MEMS sound transducer and method for producing the same

Abstract

To provide a high-performance MEMS sound transducer and a method for producing the same.SOLUTION: A MEMS sound transducer (1) for generating and / or detecting sound waves in the audible wavelength spectrum and / or in the ultrasonic range includes: a carrier (2); and at least one piezoelectric element (4) which is arranged on the carrier (2), is deflectable in the direction of a stroke axis (3), and has at least one piezoelectric layer (5) and at least one structural layer (6). Herein, electrical signals and deflections of the piezoelectric element (4) are convertible into one another by means of the at least one piezoelectric layer (5). The at least one structural layer (6) is made of a polymer, in particular a polyamide.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a MEMS acoustic transducer for generating and / or detecting sound waves, in particular in the audible wavelength spectrum and / or ultrasonic range, comprising a carrier and at least one piezoelectric element arranged on the carrier, displaceable in the direction of a pulling axis and having at least one piezoelectric layer and at least one structural layer, wherein an electrical signal can be converted into a displacement of the piezoelectric element and vice versa by the at least one piezoelectric layer. [Background technology]

[0002] Piezoelectric elements that include structural layers made of silicon are known in the art. Summary of the Invention [Problem to be solved by the invention]

[0003] The object of the present invention is to create a high performance MEMS acoustic transducer. [Means for solving the problem]

[0004] This problem is solved by a MEMS acoustic transducer and a method for producing same with the features of the independent claims.

[0005] In particular, a MEMS acoustic transducer is proposed for generating and / or detecting sound waves in the audible wavelength spectrum and / or in the ultrasonic range, which may thus be utilized as a speaker and / or microphone.

[0006] The MEMS acoustic transducer includes a carrier.

[0007] Furthermore, the MEMS acoustic transducer includes at least one piezoelectric element disposed on the carrier and displaceable in the pulling axis direction.

[0008] Furthermore, the MEMS acoustic transducer includes at least one piezoelectric layer and at least one structural layer, and the at least one piezoelectric layer allows conversion between an electric signal and a displacement of the piezoelectric element.

[0009] At least one structural layer is also made of a polymer, which may be a polyamide. Due to the presence of at least one polymeric structural layer, a higher displacement of the piezoelectric element can be achieved. Additionally or alternatively, the length of the piezoelectric element can be reduced, so that the displacement can be kept at least constant.

[0010] According to an advantageous development of the invention, it is useful if at least one piezoelectric layer is made from scandium aluminum nitride, a piezoelectric layer of this type being very robust, in particular due to the scandium content, which is preferably between 10% and 40%.

[0011] It is advantageous if the piezoelectric element includes a compensation layer. The compensation layer can compensate for the mechanical stress of the polymeric structural layer. The structural layer is made of a polymer, so that the structural layer is subjected to a force that tends to contract. At least one structural layer may be subjected to internal mechanical stresses that tend to contract the structural layer due to the manufacturing characteristics and / or the properties of the polymer. In the resting state, the piezoelectric element bends upwards or towards the structural layer. The compensation layer can compensate for the mechanical stresses. Here, the compensation layer has a mechanical stress that counteracts, compensates and / or adjusts the at least one structural layer. The compensation layer thus serves to adjust the mechanical stress of the at least one structural layer. Additionally or alternatively, the compensation layer serves to straighten the at least one structural layer. Here, the compensation layer holds the at least one structural layer in a straightened state, thereby preventing the structural layer from contracting like a rubber band due to the mechanical stress and becoming deformed in the process. Additionally or alternatively, the compensation layer serves to prevent the at least one polymeric structural layer from contracting. The compensation layer counteracts and / or is stronger and / or stiffer than the mechanical stress of the at least one polymeric structural layer. As a result, the at least one structural layer is prevented from shrinking. The forces exerted by the at least one polymeric structural layer and the forces exerted by the compensation layer act in opposite directions and / or advantageously counteract and / or cancel each other out. This prevents the structural layer from shrinking. However, the compensation layer does not prevent the displacement of the piezoelectric element. The mechanical stress of the compensation layer is matched to prevent the structural layer from shrinking like rubber, or to adjust or compensate. Furthermore, the compensation can serve to make the piezoelectric element stress-free when the piezoelectric element is in a rest position.

[0012] Furthermore, the presence of the compensation layer allows the neutral layer or neutral surface of the piezoelectric element to remain in position. The piezoelectric element is a cantilever beam, and when the piezoelectric element is displaced, compressive and tensile stresses accumulate in the piezoelectric element. The extent of the compressive and tensile stresses depends on whether the piezoelectric element is displaced upwards or downwards. The compressive stress is formed on the side in the direction of the displacement of the piezoelectric element. The tensile stress accumulates on the opposite side. This is a general principle of strength theory. On one side of the piezoelectric element, i.e., the neutral surface or neutral layer, the tensile and compressive stresses cancel each other out, and no stress is generated there. However, the displacement characteristics of the piezoelectric element depend on where this neutral surface or neutral layer is located within the piezoelectric element. The position of the neutral surface or neutral layer can be adjusted by changing the mechanical properties of the compensation layer. For example, the compensation layer can be made thicker or thinner to change the position of the neutral surface or neutral layer. The position movement or positioning of this neutral surface or neutral layer is performed parallel to the pulling axis. This allows the neutral surface or layer to be moved parallel to the pulling axis.

[0013] The piezoelectric layer is preferably arranged in the direction of the pulling axis between the carrier and the structural layer.

