Method for operating a microelectromechanical device, microelectromechanical device, microelectromechanical loudspeaker, microelectromechanical fluid pump apparatus and microelectromechanical combination component

Abstract

The invention relates to a method for operating a microelectromechanical device (1) for generating a fluid flow (F) with a displacement unit (2), wherein the displacement unit (2) has a first diaphragm (3) and a second diaphragm (4) that are arranged above a common cavity (5) and are able to move relative to one another, and wherein, in order to generate the fluid flow (F), the first diaphragm (3) is excited so as to carry out a first vibration at a first frequency (f1) and the second diaphragm (4) is excited so as to carry out a second vibration at a second frequency (f2) different from the first frequency (f1) by way of a drive apparatus (6). The invention additionally relates to a microelectromechanical device (1), to a microelectromechanical loudspeaker, to a microelectromechanical fluid pump apparatus and to a microelectromechanical combination component.

Description

[0001] Description

[0002] title

[0003] Method for operating a microelectromechanical device, microelectromechanical device, microelectromechanical loudspeaker, microelectromechanical fluid pumping device and microelectromechanical combination component

[0004] The invention relates to a method for operating a microelectromechanical device, a microelectromechanical device, a microelectromechanical loudspeaker, a microelectromechanical fluid pumping device and a microelectromechanical combination component.

[0005] State of the art

[0006] Microelectromechanical devices, also known as microelectromechanical structures under the term “MEMS”, are known from the state of the art.

[0007] For example, US 2022 / 0 315412 A1 discloses a MEMS device for in-ear headphones with two membrane sections which, in order to avoid occlusion effects, are controlled in such a way that a vent opening is formed by a difference between their respective displacement.

[0008] CN 1 10 100458 A describes an acoustic MEMS device with a carrier, at least one membrane suspended above a cavity, and at least one acoustically isolating groove on the membrane. The MEMS device can have several differently dimensioned membranes for different sound transmission frequencies. WO 20161054447 A1 describes a piezoelectric ultrasonic transducer with a membrane arranged over an opening in a substrate. A portion of the membrane is divided into several cantilevers that are mechanically coupled to one another and configured to oscillate at a common frequency.

[0009] Disclosure of the invention

[0010] According to the features of independent claim 1, a method for operating a microelectromechanical device for generating a fluid flow with a displacement unit is proposed, wherein the displacement unit has a first membrane and a second membrane which are arranged above a common cavity and are movable relative to one another, and wherein, in order to generate the fluid flow, the first membrane is excited to a first oscillation at a first frequency and the second membrane is excited to a second oscillation at a second frequency deviating from the first frequency by means of a drive device.

[0011] In other words, according to the method, the vibrations of the first and second membranes at different frequencies deliberately create a phase shift between the vibrating membranes, which can be used to generate a fluid flow. Due to the relative mobility of the first and second membranes to one another, the membranes can, depending on their phase position, for example, vibrate past one another and in doing so form a fluid opening for sucking in a fluid volume, or vibrate in the same direction to displace the fluid volume and thereby generate a fluid flow. The first and second membranes can therefore act together as a fluid pump. By appropriately exciting the first and second membranes, the vibration sequences can be influenced and various parameters for generating the fluid flow can thus be easily varied.Such variable fluid flow generation can, for example, also be advantageously used for generating sound pressure, for example through a varying phase shift. Furthermore, constant fluid flows can also be generated using the method. A fluid flow can be a moving volume of gas and / or liquid and can be described, for example, by a volume or mass flow. In some applications, the fluid flow can be embodied as an air flow, which can be advantageously used, for example, as a cooling medium or to generate sound pressure, hereinafter also referred to as a sound signal.

[0012] A displacement unit can be a micromechanical structure of the microelectromechanical device, with which a fluid flow or fluid pressure can be generated by movable structural elements. Such movable structural elements can be formed by the proposed first and second membranes, which are excited at different frequencies. In principle, it is conceivable for the displacement unit to have further movable structural elements, in particular further membranes, in addition to the first and second membranes.

[0013] A membrane can be a substantially flat, deflectable structural element with a height and length several times greater than its width. The first membrane and the second membrane can each be connected to a fixed support structure of the device and held in place by it for movement in space. A fluid opening can be formed between the first membrane and the second membrane by a relative movement of the membranes to one another.

[0014] The cavity of the device, above which the first and second membranes are arranged, can form a rear side volume of the device. A front side volume can be present on the side of the first and second membranes facing away from the rear side volume. The displacement unit can be designed to generate a fluid flow from the front side volume towards the rear side volume and vice versa. Depending on the application of the device, the cavity can be closed, have a lateral opening and / or an opening opposite the membranes, wherein the opening can lead, for example, to a pressure chamber, a device environment or another spatial volume. The first oscillation at the first frequency and the second oscillation at the second frequency can be regarded as mechanical, for example at least approximately sinusoidal oscillations of the membranes.The second frequency of the second oscillation deviates from the first frequency of the first oscillation. In particular, the second frequency can be higher than the first frequency. The first frequency and the second frequency can in particular deviate from a frequency of the generated fluid flow signals, since the fluid flow generation depends on the oscillation behavior of the membranes and not directly on the excitation frequency. Due to this frequency decoupling, according to the proposed method, for example, low-frequency sound signals with high sound power can be generated despite very small dimensions of the microelectromechanical device. To generate different frequencies, it can generally be provided for the membranes to be subjected to a different excitation frequency by different drive elements of the drive device.Alternatively or additionally, it is conceivable to design the natural frequencies of the membranes differently by suitable geometric design and dimensioning of the membranes.

[0015] The excitation of the first and second membranes is achieved by means of a drive device, for example, an electrostatic drive device. For example, the first and second membranes can be driven capacitively or by ferroelectrics. The excitation can cause an oscillating deflection of the first and second membranes. To generate a fluid flow according to the proposed method, even small deflections of the membranes are effective and effective, so that the method increases the efficiency of the device operation and the device can be operated with low energy consumption. A drive element of the drive device can be assigned to the first and / or the second membrane, which drive element is designed to excite vibrations on the membrane, for example, is mechanically coupled to the membrane.Depending on the embodiment, for example, one drive element per membrane can be provided on the drive device for excitation or a common drive element can be provided for the first or second membrane, wherein the excitation of the other membrane can be effected, for example, by a superimposed drive signal and a mechanical coupling of the first and second membranes to one another.

[0016] The microelectromechanical device can, for example, be manufactured using semiconductor technology as a layered structure on a substrate and have one or more functional layers, wherein, for example, the first and second membranes can form a first functional layer and the drive device can form a second functional layer. To manufacture the device, for example, a membrane layer can be applied to the substrate and a drive structure can be applied to the membrane layer. The membrane layer can be structured such that a first and a second membrane are formed which are movable relative to one another. The cavity can, for example, be formed in the substrate or in a further intermediate layer applied between the membrane layer and the substrate. It is clear that the described microelectromechanical device can be manufactured very easily.

