MEMS component having membrane spring and method for producing membrane spring

Abstract

The invention relates to a MEMS component (700) with a micromechanical membrane spring (1), comprising a first membrane spring element (10) and a second membrane spring element (20), which have an at least regionally convex or concave two-dimensional curvature. The first diaphragm spring element is mechanically coupled to the second diaphragm spring element such that a spring force (501) induced by the diaphragm spring is transmitted by the first and second diaphragm spring elements. Furthermore, the micromechanical membrane spring is also combined with a layer structure (600) of the MEMS component (700) such that a spring force (501) caused by the membrane spring acts substantially in the sequence direction of the layer structure (600). The device for the pre-deflection of the diaphragm spring is provided for adjusting an operating point of the diaphragm spring relative to the spring characteristic curve by means of a permanent elastic deflection of the diaphragm spring, in particular in such a way that the operating point lies within an at least approximately linear spring characteristic curve of the diaphragm spring having a low inclination. A method for manufacturing a membrane spring suitable for use in such MEMS components.

Description

Technical Field

[0001] The present invention relates to a membrane spring, in particular a micromechanical membrane spring for a MEMS component (MEMS: micro-electromechanical system, Microsystem), such as a MEMS transducer. The present invention also relates to a MEMS component with such a membrane spring, in particular a MEMS sensor or a MEMS actuator. The present invention also proposes a method for manufacturing a membrane spring of a MEMS component. Background Art

[0002] A fundamental problem with many MEMS sensors is that known, mechanically elastically deformable elements such as beams or membranes usually only deflect slightly when subjected to an applied force. Small deflections result in only low electrical signals via the transducer element. In MEMS actuators, only limitedly large forces can be generated for the desired large deflections. In principle, it is technically possible to produce very flexible beams or membranes with the desired dimensions for use in MEMS components, but due to their delicateness, the produced structures can be easily damaged during the manufacturing process or during use, for example due to overloading.

[0003] The mechanical stiffness of an elastically deformable element is described by a spring constant or a spring characteristic curve. It is well known in the mechanical field that springs or spring elements of different construction types have different spring characteristic curves, which can have a linear, progressive, decreasing-increasing, decreasing-horizontal-increasing or decreasing-negatively increasing curve. Within the framework of the present disclosure, a linear spring characteristic curve of a section is referred to as "nonlinear". Usually, MEMS sensors and MEMS actuators are designed to work in a linear stiffness range.

[0004] In the case of mechanical springs, it is generally known that the course of the spring characteristic curve can be changed within a wide range by structural modifications, for example by mechanical combination of spring elements with different spring characteristic curves. For example, slotted disc springs or tongue-shaped disc springs generally have an increased spring deflection and a reduced spring force compared to conventional disc springs. The production of such structures within the framework of micro-electromechanical systems (MEMS) is largely unknown.

[0005] Known mechanical spring elements are not necessarily suitable for use in MEMS components. For example, disk springs are usually not clamped on the inside and outside, i.e., they are loosely supported. When the disk springs deform, frictional forces are generated at these locations, which are usually undefined and cannot be used in MEMS sensors or MEMS actuators.

[0006] From document US2020 / 0284940 A1, a MEMS gravimeter with a spring-mass system is known, which includes a spring with a negative stiffness (also rigid) of the section and another spring with a positive stiffness. The spring with the negative stiffness of the section is provided by a one-dimensional bending beam, whose opposite ends are firmly fixed. Summary of the invention

[0007] Starting from this prior art, the object of the present invention is to specify a micromechanical spring element and a method for producing the same which is particularly suitable for MEMS components, in particular MEMS actuators and / or MEMS sensors.

[0008] The above-mentioned object is achieved by the subject matter of the independent claims. Advantageous embodiments of the invention are given in the dependent claims.

[0009] A MEMS component, in particular a MEMS actuator or sensor, has a micromechanical membrane spring or a micromechanical membrane spring element with at least regionally convex or concave two-dimensional curvature. The membrane spring is suitable for transmitting a spring force in the layer sequence direction of a layer composite structure of the MEMS component, and the membrane spring can be integrated in the MEMS component.

[0010] The structure of the micromechanical membrane spring is divided into two parts and includes a first membrane spring element (preferably having a linear characteristic curve) and a second membrane spring element (preferably having a nonlinear characteristic curve). The second membrane spring element has a convex or concave two-dimensional curvature at least in a region and is mechanically coupled to the first membrane spring element, so that the spring force transmitted by the first and second membrane spring elements acts as an induced spring force in the layer sequence direction of the layer structure of the MEMS component. For this purpose, the membrane spring is integrated in the layer structure of the MEMS component.

[0011] The spring characteristics of the diaphragm spring can be adapted to the particular requirements of the application by structurally modifying the first and / or second diaphragm spring element. In particular, in one embodiment, a first diaphragm spring element having a linear spring characteristic curve and a second diaphragm spring element having a nonlinear spring characteristic curve are mechanically coupled to one another, preferably so that the resulting spring characteristic curve has a small slope in a partial region.

