Micro-electromechanical device, micro-electromechanical microphone and method for producing micro-electromechanical device

Abstract

The invention relates to a microelectromechanical device (1) for capacitive fluid pressure measurement, comprising a first membrane (2) and a second membrane (3) which can be elastically deflected by the fluid pressure, a hollow space (4) being formed between the first membrane (2) and the second membrane (3), a counter electrode (5) is arranged in the hollow space, the counter electrode (5) is provided with a plurality of radial etching channels (10), and the etching channels extend from a counter electrode center (5b) to a counter electrode edge (5a) in the radial direction. The invention further relates to a microelectromechanical microphone and to a method for producing a microelectromechanical device (1).

Description

Technical Field

[0001] The invention relates to a micro-electro-mechanical device, a micro-electro-mechanical microphone and a method for manufacturing a micro-electro-mechanical device. Background Art

[0002] Microelectromechanical devices (also referred to as MEMS devices) and methods for their production are known from the prior art.

[0003] DE 10 2014 212 340 A1 discloses a MEMS microphone having a first membrane element, a counter-electrode element and a low-pressure region between the first membrane element and the counter-electrode element.

[0004] US Pat. No. 10 362 408 B2 relates to a MEMS device having a first membrane and a second membrane, between which a hollow space is formed and in which a counter-electrode is arranged.

[0005] DE 10 2017 204 023 A1 describes a MEMS device and a MEMS vacuum microphone. The MEMS device has a first and a second membrane element and a low-pressure region formed between them. A corresponding electrode structure arranged in the low-pressure region has a conductive layer, which has segments, and the segments provide electrical insulation between the first and second segments of the conductive layer.

[0006] KR 10 2022 0 089 656 A discloses a MEMS device having a first membrane, a second membrane and a third membrane, wherein the second membrane is arranged between the first membrane and the third membrane and has a plurality of openings, wherein a low-pressure region is formed between the first membrane and the third membrane, in which a plurality of electrodes extend.

[0007] US2020 / 0 145 762A1 discloses an acoustic device comprising a substrate, a first conductive membrane, and a first spacer for forming a first acoustic cavity between the first membrane and the substrate, and a second conductive membrane and a second spacer for forming a second acoustic cavity between the first membrane and the second membrane. Summary of the invention

[0008] According to the features of the independent claim 1, a micro-electromechanical device for capacitive fluid pressure measurement is proposed, wherein the device has a first membrane and a second membrane, which can be elastically deflected by fluid pressure, wherein a hollow space is formed between the first membrane and the second membrane, and a corresponding electrode is arranged in the hollow space, wherein the corresponding electrode has a plurality of radial etching channels, which extend radially from the center of the corresponding electrode to the edge of the corresponding electrode.

[0009] This provides a device that can be manufactured simply and process-safely. The etching channels in the counter-electrode can simplify the manufacture of the device, since the etching medium can be better distributed in the device, thereby achieving an acceleration and homogenization of the etching process. In addition, the etching channels can form channel openings in the counter-electrode, through which, for example, support columns can extend in order to mechanically couple the first membrane and the second membrane to each other and / or stabilize them with respect to the ambient pressure. The radial extension of the etching channels in the counter-electrode ensures a high rigidity of the counter-electrode. The plurality of etching channels can, for example, consist of at least two etching channels.

[0010] The counter electrode can have, for example, a round, for example, circular cross section. The counter electrode can have a counter electrode edge on its circumference and a geometrically defined counter electrode center between two opposite points or sections of the counter electrode edge. When manufacturing the device, the etching channel can, for example, be formed by a hollow volume in at least one material layer of the device. Alternatively or additionally, it can be that the etching channel is formed by a structure that has an etching rate that is several times higher than that of the surrounding sacrificial layer material. For example, it is advantageous to arrange a highly doped oxide region next to an undoped oxide region, which can be removed, for example, using a gaseous, hydrogen fluoride-based etching method.

[0011] The device can be arranged to carry out capacitive fluid pressure measurement. The deflection of the first and / or second film determined by the fluid pressure causes the spacing change between the deflected film and the substantially fixed corresponding electrode. The capacitance between the film and the corresponding electrode produced by such spacing change is relative to the change of basic capacitance. Therefore, the deflection of the first and / or second film can be converted into an electrical signal, thereby the device can be called an electromechanical converter.

