MICROELECTROMECHANICAL LOUDSPEAKER WITH A LARGE-AREA FORCE FIELD

A microelectromechanical loudspeaker. The loudspeaker includes a substrate, a housing arranged on the substrate, and a cavity delimited by the housing and the substrate. The loudspeaker includes a translation device, which is arranged in the cavity so as to be movable and deflectable in a specified movement direction parallel to the substrate surface and includes an arrangement of a plurality of movable fin structures, which are arranged next to one another in the movement direction and divide the cavity into a plurality of portions fluidically separated from one another, and a support structure connecting the movable fin structures to one another, and a drive device designed to deflect the translation device in the movement direction, including a plurality of drive units each including least one actuator electrode mechanically connected to the translation device and at least one stator electrode mechanically connected to the housing and/or the substrate.

FIELD

The present invention relates to a microelectromechanical loudspeaker with a large-area force field.

BACKGROUND INFORMATION

The fundamental goal or the challenge of MEMS-based loudspeakers is to achieve the highest possible SPL (sound pressure level). A high SPL is associated with a high displaced air volume. At the same time, the chip surface should be kept as small as possible for cost reasons, and therefore the SPL/chip surface characteristic variable needs to be optimized or increased.

Current MEMS loudspeakers are mostly designed as planar structures, wherein a vibratable membrane is excited in such a way that the displacement and/or compression of the fluid takes place vertically to the membrane plane. The excitation of such membranes typically takes place by means of a piezoelectric or electrostatic effect. Such an embodiment is described, for example, in U.S. Patent Application Publication No. US 2021/297787. Due to the limitation of the maximum deflection of the membrane, these systems have the disadvantage that the displacement of a large fluid volume is associated with a large surface area of the membrane and therefore with the surface of the MEMS element. A further limitation of the displaceable air volume is due to the membrane that is connected or clamped to the substrate material circumferentially. Due to this circumferential clamping, the deflection amplitude of the membrane varies across the surface of the membrane (in the clamped edge region, the deflection is virtually zero, while it is typically maximum in the center of the membrane). Such an uneven deflection of the membrane surface additionally reduces the displaced air volume and also increases the harmonic distortion (THD).

In U.S. Patent Application Publication No. US 2021/297787, structures of the membrane are proposed which reduce the uneven deflection to a certain extent, or increase the surface with maximum deflection, by providing, in the membrane center, a torsion-resistant “membrane plate,” which is embedded circumferentially in the actual membrane acting as an actuator. In general, corresponding MEMS loudspeakers with such a planar structure or membrane have a fluidically effective surface, which is in principle smaller than the chip surface. That is, an increase in the air volume to be displaced is inevitably associated with an increase in the chip surface.

The related art therefore proposes concepts which do not comprise a single membrane with vibration in the vertical direction, but which comprise a plurality of laterally or horizontally movable elements, which extend in the vertical direction. The advantage here is that the displaced volume of the fluid does not only scale with the chip surface, but can also be influenced with the vertical dimension. Due to the vertical alignment and multiplication of the membranes, the fluidically effective surface area is multiplied and can be significantly larger than the actual chip surface. MEMS loudspeakers based on this basic concept are described, for example, in PCT Patent Application No. WO 2021/144400 and WO 2021/223886, and German Patent Application No. DE 10 2019 203 914, as well as in Kaiser et al. Microsystems & Nanoengineering (2019).

PCT Patent Application No. WO 2021/223886 describes a concept with which a separation of an active drive structure and a passive displacement structure is proposed, wherein the two structures are arranged one above the other (e.g., as a wafer stack). In other words: In the document, both structures (drive and displacement) are in the same region. These two structures can be mechanically connected to one another via a coupling element, so that a deflection in the active structure results in a movement of the passive displacement structure. Proposed drive structures are, for example, typical comb structures (comb-like interlocking electrode structures) which utilize the electrostatic attractive force.

PCT Patent Application No. WO 2022/117197 describes a microfluidic structural element with vertical displacement elements that is driven by stray electric fields. The displacement elements are clamped laterally on both sides. The stray electric fields are formed via electrodes which are arranged both on the bottom side of the cover substrate and on the top side of the base substrate. The electrodes are thus aligned toward the interjacent displacement structure and have the smallest possible distances to the displacement elements. The displacement elements are thus located on the end faces (top side and bottom side of the displacement elements) in the stray field of the electrodes (the stray field or the electric field between the electrodes has a directional component vertical to the surface of the electrodes and therefore parallel to the direction of extension of the displacement elements and a directional component along the deflection of the displacement elements. When the displacement elements are electrically controlled, the individual displacement element experiences an electrostatic force (acting on the top side and bottom side of the displacement structure), which causes a lateral deflection of the displacement element (due to the stray field component in the deflection direction of the displacement elements). In contrast to the concept from PCT Patent Application No. WO 2021/223886, the displacement elements do not form a passive displacement structure, but are actively controlled with an alternating voltage.