[0012] The MEMS component has a device for pre-deflection of the membrane spring. The device for pre-deflection is provided for adjusting the permanent elastic deflection of the membrane spring, in particular adjusting the working point according to the spring characteristic curve generated by the membrane spring. Preferably, the pre-deflection of the membrane spring is carried out in such a way that the working point is located within the range of the at least approximately linear spring characteristic curve with a small slope of the membrane spring. For this purpose, the membrane spring is slightly deflected from its static position, in particular by the action of a force. By appropriate dimensioning, in particular the dimensioning of the first and / or second membrane spring element, the high spring stiffness of the membrane spring as a spring assembly element, preferably in a non-deflected state, can be significantly reduced by the pre-deflection, so that in particular a linear range of the spring characteristic curve with a small positive or negative slope can be achieved. In this way, MEMS sensors and actuators, in particular made of silicon, can be achieved, which are very strong with respect to damage due to overload during production. The stiffness of the membrane spring in operation is also reduced by the pre-deflection, so that a large movement amplitude can be achieved for sensing and / or actuation.

[0013] In an advantageous embodiment, the first membrane spring element is mechanically connected in a central region of the second membrane spring element to generate the induced spring force. Preferably, the first membrane spring element is connected in the region of the curvature of the second membrane spring element and / or in the region of the maximum spring travel of the second membrane spring element to provide the membrane spring element with the desired spring characteristics along the generated spring travel.

[0014] In an advantageous embodiment of the membrane spring, the membrane plane of the first membrane spring element is parallel to the membrane plane of the second membrane spring element. Preferably, the first membrane spring element is designed to generate a spring force acting in a direction perpendicular to the membrane plane and following a linear characteristic curve. Preferably, the second membrane spring element is designed to generate a spring force in a direction perpendicular to the membrane plane that follows a nonlinear spring characteristic curve.

[0015] In an exemplary embodiment, the first film spring element and / or the second film spring element are substantially annular in shape. The first film spring element and the second film spring element are preferably arranged concentrically with respect to one another. In an alternative embodiment, the first and / or the second film spring element are substantially configured as a lens-shaped convex structure.

[0016] Preferably, the first and / or the second membrane spring element is designed rotationally symmetrically about an axis of symmetry and is arranged concentrically with respect to the axis of symmetry.

[0017] Preferably, the membrane spring is at least partially made of silicon, particularly preferably entirely made of silicon. In particular, the first and / or second membrane spring element can be made of silicon. Silicon is a material with very good elastic properties. Due to the high purity of the material, the elastic properties of such a membrane spring are very uniform and stable. Generally speaking, a membrane spring made of silicon will not show obvious plastic deformation even at high temperatures of several hundred degrees Celsius. Silicon can be precisely structured using mature MEMS processes, and a large number of microstructured elements can be produced in parallel on a wafer at low cost.

[0018] In an advantageous embodiment, the device for pre-deflection comprises at least one cavity loaded with negative or positive pressure, which cavity is at least regionally bounded by the membrane spring, in particular at least regionally bounded by the first and / or second membrane spring element. The pressure loading of the cavity leads to a force acting on the membrane spring or at least one membrane spring element, so that the pneumatic pre-deflection of the membrane spring as a whole and a correspondingly reduced spring stiffness can be set after the joint pre-deflection. This enables a wide range of uses for MEMS sensors and actuators.

[0019] Preferably, the first film spring element is mechanically connected on the outer circumference to the layer structure and to the second film spring element such that the functional film suspended on the inner circumference of the first film spring element can be guided along a spring path parallel to the first direction.

[0020] In a preferred embodiment, the second membrane spring element is mechanically connected to the layer structure at its inner and outer periphery.The second membrane spring element is mechanically connected to the first membrane spring element in a two-dimensionally curved region between the inner and outer periphery.

[0021] The production of curved membrane springs, in particular from silicon, is a major challenge in terms of process technology, since it cannot be realized using conventional MEMS planar processes and can therefore only be integrated with difficulty into conventional process sequences for producing MEMS components.

[0022] A method for producing a two-dimensionally convexly or concavely curved membrane spring, in particular a membrane spring made of silicon, is disclosed below.

[0023] Within the framework of the present disclosure, a two-dimensionally curved membrane spring or membrane spring element refers in particular to a spring or spring element which has a curvature in at least one region of its surface relative to two mutually orthogonal directions and is therefore distinguished from a spring element which is only curved in one dimension, such as a beam spring.

[0024] For example, the production of a membrane spring which is two-dimensionally convexly or concavely curved at least in regions can take place in an additive, subtractive or modified production step.

[0025] According to a variant of the production process according to the invention, in a modified production step, at least partially exposed layers in a layer structure, in particular in the layer structure of the MEMS component already described above, are loaded with pressure and plastically deformed.

[0026] Preferably, during the plastic deformation, the at least sectionally exposed layer is heated locally, in particular by laser radiation, in order to locally limit the heating and in particular to largely avoid damaging heat input to any existing temperature-sensitive components or structures of the MEMS component.

[0027] In an advantageous embodiment, the first diaphragm spring element is mechanically connected to the second diaphragm spring element by means of laser welding.

[0028] In a preferred embodiment of the manufacturing method, at least one cavity is introduced into the layer structure of the MEMS component, the cavity is loaded with negative or positive pressure to achieve a permanent elastic pre-deflection of the membrane spring, in particular a pneumatic pre-deflection, and the cavity is then closed in a pressure-tight and gas-tight manner. The cavity is at least regionally bounded by the membrane spring, in particular at least regionally bounded by the first and / or second membrane spring element, so that a deflection of the membrane spring is caused due to the set pressure difference. The deflection of the membrane spring, in particular the deflection for setting a function corresponding to the respective application, is preferably carried out at the end of the manufacturing process. Preferably, the membrane spring has a spring characteristic curve range with high stiffness in its rest position, that is, when no external forces are applied. In its rest position, the membrane spring is in a spring characteristic range with a large slope and therefore has a high robustness against damage caused by overload during manufacturing. The deflection of the membrane spring preferably achieves a flat spring characteristic range and thus reduces the force required for further deflection of the membrane spring. Depending on the geometry of the curved membrane spring, in particular the geometry of the first and / or second membrane spring element, the common spring constant and / or the resonance frequency can be varied by means of a coupled pre-deflection and the membrane spring can thus be structurally adapted to the specific micromechanical application.

