Patent Application
20250171295
The present application is based upon and claims the right of priority to German Patent Application No. 10 2023 133 447.6, filed Nov. 29, 2023, the disclosure of which is hereby incorporated by reference herein in its entirety for all purposes.
The present subject matter 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. The MEMS transducer has a carrier and at least one piezoelectric element, which is arranged on the carrier and is deflectable in the direction of a stroke axis and has at least two piezoelectric layers and at least one carrier layer, wherein, by means of the at least two piezoelectric layers, electrical signals and deflections of the piezoelectric element can be converted from one into the other.
A need currently exists in the art for powerful MEMS transducers.
In various aspects, the present subject matter is directed to a MEMS transducer, a use of a carrier layer for a MEMS transducer, and a method for producing the MEMS transducer having the features described and claimed herein. Advantageous or preferred embodiments are in each case the subject matter of the description and/or claims.
In one aspect, the present subject matter relates to 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. The MEMS transducer can be operated as a loudspeaker and/or as a microphone and thus as a MEMS sound transducer.
The MEMS sound transducer includes a carrier.
Moreover, the MEMS transducer includes at least one piezoelectric element, which is arranged on the carrier and is deflectable in the direction of a stroke axis.
In addition, the at least one piezoelectric element has at least two piezoelectric layers and at least one carrier layer, wherein, by means of the piezoelectric layers, electrical signals and deflections of the piezoelectric element can be converted from one into the other.
In addition, at least one carrier layer is arranged between two piezoelectric layers in the direction of the stroke axis. Therefore, at least one piezoelectric layer is arranged above the carrier layer and at least one piezoelectric layer is arranged below the carrier layer in the direction of the stroke axis. As a result, the piezoelectric element can be symmetrically formed, so that the deflection properties are improved. Additionally, this allows for the arrangement of a neutral plane, or a neutral layer, centrally in the carrier layer in the direction of the stroke axis to be easily achieved. The piezoelectric element is a cantilever arm and, when the piezoelectric element is deflected, a compressive stress and a tensile stress build up therein. The regions of the compressive stress and the tensile stress depend on whether the piezoelectric element deflects upward or downward. The compressive stresses are formed on the side, in the direction of which the piezoelectric deflects. The tensile stresses build up on the opposite side. This is a general principle of the science of the strength of materials. In a plane in the piezoelectric element, specifically in the neutral plane, or in the neutral layer, the tensile stress and the compressive stress cancel each other out and, therefore, no tension occurs at such plane/layer. The deflection properties of the piezoelectric element depend, however, on the location at which this neutral plane, or neutral layer, is located in the piezoelectric element. Due to the at least one piezoelectric layer above and below the carrier layer, this neutral plane is arranged centrally.
Moreover, due to this construction of the piezoelectric element, non-linearities in the deflection of the piezoelectric layers can automatically cancel each other out, since these occur in a symmetrical manner. Specifically, due to the one piezoelectric layer above and the other piezoelectric layer below, the non-linearities cancel each other out.
It is advantageous when the piezoelectric layers are made of scandium-aluminum nitride. Such piezoelectric layers are highly robust, which is due, in particular, to the scandium content, which can preferably be between 30% and 70%. It can be particularly advantageous when the scandium content is 30%, 40%, or 50%.
It is advantageous when one piezoelectric layer is arranged in each case below and above the carrier layer in the direction of the stroke axis.
It is useful when the same number of piezoelectric layers is arranged in each case below and above the carrier layer in the direction of the stroke axis. As a result, the symmetry of the piezoelectric element is maintained.
It is also advantageous when two piezoelectric layers are arranged in each case below and above the carrier layer in the direction of the stroke axis. As a result, the performance can be increased without there being too many piezoelectric layers present.
It is advantageous when the at least one carrier layer includes at least one metal layer, in particular one metal layer. The metal layer can also 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. By means of these materials, the carrier layer can be formed using known production methods, for example by means of methods that are used in semiconductor technology. Consequently, the carrier layer can be produced in large quantities and/or at very low cost. Moreover, the aluminum layer and the silicon oxide layer have a comparable modulus of elasticity in the range of 70 GPa auf. As a result, the two layers have similar or nearly identical deflection properties.
The at least one oxide layer and/or at least one metal layer also have the advantage that they are thermally stable up to high temperatures, for example up to 1200° C.-1400° C. Consequently, the piezoelectric layers and/or electrode layers can be applied using methods from semiconductor technology, for example a CMOS-compatible method. For example, the piezoelectric layers and/or the electrode layers can be applied using a CVD (chemical vapor deposition) method.