[0014] Advantageously, the structural layer is disposed between the piezoelectric layer and the compensation layer.

[0015] It is advantageous if the compensation layer is made of a metal, in particular gold, and / or silicon dioxide, in particular TEOS, which allows the compensation layer to be produced in an advantageous manner.

[0016] It is advantageous if the length of the piezoelectric element in the longitudinal direction, in particular the length from the carrier to one free end of the piezoelectric element, is between 0.5 mm and 2 mm.

[0017] Advantageously, the compensation layer extends in the longitudinal direction of the piezoelectric element up to the carrier and / or up to the free end of the piezoelectric element.

[0018] It is advantageous if at least one piezoelectric element comprises a plurality of piezoelectric layers, in particular two to six, preferably four.

[0019] Advantageous results are obtained when the at least one piezoelectric element comprises at least one electrode layer: the electrical signal leading to the displacement of the piezoelectric element and / or the electrical signal formed when the piezoelectric element is displaced can be exchanged by using the at least one electrode layer.

[0020] Advantageously, the at least one piezoelectric element comprises at least one insulating layer.

[0021] Advantageously, at least one piezoelectric element is formed sandwiched between a plurality of piezoelectric and electrode layers.

[0022] Advantageous results are obtained when the MEMS acoustic transducer includes a coupling element capable of coupling the at least one piezoelectric element to the diaphragm.

[0023] Better results are obtained if the piezoelectric element and the coupling element are coupled to each other by at least one spring element, which is preferably arranged between the structural layer and the coupling element in the longitudinal direction of the piezoelectric element.

[0024] Advantageously, the spring element is preferably formed exclusively through the structural layer and / or from a polymer, which allows for a simple formation of the spring element, additionally or alternatively the spring element has the mechanical properties of a polymer.

[0025] It is advantageous if the piezoelectric element and the coupling element are of the same layer structure as each other.

[0026] Advantageous results are obtained when the thickness of the compensation layer is 0.2 μm to 4 μm. The thickness of the compensation layer can also be 0.5 μm to 3 μm. Furthermore, the thickness of the compensation layer can be 0.6 μm to 2 μm. Alternatively, the thickness of the compensation layer can be 1 μm to 2 μm. In this way, the presence of the compensation layer can prevent or compensate for shrinkage of the structural layer.

[0027] Better results are obtained when the thickness of the structure layer is between 10 μm and 50 μm.

[0028] It is advantageous if the at least one piezoelectric element comprises at least one recess. The presence of the recess allows the mechanical properties of the piezoelectric element to be adjusted, for example to reduce stress on the piezoelectric element and / or to adjust the operating properties. The at least one recess can be arranged in the at least one piezoelectric layer, the at least one electrode layer, the at least one insulating layer, the at least one structural layer and / or the at least one compensation layer.

[0029] Furthermore, it is advantageous if the polymeric structural layer has a modulus of elasticity between 2 and 50 GPa, in particular between 2 and 5 GPa, preferably between 3.5 and 4 GPa.

[0030] Advantageous results are obtained if the polymeric structural layer has a tensile strength of 70 to 100 MPa, in particular 85 to 95 MPa.

[0031] The above mentioned mechanical properties of the at least one structural layer allow for an increased displacement and / or allows for shortening of the piezoelectric element while at least maintaining the same displacement or increasing the displacement.

[0032] It is further advantageous if the compensation layer has a mechanical stress state equal to or at least slightly higher than at least one structural layer. Additionally or alternatively, the compensation layer has a higher resistance than the structural layer. The mechanical stress state of the compensation layer can counterbalance the mechanical stress state of at least one structural layer. The compensation layer can thereby hold at least one structural layer in an upright state. The compensation layer can thus resist or prevent the mechanical stress of the structural layer from shrinking. If several structural layers are present, the compensation layer has a mechanical stress state equal to or higher than the combined mechanical stress state of the several structural layers. Additionally or alternatively, the compensation layer can have a mechanical stress state that counterbalances the piezoelectric element or prevents it from being stressed in a neutral position. Here, the mechanical stress state depends on several factors. Here, the mechanical stress state required for the compensation layer depends on the thickness of the structural layer or the thickness of all structural layers, as well as the elastic modulus, tensile strength, and / or elasticity of the structural layer or polymer. Here, the polymer can have rubber elasticity, which elasticity causes the structural layer to shrink. The compensation layer then has a mechanical stress state that can counteract the shrinkage of the polymer. The force with which the polymer shrinks depends on the thickness and strength of the polymer, i.e., on the strength of the rubber elasticity, for example. The mechanical stress state of the compensation layer again depends on the thickness and elastic modulus of the compensation layer, or on the compressive strength.

[0033] The sizing layer has a mechanical stress state equal to or higher than that of the structural layer or the sum of all the structural layers and / or piezoelectric layers. This equal or higher mechanical stress state allows the sizing layer to hold the structural layers and / or piezoelectric layers in an upright position and provide stability. The sizing layer acts to counteract the tendency of the structural layers to contract due to its elastic properties.

[0034] It is advantageous if the mechanical stress state of the compensation layer offsets, compensates and / or adjusts the mechanical stress of at least one structural layer and / or at least one piezoelectric layer. For example, the mechanical stress of the compensation layer can be 50 MPa to 1000 MPa. Also, the mechanical stress of the compensation layer can be 100 MPa to 300 MPa. Furthermore, the mechanical stress of the compensation layer can be 240 MPa.

