the electrically conductive material itself.

[0147] Preferably, at least one layer comprising mechanical support material and / or conductive material is applied by using a coating process in a coating system. The coating process can be selected, for example, from a group comprising spray coating, mist coating and / or steam coating. The above coating processes are known to those skilled in the art and are advantageously easy to carry out.

[0148] Preferably, coating is performed in a coating system, which can be a physical coating system or a chemical coating system, preferably a plasma-supported chemical coating system, a low-pressure chemical and / or an epitaxial coating system.

[0149] Preferably, the coating is carried out in a temperature range in which the aligned polymer of the actuator material does not change, so that the enhanced piezoelectric properties are retained particularly reliably.

[0150] In particular, it is preferred that all steps of the method for providing a MEMS transducer after stretching / orienting the polymer of the actuator material are performed at a temperature that does not impair the enhanced piezoelectric properties of the actuator layer. For the process steps for providing a MEMS transducer after stretching / orienting the polymer of the actuator material, it is particularly preferred to avoid temperatures exceeding 300° C., preferably exceeding 200° C. or exceeding 150° C.

[0151] In a further preferred embodiment the method is characterized in that the vibratable membrane comprises a layer comprising an electrically conductive material, which layer acts as top electrode and / or bottom electrode.

[0152] The top electrode and / or the bottom electrode preferably refers to a layer comprising a conductive material, which extends over the entire surface of the vibrating membrane. Preferably, the layer is placed in contact with an electrode pad as an electrode, wherein preferably the conductive material in combination with the electrode may also be referred to as a top electrode and / or a bottom electrode, wherein preferably there are electronic devices on the electrode for providing a voltage and / or a current. Preferably, the electrodes are attached at the ends so that the actuator layer can be actuated from the electrodes or an electrical signal can be read out at the electrodes due to a corresponding change in the shape of the actuator layer.

[0153] The layer of conductive material, preferably metal, is particularly preferably present as a continuous or full-surface or contiguous layer of the vibratable membrane in the sense of a top electrode or bottom electrode, which forms a substantially homogeneous region. The designations top and bottom preferably refer to the position of the conductive material, so that in a cross section it can be said that the top electrode includes the conductive material above the actuator layer and the bottom electrode includes the conductive material below the actuator layer.

[0154] By means of a layer made of an electrically conductive material, preferably a metal, two or more vertical sections can advantageously be placed in contact with the end-side electrodes or electrode pads.

[0155] End side preferably means that the at least one electrode is positioned such that a current or voltage source can be contacted at one end of the vibratable membrane, preferably at that end at which the membrane is suspended from a carrier.

[0156] In a preferred embodiment, the producible MEMS transducer comprises two end side electrodes. Preferably, the electrodes at the opposite ends between which two or more vertical sections of the vibrating membrane are present can be contacted with electronic devices, such as a current or voltage source, so that one or more actuator layers in the vertical sections can be controlled by the end side electrodes.

[0157] The provision of end-side electrodes is therefore preferably distinguished from a contacting form in which the individual vertical segments are driven by separate electrodes or, in the case of a MEMS microphone, the generated electrical signal is tapped off. Preferably, the MEMS transducer therefore comprises exactly one or exactly two electrodes for the end-side contacting and no further electrodes (pads) for contacting the center of the vertical segment.

[0158] Preferably, the layer of actuator material in the vertical section acts as a component of a mechanical bimorph, wherein lateral bending of the vertical section is induced by driving the actuator layer via electrodes, or wherein a corresponding electrical signal is generated by the induced lateral bending.

[0159] In a further preferred embodiment, the method is characterized in that the vibrating membrane comprises a layer comprising a conductive material, wherein the conductive material is selected from the group comprising platinum, tungsten, (doped) tin oxide, monocrystalline silicon, polycrystalline silicon, molybdenum, titanium, tantalum, titanium-tungsten alloys, metal silicides, 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, most preferably, the fibers comprise carbon.