Furthermore, it is advantageous when the carrier layer includes multiple metal layers and multiple oxide layers. The metal layers and the oxide layers can also be arranged alternatingly one above the other. As a result, a sandwich-like construction of the carrier layer is formed. Such a carrier layer is therefore a stack including multiple layers, preferably including at least one metal layer and at least one, in particular at least two, oxide layer(s). The carrier layer can also be a structural layer.
It is advantageous when the uppermost layer and the lowermost layer in the direction of the stroke axis is an oxide layer in each case. In the layered construction of the carrier layer by means of the at least one metal layer and the at least two oxide layers, the uppermost layer and the lowermost layer in the direction of the stroke axis is an oxide layer in each case. This has the advantage that the oxide layer, in particular the silicon oxide layer, has the highest thermal stability. The piezoelectric layer and/or the electrode layer are/is applied, in particular at higher temperatures, onto this oxide layer, which forms both the uppermost layer and the lowermost layer. The oxide layer does not change at the higher temperatures.
The oxide layer, in particular the silicon oxide layer, can also be easily machined. For example, this layer can be chemically-mechanically polished. Such a method is known as CMP (chemical mechanical polishing, or chemical mechanical planarization). The oxide layer, in particular the silicon oxide layer, can thereby be made very flat and/or planar.
According to one advantageous enhanced embodiment of the present subject matter, it is useful when the at least one carrier layer is made of a polymer. The polymer can be a polyamide. By means of the at least one carrier layer made of polymer, greater deflections of the piezoelectric element can be achieved. Additionally or alternatively, a length of the piezoelectric element can also be shortened, while the deflections can be held at least constant.
It is advantageous when the piezoelectric element has a length in the longitudinal direction thereof, in particular from the carrier to a free end of the piezoelectric element, between 0.5 mm and 2 mm.
It is advantageous when the at least one piezoelectric element includes multiple, in particular between two and six, preferably four, piezoelectric layers.
An advantage results when the at least one piezoelectric element includes at least one electrode layer. The electrical signals can be exchanged by means of the at least one electrode layer, which electrical signals result in the deflection of the piezoelectric element and/or are formed when the piezoelectric element is deflected.
It is advantageous when the at least one piezoelectric element includes at least one insulation layer.
It is advantageous when the at least one piezoelectric element is formed from the multiple piezoelectric layers and the electrode layers in a sandwich-like manner.
An advantage results when the MEMS sound transducer includes a coupling element, by means of which the at least one piezoelectric element can be coupled to a diaphragm.
An improvement results when the piezoelectric element and the coupling element are coupled together by means of at least one spring element, which at least one spring element is preferably arranged between the carrier layer and the coupling element in the longitudinal direction of the piezoelectric element.
It is advantageous when the spring element is formed, preferably exclusively, by the carrier layer. As a result, the spring element can be easily formed.
It is advantageous when the spring element is made of a polymer, in particular of polyamide. Additionally or alternatively, the spring element has the mechanical properties of the polymer.
It is useful when the piezoelectric element and the coupling element have the same layered construction.
An improvement results when the carrier layer is between 5 μm and 100 μm thick. Preferably, the carrier layer has a thickness of less than 100 μm.
Moreover, it is advantageous when the carrier layer has a modulus of elasticity between 40 GPa and 300 GPa.
Due to the aforementioned mechanical properties of the at least one carrier layer, the deflections can be enlarged and/or the piezoelectric element can be shortened while the size of the deflection at least remains the same or the deflection enlarges.
The present subject matter also relates to a use of the carrier layer for the MEMS transducer. The MEMS transducer has at least one feature of the preceding description and/or the following description. Additionally or alternatively, the carrier layer has at least one feature of the preceding description and/or the following description. In particular, the carrier layer can include 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 associated therewith.
The present subject matter also relates to 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. The method for producing the MEMS transducer can be carried out such that the MEMS transducer is formed having at least one feature of the preceding description and/or the following description.
In the method, at least one piezoelectric element is formed on a carrier, which piezoelectric element has at least two piezoelectric layers and at least one carrier layer coupled thereto.
Moreover, in the method, the carrier layer is arranged between at least two piezoelectric layers. As a result, a symmetrical construction of the piezoelectric element, in particular in the direction of the stroke axis, can be formed. Consequently, advantageous deflection properties can be obtained.