[0035] The mechanical stress required for the shaping layer can be determined by various factors. Such factors include the thickness of the structural layer, the elastic modulus, tensile strength, elasticity of the structural layer or polymer, etc. As the structural layer becomes thicker, a correspondingly stiffer shaping layer and / or a shaping layer with higher mechanical stress is required to adjust the elastic force. The shaping layer thus advantageously has the ability to offset this shrinkage.

[0036] The force with which the polymer contracts depends on several factors. These factors include the thickness of the polymer and the strength of the elastic properties of the polymer. The thicker the polymer, the greater the mechanical stresses that will be generated. The mechanical stresses of the compensation layer are also determined by the thickness and elastic modulus of the compensation layer itself. A thick compensation layer with a high elastic modulus can offset the greater mechanical stresses of the polymer.

[0037] Advantageously, the compensation layer has sufficient strength to adjust the elastic restoring force of the structural layer, thereby keeping the entire structure stable.

[0038] Furthermore, it is advantageous if the compensation layer comprises a reinforcing structure. For example, the compensation layer may comprise or be formed as a strip-shaped reinforcing structure, which on the one hand can provide the necessary mechanical stress to prevent shrinkage of the structural layer, and on the other hand can reduce material and / or allow for a more arbitrary arrangement of material.

[0039] Advantageously, the polymer structural layer is formed to have an amplitude of 3% to 10%.

[0040] Furthermore, a method for manufacturing a MEMS acoustic transducer, in particular for generating and / or detecting acoustic waves in the audio wavelength spectrum and / or ultrasonic range, is proposed, which method can be performed such that a MEMS acoustic transducer is formed with at least one of the features described above and / or below.

[0041] In this method, at least one piezoelectric element is formed on a carrier, the piezoelectric element including at least one piezoelectric layer and at least one structural layer coupled thereto.

[0042] Additionally, a polymer is disposed over the piezoelectric layer to form at least one structural layer.

[0043] It is useful if at least one of the piezoelectric layers is formed from aluminum scandium nitride.

[0044] Furthermore, it is advantageous if the at least one piezoelectric element is formed from a plurality of, in particular from two to six, in particular four, piezoelectric layers.

[0045] Advantageously, the at least one piezoelectric element is formed sandwiched between a plurality of piezoelectric layers and at least one electrode layer.

[0046] A plurality of piezoelectric layers and a plurality of electrode layers may be arranged in alternating fashion.

[0047] Furthermore, it may be advantageous to arrange at least one insulating layer during the formation of the at least one piezoelectric element.

[0048] A polymer structural layer is usefully disposed on the side of the piezoelectric layer facing away from the carrier.

[0049] Better results are obtained if a polymer structural layer is arranged on the at least one piezoelectric layer after the piezoelectric layer and / or the coupling elements have been formed and / or after the carrier, the piezoelectric layer and / or the coupling elements have been post-processed, in particular by etching, and in particular separated from one another.

[0050] Advantageously, the piezoelectric element and the coupling element are preferably layered together on a carrier.

[0051] It is advantageous if, after the piezoelectric elements and the coupling elements have been assembled in the layer structure, they are at least partially separated from one another, in particular by etching.

[0052] It is furthermore advantageous if at least one polymer structural layer is laminated onto the piezoelectric layer and / or onto the coupling element, particularly preferably in the form of a self-adhesive polymer film.

[0053] When two structural layers are formed, the structural layers are preferably disposed one above the other and / or are formed from the same or different polymers, which can provide advantageous results.

[0054] The lamination process of the polymeric structural layer is advantageously carried out at a temperature between 70°C and 90°C.

[0055] Advantageously, a polymer curing step is carried out after the lamination process, this curing step being preferably carried out at a temperature between 150° C. and 200° C. and / or for a period of between 0.5 and 2 hours.

[0056] According to an advantageous development of the invention, it is useful if a compensation layer is arranged on the structural layer.

[0057] It is useful if at least one of the polymeric structural layers is post-treated.

[0058] Further advantages of the present invention are described in the following embodiments. [Brief description of the drawings]

[0059] [Figure 1] 1 is a schematic cross-sectional view of a MEMS acoustic transducer comprising a piezoelectric element consisting of at least one piezoelectric layer and at least one structural layer. [Diagram 2]1 is a schematic cross-sectional view of a MEMS acoustic transducer comprising two piezoelectric elements and one coupling element. [Diagram 3] 1 is a schematic cross-sectional view of a MEMS acoustic transducer comprising two piezoelectric elements and two coupling elements. [Figure 4] 1 is a schematic cross-sectional view of a MEMS acoustic transducer having a layer structure. [Diagram 5] FIG. 2 is a top view of a MEMS acoustic transducer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0060] FIG. 1 shows a perspective view of a MEMS acoustic transducer 1. The MEMS acoustic transducer 1 can generate sound waves, for example in the audible wavelength spectrum, and thus can be used as a MEMS speaker. The MEMS acoustic transducer 1 can additionally or alternatively be used to detect sound waves in the audible wavelength spectrum, and thus can be used as a MEMS microphone. Furthermore, the MEMS acoustic transducer 1 can be arranged, for example, in a smartphone, which allows, for example, making calls or listening to music. The MEMS acoustic transducer 1 can also be arranged, for example, in headphones.

[0061] A further application of the MEMS acoustic transducer 1 can be the generation and / or detection of sound waves in the ultrasonic range, for example the MEMS acoustic transducer 1 can be arranged in an ultrasonic sensor, such as a distance sensor.