In addition to the high technological obstacle for industrial implementation, a disadvantage of this concept or drive concept of the displacer is in particular the low maximum deflection of the displacement elements; this deflection is in the range of a few micrometers (for principle-related reasons, this deflection can at most be only half the distance between the fixed electrodes). Due to this small deflection, a high SPL requires both many vertically arranged displacement elements with a small distance from one another (high periodicity) and high displacement elements in the vertical extension. Both necessities together lead to high requirements for the design (specification and tolerances) of the displacement elements, which casts technological feasibility into doubt.

The small deflection of the vertical displacement structures from PCT Patent Application No. WO 2022/117197 is in particular due to the fact that the surface of the electric force field in which a force can be exerted on the movable membrane or displacement structure is significantly limited. This also significantly limits the force for deflection. The limitation of the force field (and thus of the driving force) acting on the displacement structure is due to the fact that only the top sides and bottom sides of the vertically aligned (a few micrometers thin) displacement elements (end faces) are located in the force field (electric field). In other words, the very thin, a few micrometers wide end face of the vertically arranged displacement elements (membranes), which is located in the delimited force field of fixed, opposing electrodes, is “responsible” (so to speak) for the deflection or driving force of the entire membrane. The surfaces of the end faces are very small in comparison to the total extension of the membrane/displacement structure to be deflected and, as a result, so is the driving force. Or, in other words, the surface of the electric field in which the laterally deflectable membrane is located is small and thus also the possible driving force. A driving force that is too low results in a smaller deflection (and thus reduced output power of the loudspeaker) or else a more stringent specification with respect to the stiffness or mass of the displacement structure to be deflected. These increased requirements are inevitably associated with an increased risk with respect to industrial feasibility.

An object of the present invention is to provide an actuator structure for a MEMS-based loudspeaker concept with vertically aligned and laterally deflectable displacement structures, taking into account the technological producibility and a reduced process complexity, said actuator structure having high surface utilization for generating a large-area force field. This object may be achieved by certain features of the present invention. Advantageous example embodiments of the present invention are disclosed herein.

According to an example embodiment of the present invention, a microelectromechanical loudspeaker is provided, comprising a substrate with a substrate surface, a housing arranged on the substrate, a cavity delimited by the housing and the substrate, a translation device, which is arranged in the cavity so as to be movable and deflectable in a specified movement direction parallel to the substrate surface and comprises an arrangement of a plurality of movable fin structures, which are arranged next to one another in the movement direction and divide the cavity into a plurality of portions fluidically separated from one another, and a support structure connecting the movable fin structures to one another. Furthermore, the micromechanical loudspeaker comprises a drive device designed to deflect the translation device in the movement direction, comprising a plurality of drive units in each case comprising at least one actuator electrode mechanically connected to the translation device and at least one stator electrode mechanically connected to the housing and/or the substrate, wherein the actuator and stator electrodes assigned in each case to a drive unit are designed, when they are subjected to different electrical potentials, to generate an electrostatic force that accelerates the translation device in the movement direction. At least some of the movable drive electrodes are arranged on the support structure. Due to the accommodation of the drive electrodes on the support structure, a higher surface utilization for generating a large-area force field can be achieved and the driving force of the displacement structures can be increased. With the proposed design of the actuator structure, the active chip surface required for air displacement can thus be better utilized.

In one example embodiment of the present invention, it is provided that immovable fin structures arranged on the substrate or housing are in each case provided between two directly adjacent, movable fin structures. In this case, a gas volume that can be compressed by a movement of the movable fin structures in the movement direction is formed in each case between the movable fin structures and the immovable fin structures directly adjacent to them. This embodiment makes a particularly simple structure of the MEMS loudspeaker possible.

In a further example embodiment of the present invention, it is provided that two translation devices moving in opposite directions and comprising in each case a movable support structure and a plurality of movable fin structures arranged on the relevant support structure are provided in the cavity. The movable fin structures of the two translation devices are arranged alternately in the movement direction in such a way that a gas volume that can be compressed by a relative movement of the relevant fin structures is in each case formed between the movable fin structures of the first translation device and the movable fin structures of the second translation device. By means of this measure, a particularly large amount of gas can be displaced. This increases the efficiency of the MEMS loudspeaker.

In a further example embodiment of the present invention, it is provided that some of the actuator electrodes are arranged on the top side and/or on the bottom side of the at least one movable fin structure. This allows the surface available for the drive electrodes to be increased.