[0029] According to another variant of the production method, the at least partially convex or concave two-dimensional curvature of the membrane spring or membrane spring element is formed in an additive manufacturing step by depositing partially overlapping layers, in particular layers made of silicon or polysilicon layers. Particularly preferably, a plurality of individual layers are superimposed on one another and are appropriately structured. For example, trenches are etched into the applied layer and filled with a filler, in particular an oxide, before the next layer is applied.

[0030] According to another variant of the production method, the at least regionally convex or concave two-dimensional curvature of the membrane spring is formed in a subtractive production step by material ablation of an essentially flat substrate, wherein material is removed from opposite end sides of the substrate, for example by laser ablation or by isotropic etching.

[0031] Manufacturing such a membrane spring, especially a membrane spring having a strong membrane thickness and a small spring stiffness after pre-deflection, can realize a wide range of applications of MEMS transducers, especially MEMS sensors and MEMS actuators, such as:

[0032] - pressure sensors, in particular pressure sensors with a large pressure range;

[0033] -speaker;

[0034] -microphone;

[0035] - (Plate) gravimeter, balance;

[0036] - Z actuators with large travel, e.g. for focusing optics;

[0037] - Energy harvesters;

[0038] - Helmholtz resonators, in particular as acoustic damping elements;

[0039] - a relay, in particular a monostable or bistable relay;

[0040] Microelectromechanical ultrasonic transducers, in particular PMUTs (English: Piezoelectric Micromachined Ultrasonic Transducers), in which a thin piezoelectric transducer layer is applied to a membrane, in particular a membrane made of silicon, and the membrane is deflected by the transducer layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Further details and advantages of the present invention are explained in more detail below with reference to the embodiments shown in the accompanying drawings. It is shown that:

[0042] Figures 1a to 1c Subtractive manufacturing method for producing a two-dimensionally curved membrane spring by means of laser ablation;

[0043] Figures 2a to 2f Subtractive manufacturing method for membrane springs with two-dimensional curvature produced by RIE etching; Figure 3a and 3b Subtractive manufacturing method for producing two-dimensionally curved membrane springs with the aid of a three-dimensional polymer etching mask;

[0044] Figure 4a and 4b A method for manufacturing a membrane spring that generates a two-dimensional curvature by means of a prototype;

[0045] Figures 5a to 5eA method for producing a two-dimensionally curved membrane spring by means of a prototype and laser structuring is illustrated by means of a cross-sectional view;

[0046] Figure 6 Laser loading of a prototype for a membrane spring in top view;

[0047] Figure 7a and 7b according to Figures 5a to 5e A schematic cross-sectional view of a membrane spring manufactured by the process shown; Figure 8a to Figure 8g Additive manufacturing method for producing a two-dimensionally curved membrane spring or a two-dimensionally curved membrane spring element;

[0048] Figures 9a to 9l A method for producing a membrane spring with coupled membrane spring elements by means of a prototype;

[0049] Fig.10a and 10b A membrane spring with membrane spring elements coupled to one another and a device for pre-deflecting a functional membrane in a perspective view;

[0050] Fig.11a and 11b A production method for producing a membrane spring having membrane spring elements coupled to one another and produced using additive or subtractive technology;

[0051] Fig.12 A production method for producing a membrane spring with a high mass on a functional membrane, in particular for use in energy harvesters. DETAILED DESCRIPTION

[0052] In all figures, identical or mutually corresponding elements are provided with the same reference symbols.

[0053] The exemplary embodiments shown in the figures have a rotationally symmetrical, in particular circular or annular, membrane geometry, but are not to be understood as restrictive, as deviations from this are also possible.

[0054] According to Figure 1 to Figure 6 , 8, 9, 11 and 12 describe different methods for producing a two-dimensional curved membrane spring 1 for a MEMS component 700, in particular a curved membrane spring 1 with a nonlinear spring characteristic, ie a two-dimensional curved membrane spring. The two-dimensional curved membrane spring 1 is preferably made of silicon.

[0055] Figure 1c , 2f, 7, 8g, 91 and 10, 11b and 12 show a membrane spring 1 manufactured by means of the method described here, which is at least regionally two-dimensionally convexly or concavely curved. The membrane spring 1 is configured to transmit a spring force 501 in a first direction 601 substantially perpendicular to the membrane plane 500. Preferably, the membrane spring 1 is configured to transmit the spring force 501 in the layer sequence direction of the layer structure 600 of the MEMS component 700.

[0056] 9, 11 and 12 illustrate a method for manufacturing a membrane spring 1 which can be permanently elastically pre-deflected and comprises two membrane spring elements 10, 20 which are mechanically coupled to each other. To this end, at least one of the membrane spring elements 10, 20 has a two-dimensional convex and / or concave curvature, wherein the first membrane spring element 10 preferably has a linear spring characteristic curve and the second membrane spring element 20 preferably has a nonlinear spring characteristic curve. The membrane spring elements 10, 20 are mechanically coupled to each other so that the membrane spring 1 as a whole has a nonlinear characteristic curve. The spring characteristic curve of such a membrane spring 1 formed by the mechanical coupling of membrane spring elements 10, 20 having linear (l-) and nonlinear (nl-) spring characteristic curves is generally of a nonlinear nature and can also be referred to as a linear-nonlinear (lnl-) spring characteristic curve.