[0062] The MEMS acoustic transducer 1 also includes a carrier 2 on which the basic structure of the MEMS acoustic transducer 1 can be formed. The carrier 2 may include, for example, a semiconductor substrate manufactured using an etching process. For example, the carrier 2 may be formed from silicon and / or may be in the form of a wafer. In this figure, two carriers 2 are shown. However, it is also possible to form the carrier 2 as a frame, in which in this cross-sectional view both elements of the carrier 2 shown here are connected. For example, the carrier 2 may be formed as a rectangle in the top view. For example, the top view may be aligned with the direction of the pulling axis 3 described below. For example, the top view may be parallel to the axis 3. For example, if the carrier 2 is formed as a frame, at least one piezoelectric element 4 may at least partially face the inside of the carrier 2.

[0063] Furthermore, at least one piezoelectric element 4 is disposed on the carrier 2. The at least one piezoelectric element 4 can also be bonded to the carrier 2. The at least one piezoelectric element 4 can be displaced along the illustrated pulling axis 3. The at least one piezoelectric element 4 can then convert an electrical signal into a displacement, which allows the MEMS acoustic transducer 1 to be used as a speaker or to generate sound waves. Additionally or alternatively, the at least one piezoelectric element 4 can also be used to convert a displacement into an electrical signal, which allows the MEMS acoustic transducer 1 to be used as a microphone or to detect sound waves.

[0064] At least one piezoelectric element 4 includes a free end 8 , which is displaceable along a pulling axis 3 .

[0065] The piezoelectric element 4 further includes at least one piezoelectric layer 5. The at least one piezoelectric layer 5 is formed from a piezoelectric material. The at least one piezoelectric layer 5 is capable of converting an electrical signal into a displacement and / or a displacement into an electrical signal. The piezoelectric layer 5 may be formed, for example, from lead zirconate titanate (PZT). Alternatively, the piezoelectric layer 5 may be formed from scandium aluminum nitride (ScAIN).

[0066] In addition, the piezoelectric element 4 includes at least one structural layer 6. The structural layer 6 is coupled to the at least one piezoelectric layer 5. According to the present embodiment, the at least one structural layer 6 is arranged on the side of the at least one piezoelectric layer 5 facing away from the carrier 2. Additionally or alternatively, the at least one piezoelectric layer 5 is arranged between the carrier 2 and the at least one structural layer 6. By using the at least one structural layer 6, the at least one piezoelectric layer 5 can be stabilized. Furthermore, the at least one structural layer 6 can prevent the at least one piezoelectric layer 5 from being damaged during a displacement. The at least one structural layer 6 can also function as a carrier layer for the at least one piezoelectric layer 5, 25.

[0067] Moreover, here the structural layer 6 is formed from a polymer. Thus, the structural layer 6 is a polymer structural layer. The polymer may be a polyamide. Since the polymer is soft, especially compared to silicon, the piezoelectric element 4 can be made smaller while still allowing a high displacement of the piezoelectric element 4. The operation or performance of the piezoelectric element 4 depends, among other things, on the strength or amplitude of the displacement. Since the polymer is soft, especially compared to silicon, a certain displacement is possible even if the dimensions of the piezoelectric element 4, especially the length, are small.

[0068] According to this embodiment, at least one piezoelectric element 4 includes at least one compensation layer 7. The compensation layer 7 can adjust the stress that occurs when the polymer structural layer 6 shrinks. The compensation layer 7 can prevent the piezoelectric element 4 from bending upwards or away from the carrier 2 in the rest state due to the shrinkage of the polymer structural layer 6. However, the compensation layer 7 can also adjust the neutral plane 14 (or layer) of the piezoelectric element 4. The neutral plane 14 is a term used in strength theory and / or stress theory and is also known as the neutral axis or zero line. The neutral axis or neutral plane 14, or the zero line, is a plane or line in the piezoelectric element 4 where no stress occurs, because tensile and compressive stresses cancel each other out. In contrast, tensile and compressive stresses act above and below it. Here, tensile or compressive stresses naturally occur only when the piezoelectric element 4 is displaced. For example, when the piezoelectric element 4 is displaced upwards, i.e. away from the carrier 2, a compressive stress acts on the upper region of the piezoelectric element 4 and a tensile stress acts on the lower region of the piezoelectric element 4. On the other hand, when the piezoelectric element 4 is displaced downwards, i.e. towards the carrier 2, the compressive and tensile stresses are reversed. Neither tensile nor compressive stress acts on the neutral surface 14 or neutral layer, where this surface 14 or this layer is arranged between the upper and lower sides of the piezoelectric element 4. Due to the presence of the compensation layer 7, the position of the neutral axis or neutral surface 14 (or neutral layer) or the zero line can be adjusted to the height of the pulling axis 3 or in the direction of the pulling axis 3. By utilizing the compensation layer 7, in particular the mechanical properties of the compensation layer 7, i.e. the mechanical stress, the thickness, etc., the neutral surface 14 can be moved in the direction along the pulling axis 3. The neutral surface 14 can be moved or positioned in the direction of the upper side 15 of the piezoelectric element 4 or in the direction of the lower side 16 of the piezoelectric element 4. The lower side 16 of the piezoelectric element 4 is the side facing the carrier 2. On the other hand, the upper side 15 of the piezoelectric element 4 is the side facing away from the carrier 2 .