It is also useful when an oxide layer, in particular a silicon oxide layer, is machined by means of chemical mechanical polishing. As a result, the oxide layer is made flat and/or planar. The at least one piezoelectric layer and/or at least one electrode layer is then applied onto this flat and/or planar oxide layer.
It is advantageous when the piezoelectric layers are formed on the carrier layer by means of semiconductor production methods.
It is also advantageous when the piezoelectric layers are deposited on the carrier layer. The piezoelectric layer, at least the first piezoelectric layer, can also be deposited on the oxide layer. All subsequent piezoelectric layers are then deposited one after the other.
It is also advantageous when the piezoelectric layers are formed on the carrier layer and/or the carrier layer is formed by means of chemical vapor deposition. As a result, well understood methods are used for forming the piezoelectric layers and/or the electrode layers. In addition, such methods can be particularly easily carried out.
The metal layer, the oxide layer, the electrode layer, and/or the piezoelectric layer can be formed, and/or, in particular on existing layers, arranged using CMOS-compatible methods.
Furthermore, it is useful when, after the piezoelectric layers and/or the carrier layer have/has been formed, at least one region is removed, in particular by means of etching. The piezoelectric layers and/or the carrier layer can be built up on each other by means of the method steps described here.
It is useful when the piezoelectric layers are made of scandium-aluminum nitride.
It is also advantageous when the at least one piezoelectric element is formed having multiple, in particular between two and six, in particular four, piezoelectric layers. By using multiple piezoelectric layers, the power of the piezoelectric element can be increased.
Moreover, it is advantageous when the same number of piezoelectric layers are arranged above and below the carrier layer in the direction of the stroke axis.
For example, it is advantageous when in each case two piezoelectric layers are arranged above and below the carrier layer in the direction of the stroke axis, such that the piezoelectric element includes four piezoelectric layers overall.
It is useful when the at least one piezoelectric element is formed of the multiple piezoelectric layers and at least one electrode layer in a sandwich-like manner.
The multiple piezoelectric layers and multiple electrode layers can be arranged alternatingly one above the other.
Moreover, it is advantageous when at least one insulation layer is included in the build-up of the at least one piezoelectric element.
It is useful when the carrier layer made of the polymer is arranged on a side of the piezoelectric layer facing away from the carrier.
An improvement results when the carrier layer made of the polymer is provided on the at least one piezoelectric layer after the piezoelectric layer and/or a coupling element have/has been formed, and/or after the carrier, the piezoelectric layer, and/or the coupling element have/has been reworked, in particular separated from one another, in particular by means of etching.
It is useful when the piezoelectric element and the coupling element are built up together in a layered construction, this preferably being carried out on the carrier.
It is advantageous when, once the piezoelectric element and the coupling element have been built up in a layered construction, these are separated from one another, at least in some sections, in particular by means of etching.
Moreover, a method can be carried out in order to provide the MEMS transducer according to the preceding description and/or the following description.
Further advantages of the invention are described in the following exemplary embodiments, wherein:
A further area of application of the MEMS sound transducer can also be that of generating and/or detecting 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 includes a carrier 2, which can form a framework of the MEMS transducer 1. The carrier 2 can include, for example, a semiconductor substrate, which can be produced in an etching process. The carrier 2 can be made, for example, of silicon and/or have the shape of a wafer. Two carriers 2 are shown in the present view of
Moreover, at least one piezoelectric element 4 is arranged on the carrier 2. The at least one piezoelectric element 4 can also be coupled to the carrier 2. The at least one piezoelectric element 4 can be deflected along the stroke axis 3 shown in
The at least one piezoelectric element 4 has a free end 8, which can deflect along the stroke axis 3.
The piezoelectric element 4 also includes 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 electrical signals into deflections and/or deflections into electrical signals. The at least two piezoelectric layers 5, 25 can also be made of scandium-aluminum nitride (ScAIN).
In addition, the piezoelectric element 4 includes at least one carrier layer 6. This is coupled to the at least two piezoelectric layers 5, 25. At least one piezoelectric layer 5, 25 is arranged 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. Furthermore, by means of the at least one carrier layer 6, the at least one piezoelectric layer 5, 25 can be prevented from breaking during deflection. The at least one carrier layer 6 can also act as a carrier layer for the at least one piezoelectric layer 5, 25.
