MEMS TRANSDUCER WITH INCREASED PERFORMANCE

Abstract

The invention relates to a MEMS transducer comprising a vibratable membrane for generating or receiving pressure waves in a fluid in a vertical direction, wherein the vibratable membrane is supported by a carrier and the vibratable membrane exhibits two or more vertical sections which are formed parallel to the vertical direction and comprise at least one layer of actuator material. The end of the vibratable membrane is preferably connected to an electrode, such that the two or more vertical sections can be induced to vibrate horizontally by driving the at least one electrode, or such that an electrical signal can be generated at the at least one electrode when the two or more vertical sections are induced to vibrate horizontally.

Claims

1. A microelectromechanical system (MEMS) transducer for interacting with a volume flow of a fluid comprising a carrier, a vibratable membrane for generating or receiving pressure waves of the fluid in a vertical direction, the vibratable membrane being supported by the carrier, wherein the vibratable membrane is manufactured together with the carrier in a semiconductor process, wherein the vibratable membrane exhibits two or more vertical sections formed substantially parallel to the vertical direction and comprising at least one layer of an actuator material, wherein at least one end of the vibratable membrane is connected to at least one electrode, such that the two or more vertical sections can be induced to vibrate horizontally by driving the at least one electrode or such that an electrical signal can be generated at the at least one electrode when the two or more vertical sections are induced to vibrate horizontally.

2. The MEMS transducer according to claim 1, wherein the MEMS transducer is a MEMS loudspeaker, wherein air volumes are present between the vertical sections, which, as a result of the horizontal vibrations, are moved along a vertical direction of emission to generate sound waves, or the MEMS transducer is a MEMS microphone, wherein air volumes are present between the vertical sections, which are moved along a vertical direction of detection when sound waves are received.

3. The MEMS transducer according to claim 1, wherein the two or more vertical sections comprise at least two layers, one layer comprising an actuator material and a second layer comprising a mechanical support material, wherein at least the layer comprising the actuator material is connected to an electrode, such that horizontal vibrations can be generated by a change in shape of the actuator material relative to the mechanical support material or such that horizontal vibrations cause a change in shape of the actuator material relative to the mechanical support material and generate an electrical signal.

4. The MEMS transducer according to claim 1, wherein the two or more vertical sections comprise at least two layers, both layers comprising an actuator material and each being connected respectively to an electrode, and the horizontal vibrations being able to be generated by a change in shape of one layer relative to the other layer, or the horizontal vibrations causing a change in shape of one layer relative to the other layer and generating an electrical signal.

5. The MEMS transducer according to claim 1, wherein the carrier comprises two side regions between which the vibratable membrane is arranged in a horizontal direction.

6. The MEMS transducer according to claim 1, wherein the vibratable membrane is formed by a lamellar structure or meander structure.

7. The MEMS transducer according to claim 1, wherein the vibratable membrane is formed by a meander structure with alternating vertical and horizontal sections, at least two of the horizontal sections having attached to them retaining structures which are connected directly or indirectly to the carrier.

8. The MEMS transducer according to claim 1, wherein the actuator material comprises a piezoelectric material, a polymer piezoelectrical material and/or electroactive polymers (EAP).

9. The MEMS transducer according to claim 1, wherein the vibratable membrane comprises three layers, an upper layer being formed by a conductive material, a middle layer being formed by an actuator material, and a lower layer being formed by a conductive material, wherein the conductive material of the upper and/or lower layer is preferably a mechanical support material.

10. The MEMS transducer according to claim 1, wherein the vibratable membrane comprises two layers of actuator material, which are separated by a middle layer of conductive material, wherein the middle layer is connected to a first electrode and at least one of the two layers of actuator material is connected to a second electrode via a further layer of conductive material.

11. (canceled)

12. The MEMS transducer according to claim 1, wherein the vibratable membrane is coated with a layer of a non-stick material.

13. The MEMS transducer according to claim 1, wherein the vibratable membrane supported by the carrier is arranged in a front side of a housing which encloses a rear resonant volume.

