MEMS converter with at least one metal and one oxide layer

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 in the ultrasonic range, comprising a carrier (2) and at least one piezoelectric element (4) arranged on the carrier (2) and deflectable in the direction of a stroke axis (3), said element having at least one piezoelectric layer (5, 25, 35, 36) and at least one carrier layer (6), wherein electrical signals and deflections of the piezoelectric element (4) can be converted into one another by means of the at least one piezoelectric layer (5, 25, 35, 36). According to the invention, the carrier layer (6) comprises at least one metal layer (41-43) and at least one oxide layer (37-40). The invention also relates to a use of the structural layer (6) for MEMS transducers (1) and a method for manufacturing the MEMS transducer (1).

Description

The present invention relates to a MEMS transducer, in particular a MEMS sound transducer unit, preferably for generating and / or detecting sound waves in the audible wavelength spectrum and / or in the ultrasonic range, having a carrier and having at least one piezoelectric element which is arranged on the carrier and deflectable in the direction of a stroke axis and has at least one piezoelectric layer and at least one carrier layer, wherein electrical signals and deflections of the piezoelectric element can be converted into one another by means of the at least one piezoelectric layer.It is an object of the present invention to provide a high-performance MEMS transducer.The object is achieved by a MEMS transducer, a use of a carrier layer for a MEMS transducer and a production method of the MEMS transducer having the features of the independent claims. Advantageous or preferred embodiments are each the subject matter of a corresponding dependent claim.A MEMS transducer, preferably a MEMS sound transducer, is proposed, in particular for generating and / or detecting sound waves in the audible wavelength spectrum and / or in the ultrasonic range. The MEMS transducer can be operated as loudspeaker and / or as microphone and thus as MEMS sound transducer.The MEMS sound transducer comprises a carrier.Furthermore, the MEMS transducer comprises at least one piezoelectric element arranged on the carrier and deflectable in the direction of a stroke axis.In addition, the at least one piezoelectric element has at least one piezoelectric layer and at least one carrier layer, wherein electrical signals and deflections of the piezoelectric element can be converted into one another by means of the piezoelectric layers.Furthermore, the carrier layer comprises at least one metal layer and at least one oxide layer.It is advantageous if the piezoelectric layers are formed from scandium aluminum nitrite. Such piezo layers are very robust, which is particularly due to the scandium component, which may preferably be between 30% and 70%. It can be particularly advantageous if the scandium proportion is 30%, 40 or 50%.It is advantageous if the at least one piezo layer is arranged below or above the carrier layer in the direction of the stroke axis.It is likewise advantageous if two piezoelectric layers are arranged below or above the carrier layer in the direction of the stroke axis.It is furthermore advantageous if the metal layer is an aluminum layer. Additionally or alternatively, it is advantageous if the oxide layer is a silicon oxide layer. By means of these materials, the carrier layer can be formed by known production methods, for example by means of methods which are used in semiconductor technology. The carrier layer can consequently be produced in large quantities and / or very cost-effectively. Furthermore, the aluminum and silicon oxide layers have a comparable modulus of elasticity in the range of 70GPa. As a result, both layers have similar or almost identical deflection properties.The at least one oxide layer and / or at least one metal layer further have the advantage that they are thermally stable to high temperatures, for example up to 1200° C.-1400° C. As a result, the piezo layers and / or electrode layers can be applied by means of methods of semiconductor technology, for example a CMOS-compatible method. For example, the piezoelectric layers and / or the electrode layers can be applied by means of a CVD method (chemical vapor deposition).It is furthermore advantageous if the carrier layer comprises a plurality of metal layers and a plurality of oxide layers. The metal and oxide layers may also be alternately stacked and / or stacked. This forms a sandwich-like structure of the carrier layer. Such a carrier layer is thus a stack of a plurality of layers, preferably 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.It is advantageous if the uppermost or the lowermost layer is an oxide