In a further example embodiment of the present invention, it is provided that the housing comprises a frame structure laterally enclosing the cavity, wherein the movable support structure is designed in the shape of a frame, in which the movable fin structures are laterally clamped. At least some of the actuator electrodes are arranged on the end faces of the support structure. Finally, the stator electrodes assigned to the relevant actuator electrodes are arranged on the inner sides of the frame structure that are arranged opposite the relevant end faces of the support structure. This allows the surface available for the drive electrodes to be increased.

In a further example embodiment of the present invention, it is provided that the housing comprises a frame structure laterally enclosing the cavity, wherein the movable support structure is designed in the shape of a frame, in which the movable fin structures are laterally clamped. Furthermore, at least some of the actuator electrodes are arranged on the outer side of the side walls of the support structure. The stator electrodes assigned to the relevant actuator electrodes are arranged on the inner sides of the frame structure that are arranged opposite the relevant side walls of the support structure. This also allows the surface available for the drive electrodes to be increased.

In a further example embodiment of the present invention, it is provided that the housing comprises a frame structure, which laterally encloses the cavity and in which the movable fin structures are laterally clamped. In a central region of the fin structures, the movable support structure interconnects the movable fin structures arranged next to one another in the movement direction. By means of this embodiment, the gas volume of the cavity can be increased.

In a further example embodiment of the present invention, it is provided that at least some of the movable fin structures on the top and/or bottom sides comprise lateral expansion structures, which extend in the movement direction and in each case comprise a plurality of actuator electrodes arranged next to one another in the movement direction. By means of such lateral expansions and the associated increase in the surface available for the arrangement of the actuator electrodes, the number of drive units can be increased. This results in a greater driving force.

In a further example embodiment of the present invention, it is provided that the actuator electrodes and the stator electrodes assigned to them in each case comprise a plurality of rail-shaped structures extending in the movement direction, wherein the rail-shaped structures of the actuator electrodes and the rail-shaped structures of the stator electrodes interlock like a comb. This allows the effective electrode surface of the drive electrodes to be significantly increased. Overall, this results in a greater driving force.

In a further example embodiment of the present invention, it is provided that the actuator electrodes and the stator electrodes are in each case planar and are arranged opposite one another and separated from one another by a defined gap. By means of this flat design of the drive electrodes and their non-overlapping arrangement, relatively large stroke movements of the translation device can be realized.

In a further example embodiment of the present invention, it is provided that the actuator electrodes and the stator electrodes are in each case arranged next to one another in the movement direction and form two interlocking, crenellated structures. With the crenellated, interlocking electrode structures, the electric field that can be used for the movable electrodes is significantly increased. The increase in the surface of the electric field results in a significant increase in the driving force.

In a further example embodiment of the present invention, it is provided that the actuator electrodes and the stator electrodes assigned to them are in each case designed in the form of a plurality of electrode plates, which are arranged one below the other in a direction perpendicular to the substrate surface and extend in parallel with the substrate surface. The electrode plates of the actuator electrodes and the electrode plates of the stator electrodes are arranged alternately in the direction perpendicular to the substrate plane and are in each case connected to one another via their own connection structure. With this meandering electrode arrangement, a particularly high increase in the surface of the force field is achieved, which is associated with a significant increase in the driving force.

In a further example embodiment of the present invention, it is provided that at least some of the actuator electrodes in each case comprise a two-dimensional arrangement of stamp electrodes extending in the movement direction and connected to one another via a connection structure. The stator electrodes assigned to the relevant actuator electrodes in each case comprise an arrangement of correspondingly shaped hole electrodes, wherein each hole electrode is designed to receive the stamp electrode assigned to it. Due to the further segmentation of the electrode structure perpendicular to the substrate surface, a further significant increase in the surface of the force field is achieved. This results in a further increase in the driving force.

In a further example embodiment of the present invention, it is provided that the stamp electrodes in each case have a cross-sectional profile with expansions extending perpendicularly to the movement direction. The hole electrodes assigned to these stamp electrodes have a cross-sectional profile adapted to the cross-sectional profile of the stamp electrodes. By means of such expansions, the effective electrode surface can be significantly increased. This is associated with a significant increase in the force field and thus also in the resulting driving force.

In a further example embodiment of the present invention, it is provided that the cross-sectional profile of the stamp electrodes is designed in the shape of a double-T-beam or cross. These two cross-sectional profiles are associated with a significant increase in the electrode surface and thus allow a significant increase in the force field and the driving force achievable thereby. At the same time, these cross-sectional profiles can be realized particularly simply by means of the processes used to produce microelectromechanical structures.

Finally, in a further example embodiment of the present invention, it is provided that the support structure comprises a displacement support, which connects the movable fin structures of the translation device to one another, and a drive support, which is mechanically connected to the displacement support and connects the actuator electrodes of the translation device to one another. Due to the spatial separation of the displacement structures and the drive structures, particularly efficient drive devices can be realized.