[0160] A conductive material selected from the group consisting of platinum, tungsten, (doped) tin oxide, single crystal silicon, polycrystalline silicon, molybdenum, titanium, tantalum, titanium-tungsten alloys, metal silicides, aluminum, graphite, copper is particularly suitable for being applied to the actuator layer as part of a coating process, in particular after the polymer foil has been mechanically stretched.

[0161] Conductive materials such as superelastic metals or conductive materials with fiber reinforcement are particularly suitable for mechanical stretching in combination with polymer foils.

[0162] Superelastic metals preferably refer to metals that belong to superelastic materials and exhibit so-called pseudoelastic or superelastic behavior. Under high stress, they can undergo reversible deformation and reach a high degree of elongation. This "elastic" deformation can exceed the elasticity of the metal by up to twenty times. The reason for this behavior is the phase transformation within the material. Various metal alloys can be used here, for example alloys including copper, zinc and aluminum or copper, aluminum and nickel or nickel and titanium.

[0163] Fiber-reinforced materials, such as materials reinforced with fibers including carbon, can have a favorable effect on both the support function and the electrical conductivity. Thus, a higher mechanical resistance can be advantageously generated by the fiber reinforcement, so that the stress gradient generated during the deformation of the vertical section is increased, and at the same time the electrical conductivity can be increased by selecting a corresponding crystal structure of the fibers (e.g. carbon).

[0164] In a further preferred embodiment the method is characterized in that the vibratable membrane comprises a layer comprising a mechanical support material, wherein the mechanical support material is selected from the group comprising single crystal silicon, polycrystalline silicon and / or doped polycrystalline silicon.

[0165] The above materials have proven to be particularly advantageous for use as support layers. In addition, they are particularly well suited to being applied to the actuator layer as part of a coating process, for example after mechanical stretching.

[0166] In a further preferred embodiment, the method is characterized in that the actuator material is provided in the form of a polymer liquid and the shaped part is immersed in the polymer liquid, wherein, after the shaped part is in contact with the polymer liquid, the polymer of the actuator material undergoes a directional arrangement such that the dipole moment of the polymer increases and the piezoelectric properties of the actuator material are enhanced, wherein preferably, the shaped part comprises a comb-like structure comprising comb teeth.

[0167] The polymers of the polymer liquid are aligned by immersing the shaped part in the polymer liquid. In a preferred embodiment, the shaped part can be provided with an intermediate coating for this purpose, which aligns the polymers. It can also be preferred that the shaped part is formed from a semiconductor material, wherein a crystal orientation is used to align the growing polymer layer. By selecting or configuring the shaped part accordingly, the desired alignment of the polymers of the polymer liquid can be advantageously achieved and the piezoelectric properties of the resulting actuator layer can be increased.

[0168] Preferably, the shaped part is immersed in the polymer liquid at a temperature above the glass transition temperature of the polymer liquid so that oriented alignment of the polymer is more easily provided.

[0169] In a further preferred embodiment, the method is characterized in that after contacting the shaped part with the polymer liquid, the polymer liquid adheres to the shaped part and hardens to form an actuator layer comprising vertical segments and horizontal segments, wherein, preferably after forming the actuator layer, the actuator layer is coated with a layer comprising a conductive material and / or a mechanical support material.

[0170] The alignment of the polymers of the polymer liquid can take place in particular if the alignment is frozen or obtained after the immersion of the shaped part (in the viscous state).

[0171] In a further preferred embodiment, the method is characterized in that at least partial sections, preferably the entire section, of the shaped component are removed after the contact with the actuator material, preferably by an etching process and / or by a heat treatment.

[0172] The etching process and / or heat treatment may advantageously expose the serpentine structure including the vertical segments and the horizontal segments such that vibration capability is provided.

[0173] The etching process is preferably a process for etching, i.e. a process for removing material to remove a shaped part. Preferably, the etching process is selected from a group comprising a wet chemical etching process and / or a dry etching process, preferably a physical and / or chemical dry etching process, particularly preferably consisting of reactive ion etching and / or reactive ion deep etching (Bosch process), or a combination of the above etching processes.