layer in the direction of the lifting axis. In the case of the layer-by-layer construction of the carrier layer by means of the at least one metal layer and at least two oxide layers, the uppermost and / or the lowermost layer is an oxide layer in the direction of the lifting axis. This has the advantage that the oxide layer, in particular the silicon oxide layer, has the highest temperature resistance. The piezo layer and / or the electrode layer is applied to these oxide layers, which form both the uppermost and the lowermost layer, in particular at higher temperatures. The oxide layer does not change at the higher temperatures.The oxide layer, in particular the silicon oxide layer, can also be processed in a simple manner. For example, this layer can be chemically mechanically polished. Such a method is known as chemical mechanical polishing (CMP). The oxide layer, in particular the silicon oxide layer, can thereby be formed very flat and / or planar.It provides advantages if the piezoelectric element has a length in its longitudinal direction, in particular from the carrier to a free end of the piezoelectric element, of between 0.5 mm and 2 mm.It is advantageous if the at least one piezo layer is arranged only on one side of the carrier layer in the direction of the stroke axis.Additionally or alternatively, it is advantageous if the at least one piezoelectric layer is on one side of the carrier layer in the direction of the stroke axis and the side opposite thereto is free of the at least one piezoelectric layer.It is advantageous if the at least one piezo layer is arranged between the carrier and the carrier layer, only and / or exclusively, in the direction of the stroke axis. By the described arrangement of the at least one piezoelectric layer only on one side of the carrier layer, the piezoelectric element can be produced in a simple and uncomplicated manner.It is advantageous if the at least one piezoelectric element comprises a plurality of piezoelectric layers, in particular between two and six, preferably four piezoelectric layers.An advantage results if the at least one piezoelectric element comprises at least one electrode layer. With the aid of the at least one electrode layer, the electrical signals can be exchanged, which lead to the deflection of the piezoelectric element and / or which are formed when the piezoelectric element is deflected.It is advantageous if the at least one piezoelectric element comprises at least one insulation layer.It is advantageous if the at least one piezoelectric element is formed in a sandwich-like manner from the plurality of piezoelectric layers and the electrode layers.An advantage results if the MEMS sound transducer comprises a coupling element, by means of which the at least one piezoelement can be coupled to a membrane.An improvement results if the piezoelectric element and the coupling element are coupled to one another by means of at least one spring element, wherein the at least one spring element is preferably arranged between the carrier layer and the coupling element in the longitudinal direction of the piezoelectric element.Advantages are obtained if the spring element is preferably formed exclusively by the carrier layer. As a result, the spring element can be formed in a simple manner.It is advantageous if the spring element is formed from the or a polymer, in particular from polyamide. Additionally or alternatively, the spring element has the mechanical properties of the polymer.It is advantageous if the piezoelectric element and the coupling element have the same layered construction with respect to one another.An improvement results if the carrier layer is between 5 μm and 100 μm thick. The carrier layer preferably has a thickness of less than 100 μm.Furthermore, it is advantageous if the carrier layer has an elastic modulus between 40 and 300GPa.The deflections can be increased by the above-mentioned mechanical properties of the at least one carrier layer and / or the piezo element can be shortened at an at least constant magnitude of the deflection or at an increase of the deflection.Furthermore, it is advantageous if the piezoelectric element comprises at least one compensation layer. This compensation layer can be arranged on the carrier layer and / or on the at least one piezo layer. The carrier layer can be arranged between the compensation layer and the at least one piezo layer. With the aid of the compensation layer, the neutral plane can be displaced along the stroke axis.It is also advantageous if the at least one piezo layer is arranged between the carrier and the carrier layer in the direction of the stroke axis.Furthermore, a use of the carrier layer for the MEMS transducer is proposed. The MEMS transducer has at least one feature of the preceding and / or