[0057] The method described here is particularly suitable for providing a membrane spring 1 made of silicon with a lnl spring characteristic curve and providing it in a wafer composite structure, for example in a layer structure 600 of a MEMS component 700 to be produced. In particular, the method described can be combined with conventional production processes for producing other microelectromechanical functional elements, such as sensor or actuator elements.

[0058] The figure shows a schematic method for producing a membrane spring 1 with a two-dimensional curvature. It is to be understood that the method shown is also suitable for providing the membrane spring elements 10 and 20 mentioned above and below as separate components.

[0059] Figures 1a to 1c The method for producing a membrane spring 1 or a membrane spring element 10, 20 using subtractive technology comprises the following steps:

[0060] - providing a substrate 1000 made of a semiconductor material (eg silicon) (see in particular Figure 1a ), wherein the end side surfaces of the substrate 1000 of opposite values ​​are hereinafter referred to as the front side 1001 and the rear side 1002;

[0061] - Removing material from the front side 1001 and the back side 1002 of the substrate 1000 (also referred to as material flaking) so as to provide a membrane spring 1 or a membrane spring element 10, 20 with a two-dimensional convex or concave curvature (see in particular Figure 1b and 1c);

[0062] like Figure 1b and Figure 1c As shown, the process of removing materials from the front side 1001 and the back side 1002 of the substrate 1000 can be performed simultaneously or in steps.

[0063] With subtractive technology, the resulting geometry of the produced component can be configured almost arbitrarily; in particular, the film thickness can be varied locally, for example in the radial and / or tangential direction.

[0064] In particular, it is provided that local surface structuring, for example in the form of depressions, grooves, etc., is introduced radially or rotationally symmetrically on the front and / or rear sides 1001, 1002 of the diaphragm spring 1 or the diaphragm spring element 10, 20. In particular, it is possible to produce a diaphragm spring 1 or a diaphragm spring element 10, 20 whose geometry is comparable to that of a disc spring of different variants and which is, for example, grooved, locally reinforced and / or provided with other surface contours. The spring characteristic curve of the produced diaphragm spring 1 or diaphragm spring element 10, 20 can be modified as a result of the surface structuring and can be adapted in particular to the technical application.

[0065] exist Figures 1a to 1c In the exemplary embodiment shown, the semiconductor material is removed by means of laser ablation. Optionally, a post-processing of the surface produced by material ablation can be carried out, in particular by means of isotropic etching, for example wet chemical etching or by means of RIE (Reactive Ion Etching). In this optional method step, any mechanical stresses and / or surface roughness still present after the laser processing can be compensated in an advantageous manner.

[0066] Another possibility for appropriate stripping of the semiconductor material of the substrate 1000 from the front side 1001 and the back side 1002 is to use three-dimensionally structured etching masks 1011, 1012, in particular polymer etching masks, such as Figures 2a to 2f The shapes of the etching masks 1011, 1012 are selected according to a defined etching selectivity (i.e., the ratio of the removal rate of the mask material to the removal rate of the semiconductor material of the substrate 1000) so as to be transferred into the semiconductor material by RIE etching, see in particular Figures 2b to 2f .

[0067] exist Figures 2a to 2f In the method shown in FIG. 1 , the front side 1001 of the substrate 1000 is structured in a first method step by applying a first etching mask 1011 (see in particular FIG. 1 ). Figures 2b to 2d ), and the back side 1002 of the substrate 1000 is structured in a second method step by applying a second etching mask 1012 (see in particular Figure 2e and2f ).

[0068] The etching masks 1011, 1012 can be provided in particular by applying a lacquer, by means of gray-tone lithography or by means of holographic lithography. The production of suitable three-dimensional etching masks 1011, 1012 can be carried out by means of replication in a wafer composite structure, such as Figure 3a and 3b In order to transfer the 3D structural shape of the mask uniformly into the semiconductor material, a minimum selectivity close to the value 1 is advantageous, especially during trench etching. The selectivity can be adjusted in a targeted manner in a known manner via a plurality of process parameters.

[0069] Figures 8a to 8c The production of a membrane spring 1 or a membrane spring element 10, 20 by additive technology is schematically illustrated. The two-dimensionally convexly or concavely curved membrane spring 1 or the two-dimensionally convexly or concavely curved membrane spring element 10, 20 is produced by successively depositing individual layers 2001, ..., 2005 of semiconductor material, preferably silicon or polysilicon. The layers 2001, ..., 2005 or silicon layers, such as Figures 8a to 8e Schematically shown, deposited onto substrate 1030, and structured by DRIE etching (English: Deep Reaction Ion Etching) after the corresponding deposition. Then, a groove 2010 parallel to the layer sequence direction 2050 is etched in the deposited layers 2001 to 2005. After the corresponding structuring, the groove 2010 or the groove area etched in the deposited layers 2001, ..., 2005 is filled with oxide. After the corresponding deposition process, an oxide layer 2011, ..., 2014 is applied regionally on the previously deposited layers 2001, ..., 2005 and appropriately structured.