[0017] Consequently, both membranes contribute to pressure generation and the opening and closing of a correspondingly designed valve. In particular, a wide opening can be achieved with the same layer thickness of both membranes and the same amplitude of the membranes. The valve opens at an amplitude equivalent to half the layer thickness. Conveniently, the membrane with the lower natural frequency can also be operated at a higher amplitude, which in this arrangement positively supports both the opening of the valve and the pressure buildup.

[0018] Another advantage is that the pressure buildup occurs locally at the point where the valve opens and closes, thus achieving even better pumping efficiency. Depending on the configuration, application, and frequency, this eliminates the need for a closed volume in which excess pressure builds up below or above the diaphragm system.

[0019] In a particularly advantageous variant, the product of amplitude and membrane size of adjacent individual membranes is selected such that it is of the same order of magnitude. During the counter-oscillation of the two membranes, the valve is closed but no pressure is built up, thus passing through a neutral state. According to one embodiment, an edge region of the first membrane can at least partially border essentially directly on an edge region of the second membrane. Essentially means that the gap distance between the membranes is predominantly smaller than the layer thickness of the membranes, with the gap distance being implemented for manufacturing reasons.

[0020] According to one embodiment, the second frequency of the second oscillation can be substantially twice the first frequency of the first oscillation. For example, the second frequency can be substantially twice the first frequency. For example, the second frequency can be substantially twice the first frequency plus or minus a maximum of 25 percent of the first frequency. The second membrane can therefore go through approximately two periods during one period of the first membrane, i.e., oscillate at least approximately twice as fast as the first membrane. This makes it possible to achieve a favorable phase relationship between the membranes, which enables efficient fluid flow generation.

[0021] According to one embodiment, the first frequency and / or the second frequency can be at least 20 kHz. This allows excitation of the first and / or second membrane outside the humanly audible frequency range. Accordingly, operation of the device can be enabled without audible pumping noise or disturbing harmonics. Furthermore, at such high frequencies, many oscillations are generated per unit of time, so that a high energy conversion per unit of time occurs and, for example, a high pumping power or a high sound power can be achieved during operation of the device. As already explained, a sound frequency that can be generated by means of fluid flow pulses can be decoupled from the first or second frequency as the excitation frequency, so that according to the proposed method, for example, low-frequency sound signals with high sound power can be generated despite the very small dimensions of the microelectromechanical device.For example, it is conceivable to select frequency ranges from 50 to 400 kHz for the first frequency of the first oscillation and the second frequency of the second oscillation. This allows very small and rigid microelectromechanical structures to be used for the device. This results in high efficiency and area utilization of the microelectromechanical device.

[0022] According to one embodiment, a fluid flow direction, a fluid flow rate, and / or a differential pressure of the fluid flow can be controlled by controlling the phases, frequencies, and / or amplitudes of the first oscillation of the first membrane and the second oscillation of the second membrane. Accordingly, the properties of the generated fluid flow can be specifically influenced by targeted, individual excitation of the first and second membranes with different oscillation characteristics. In particular, precise fine adjustment of the desired fluid flow can be achieved by continuously variable drive signals for the first and second membranes. For example, it can be provided that a phase change is set in such a way that, starting from two identical oscillations, a phase shift of +90° or -90° is achieved.

[0023] According to one embodiment, a fixed phase relationship can be set between the first oscillation of the first membrane and the second oscillation of the second membrane. This makes it possible to achieve continuous, in particular constant, fluid flow generation. A fixed phase relationship can be advantageous, for example, for operating the device for ventilation and cooling purposes. For example, due to the compact and flat design of the microelectromechanical device, it is conceivable to use it as a cooling device in electronic devices, in particular in mobile electronic devices. The proposed advantageous option of operating the device at excitation frequencies of at least 20 kHz, above the human audible range, enables low-noise and energy-efficient use of the device as a cooling device.

[0024] Alternatively or additionally, one embodiment proposes varying the phase relationship between the first oscillation of the first membrane and the second oscillation of the second membrane in order to generate a sound signal. This allows the generated fluid flow to be varied and used to generate a sound signal. This enables advantageous use of the microelectromechanical device as a loudspeaker. The first frequency of the first oscillation and the second frequency of the second oscillation can, in particular, deviate from a frequency of the generated fluid flow signals, since the generation of the fluid flow depends on the oscillation behavior of the membranes and not directly on the excitation frequency. Due to this frequency decoupling, the proposed method can, for example, generate low-frequency sound signals with high sound power despite the very small dimensions of the microelectromechanical device.Accordingly, for example, an efficient use of the device as a bass loudspeaker is conceivable, whereby, using the proposed method, high sound energy can be generated at low sound frequencies. The sound signal generated by the first and second membranes can be considered quasi-beat, since no actual beat is generated in the narrow acoustic sense, but rather is simulated by the interplay of the membrane vibrations. In principle, it can be advantageous for a start-up phase of operation as a loudspeaker to initially maintain a constant phase relationship until the loudspeaker has reached the desired operating pump power, and then to begin varying the phase relationship to generate acoustic signals.

[0025] In principle, depending on the application of the device and the method, it is conceivable to configure the device to generate either a continuous or a varied fluid flow. To achieve a corresponding change in the fluid flow, only the phase relationship between the first and second membranes needs to be adjusted in terms of control technology using suitable drive signals, so that no structural modification of the device is required for alternating operation.

[0026] According to one embodiment, a sound frequency of the sound signal can be controlled via a frequency difference between the first frequency of the first oscillation and the second frequency of the second oscillation, and / or a sound intensity of the sound signal can be controlled via the amplitude of the first oscillation and / or the second oscillation. Accordingly, for example, when the device is used as a bass loudspeaker, a bass frequency and / or a bass volume of the bass signal can be continuously adjusted by appropriately influencing the relative oscillation behavior of the membranes to one another, for example, via their relative phase relationship.

[0027] According to one embodiment, the first membrane and the second membrane can each be excited by a drive element of the drive device. This allows the first and second membranes to be excited to individual vibrations in a simple and direct manner. Furthermore, frequency differences between the first and second membranes can be efficiently generated, so that, for example, the frequency of a sound signal generated by the displacement unit can be precisely controlled over a wide frequency range.

[0028] According to one embodiment, the first membrane and the second membrane can be mechanically coupled to one another. This makes it possible to at least partially transmit oscillatory movements of one membrane to the other membrane. The mechanical coupling of the first and second membranes can be achieved, for example, by suitable structuring of a membrane layer of the device. The mechanical coupling can be achieved, for example, by coupling points flanking a separating gap between the membranes. Depending on the design of the mechanical coupling, for example by different elasticities of the coupling, the relative oscillation behavior of the membranes to one another can also be specifically influenced. The coupling can, for example, be implemented in each case by a spring element.