[0069] For example, the compensation layer 7 can be made of a metal, such as gold. Additionally or alternatively, the compensation layer 7 can be made of silicon dioxide, particularly TEOS. By using these materials, the mechanical properties of the compensation layer 7 can be easily formed.

[0070] According to this example embodiment, the MEMS acoustic transducer 1 includes a coupling element 9 that can couple at least one piezoelectric element 4 to a diaphragm 11 of the illustrated MEMS acoustic transducer 1. By using the coupling element 9, the displacement of the piezoelectric element 4 can be transferred to the diaphragm 11 when sound waves are generated by the diaphragm 11. Additionally or alternatively, the displacement of the diaphragm 11 can also be transferred to the piezoelectric element 4 when sound waves are detected by using the diaphragm 11.

[0071] As shown, it is advantageous to arrange a coupling plate 12 between the coupling element 9 and the diaphragm 11. By means of the coupling plate 12 a planar transmission of the displacements between the coupling element 9 and the diaphragm 12 is achieved. According to the present embodiment a further diaphragm frame 13 is shown, by means of which the diaphragm 11 can be arranged on the carrier 2.

[0072] Furthermore, the at least one piezoelectric element 4 has a length 33. The length 33 is defined here as the length from the carrier 2 to the free end 8 of the at least one piezoelectric element 4. The length 33 is between 0.5 mm and 2 mm. The structural layer 6 allows the piezoelectric element 4 to have this length 33, which allows a large displacement along the pulling axis 3. The displacement of the at least one piezoelectric element 4, in particular at the free end 8, may be at least 3%, preferably at least 10%.

[0073] The thickness 34 of the at least one piezoelectric element 4 may be 2 μm to 50 μm. The thickness 34 is oriented parallel to the pulling axis 3 and / or perpendicular to the layer of the at least one piezoelectric element 4 (see FIG. 4). Here, the partial thickness of the at least one compensation layer 7 may be 0.5 μm to 3 μm. For example, as shown in FIG. 4, if multiple compensation layers 7 are present, these multiple compensation layers 7 may have a partial thickness of 0.5 μm to 3 μm in total.

[0074] Furthermore, the at least one piezoelectric element 4 may include at least one recess 35, which is not shown in this figure. The at least one recess 35 may extend at least partially between the upper side 15 and the lower side 16. The at least one recess 35 may extend from the upper side 15 and / or the lower side 16 in the direction of the opposite upper side 15 or lower side 16, respectively. The presence of these recesses 35 may reduce stresses in the piezoelectric element 4 or in the at least one piezoelectric layer 5, the at least one structural layer 6 and / or the compensation layer 7. Additionally or alternatively, the recess 35 extends in the direction of the pulling axis 3.

[0075] Features already described in at least one previous figure will not be described again for the sake of brevity. Features may also be described in this figure or at least one subsequent figure. Furthermore, identical features will be labeled with the same reference numerals for the sake of brevity. Additionally, for the sake of clarity, not all features in the following figures will be illustrated and / or labeled. However, a feature illustrated in one or more previous figures may also be present in this figure or in one or more subsequent figures. Furthermore, for the sake of clarity, a feature may only be illustrated and / or labeled in this figure or in one or more subsequent figures. However, a feature illustrated only in one or more subsequent figures may already be present in this figure or in a previous figure.

[0076] 2 shows a schematic side view of a MEMS acoustic transducer 1, which comprises two piezoelectric elements 4, 17. As already explained, not all features are further described here. For example, the features of the first piezoelectric element 4 have already been explained for FIG. 1. Advantageously, both piezoelectric elements 4, 17 shown here are identically formed. The second piezoelectric element 17 therefore has the same features as the first piezoelectric element 4.

[0077] As can also be seen, both piezoelectric elements 4, 17 are coupled to the diaphragm 11 via one coupling element 9. Furthermore, a first spring element 10 is disposed between the first piezoelectric element 4 and the coupling element 9, and a second spring element 18 is disposed between the second piezoelectric element 17 and the coupling element 9. Thus, both piezoelectric elements 4, 17 together displace the diaphragm 11 via the coupling element 9 shown here. Additionally or alternatively, the displacement of the diaphragm 11 can be transferred to both piezoelectric elements 4, 17 via the coupling element 9.

[0078] 3 shows a MEMS acoustic transducer 1 with two piezoelectric elements 4, 17 and two coupling elements 9, 19. Also, individual features will not be explained again here if they are already known at least from the previous figures.

[0079] As shown in this embodiment, the first piezoelectric element 4 is coupled to a diaphragm 11 by a first coupling element 9. Also, a first spring element 10 is disposed between the first coupling element 9 and the first piezoelectric element 4. Additionally or alternatively, a first coupling plate 12 is disposed between the first coupling element 9 and the diaphragm 11.

[0080] Furthermore, the second piezoelectric element 17 is coupled to the diaphragm 11 by a second coupling element 19. A second spring element 18 is disposed between the second piezoelectric element 17 and the second coupling element 19. A second coupling plate 20 is disposed between the second coupling element 19 and the diaphragm 11. In the illustrated embodiment, both piezoelectric elements 4, 17 can be coupled to the diaphragm 11 in a more or less independent manner.

[0081] As an alternative to the illustrated embodiment, both coupling elements 9, 19 shown here may be coupled to the diaphragm 11 by a single coupling plate 12, 20. For example, both coupling plates 12, 20 shown here may be integrated into one coupling plate 12, 20.

