MEMS transducer having carrier layer and at least two piezoelectric layers

Abstract

The invention relates to a MEMS transducer (1), in particular a MEMS sound transducer unit, preferably for generating and / or detecting sound waves in the audible wavelength spectrum and / or ultrasound range, comprising a carrier (2) and at least one piezoelectric element (4) which is arranged on the carrier (2) and which can be deflected in the direction of a lifting axis (3), the piezoelectric element has at least two piezoelectric layers (5, 25, 35, 36) and at least one carrier layer (6), wherein an electrical signal and a deflection of the piezoelectric element (4) can be converted into each other by means of the at least one piezoelectric layer (5, 25, 35, 36). According to the invention, the carrier layer (6) is arranged between the two piezoelectric layers (5, 25, 35, 36) in the direction of the lifting axis (3). The invention further relates to the use of the carrier layer (6) for a MEMS transducer (1) and to a method for producing the MEMS transducer (1).

Description

Technical Field

[0001] The present invention relates to a MEMS transducer, in particular a MEMS acoustic transducer unit, preferably for generating and / or detecting sound waves in the audible wavelength spectrum and / or in the ultrasonic range. The MEMS transducer has a carrier and at least one piezoelectric element arranged at the carrier and deflectable in the direction of a lift axis. The piezoelectric element has at least two piezoelectric layers and at least one carrier layer, wherein an electrical signal and a deflection of the piezoelectric element can be converted into each other by means of the at least one piezoelectric layer. Summary of the Invention

[0002] The object of the present invention is to create a high-performance MEMS transducer.

[0003] This object is achieved by a MEMS transducer having the features of the independent claims, the use of a carrier layer for a MEMS transducer, and a method for manufacturing a MEMS sensor. Advantageous or preferred embodiments are each the subject matter of the dependent claims.

[0004] The present invention provides a MEMS transducer, preferably a MEMS acoustic transducer, in particular for generating and / or detecting sound waves in the audible wavelength spectrum and / or in the ultrasonic range. The MEMS transducer can operate as a loudspeaker and / or a microphone and thus as a MEMS acoustic transducer.

[0005] The MEMS acoustic transducer includes a carrier.

[0006] Furthermore, the MEMS transducer includes at least one piezoelectric element arranged at the carrier and deflectable in the direction of a lift axis.

[0007] In addition, the at least one piezoelectric element has at least two piezoelectric layers and at least one carrier layer, wherein an electrical signal and a deflection of the piezoelectric element can be converted into each other by means of these piezoelectric layers.

[0008] In addition, at least one carrier layer is arranged between two piezoelectric layers in the direction of the lifting axis. Thus, in the direction of the lifting axis, at least one piezoelectric layer is arranged above the carrier layer, and at least one piezoelectric layer is arranged below the carrier layer. Thereby, the piezoelectric element can be configured symmetrically, thus improving the deflection characteristics. Thereby, it can be achieved in a simple manner that the neutral layer or neutral plane is arranged in the middle of the carrier layer in the direction of the lifting axis. The piezoelectric element is a cantilever, and when the piezoelectric element deflects, compressive stress and tensile stress are formed therein. The regions of compressive stress and tensile stress depend on whether the piezoelectric element deflects upward or downward. Compressive stress is formed on one side of the deflection direction of the piezoelectric element. Tensile stress is formed on the opposite side. This is the general principle of strength theory. In a plane of the piezoelectric element, that is, within the neutral layer or neutral plane, the tensile stress and compressive stress cancel each other out, so there is no stress there. However, the deflection characteristics of the piezoelectric element depend on the position of this neutral layer or neutral plane within the piezoelectric element. By means of the at least one piezoelectric layer above and below the carrier layer, the neutral layer is arranged in the middle.

[0009] Furthermore, with this structure of the piezoelectric element, the non-linearity during the deflection of the piezoelectric layer can be automatically eliminated because they occur symmetrically and through one piezoelectric layer above and another piezoelectric layer below, the non-linearities cancel each other out.

[0010] Advantageously, the piezoelectric layer is composed of scandium aluminum nitride. These piezoelectric layers are very strong, which is particularly attributed to the scandium content, which can preferably be between 30% and 70%. It can be particularly advantageous if the scandium content is 30%, 40% or 50%.

[0011] Advantageously, piezoelectric layers are arranged above and below the carrier layer in the direction of the lifting axis.