The present invention is explained in more detail below with reference to figures.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

The present invention disclosed herein provides an actuator structure or translation device for a MEMS-based loudspeaker concept with vertically aligned and laterally deflectable displacement structures, the actuator structure or translation device having a high surface utilization for generating a large-area force field. The entire actuator structure, as a sum of all substructures, comprises a large-area electric field, i.e., the surface perpendicular to the electric field, which is aligned in parallel with the movement direction of the membrane or displacement structure and in which an assigned counter electrode experiences an electrostatic force. The translation device for generating the large-area force field, which does not necessarily have to be continuous, is not or only insignificantly associated with an increase in the chip surface. Rather, the proposed design of the actuator structure optimally utilizes the active chip surface required for air displacement.

Furthermore, the feasibility or simplicity of the production process in terms of process technology is ensured in that a largely planar design of the actuator structure is proposed in one exemplary embodiment. A concept that can be realized with a planar technology based on layer deposition is advantageous over a concept that necessarily requires deep structuring technology.

Due to the actuator concept proposed here, which includes an actuator arrangement or translation device and an actuator method, the total, added-up surface of the electric field is maximized. This refers to the component of the electric field with a field direction parallel to the movement direction, since only this component of the electric field can be used for an electrostatic force in the movement direction. In this respect, the term “surface” is understood to mean the surface that is perpendicular to these electric field lines. The surface of the force field is maximized by a multiple arrangement of drive structures, comprising fixed electrodes (stator electrodes) and movable electrodes (actuator electrodes).

Exemplary MEMS structures, in which the actuator concept according to the present invention with a large-area actuator arrangement for a large-area force field is realized in different ways, are described below. The MEMS loudspeaker concept described comprises vertically extended, deflectable and laterally movable fins, or fin structures, which serve as displacement elements for displacing air.

In the following exemplary embodiments, the immovable electrodes for generating a static electric field (stray electric field) are, by way of example, arranged fixedly on the cover wafer or base wafer, while the movable electrodes are mechanically connected to the movable fin structures and generate an alternating electric field that interacts with the static electric field. In principle, however, this arrangement can be designed the other way around, wherein the movable electrodes mechanically connected to the fin structures serve to generate a static electric field, while the immovable electrodes arranged fixedly on the cover wafer or base wafer generate the alternating electric field.

FIG.1shows a cross-section of a MEMS loudspeaker100with two laterally movable fin structures160.2,160.3with a relative movement with respect to a fixed wall or fin structure.

The dashed frame illustrates the drive principle with two fixed drive electrodes (stator electrodes)173.1,173.2, each of which is subjected to a different electrical potential, for generating an electric field, in which the movable drive electrode (actuator electrode)180, which is mechanically connected at the end face to the movable fin structure160, experiences a laterally aligned force in or counter to the movement direction x. An alternating potential is applied to the movable actuator electrode180, so that this electrode180experiences a directional, laterally aligned force in the static (stray) electric field of the fixed stator electrodes173.1,173.2. Each actuator electrode180, together with the stator electrodes173.1,173.2assigned to it, forms a separate drive unit172.5,172.6in each case.

In addition to this electrode arrangement, a support structure151serving as a frame or shuttle is provided, which moves with the fin structures160. In the present embodiment, the support structure151has the shape of a frame, in which the movable fin structures160are laterally clamped.

Additional movable electrodes180are arranged on the top and bottom sides154,155of the support structure151and, with immovable electrodes173.1,173.2arranged correspondingly opposite on the surface111of the substrate wafer110and on the bottom side132of the cover structure (cover wafer)130, form additional drive units172.1,172.2. The additional drive units172.1,172.2cause an increase in the surface of the force field.

FIG.2shows a plane section of the MEMS loudspeaker ofFIG.1parallel to the substrate surface111at the height of the stator electrodes173.1,173.2arranged on the cover structure. Here, it can be seen that the frame-like shape of the support structure151comprises two longitudinal portions159.1,159.2aligned in the movement direction x and two transverse portions159.3,159.4extending transversely to the movement direction x. The support structure151is arranged in a cavity140laterally enclosed by a frame structure135forming the chip frame of the housing130and is fastened to the housing130and in particular to the frame structure135and/or to the substrate110via suitable elastic spring structures (not shown here) so as to be deflectable in the movement direction x. The fin structures1601up to1605are clamped between the two longitudinal portions159.1,159.2, wherein the outer fin structures1601and1605simultaneously form the transverse portions159.3,159.4of the support structure151. The fin structures160.1to160.5divide the cavity140into four separate partial cavities141. In each of these partial cavities141, a fixed wall123is arranged, which is designed in the form of a fin structure mechanically clamped between the substrate111and the cover structure131and by means of which the relevant partial cavity141is divided into two fluidically separated partial volumes141.1,141.2in each case. Due to this arrangement, when the translation device150moves in the movement direction x, the gas volume arranged in a partial volume141.1reduced by this movement is compressed, while the gas volume contained in the relevant complementary partial volume141.2simultaneously expands, and vice versa. When the translation device151moves in the opposite direction, the previously compressed gas volumes expand, while the previously expanded gas volumes are compressed. When a gas volume is compressed, the corresponding gas escapes through a ventilation opening102,103assigned to the corresponding partial volume141.1,141.2within the substrate111or the cover structure131. Conversely, when a gas volume expands, the gas flows through the corresponding ventilation opening102,103into the corresponding partial volume141.1,141.2.