[0174] The above-mentioned etching processes are known to those skilled in the art and may be selected accordingly to ensure effective removal of the shaped features.

[0175] Preferably, the shaped part can also be removed by heat treatment. Heat treatment preferably refers to a process of removing the shaped part by using the effect of heat. The choice of temperature depends on the material constituting the shaped part.

[0176] After exposing the serpentine structure and providing the vibratable membrane, it is placed in contact with the carrier.Preferably, the vibratable membrane is placed in contact with the support at its ends so that the membrane extends in a horizontal direction.

[0177] In a further preferred embodiment, the method is characterized in that the shaped part and / or the carrier comprises a material selected from the group consisting of single-crystal silicon, polycrystalline silicon, silicon dioxide, silicon carbide, silicon germanium, silicon nitride, nitride, germanium, carbon, gallium arsenide, gallium nitride, indium phosphide and / or glass.

[0178] These materials are easy to process and inexpensive in semiconductor and / or microsystem production and are suitable for large-scale applications. In particular, the carrier and / or the housing can be produced flexibly due to the material and / or the production method. In particular, the MEMS transducer comprising the vibratable membrane and the carrier together can preferably be produced in a (semiconductor) process, preferably on a wafer. This further simplifies and reduces the production costs, so that compact and robust MEMS transducers can be produced cost-effectively.

[0179] In a preferred embodiment of the invention, the carrier comprises two side regions, preferably four side regions, between which the diaphragm is arranged in horizontal direction.

[0180] The carrier is preferably a frame structure, which is essentially formed by a continuous outer boundary in the form of side walls of the free planar area. The frame structure is preferably stable and rigid. In the case of an angular frame shape (triangular, square, hexagonal or generally polygonal profile), the individual side areas that 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 carrier.

[0181] Preferably, the carrier comprises four side regions, preferably with an additional end face, which is generally parallel to the drawn cross section.These two further side walls span the frame structure.

[0182] Preferably, for example in embodiments where mechanical stretching is preferred, the carrier may be provided by a shaped component. For example, in the case of mechanical stretching, it may be preferred that the housing of the MEMS transducer is provided by the interaction of two shaped components.

[0183] In a further aspect, the invention relates to a MEMS transducer for interacting with a volume flow of a fluid, producible according to the method described above.

[0184] Those skilled in the art will recognize that the technical features, definitions and advantages of the preferred embodiments of the method for producing a MEMS transducer are also applicable to the MEMS transducer, and vice versa.

[0185] Surprisingly, the preferred method steps for producing a MEMS transducer result in a MEMS transducer characterized by excellent acoustic, electrical and mechanical properties, in particular for a vibratable membrane. The shape of the serpentine structure can be adjusted particularly accurately, for example by selecting the stretch coefficient. In particular, the shape of the vertical segment and / or the horizontal segment can be determined particularly easily. The displacement of the vertical segment can be advantageously adjusted by stretching and / or aligning the polymer of the actuator material, so that the produced MEMS transducer can be effectively used in a plurality of applications. Therefore, the preferred embodiments of the method have an influence on the structural properties of the MEMS transducer and thus on the functional properties.

[0186] The improved properties of the MEMS transducer are particularly evident during operation. Due to the enhanced piezoelectric properties, a vibrating membrane is advantageously provided which generates a correspondingly higher electrical measurement signal when the vertical segment is displaced. Conversely, by applying a voltage, a greater displacement of the vertical segment can be generated, so that a higher volume flow of fluid (particularly air) can be expelled. The MEMS transducer is therefore characterized by a particularly high performance level and desirable acoustic properties.

[0187] Advantageously, the MEMS transducer has an actuator layer with good piezoelectric properties, so that the vibratable membrane in particular exhibits improved performance. In this way, a greater displacement of the vertical section can be advantageously achieved if sound pressure waves are to be detected in the case of a MEMS microphone or are to be emitted in the case of a MEMS loudspeaker.