[0082] Fig. 4 shows a schematic side cross-sectional view of the layer structure of the MEMS acoustic transducer 1. Fig. 4 shows the schematic structure of the MEMS acoustic transducer 1 of Fig. 1, but does not include the region to the right of the coupling element 9. That is, the right part of the carrier 2 of Fig. 1 is not shown in Fig. 4.

[0083] 4, an assembly direction 21 is shown. Along this assembly direction 21, each layer of the MEMS acoustic transducer 1 shown here can be assembled. It should be noted that each layer can be disposed across the entire width of the MEMS acoustic transducer 1 shown here. That is, the areas not shown with lines will be formed later.

[0084] As a first step of the manufacturing method, a carrier 2 is provided over the entire width of the MEMS acoustic transducer 1 shown here, on which a first electrode layer 22 can be arranged according to an assembly direction 21. In a further manufacturing method, a first piezoelectric layer 5 can be formed on the first electrode layer 22. On the first piezoelectric layer 5, a second electrode layer 24 can be formed. On the second electrode layer 24, a second piezoelectric layer 25 can be formed. On the second piezoelectric layer 25, a third electrode layer 26 can be formed. In FIG. 1, only the first piezoelectric layer 5 is shown. In FIG. 4 shown here, the piezoelectric element 4 is shown in more detail. Advantageously, the piezoelectric element 4 can include a number of piezoelectric layers 5, 25. For example, the piezoelectric element 4 can include between two and six piezoelectric layers 5, 25. In an advantageous embodiment, the piezoelectric element 4 can include four piezoelectric layers 5, 25. The electrode layers 22,24,26 described herein serve to conduct electrical signals to and / or extract electrical signals from the at least one piezoelectric layer 5,25.

[0085] According to this embodiment example, the presently shown coupling element 9 and the presently shown piezoelectric element 4 are assembled in the same layer. The presently shown coupling element 9 thus comprises a part of the carrier 2, the first electrode layer 22, the first piezoelectric layer 5, the second electrode layer 24, the second piezoelectric layer 25 and / or the third electrode layer 26. However, these layers of the coupling element 9 only have the effect of assembling the coupling element 9. If the coupling element 9 and the at least one piezoelectric element 4 are assembled in the same layer, this is advantageous for the manufacturing method. This allows the coupling element 9 and the at least one piezoelectric element 4 to be formed at the same time. In a process step subsequent to the assembly of the coupling element 9 and the at least one piezoelectric element 4, they can be separated from each other, for example by etching.

[0086] Furthermore, a first insulating layer 27 can also be arranged. Furthermore, a contact layer 29 can be arranged for conducting electrical signals to and / or from the at least one piezoelectric layer 5, 25. Additionally or alternatively, a second insulating layer 28 can also be formed. The at least one insulating layer 27, 28 serves to electrically insulate electrical conductors, e.g. the contact layer and / or the at least one piezoelectric layer 5, 25.

[0087] After these layers have been formed, a first free space 30 can be formed, for example by etching. The formation of the first free space 30 separates the piezoelectric element 4 shown here from the coupling element 9, making the piezoelectric element 4 displaceable, in particular relative to the carrier 2. The piezoelectric element 4 and the coupling element 9 are coupled by using a first spring element 10 after the formation of the first free space 30.

[0088] At least one structural layer 6 made of polymer is formed on at least one piezoelectric layer 5, 25 and / or on at least one electrode layer 22, 24, 26 shown here. According to this embodiment example, a second structural layer 31 is arranged on the first structural layer 6. A multiplicity of these structural layers 6, 31 allows the thickness 34 of the resulting layer to be increased. At least one structural layer 6, 31 can be laminated, for example, in the form of a film, in particular a polymer film, on at least one piezoelectric layer 5, 25 and / or on at least one electrode layer 22, 24, 26 and / or on at least one insulating layer 27, 28 and / or on at least one contact layer 29. For example, the thickness 34 of at least one structural layer 6, 31 can be twice the thickness of the polymer film, and both structural layers 6, 31 shown here can be formed by laminating the polymer film twice. However, both structural layers 6, 31 can also be considered as a single structural layer 6, 31.

[0089] In this embodiment example, two piezoelectric layers 5, 25 are shown. If the piezoelectric layers 5, 25 are made of aluminum scandium nitride, it is advantageous if at least one piezoelectric element 4, 17 comprises two to six, in particular four, piezoelectric layers 5, 25.

[0090] After forming at least one structural layer 6, 31, a second free space 32 can be formed therein, via which a connection can be made to the contact layer 29 shown here.

[0091] 4, there is further shown a first spring element 10, which is here formed by a first and a second structural layer 6, 31.

[0092] Furthermore, a compensation layer 7 is shown here. The compensation layer 7 extends in the longitudinal direction of the piezoelectric element 4 from the carrier 2 to the spring element 10.

[0093] The layers described in FIG. 4 may be formed, at least in part, by using lithographic processes.

[0094] 5 shows one embodiment of a MEMS acoustic transducer 1 in a top view, where the top view is parallel to, along, or in the same direction as the pulling axis 3.

[0095] A total of six piezoelectric elements 4, 17, 36-39 are shown here, arranged in a particularly regular polygon, in this case a hexagon.