[0070] The at least regional convex or concave two-dimensional curvature of the membrane spring 1 is formed in an additive manufacturing step by depositing regionally overlapping layers 1001, ..., 2005. The geometry of the membrane spring 1 or membrane spring element 10, 20 produced in this way and the resulting spring characteristic curve can be predetermined by the thickness of the individual layers 2001, ..., 2005, the overlap of the individual layers 2001, ..., 2005 (especially in the direction of the layer sequence 2050) and / or the structuring in the individual layers 2001, ..., 2005. For this purpose, grooves can be introduced in the radial direction, for example. (For example, by means of XeF 2 After the arched components 1, 10, 20 are exposed, the components are constructed in a stepped manner in cross section according to the thickness of the individual layers 2001, ..., 2005, such as in particular Figure 8f as shown in .

[0071] like Figure 8gAs shown in , in a subsequent optional method step, the surface is smoothed, for example by tempering, in particular tempering in a hydrogen atmosphere. In this case, any residual mechanical stresses that may still exist are reduced in an advantageous manner.

[0072] exist Figure 8g In the method step, the opening 2020 on the front side 1001 of the manufactured component is preferably closed, in particular by means of laser loading. Optionally, it is provided that an access opening 2030 is provided in the substrate 1030, in particular for pressurizing the cavity 140 adjoining the membrane spring 1 or the membrane spring element 10, 20.

[0073] 4 to 7 schematically illustrate the production of a membrane spring 1 or a membrane spring element 10, 20 in a prototyping technology. In this process, a thin layer 100, usually made of silicon, of a layer composite, in particular an SOI wafer (SOI: Silicon-on-Insulator), is exposed. The layer 100 is arranged on a substrate 120, which is also usually made of silicon, and is separated from the substrate by an intermediate insulating layer 110, in particular made of oxide. The layer 100 is exposed locally, for example by trench etching from the back side of the substrate 120. The insulating layer 110 is then completely or at least regionally removed from the back side of the exposed layer 100.

[0074] For example, Figure 4b It is shown that a section of the insulating layer 110 optionally remains in the central region of the exposed layer 100 , which after the modification provides a functional membrane 70 of the membrane spring 1 or the membrane spring element 10 , 20 .

[0075] For the reshaping, a pressure difference is established between the front side and the back side of the exposed layer 100, for example, 1 bar ambient pressure on the front side and a vacuum on the back side. In particular, the cavity 140 formed between the back side of the exposed layer 100 and the further substrate 150 can be evacuated. During the heating process, optionally in a hydrogen environment, the exposed layer 100 for the membrane spring 1 or the membrane spring element 10, 20 is plastically deformed under pressure loading. As in particular in Figure 4b As shown in , the insulating layer 110 that may remain in the center of the film on the back side can serve as a mechanical stop. The insulating layer 110 that remains regionally can also be used to locally limit or reduce plastic deformation ("flow").

[0076] Before the heating process, the front and / or back side of the exposed layer 100 can be locally structured. In order to adjust the spring properties and define areas with greater plastic deformation during the heating process, local recesses, such as locally thinned areas, etc. can be introduced. After cooling and elimination of the pressure difference, a two-dimensionally curved membrane 1 or a two-dimensionally curved membrane spring element 10, 20 is produced, which has reduced intrinsic mechanical stresses.

[0077] Figures 5a to 5e A method for producing a membrane spring 1 or a membrane spring element 10 , 20 is presented, the method comprising the following steps:

[0078] - providing a layer structure 600, in particular an SOI wafer, having a layer 100, in particular made of silicon, an insulating layer 110 and a substrate 120, see in particular Figure 5a ;

[0079] - exposing the layer 100 in the layer structure 600, wherein the substrate 120 and the insulating layer 110 are removed in regions, see in particular Figure 5b ;

[0080] - applying pressure to the exposed layer 100 , wherein a pressure difference is established between the end faces of the exposed layer 100 ; and

[0081] - under at least local heating, the exposed layer 100 is plastically deformed, in particular see Figures 5c to 5e .

[0082] As in Figure 5d , as shown in 5e and 6, the plastic deformation of the exposed layer 100 can be achieved by local softening of the material, in particular by means of laser loading. The laser loading can optionally be carried out in a hydrogen environment. For plastic modification, the exposed layer 100 is deflected by pressure loading. The exposed layer 100 is heated regionally, preferably locally by means of laser radiation, so that the exposed layer can be plastically deformed. The parameters of the laser radiation, such as wavelength and / or pulse duration, are selected so that the material of the exposed layer 100 can be heated efficiently and uniformly. In order to couple the energy of the laser beam as uniformly as possible over the substrate thickness, the absorption characteristics of the exposed layer 100 can optionally be adjusted by means of corresponding doping materials (especially doped silicon).

[0083] As in Figure 5d , 5e and 6, the laser beam is repeatedly deflected onto the exposed layer 100 along a trajectory 3010 by a controllable optical deflection unit (scanner). With rapid repetition and sufficiently high energy coupling, the material of the exposed layer 100 is heated relatively uniformly along the trajectory 3010, so that the material can be deformed when a temperature sufficient for plastic deformation is reached. Figure 6As shown in , the extent and location of the plastic deformation can be predetermined by a selected trajectory 3010 of the laser beam 3000 on the film surface and can therefore be varied in particular in the tangential and / or radial direction.