The carrier layer 6 can be made, for example, of a polymer. The carrier layer 6 is, therefore, a polymeric carrier layer. The polymer can be a polyamide. A polymer is softer, in particular in comparison with silicon, and therefore the piezoelectric element 4 can be made smaller, while high deflections of the piezoelectric element 4 are still possible. A performance, or power, of the piezoelectric element 4 depends inter alia on the intensity of the deflection or also on the elongation. Due to the soft polymer, in particular in comparison with silicon, consistent deflections are possible in combination with smaller dimensions, in particular a shorter length, of the piezoelectric element 4.
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 greater detail in
According to the present exemplary 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 a diaphragm 11 (shown in
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 made, for example, of a polymer. The spring element 10 therefore has a flexibility.
It is advantageous when a coupling plate 12 is arranged between the coupling element 9 and the diaphragm 11, as shown in
Moreover, the at least one piezoelectric element 4 has a length 33. The length 33 is defined in this case 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. Due to the carrier layer 6, the piezoelectric element 4 can have this length 33, while 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 stroke axis 3 and/or perpendicularly to the layers of the at least one piezoelectric element 4 (cf.
Moreover, the at least one piezoelectric element 4 can have at least one recess (not shown in
The top side 15 faces the diaphragm 11 in the embodiment shown in
A neutral plane 14 is also shown in
Features that have already been described with reference to the at least one preceding figure are not explained once more for the sake of simplicity. Furthermore, features can also be first described in this figure or in at least one of the following figures. Moreover, identical reference characters are utilized for identical features for the sake of simplicity. In addition, all features may not be shown again in the following figures and/or provided with a reference character for the sake of clarity. Features shown in one or more of the preceding figures can also be present in this figure or in one or more of the following figures, however. Furthermore, features can also be shown and/or provided with a reference character first in this feature or in one or more of the following features for the sake of clarity. Nevertheless, features that are first shown in one or more of the following figures can also be already present in this figure or in a preceding figure.
The at least two piezoelectric layers 5, 25 are shown in
Furthermore, multiple electrode layers 22, 23, 26, 27 are shown in
Due to the two piezoelectric layers 5, 25, 35, 36 in each case above and below the carrier layer 6, there are three electrode layers 22, 23, 26-29 in each case above and below the carrier layer 6. One piezoelectric layer 5, 25, 35, 36 is arranged in each case between two electrode layers 22, 23, 26-29. In the direction of the stroke axis 3, there is, therefore, one electrode layer 22, 23, 26-29 on each side of each piezoelectric layer 5, 25, 35, 36. Thus, each piezoelectric layer 5, 25, 35, 36 can be supplied with the electrical signal, or it can conduct the electrical signal away.
The at least one metal layer 41-43 can preferably be made of aluminum. Additionally or alternatively, the at least one oxide layer 37-40 can be made of silicon oxide. By means of these materials, the carrier layer 6 can be formed using known production methods, for example by means of methods that are used in semiconductor technology.
The at least one oxide layer 37-40 and/or at least one metal layer 41-43 also have the advantage that they are thermally stable up to high temperatures, for example up to 1200° C.-1400° C. Consequently, the piezoelectric layers 5, 25, 35, 36 and/or the electrode layers 22, 23, 26-29 can be applied using methods from semiconductor technology. For example, the piezoelectric layers 5, 25, 35, 36 and/or the electrode layers 22, 23, 26-29 can be applied using a CVD (chemical vapor deposition) method.
In this exemplary embodiment of
Moreover, an electrode layer 22, 23, 26-29 can also extend partially between the piezoelectric layer 5, 25, 35, 36 and the adjacent oxide layer 37-40.
As is shown in
As is apparent in
It is advantageous when the carrier layer 6 has an oxide layer 37-40 above and below in the direction of the stroke axis 3. Furthermore, the uppermost and the lowermost layers of the layered construction of the carrier layer 6 can be an oxide layer 37-40. Additionally, one metal layer 41-43 is arranged in each case between two oxide layers 37-40. Therefore, the number of oxide layers 37-40 is one greater than the number of metal layers 41-43.
The oxide layers 37-40 have the advantage that they can be easily further machined. For example, the oxide layers 37-40 can be machined by means of chemical mechanical polishing. As a result, a flat and/or planar surface is formed on the oxide layer 37-40, on which surface the at least one piezoelectric layer 5, 25, 35, 36 and/or the electrode layer 22, 23, 26-29 are/is then arranged. It is therefore advantageous when the uppermost and the lowermost layers of the carrier layer are an oxide layer 37-40.
There are four oxide layers 37-40 and three metal layers 41-43 in the embodiment shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2023 133 447.6 | Nov 2023 | DE | national |