FIG.3shows a cross-section of the MEMS loudspeaker ofFIGS.1and2in a second sectional plane, which runs along the ventilation opening102and is indicated inFIG.2by means of a second dot-dashed line. As indicated here, the gap between the actuator electrodes180arranged on the top side154of the support structure151and the fin structure160and the stator electrodes173.1,173.2arranged on the bottom side132of the cover structure131preferably has the smallest possible width, in order to achieve the best possible fluidic separation of adjacent partial volumes. The small gap width also makes better electrostatic interaction between the complementary drive electrodes possible, which is associated with a higher force effect.

Furthermore, it can be seen inFIG.3that the cover structure131can comprise suitable reinforcement structures134, which increase the stability of the MEMS structures, in the region of the ventilation openings102.

As an alternative to the design of the MEMS loudspeaker100shown inFIG.2, in which the movable fin structures160are clamped in a frame-shaped support structure151, translation devices150with internal support structures151can also be realized.FIG.4shows a corresponding exemplary embodiment, wherein it can be seen that the support structure151arranged in a central region of the cavity140and connecting the fin structures160to one another is, in each case, mechanically connected to the relevant fin structures in a central portion of the movable fin structures160. Furthermore, it can be seen that the individual fin structures160are clamped in the frame structure135. In order to allow a relative movement of the fin structures relative to the rigid frame structure135, the relevant fin structures160must have sufficiently high elasticity at least in the portions directly adjacent to the frame structure135. Alternatively, it is however also possible to mechanically connect the movable fin structures160to the frame structure135via special elastic coupling elements (not shown here). In a further alternative embodiment, the fin structures can also be formed without a direct mechanical connection to the frame structure135. In this case, the support structure151can be mechanically fastened to the housing130(in particular to the frame structure135) and/or to the substrate110by means of suitable elastic coupling elements.

As can also be seen inFIG.4, the immovable fin structures123, in each case arranged between two directly adjacent, movable fin structures160, are constructed in two parts in this embodiment, wherein each of the two portions123.1,123.2separated from one another by the support structure151is in each case fastened on one side to the frame structure135. In the event that the support structure151does not extend over the entire height of the movable fin structures, the immovable fin structures123.1,123.2can also be connected to one another by a central portion not shown here. In this case, the immovable fin structures can comprise a suitable opening for the support structure151(not shown here).

The substantial difference between the embodiment variant shown inFIG.4and the concept shown inFIG.2is substantially the internal support structure or shuttle structure151. The fin structures160are integrated on both sides not in a frame-shaped support structure151, but directly in the frame structure135(chip frame). The internal support structure151does not have to be formed over the entire height (like the support structure inFIG.2, for example). Rather, this support structure135can be designed only as a mechanical coupling structure which is mechanically connected at the end face to the fin structures160and thus mechanically couples the fin structures160to one another. Here as well, in addition to the force field in the end-face region of the fin structures160, the surface for generating the force field is increased by also utilizing the surface of the support structure151for accommodating further drive units172.1.

FIG.5shows a cross-section through the MEMS loudspeaker structure100ofFIG.4. It can be seen that the structure and thus also the function of a functional unit formed between two directly adjacent, movable fin structures160substantially correspond to the first embodiment shown inFIG.2.

While a single gas volume is always compressed in the above-described exemplary embodiments by a movement of a movable fin structure relative to a fixed fin structure serving as a rigid wall, a corresponding gas volume in the embodiment shown inFIG.5is achieved by an opposite movement of two independently deflectable translation devices151.1,151.2. The two translation devices150.1,150.2substantially correspond to the translation device150.1shown inFIG.4with internal support structures151, although no fixed walls are introduced here, but rather two adjacent fin structures160move relative to one another.