[0084] Pulsed and continuous laser radiation, in particular continuous wave laser (Dauerstrichlaser) laser radiation, are suitable for processing the exposed layer 100. In addition, the degree of local plastic deformation can be adjusted, for example, by laser energy density, irradiation duration and / or pressure loading. In the extended scheme, it is provided that these parameters can be adjusted according to the deformation measured on site during the process, so that the desired deformation of the exposed layer 100 is realized corresponding to the predetermined two-dimensional camber. The advantage of this modified method is that the membrane is flat before deformation, so that functional sensor or actuator elements, such as piezoresistive or piezoelectric elements, wiring planes, etc. can be manufactured on a flat wafer surface by means of a conventional MEMS process. However, these elements may be destroyed at the high temperatures usually required for the plastic deformation of the exposed layer 100. The use of laser radiation advantageously realizes the formation of a local temperature influence on the exposed layer 100 to be modified, and this local temperature influence is basically limited to the irradiated area. The membrane spring 1 or the membrane spring elements 10 , 20 can therefore be produced in a wafer or layer composite, so that damage to other functional elements of the MEMS component 700 to be produced can be largely avoided and scrap can be reduced.

[0085] Figure 7a The diaphragm spring 1 or the diaphragm spring element 10 , 20 produced by reshaping is shown in a side view without an existing pressure difference. Figure 7b Accordingly, a diaphragm spring 1 or a diaphragm spring element 10, 20 with pneumatic pre-deflection is shown, wherein the cavity 140 is charged with negative pressure or positive pressure. The cavity 140 is bounded regionally by the diaphragm spring 1 or the diaphragm spring element 10, 20, so that an elastic pre-deflection can be achieved by pressure loading. The pneumatic pre-deflection of the diaphragm spring 1 or the diaphragm spring element 10, 20 serves to adjust the operating point of the diaphragm spring 1 with respect to the spring characteristic curve, in particular so that the operating point is within the range of the at least approximately linear spring characteristic curve with a small slope.

[0086] Figures 9a to 9lA method for producing a MEMS component 700 is shown, which has a membrane spring 1 configured as a spring assembly, which comprises a first and a second membrane spring element 10, 20 mechanically coupled to one another. The membrane spring elements 10, 20 have a two-dimensionally convexly or concavely curved cross section and are mechanically coupled to one another so that the resulting spring force 501 follows a nonlinear, in particular linear-nonlinear, spring characteristic curve. Shown is a schematic layer structure and an example of a process sequence for producing such a spring assembly with an integrated device for pre-deflecting the membrane spring elements 10, 20 mechanically coupled to one another. For example, the MEMS component 700 can be a MEMS loudspeaker.

[0087] In a first step, a first, a second and a third wafer 41, 42 and 43, in particular wafers made of silicon, are provided. Figure 9a .

[0088] The third wafer 43 is provided with a rotationally symmetrical passage opening 44 in the region of the functional film. On the outside of the passage opening 44, smaller further passage openings 45 and 46 are also provided in the third wafer 43. The further passage openings 45 and 46 can be recessed relative to the surface of the third wafer 43 on the front side.

[0089] A bonding agent 47 for hermetic bonding may be optionally applied in regions on the back side of the third wafer 43. Wafer bonding (also called wafer bonding) can be performed with the aid of conventional MEMS processes and equipment, for example by hermetic glass bonding or eutectic bonding.

[0090] In the embodiment shown, the second wafer 42 comprises three layers 48 , 49 , 50 , wherein the thickness of the first layer 48 of the second wafer 42 is preferably selected to ensure handling of the second wafer 42 during the manufacturing method.

[0091] The second layer 49 and / or the third layer 50 of the second wafer 42 are optionally polysilicon layers. Thin oxide layers 51 and 52 are introduced between the layers 48, 49 and 50. The second membrane spring element 20 with a nonlinear characteristic curve is produced from the second layer 49 of the second wafer 42. The thickness of the second layer 49 of the second wafer 42 is preferably designed according to the desired spring characteristic curve. The desired curvature height of the second membrane spring element 20, which is formed by the second layer 49, is defined by the thickness of the third layer 50 of the second wafer 42. In the third layer 50 of the second wafer 42, a groove 53 is introduced at the location of the further passage opening 46. A further rotationally symmetrical, in particular annular groove 54 defines the clamping or width of the second membrane spring element 20.

[0092] The first wafer 41 consists of three layers 55, 56 and 57. The thickness of the first layer 55 of the first wafer 41 is preferably selected such that handling of the first wafer 41 is ensured during the manufacturing method. The second layer 56 and / or the third layer 57 of the first wafer 41 can optionally consist of polysilicon. Thin oxide layers 58, 59 are introduced between the layers 55, 56, 57. The first membrane spring element 10 with a linear characteristic curve is produced from the second layer 56 of the first wafer 41. Its thickness is designed according to the desired spring characteristic curve. The thickness of the third layer 57 of the first wafer 41 defines the desired curvature height of the first membrane spring element 10, which is formed by the second layer 56. Annular grooves 60 and 61 are introduced into the third layer 57. The groove 60 defines the clamping or width of the first membrane spring element 10 with a linear characteristic curve. The connection element 62, which is particularly annular and remains between the grooves 60 and 61, serves for the mechanical connection or mechanical coupling of the first and second membrane spring elements 10, 20. The connecting element 62 is at least located along its periphery (see in particular Figure 9d ) is interrupted by a transverse opening 63.

[0093] The third layer 57 of the first wafer 41 and the third layer 50 of the second wafer 42 are aligned facing each other and bonded to each other (see in particular Figure 9b and 9c ). Suitable direct bonding processes, preferably with the introduction of heat, are known to the person skilled in the art. After cooling, a negative pressure, preferably a vacuum, is set in the concentrically arranged cavity 66 formed by the grooves 60, 61, 54.