[0012] Beneficially, the same number of piezoelectric layers are respectively arranged below and above the carrier layer in the direction of the lifting axis. Thereby, the symmetry of the piezoelectric element is maintained. Equally advantageously, two piezoelectric layers are respectively arranged below and above the carrier layer in the direction of the lifting axis. Thereby, the performance can be improved without setting too many piezoelectric layers. Advantageously, the at least one carrier layer includes at least one metal layer, particularly a metal layer. Additionally, the metal layer can be an aluminum layer. Additionally or alternatively, the at least one carrier layer can include at least one oxide layer. The oxide layer can be a silicon oxide layer. With the aid of these materials, the carrier layer can be constructed using known manufacturing methods, such as methods used in semiconductor technology. Thus, the carrier layer can be manufactured in large quantities and / or very inexpensively. Furthermore, the aluminum layer and the silicon oxide layer have similar E-moduli (elastic moduli) in the range of 70 GPa. Therefore, the two layers have similar or almost the same deflection characteristics.

[0013] The at least one oxide layer and / or at least one metal layer further have the advantage that they are heat-resistant or even high-temperature resistant, for example resistant to high temperatures of up to 1200 °C - 1400 °C. Therefore, the piezoelectric layer and / or the electrode layer can be applied by means of methods of semiconductor technology, for example methods compatible with CMOS. For example, the piezoelectric layer and / or the electrode layer can be applied by means of chemical vapor deposition (CVD) methods.

[0014] It is also advantageous that the carrier layer includes several metal layers and several oxide layers. In addition, the metal layers and the oxide layers can be arranged alternately and overlappingly. Thereby, a sandwich structure of the carrier layer is formed. Such a carrier layer is thus a stack composed of multiple layers, preferably a stack composed of at least one metal layer and at least one, in particular at least two, oxide layers. The carrier layer can also be a structural layer in this case.

[0015] Advantageously, in the direction of the lift axis, the uppermost layer and the lowermost layer are oxide layers. When the carrier layer is hierarchically constructed by means of the at least one metal layer and the at least two oxide layers, in the direction of the lift axis, the uppermost layer and the lowermost layer are oxide layers. The advantage of this is that the oxide layer, in particular the silicon oxide layer, has the highest temperature resistance. The piezoelectric layer and / or the electrode layer are applied on the oxide layer (which forms both the uppermost layer and the lowermost layer), especially at higher temperatures. The oxide layer does not change at higher temperatures.

[0016] In addition, the oxide layer, in particular the silicon oxide layer, can be simply processed. For example, the layer can be polished by a chemical mechanical method. Such a method is called chemical mechanical polishing, also known as chemical mechanical planarization (CMP, English : “chemical mechanical polishing”, also known as “chemical mechanical planarization”). Therefore, the oxide layer, in particular the silicon oxide layer, can be constructed to be very flat and / or level.

[0017] According to an advantageous improvement of the present invention, it is useful that the at least one carrier layer is composed of a polymer. In this case, the polymer can be polyamide. By means of the at least one carrier layer made of a polymer, a greater degree of deflection of the piezoelectric element can be achieved. Additionally or alternatively, the length of the piezoelectric element can also be shortened, wherein the deflection can at least be kept constant. Advantageously, the piezoelectric element has a length between 0.5 mm and 2 mm in its longitudinal direction, especially from the carrier to the free end of the piezoelectric element.

[0018] Advantageously, the at least one piezoelectric element comprises several piezoelectric layers, in particular between two and six, preferably four.

[0019] Advantageously, the at least one piezoelectric element comprises at least one electrode layer. By means of the at least one electrode layer, electrical signals can be exchanged which cause the piezoelectric element to deflect and / or which are formed when the piezoelectric element deflects.

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

[0021] Advantageously, the at least one piezoelectric element is configured as a sandwich-like consisting of several piezoelectric layers and electrode layers.

[0022] Advantageously, the MEMS acoustic transducer comprises a coupling element by means of which the at least one piezoelectric element can be coupled to the membrane.

[0023] Improved is that the piezoelectric element and the coupling element are coupled together by means of at least one elastic element, wherein the at least one elastic element is preferably arranged between the carrier layer and the coupling element in the longitudinal direction of the piezoelectric element.

[0024] Advantageously, the elastic element, preferably exclusively, is formed by the carrier layer. Thereby, the elastic element can be constructed simply.

[0025] Advantageously, the elastic element consists of the polymer or a polymer, in particular polyamide. Additionally or alternatively, the elastic element has the mechanical properties of a polymer.

[0026] Advantageously, the piezoelectric element and the coupling element have the same layer structure as each other.

[0027] Improved is that the thickness of the carrier layer is between 5 µm and 100 µm. Preferably, the carrier layer has a thickness of less than 100 µm.

[0028] Further advantageously, the carrier layer has an E modulus (elastic modulus) between 40 GPa and 300 GPa.

[0029] Due to the above mechanical properties of the at least one carrier layer, the deflection can be increased and / or the piezoelectric element can be shortened in the case of at least the same deflection or with increasing deflection.