[0029] In the inventive approach, disadvantages are avoided in that the second membrane is coupled and also carries out its oscillation. The first membrane is operated at half the frequency of the second membrane, so the first membrane can function as a valve. Due to this sympathetic arrangement, each oscillation of the second membrane can be used as a pumping cycle. In the inventive arrangement, both membranes contribute to the pumping cycle. What is particularly advantageous is that the first membrane is operated at the fundamental frequency and can therefore be designed as a relatively large membrane with a lot of deflection. The second membrane is operated at half the fundamental frequency and therefore needs to be designed to be rather soft. Because the second membrane oscillates with the first membrane, it can be arranged within the second membrane, in a region with a high amplitude of the first membrane.This arrangement makes it possible to choose a very large adjacent area of ​​the two membranes and thus achieve a high efficiency of the valve.

[0030] In practice, both drives are operated at the fundamental frequency and simultaneously superimposed with half the fundamental frequency. To control the valve and thus the air flow, the phase and / or amplitude of the fundamental frequency and the superimposed half the fundamental frequency are regulated in the first and second drives. In the simplest case, the fundamental frequency is applied to both drives with the same phase and amplitude. Half the fundamental frequency is superimposed on the first drive with a constant phase to the fundamental frequency, also preferably with a constant amplitude. Half the fundamental frequency is superimposed on the second drive with a variable phase to the fundamental frequency, also preferably with a constant amplitude. The pumping direction and pumping volume are controlled by changing the phase.

[0031] Due to the preferred suspension of the first membrane on springs on the second membrane, the first membrane is suspended rather softly and, by appropriately dimensioning the spring, its natural frequency can be designed to be half the natural frequency of the second membrane.

[0032] In contrast to the prior art, the structure according to the invention provides all of these advantages:

[0033] 1. The possibility of arranging the first membrane inside the second membrane and using both membranes as a pump membrane enables optimal close positioning.

[0034] 2. Since the valve function is integrated in the pump membrane, all available chip area can be used for the pump membrane, thus achieving maximum amplitude.

[0035] 3. Due to the possibility of arranging the first membrane inside the second membrane, a very long opening range of the valve can be achieved over a very large membrane area, which leads to a good opening capacity of the valve.

[0036] 4. The arrangement according to the invention can be manufactured using a layer system from which both membranes are produced. This allows the gap between the movable membranes to be selected very narrowly during the manufacturing process, ensuring good valve closing capacity and low backflow at the pump membrane. At the same time, the structure can be manufactured cost-effectively.

[0037] 5. The system allows a pumping cycle to be performed with each oscillation of the second diaphragm, thus achieving high pumping performance. Furthermore, the diaphragm system is very compact due to its nested arrangement. It can be built very small and thus in a geometry that allows for very high natural frequencies.

[0038] According to one embodiment, the first membrane and the second membrane can be excited by a superimposed drive signal from a drive element assigned to the first membrane or the second membrane. This makes the method efficient and eliminates the need for a separate drive element for each of the first and second membranes. Furthermore, a high fluid volume can be pumped with just one drive element for the first and second membrane, thus achieving high pumping or sound power. A membrane connected to a directly driven membrane by a suitable coupling can, for example, execute the basic movement of the driven membrane and additionally receive a phase shift due to the type of coupling and / or a superimposed drive signal.It is conceivable to position a center of gravity asymmetrically with respect to a pivot point of the coupled membrane in order to be able to apply a superimposed drive signal to the driven membrane and to the coupled membrane in a favorable manner.

[0039] According to one embodiment, the device can have at least two first membranes which are excited to the first oscillation at the first frequency by means of the drive device, and / or at least two second membranes which are excited to the second oscillation at the second frequency by means of the drive device. By exciting more than one first membrane to a first oscillation at a first frequency and / or more than one second membrane to a second oscillation at a second frequency, the generation of the fluid flow can be improved and, for example, a pumping or sound power can be increased. The first and second membranes can, for example, be arranged alternately next to one another in order to be able to optimally utilize the dynamic relative oscillation behavior of the first and second membranes to one another.According to one embodiment, several or all of the first and second membranes 3, 4 of the displacement unit 2 can be arranged together above the cavity 5. Additionally or alternatively, several or all of the first and second membranes 3, 4 can be arranged above separate cavities 5, for example, a first and second membrane 3, 4 can be arranged in pairs above each cavity 5.

[0040] According to one embodiment, two second membranes can be mechanically coupled to a first membrane arranged between the two second membranes, wherein the second membranes and the first membrane are excited by a superimposed drive signal from drive elements of the drive device assigned to the second membranes. This forms a rocker structure with which the device can be operated efficiently. The second frequency of the second oscillation of the second membrane can be substantially twice as high as the first frequency of the first oscillation. The excitation of the second membranes can be effected by a symmetrical signal that is applied to a drive element of the drive device assigned to a respective second membrane.The excitation of the first membrane can be achieved by a superimposed differential signal, which is additionally applied to the drive elements of the second membranes and transmitted to the first membrane through the mechanical coupling between the second membranes and the first membrane. The resulting rocker structure allows for optimized fluid flow generation. For example, a large volume of fluid can be pumped per pumping movement of the displacement unit.In addition, the opposing movements of the differently oscillating first membrane and second membranes can achieve an increased number of pumping movements per oscillation cycle. For example, with a second frequency of the second membranes that is approximately twice as high as the first frequency of the first membrane, the proposed membrane arrangement can have multiple oscillation phases per oscillation cycle, during which the first membrane and the second membranes oscillate in the same direction and can thus pump a volume of fluid. One oscillation cycle can, for example, correspond to one period of the first oscillation of the first membrane. The first membrane is preferably coupled to the two second membranes with springs.

[0041] The invention also relates to a microelectromechanical device for generating a fluid flow with a displacement unit, wherein the displacement unit has a first membrane and a second membrane which are arranged above a common cavity and are movable relative to one another, wherein the device has a drive device which is designed to excite the first membrane to a first oscillation at a first frequency and to excite the second membrane to a second oscillation at a second frequency which differs from the first frequency.

[0042] The proposed microelectromechanical device can also achieve the aforementioned advantages of simple and variable fluid flow generation with two differently vibrating membranes. The microelectromechanical device can be configured to operate according to the method described above.

[0043] According to one embodiment, the second membrane can have a natural frequency that is substantially twice the natural frequency of the first membrane. For example, the natural frequency of the second membrane can be substantially twice the first frequency. For example, the natural frequency of the second membrane can be substantially twice the natural frequency of the first membrane plus or minus a maximum of 25 percent of the first frequency. As a result, when the membranes are excited in the range of their natural frequency or close to their natural frequency, a favorable phase relationship can be achieved between the first and second membranes, which enables efficient fluid flow generation. In the range of the natural frequencies of the membranes, larger amplitudes can be generated with the same excitation energy than outside the natural frequency range.The natural frequency of the first and second membranes can be influenced, for example, by their geometric design and dimensions. For example, the second membrane can be designed to be narrower, shorter, or thinner than the first membrane, for example, essentially half as wide, half as long, or half as thick as the first membrane.

