MEMS comprising a comb drive, and method for producing same

Abstract

The invention relates to a MEMS comprising a comb drive with a first finger structure, comprising a first plurality of electrode fingers, and a second finger structure, comprising a second plurality of electrode fingers, which form an interlaced arrangement relative to one another parallel to a substrate plane of the MEMS. The comb drive is designed to provide a translational relative movement between the first finger structure and second finger structure on the basis of an electrostatic force in order to change the distance between the first finger structure and the second finger structure parallel to the substrate plane. The first plurality of electrode fingers and the second plurality of electrode fingers are curved perpendicularly to the substrate plane.

Description

[0001] MEMS with a comb drive and method for manufacturing the same

[0002] Description

[0003] The present invention relates to a MEMS with a comb drive having curved electrode fingers. The present invention further relates to a method for manufacturing such a MEMS and, in particular, to a comb drive with optimized nonlinear behavior.

[0004] Microelectromechanical systems (MEMS) can be implemented for actuator and / or sensor operation, among other things. For actuator operation, force elements can be provided that provide a force to generate a signal and / or a movement. For example, movement within a MEMS can be provided by a comb drive, in which electrode fingers of relatively movable finger structures interlock, and an electrostatic force is generated between the finger structures based on electrostatic forces to provide the relative movement.

[0005] The use of such a comb drive is described, for example, in WO 2021 / 223886 A1, see, for example, Figs. 12a-d. This document describes a space-efficient MEMS.

[0006] WO 02 / 19509 A2 describes a comb drive arrangement with comb drive fingers with irregular cross-sections, which increases the ratio of drive force per applied voltage. The increase in drive force due to the geometry of the comb drive fingers is achieved without the need to increase the voltage. Comb drive fingers can be designed as wedge-shaped structures in plan view; moreover, the comb drive fingers have frustoconical structures in plan view. A disadvantage is that no change in the counterforce due to the movement caused by the finger forces is taken into account; in other words, the force curve is continuous but is not adapted to a characteristic curve of the counterforce.

[0007] US 2016 / 268927 A1 describes a comb drive device with non-parallel comb fingers, which is said to be suitable for linearizing the capacitance between corresponding comb finger gaps during an arcuate movement. A disadvantage is that no change in the counterforce due to the movement caused by the finger forces is taken into account and is not adapted to the counterforce characteristic curve.

[0008] DE 10 2017 206 183 A1 describes rectangular comb actuators as MEMS actuators. The disadvantage of this structure is that the shape of the finger does not influence the force characteristics.

[0009] US 2013 / 009716 A1 describes a MEMS resonator with comb electrodes. Here, too, the finger shape is not coordinated with the force characteristics.

[0010] The disadvantage of previously known solutions is that the stiffness of the deformable elements is nonlinear with respect to the transmission behavior. In an exemplary audio application of MEMS, these nonlinearities generate higher harmonics under harmonic excitation, which lead to unfavorable distortion of the audio signal.

[0011] MEMS with comb drives that show a linearized behavior of the force-deflection curve would therefore be desirable.

[0012] An object of the present invention is therefore to provide a MEMS and a method for manufacturing the same, in which a comb drive has a linearized relationship of a force-displacement curve.

[0013] This problem is solved by the subject matter of the independent patent claims.

[0014] A key idea of ​​the present invention is to provide a comb drive for a translational movement, in which electrode fingers of both intermeshing finger structures are curved in plan view, i.e. parallel to the substrate plane of the MEMS. The respective curvatures make it possible to adapt the force-deflection behavior. Unlike in WO 02 / 19509 A2 and US 2016 / 268927 A1, both sides of the comb drive are curved and a translational movement, i.e. one directed towards each other in a straight line, is implemented at the same time. According to one embodiment, a MEMS is provided which has a comb drive with a first finger structure comprising a first plurality of electrode fingers and with a second finger structure comprising a second plurality of electrodes, which form an interlaced arrangement parallel to a substrate plane of the MEMS.The comb drive is configured to provide a translational relative movement between the first finger structure and the second finger structure based on an electrostatic force for changing a distance between the first finger structure and the second finger structure parallel to the substrate plane. The first plurality of electrode fingers and the second plurality of electrode fingers are curved perpendicular to the substrate plane. This advantageously enables the adaptation of a force-deflection curve.

[0015] According to one embodiment, an electrode finger of the first finger structure and / or the second finger structure is formed from a first electrode finger end to a second, opposite electrode finger end such that an undercut is arranged in a plane perpendicular to the substrate plane. The undercut, in conjunction with the translational movement, enables a particularly precise and advantageous adaptation of the force-deflection curve.