[0030] Furthermore, the present invention provides the use of a carrier layer for a MEMS transducer. The MEMS transducer has at least one of the features described above and / or below. Additionally or alternatively, the carrier layer has at least one of the features described above and / or below. In particular, the carrier layer may include at least one metal layer, especially an aluminum layer, and / or at least one oxide layer, especially a silicon oxide layer, and may optionally include at least one additional feature associated therewith.

[0031] In addition, the present invention provides a method for manufacturing a MEMS transducer, preferably a MEMS acoustic transducer, especially for generating and / or detecting sound waves in the audible wavelength spectrum and / or in the ultrasonic range. The method for manufacturing the MEMS transducer can be carried out such that the MEMS transducer is configured to have at least one of the features described above and / or hereinafter.

[0032] In this method, at least one piezoelectric element is constructed on a carrier, the piezoelectric element including at least two piezoelectric layers and at least one carrier layer coupled thereto.

[0033] Furthermore, in this method, a carrier layer is arranged between at least two piezoelectric layers. Thereby, a symmetric structure of the piezoelectric element can be formed, especially in the direction of the lift axis. Thus, advantageous deflection characteristics can be achieved. It is also beneficial to process the oxide layer, especially the silicon oxide layer, by chemical mechanical polishing. Thereby, the oxide layer is made flat and / or planar. Then, the at least one piezoelectric layer and / or electrode layer is applied on the flat and / or planar oxide layer.

[0034] Advantageously, the piezoelectric layer is constructed on the carrier layer by means of semiconductor manufacturing methods.

[0035] Furthermore, it is advantageous to deposit the piezoelectric layer on the carrier layer. In this case, the piezoelectric layer, at least the first piezoelectric layer, can also be deposited on the oxide layer. Then, all other subsequent piezoelectric layers are deposited layer by layer.

[0036] It is also advantageous to construct the piezoelectric layer and / or the carrier layer on the carrier layer by chemical vapor deposition. Thereby, the method for constructing the piezoelectric layer and / or the electrode layer is easy to understand. In addition, such methods can be carried out particularly simply.

[0037] In this case, metal layers, oxide layers, electrode layers, and / or piezoelectric layers can be constructed and / or especially arranged on existing layers using CMOS-compatible methods.

[0038] It is further beneficial to remove at least one region, especially by etching, after constructing the piezoelectric layer and / or the carrier layer. By means of the method steps described herein, the piezoelectric layer and / or the carrier layer can be built layer by layer.

[0039] Advantageously, the piezoelectric layer is composed of aluminum scandium nitride.

[0040] Furthermore, it is advantageous to configure the at least one piezoelectric element to have several piezoelectric layers, in particular between two and six, especially four. By means of several piezoelectric layers, the performance of the piezoelectric element can be enhanced.

[0041] Further advantageously, in the direction of the lifting axis, the same number of piezoelectric layers are arranged above and below the carrier layer.

[0042] For example, advantageously, two piezoelectric layers are respectively arranged above and below the carrier layer in the direction of the lifting axis, such that the piezoelectric element includes a total of four piezoelectric layers.

[0043] Advantageously, the at least one piezoelectric element is configured to be sandwich-shaped, consisting of several piezoelectric layers and at least one electrode layer.

[0044] These several piezoelectric layers and several electrode layers can be arranged alternately and overlappingly.

[0045] Further advantageously, when constructing the at least one piezoelectric element, at least one isolation layer is arranged.

[0046] Advantageously, the carrier layer made of polymer is arranged on the side of the piezoelectric layer facing away from the carrier.

[0047] Improved is when the carrier layer made of polymer is arranged on the at least one piezoelectric layer after the piezoelectric layer and / or the coupling element are formed and / or after the carrier, piezoelectric layer and / or coupling element have undergone post-treatment, in particular post-treatment by etching, especially after being separated from each other.

[0048] Advantageously, the piezoelectric element and the coupling element are configured together to be layered, which is preferably carried out on the carrier.

[0049] Advantageously, after the piezoelectric element and the coupling element are constructed in a layered manner, they are at least partially separated from each other, especially by means of etching.

[0050] Furthermore, a method can be implemented to create the MEMS transducer as described in one or more of the above and / or below. Description of the Drawings

[0051] Other advantages of the present invention are described in the following embodiments. Among them: Figure 1 A schematic cross-sectional view of a MEMS transducer is shown, which has a piezoelectric element composed of two piezoelectric layers and at least one carrier layer; Figure 2Shows a schematic cross-sectional view of a piezoelectric element having two piezoelectric layers and at least one carrier layer; Figure 3 Shows a schematic cross-sectional view of a piezoelectric element having two piezoelectric layers each above and below the carrier layer in the direction of the lift axis; Figure 4 Shows a schematic cross-sectional view of a carrier layer composed of a metal layer and an oxide layer; Figure 5 Shows a top view of a MEMS transducer having several piezoelectric elements. Detailed Description