[0096] According to this embodiment example, the piezoelectric elements 4, 17, 36-39 are respectively coupled to the coupling element 9 by means of spring elements 10, 18, 40-43. Thus, here also six spring elements 10, 18, 40-43 are shown. Furthermore, here only one coupling element 9 is present. Alternatively, at least one further coupling element can be provided such that the piezoelectric elements 4, 17, 36-39 can be coupled to the diaphragm 11 by multiple coupling elements.

[0097] Further, recesses 35 are shown here. At least one piezoelectric element 4, 17, 36-39 may include at least one recess 35. By means of the recess 35, mechanical properties, such as mechanical stress and / or movement properties, of the piezoelectric element 4, 17, 36-39 may be adjusted. Here, at least one recess 35 may extend into the piezoelectric layer, the structural layer and / or the compensation layer of the corresponding piezoelectric element 4, 17, 36-39.

[0098] Further, cut plane 44 is shown here. For example, Fig. 2 shows a cross section along cut plane 44. However, for example, recess 35 is not shown in Fig. 2. [Explanation of symbols]

[0099] 1. MEMS acoustic transducer 2. Carrier 3 Lifting shaft 4. First Piezoelectric Element 5 First Piezoelectric Layer 6 First structural layer 7 Compensation layer 8 free end 9 First coupling element 10 First spring element 11 Diaphragm 12 First connecting plate 13 Diaphragm frame 14 Midplane 15 Upper 16 Lower side 17 Second piezoelectric element 18 Second spring element 19 Second coupling element 20 Second connecting plate 21 Assembly Direction 22 First electrode layer 24 Second electrode layer 25 Second Piezoelectric Layer 26 Third electrode layer 27 First insulating layer 28 Second insulating layer 29 Contact layer 30 The First Free Space 31 Second structural layer 32 The Second Free Space 33 Length 34 Thickness 35 Recess 36 Third Piezoelectric Element 37 Fourth Piezoelectric Element 38 Fifth Piezoelectric Element 39 6th Piezoelectric Element 40 Third spring element 41 Fourth spring element 42 Fifth spring element 43 6th spring element 44 Cut surface

Claims

1. A MEMS acoustic transducer (1) for generating and / or detecting sound waves, in particular in the audible wavelength spectrum and / or in the ultrasonic range, comprising: A carrier (2); at least one piezoelectric element (4, 17) arranged on said carrier (2), displaceable in the direction of a pulling axis (3), and having at least one piezoelectric layer (5, 25) and at least one structural layer (6, 31); wherein an electric signal and a displacement of the piezoelectric element (4) can be converted into each other by the at least one piezoelectric layer (5, 25), 13. A MEMS acoustic transducer, characterized in that said at least one structural layer (6, 31) is made from a polymer, in particular a polyamide.

2. 2. A MEMS acoustic transducer according to claim 1, characterized in that said at least one piezoelectric layer (5, 25) is made from aluminium-scandium nitride.

3. 10. A MEMS acoustic transducer according to any one of the preceding claims, characterized in that the piezoelectric element (4, 17) comprises a compensation layer (7) for adjusting the mechanical stress of the at least one structural layer (6, 31) and / or for straightening the at least one structural layer (6, 31).

4. 10. A MEMS acoustic transducer according to any one of the preceding claims, characterized in that the piezoelectric layer (5, 25) is arranged between the carrier (2) and the structural layer (6, 31) in the direction of the pulling axis (3).

5. 10. A MEMS acoustic transducer according to any one of the preceding claims, characterized in that the structural layer (6, 31) is arranged between the piezoelectric layer (5, 25) and the compensation layer (7).

6. 10. The MEMS acoustic transducer according to claim 9, characterized in that the compensation layer (7) is formed from a metal, in particular gold, and / or from silicon dioxide, in particular TEOS, and / or the compensation layer (7) has a thickness (34) of 0.2 μm to 4 μm, in particular 0.5 μm to 3 μm, preferably 0.6 μm to 2 μm, preferably 1 μm to 2 μm.

7. A MEMS acoustic transducer according to any one of the preceding claims, characterized in that the length (33) of the piezoelectric element (4, 17) in the longitudinal direction, in particular the length from the carrier (2) to one free end (8) of the piezoelectric element (4, 17), is between 0.5 mm and 2 mm.

8. 10. The MEMS acoustic transducer according to claim 9, wherein the compensation layer (7) extends in the longitudinal direction of the piezoelectric element (4, 17) to the carrier (2) and / or to the free end (8) of the piezoelectric element (4, 17).

9. said at least one piezoelectric element (4, 17) comprises a plurality of, in particular two to six, preferably four, piezoelectric layers (5, 25); and / or said at least one piezoelectric element (4, 17) comprising at least one electrode layer (22, 24, 26); and / or 10. A MEMS acoustic transducer according to any one of the preceding claims, characterized in that the at least one piezoelectric element (4, 17) comprises at least one insulating layer (27, 28).

10. 10. A MEMS acoustic transducer according to any one of the preceding claims, characterized in that the at least one piezoelectric element (4, 17) is sandwiched between the plurality of piezoelectric layers (5, 25) and the electrode layers (22, 24, 26).

11. 10. A MEMS acoustic transducer according to any one of the preceding claims, characterized in that the MEMS acoustic transducer (1) comprises a coupling element (9, 19) capable of coupling the at least one piezoelectric element (4, 17) to a diaphragm (11).

12. 10. A MEMS acoustic transducer according to any one of the preceding claims, characterized in that the piezoelectric element (4, 17) and the coupling element (9, 19) are coupled to one another by at least one spring element (10, 18), wherein the at least one spring element (10, 18) is arranged in the longitudinal direction of the piezoelectric element (4, 17), preferably between the structural layer (6, 31) and the coupling element (9, 19).