[0016] According to one embodiment, facing sides of interlocking electrode fingers are formed congruently to one another, at least within a working area. This enables further optimization of the force-deflection curve. A congruent design of facing side surfaces can also be achieved independently of the undercut.

[0017] According to one embodiment, a side surface of an electrode finger of the first finger structure or the second finger structure has a concave section extending from a first electrode finger end to a second, opposite electrode finger end. The concave section can allow for good adjustment of the deflection behavior of the comb drive with respect to its radius.

[0018] According to one embodiment, the concave section is shaped such that a curvature with a radius is provided that is different from a curvature of the electrode finger at a free end of the electrode finger. According to one embodiment, the concave section is arranged between a first side wall section of the electrode finger and a second side wall section of the electrode finger. Starting from a clamped end of the electrode finger, the first side wall section is inclined at a first angle relative to a main extension direction of the electrode finger. The second side wall section of the electrode finger is inclined at a second angle relative to the main extension direction of the electrode finger towards a free end of the electrode finger. The first angle has a value of at most 30 degrees and the second angle has a value of at most 45 degrees.These values ​​result in a particularly high degree of linearity of the deflection behavior.

[0019] According to one embodiment, at least one of the electrode fingers has a combination of an undercut on a non-clamped side of the electrode finger and a widened portion of the electrode finger on a clamped side of the electrode finger. This enables adaptation to an undercut of an opposite electrode finger by means of the widened portion of the electrode finger at the clamped end.

[0020] According to one embodiment, the at least one electrode finger has a larger electrode finger width on the clamped side than on the non-clamped side.

[0021] According to one embodiment, a wave-shaped recess is arranged between a first side surface of a first electrode finger of the first finger structure and a second side surface of a second electrode finger of the second finger structure facing the first side surface. A wave shape enables compensation for mechanical nonlinearities.

[0022] According to one embodiment, a curvature of curved electrode fingers is adapted to a nonlinear stiffness of the comb drive, wherein a curvature-based force variation in the comb drive and along a direction of movement of the comb drive compensates for a deflection-based stiffness variation of the comb drive within a tolerance range. This allows the force-deflection curve to be optimized.

[0023] According to one embodiment, the MEMS is designed based on the curvature of curved electrode fingers to obtain a linearized relationship between the deflection of the comb drive and the generated electrostatic force of the comb drive, which enables precise control of the MEMS.

[0024] According to one embodiment, the first finger structure and the second finger structure form a first structure pair. The MEMS has at least one further structure pair connected in series with the first structure pair along a force direction of the comb drive. This enables an increase in the force generated in the comb drive.

[0025] According to one embodiment, the MEMS is designed such that, starting from a curved region of the electrode finger, a substantially rectangular region is arranged towards a free end or a clamped end.

[0026] According to one embodiment, the MEMS is configured as a loudspeaker. Such a loudspeaker can reproduce high-quality audio signals, for example, by suppressing harmonic interference due to the maintained linearity.

[0027] According to one embodiment, a method for manufacturing a MEMS comprises arranging a comb drive with a first finger structure comprising a first plurality of electrode fingers and with a second finger structure comprising a second plurality of electrode fingers, such that the first plurality of electrode fingers and the second plurality of electrode fingers form an interlaced arrangement with the first plurality parallel to a substrate plane of the MEMS. The method is carried out such that the first plurality of electrode fingers and the second plurality of electrode fingers are curved perpendicular to the substrate plane; and such that an electrode finger of the first finger structure or the second finger structure has an undercut in a plane perpendicular to the substrate plane, starting from a first electrode finger end toward a second opposite electrode finger end.

[0028] Further advantageous embodiments are the subject of further patent claims.

[0029] Particularly preferred embodiments of the present invention are explained below with reference to the accompanying drawings. They show:

[0030] Fig. 1a is a schematic plan view of a comb drive according to one embodiment; Fig. 1b is an enlarged view of a portion of the comb drive from Fig. 1a;

[0031] Fig. 2 is a schematic exemplary diagram of a drive structure according to an embodiment, with two comb drives connected in series to enable active deflection along positive and negative y-direction;

[0032] Fig. 3 is a schematic plan view of a part of an electrode finger according to an embodiment, which can be used, for example, as electrode finger a according to Figs. 1a and 1b;

[0033] Fig. 4 is a schematic plan view of a comb drive according to an embodiment, in which the serial connection of at least two comb drives along the direction of force is shown schematically;

[0034] Fig. 5 is a schematic block diagram of a comb drive according to an embodiment in a plan view, in which an asymmetrical arrangement is shown compared to the symmetrical arrangement in Fig. 4;

[0035] Fig. 6 is a schematic representation of an electrode finger according to an embodiment in which the approximate shape of the electrodes is designed as steps;

[0036] Fig. 7a is a schematic plan view of an electrode finger according to an embodiment with an extension at a clamped end;

[0037] Fig. 7b is a schematic plan view of an electrode finger according to an embodiment with an extension at a free end; and

[0038] Fig. 8 is a schematic flow diagram of a method according to an embodiment.