[0052] Figure 1 Shows a schematic cross-sectional view of the MEMS transducer 1. The MEMS transducer 1 can also be a MEMS acoustic transducer. With the MEMS acoustic transducer, for example, sound waves within the audible wavelength spectrum can be generated, so that it can be operated as a MEMS speaker. With the MEMS acoustic transducer, sound waves within the audible wavelength spectrum can be additionally or alternatively detected, so that it can be operated as a MEMS microphone. Additionally, the MEMS acoustic transducer can be arranged, for example, in a smartphone to enable, for example, making calls or listening to music. The MEMS acoustic transducer can also be arranged, for example, in headphones. However, pressure can also be generated and / or detected with the MEMS transducer 1.

[0053] However, another application area of the MEMS acoustic transducer can also be the generation and / or detection of sound waves in the ultrasonic range. The MEMS acoustic transducer can be arranged, for example, in an ultrasonic sensor, such as a distance sensor.

[0054] Additionally, the MEMS transducer 1 includes a carrier 2, which can form the basic framework of the MEMS transducer 1. The carrier 2 can, for example, include a semiconductor substrate, which can be fabricated in an etching process. The carrier 2 can, for example, be composed of silicon and / or have the shape of a wafer. Two carriers 2 are shown in the current view. However, the carrier 2 can be configured as a frame, so that in the cross-sectional view shown here, the two elements of the carrier 2 shown here are joined together. For example, the carrier 2 can be configured as rectangular in a top view. The top view can be oriented, for example, towards the lift axis 3 to be described below. The top view can be parallel to the lift axis 3. For example, if the carrier 2 is configured as a frame, the at least one piezoelectric element 4 can face at least partially towards the interior of the carrier 2.

[0055] At least one piezoelectric element 4 is further arranged at the carrier 2. The at least one piezoelectric element 4 can additionally be coupled to the carrier 2. The at least one piezoelectric element 4 can be deflected along the shown lift axis 3. The at least one piezoelectric element 4 can hereby convert an electrical signal into a deflection, such that the MEMS transducer 1 operates as a loudspeaker or can generate sound waves. Additionally or alternatively, a deflection can also be converted into an electrical signal by means of the at least one piezoelectric element 4, such that the MEMS transducer 1 can operate as a microphone or can detect sound waves. However, a pressure can also be generated by means of the deflection. Additionally or alternatively, a pressure can also be detected, since this causes a deflection of the at least one piezoelectric element 4.

[0056] The at least one piezoelectric element 4 comprises a free end 8, which can be deflected along the lift axis 3.

[0057] The piezoelectric element 4 further comprises at least two piezoelectric layers 5, 25. The at least two piezoelectric layers 5, 25 are made of a piezoelectric material. The at least two piezoelectric layers 5, 25 can convert an electrical signal into a deflection and / or a deflection into an electrical signal. The at least two piezoelectric layers 5, 25 can be made of scandium aluminum nitride (ScAlN).

[0058] Furthermore, the piezoelectric element 4 comprises at least one carrier layer 6. The at least one carrier layer is coupled to the at least two piezoelectric layers 5, 25. At least one piezoelectric layer 5, 25 is arranged here between the carrier 2 and the at least one carrier layer 6. By means of the at least one carrier layer 6, the at least one piezoelectric layer 5, 25 can be stabilized. Additionally, the at least one piezoelectric layer 5, 25 can be prevented from breaking during deflection by means of the at least one carrier layer 6. The at least one carrier layer 6 can also serve as a carrier layer for the at least one piezoelectric layer 5, 25. The carrier layer 6 can for example be made of a polymer. The carrier layer 6 is thus a polymer carrier layer. The polymer can be a polyamide. The polymer is softer, in particular softer than silicon, such that the piezoelectric element 4 can be made smaller, wherein a high deflection of the piezoelectric element 4 is still feasible. The performance or behavior of the piezoelectric element 4 mainly depends on the degree of deflection or elongation. By means of the soft polymer, in particular compared to silicon, it is feasible to maintain the same deflection with a smaller size of the piezoelectric element 4, in particular a shorter length.

[0059] Alternatively, the carrier layer 6 can also have at least one metal layer 41 - 43 and / or at least one oxide layer 37 - 40, as shown in more detail in Figure 4 as shown more specifically below.

[0060] According to this embodiment, the MEMS transducer 1 includes a coupling element 9, by means of which the at least one piezoelectric element 4 can be coupled to the membrane 11 of the MEMS transducer 1 shown here. With the aid of the coupling element 9, if the MEMS transducer 1 is a MEMS acoustic transducer, when an acoustic wave is generated by means of the membrane 11, the deflection of the piezoelectric element 4 can be transmitted to the membrane 11. Additionally or alternatively, if the MEMS transducer 1 is a MEMS acoustic transducer, when an acoustic wave is detected by means of the membrane 11, the deflection of the membrane 11 can also be transmitted to the piezoelectric element 4.