[0188] The present invention will be explained below with reference to the accompanying drawings and examples. The examples and drawings are used to illustrate the preferred embodiments of the present invention, but are not intended to limit the present invention.

[0189] Attached photos BRIEF DESCRIPTION OF THE DRAWINGS

[0190] Figure 1 Schematic diagram of the preferred method steps for producing a MEMS transducer

[0191] Figure 2 Further schematic diagram of preferred method steps for producing a MEMS transducer

[0192] Figure 3Further schematic diagrams of preferred method steps for producing a MEMS transducer

[0193] Detailed description of the drawings

[0194] Figure 1 A schematic diagram showing preferred method steps is shown.

[0195] Figure 1 a shows a first forming part 13 and a second forming part 15. The first forming part or first comb structure 13 and the second forming part or second comb structure 15 are configured as comb structures, ie they comprise comb teeth 9 which however point out of the sheet plane or into the sheet plane in the illustration.

[0196] Furthermore, the actuator material is shown in the form of a polymer foil 3 and a layer comprising a mechanical support material 11. The polymer foil 3 is applied to the mechanical support material 11.

[0197] Figure 1 b shows that the polymer foil 3 and the layer comprising the mechanical support material 11 are applied to the teeth of the second comb structure 15 .

[0198] Figure 1 c shows that the first comb structure 13 is guided in the direction of the polymer foil 3 and the layer comprising the mechanical support material 11. As a result, the individual teeth of the first comb structure 13 are guided into the empty areas of the second comb structure 15. As a result, a serpentine structure for the actuator layer 6 is formed under the interaction of the first comb structure 13 and the second comb structure 15, wherein the serpentine structure has a vertical section and a horizontal section.

[0199] The final distance between the first comb structure 13 and the second comb structure 15, in particular the final distance between the tips of the comb teeth, can advantageously determine the length of the vertical section of the vibratable membrane. The shape of the two comb structures 13, 15 also adjusts the shape of the actuator layer and thus the shape of the vibratable membrane. The final distance between the first comb structure 13 and the second comb structure 15 is determined by the displacement of the comb structures 13, 15.

[0200] The polymer foil 3 is preferably fixed at the end regions of the comb structures 13 and / or 15 , so that the polymer foil 3 is stretched or elongated by the interaction of the first comb structure 13 with the second comb structure 15 to obtain a corresponding serpentine structure.

[0201] Figure 2 Further preferred method steps for configuring the serpentine structure are shown.

[0202] Figure 2a shows a shaped part 7 in the form of a comb-like structure 7 having comb teeth 9. Advantageously, the structure of the comb teeth 9 makes it particularly easy to obtain a serpentine structure for the structure of the oscillatable membrane.

[0203] exist Figure 2 In b, an actuator material in the form of a polymer foil 3 and a layer comprising a mechanical support material 11 are provided, wherein these are applied to the teeth 9 of a comb structure 7 .

[0204] Figure 2 c shows that the comb structure has openings, wherein the openings are formed on the trunk 8 of the comb structure 7 on which the teeth 9 are arranged. The arrows show the application of a low pressure, so that partial areas of the polymer foil 3 and the layer comprising the mechanical support material 11 are stretched.

[0205] During the application of the low pressure, the polymer foil 3 is fixed at the end region of the chamber structure 7, so that the polymer foil 3 is stretched accordingly. Preferably, the entire polymer foil is stretched along one dimension of the comb teeth 9 arranged in a row one behind the other, wherein the degree of stretching or elongation can be adjusted by the level and / or duration of the applied low pressure.

[0206] In particular, substantially the same low pressure is applied through each opening to achieve the most uniform possible mechanical stretching of the polymer foil 3. The mechanical stretching with the low pressure may be influenced by the size of the opening and / or the magnitude of the low pressure. The lower the pressure and / or the larger the opening, the faster the mechanical stretching of the polymer foil 3 to provide a serpentine structure.

[0207] Figure 3 Further schematic diagrams show preferred method steps.

[0208] exist Figure 3 In a, a polymer liquid 3 and a forming component 7 are provided, wherein the forming component 7 is in the form of a comb-like structure 7 including comb teeth 9.