[0039] Before exemplary embodiments of the present invention are explained in more detail below with reference to the drawings, it is pointed out that identical, functionally identical or equivalent elements, objects and / or structures in the different figures are provided with the same reference numerals, so that the description of these elements shown in different exemplary embodiments is interchangeable or can be applied to one another.

[0040] The embodiments described below are described in conjunction with numerous details. However, embodiments may also be implemented without these detailed features. Furthermore, for clarity, embodiments are described using block diagrams instead of detailed illustrations. Furthermore, details and / or features of individual embodiments may be readily combined with one another, unless explicitly described otherwise.

[0041] Fig. 1a shows a schematic top view of a comb drive 10 according to an embodiment, with some of the details of the comb drive 10 being highlighted in Fig. 1b. The comb drive 10 has a first finger structure 12 with a plurality of electrode fingers 14i-14e, wherein the number of electrode fingers 14 of the finger structure 12 can have any value from at least 2, such as 3, 4, 5, 6, 10 or more, such as at least 15, at least 20 or more.

[0042] The comb drive 10 further comprises a second finger structure 16 with a plurality of electrode fingers 181-185 in a number equal to or different from that of the finger structure 12. The finger structures 12 and 16 can be arranged entirely or partially parallel to a substrate plane of the comb drive or of a MEMS having the comb drive 10. This means that, starting from one of the two finger structures 12 or 16, the other finger structure 16 or 12 can be arranged parallel to a y-direction parallel to the substrate plane. The fingers 141-146 on the one hand and 181-185 on the other hand can form an interlaced arrangement, meaning that an electrode finger of the other electrode structure 16 or 12 can be arranged between each two electrode fingers of a finger structure 12 or 16.A potential difference between electrode fingers of the first finger structure 12 and electrode fingers of the second finger structure 16 can cause an electrostatic force that leads to a translational movement along the y-direction between the finger structures 12 and 16 relative to each other.

[0043] The electrostatic force can be used to change a distance between the finger structures

[0044] 12 and 16 parallel to the substrate plane along the y-direction. Fig. 1b shows an enlarged view of a portion of the comb drive 10 from Fig. 1a. It shows that the first plurality of electrode fingers 14 and the second plurality of electrode fingers 18 are curved perpendicular to the substrate plane x / y. This can be understood to mean that main sides 14A and 18A of the electrode fingers 14i and 142, which can be arranged perpendicular to the substrate plane x / y, are curved, in particular when extending along the y-direction. A recess 33 between the side surfaces 14A and 18A can be wave-shaped. Depending on the geometry of the electrode fingers, a wave shape can also be deviated from in some embodiments, at least in the plan view shown, in particular from a continuous wave shape, see, for example, Fig. 6.

[0045] The y-direction can be understood as the main extension direction of the electrode fingers starting from attachments 22 of the first finger structure 12 or 24 of the second electrode structure 16. The curvature can be represented in the projection of the electrode fingers 14i and 18i in a plane parallel to the substrate plane. However, further additional curvatures, for example relative to a y / z plane, which is not visible in the view shown in Fig. 1b, are not excluded. Synonymously expressed, at least one electrode finger or at least one side or surface thereof facing an adjacent electrode finger has a curved profile.

[0046] The curvatures of the main sides 14A and 14B, at least in the main side sections of the electrode fingers 14i and 18i, are explained in detail below. The respective parameterizations can be implemented independently of one another, but also in combination with one another. The described adjustments of the curvatures are particularly related to a working range of the electrode fingers 14i and 18i or of the finger structures 12 and 16. In the context of the embodiments described herein, a working range is understood to be a deflection range of the comb drive 10, within which the surfaces of the electrode fingers are displaced relative to one another and the main sides are arranged opposite one another.For example, to avoid mechanical contact between an electrode finger 14 and an opposing fastening region 24 or between an electrode finger 18 and an opposing fastening region 22, a remaining distance can be provided, which results in no overlap with a neighboring electrode finger in parts of the electrode finger adjacent to the fastenings 22 and / or 24. Optimizations can be omitted at these points without negatively impacting the adaptation of the deflection behavior described herein.