[0061] According to this embodiment, the piezoelectric element 4 is coupled to the coupling element 9 by means of an elastic element 10. The elastic element 10 can be composed of a polymer, for example. The elastic element 10 thus has flexibility. Advantageously, as shown here, a coupling plate 12 is arranged between the coupling element 9 and the membrane 11. With the aid of the coupling plate 12, planar transmission of the deflection between the coupling element 9 and the membrane 12 can be achieved. According to this embodiment, a membrane frame 13 is also shown, by means of which the membrane 11 can be arranged on the carrier 2.

[0062] Furthermore, the at least one piezoelectric element 4 has a length 33. The length 33 is defined here as extending from the carrier 2 to the free end 8 of the at least one piezoelectric element 4. The length 33 can be between 0.5 mm and 2 mm. Through the carrier layer 6, the piezoelectric element 4 can have the length 33, where large deflections along the lift axis 3 are feasible. The deflection of the at least one piezoelectric element 4, especially at the free end 8, can be at least 3%, preferably at least 10%. The thickness 34 of the at least one piezoelectric element 4 can be between 2 μm and 50 μm. The thickness 34 is oriented parallel to the lift axis 3 and / or perpendicular to the layer of the at least one piezoelectric element 4 (see Figure 4 ) Furthermore, the at least one piezoelectric element 4 can have at least one notch not shown in this figure. The at least one notch can extend at least partially between the upper side 15 and the lower side 16. The at least one notch can extend from the upper side 15 and / or from the lower side 16 in the direction of the corresponding opposite upper side or lower side 15, 16. By means of these notches, the stress in the piezoelectric element 4 or in the at least one piezoelectric layer 5 and / or in the at least one carrier layer 6 can be reduced. In this case, the upper side 15 can also be referred to as the first side, and the lower side 16 can be referred to as the second side.

[0063] The upper side 15 faces the membrane 11 here. The lower side 16 faces away from the membrane 11. By means of the two terms "upper side 15" and "lower side 16", the two terms "above" and "below" are also defined. The "upper side 15" and "lower side 16" as well as "above" and "below" refer to the direction of the lifting axis 3.

[0064] Furthermore, the neutral layer 14 is shown here. The neutral layer 14 is a concept in strength theory and is also referred to as the neutral fiber (neutraler Faser) or the zero line (Nulllinie). The neutral line or the neutral layer 14 or the zero line is here a plane or a line in the piezoelectric element 4, where the tensile stress and the compressive stress cancel each other out, so that there is no stress there. In contrast, above and below it, either tensile stress or compressive stress acts. Of course, the tensile stress or compressive stress only occurs in this case when the piezoelectric element 4 is deflected. For example, if the piezoelectric element 4 deflects upwards, i.e., in the direction away from the carrier 2, compressive stress acts in the upper region of the piezoelectric element 4 and tensile stress acts in the lower region of the piezoelectric element 4. In contrast, if the piezoelectric element 4 deflects downwards, i.e., towards the carrier 2, the compressive stress and the tensile stress are swapped. In the neutral layer 14 or in the neutral plane, there is neither tensile stress nor compressive stress, where the central layer 14 or the neutral plane is arranged between the upper side 15 and the lower side 16 of the piezoelectric element 4. By means of the first piezoelectric layer 5 and the second piezoelectric layer 25 above and below the carrier layer 6 in the direction of the lifting axis 3, the position of the neutral line or the neutral layer 14 (or plane) or the zero line is adjusted in height or in the direction of the lifting axis 3. Since the two piezoelectric layers 5, 25 are also constructed to be the same as each other, i.e., made of the same material (e.g., AlScN) and / or have the same thickness 34, the neutral layer 14 is arranged in the middle of the piezoelectric element 4 and / or the carrier layer 6.

[0065] For the sake of simplicity, features that have already been described in at least one of the previous figures may not be explained again. Additionally, features may also only be described in at least one of this figure or the subsequent figures. Further, for the sake of simplicity, the same reference numerals are used for the same features. Moreover, for the sake of clarity, not all features may be shown and / or not all features may be labeled with reference numerals in the subsequent figures. However, features shown in one or several of the previous figures may also be present in one or several of this figure or the subsequent figures. Additionally, for the sake of clarity, features may also only be shown and / or labeled with reference numerals in this figure or the subsequent figures. Nevertheless, features that are only shown in one or several of the subsequent figures may also already be present in this figure or the previous figures.