subsequent description. Additionally or alternatively, the carrier layer has at least one feature of the preceding and / or subsequent description. In particular, the carrier layer can comprise at least one metal layer, in particular an aluminum layer, and / or at least one oxide layer, in particular a silicon oxide layer, and optionally at least one further feature connected thereto.A method for producing a MEMS transducer, preferably a MEMS sound transducer, in particular for generating and / or detecting sound waves in the audible wavelength spectrum and / or in the ultrasonic range, is also proposed. The method for producing the MEMS transducer can be carried out in such a way that the MEMS transducer is formed with at least one feature of the preceding and / or following description.In the method, at least one piezoelectric element is formed on a carrier, which piezoelectric element comprises at least two piezoelectric layers and at least one carrier layer coupled thereto.Furthermore, in the method, the carrier layer is arranged between at least two piezoelectric layers. As a result, a symmetrical structure of the piezoelectric element, in particular in the direction of the stroke axis, can be formed. As a result, advantageous deflection characteristics can be achieved.It is also advantageous if an oxide layer, in particular a silicon oxide layer, is processed by means of chemical-mechanical polishing. As a result, the oxide layer is formed flat and / or planar. The at least one piezo layer and / or an electrode layer is then applied to this flat and / or planar oxide layer.It is advantageous if the piezoelectric layers are formed on the carrier layer by means of semiconductor production methods.It is also advantageous if the piezo layers are deposited on the carrier layer. The piezo layer, at least the first piezo layer, can also be deposited on the oxide layer. All the further following piezo layers are then deposited on top of one another.It is likewise advantageous if the piezoelectric layers are formed on the carrier layer and / or the carrier layer by means of chemical vapor deposition. As a result, well-understood methods for forming the piezoelectric layers and / or the electrode layers are used. In addition, such methods can be carried out particularly easily.The metal layer, the oxide layer, the electrode layer and / or the piezo layer can be formed and / or, in particular, arranged on already existing layers using CMOS-compatible methods.Furthermore, it is advantageous if, after the formation of the piezoelectric layers and / or of the carrier layer, at least one region is removed, in particular by means of etching. With the aid of the method steps described here, the piezoelectric layers and / or the carrier layer can be built up on top of one another.It is useful if the piezoelectric layers are formed from scandium aluminum nitrite.It is furthermore advantageous if the at least one piezoelectric element is formed with a plurality of piezoelectric layers, in particular between two and six, in particular four piezoelectric layers. The performance of the piezoelectric element can be increased by means of a plurality of piezoelectric layers.Furthermore, it is advantageous if the same number of piezoelectric layers is arranged above and below the carrier layer in the direction of the stroke axis.For example, it is advantageous if two piezoelectric layers are arranged above and below the carrier layer in the direction of the stroke axis, so that the piezoelectric element comprises a total of four piezoelectric layers.It is advantageous if the at least one piezoelectric element is formed in a sandwich-like manner from the plurality of piezoelectric layers and at least one electrode layer.The plurality of piezoelectric layers and the plurality of electrode layers may be alternately stacked.Furthermore, it is advantageous if at least one insulation layer is arranged when forming the at least one piezoelectric element.It is useful if the carrier layer made of the polymer is arranged on a side of the piezo layer facing away from the carrier.An improvement results if the carrier layer made of the polymer is arranged on the at least one piezoelectric layer after the piezoelectric layer and / or a coupling element are formed and / or after the carrier, the piezoelectric layer and / or the coupling element are remachined, in particular separated from one another, in particular by etching.It is advantageous if the piezoelectric element and the coupling element are formed together in layers, this preferably taking place on the carrier.It provides advantages if, after the piezoelectric element and the coupling element have been built up layer by layer, they are separated from one another at least in sections, in particular by