[0047] Some of the embodiments described herein relate to MEMS with a comb drive, in which one or more electrode fingers of the finger structure 12 and / or 16 have an undercut 26i or 262 in a plane perpendicular to the substrate plane, starting from a first electrode finger end, approximately adjacent to the fastening region 22 or 24, toward an opposite second electrode finger end, approximately the movable or deflectable end. An undercut 26i or 262 can be understood to prevent removal of the structure from a one-piece molding tool, for example, when considering an injection molding process as a thought experiment, parallel to the y-direction. For example, the thickening obtained by the undercut or undercut 26i toward the movable or free end 28i can prevent removal along the positive y-direction from the thought-experimental molding tool.Likewise, removal of the electrode finger 181 along the negative y-direction may be prevented due to the thickening towards the free end 282.

[0048] A shape or geometry of the electrode finger and / or the undercut 26i and / or 262 can have a continuous shape, but can also have a substantially rectangular shape or a combination of several substantially rectangular shapes, as exemplified by steps 32i-32?. The stepped shape enables good compatibility with etching processes, wherein it is possible, but not required, to provide rectangular angles between the steps 32i-32?. As discussed with reference to Fig. 6, typical sizes of a resulting stepped shape can be in the range of 300 nm or more, approximately down to approximately 5 pm. Alternatively, a substantially continuous shape can also be implemented.

[0049] Independently, but especially in combination with the undercuts 26i and 262, the mutually facing sides 14A and 18A of the interlocking electrode fingers 14i and 18i can be formed congruently. This means that the main side 14A can be congruent with side 18A, at least when viewed within the working area, upon rotation of 180 degrees around the z-axis, possibly with additional translational displacement. In other words, Figure 1b shows a comb drive optimized for the elimination / reduction of the nonlinear transmission components of a microbeam and / or a membrane.

[0050] Fig. 2 shows a schematic exemplary diagram of a drive structure with two comb drives 10i and 102, which are connected in series to enable active deflection along the positive and negative y-direction. Thus, three states 34i, 342, and 343 are shown as examples. In state 34i, a comb drive structure 102 is activated and the distance between the electrode fingers there is small to minimal, while the electrode fingers in the comb drive structure 10i have an increased distance. A state 342 has a reference state, for example, without actuation, which can correspond to the zero point on a y-axis. A state 343 corresponds to a state inverted to state 34i, in which the comb drive structure 10i is activated, resulting in a deflection y2 of the comb drive structure that can be opposite to a deflection y1 of state 34i.

[0051] The diagram shows an example Coulomb force curve for an example non-optimized structure. Non-optimized here can be understood as the interaction between the force curve of the drive and the counterforce / restoring force of the mechanism. It can also be understood that this represents an obvious geometric deflection. According to the state of the art, such an obvious design is a straight-line profile of the finger electrode flanks, in particular without an undercut.

[0052] In contrast, a curve 38 shows a Coulomb force of the comb drives optimized using the curvatures and electrode finger geometries described herein, which can be adapted to a nonlinear stiffness 42 of the mechanical system due to the adaptation of the electrode finger curvature. This means that the curvature can be used to adjust the electrode fingers in such a way that the Coulomb force 38 matches the nonlinear stiffness, thereby resulting in an overall linearization of the force-deflection curve.

[0053] The superposition of curves 38 and 42 illustrates an embodiment in which a curvature of curved electrode fingers is adapted to a nonlinear stiffness of the chamber drive, and a curvature-based force variation in the comb drive and along a movement direction of the comb drive compensates for a deflection-based stiffness variation of the comb drive within a tolerance range of preferably less than 20%, less than 10%, or less than 5%. According to such an embodiment, curved electrode fingers can have a linearized relationship between the deflection of the comb drive and the electrostatic force generated by the comb drive. The linearization is evident in the fact that curve 42 and curve 38 are congruent.This results in a linearity for the system behavior, which can also be understood as meaning that for the same change in the path (y) an equal response in the force (F) is obtained, both during drive or deflection and during restoring.

[0054] In other words, Fig. 2 shows a deformable element with a geometry deviating from a rectangle and a force-displacement curve matching the nonlinearity of a microbeam.

[0055] Fig. 3 shows a schematic top view of a portion of an electrode finger 44 according to an embodiment, which can be used, for example, as electrode finger 14 and / or electrode finger 18. The design parameters described herein can be implemented independently of one another, but also in combination. Fig. 3 shows only a portion of the electrode finger 44, which is divided along a cutting axis 46. Along the x-direction, the electrode finger 44 can be constructed with mirror symmetry or deviate from mirror symmetry, which can depend on the respective adjacent electrode finger associated with the opposite finger structure.