[0066] Figure 2 A detailed schematic cross-sectional view of the piezoelectric element 4 is shown. For the sake of clarity, in Figure 2A more detailed structure of the piezoelectric element 4 is described in

[0067] Here, at least two piezoelectric layers 5, 25 are shown. The piezoelectric layer 5, i.e., the first piezoelectric layer 5, is arranged above or on the upper side 15 of the carrier layer 6, and the piezoelectric layer 25, i.e., the second piezoelectric layer 25, is arranged below or on the lower side 16 of the carrier layer 6. Thus, a symmetric structure of the piezoelectric element 4 can be achieved, so that the neutral layer 14 is arranged in the middle of the piezoelectric element 4 or the carrier layer 6. Thereby, the deflection characteristics of the piezoelectric element 4 are improved. For example, the non-linearity of the at least two piezoelectric layers 5, 25 can be compensated for each other.

[0068] In addition, several electrode layers 22, 23, 26, 27 are shown here. In this embodiment, the first and second electrode layers 22, 23 are assigned to the first piezoelectric layer 5, and the third and fourth electrode layers 26, 27 are assigned to the second piezoelectric layer 25. By means of the electrode layers 22, 23, 26, 27, electrical signals can be supplied to these piezoelectric layers 5, 25 to cause them to deflect, or electrical signals can be derived when they deflect by themselves.

[0069] Figure 3 An embodiment of the piezoelectric element 4 is shown, which includes a carrier layer 6 and four piezoelectric layers 5, 25, 35, 36. In this embodiment, two piezoelectric layers 5, 25, i.e., the first and second piezoelectric layers 5, 25 here, are arranged above the carrier layer 6, and two piezoelectric layers 35, 36, i.e., the third and fourth piezoelectric layers 35, 36, are arranged below it. Therefore, the performance of the piezoelectric element 4 can be improved compared to, for example, Figure 2 the piezoelectric element 4 having two piezoelectric layers 5, 25 shown. However, in this embodiment, the same number of piezoelectric layers 5, 25, 35, 36 are arranged above and below the carrier layer 6, so the piezoelectric element 4 is also symmetrically constructed. In particular, the neutral layer 14 is arranged in the middle.

[0070] Due to the two piezoelectric layers 5, 25, 35, 36 above and below the carrier layer 6, three electrode layers 22, 23, 26 - 29 are respectively arranged above and below the carrier layer 6. A piezoelectric layer 5, 25, 35, 36 is arranged between each two electrode layers 22, 23, 26 - 29. Thus, in the direction of the lifting shaft 3, an electrode layer 22, 23, 26 - 29 is arranged on both sides of each piezoelectric layer 5, 25, 35, 36. In this way, electrical signals can be applied to each piezoelectric layer 5, 25, 35, 36, or electrical signals can be derived.

[0071] Figure 4An embodiment of the carrier layer 6 is shown by a sectional view. As can be seen here, the carrier layer 6 is composed of additional layers 37 - 43. The carrier layer 6 may at least include oxide layers 37 - 40 and / or metal layers 41 - 43. The lifting shaft 3 and the neutral layer 14 are depicted here. In particular, with the aid of the lifting shaft 3, it becomes clear again what is meant by "above" and "below".

[0072] The at least one metal layer 41 - 43 may preferably be composed of aluminum. Additionally or alternatively, the at least one oxide layer 37 - 40 may be composed of silicon oxide. With these materials, the carrier layer 6 can be constructed by known manufacturing methods, for example, by methods used in semiconductor technology.

[0073] The at least one oxide layer 37 - 40 and / or the at least one metal layer 41 - 43 additionally have the advantage that they are heat-resistant or even high-temperature resistant, for example, resistant to high temperatures up to 1200 °C - 1400 °C. Therefore, the piezoelectric layers 5, 25, 35, 36 and / or the electrode layers 22, 23, 26 - 29 can be applied by methods of semiconductor technology. For example, the piezoelectric layers 5, 25, 35, 36 and / or the electrode layers 22, 23, 26 - 29 can be applied by chemical vapor deposition (CVD) methods.

[0074] In this embodiment, the carrier layer 6 includes four oxide layers 37 - 40 and three metal layers 41 - 43, as can be seen here, which are advantageously arranged overlappingly and alternately in the direction of the lifting shaft 3. Additionally, oxide layers 37, 40 are arranged above and below in the direction of the lifting shaft 3. Compared with the previous figures, in the direction of the lifting shaft 3, at least one piezoelectric layer 5, 25, 35, 36 is arranged above the first oxide layer 37 shown here, and in the direction of the lifting shaft 3, at least one piezoelectric layer 5, 25, 35, 36 is arranged below the fourth oxide layer 40 shown here. In this case, the first and fourth oxide layers 37, 40 shown here can also be directly adjacent to the electrode layers 22, 23, 26 - 29. Only then can the piezoelectric layers 5, 25, 35, 36 be adjacent to the electrode layers 22, 23, 26 - 29. However, this is only the case when one of the electrodes for the piezoelectric layers 5, 25, 35, 36 is also constructed as one of the electrode layers 22, 23, 26 - 29. The electrodes for the piezoelectric layers 5, 25, 35, 36 can also be arranged at the end faces of the piezoelectric layers 5, 25, 35, 36. At this time, the piezoelectric layers 5, 25, 35, 36 may be directly adjacent to the first or fourth oxide layer 37, 40.