[0094] In a subsequent method step, the first layer 48 of the second wafer 42 is removed (see in particular Figure 9d ). After the first layer 48 of the second wafer 42 has been removed, the exposed section of the second layer 49 is curved in the direction of the cavity 66 due to the applied pressure difference. The curvature continues until the exposed section of the second layer 49 contacts the connecting element 62, wherein the second layer 49 is formed for the second membrane spring element 20 and the partial region 68 of the cavity 66 is separated from the connecting element 62. This method step is preferably supported by annealing in a hydrogen atmosphere.

[0095] In a further method step, the central region 80 of the second layer 49 which is modified for the second membrane spring element 20 is firmly connected to the connecting element 62. This is done, for example, locally by means of laser welding (see in particular Fig.9e ).

[0096] The cavity 66 is then ventilated by locally removing the second layer 49 of the second wafer 42 in the region of the passage opening 46 (see in particular Figure 9fSince the partial region 68 of the cavity 66 is connected to the environment via the transverse opening 63 , the ambient pressure is set in the partial region 68 .

[0097] Figure 9g The wafer stack consisting of the first, second and third wafers 41, 42 and 43 after bonding is shown. In the wafer stack structure, an annular, tightly sealed cavity 67 is thus produced between the third wafer 43 and the curved membrane spring element 20. The position and size of the passage opening 45 are determined so that it forms an access opening to the cavity 67. The passage opening 46 is located above the recess 53 and forms an access opening to the cavity 66, which has a partial area 68. In the area of ​​the passage opening 44 of the third wafer 43, the layers 49, 50, 57 are regionally removed by means of trench etching and oxide etching (see in particular Figure 9h ).

[0098] Figure 9i , 9j and 9k show the removal of the first layer 55 of the first wafer 41 and the construction of a functional sensor or actuator element on the exposed, closed and flat second layer 56 of the first wafer 41.

[0099] Second layer 56 of first wafer 41 forms functional membrane 70 and first membrane spring element 10 with linear spring characteristic. First membrane spring element 10 with linear spring characteristic is mechanically coupled to curved membrane spring element 20 via connecting element 62 and thus integrally forms membrane spring 1.

[0100] The cavity 67 is evacuated through the passage opening 45 and then permanently and tightly closed by means of a laser process, in particular a laser resealing process, by a closing device 460 (see in particular Figure 9l ). The pressure difference thus established between the cavities 67 and 66 / 68 leads to a vertical pre-deflection of the membrane spring 1, which is formed as a spring combination element by the first and second membrane spring elements 10, 20. Due to the clamping of the membrane spring 1 on its outer periphery, the functional membrane 70 as a whole is biased in the layer sequence direction, which coincides with the first direction 601. The mechanical restoring force of the combined membrane spring elements 10, 20 is in a state of force equilibrium with the compression force generated by the pressure difference between the inside and the outside of the cavity 67. After the deflection of the membrane spring 1, the membrane spring preferably has a reduced spring stiffness, and the functional membrane 70 therefore has a soft suspension.

[0101] The first membrane spring element 10 of the MEMS component 700 is mechanically connected to the layer structure 600 on its outer periphery and is also mechanically connected to the second membrane spring element 20, so that the functional membrane 70 suspended on the inner periphery of the first membrane spring element 10 is movably guided along a spring path parallel to the first direction 601. The annular second membrane spring element 20 of the MEMS component 700 is clamped on both sides to transmit a substantially linear-nonlinear or nonlinear force depending on the deflection. The second membrane spring element is mechanically connected to the layer structure 600 on its inner periphery and outer periphery and is mechanically connected to the first membrane spring element 10 in a central, two-dimensionally curved region. The first membrane spring element 10 has a substantially linear characteristic curve, so that the spring characteristic curve of the coupled membrane spring substantially follows a nonlinear spring characteristic curve, in particular a linear-nonlinear spring characteristic curve, in particular in a region with a small positive or negative spring constant after pre-deflection.

[0102] FIG. 10 shows a perspective view of a MEMS component 700, which corresponds to the MEMS component in FIG. Figures 9a to 9l The method shown in is used for manufacturing. In this manufacturing method, the curved second membrane spring element 20 is manufactured by means of reshaping. The reshaping process is integrated into the entire process flow.

[0103] Alternatively, the curved second membrane spring element 20 in the second wafer 42 can be produced as a separate component by means of additive or subtractive technology, in particular by means of one of the methods shown in FIGS. 1 to 8 , and then bonded to the first wafer 41 . Fig.11a and 11b Such a fabrication is schematically illustrated in FIG. Figures 9e to 9l The process steps remain unchanged to the greatest extent. In this alternative process, other methods, such as eutectic bonding, can also be used to bond the first wafer 41 and the second wafer 42.

[0104] Fig.12 An embodiment is shown in which a large mass is fastened to the functional film 70. This corresponds essentially to Figure 9h A state of the art process with a modified third wafer 43 having a recess 81 instead of a channel opening 44. For example, when using such a MEMS component 700 as an energy harvester, a large mass and a soft but strong spring suspension are advantageous.