[0056] A side surface 44A of the electrode finger 44 may have a concave portion 52 extending from a fixed end 48 to an unfixed or free end 28. The concave portion 52 may include a curvature with a radius R2 that is different from a curvature Ri of the electrode finger 44 at the free end 28. Preferably, the radius R2 is larger than the radius Ri.

[0057] The concave section 52 can be arranged between sidewall sections 54i and 542. The sidewall section 54i can be arranged in front of the sidewall section 542, starting from the clamped end 48 toward the free end 28. The first sidewall section 54i can be inclined at an angle α relative to the main extension direction y of the electrode finger 44. The second sidewall section 542 of the electrode finger can be inclined at an angle α toward the free end 28 of the electrode finger relative to the main extension direction 28 of the electrode finger. The angle α preferably has a value of at most 30 degrees and the angle α a value of at most 45 degrees. - Within the structure, the following can apply:

[0058] For yi : yi > y2

[0059] For y2: 0 < y2< finger length or total dimension along y

[0060] For x2: x2> R2

[0061] For b: b > 0

[0062] For Ri: Ri > 0

[0063] For R2: R2> 0

[0064] In other words, the angles 0 and φ can be selected such that the Coulomb force and restoring force curves have similar values, preferably as closely as possible to each other or approximately match. The angle at the undercut can be designed such that it lies in a range of 0 degrees < 6 < 30 degrees, preferably 0.5 degrees < 6 < 10 degrees, and the angle at the attached side with the substrate in a range of 0 degrees < <p < 45 Grad, bevorzugt 1 Grad < <p < 15 Grad liegt.

[0065] The contour shown in Fig. 3 can be constructed geometrically / parametrically or approximated using splines or similar techniques, for example, as part of a design process, to enable subsequent implementation by etching and / or growth. Fig. 3 also shows that both the arrangement of an undercut discussed in Fig. 1b and a widening of the electrode finger are implemented at the clamped end.

[0066] According to embodiments, the electrode finger 44 can have a larger electrode finger width, i.e., a dimension along the x-direction, on the clamped side 48 connected to the substrate than on the non-clamped free side 28.

[0067] In other words, Fig. 3 shows a deformable element with an undercut on the freely movable side and a thickening on the side connected to the substrate, wherein an angle θ > 0 and αp > 0 is provided. A design according to such an embodiment can also be implemented such that the base of the finger is at least substantially straight and the thickening at the fingertip is greater than the thickness / width of the finger at the base, i.e., the clamping.

[0068] Fig. 4 shows a schematic plan view of a comb drive 40 according to an embodiment, in which the serial connection of at least two comb drives 10i and 102 along the force direction y is shown schematically, which was already discussed in Fig. 2. The representation of the electrode fingers 14 and 18 is shown as rectangular by way of example, wherein the electrode fingers are actually formed in correspondence with the comb drive 10, as shown by the cutout 56, which is designed in accordance with Fig. 1b.

[0069] The electrode finger structures 12i and 122 of the comb drives 10i and 102 can, for example, be arranged relatively immovably on a substrate 58. In contrast, the finger structures 16i and 162 can be arranged movably and, in a preferred embodiment, form a common movable element 62 or be part thereof. The finger structures 12i and 161 can form a first structure pair, wherein at least one further structure pair comprising the finger structures 122 and 162 can be arranged, which is connected in series with the first structure pair along the force direction y of the comb drive 40. By controlling the comb drive 40 and the symmetrical arrangement of the structure pairs along the force direction, a particularly advantageous movement can be achieved. Optionally, further comb drives 10 and / or 40 can be connected in series or in parallel.Mechanical components can provide both linear and nonlinear influences. These influences relate to mechanical components. For example, linear elements can provide a constant, non-varying increase in the ratio of force F to displacement y, dF / dy, and vice versa, while nonlinear elements can provide a variable increase.

[0070] In other words, Fig. 4 shows an optimized deformable element embedded in a symmetric push-pull arrangement.

[0071] Fig. 5 shows a schematic block diagram of a comb drive 50 according to an embodiment in a plan view, in which, compared to the symmetrical arrangement in Fig. 4, an asymmetrical arrangement of the finger structure 16, which is arranged movably relative to the finger structure 12, is shown. Here, too, the supposedly rectangular shape of the electrode fingers 14 and 18 is actually curved, as shown by the cutout 56.

[0072] In other words, Fig. 5 shows an optimized deformable element embedded in an asymmetric arrangement.