[0075] Furthermore, the electrode layers 22, 23, 26 - 29 can also extend sectionally between the piezoelectric layers 5, 25, 35, 36 and the adjacent oxide layers 37 - 40.

[0076] As shown here, the oxide layers 37 - 40 extend laterally beyond the metal layers 41 - 43. Additionally or alternatively, some of the oxide layers, in particular all of the oxide layers 37 - 40 and the metal layers 41 - 43, may also be flush and / or coincident.

[0077] As can be seen in Figure 4 the carrier layer 6 shown here includes four oxide layers 37 - 40 and three metal layers 41 - 43. Alternatively, the carrier layer 6 may also include only two oxide layers 37 - 40 and one metal layer 41 - 43. Further alternatively, the carrier layer 6 may also include several oxide layers 37 - 40, for example eleven, and several metal layers 41 - 43, for example ten.

[0078] Advantageously, the carrier layer 6 has oxide layers 37 - 40 above and below in the direction of the lift axis 6. Additionally, the uppermost and lowermost layers of the layered structure of the carrier layer 6 may be oxide layers 37 - 40. Additionally, metal layers 41 - 43 are each arranged between two oxide layers 37 - 40. Thus, the number of oxide layers 37 - 40 is one greater than the number of metal layers 41 - 43.

[0079] The oxide layers 37 - 40 have the advantage that they can be further processed well. For example, the oxide layers 37 - 40 can be processed by chemical mechanical polishing. Thus, a flat and / or smooth surface is formed on the oxide layers 37 - 40, and then the at least one piezoelectric layer 5, 25, 35, 36 and / or electrode layer 22, 23, 26 - 29 is arranged on this surface. Thus, it is advantageous that the uppermost and lowermost layers of the carrier layer are oxide layers 37 - 40.

[0080] Here there are four oxide layers 37 - 40 and three metal layers 41 - 43 in order to obtain a thickness 34 of the piezoelectric element 4 of approximately 7 µm, which is advantageous for the deflection and performance of the piezoelectric element 4. The number of oxide layers 37 - 40 and metal layers 41 - 43, and the thickness 34 of the piezoelectric element 4, also depend on the length 33 of the piezoelectric element 4 in this case.

[0081] Figure 5 A top view of an embodiment of the MEMS transducer 1 is shown. In this embodiment, the carrier 2 is configured as a hexagon. Further, six piezoelectric elements 4a - 4f are shown here. Additionally, each of the six piezoelectric elements 4a - 4f has an associated elastic element 10a - 10f. The six piezoelectric elements 4a - 4f and / or the six elastic elements 10a - 10f are coupled to a coupling element 9, which couples the piezoelectric elements 4a - 4f to a membrane 11 not shown here. By using several piezoelectric elements 4a - 4f, the performance of the MEMS transducer 1 can be improved.

[0082] List of Reference Numerals 1 MEMS transducer 2 carrier 3 lifting shaft 4 piezoelectric element 5 first piezoelectric layer 6 carrier layer 8 free end 9 coupling element 10 elastic element 11 membrane 12 first coupling plate 13 membrane frame 14 neutral layer 15 upper side 16 lower side 22 first electrode layer 23 second electrode layer 25 second piezoelectric layer 26 third electrode layer 27 fourth electrode layer 28 fifth electrode layer 29 sixth electrode layer 33 length 34 thickness 35 third piezoelectric layer 36 fourth piezoelectric layer 37 first oxide layer 38 second oxide layer 39 third oxide layer 40 fourth oxide layer 41 first metal layer 42 second metal layer 43 third metal layer

Claims

1. A MEMS transducer (1), in particular a MEMS acoustic transducer unit, preferably for generating and / or detecting acoustic waves in the audible wavelength spectrum and / or in the ultrasonic range, the MEMS transducer having Vector (2) and at least one piezoelectric element (4) arranged on the carrier (2) and capable of being deflected in the direction of the lifting axis (3), The piezoelectric element comprises at least two piezoelectric layers (5, 25, 35, 36) and at least one carrier layer (6), wherein an electrical signal and a deflection of the piezoelectric element (4) can be converted into one another by means of the at least one piezoelectric layer (5, 25, 35, 36). Features ， The carrier layer (6) is arranged between two piezoelectric layers (5, 25, 35, 36) in the direction of the lifting axis (3).