14. A manufacturing method for a MEMS transducer according to claim 1 comprising the following steps: etching of a substrate, to form a structuring, applying at least two layers, wherein at least a first layer comprises an actuator material and a second layer comprises a mechanical support material, or at least two layers comprise an actuator material. connecting of the first and/or second layer to an electrode, and etching and optional removal of the etch stop, such that a vibratable membrane is supported by a carrier formed by the substrate, the vibratable membrane comprising at least two or more vertical sections for generating or receiving pressure waves of the fluid in a vertical direction, which sections are formed parallel to the vertical direction and such that the two or more vertical sections can be induced to vibrate horizontally by driving the at least one electrode, or such that when the two or more vertical sections are induced to vibrate horizontally, an electrical signal can be generated at the at least one electrode.

15. The manufacturing method for a MEMS transducer according to claim 16 comprising the following steps: obtaining a plurality of individual piezoceramic elements comprising a sacrificial layer, a layer of conductive material, and a layer of piezoelectric material, defining holes for interlayer connection in the piezoceramic elements and metal filling, stacking the piezoceramic elements so as to obtain a stack of piezoceramic elements connected by metal bridges, and removing the sacrificial layer and insertion of the stack of piezoceramic elements into a carrier, wherein the piezoceramic elements are respectively connected to an electrode, such that a vibratable membrane is supported by the carrier, the vibratable membrane comprising at least two or more vertical sections for generating or receiving pressure waves of the fluid in a vertical direction, which sections are formed parallel to the vertical direction and such that the two or more vertical sections can be induced to vibrate horizontally by driving the at least one electrode, or such that when the two or more vertical sections are induced to vibrate horizontally, an electrical signal can be generated at the at least one electrode.

16. A MEMS transducer for interacting with a volume flow of a fluid comprising a carrier, a vibratable membrane for generating or receiving pressure waves of the fluid in a vertical direction, the vibratable membrane being supported by the carrier, wherein the vibratable membrane exhibits two or more vertical sections formed substantially parallel to the vertical direction and comprising at least one layer of an actuator material, wherein at least one end of the vibratable membrane is connected to at least one electrode, such that the two or more vertical sections can be induced to vibrate horizontally by driving the at least one electrode or such that an electrical signal can be generated at the at least one electrode when the two or more vertical sections are induced to vibrate horizontally, and wherein the vertical sections of the vibratable membrane comprise two layers, wherein a first layer consists of an actuator material, a second layer consists of a conductive support material and wherein the vertical sections are connected via horizontal metal bridges and wherein the vertical sections are respectively connected to an electrode.

17. The MEMS transducer according to claim 1 wherein the carrier is formed of a substrate selected from the group consisting of monocrystalline silicon, polysilicon, silicon dioxide, silicon carbide, silicon germanium, silicon nitride, nitride, germanium, carbon, gallium arsenide, gallium nitride, indium phosphide and glass.

18. The MEMS transducer according to claim 8 wherein the piezoelectric material is selected from a group comprising lead zirconate titanate (PZT), aluminum nitride (AlN), aluminum scandium nitride (AlScN) and zinc oxide (ZnO).

19. The MEMS transducer according to claim 13 wherein a ventilation opening is present in the housing for avoiding acoustic short circuits and/or for supporting the sound.

20. The method of claim 14, further comprising applicating an etch stop.

21. The method of claim 15, further comprising during the stacking of the piezoceramic elements a step of dicing them.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0189] FIG. 1 Diagram of a cross-section of a preferred embodiment of a MEMS loudspeaker according to the invention, (A): idle and (B): during driving.

[0190] FIG. 2 Diagram of a preferred manufacturing method for a MEMS loudspeaker with a vibratable membrane that exhibits a meander shape in cross-section. (A) An etching of the substrate 8 from a top or front side to form a structuring. (B) a layer of an etch stop 9 is applied, which may be TEOS or PECVD, for example. (C) A layer of mechanical support material 10 and a layer of actuator material 11 are applied to the etch stop 9. (D) A piezoelectric material can be used for the actuator material 11. (E) shows the preferred application of a full-surface top electrode as a layer of a conductive material 12. (F) End-side connection can be achieved, for example, by means of an electrode pad 13. (G) Further etching of the substrate 8 from the bottom side and removal of the etch stop.

[0191] FIG. 3 Diagram of a first preferred embodiment of a MEMS loudspeaker with a vibratable membrane in meander shape, the horizontal sections of which are supported by retaining structures.

[0192] FIG. 4. Diagram of a second preferred embodiment of a MEMS loudspeaker with a vibratable membrane in meander shape, the horizontal sections of which are supported by retaining structures.