[0073] Fig. 6 shows a schematic representation of an electrode finger 64 according to an embodiment in which the approximate shape of the fingers or electrodes is embodied as steps 32. Even if the step elements 32 are merely shown forming a side wall 64A, the electrode finger 64 is not necessarily hollow or shaped to have a cavity, but rather, according to preferred embodiments, is a solid body. At least in the region of the undercut, but possibly also in the further course or other regions of the electrode finger 64, the electrode finger 64 can have one or more rectangular shapes. A plurality of rectangular shapes can form a step shape, wherein a step height of the step shape is constant or variable within the step shape and can, for example, have a value of at least 100 nm up to several pm.The steps do not necessarily have to be arranged discontinuously or at right angles to each other, but can, for example due to etching processes, have a curvature between adjacent steps, which can, for example, have a radius of at least 200 nm or 300 nm up to about 500 pm.

[0074] This means that the electrode finger shape of the electrode finger 44 can be approximated by one or more rectangular shapes.

[0075] In other words, Fig. 6 shows an approximate shape with steps.

[0076] Fig. 7a shows a schematic plan view of an electrode finger 68 according to an exemplary embodiment, which can be used as an electrode finger of the first finger structure 12 and / or the second finger structure 16, wherein, in accordance with Fig. 3 and Fig. 6, only one half of the electrode finger is shown. The electrode finger 68 can have the electrode finger 44 from Fig. 3 or a shape modified therefrom and can be arranged on a rectangular or square extension 72, from which the electrode finger 44 emerges along the main extension direction y. The extension 72 can provide an intermediate section with respect to the substrate or fastenings 22 or 24 with respect to the electrode finger 14 and / or 18, for example outside a working area of ​​the electrode fingers.This means that between a fastening 74 of the finger structure and curved or approximated by at least a step shape and / or undercuts, a section of the electrode finger 68 can be arranged, which has a rectangular or square cross-section in the x / z plane and may possibly have a cross-section that is invariable along the y-direction.

[0077] Fig. 7b shows a schematic plan view of an electrode finger 76, in which a section 76 starting from the undercut 26 can have a rectangular shape, as described for the extension 72. This can, for example, prevent a curvature at the free end 28, which can be advantageous, for example, in the case of mechanical contact with another element. In this embodiment, the extension 72 can also be arranged within the working area of ​​the comb drive.

[0078] In other words, the geometry of the electrode finger 76' can transition into a rectangular shape starting from the undercut 26. Fig. 7a and Fig. 7b show a finger that transitions into a rectangular shape at one of its ends. These configurations can be easily combined with one another, so that an extension can be arranged at both ends of the finger.

[0079] Fig. 8 shows a schematic flow diagram of a method 800 according to an embodiment. This comprises a step 810 in which a comb drive is arranged with a first finger structure comprising a first plurality of electrode fingers and with a second finger structure comprising a second plurality of electrode fingers. This is carried out such that the first plurality of electrode fingers and the second plurality of electrode fingers are curved perpendicular to the substrate plane and such that an electrode finger of the first finger structure or the second finger structure has an undercut in a plane perpendicular to the substrate plane, starting from a first electrode finger end toward a second opposite electrode finger end.

[0080] Embodiments described herein relate to MEMS components, which can be embodied as layer stacks consisting of at least one substrate layer in which the electrodes and the passive elements are arranged. Further layers relate, for example, to a base, which can also be referred to as a handling wafer, and a cover, which can also be referred to as a cover wafer. Both the cover wafer and the handling wafer can be connected to the substrate plane using material-to-material processes, preferably bonding, whereby acoustically sealed gaps can be created in components. In this gap, which can correspond to the device plane, deformable elements deform; in other words, in-plane deformation can occur, for example triggered by comb drives described herein.This is particularly advantageous for embodiments of the present invention relating to MEMS implemented as loudspeakers.

[0081] The layers can, for example, comprise electrically conductive materials, such as doped semiconductor materials and / or metal materials. The layered arrangement of electrically conductive layers enables a simple design, since electrodes, such as those for deflectable elements and passive elements, can be formed by selectively dissolving them from the layer. If electrically non-conductive materials are to be arranged, this can be achieved by applying these materials layer by layer using a deposition process.

[0082] In the MEMS-based loudspeakers described herein, a conventional membrane is replaced by microbeams, as described, for example, in DE 2017 206 766 A1, using passive beams that are deflected by electrostatic comb drives. Both the arrangement with the membrane and the microbeams can require a comparatively large displacement during operation. These large deflections lead to nonlinear effects exerting a significant influence on the transmission behavior, with voltage stiffening playing a particularly important role. Due to this nonlinearity, higher harmonics are generated under harmonic excitation, which can lead to distortion of the loudspeaker's audio signal, which is undesirable.With the embodiments described herein, the transmission behavior of the comb drive at large displacements is modified such that the nonlinearities can preferably be completely eliminated or significantly reduced.