[0209] Figure 3 b shows the comb-like structure 7 immersed in the polymer liquid 5. When the comb-like structure 7 is placed in contact with the polymer liquid 5 or immersed in the polymer liquid 5, the polymer of the actuator material or the polymer liquid 5 is oriented, so that the dipole moment of the polymer increases and the piezoelectric properties of the actuator material are enhanced. The polymer of the polymer liquid 5 is oriented by immersing the shaped part 7 in the polymer liquid 5.

[0210] Figure 3 c shows that the polymer liquid 5 adheres to the comb structure 7 and hardens to form the actuator layer 6 as a serpentine structure including vertical segments and horizontal segments.

[0211] Once the actuator layer 6 is formed, the comb structure 7 is removed, which can be achieved, for example, by an etching process and / or a heat treatment (see Figure 3 d).

[0212] References

[0213] 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>

[0214] 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, CHINA, June 18-22, 2017.

[0215] Bert Kaiser, Sergiu Langa, Lutz Ehrig, Michael Stolz, Hermann Schenk, Holger Conrad, Harald Schenk, Klaus Schimmanz and David Schuffenhauer, Concept and proof for an all-silicon MEMS microspeaker utilizing air chambers Microsystems & Nanoengineering volume 5, Article number: 43(2019).

[0216] Da Silva, Aline Bruna, et al. Effect of drawing on the dielectric properties and polarization of pressed solution cast β-PVDF films. Journal of materials science 45.15(2010): 4206-4215.

[0217] Gade, Harshal, Sreevalli Bokka, and George G. Chase. Polarization treatments of electrospun PVDF fiber mats. Polymer 212(2021): 123152.

[0218] List of reference numerals

[0219] 1 Vibratable membrane

[0220] 3 Polymer foil

[0221] 5 Polymer liquid

[0222] 6 Actuator Layer

[0223] 7 Shaped part, preferably as a comb-like structure

[0224] 8 Main cadres

[0225] 9 teeth

[0226] 11 includes a layer of mechanical support material, a support layer

[0227] 13 First forming part, preferably as a first comb structure

[0228] 15 A second shaped part, preferably as a second comb structure.

Claims

1. A method for producing a MEMS transducer for interacting with a volume flow of a fluid, the MEMS transducer comprising: -Carrying parts a vibratable membrane (1) for generating or receiving pressure waves of the fluid in a vertical direction, wherein the vibratable membrane is held by the carrier, The vibrating membrane (1) adopts a serpentine structure having a vertical segment and a horizontal segment, wherein the vertical segment is configured to be substantially parallel to the vertical direction, and the horizontal segment connects the vertical segments to each other, and wherein the vibrating membrane (1) includes at least one actuator layer (6) made of an actuator material and in contact with at least one electrode, so that the vertical segment can be caused to vibrate horizontally by driving the at least one electrode, or when the vertical segment is caused to vibrate horizontally, 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 shaped part (7, 13, 15) for configuring the vibratable membrane (1) with the actuator layer (6) in the form of a serpentine structure, b) providing an actuator material comprising a polymer, wherein the actuator material is in the form of a polymer foil (3) or a polymer liquid (5), c) placing the shaping part (7, 13, 15) in contact with the actuator material to shape the actuator layer (6), wherein during the contact between the shaping part and the actuator material, the polymer of the actuator material is oriented and / or stretched so that the dipole moment of the polymer is increased and the piezoelectric properties of the actuator material are enhanced.

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

3. The method according to one or more of the preceding claims, It is characterized in that The actuator layer (6) has a relative dielectric constant ε of 1-15 r , preferably 5-15, particularly preferably 7-12, and / or The actuator layer (6) has a piezoelectric charge coefficient of 1-50 pC / N, preferably between 1-5 pC / N, particularly preferably 5-30 pC / N, most preferably 30-50 pC / N.