[0044] According to one embodiment, the first membrane can have a recess and / or the second membrane can have a stiffening structure. The natural frequency can therefore also be influenced by changing the stiffness of the membrane. For example, a stiffening structure, for example in the form of a stiffening lip, can be molded onto the membrane to increase the stiffness and thus the natural frequency. For example, a recess can be introduced into the membrane to reduce the stiffness and thus the natural frequency. Stiffening structures or recesses can also be used to specifically influence the movement pattern of the membranes, for example, to be able to move a larger volume of fluid.

[0045] According to one embodiment, the natural frequency of the first membrane and / or the natural frequency of the second membrane can be at least 20 kHz. This allows efficient excitation of the first and / or second membrane outside the humanly audible frequency range. Accordingly, operation of the device without audible pumping noise or disruptive harmonics is enabled. Furthermore, at such high frequencies, many oscillations can be generated per unit of time, so that the proposed device can achieve a high energy conversion per unit of time and, for example, a high pumping power or a high sound power.

[0046] According to one embodiment, a sealing lip can be provided between the first membrane and the second membrane. This allows a favorable seal to be achieved for improved pumping behavior of the displacement unit without impairing the mechanical behavior of the membranes. Alternatively or additionally, it can be provided, for example, that the first membrane and the second membrane are thinned at their mutually facing ends or at their transition region in order to favorably influence the pumping behavior of the displacement unit. Such thinning can have an advantageous effect, for example, depending on the properties of the fluid to be pumped or depending on the basic thickness of the membrane.

[0047] According to one embodiment, a drive element of the drive device can be assigned to each of the first and second membranes. This allows the first and second membranes to be excited to individual vibrations in a simple and direct manner.

[0048] According to one embodiment, the first membrane and the second membrane can be mechanically coupled to each other. This allows vibrational movements of one membrane to be at least partially transmitted to the other membrane.

[0049] According to one embodiment, the first membrane and the second membrane can be configured for excitation by a superimposed drive signal from a drive element associated with the first membrane or the second membrane. This makes it possible to provide an efficient and simply constructed device. Furthermore, a single drive element for the first and second membranes can be used to pump a high fluid volume, thus achieving high pumping or acoustic performance.

[0050] According to one embodiment, the device can have at least two first membranes configured to excite the first oscillation at the first frequency by means of the drive device, and / or at least two second membranes configured to excite the second oscillation at the second frequency by means of the drive device. This makes it possible to provide an efficient device that is suitable, for example, for generating high pump or sound power levels. The first and second membranes can, for example, be arranged alternately next to one another in order to optimally utilize the dynamic relative oscillation behavior of the first and second membranes to one another.

[0051] According to one embodiment, two second membranes can be mechanically coupled to a first membrane arranged between the two second membranes, wherein the second membranes and the first membrane are configured for excitation by a superimposed drive signal from drive elements of the drive device assigned to the second membranes. This forms a rocker structure with which an efficient device can be provided. The second membranes can be designed to be excited at a frequency approximately twice as high as the first membrane; for example, through suitable geometric design and dimensioning, the second membranes can have a natural frequency twice as high as that of the first membrane.

[0052] The invention also relates to a microelectromechanical loudspeaker comprising a microelectromechanical device according to one of the above-described features, wherein the displacement unit of the device is configured to generate a sound signal, and wherein the microelectromechanical loudspeaker comprises a signal processing unit for applying and processing signals from the microelectromechanical device. Due to the above-described design of the device, the proposed microelectromechanical loudspeaker enables efficient and powerful sound pressure generation despite the very small dimensions of the device, since the sound energy and sound frequency of the generated fluid flow do not depend directly on the excitation frequency at the membranes, but rather on their relative vibration behavior to one another, which can be easily and dynamically controlled.In particular, the proposed loudspeaker can also generate low-frequency sound signals with high sound power. Accordingly, an efficient and powerful use of the loudspeaker as a bass loudspeaker is conceivable, for example. The sound signal generated by the first and second membranes can be regarded as quasi-beat, since no actual beat is generated in the narrow acoustic sense, but is simulated by the interaction of the membrane vibrations. The invention also relates to a microelectromechanical fluid pump device comprising a microelectromechanical device according to one of the features described above, wherein the displacement unit of the device is configured to generate a pumping current, and wherein the microelectromechanical fluid pump device comprises a signal processing unit for applying and processing signals from the microelectromechanical device.The proposed fluid pumping device enables powerful, efficient, and quiet fluid delivery, for example, for cooling systems in electrical or mobile devices. A pumping flow can, for example, be an at least approximately continuous fluid flow.

[0053] The invention also relates to a microelectromechanical combination component comprising a microelectromechanical device according to one of the above-described features, wherein the displacement unit of the device is configured to selectively generate a sound signal or a pumping current, and wherein the microelectromechanical combination component comprises a signal processing unit for applying and processing signals from the microelectromechanical device. The proposed combination component can be advantageously used, for example, in a mobile device to be operated selectively or as needed as a cooling device or as a loudspeaker.

[0054] When operated as a fluid pump device, for example, a constant phase relationship can be maintained between the first oscillation of the first diaphragm and the second oscillation of the second diaphragm. When operated as a loudspeaker, the phase relationship between the first oscillation of the first diaphragm and the second oscillation of the second diaphragm can be specifically changed to generate a sound signal. In principle, it can be advantageous for a start-up phase of operation as a loudspeaker to initially maintain a constant phase relationship until the loudspeaker has reached the desired operating pumping power, and then to begin varying the phase relationship to generate acoustic signals. In general, in the context of this application, the words "a / an", unless expressly defined otherwise, are not to be understood as numerals, but as indefinite articles with the literal meaning of "at least one / an".For example, a structure that is “multiple” larger or smaller can refer to a value that is at least twice as high or small.

[0055] The invention permits various embodiments and is explained in more detail below using exemplary embodiments with the accompanying drawings. They show:

[0056] Fig. 1a - a schematic basic principle of a microelectromechanical device according to a first embodiment in a side view;

[0057] Fig. 1b - a schematic basic principle of the device according to the first embodiment in a plan view;

[0058] Fig. 2a-2i - a method for operating the device according to the first

[0059] Embodiment based on an oscillation cycle;

[0060] Fig. 3a - a schematic basic principle of a microelectromechanical device according to a second embodiment in a side view;

[0061] Fig. 3b - a schematic basic principle of the device according to the second embodiment in a plan view;

[0062] Fig. 4a-4i - a method of operating the device according to the second

[0063] Embodiment based on an oscillation cycle;

[0064] Fig. 5a - a schematic basic principle of a microelectromechanical device according to a third embodiment in a cross-sectional side view;

[0065] Fig. 5b - a schematic basic principle of the device according to the third embodiment in a plan view;

[0066] Fig. 6a - a schematic basic principle of a microelectromechanical device according to a fourth embodiment in a cross-sectional side view;

[0067] Fig. 6b - a schematic basic principle of the device according to the fourth embodiment in a plan view; Fig. 7a - a schematic basic principle of a microelectromechanical device according to a fifth embodiment in a cross-sectional side view;

[0068] Fig. 7b - a schematic basic principle of the device according to the fifth embodiment in a plan view;