[0105] The production method shown has in particular the following features:

[0106] - producing a two-dimensionally curved second membrane spring element 20 with a nonlinear spring characteristic curve;

[0107] - producing a first membrane spring element 10 having a linear spring characteristic curve;

[0108] - a mechanical connection is established between the first membrane spring element 10 and the second membrane spring element 20, optionally connected to form a membrane spring 1 via a connecting element 62, said membrane spring corresponding to a linear-nonlinear spring combination, on which the functional membrane 70 is suspended;

[0109] - producing a tight cavity 67 below the membrane spring element 20 and a pneumatic space half or at least one cavity 66 , 68 above the membrane spring element 20 , so that a pressure difference between the cavities 67 and 66 / 68 leads to a pre-deflection of the membrane spring element 20 ;

[0110] - applying a functional layer to the planar, non-deflected functional film 70 and / or the film spring element 10;

[0111] A pressure difference is established between the pneumatic cavities 67 and 66 / 68 above and / or below the membrane spring element 20 , in particular by evacuating the cavity 67 or temporarily evacuating the cavities 66 , 68 via the passage openings 45 , 46 .

[0112] - establishing a pre-deflection of the membrane spring 1 designed as a spring assembly element, so that the common spring rate is reduced by the deflection, so that the operating point is placed in the range of the spring characteristic curve with a small slope;

[0113] The cavity 67 is permanently closed, for example in the evacuated state, which corresponds to the establishment of a permanent pre-deflection of the membrane spring 1 .

Claims

1. A MEMS component (700), in particular a MEMS actuator or a sensor, comprising a micromechanical membrane spring (1), the micromechanical membrane spring comprising a first membrane spring element (10) and a second membrane spring element (20), the first membrane spring element and the second membrane spring element having at least regionally convex or concave two-dimensional curvatures, wherein: The first membrane spring element (10) is mechanically coupled to the second membrane spring element (20) so that the spring force (501) induced by the membrane spring (1) is transmitted by the first and second membrane spring elements (10, 20), wherein the micromechanical membrane spring (1) is integrated in the layer structure (600) of the MEMS component (700) so that the spring force (501) induced by the membrane spring (1) acts essentially along the layer sequence direction of the layer structure (600), wherein the device for pre-deflecting the membrane spring (1) is provided for adjusting the working point of the membrane spring (1) relative to the spring characteristic curve by permanent elastic deflection of the membrane spring (1), in particular so that the working point is located in the region of the spring characteristic curve of the membrane spring (1) having a low slope and being at least approximately linear.

2. The MEMS component (700) according to claim 1, wherein: The first membrane spring element (10) is mechanically coupled to the second membrane spring element (20) such that the induced spring force (501) follows a nonlinear spring characteristic curve.

3. The MEMS component (700) according to any one of the preceding claims, wherein: The first diaphragm spring element (10) is designed to generate a spring force that follows a linear characteristic curve, while the second diaphragm spring element (20) is designed to generate a spring force that follows a nonlinear spring characteristic curve.

4. The MEMS component (700) according to any one of the preceding claims, wherein: The first membrane spring element (10) is mechanically connected in a central region (80) of the second membrane spring element (20) for generating an induced spring force.

5. The MEMS component (700) according to any one of the preceding claims, wherein: The first and second membrane spring elements (10, 20) are substantially annular in shape and are arranged concentrically with respect to one another.

6. The MEMS component (700) according to any one of the preceding claims, wherein: The membrane spring (1) at least partially, in particular the first membrane spring element and / or the second membrane spring element (10, 20), consists of silicon.

7. The MEMS component (700) according to any one of the preceding claims, wherein: The device for pre-deflection comprises at least one cavity (66, 67, 140) which is acted upon by negative or positive pressure and which is at least regionally bounded by the membrane spring (1), in particular at least regionally by the first membrane spring element and / or the second membrane spring element (10, 20).

8. The MEMS component (700) according to any one of the preceding claims, wherein: The first membrane spring element (10) is mechanically connected to the layer structure (600) on the outer periphery and to the second membrane spring element (20) so that the functional membrane (70) suspended on the inner periphery of the first membrane spring element (10) is movably guided along a spring path parallel to the layer sequence direction.

9. The MEMS component (700) according to any one of the preceding claims, wherein: The second membrane spring element (20) is mechanically connected to the layer structure (600) at its inner circumference and its outer circumference and is mechanically connected to the first membrane spring element (10) in the region of the central two-dimensional curvature.

10. A method for producing a membrane spring (1) of a MEMS component (700), in particular a MEMS component (700) according to any one of the preceding claims, wherein: The production of at least regionally convex or concave two-dimensional curvature of the membrane spring (1) comprises additive, subtractive or modified production steps.

11. The method according to claim 14, wherein: In a modified manufacturing step, the at least regionally convex or concave two-dimensional curvature of the membrane spring (1) is manufactured in the layer structure (600) of the MEMS component (700), so that at least partially exposed layers (56, 59, 100) of the layer structure (600) are loaded with pressure and plastically deformed.

12. The method according to claim 15, wherein: During the plastic deformation, the sectionally exposed layer (56, 59, 100) is heated locally, in particular by means of laser radiation.

13. The method according to claim 15 or 16, wherein: The first membrane spring element (10) is mechanically connected to the second membrane spring element (20) of the membrane spring (1) by means of laser welding.

14. A method according to any one of the preceding claims 15 to 17, wherein: In order to permanently elastically pre-deflect the membrane spring (1), at least one cavity (67, 140) introduced into the layer structure (600) is loaded with negative pressure or positive pressure and is sealed in an airtight manner, wherein the cavity (67, 140) is at least regionally bounded by the membrane spring (1), in particular at least regionally bounded by the first membrane spring element and / or the second membrane spring element (10, 20).

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