[0083] The reduction of nonlinearity can be achieved by representing the nonlinear stiffness, i.e., the restoring force against displacement, as a function of the Coulomb force, i.e., the electrostatic force. If the curves match at least approximately, preferably exactly, the nonlinearity is reduced or even eliminated, thus at least partially eliminating the distortions within the electromechanical system. If the curves match approximately, a small residual distortion may remain, but this is far below the level of a system not optimized for this purpose and, in this respect, still offers advantages.

[0084] The optimization of such an electromechanical system can be explained using a comb finger. Typically, straight fingers (elements) are used, which exhibit a nearly linear transmission behavior but are unable to cancel the nonlinearity resulting from the membrane / beam. According to the invention, the cancellation of the nonlinearity is made possible by changing the geometry of the comb finger / deformable element such that, upon deflection, the Coulomb force follows the nonlinear restoring force, see Fig. 2. This can be achieved, for example, by combining an undercut on the unclamped side of the deformable element / electrode finger with a widening of the deformable element on the side attached to the substrate.The widening, i.e., an increase in dimension b along x, refers to the width of the electrode at the tip of the finger, approximately at the widest point, marked by yi. A widening factor is preferably less than a factor of 2.

[0085] The deformable element or comb drive thus has a wave-shaped recess. The dimensions and, in particular, the angles are selected as discussed in connection with Fig. 3. Previously known solutions describe rectangular or curved microbeams. These geometries can lead to distortion of the audio signal due to nonlinearities. To eliminate or reduce the nonlinear transmission components, the geometry of the microbeam is therefore modified according to the invention so that its stiffness is dependent on the Coulomb force. The microbeams have a curvature and, for example, an undercut on the unclamped side and possibly a widened portion on the clamped side. This creates a microbeam that, together with an adjacent microbeam, can provide a wave-shaped recess.

[0086] Aspects of embodiments described herein relate to MEMS devices and methods directed thereto. Some embodiments relate to a MEMS with a deformable element or electrode finger, characterized in that the deformable element has at least one wave-shaped recess. Some embodiments relate to a MEMS with a deformable element or comb drive, characterized in that the deformable element has a larger extension on the side connected to the substrate than the freely movable side.

[0087] Some embodiments relate to a MEMS, wherein the angle of the movable element or the movable electrode fingers on the side connected to the substrate is arranged at an angle of 0° to 45°, preferably 1° to 15°, and an angle on the freely movable side is in a range of > 0° and < 30°, preferably at least 0.5° and at most 10°.

[0088] Some embodiments of the present invention provide a MEMS transducer in which the deformable elements or finger structures are embedded in a symmetrical arrangement. Other embodiments provide a MEMS transducer in which the deformable elements or finger structures are embedded in an asymmetrical arrangement.

[0089] Some embodiments of the present invention provide a system in which the undercut is simulated by an approximation using steps. Some embodiments of the present invention provide a system in which the undercut transitions into a rectangular shape (see Fig. 7b), or originates or starts from it, for example, at the base of the finger element (see Fig. 7a).

[0090] The embodiments of a comb drive described herein can be used for the deflection or movement of a movable element for fluid displacement. This can involve an in-plane movement of a fin structure in the same or a different MEMS plane as the comb drive. Alternatively or additionally, membrane structures can also be deflected, for example, directly or using direction-deflecting lever mechanisms.

[0091] Although some aspects have been described in connection with a device, it is to be understood that these aspects also represent a description of the corresponding method, so that a block or component of a device can also be understood as a corresponding method step or as a feature of a method step. Analogously, aspects described in connection with or as a method step also represent a description of a corresponding block, detail, or feature of a corresponding device. The embodiments described above merely illustrate the principles of the present invention. It is to be understood that modifications and variations of the arrangements and details described herein will be apparent to others skilled in the art.Therefore, it is intended that the invention be limited only by the scope of the following claims and not by the specific details presented in the description and explanation of the embodiments herein.

Claims

Patent claims 1. A MEMS comprising: a comb drive (10; 40; 50) having a first finger structure (12) comprising a first plurality of electrode fingers (14) and having a second finger structure (16) comprising a second plurality of electrode fingers (18) which form an interlaced arrangement with the first plurality parallel to a substrate plane (x / y) of the MEMS; wherein the first plurality of electrode fingers (14) and the second plurality of electrode fingers (16) are curved perpendicular to the substrate plane; and wherein an electrode finger (14, 18) of the first finger structure or the second finger structure has an undercut (26) in a plane perpendicular to the substrate plane, starting from a first electrode finger end (48) towards a second opposite electrode finger end (28).