etching.Furthermore, a method may be performed to provide the MEMS transducer according to one or more of the preceding and / or subsequent description.Further advantages of the invention are described in the following exemplary embodiments. The following are shown: FIG. 1 shows a schematic sectional view of a MEMS transducer having a piezoelectric element composed of two piezoelectric layers and at least one carrier layer, FIG. 2 shows a schematic sectional view of the piezoelectric element with two piezoelectric layers and at least one carrier layer, FIG. 3 shows a schematic sectional view of the piezoelectric element with in each case two piezoelectric layers above and below the carrier layer in the direction of the stroke axis, and FIG. 4 shows a schematic sectional view of the carrier layer made of metal layers and oxide layers.FIG. 1 shows a schematic sectional view of a MEMS transducer 1. the MEMS transducer 1 can also be a MEMS sound transducer. By means of the MEMS sound transducer, for example, sound waves in the audible wavelength spectrum can be generated, so that the latter can be operated as a MEMS loudspeaker. With the aid of the MEMS sound transducer, sound waves in the audible wavelength spectrum can additionally or alternatively be detected, so that the latter can be operated as a MEMS microphone. The MEMS sound transducer can furthermore be arranged, for example, in a smartphone, in order to enable, for example, the telephony or the listening of music. The MEMS sound transducer can also be arranged in a headset, for example. However, pressures can also be generated and / or pressures detected by means of the MEMS transducer 1.A further field of application of the MEMS sound transducer can, however, also be the generation and / or detection of sound waves in the ultrasonic range. The MEMS sound transducer can be arranged, for example, in an ultrasonic sensor, for example a distance sensor.The MEMS transducer 1 further comprises a carrier 2, which can form a basic framework of the MEMS transducer 1. The carrier 2 may comprise, for example, a semiconductor substrate which may be produced in an etching process. The carrier 2 can be formed from silicon, for example, and / or have the shape of a wafer. In the present view, two beams 2 are shown. However, the carrier 2 can be designed as a frame, so that in this sectional view shown here the two elements of the carrier 2 shown here are contiguous. For example, the carrier 2 can be rectangular in a plan view. The top view can be oriented, for example, in the direction of a lifting axis 3 explained below. The top view can be parallel to the lifting axis 3, for example. For example, the at least one piezoelectric element 4 can face at least partially toward an interior of the carrier 2 if the carrier 2 is designed as a frame, for example.Furthermore, at least one piezoelectric element 4 is arranged on the carrier 2. The at least one piezoelectric element 4 can furthermore be coupled to the carrier 2. The at least one piezoelectric element 4 can be deflected along the stroke axis 3 shown. The at least one piezoelectric element 4 can convert electrical signals into deflections, so that the MEMS transducer 1 is operated as a loudspeaker or the sound waves can be generated. Additionally or alternatively, deflections can also be converted into electrical signals with the aid of the at least one piezoelectric element 4, so that the MEMS transducer 1 is operated as a microphone or the sound waves can be detected. However, pressures can also be generated by means of the deflections. Additionally or alternatively, pressures can also be detected, since these cause a deflection of the at least one piezoelectric element 4.The at least one piezoelectric element 4 comprises a free end 8, which can deflect along the lifting axis 3.The piezoelectric element 4 furthermore comprises at least one piezoelectric layer 5, 25, 35, 36. The at least one piezoelectric layer 5, 25, 35, 36 can convert electrical signals into deflections and / or deflections into electrical signals. The at least one piezoelectric layer 5, 25, 35, 36 can be formed from scandium aluminum nitrite (ScAlN).Furthermore, the piezoelectric element 4 comprises at least one carrier layer 6, which is coupled to the at least one piezoelectric layer 5, 25, 35, 36. At least one piezoelectric layer 5, 25, 35, 36 is arranged here between the carrier 2 and the at least one carrier layer 6. With the aid of the at least one carrier layer 6, the at least one piezoelectric layer 5, 25, 35, 36 can be stabilized. Furthermore, the at least one carrier layer 6 can be used to prevent the at least one piezoelectric layer 5, 25, 35, 36 from breaking during deflection. The at least one carrier layer 6 can also serve as a carrier layer for the at least one