[0069] Fig. 8a - a schematic basic principle of a microelectromechanical device according to a sixth embodiment in a cross-sectional side view;

[0070] Fig. 8b - a schematic basic principle of the device according to the sixth embodiment in a plan view;

[0071] Fig. 9a - a schematic basic principle of a microelectromechanical device according to a seventh embodiment in a cross-sectional side view;

[0072] Fig. 9b - a schematic basic principle of the device according to the seventh embodiment in a plan view;

[0073] Fig. 10a - a schematic basic principle of a microelectromechanical device according to an eighth embodiment in a cross-sectional side view;

[0074] Fig. 10b - a schematic basic principle of the device according to the eighth embodiment in a plan view;

[0075] Fig. 11a - a schematic basic principle of a microelectromechanical device according to a ninth embodiment in a cross-sectional side view;

[0076] Fig. 11b - a schematic basic principle of the device according to the ninth embodiment in a plan view;

[0077] Fig. 12a-12c - Simulation diagrams to illustrate the resulting pumping power over time for different phase relationships of membranes vibrating differently from each other;

[0078] Fig. 13 - a schematic diagram of a microelectromechanical component with a microelectromechanical device.

[0079] 1a and 1b show a schematic basic principle of a microelectromechanical device 1 according to a first embodiment in a side view and a top view. The device 1 is configured to generate a fluid flow F, for example, shown schematically in Fig. 2a, and can be used, for example, as a fluid pump or to generate sound pressure. To generate the fluid flow F, the device 1 has a displacement unit 2. The displacement unit 2 has a first membrane 3 and a second membrane 4, which are arranged above a common cavity 5. According to the exemplary embodiment shown, the device 1 can be manufactured as a layered structure on a substrate 7, wherein the cavity 5 has been produced in the substrate 7 and the membranes 3, 4 have been produced as a structured functional layer. According to the exemplary embodiment shown, the membranes 3, 4 are laterally anchored and protrude above the cavity 5.For sealing and improved pumping performance, a sealing lip 12 is formed on each of the first membrane 3 and the second membrane 4.

[0080] The first membrane 3 and the second membrane 4 are movable relative to one another. The membranes 3, 4 can, for example, oscillate together in one direction or oscillate past one another. A separating gap 8 can be provided between the first membrane 3 and the second membrane 4 to enable the relative mobility of the membranes 3, 4 to one another. The device 1 has a drive device 6 with a drive element 6a for the first membrane 3 and with a drive element 6b for the second membrane 4. The drive elements 6a, 6b are coupled to the respective associated membrane 3, 4 and are configured to excite the membranes 3, 4 to individual oscillations independently of one another.Here, the drive device 6 is designed to excite the first membrane 3 to a first oscillation at a first frequency h and the second membrane 4 to a second oscillation at a second frequency f2, wherein the second frequency f2 deviates from the first frequency h. This can produce a phase shift between the oscillating membranes, which can be used to generate the fluid flow F. The oscillation sequences of the membranes 3, 4 can be varied by control technology, and various parameters of the fluid flow generation can thereby be influenced. The variable fluid flow generation can, for example, be advantageously used to generate sound pressure. In addition, constant fluid flows F can also be generated.

[0081] In the example according to the first embodiment, the second frequency f2 of the second oscillation can be substantially twice as high as the first frequency fi of the first oscillation, so that the second membrane 4 oscillates approximately twice as fast as the first membrane 3. For this purpose, the second membrane 4, as shown in Fig. 1b, can be dimensioned with a smaller width b2 compared to the width bi of the first membrane 3 in order to achieve a higher natural frequency of the second membrane 4. Doubling the frequency results in a phase relationship between the oscillations of the membranes 3, 4 that is favorable for fluid flow generation.

[0082] 2a to 2i show, in a schematic manner, a method for operating the device 1 according to the first embodiment, based on an oscillation cycle using side views of the device 1. The oscillation cycle is shown in maximum power operation, for example maximum pumping operation, in which zero crossings of the first oscillation of the first membrane 3 coincide with zero crossings of the second oscillation of the second membrane 4. According to the exemplary embodiment shown, the second frequency f2 of the second oscillation of the second membrane 4 is essentially twice as high as the first frequency fi of the first oscillation of the first membrane 3, so that the second membrane 4 oscillates approximately twice as fast as the first membrane 3. A period of the first oscillation of the first membrane 1, which according to the example here corresponds to an oscillation cycle, is referred to below as T.A first direction Ri of the membranes 3, 4 corresponds to a deflection direction of the membranes 3, 4 in the direction of the cavity 5, while a second direction R2 of the membranes 3, 4 corresponds to a deflection direction of the membranes 3, 4 in a deflection direction opposite to the first direction Ri.

[0083] In Fig. 2a, an oscillation cycle of the displacement unit 2 begins. The first membrane 3 and the second membrane 4 oscillate together in the first direction Ri, thereby moving a fluid volume in the cavity 5, so that a fluid flow F is generated. This fluid volume movement is simply referred to below as the pumping movement. At this point in time, the first membrane 3 and the second membrane 4 oscillate in phase, there is no phase shift between the first membrane 3 and the second membrane 4, and the separation gap 8 between the first membrane 3 and the second membrane 4 is at least approximately closed.

[0084] Fig. 2b shows a state of the displacement unit 2 at 1 / 8 T. In this state, the faster-oscillating second membrane 4 has already reached its maximum deflection in the first direction Ri and begins to swing back in the second direction R2, while the first membrane 3 continues to oscillate in the first direction Ri. Due to the different deflection states of the membranes 3, 4, the separation gap 8 opens and begins to form a fluid opening through which a fluid volume can be sucked in from a side facing away from the cavity 5.

[0085] Fig. 2c shows a state of the displacer unit 2 at 2 / 8 T. In this state, the faster-oscillating second diaphragm 4 has reached its zero crossing, while the first diaphragm 3 has reached its maximum deflection in the first direction Ri and begins to swing back in the second direction R2. In this state, the fluid opening between the diaphragms 3, 4 is maximized.

[0086] Fig. 2d shows a state of the displacer unit 2 at 3 / 8 T. In this state, the faster-oscillating second diaphragm 4 has reached its maximum deflection in the second direction R2 and begins to oscillate again in the first direction Ri. The first diaphragm 3 continues to oscillate in the second direction R2. The fluid opening between the diaphragms 3, 4 begins to close.

[0087] Fig. 2e shows a state of the displacer unit 2 at 4 / 8 T, in which half a period has elapsed. In this state, the first membrane 3 and the second membrane 4 each reach their zero crossing, but with different directions of oscillation, so that almost no fluid volume is pumped. The fluid opening between the membranes 3, 4 is largely closed. Fig. 2f shows a state of the displacer unit 2 at 5 / 8 T. In this state, the faster-oscillating second membrane 4 has reached its maximum deflection in the first direction Ri for the second time, while the first membrane 3 continues to oscillate in the second direction R2. The fluid opening between the membranes 3, 4 begins to open again.