[0193] FIG. 5 Diagram of a preferred embodiment of a MEMS loudspeaker with two actuator layers separated by a middle layer made of a conductive material.

[0194] FIG. 6 Diagram of preferred drive systems for operating the MEMS loudspeakers. (A) A preferred drive system for a MEMS loudspeaker with an actuator layer 11 and a passive mechanical support layer 10. (B) a preferred drive system for a MEMS loudspeaker with two actuator layers 11 separated by a middle layer of a conductive material 12, preferably metal.

[0195] FIG. 7 Diagram of a preferred integration of a MEMS loudspeaker in the front of a housing with rear resonant volume.

[0196] FIG. 8 Diagram of a preferred manufacturing method for a MEMS loudspeaker with a vibratable membrane having a meander shape in cross-section, with only the vertical sections having a layer of actuator material. (A) An etching of the substrate 8 from a top or front side to form a structuring. (B) A layer of an etch stop 9 is applied, which may be TEOS or PECVD, for example. (C) A layer of a mechanical support material 10 is applied to the etch stop 9. (D) An actuator material 11 is applied to the etch stop 9. (E) The actuator layer 11 is not connected as a continuous layer to an upper conductive layer. (F) A spacer etching of the actuator layer 11 is performed in the horizontal sections of the membrane, such that only the vertical sections of the membrane still have a layer of an actuator material 11. (G) A continuous dielectric layer 18 is then preferably applied to prevent a short circuit between the top and bottom electrodes which are to be applied later. (H) A continuous conductive layer as top electrode 12 allows front-side connection. (I) further etching of substrate 8 from the backside and optionally applying a continuous conductive layer 12 as a backside electrode. (J) further etching of substrate 8 from the underside and optionally applying a continuous conductive layer 12 as a backside electrode.

[0197] FIG. 9 Diagram of a preferred structuring of a substrate in crystal form to form deep trenches by means of a crystal orientation-dependent etching process.

[0198] FIG. 10 Diagram of a preferred manufacturing method for a MEMS loudspeaker with a vibratable membrane based on individual piezoceramic elements. (A) a plurality of individual piezoceramic elements 19 are provided comprising a layer of mechanical support material 10 (e.g. doped polysilicon) and a layer of piezoelectric material 11. (B) A sacrificial layer 20 is further applied. (C) holes are defined for interlayer connection and metal filling 21. (D) The piezoceramic elements 19 are stacked. (E) Two or more stacks of piezoceramic elements 19 are obtained, which are connected by metal bridges 21. (F) The piezoceramic elements 19 are cut (dicing 22). (G) The first and last piezoceramic elements each being connected to an electrode 13.

[0199] FIG. 11 Diagram of a preferred electrical connection of a MEMS loudspeaker with a vibratable membrane based on individual piezoceramics. (A) Top view of the MEMS loudspeaker. (B) Side view of the MEMS loudspeaker; (a) illustration of front side or upper side and rear side or lower side; (b) Parallel driving.

[0200] FIG. 12 Diagram of a preferred manufacturing method for a MEMS loudspeaker with a vibratable membrane based on individual piezoceramic elements. (A) To secure the piezoceramic elements 19, it may be preferred to use an adhesive, which is preferably first applied to recesses 27. (B) After securing the piezoceramic elements 19 in the respective recesses 27 of the lower frame 26, the adhesive can be applied to the piezoceramic elements 19 such that the upper frame secures the piezoceramic elements 19 on the upper side. (C) The composite frame 25, 26 may act as a carrier for the vertical sections 2.

DETAILED DESCRIPTION

[0201] FIG. 1 illustrates a preferred embodiment of a MEMS loudspeaker according to the invention. FIG. 1 (A) shows an idle state, while FIG. 1, (B) illustrates two phases during driving the MEMS loudspeaker.

[0202] The MEMS loudspeaker comprises a vibratable membrane 1 for generating sound waves in a vertical direction of emission, the vibratable membrane 1 being held in a horizontal position by a carrier 4. In cross-section, the vibratable membrane 1 has a meander structure with horizontal 3 and vertical sections 2. The vertical sections are formed parallel to the direction of emission and exhibit at least one actuator layer, for example a layer made of a piezoelectric material. Connection of the vibratable membrane 1 and the actuator layer is preferably achieved by means of electrodes at the ends. For this purpose, for example, an electrode pad (not shown) may be located on the carrier 4.