piezoelectric layer 5, 25, 35, 36. In this exemplary embodiment of FIG. 1, a first piezoelectric layer 5 is shown.The support layer 6 also comprises at least one metal layer 41-43 and at least one oxide layer 37-40, as shown in more detail in Fig. 4.The at least one piezoelectric layer 5, 25, 35, 36 is furthermore arranged only on one side of the carrier layer 6. According to the present exemplary embodiment, the at least one piezoelectric layer 5, 25, 35, 36 is arranged between carrier 2 and carrier layer 6 in the direction of lifting axis 3. Alternatively, the at least one piezoelectric layer 5, 25, 35, 36 can also be arranged on the carrier layer 6 on the side facing away from the carrier 2. Consequently, in this alternative exemplary embodiment, the carrier layer 6 is arranged between the carrier 2 and the at least one piezoelectric layer 5, 25, 35, 36 in the direction of the stroke axis 3.According to the present exemplary embodiment, the MEMS transducer 1 comprises a coupling element 9, with which the at least one piezoelement 4 can be coupled to a membrane 11 of the MEMS transducer 1 shown here. With the aid of the coupling element 9, the deflections of the piezoelectric element 4 can be transmitted to the membrane 11 if the sound waves are generated by means of the membrane 11 if the MEMS transducer 1 is a MEMS sound transducer. Additionally or alternatively, the deflections of the membranes 11, if the sound waves are detected with the aid of the membrane 11, can also be transmitted to the piezoelectric element 4 if the MEMS transducer 1 is a MEMS sound transducer.According to the present exemplary embodiment, the piezoelectric element 4 is coupled to the coupling element 9 by means of a spring element 10. The spring element 10 can be formed, for example, from a polymer. The spring element 10 thereby has flexibility.It is advantageous if, as shown here, a coupling plate 12 is arranged between the coupling element 9 and the membrane 11. By means of the coupling plate 12, a planar transmission of the deflections between the coupling element 9 and the membrane 12 can be achieved. According to the present exemplary embodiment, a membrane frame 13 is also shown, with which the membrane 11 can be arranged on the carrier 2.Furthermore, the at least one piezoelectric element 4 has a length 33. The length 33 is defined here 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. The piezoelectric element 4 can have this length 33 through the carrier layer 6, wherein large deflections along the stroke axis 3 are possible. The deflection of the at least one piezoelectric element 4, in particular at the free end 8, can be at least 3%, preferably at least 10%.A 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 lifting axis 3 and / or perpendicular to the layers of the at least one piezoelectric element 4 (cf. FIG. 4 ).Furthermore, the at least one piezoelectric element 4 can have at least one cutout, not shown in this figure. The at least one recess may extend at least partially between the top side 15 and the bottom side 16. The at least one cutout can extend from the upper side 15 and / or from the lower side 16 in the direction of the correspondingly opposite upper side or lower side 15, 16. With the aid of these recesses, stresses in the piezoelectric element 4 or in the at least one piezoelectric layer 5, 25, 35, 36 and / or in the at least one carrier layer 6 can be reduced.The upper side 15 here faces the membrane 11. The underside 16 faces away from the membrane 11. The terms upper side 15 and lower side 16 also define the terms above and below. The terms upper side 15 and lower side 16 and above and below refer to the direction of the lifting axis 3.Furthermore, a neutral plane 14 is shown here. The neutral plane 14 is a term from the strength gauge and is also referred to as a neutral fiber or zero line. The neutral fiber or neutral plane 14 or the zero line is the plane or line in the piezoelectric element 4 where the tensile and compressive stresses cancel out, so that no stress occurs there. Above and below, however, either tensile or compressive stresses act. The tension or compressive stress occurs, of course, only when the piezoelectric element 4 deflects. If the piezoelectric element 4 is deflected, for example, upward, i.e., in the direction away from the carrier 2, compressive stress acts in an upper region of the piezoelectric element 4 and tensile stress acts in a lower region of the piezoelectric element 4. If, on the other hand, the piezoelectric element 4 deflects downward, i.e. toward the carrier 2, the compressive stress and the tensile stress are interchanged. Neither tensile stress nor compressive stress acts in the neutral plane 14 or in the neutral layer, wherein this plane 14 or this layer is arranged between