[0088] Fig. 2g shows a state of the displacer unit 2 at 6 / 8 T. In this state, the faster-oscillating second diaphragm 4 has again reached its zero crossing, while the first diaphragm 3 has reached its maximum deflection in the second direction R2 and begins to swing back in the first direction Ri. In this state, the fluid opening between the diaphragms 3, 4 is again at its maximum.

[0089] Fig. 2h shows a state of the displacer unit 2 at 7 / 8 T. In this state, the second membrane 4 has reached its maximum deflection in the second direction R2 for the second time, while the first membrane 3 continues to oscillate in the first direction Ri. The fluid opening between the membranes 3, 4 begins to close again.

[0090] Fig. 2i shows a state of the displacer unit 2 at 8 / 8 T, which again corresponds to the initial position shown in Fig. 2a. At 8 / 8 T, a full period of the first oscillation has elapsed. The first membrane 3 and the second membrane 4 oscillate together in the first direction Ri and thereby move a fluid volume in the cavity 5, so that a fluid flow F is generated. At this point in time, the first membrane 3 and the second membrane 4 oscillate in phase, there is no phase shift between the first membrane 3 and the second membrane 4, and the fluid opening between the first membrane 3 and the second membrane 4 is at least approximately closed.

[0091] 3a and 3b show a schematic basic principle of a microelectromechanical device 1 according to a second embodiment in a side view and a top view. In this embodiment, the displacer unit 2 has a first membrane 3, which is arranged between two second membranes 4 and is mechanically coupled to them via coupling points 9. The first membrane 3 and the second membranes 4 form a rocker structure. Between the first membrane 3 and the second membranes 4 there are two separating gaps 8 and four coupling points 9. The coupling points 9 can form or enclose a pivot axis of the first membrane 3. Each of the second membranes 4 is assigned a drive element 6b of the drive device 6, which is designed to excite the second membranes 4 with the second frequency f2. According to the exemplary embodiment shown, no separate drive element is assigned to the first membrane 3.The first membrane 3, on the other hand, is excited via a differential signal superimposed on the drive signal of the drive elements 6b and via the mechanical coupling between the second membranes 4 and the first membrane 3, so that the movement of the second membranes 4 is at least partially transmitted to the first membrane 3. The drive signal of the drive device 6 can be applied to the drive elements 6b as a symmetrical signal and superimposed with the differential signal. The drive signal of the drive elements 6b then leads to a second oscillation of the second membranes 4 at the second frequency f2 and to a first oscillation of the first membrane 3 at the first frequency fi. Compared to the example according to the first embodiment, the rocker structure can generate more pumping movements per oscillation cycle, in which the first membrane 3 and the second membranes 4 oscillate in phase, as will be shown below with reference to Fig.4a to 4i in the cycle description. Furthermore, the multiple membranes 3 and 4 allow a particularly high fluid volume to be pumped per pumping stroke.

[0092] 4a to 4i show, in a schematic manner, a method for operating the device 1 according to the second embodiment, using an oscillation cycle based on side views of the device 1. The oscillation cycle is shown in maximum power operation, for example maximum pumping operation, in which zero crossings of the first oscillation of the first membrane 3 coincide with zero crossings of the second oscillation of the second membranes 4. According to the exemplary embodiment shown, the second frequency f2 of the second oscillation of the second membranes 4 is essentially twice as high as the first frequency h of the first oscillation of the first membrane 3, so that the second membranes 4 oscillate approximately twice as fast as the first membrane 3. A period of the first oscillation of the first membrane 1, which can correspond to a complete oscillation cycle, is referred to below as T.A first direction Ri of the membranes 3, 4 corresponds to a deflection direction of the membranes 3, 4 in the direction of the cavity 5, while a second direction R2 of the membranes 3, 4 corresponds to a deflection direction of the membranes 3, 4 in a deflection direction opposite to the first direction Ri.

[0093] In Fig. 4a, an oscillation cycle of the displacer unit 2 begins. The first membrane 3 and the second membranes 4 begin to oscillate together in the second direction R2 and thereby move a fluid volume on the side of the membranes 3, 4 facing away from the cavity 5, so that a fluid flow F is generated. At this time, the first membrane 3 and the second membranes 4 oscillate in phase, there is no phase shift between the first membrane 3 and the second membranes 4 and the separation gaps 8 between the first membrane 3 and the second membranes 4 are at least approximately closed.

[0094] Fig. 4b shows a state of the displacer unit 2 at 1 / 8T. In this state, the faster-oscillating second diaphragms 4 have already reached their maximum deflection in the second direction R2 and begin to swing back in the first direction Ri, while the first diaphragm 3 continues to oscillate in the second direction R2. Due to the different deflection states of the diaphragms 3, 4, the separation gaps 8 open and begin to form fluid openings through which a fluid volume can be sucked in from the side of the cavity 5.

[0095] Fig. 4c shows a state of the displacer unit 2 at 2 / 8 T. In this state, the faster-oscillating second diaphragms 4 have reached their zero crossing, while the first diaphragm 3 has reached its maximum deflection in the second direction R2 and is carried along by the second diaphragms 4 in the first direction Ri, so that the first diaphragm 3 begins to swing back in the first direction Ri. In this state, the fluid openings between the diaphragms 3, 4 are maximized. Fig. 4d shows a state of the displacer unit 2 at 3 / 8 T. In this state, the faster-oscillating second diaphragms 4 have reached their maximum deflection in the first direction Ri and begin to swing back in the second direction R2. Due to the mechanical coupling and rocker structure of the diaphragms 3, 4, the second diaphragms 4 carry the first diaphragm 3 along in the second direction R2.The fluid openings between membranes 3, 4 begin to close.

[0096] Fig. 4e shows a state of the displacement unit 2 at 4 / 8 T, in which half a period has elapsed. In this state, the first membrane 3 and the second membrane 4 each reach their zero crossing, specifically in the same directions of oscillation, so that a fluid volume is moved on the side of the membranes 3, 4 facing away from the cavity 5, and a fluid flow F is generated. Thus, according to the method of the second embodiment, a pumping motion can be generated even after half a period. The fluid openings between the membranes 3, 4 are largely closed.

[0097] Fig. 4f shows a state of the displacer unit 2 at 5 / 8 T. In this state, the faster-oscillating second diaphragms 4 have already reached their maximum deflection in the second direction R2 and begin to swing back in the first direction Ri, while the first diaphragm 3 continues to swing in the second direction R2. A comparison with Fig. 4b at 1 / 8 T shows that the first diaphragm 3 swings out in an opposite orientation due to the entrainment by the second diaphragms 4, so that a bilateral rocking motion is realized over the course of the oscillation cycle. In this state, the fluid openings begin to open.

[0098] Fig. 4g shows a state of the displacer unit 2 at 6 / 8 T. In this state, the faster-oscillating second diaphragms 4 have reached their zero crossing, while the first diaphragm 3 has reached its maximum deflection in the second direction R2 and is carried back into the first direction Ri by the second diaphragms 4, so that the first diaphragm 3 begins to swing back into the first direction Ri. In this state, the fluid openings between the diaphragms 3, 4 are maximized.