13. 10. A MEMS acoustic transducer according to any one of the preceding claims, characterized in that the spring element (10, 18) is preferably formed exclusively through the structural layer (6, 31) and / or from a polymer.

14. 10. A MEMS acoustic transducer according to any one of the preceding claims, characterized in that the piezoelectric element (4, 17) and the coupling element (9, 19) are of the same layer structure.

15. A MEMS acoustic transducer according to any one of the preceding claims, characterized in that the structural layer (6, 31) is between 10 μm and 50 μm thick.

16. 10. A MEMS acoustic transducer according to any one of the preceding claims, characterized in that the at least one piezoelectric element (4, 17) comprises at least one recess (35), wherein the recess is preferably arranged in the at least one piezoelectric layer (5, 25), the at least one electrode layer (22, 24, 26), the at least one insulating layer (27, 28), the at least one structural layer (6) and / or the at least one compensation layer (7).

17. the elastic modulus of the polymeric structural layer (6, 31) is between 2 and 50 GPa, in particular between 2 and 5 GPa, preferably between 3.5 and 4 GPa; and / or the tensile strength of the polymeric structural layer (6, 31) is between 70 and 100 MPa, in particular between 85 and 95 MPa; and / or A MEMS acoustic transducer according to any one of the preceding claims, characterized in that the polymer structural layer (6, 31) is applied with a swing range of 3% to 10%.

18. 10. The MEMS acoustic transducer according to claim 9, wherein the compensation layer (7) has a mechanical stress equal to or higher than that of the at least one structural layer (6, 31), wherein the mechanical stress of the compensation layer (7) compensates for the mechanical stress of the at least one structural layer (6, 31).

19. 10. A MEMS acoustic transducer according to any one of the preceding claims, characterized in that the mechanical stress state of the compensation layer (7) counteracts, compensates and / or adjusts the mechanical stress of the at least one structural layer (6, 31) and / or the at least one piezoelectric layer (5, 25), wherein the compensation layer (7) preferably has a mechanical stress of 50 MPa to 1000 MPa, in particular 240 MPa.

20. A method for manufacturing a MEMS acoustic transducer (1), in particular for generating and / or detecting sound waves in the audio wavelength spectrum and / or in the ultrasonic range, preferably formed according to any one of the preceding claims, comprising: The method includes forming at least one piezoelectric element (4, 17) on a carrier (2), the piezoelectric element (4, 17) including at least one piezoelectric layer (5, 25) and at least one structural layer (6, 31) bonded thereto; 4. A method according to claim 3, wherein said at least one piezoelectric layer (5, 25) is made from aluminium scandium nitride.

21. 21. A method according to claim 20, characterized in that a polymer is disposed on the piezoelectric layer (5, 25) to form the at least one structural layer (6, 31).

22. 10. The method according to any one of the preceding claims, characterized in that the at least one piezoelectric element (4, 17) is formed of a plurality, in particular of two to six, preferably four, piezoelectric layers (5, 25).

23. 10. A method according to any one of the preceding claims, characterized in that the at least one piezoelectric element (4, 17) is formed sandwiched between the plurality of piezoelectric layers (5, 25) and at least one electrode layer (22, 24, 26).

24. 10. A method according to any one of the preceding claims, characterized in that, when forming the at least one piezoelectric element (4, 17), at least one insulating layer (27, 28) is arranged.

25. 10. The method according to claim 9, characterized in that the polymer structural layer (6, 31) is arranged on the side of the piezoelectric layer (5, 25) facing away from the carrier (2).

26. 10. The method according to claim 9, characterized in that the polymer structural layer (6, 31) is arranged on the at least one piezoelectric layer (5, 25) after the piezoelectric layer (5, 25) and / or the coupling elements (9, 19) have been formed and / or after the carrier (2), the piezoelectric layer (5, 25) and / or the coupling elements (9, 19) have been post-processed, in particular by etching, and in particular separated from one another.

27. 10. A method according to any one of the preceding claims, characterised in that the piezoelectric elements (4, 17) and the coupling elements (9, 19) are preferably formed together in layers on the carrier (2).

28. 10. A method according to any one of the preceding claims, characterized in that after the piezoelectric elements (4, 17) and the coupling elements (9, 19) have been assembled in a layer structure, they are at least partially separated from one another, in particular by etching.

29. 10. The method according to claim 9, wherein the at least one polymer structural layer (6, 31) is applied onto the piezoelectric layer (5, 25) and / or onto the coupling element (9, 19), particularly preferably in the form of a self-adhesive polymer film.

30. 10. The method according to any one of the preceding claims, characterized in that two structural layers (6, 31) are formed, said structural layers being preferably arranged one on top of the other and / or being made of the same or different polymers.

31. the polymeric structural layer (6, 31) is surface treated at a temperature between 70°C and 90°C; and / or 10. The method according to any one of the preceding claims, characterized in that the surface treatment is followed by a curing step of the polymer, wherein this curing step is preferably carried out at a temperature between 150°C and 200°C and / or for a period of between 0.5 hours and 2 hours.

32. 10. The method according to any one of the preceding claims, characterized in that a compensation layer (7) is arranged on the structural layer (6, 31).

33. 10. A method according to any one of the preceding claims, characterized in that the at least one polymeric structural layer (6, 31) is post-treated.

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