As can be seen inFIG.6, which shows a plane section of the MEMS loudspeaker100ofFIG.5parallel to the substrate surface111at the height of the stator electrodes173.1,173.2arranged on the cover structure, the movable fin structures160.1,160.3,160.5,160.7and160.9are assigned to the first translation device150.1and are connected to one another by a first support structure151.1, while the movable fin structures160.2,160.4,160.6,160.8and160.10are assigned to the second translation device150.2and are connected to one another by a second support structure151.2. Due to this arrangement results, an offset of the two translation devices150.1,150.2is produced in the movement direction x. The two support structures151.1,151.2are mechanically decoupled from one another in order to make movement of the two translation devices150.1,150.2in opposite directions possible. For this purpose, the movable fin structures160.2,160.4,160.6,160.8and160.10have suitable recesses or openings163, through which the support structure151.1of the first translation device150.1protrudes. Analogously, the movable fin structures160.3,160.5,160.7and160.9have corresponding recesses or openings163, through which the support structure151.2of the second translation device150.2protrudes.

In order to ensure sufficient movement of the two translation devices, the fin structures160.1to160.10can be designed to be elastic. This elasticity can in particular be particularly pronounced in the outer portions of the fin structures that are adjacent to the frame structure135. Alternatively, it is however also possible to mechanically connect the movable fin structures160to the frame structure135via special elastic coupling elements (not shown here). In a further alternative embodiment, the fin structures160can also be formed without a direct mechanical connection to the frame structure135. In this case, the support structure151can be mechanically fastened to the housing130(in particular to the frame structure135) and/or to the substrate110by means of suitable elastic coupling elements (not shown here).

In order to further increase the driving force, it may be useful to increase the surface of the force field achieved by the drive electrodes. This can advantageously be achieved by increasing the number of drive electrodes. If there is no longer enough free space available for accommodating the electrodes on the translation device, the movable fin structures and/or the movable support structures can be equipped with lateral expansion structures.FIG.7shows a cross-section of an advanced design of the embodiment described in connection withFIG.2. On their top and bottom sides, the movable fin structures160.1to160.5have additional planes, in which corresponding lateral expansion structures164are formed. Through a suitable structuring of the additional planes on the end faces of the fin structures160.1to160.5, a type of canopy is in each case realized, on which the electrodes are arranged in a planar manner. With this measure, the surface of the force field can now be significantly increased. As can be seen inFIG.7, the lateral expansions164.1on the top side of the fin structures160.1to160.5can extend in the movement direction x, while the lateral expansions164.2on the bottom side of the fin structures160.1to160.5extend in the opposite direction. In this way, the symmetry of the partial volume portions can be maintained.

FIG.8shows a plane section of the MEMS loudspeaker100ofFIG.7parallel to the substrate surface111at the height of the stator electrodes173.1,173.2arranged on the cover structure. The sectional plane ofFIG.7is indicated by a dot-dashed line. Here, it can be seen that the lateral expansions164, in particular in the regions above and below the partial volumes141, result in a significant increase in the total electrode surface.

FIG.9shows a further possible embodiment of the MEMS loudspeaker100, in which the side surfaces of the frame structure135and the support structure151are utilized to increase the force field. As can be seen in this cross-sectional view of the MEMS loudspeaker100, the side walls156of the support structure151along the movement direction x and the inner sides136of the frame structure135that are opposite them can be formed with alternating electrode arrangements173.1,173.2,180, so that these surfaces136,156also contribute to the increase in the surface of the force field.

FIG.10shows a plane section of the MEMS loudspeaker100ofFIG.9parallel to the substrate surface111at the height of the stator electrodes173.1,173.2arranged on the cover structure131. The dot-dashed line illustrates the sectional plane ofFIG.9. It can be seen that the actuator electrodes180arranged on the two side walls156.1,156.2of the frame-shaped support structure135and the stator electrodes173.1,173.2arranged opposite them on the two inner sides136.3,136.4of the frame structure135in each case form corresponding drive units172.3, which are preferably arranged along the entire length of the side walls156.1,156.2of the frame-shaped support structure151.

Additionally or alternatively, the end-face side surfaces156.1,156.2of the support structure151with respect to the movement direction x can furthermore also be designed as electrodes of a parallel plate capacitor. By applying a corresponding potential to the electrodes, an attractive force can in each case be generated at one of the two end faces.FIG.10shows two corresponding drive units172.4, in each case comprising an actuator electrode180arranged on an end face157.1,157.2of the support structure151and a stator electrode173arranged on an inner side136.1,136.2of the frame structure135that faces the relevant end face157.1,157.2.

FIG.11shows an alternative design of the electrodes for a further increase in the surface of the electric field, with the drive electrodes interlocking in a crenellated shape. In the embodiments described above, the MEMS loudspeakers have planar electrode structures. Due to the planar design of the drive electrodes180,173in the movement direction x, the (stray) electric field that can be used by the relevant counter electrode and is located between the relevant actuator electrode and stator electrode is very weak, since it depends, among other things, on the distance between the movable electrode and the fixed electrode. With the crenellated, interlocking electrode structure shown inFIG.11, this electric field (field lines parallel to the movement direction in the region of the movable electrode) that can be used for the movable actuator electrode180is significantly increased. In principle, the crenellated design of the electrodes (fixed and movable) can be combined with all previously presented options.