2. MEMS transducer according to the preceding claim, Features The piezoelectric layer (5, 25, 35, 36) is composed of scandium aluminum nitride, wherein the scandium content is between 30% and 70%, preferably 30%, 40% or 50%.

3. MEMS transducer according to one or more of the preceding claims, Features In the direction of the lifting axis (3), piezoelectric layers (5, 25, 35, 36) are arranged below and above the carrier layer (6).

4. MEMS transducer according to one or more of the preceding claims, Features In the direction of the lifting axis (3), the same number of piezoelectric layers (5, 25, 35, 36) are arranged below and above the carrier layer (6).

5. MEMS transducer according to one or more of the preceding claims, Features In the direction of the lifting axis (3), two piezoelectric layers (5, 25, 35, 36) are arranged below and above the carrier layer (6).

6. MEMS transducer according to the preceding claim, Features The at least one carrier layer (6) comprises at least one metal layer (41-43), in particular an aluminum layer, and / or at least one oxide layer (37-40), in particular a silicon oxide layer.

7. MEMS transducer according to the preceding claim, Features The carrier layer (6) comprises several metal layers (41-43) and several oxide layers (37-40), which are preferably arranged alternately and overlappingly.

8. MEMS transducer according to the preceding claim, Features In the direction of the lifting axis (3), the uppermost layer and the lowermost layer are oxide layers (37-40).

9. MEMS transducer according to the preceding claim, Features The at least one carrier layer (6) consists of a polymer, in particular a polyamide.

10. MEMS transducer according to one or more of the preceding claims, Features The piezoelectric element (4) has a length (33) in its longitudinal direction of between 0.5 mm and 2 mm, in particular from the carrier (2) to the free end (8) of the piezoelectric element (4).

11. MEMS transducer according to one or more of the preceding claims, Features , the at least one piezoelectric element (4) comprises several piezoelectric layers (5, 25, 35, 36), in particular between two and six, preferably four, and / or The at least one piezoelectric element (4) comprises at least one electrode layer (22, 23, 26-29), and / or The at least one piezoelectric element (4) comprises at least one isolation layer.

12. MEMS transducer according to one or more of the preceding claims, Features The MEMS transducer (1) comprises a coupling element (9), by means of which the at least one piezoelectric element (4) can be coupled to a membrane (11).

13. MEMS transducer according to one or more of the preceding claims, Features The piezoelectric element (4) and the coupling element (9) are coupled together by means of at least one elastic element (10), wherein the at least one elastic element (10) is arranged between the carrier layer (6) and the coupling element (9) in the longitudinal direction of the piezoelectric element (4).

14. MEMS transducer according to one or more of the preceding claims, Features The elastic element (10) is preferably formed exclusively by the carrier layer (6) and / or consists of the polymer or a polymer.

15. Use of a carrier layer (6) for a MEMS transducer (1), wherein the MEMS transducer (1) is formed at least as claimed in any one of the preceding claims and / or wherein the carrier layer (6) is formed as at least one of the claims.

16. A method for manufacturing a MEMS transducer (1), in particular a MEMS acoustic transducer unit, preferably for generating and / or detecting acoustic waves in the audible wavelength spectrum and / or in the ultrasonic range, The MEMS transducer (1) preferably has at least one feature of the above claims, At least one piezoelectric element (4) is arranged on the carrier (2) and is deflectable in the direction of the lifting axis (3). The piezoelectric element comprises at least two piezoelectric layers (5, 25, 35, 36) and at least one carrier layer (6), wherein an electrical signal and a deflection of the piezoelectric element (4) can be converted into one another by means of the at least two piezoelectric layers (5, 25, 35, 36). Features ， The carrier layer (6) is arranged between at least two piezoelectric layers (5, 25, 35, 36).

17. The method according to the preceding claim, Features , the oxide layer (37-40), in particular the silicon oxide layer, of the carrier layer (6) is processed by chemical mechanical polishing.

18. The method according to one or more of the preceding claims, Features The piezoelectric layer (5, 25, 35, 36) is formed on the carrier layer (6) by means of a semiconductor manufacturing method.

19. The method according to one or more of the preceding claims, Features , the piezoelectric layer (5, 25, 35, 36) is deposited on the carrier layer (6), in particular on the oxide layer (37-40).

20. The method according to one or more of the preceding claims, Features The piezoelectric layer (5, 25, 35, 36) is formed on the carrier layer (6) by means of chemical vapor deposition and / or the carrier layer (6) is formed.

21. The method according to one or more of the preceding claims, Features After the piezoelectric layer (5, 25, 35, 36) and / or the carrier layer (6) has been formed, at least one region is removed, in particular by etching.

Images