an upper side 15 and an underside 16 of the piezoelectric element 4. With the aid 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 fiber or neutral plane 14 (or layer) or of the zero line is adjusted in the height or in the direction of the lifting axis 3. Since the two piezoelectric layers 5, 25, 35, 36 are also configured identically to one another, i.e. are formed from the same material, for example AlScN, and / or have the same thickness 34, the neutral plane 14 is arranged centrally in the piezoelectric element 4 and / or in the carrier layer 6.The MEMS transducer 1 shown here has only one piezoelectric element 4. Alternatively, the MEMS transducer 1 can also have a plurality of piezoelectric elements 4, which are coupled to one or to a plurality of membranes 11.Features which are already described in the at least one preceding figure cannot be explained again for the sake of simplicity. Furthermore, features can also be described only in this or in at least one of the following figures. Furthermore, for the sake of simplicity, the same reference numerals are used for the same features. Moreover, for the sake of clarity, not all features can be shown in the following figures and / or provided with a reference sign. However, features shown in one or more of the preceding figures may also be present in this or in one or more of the following figures. Furthermore, for the sake of clarity, features can also be shown only in this figure or in one or more of the following figures and / or be provided with a reference sign. Nevertheless, features which are only shown in one or more of the following figures may also already be present in this or a preceding figure.FIG. 2 shows a more detailed schematic sectional view of the piezoelectric element 4; for the sake of clarity, the more precise structure of the piezoelectric element 4 is explained in this FIG. 2.At least two piezoelectric layers 5, 25 are shown here, wherein both piezoelectric layers 5, 25 are arranged on one side of the carrier layer 6.Furthermore, a plurality of electrode layers 22, 23, 26 are shown here. In this embodiment, three electrode layers 22, 23, 26 are shown. With the aid of the electrode layers 22, 23, 26, the two piezoelectric layers 5, 25 can be supplied with an electrical signal, so that they deflect, or the electrical signal can be dissipated when they themselves are deflected.As can be seen here, the piezoelectric layers 5, 25 and the electrode layers 22, 23, 26 are arranged alternately one above the other. A piezoelectric layer 5, 25 is arranged between each of two electrode layers 22, 23, 26.FIG. 3 shows an exemplary embodiment of the piezoelectric element 4, which comprises a carrier layer 6 and four piezoelectric layers 5, 25, 35, 36. Furthermore, five electrode layers 22, 23, 26, 27, 28 are shown. The piezoelectric layers 5, 25, 35, 36 and the electrode layers 22, 23, 26, 27, 28 are arranged alternately one above the other. The piezoelectric layers 5, 25, 35, 36 and the electrode layers 22, 23, 26, 27, 28 are arranged, in particular only, on one side of the carrier layer 6.FIG. 4 shows an exemplary embodiment of the carrier layer 6 in a sectional view. As can be seen here, the carrier layer 6 is formed from further layers 37- 43. The carrier layer 6 comprises at least one oxide layer 37- 40 and at least one metal layer 41- 43. In particular by means of the lifting axis 3 it is again clear, which means above and below.The at least one metal layer 41- 43 can preferably be formed from aluminum. Additionally or alternatively, the at least one oxide layer 37- 40 can be formed from silicon oxide. By means of these materials, the carrier layer 6 and the at least one piezoelectric layer 5, 25, 35, 36 arranged thereon can be formed using known production methods, for example by means of methods which are used in semiconductor technology, for example CMOS-compatible methods.The at least one oxide layer 37- 40 and / or at least one metal layer 41- 43 furthermore have the advantage that they are resistant to thermal to high temperatures, for example up to 1200° C. - 1400° C. As a result, the piezoelectric layers 5, 25, 35, 36 and / or the electrode layers 22, 23, 26- 29 can be applied by means of methods of semiconductor technology, for example the CMOS-compatible methods. For example, the piezoelectric layers 5, 25, 35, 36 and / or the electrode layers 22, 23, 26- 29 can be applied by means of a CVD method (chemical vapor deposition).In this exemplary embodiment, the carrier layer 6 comprises four oxide layers 37- 40 and three metal layers 41- 43, which, as can be seen here, are advantageously arranged alternately one above the other in the direction of the lifting axis 3. In the direction of the lifting axis 3, an oxide layer 37, 40 is also arranged at