[0203] Preferably, the vertical sections are mechanical bimorphs which can be induced to produce horizontal vibrations as a result of appropriate driving. For this purpose, the vertical sections 2 may comprise, for example, a first layer of an actuator material and a second layer of a mechanical support material. By driving the actuator layer, a stress gradient and consequently a curvature or vibration can be generated. Likewise, it may also be preferred that the vertical sections 2 comprise two actuator layers which are driven in opposite directions in order to cause a curvature of the vertical sections 2 as a result of a corresponding relative change in shape.

[0204] FIG. 1, (B) illustrates by way of example two phases during driving. Advantageously, due to the plurality of vertical sections 2 of the vibratable membrane 1, an increased total volume can be moved in the vertical direction of emission with small horizontal movements (curvature) of a few micrometers, and thus used for sound generation. The driving allows here a particularly efficient implementation, since during one phase almost the entire air volume between the vertical sections can be moved up or down along the direction of emission.

[0205] FIG. 2 schematically shows a preferred manufacturing method for providing a MEMS loudspeaker with a vibratable membrane 1 which has a meander shape in cross-section. A vibratable membrane with a meander shape in cross-section may also preferably be referred to as a folded membrane or bellows.

[0206] FIG. 2, (A) shows an etching of the substrate 8 from a top or front side to form a structuring. In the process step, parallel deep trenches are etched into the substrate 8. The formed structure represents bellows or, in cross-section, a meander.

[0207] Subsequently, a layer of an etch stop 9 (FIG. 2, (B)) is applied, which may be TEOS or PECVD, for example. A layer of mechanical support material 10 (FIG. 2, (C)) and a layer of actuator material 11 are applied to the etch stop 9. The mechanical support material 10 can be, for example, doped polysilicon, while a piezoelectric material can be used for the actuator material 11. As layer thicknesses, 1 μm may be preferred, for example. Preferably, the piezoelectric material may have a C-axis orientation perpendicular to the surface such that a transverse piezoelectric effect is used. Other orientations and, for example, the utilization of a longitudinal effect may also be preferred.

[0208] FIG. 2, (E) shows the preferred application of a full-surface top electrode as a layer of a conductive material 12. End-side connection can be achieved, for example, by means of an electrode pad 13 (FIG. 2, (F)).

[0209] FIGS. 2, (F) and 2, (G) illustrate further etching of the substrate 8 from the rear and bottom sides, respectively, and removal of the etch stop.

[0210] The manufacturing steps 2, (A)-(G) thus result in a vibratable membrane 1 which exhibits a meander structure in cross section. Advantageously, a continuous actuator layer 11 and the provision of end-side connections 13 allow efficient driving the vertical sections 2 to produce horizontal vibrations (see FIG. 1). As can be seen in FIG. 2, (G), driving is preferably achieved by means of two electrodes, such the actuator layer 12 is preferably connected both from a front side (top electrode, conductive layer 12) and from a rear side (bottom electrode, via conductive mechanical support material 10) (see FIG. 6, (A)).

[0211] Retaining structures 14 may be provided to stabilize the membrane 1 suspended between the side walls of the carrier 4. As shown in FIGS. 3 and 4, these can preferably support horizontal sections 3 of the vibratable membrane 1. Advantageously, the horizontal sections 3 are mechanically neutral (see FIG. 1, (B)), such that no undesirable stresses are induced between the membrane 1 and the retaining structure 14 or carrier 4 during driving.

[0212] FIG. 5 illustrates a preferred alternative embodiment of a MEMS loudspeaker wherein the vibratable membrane 1 comprises two actuator layers separated by a middle layer of a conductive material 12, preferably metal. The middle layer is connected to a first end-side electrode pad 13, while in the embodiment shown the upper actuator layer 11 is connected to a second end-side electrode pad 13 via a further layer of conductive material 12.

[0213] FIG. 6 illustrates preferred drive systems for operating the MEMS loudspeakers described.