In order to maximize the driving force of the MEMS loudspeaker, the surface of the force field realized between the complementary drive electrodes can be increased by a special design of these electrodes.FIG.12, by way of example, shows a modified drive unit, in which the effective electrode surfaces are increased in that the complementary electrodes (fixed and movable)173,180comprise rail-shaped structures174,181, which interlock like a comb. The movement direction x is in the image plane in this cross-sectional drawing, so that the electrode structure172.1formed by the actuator electrode180and stator electrode173can also be considered as a rail (or “railway”).

The concept of the comb-like interlocking electrodes can in principle also be realized with electrode structures that are arranged in parallel with the substrate surface111. The following figures show further exemplary MEMS structures within the meaning of the present invention. Here, the actuator concept according to the present invention is also to be realized with a large-area actuator arrangement for a force field that has a surface as large as possible. As already described in connection withFIGS.1to11, a drive device or actuator device is to drive one or more displacement elements separated therefrom, with fin structures that extend in the vertical direction and are deflectable in the movement direction x and laterally movable. The concept described below focuses on the design of the drive. The fin structures serving as displacement elements can be supplemented in the following embodiments analogously to the above-described embodiments.

The arrangement shown in theFIG.13can, for example, be a more advantageous design of the drive devices170shown inFIG.2or4. The basic principle is a multiplication (here vertical) perpendicular to the movement direction x of the electrode structures used in principle inFIG.2or4, so that, in combination with a segmentation of the individual drive electrodes173,180along the movement direction x, a multiplication of the sum of all forces generated by the drive in the movement direction x can be achieved. This advantage can be particularly well exploited if the drive device170is spatially separated from the actual displacement structures160. The force transfer is realized via a displacement support152which serves as a shuttle for the movable displacement elements160and is mechanically connected, on the one side, to the drive support153likewise serving as a shuttle for the actuator electrodes180and, on the other side, to the individual movable fin structures160serving as displacement elements. The drive support153concentrates the tensile force of all drive units fastened thereto onto the displacement support152and causes a rectification over its entire lateral extension.

The drive principle corresponds to the drive unit172.1(marked with a dashed frame) described in connection withFIG.1. Each drive unit172preferably comprises two fixed electrodes (stator electrodes)173.1,173.2for generating an electric field and a movable electrode (actuator electrode)180, which experiences a laterally aligned force in the electric field and transfers this force to the movable fin structures mechanically connected at the end face. In contrast to the embodiments already described, the fin structure160(displacement element) mechanically connected at the end face inFIG.2is replaced by a structure, which serves as a drive support153and moves bidirectionally between the two stator electrodes173.1,173.2.

The above-described arrangement is now improved in that the drive unit formed from the actuator electrode180and stator electrode173is multiplied vertically in this way. Perpendicularly to the movement direction x, this generates a meander structure, which is directly associated with an increase in the surface of the force field. The result is the 2D comb actuator shown inFIG.13. The multiplication can be realized technologically via a layer stacking technique commonly used in semiconductor manufacturing, e.g., by means of a sequence of poly-Si deposition, trench, sacrificial oxide, oxide structuring, poly-Si, etc.

As can be seen inFIG.13, each stator electrode173.1,173.2comprises electrode plates176, which are arranged one above the other in the vertical direction z and are mechanically and electrically connected to one another by means of connection structures177arranged therebetween in each case. The actuator electrode180also comprises electrode plates184, which are correspondingly arranged one above the other and are mechanically and electrically connected to one another by means of connection structures186arranged therebetween in each case. The electrode plates177,184are in each case arranged offset from one another in the vertical direction z, such that the electrode plates184of the actuator electrode180can move back and forth between the electrode plates176of the stator electrodes173.1,173.2in the movement direction x.

As can also be seen inFIG.13, the stator electrodes173.1,173.2can in each case be suitably segmented in the center in such a way that a movement of the connection structures186of the actuator electrode180in the movement direction x between the two segments175.1,175.2of the stator electrodes173.1173.2can take place without hindrance.

As can also be seen inFIG.13, the actuator electrode180is fastened together with further actuator electrodes to a common drive support153, which is mechanically connected, for example by means of a suitable coupling structure158(here only indicated by the dashed line), to a displacement support152located above or below it.