[0099] Fig. 4h shows a state of the displacer unit 2 at 7 / 8 T. In this state, the faster-oscillating second membranes 4 have reached their maximum deflection in the first direction Ri and begin to swing back in the second direction R2. Due to the mechanical coupling and rocker structure of the membranes 3, 4, the second membranes 4 carry the first membrane 3 back in the second direction R2. The fluid openings between the membranes 3, 4 begin to close.

[0100] Fig. 4i shows a state of the displacement unit 2 at 8 / 8 T, which again corresponds to the initial position shown in Fig. 4a. At 8 / 8 T, a full period of the first oscillation has elapsed. In this state, the first membrane 3 and the second membrane 4 each reach their zero crossing, specifically in the same oscillation directions, so that a fluid volume is moved on the side of the membranes 3, 4 facing away from the cavity 5, and a fluid flow F is generated. The fluid openings between the membranes 3, 4 are at least approximately closed.

[0101] 5a and 5b show a schematic basic principle of a microelectromechanical device 1 according to a third embodiment in a cross-sectional view according to the cross-sectional line shown in dashed lines in Fig. 5b and a top view. According to the exemplary embodiment shown, the displacer unit 2 has a plurality of, here two, first membranes 3 and a plurality of, here two, second membranes 4. This makes it possible to generate a high pumping or sound power. The first and second membranes 3, 4 are arranged alternately next to one another. According to the embodiment shown, the first membranes 3 and the second membranes 4 are arranged above the common cavity 5. According to other exemplary embodiments, it is conceivable, for example, to arrange a first membrane 3 and a second membrane 4 in pairs above a respective cavity 5.Each first membrane 3 is assigned a drive element 6a, and each second membrane 4 is assigned a drive element 6b of the drive device 6. The first membranes 3 are configured for excitation at a first frequency fi, and the second membranes 4 are configured for excitation at a second frequency f2. For this purpose, for example, a thickness di of the first membrane 3 can be smaller than a thickness d2 of the second membranes 4 in order to configure the natural frequencies of the membranes 3 and 4 according to the intended excitation.

[0102] 6a and 6b show a schematic basic principle of a microelectromechanical device 1 according to a fourth embodiment in a cross-sectional view according to the cross-sectional line shown in dashed lines in Fig. 6b and a plan view. The fourth embodiment corresponds to a variant of the third embodiment in which the different natural frequencies of the first membranes 3 and the second membranes 4 are not determined by a different thickness d1 and d2, but rather the second membranes 4 have a stiffening structure 10, which in the present case is designed as a molded-on stiffening lip 10a or, as shown, as several molded-on stiffening lips 10a per membrane 4. As a result, the natural frequency of the second membranes 4 can be increased in a targeted and simple manner.

[0103] 7a and 7b show a schematic basic principle of a microelectromechanical device 1 according to a fifth embodiment in a cross-sectional view according to the cross-sectional line shown in dashed lines in Fig. 7b and a plan view. The fifth embodiment corresponds to a variant of the third and fourth embodiments in which the different natural frequencies of the first membranes 3 and the second membranes 4 are not determined by a different thickness d1 and d2 or by a stiffening structure 10, but rather the stiffness and thus the natural frequency of the first membranes 3 is specifically reduced by recesses 11. The recess 11 can be produced, for example, by structuring the first membranes 3.

[0104] 8a and 8b show a schematic basic principle of a microelectromechanical device 1 according to a sixth embodiment in a cross-sectional view according to the cross-sectional line shown in dashed lines in Fig. 8b and a plan view. In the sixth embodiment, a first membrane 3 and a second membrane 4 are provided for the displacement unit 2, wherein the first membrane 3 and the second membrane 4 are generally movable relative to one another by means of separating gaps 8, but are additionally mechanically coupled to one another via coupling points 9. The first membrane 3 and the second membrane 4 are excited by a superimposed drive signal from a drive element 6a assigned to the first membrane 3. With the sixth embodiment shown, a very simply designed device 1 with a compact design can be provided.

[0105] 9a and 9b show a schematic basic principle of a microelectromechanical device 1 according to a seventh embodiment in a cross-sectional view according to the cross-sectional line shown in dashed lines in Fig. 9b and a plan view. The seventh embodiment corresponds to a variant of the first embodiment, in which, however, a sealing lip 12 is provided between the first membrane 3 and the second membrane 4. This makes it possible to achieve favorable sealing for improved pumping behavior of the displacer unit 2 without impairing the mechanical behavior of the membranes 3, 4. Alternatively or additionally, it can be provided, for example, that the first membrane 3 and the second membrane 4 are thinned at their mutually facing ends or at their transition region in order to favorably influence the pumping behavior of the displacer unit 2.

[0106] 10a and 10b show a schematic basic principle of a microelectromechanical device 1 according to an eighth embodiment in a cross-sectional view according to the cross-sectional line shown in dashed lines in Fig. 10b and a plan view. The eighth embodiment corresponds to a variant of the sixth embodiment, wherein the mechanical coupling region with coupling points 9 is geometrically designed differently and positioned differently in order to vary the relative dynamic behavior of the first membrane 3 and the second membrane 4 to one another. By mounting the center of gravity in relation to the pivot point of the second membrane 4 asymmetrically offset compared to the sixth embodiment, the second membrane 4 and the first membrane 3 can be favorably driven by a superimposed drive signal.

[0107] 11a and 11b show a schematic basic principle of a microelectromechanical device 1 according to a ninth embodiment in a cross-sectional view according to the cross-sectional line shown in dashed lines in Fig. 11b and a plan view. The ninth embodiment shows a variant in which the first membrane 3 is arranged between two wide membranes 4 and mechanically coupled to them, but has at least one separate drive element 6a, here two drive elements 6a. This allows, on the one hand, movements between the membranes 3, 4 to be at least partially transmitted to one another, but at the same time, the separate drive elements 6a, 6b can be used to generate particularly advantageous frequency differences between the first membrane 3 and the second membranes 4.

[0108] Figs. 12a to 12c show simulation diagrams to illustrate the resulting pump power over time for different phase relationships of differently vibrating membranes 3, 4 according to the proposed method. Fig. 12a illustrates a pump power at a frequency difference between the first oscillation of the first membrane 3 and the second oscillation of the second membrane 4, where the second frequency f2 corresponds to twice the first frequency fi. Fig. 12b illustrates a pump power at a frequency difference between the first oscillation of the first membrane 3 and the second oscillation of the second membrane 4, where the second frequency f2 corresponds to 1.9 times the first frequency fi.Figure 12c illustrates a pumping performance with a frequency difference between the first oscillation of the first membrane 3 and the second oscillation of the second membrane 4, where the second frequency f2 corresponds to 1.8 times the first frequency fi. In the individual diagrams, the phase relationship between the membranes 3, 4 is kept constant, i.e., does not vary. The waveform evident in the graphs can be attributed to a slight backflow between the membranes 3, 4, since in practice, according to the simulations shown, the fluid opening is not completely closed. The simulation diagrams provide examples of how the pumping behavior of the device 1 can be influenced via the frequency relationship between the oscillations of the first membrane 3 and the second membrane 4. For example, the frequency and amplitude of the pumping signal can be varied by changing the frequency relationship, as can be seen, for example, when comparing Fig.12b and 12c. Thus, the device 1 can also be advantageously used, for example, to generate sound signals.