4. The method according to one or more of the preceding claims, It is characterized in that The actuator material is provided in the form of the polymer foil (3), wherein the polymer foil is mechanically stretched by the forming member (7, 13, 15) to form the actuator layer (6) into the serpentine structure comprising the vertical section and the horizontal section.

5. The method according to the preceding claim, It is characterized in that The shaping element (7, 13, 15) has a comb-like structure (7, 13, 15) with comb teeth (9).

6. The method according to one or more of the preceding claims, It is characterized in that The shaped part (7, 13, 15) comprises a comb structure (7) comprising comb teeth (9), and the comb structure (7) has openings, wherein the actuator material is applied as a polymer foil (3) to the comb teeth (9) of the comb structure (7), and A low pressure, preferably a vacuum, is applied through the opening, so that a partial area of ​​the polymer foil (3) is mechanically stretched in the direction of the opening, so that a serpentine structure is formed.

7. The method according to one or more of the preceding claims, It is characterized in that The actuator material is applied as a polymer foil (3) to a first comb structure (13), wherein a second comb structure (15) is guided in the direction of the polymer foil (3) and the respective comb teeth of the first comb structure (13) and the second comb structure (15) are guided into empty areas, so that the serpentine structure comprising the vertical segment and the horizontal segment is formed in the interaction of the first comb structure (13) and the second comb structure (15).

8. The method according to one or more of the preceding claims, It is characterized in that The actuator material is provided in the form of the polymer foil (3), to which at least one layer comprising a mechanical support material (11) and / or an electrically conductive material is additionally applied, wherein the layer comprising the mechanical support material (11) and / or the layer comprising the electrically conductive material also undergoes mechanical stretching when in contact with the shaped part (7, 13, 15).

9. The method according to one or more of the preceding claims, It is characterized in that After mechanical stretching, the actuator material in the form of the polymer foil (3) is additionally coated with at least one layer comprising a mechanical support material (11) and / or an electrically conductive material.

10. The method according to one or more of the preceding claims, It is characterized in that The vibratable membrane (1) comprises a layer comprising a conductive material, wherein the conductive material is selected from the group consisting of platinum, tungsten, (doped) tin oxide, single crystal silicon, polycrystalline silicon, molybdenum, titanium, tantalum, titanium-tungsten alloys, metal silicides, aluminum, graphite, copper, Wherein, the conductive material is preferably a superelastic metal, Therein, it is particularly preferred that the electrically conductive material comprises a fiber reinforcement, wherein for the fiber reinforcement, the electrically conductive material comprises fibers, wherein it is particularly preferred that the fibers comprise carbon.

11. The method according to one or more of the preceding claims, It is characterized in that The vibratable membrane (1) comprises a layer comprising a mechanical support material (11), wherein the mechanical support material is selected from the group comprising single crystal silicon, polycrystalline silicon and / or doped polycrystalline silicon.

12. The method according to one or more of the preceding claims, It is characterized in that The actuator material is provided as a polymer liquid (5), and the shaped part (7, 13, 15) is immersed in the polymer liquid (5), wherein, after placing the shaped part (7, 13, 15) in contact with the polymer liquid (5), the polymer of the actuator material undergoes directional alignment, so that the dipole moment of the polymer increases and the piezoelectric properties of the actuator material are enhanced, Preferably, the forming component (7, 13, 15) comprises a comb-like structure (7) comprising comb teeth (9).

13. The method according to one or more of the preceding claims, It is characterized in that After placing the shaped parts (7, 13, 15) in contact with the polymer liquid (5), the polymer liquid (5) adheres to the shaped parts and hardens to form the actuator layer including vertical sections and horizontal sections, Preferably, after forming the actuator layer (6), the actuator layer (6) is coated with a layer comprising a conductive material and / or a mechanical support material (11).

14. The method according to one or more of the preceding claims, It is characterized in that At least partial sections, preferably the entire section, of the shaped part (7, 13, 15) are removed after contact with the actuator material (5), preferably by an etching process and / or a heat treatment.

15. A MEMS transducer for interacting with a volume flow of a fluid, producible according to the method of one or more of the preceding claims.

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