2. MEMS according to claim 1, wherein the undercut (26) is arranged on at least one side surface facing an adjacent electrode finger.

3. MEMS according to claim 1 or 2, wherein the comb drive is configured to provide a translational relative movement between the first finger structure (12) and the second finger structure (16) based on an electrostatic force for changing a distance between the first finger structure (12) and the second finger structure (16) parallel to the substrate plane.

4. MEMS according to one of the preceding claims, wherein a projection of the undercut (26) into the substrate plane has a substantially rectangular shape; or wherein a projection of the undercut (26) into the substrate plane has a combination of several substantially rectangular shapes.

5. MEMS according to one of the preceding claims, wherein mutually facing sides (14A, 18A) of intermeshing electrode fingers are formed congruently at least within a working region.

6. MEMS according to one of the preceding claims, wherein a side surface (44A) of an electrode finger (44) of the first finger structure or the second finger structure has a concave section (52) starting from a first electrode finger end (48) towards a second opposite electrode finger end (28).

7. MEMS according to claim 6, wherein the concave portion (52) comprises a curvature with a radius (R2) that is different from a curvature (Ri) of the electrode finger at a free end (28) of the electrode finger.

8. MEMS according to claim 6 or 7, wherein the concave section (52) is arranged between a first side wall section (54i) of the electrode finger, which, starting from a clamped end (48) of the electrode finger, is inclined at a first angle ( <p) geneigt ist, und einem zweiten Seitenwandabschnitt (542) des Elektrodenfingers, der hin zu einem freien Ende (28) des Elektrodenfingers gegenüber der Haupterstreckungsrichtung (y) des Elektrodenfingers mit einem zweiten Winkel (0) geneigt ist, angeordnet ist; wobei der erste Winkel (<p) einen Wert von höchstens 30° aufweist und der zweite Winkel (0) einen Wert von höchstens 45° aufweist.

9. MEMS according to one of the preceding claims, wherein at least one of the electrode fingers has a combination of an undercut (26) on a non-clamped side (28) of the electrode finger and a widening of the electrode finger on a clamped side (48) of the electrode finger opposite the non-clamped side.

10. MEMS according to claim 9, wherein the at least one electrode finger has a greater electrode finger width on the clamped side (48) than on the non-clamped side (28).

11. MEMS according to one of the preceding claims, wherein a first side surface (14A) of a first electrode finger (14i) of the first finger structure (12) and a second side surface (18A) of a second electrode finger (18i) of the second finger structure (16) facing the first side surface (14A) are formed congruently within a working range of the comb drive.

12. MEMS according to one of the preceding claims, wherein a wave-shaped recess (33) is arranged between a first side surface (14A) of a first electrode finger (14i) of the first finger structure (12) and a second side surface (18A) of a second electrode finger (18i) of the second finger structure (18) facing the first side surface (14A).

13. MEMS according to one of the preceding claims, wherein a curvature of curved electrode fingers is adapted to a nonlinear stiffness of the comb drive (10; 40; 50); wherein a curvature-based force variation in the comb drive and along a movement direction (y) of the comb drive compensates for a deflection-based stiffness variation of the comb drive within a tolerance range.

14. MEMS according to claim 13, which has a linearized relationship between deflection of the comb drive (10; 40; 50) and generated electrostatic force of the comb drive based on the curvature of curved electrode fingers.

15. MEMS according to one of the preceding claims, wherein the first finger structure (12i) and the second finger structure (161) form a first structure pair; and the MEMS has at least one further structure pair (12i, 162) connected in series with the first structure pair along a force direction (y) of the comb drive.

16. MEMS according to one of the preceding claims, in which a substantially rectangular region (72, 76) is arranged starting from a curved region of the electrode finger towards a free end (28) or a clamped end (48).

17. MEMS according to one of the preceding claims, which is formed as a loudspeaker.

18. A method (800) for manufacturing a MEMS comprising the following steps: Arranging (810) a comb drive with a first finger structure comprising a first plurality of electrode fingers and with a second finger structure comprising a second plurality of electrode fingers, such that the first plurality of electrode fingers and the second plurality of electrode fingers form an interlaced arrangement with the first plurality parallel to a substrate plane of the MEMS; such that the first plurality of electrode fingers and the second plurality of electrode fingers are curved perpendicular to the substrate plane; such that an electrode finger of the first finger structure or the second finger structure, starting from a first electrode finger end towards a second opposite electrode finger end, has an undercut in a plane perpendicular to the substrate level.

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