[0214] FIG. 6, (A) shows a preferred drive system for a MEMS loudspeaker with an actuator layer 11 and a passive mechanical support layer 10. Preferably, the driving is performed by means of two end-side electrode pads 13, such that the horizontal vibrations can be generated by a change in shape of the actuator material relative to the mechanical support material. The actuator layer 11 is preferably connected both from a front side (top electrode 13, conductive layer 10) and from a rear side (bottom electrode 13, conductive mechanical support material 10). For example, an AC voltage as an audio input signal can be applied to the front-side electrode pad 13 (left), while the rear-side electrode pad 13 (right) is grounded.

[0215] FIG. 6, (B) shows a preferred drive system for a MEMS loudspeaker with two actuator layers 11 separated by a middle layer of a conductive material 12, preferably metal.

[0216] An upper actuator layer 11 is preferably driven from a front side (top electrode 13 and upper conductive layer 12) and the middle conductive layer 12. A lower actuator layer 11 is preferably driven from a rear side (bottom electrode 13 and lower conductive layer 12) and the middle conductive layer 12. In the illustrated embodiment, an AC voltage can be applied as an audio input signal to, for example, the electrode pads 13 (left) used for the top and bottom, while the middle layer 12 is grounded via another electrode pad 13 (right).

[0217] FIG. 7 shows an example of a preferred integration of a MEMS loudspeaker according to the invention in a housing 15. Preferably, the vibratable membrane 1 held by the carrier 4 is arranged in a front side of a housing (sound port). The housing also encloses a rear resonant volume (back volume 16). A ventilation opening 17 can be provided to prevent acoustic short circuits or to support the sound.

[0218] FIG. 8 illustrates an alternative manufacturing method for providing a MEMS loudspeaker with a vibratable membrane 1 according to the invention. The process steps shown in FIG. 8, (A)-(D) are analogous to FIG. 2.

[0219] FIG. 8, (A) shows an etching of the substrate 8 from a top or front side to form a structuring, preferably a meander structure. In this process step, parallel deep trenches are etched into the substrate 8. The formed structure represents bellows or, in cross-section, a meander.

[0220] Subsequently, a layer of an etch stop 9 (FIG. 2, (B)) is applied, which may be TEOS or PECVD, for example. A layer of a mechanical support material 10 (FIG. 2, (C)) and an actuator material 11 is applied to the etch stop 9. The mechanical support material 10 may, for example, be doped polysilicon, while a piezoelectric material is preferably used for the actuator material 12.

[0221] In contrast to the embodiment shown in FIG. 2, the actuator layer 11 is not connected as a continuous layer to an upper conductive layer. Instead, spacer etching (FIG. 8, (F)) of the actuator layer 11 is performed in the horizontal sections of the membrane, such that only the vertical sections of the membrane still have a layer of an actuator material 11.

[0222] A continuous dielectric layer 18 is then preferably applied to prevent a short circuit between the top and bottom electrodes which are to be applied later (FIG. 8, (G)). A continuous conductive layer as top electrode 12 allows front-side connection (FIG. 8, (H)).

[0223] FIGS. 8I and 8J illustrate further etching of substrate 8 from the backside or underside and optionally applying a continuous conductive layer 12 as a backside electrode.

[0224] FIG. 9 illustrates a preferred way of providing a structured substrate 8. In a manner similar to the process step shown in FIG. 8, (A), parallel deep trenches are etched into the substrate 8. The formed structure represents bellows or, in cross-section, a meander, onto which a vibratable membrane can be applied in meander form.

[0225] The preferred provision of the structured substrate 8 in FIG. 9 is characterized by the utilization of a crystal structure of the substrate 8, wherein the trenches are formed along a lattice vector of the crystal structure.

[0226] In this way, particularly smooth, quasi-crystalline trenches with a large depth of more than 200 μm, 400 μm or more can be obtained with high-precision orientation. It is also advantageous that the surface normal of the side surfaces of the trenches is aligned with a lattice vector which is orthogonal to the lattice vector in whose direction the etching process has taken place.

[0227] For example, if silicon is used as a substrate, the silicon substrate 8 may be present as shown in FIG. 9, preferably aligned with a surface orientation of the Miller indices <110>. Preferably, therefore, the lattice vector of the crystal structure <110> is perpendicular to the surface of the still unstructured substrate. By means of an etch mask 24, for example an SiO.sub.2 hard mask, horizontal areas or stripes on the substrate surface can be defined which are not to be etched.