FIG.14shows a plan view of an embodiment with two drive supports153.1,153.2moving in opposite directions to one another. Each of the drive supports153.1,153.2is mechanically connected to a corresponding displacement support (not shown here) via a coupling structure158(also not shown here). The two drive supports153.1,153.2can be suspended via suitable spring structures190in the chip frame, wherein the electrical potential can then also be applied to the actuator electrodes180via the spring structures190. The two drive supports152.1,152.2in each case comprise two portions159.1,159.2, which extend in the movement direction x and between which actuator electrodes180are in each case clamped. In the following exemplary embodiment, the actuator electrodes180have a vertical arrangement, which is analogous to the embodiments shown inFIG.13and comprises a plurality of electrode plates184electrically connected to one another. As indicated by the dashed lines, the electrode plates184of the actuator electrodes180in each case extend between the electrode plates176of the stator electrodes173.1,173.2, which are likewise designed in the form of a vertical arrangement of a plurality of electrode plates.

FIG.15illustrates a further, particularly advantageous embodiment with respect to increasing the surface of the force field. On the basis of the electrode arrangement ofFIG.13, a further segmentation of the electrode structure is formed perpendicularly to the vertical multiplication direction z. Due to the vertical connections177between the electrode plates176of a stator electrode173, stator hole electrodes178are created. Complementarily thereto, suitable actuator electrode stamps185, which can be countersunk electrostatically bidirectionally into the relevant electrode holes178of the complementary stator electrode173, are created fromFIG.13by segmentation of the electrode plates184of the actuator electrode180perpendicular to the movement direction x and perpendicular to the multiplication direction z. This results in a 3D comb actuator172that can deliver many times the force of a classic in-plane comb actuator. In addition, this structure in principle provides the technological potential to further increase the generated force by reducing the horizontal and vertical electrode gaps (F˜1/d) between the stamp electrodes185and the hole electrodes178.

FIG.16shows the design of a drive device170with two drive supports153.1,153.2moving in opposite directions to one another, in each case with a plurality of drive units172ofFIG.15in the plan view (left side) and in four cross-sections (right side) perpendicular to the movement direction x. The vertical sequence of the electrode structures makes a 2-periodic interlocking of the drive shuttle structure possible, so that bidirectionality can be implemented within the drive plane by two drive supports (shuttles)153.1,153.2moving in opposite directions. The drive supports152.1,152.2can be suspended via suitable spring structures190in the chip frame, wherein the electrical potential can in this case also be applied to the actuator electrodes180via the spring structures190.

FIG.17illustrates the advantage of the particular design, shown inFIGS.15and16, of the drive electrodes in the form of stamp electrodes and hole electrodes. Shown is a detailed representation of the second cross-section ofFIG.16, in which the stamp electrodes185are arranged within the hole electrodes178. A unit cell (marked with a dashed line) of the electrodes ofFIG.16is compared to a corresponding electrode region of the embodiment shown inFIG.14. It can be seen that the loss, associated with the vertical segmentation, of the horizontal electrode surfaces with width E in the 2D comb actuator ofFIG.14is overcompensated by a gain of vertical electrode surfaces with height F, since the distance F is greater than the distance E. This leads to a further increase in the force surface. It is also apparent that the effective electrode surface of the stamp electrodes185and the associated hole electrodes178becomes the larger, the higher the relevant electrodes are designed. Depending on the design and technological possibilities, this effect can be further increased if the width of the vertical gaps between the stamp electrodes185and the vertical side walls of the hole electrodes178and the vertical webs between the hole electrodes178are reduced.

FIG.18illustrates a further possibility for increasing the driving force by way of example. In this case, the effective surface of the force field is increased in that the profile of the stamp electrode185is shaped by additional planes in such a way that new surfaces for the effective force field are created. For example, an additional effective electrode surface between the two complementary drive electrodes can be created by a meandering interlocking of the stamp electrodes184and the hole electrodes178. In the present example, the stamp electrode185of the actuator electrode180has a cross-sectional profile in the shape of a double-T-beam. The associated hole electrode178of the stator electrode173has a cross-sectional profile correspondingly adapted to the stamp electrode185. In principle, however, differently shaped cross-sectional profiles of the electrodes are also possible, with which the effective electrode surface and thus also the electric field between the complementary drive electrodes can be increased in a suitable manner.

The concepts illustrated inFIGS.13to18for increasing the effective electrode surface make it possible to deliver a significantly higher force per chip surface in comparison to a classic in-plane comb drive. Even in an embodiment with only two repetitions of the proposed actuator planes, the segmented electrode structures deliver between 65% and 135% more force per chip surface in comparison to a standard comb drive. The embodiments ofFIGS.13and15make it possible to reduce horizontal or vertical gaps and the structure widths of the actuator layer thickness and web width through technological improvement and thus to generate a further multiplication of the surface of the force field per chip surface. In contrast, the classic in-plane comb drive is not believed to have this technological evolution potential, since an increase in the comb layer thickness (actuator and stator) is generally associated with an increase in the gaps.

Although the present invention has been illustrated and described in detail by the preferred exemplary embodiments, the present invention is not limited to the disclosed examples. Rather, other variations can also be derived therefrom by a person skilled in the art without departing from the scope of the present invention.