[0109] Fig. 13 schematically shows a microelectromechanical component 20 with a device 1 according to the above-described features and a signal processing unit 21, which is connected to the device 1 by a signal connection 22 and is designed to apply and process signals from the microelectromechanical device 1. The micromechanical component 20 can be designed, in particular, as a loudspeaker, as a fluid pumping device, or as a combination component. The microelectromechanical component 20 can be implemented, for example, as a system-on-chip.

Claims

Claims 1. Method for operating a microelectromechanical device (1) for generating a fluid flow (F) with a displacement unit (2), wherein the displacement unit (2) has a first membrane (3) and a second membrane (4) which are arranged above a common cavity (5) and are movable relative to one another, and wherein, in order to generate the fluid flow (F), the first membrane (3) is excited to a first oscillation at a first frequency (fi) and the second membrane (4) is excited to a second oscillation at a second frequency (f2) which differs from the first frequency (fi) by means of a drive device (6).

2. The method according to claim 1, wherein an edge region of the first membrane (3) at least partially adjoins substantially directly an edge region of the second membrane (4).

3. The method according to claim 1 or 2, wherein the second frequency (f2) of the second oscillation is substantially twice as high as the first frequency (fi) of the first oscillation.

4. Method according to one of the preceding claims, wherein the first frequency (fi) and / or the second frequency (f2) is at least 20 kHz.

5. Method according to one of the preceding claims, wherein a fluid flow direction, a fluid flow quantity and / or a differential pressure of the fluid flow (F) are controlled by controlling the phases, the frequencies (fi, f2) and / or the amplitudes of the first oscillation of the first membrane (3) and the second oscillation of the second membrane (4).

6. Method according to one of the preceding claims, wherein a fixed phase relationship is set between the first oscillation of the first membrane (3) and the second oscillation of the second membrane (4).

7. Method according to one of the preceding claims, wherein the phase relationship between the first vibration of the first membrane (3) and the second vibration of the second membrane (4) is varied in order to generate a sound signal.

8. The method according to claim 7, wherein a sound frequency of the sound signal is controlled via a frequency difference between the first frequency (fi) of the first oscillation and the second frequency (f2) of the second oscillation and / or wherein a sound intensity of the sound signal is controlled via the amplitude of the first oscillation and / or the second oscillation.

9. Method according to one of the preceding claims, wherein the first membrane (3) and the second membrane (4) are each excited by a drive element (6a, 6b) of the drive device (6).

10. Method according to one of the preceding claims, wherein the first membrane (3) and the second membrane (4) are mechanically coupled to one another.

11. The method according to claim 10, wherein the first membrane (3) and the second membrane (4) are excited by a superimposed drive signal of a drive element (6a, 6b) associated with the first membrane (3) or the second membrane (4).

12. Method according to one of the preceding claims, wherein the device (1) has at least two first membranes (3) which are excited to the first oscillation at the first frequency (fi) by means of the drive device (6), and / or at least two second membranes (4) which are excited to the second oscillation at the second frequency (f2) by means of the drive device (6).

13. Method according to one of the preceding claims, wherein two second membranes (4) are mechanically coupled to a first membrane (3) arranged between the two second membranes (4), and wherein the second membranes (4) and the first membrane (3) are excited by a superimposed drive signal from drive elements (6b) of the drive device (6) assigned to the second membranes (4).

14. Microelectromechanical device (1) for generating a fluid flow (F) with a displacement unit (2), wherein the displacement unit (2) has a first membrane (3) and a second membrane (4) which are arranged above a common cavity (5) and are movable relative to one another, wherein the device (1) has a drive device (6) which is designed to excite the first membrane (3) to a first oscillation at a first frequency (fi) and to excite the second membrane (4) to a second oscillation at a second frequency (f2) which differs from the first frequency (fi).

15. Device (1) according to claim 14, wherein an edge region of the first membrane (3) at least partially adjoins substantially directly an edge region of the second membrane (4).

16. Device (1) according to claim 14 or 15, wherein the second membrane (4) has a natural frequency which is substantially twice as high as the natural frequency of the first membrane (3).

17. Device (1) according to one of claims 14 to 16, wherein the first membrane (3) has a recess (11) and / or wherein the second membrane (4) has a stiffening structure (10).

18. Device (1) according to one of claims 14 to 17, wherein the natural frequency of the first membrane (3) and / or the natural frequency of the second membrane (4) is at least 20 kHz.

19. Device (1) according to one of claims 14 to 18, wherein a sealing lip (12) is provided on or between the first membrane (3) and the second membrane (4).

20. Device (1) according to one of claims 14 to 19, wherein the first membrane (3) and the second membrane (4) are each assigned a drive element (6a, 6b) of the drive device.

21. Device (1) according to one of claims 14 to 20, wherein the first membrane (3) and the second membrane (4) are mechanically coupled to one another.

22. Device (1) according to claim 21, wherein the first membrane (3) and the second membrane (4) are arranged to be excited by a superimposed drive signal of a drive element (6a, 6b) associated with the first membrane (3) or the second membrane (4).

23. Device (1) according to one of claims 14 to 22, wherein the device (1) has at least two first membranes (3) which are arranged to be excited with the first oscillation at the first frequency (fi) by means of the drive device (6), and / or at least two second membranes (4) which are arranged to be excited with the second oscillation at the second frequency (f2) by means of the drive device (6).

24. Device according to one of claims 14 to 23, wherein two second membranes (4) are mechanically coupled to a first membrane (3) arranged between the two second membranes (4), and wherein the second membranes (4) and the first membrane (3) are arranged for excitation by a superimposed drive signal from the second membranes (4) associated drive elements (6b) of the drive device (6).

25. A microelectromechanical loudspeaker comprising a microelectromechanical device (1) according to any one of claims 14 to 24, wherein the displacement unit (2) of the device (1) is configured to generate a sound signal, and a signal processing unit (21) for applying and processing signals of the microelectromechanical device (1).

26. Microelectromechanical fluid pumping device, comprising a microelectromechanical device (1) according to one of claims 14 to 24, wherein the displacement unit (2) of the device (1) is configured to generate a pumping current, and a signal processing unit (21) for applying and processing signals of the microelectromechanical device (1).

27. A microelectromechanical combination component comprising a microelectromechanical device (1) according to one of claims 14 to 24, wherein the displacement unit (2) of the device (1) is configured to selectively generate a sound signal or a pumping current, and a signal processing unit (21) for applying and processing signals of the microelectromechanical device (1).

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