the top and bottom. The at least one piezo layer 5, 25, 35, 36 can be arranged on the first or fourth oxide layer 37, 40 shown here. It is advantageous if the at least one piezoelectric layer 5, 25, 35, 36 is arranged on an oxide layer 37- 40, since the oxide layer 37- 40 is temperature-resistant and can be worked well. On the side on which no piezoelectric layer 5, 25, 35, 36 is arranged, the carrier layer 6 can end with a metal layer 41- 43 or an oxide layer 37- 40.Furthermore, the oxide layer 37- 40 can also be adjoined first by an electrode layer 22, 23, 26- 29, which is then adjoined in turn by the piezoelectric layer 5, 25, 35, 36. However, this is only the case if an electrode for the piezoelectric layer 5, 25, 35, 36 is also formed as an electrode layer 22, 23, 26-29. The electrode for the piezoelectric layer 5, 25, 35, 36 can also be arranged on an end face of the piezoelectric layer 5, 25, 35, 36. Then, the piezo layer 5, 25, 35, 36 could directly adjoin the first or fourth oxide layer 37, 40.Furthermore, an electrode layer 22, 23, 26- 29 can also extend in sections between piezoelectric layer 5, 25, 35, 36 and the adjoining oxide layer 37- 40.As shown here, the oxide layers 37-40 protrude laterally beyond the metal layers 41-43. Additionally or alternatively, some, in particular all, oxide layers 37- 40 and metal layers 41- 43 can also be flush and / or congruent.As can be seen in FIG. 4, the carrier layer 6 shown here comprises four oxide layers 37- 40 and three metal layers 41- 43. Alternatively, the carrier layer 6 can also comprise only two or one oxide layers 37- 40 and one metal layer 41- 43. Furthermore alternatively, the carrier layer 6 can also comprise a plurality of oxide layers 37- 40, for example eleven, and a plurality of metal layers 41- 43, for example ten.It is advantageous if the carrier layer 6 has an oxide layer 37- 40 at the top and bottom in the direction of the lifting axis 6. Furthermore, the uppermost and the lowermost layer of the layered construction of the carrier layer 6 can be an oxide layer 37- 40. In addition, a metal layer 41- 43 is arranged between two oxide layers 37- 40 in each case. Thus, the number of oxide layers 37-40 is larger than the number of metal layers 41-43 by one.The oxide layers 37- 40 have the advantage that they can be further processed well. For example, the oxide layers 37- 40 may be processed by chemical mechanical polishing. As a result, a flat and / or planar surface is formed on the oxide layer 37- 40, on which the at least one piezoelectric layer 5, 25, 35, 36 and / or the electrode layer 22, 23, 26- 29 is then arranged. Therefore, it is advantageous if the uppermost and the lowermost layer of the carrier layer is an oxide layer 37- 40.Here, four oxide layers 37- 40 and three metal layers 41- 43 are provided to obtain a thickness 34 of the piezoelectric element 4 of about 7 μm, which is advantageous for the deflection and for the performance of the piezoelectric element 4. The number of oxide layers 37- 40 and metal layers 41- 43 and thus the thickness 34 of the piezoelectric element 4 also depends here on the length 33 of the piezoelectric element 4.List of reference characters1 MEMS transducer 2 carrier 3 lifting axis 4 piezoelectric element 5 first piezoelectric layer 6 carrier layer 8 free end 9 coupling element 10 spring element 11 membrane 12 first coupling plate 13 membrane frame 14 neutral plane 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 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

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 in the ultrasonic range, having a carrier (2) and having at least one piezoelectric element (4) which is arranged on the carrier (2) and deflectable in the direction of a stroke axis (3) and has at least one piezoelectric layer (5, 25, 35, 36) and at least one carrier layer (6), wherein electrical signals and deflections of the piezoelectric element (4) can be converted into one another by means of the at least one piezoelectric layer (5, 25, 35, 36), characterized in that the carrier layer (6) comprises at least one metal layer (41-43) and at least one oxide layer (37-40).MEMS transducer according to the preceding claim, characterized in that the piezoelectric layer (5, 25, 35, 36) is formed from scandium-aluminum nitrite, wherein a scandium proportion is between 30% and 70%, preferably 30%, 40% or 50%.MEMS transducer according to one or more of the preceding claims, characterized in that the metal layer (41-43) is an aluminum layer and / or that the oxide layer (37-40) is a silicon oxide layer.MEMS transducer according to the preceding claim, characterized in that the carrier layer (6) comprises a plurality of metal layers (41-43) and a plurality of oxide layers (37-40), which are preferably arranged and / or stacked alternately one above the other.MEMS transducer according to one or more of the preceding claims, characterized in that the at least one piezo layer (5, 25, 35, 36) is arranged on the oxide layer (37 - 40).MEMS transducer according to one or more of the preceding claims, characterized in that a piezoelectric layer (5, 25, 35, 36) is arranged below or above the carrier layer (6) in the direction of the lifting axis (3).MEMS transducer according to one or more of the preceding claims, characterized in that the at least one piezoelectric layer (5, 25, 35, 36) is arranged on only one side of the carrier layer (6) in the direction of the lifting axis (3), and / or in that the at least one piezoelectric layer (5, 25, 35, 36) and the side of the carrier layer (6) opposite thereto is free of the at least one piezoelectric layer (5, 25, 35, 36) in the direction of the lifting axis (3).MEMS transducer according to one or more of the preceding claims, characterized in that the at least one piezoelectric layer (5, 25, 35, 36) is arranged, only and / or exclusively, between carrier (2) and carrier layer (6) in the direction of the stroke axis (3).MEMS transducer according to one or more of the preceding claims, characterized in that the piezoelectric element (4) has a length (33) in its longitudinal direction, in particular from the carrier (2) to a free end (8) of the piezoelectric element (4), of between 0.5 mm and 2 mm.MEMS transducer according to one or more of the preceding claims, characterized in that the at least one piezoelectric element (4) comprises a plurality of piezoelectric layers (5, 25, 35, 36), in particular between two and six, preferably four, piezoelectric layers, and / or in that the at least one piezoelectric element (4) comprises at least one electrode layer (22, 23, 26-28), and / or in that the at least one piezoelectric element (4) comprises at least one insulation layer.MEMS transducer according to one or more of the preceding claims, characterized in that the MEMS transducer (1) comprises a coupling element (9), by means of which the at least one piezoelement (4) can be coupled to a membrane (11).MEMS transducer according to one or more of the preceding claims, characterized in that the piezoelectric element (4) and the coupling element (9) are coupled to one another by means of at least one spring element (10), wherein the at least one spring element (10) is arranged in the longitudinal direction of the piezoelectric element (4) preferably between the carrier layer (6) and the coupling element (9).MEMS transducer according to one or more of the preceding claims, characterized in that the spring element (10) is formed, preferably exclusively, by the carrier layer (6) and / or a polymer.Use of a carrier layer (6) for a MEMS transducer (1), wherein the MEMS transducer (1) is formed according to at least one of the preceding claims and / or wherein the carrier layer (6) is formed according to at least one of the claims.Method for producing 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 in the ultrasonic range, wherein the MEMS transducer (1) preferably has at least one feature of the preceding claims, in which at least one piezoelectric element (4) deflectable in the direction of a stroke axis (3) is arranged on a carrier (2), said piezoelectric element having at least two piezoelectric layers (5, 25, 35, 36) and at least one carrier layer (6), wherein electrical signals and deflections of the piezoelectric element (4) can be converted into one another by means of the at least two piezoelectric layers (5, 25, 35, 36), characterized in that the carrier layer (6) is formed as at least one metal layer (41 - 43) and at least one oxide layer (37 - 40).Method according to the preceding claim, characterized in that an oxide layer (37 - 40), in particular a silicon oxide layer, of the carrier layer (6) is processed by means of chemical-mechanical polishing.Method according to one or more of the preceding claims, characterized in that the piezoelectric layers (5, 25, 35, 36) are formed on the carrier layer (6) by means of semiconductor production methods.Method according to one or more of the preceding claims, characterized in that the piezoelectric layers (5, 25, 35, 36) are deposited on the carrier layer (6), in particular on the oxide layer (37 - 40).Method according to one or more of the preceding claims, characterized in that the piezo layers (5, 25, 35, 36) are formed on the carrier layer (6) and / or the carrier layer (6) by means of chemical vapor deposition.Method according to one or more of the preceding claims, characterized in that after the formation of the piezoelectric layers (5, 25, 35, 36) and / or of the carrier layer (6), at least one region is removed, in particular by means of etching.

Images