[0228] Smooth and precisely oriented trenches are obtained by anisotropic etching with a preferred direction along the <110> orientation of the silicon crystal, versus a <111> orientation. For this purpose, wet chemical processes can be advantageously used, which are suitable for mass production in a batch process. For example, potassium hydroxide exhibits a clear directional preference for etching along the <110> versus a <111> crystal orientation. As shown in Sato et al. 1988, the etch rate for KOH on a silicon monocrystal in <110> is 1.455 μm/min, while the etch rate in the <111> orientation is only 0.005 μm/min. Due to the anisotropic etch rates, deep trenches with a low underetch can be obtained using the wet chemical process.

[0229] For example, to form 400 μm deep trenches, KOH can be applied to a <110> oriented silicon substrate for 275 min. Due to the etch rate being reduced by a factor of 291 in the orthogonal <111> orientation, only 1.37 μm of underetching will occur during the period. Even a variation in the local strength of the underetching process, will result in orientation variations well below 1° with respect to the large depth of the trenches of 400 μm. Instead, with a high degree of accuracy, the process can achieve almost perfectly vertical deep trenches, characterized by a smooth, quasi-crystalline orientation.

[0230] As a further advantage, the thus obtained sidewalls of the trenches on which the vertical sections of the membrane are formed are in a crystal orientation (here: <111>). This circumstance facilitates a columnar growth of piezoelectric materials, such as AIN or PZT: This can ensure in a particularly precise manner that the piezoelectric material has a c-axis orientation perpendicular to the surface of the vertical sections, such that a transverse piezoelectric effect can be used for the formation of the horizontal vibrations.

[0231] FIG. 10 illustrates a preferred manufacturing method for providing a MEMS loudspeaker with a vibratable membrane based on individual piezoceramics.

[0232] Firstly, a plurality of individual piezoceramic elements 19 are provided comprising a layer of mechanical support material 10 (e.g. doped polysilicon) and a layer of piezoelectric material 11 as well as a sacrificial layer 20 (see FIGS. 10, (A) and 10, (B)). The sacrificial layer 20 may be, for example, a photoresist. Preferably, the layer of mechanical support material 10 can be electrically conductive to ensure connection. It is also possible to apply one or two layers of conductive material 12 to the one layer of piezoelectric material 11, which serve to make an electrical connection with the piezoelectric material.

[0233] Subsequently, holes are defined for interlayer connection and metal filling 21 (see FIG. 10, (C)). The piezoceramic elements 19 are stacked (FIG. 10, (D)) and cut (dicing 22, FIG. 10, (F)) such that two or more stacks of piezoceramic elements 19 are obtained, which are connected by metal bridges 21 (see FIG. 10, (E) and (F)).

[0234] After removal of the sacrificial layer 20 (FIG. 10, (F)), the stacked piezoceramic elements 19 are inserted into a carrier 4, preferably with the first and last piezoceramic elements each being connected to an electrode 13 (FIG. 10, (G)).

[0235] In this way, a vibratable membrane 1 is also obtained between a carrier 4, which comprises at least two or more vertical sections 2 for generating sound waves in a vertical direction of emission, which are formed parallel to the direction of emission and can be driven to vibrate horizontally.

[0236] The actuator principle is preferably also based here on a relative change in shape of the actuator layer 11 with respect to the mechanical support layer 10. A continuous actuator layer is not necessary for this. The connection of all vertical sections 2 by end-side driving is ensured by the metal bridges 23 in combination with conductive layers 12.

[0237] FIG. 11 illustrates a preferred electrical connection of the MEMS loudspeaker with a vibratable membrane based on individual piezoceramics.

[0238] FIG. 11, (A) is a top view and FIG. 11, (B) a side view of the MEMS loudspeaker. Individual lamellae or vertical sections are driven in parallel via the electrode pads 13, wherein u-shaped spacers are present on each side of the lamellae and create a mechanical and electrical connection to the next lamella.

[0239] FIG. 12 illustrates an alternative manufacturing method for providing a MEMS loudspeaker with a vibratable membrane based on individual piezoceramics.

[0240] Advantageously, in contrast to the embodiment according to FIG. 10 or 11, structured connection can be dispensed with in the embodiment shown. Instead, as explained below, a connection can be made by means of a continuous conductive surface from the front (front electrode) or rear (backside electrode).

[0241] In a manner similar to the manufacturing method according to FIG. 10, a plurality of individual piezoceramic elements 19 are provided comprising a layer of mechanical support material 10 (e.g. doped polysilicon) and a layer of piezoelectric material 11. Preferably, the layer of mechanical support material 10 is electrically conductive.

[0242] Furthermore, an upper frame 25 and a lower frame 26 are provided respectively having recesses or grooves 27 for receiving the piezoceramic elements 19. Preferably, the upper and lower frames are made of an electrically non-conductive material, for example a polymer. Preferably, a 3D printing process can be used to form the frames.

[0243] To secure the piezoceramic elements 19, it may be preferred to use an adhesive, which is preferably first applied to recesses 27 (see FIG. 12, (A)). After securing the piezoceramic elements 19 in the respective recesses 27 of the lower frame 26, the adhesive can be applied to the piezoceramic elements 19 such that the upper frame secures the piezoceramic elements 19 on the upper side (see FIG. 12, (B)).

[0244] For the purpose of connecting the individual lamellae or piezoceramic elements 19, a continuous layer of conductive material, preferably metal, is preferably applied (not visibly) from the front (front electrode) or from the rear (backside electrode). For example, by means of a sputtering process.

[0245] In this manner, it is also possible to obtain a vibratable membrane 1 which, for the purpose of generating sound waves in a vertical direction of emission, comprises at least two or more vertical sections 2 which are formed parallel to the direction of emission and can be induced to vibrate horizontally. The composite frame 25, 26 may act as a carrier for the vertical sections 2.

REFERENCE LIST

[0246] 1 Vibratable membrane

[0247] 2 Vertical sections of the vibratable membrane

[0248] 3 Horizontal sections of the vibratable membrane

[0249] 4 Carrier

[0250] 5 Air volumes between the vertical sections

[0251] 8 Substrate

[0252] 9 Etch stop

[0253] 10 Layer of mechanical support material, preferably doped polysilicon

[0254] 11 Layer of actuator material (actuator layer), preferably a piezoelectric material

[0255] 12 Layer of conductive material, preferably metal

[0256] 13 Connection of the electrode, preferably electrode pad

[0257] 14 Retaining structures

[0258] 15 Housing

[0259] 16 Rear resonant volume

[0260] 17 Ventilation opening

[0261] 18 Layer of dielectric material

[0262] 19 Piezoceramic element(s)

[0263] 20 Sacrificial layer

[0264] 21 Defined holes for interlayer connection with metal filling

[0265] 22 Cutting (Dicing)

[0266] 23 Metal bridges

[0267] 24 Etching mask

[0268] 25 Upper frame

[0269] 26 Lower frame

LITERATURE

[0270] F. Stoppel, C. Eisermann, S. Gu-Stoppel, D. Kaden, T. Giese and B. Wagner, NOVEL MEMBRANE-LESS TWO-WAY MEMS LOUDSPEAKER BASED ON PIEZOELECTRIC DUAL-CONCENTRIC ACTUATORS, Transducers 2017, Kaohsiung, TAIWAN, Jun. 18-22, 2017.

[0271] Iman Shahosseini, Elie LEFEUVRE, Johan Moulin, Marion Woytasik, Emile Martincic, et al. Electromagnetic MEMS Microspeaker for Portable Electronic Devices. Microsystem Technologies, Springer Verlag (Germany), 2013, pp.10. <hal-01103612>.

[0272] Bert Kaiser, Sergiu Langa, Lutz Ehrig, Michael Stolz, Hermann Schenk, Holger Conrad, Harald Schenk, Klaus Schimmanz and David Schuffenhauer, Concept and proof for an all-silicon MEMS microspeaker utilizing air chambers Microsystems & Nanoengineering volume 5, Article number: 43 (2019).

[0273] Kazuo Sato, Mitsuhiro Shikida, Yoshihiro Matsushima, Takashi Yamashiro, Kazuo Asaumi, Yasuroh Nye, and Masaharu Yamamoto, Characterization of orientation-dependent etching properties of single-crystal silicon: effects of KOH concentration, Sensors and Actuators A 64 (1988) 87-93).

[0274] Seidel, H., Csepregi, L., Neuberger, A., and Baumgartel, H. (1990). Anisotropic etching of Crystalline Silicon in Alkaline Solutions. Journal of The Electrochemical Society 137. 10.1149/1.2086277.