[0012] The device can be manufactured by a structured material layer applied to a substrate. The second film can be arranged closer to the substrate than the first film, so that the first film can also be referred to as a film facing away from the substrate, and the second film can also be referred to as a film facing the substrate. The first film can extend substantially parallel to the second film. The first film and the second film can extend substantially parallel to the surface of the substrate. A substrate recess can be formed in the substrate, which can, for example, constitute the front volume and / or rear volume of the device. The second film can span the substrate recess. In particular, the main film portion of the second film (to be explained below) can span the substrate recess.

[0013] The first film and the second film can be elastically deflected by fluid pressure, and the first film and the second film can be, for example, respectively composed of elastically displaceable and / or elastically deformable material layers. The film thickness of the first and / or second film can be, for example, defined by the layer thickness of the film layer constituting the film, and the film thickness of the first and / or second film can be, for example, 0.2 to 2 microns. The film diameter can be, for example, 400-2000 microns, which can be equivalent to the extension of the film perpendicular to the film edge thickness and parallel to the substrate surface. The elastically deflectable film can be understood as a reversibly deflected film, and when the fluid pressure generating the effect is reduced or stopped, the film will strive to return to its initial position and / or initial shape. The first and / or second film can be shifted between the initial position and the deflected position, especially steplessly shifted. The first film can be deflected due to the fluid pressure acting on the first film. The second film can be deflected due to the fluid pressure acting on the second film. The first and second films can be, for example, mechanically coupled and stabilized relative to the ambient pressure of the device by a support column extending between the films, especially substantially vertically between the films. Due to the mechanical coupling, the first and second membranes can also deflect together and synchronously when fluid pressure acts on the first or second membrane. The fluid pressure can be, for example, a static, quasi-static or dynamic fluid pressure, and can also represent, for example, a mechanical fluid pressure vibration such as an acoustic vibration, which causes a mechanical vibration of the first and / or second membrane.

[0014] The first membrane and / or the second membrane can have a round, for example, circular cross-section. The first and / or the second membrane can be limited by the membrane edge in its circumference and have a geometrically defined membrane center between two opposite points or sections of the membrane edge. The first and / or the second membrane can have the following membrane edge section: the membrane edge section can, for example, extend radially from the membrane edge toward the membrane center on a section of up to 20% of the membrane diameter. The membrane edge section can be a surrounding membrane edge section. The area of ​​the membrane starting from the membrane edge section to the opposite membrane edge section (in other words, the membrane area adjacent to the membrane edge section in the direction of the membrane center) can be called the main membrane section. When the fluid pressure acts, a greater deflection of the membrane may be caused in the main membrane section than in the membrane edge section. In other words, when deflected, the main membrane section is displaced and / or deformed, for example bent, more strongly than in the membrane edge section. The membrane edge section and the main membrane section can directly transition to each other. The terms "membrane main section" and "membrane edge section" may refer to the surface of the largest extension of the first membrane. Optionally, the first membrane and / or the second membrane may have an electrically insulating layer between the membrane edge section and the membrane main section in order to create a structural separation between the two sections and to focus the capacitance measurement area even more strongly on the membrane main section.

[0015] The hollow space formed between the first and second membranes is bounded by the first membrane and the second membrane. A lateral hollow space boundary extends between the first and second membranes, in particular extends around the first and second membranes substantially perpendicularly, which can be formed, for example, by a counter-electrode layer of the device between the membranes and / or a further material layer. The hollow space can be sealed substantially fluid-tight.

[0016] According to one embodiment, the corresponding electrode can be spaced apart from the lateral hollow space boundary of the hollow space by a free space channel that surrounds the corresponding electrode at least in sections, wherein the corresponding electrode has at least one support arm, which is anchored to the lateral hollow space boundary and can be conductively contacted. Thus, a defined capacitance measurement area is provided on the corresponding electrode to detect the capacitance change caused by the deflection of the first and / or second membrane. The measurement of parasitic capacitance can be reduced or avoided by the gap provided by the free space channel that surrounds the corresponding electrode, thereby improving the accuracy of the detected measurement signal. In other words, the free space channel can achieve electrical insulation of the corresponding electrode, which leads to more accurate measurement results. In addition, the free space channel has the following advantages: it can form an etching medium distribution channel in the manufacture of the device, and the etching medium distribution channel can help to accelerate and homogenize the etching process, for example, when etching at least one sacrificial layer to form a hollow space. The free space channel can have a larger channel cross section than the radial etching channel of the corresponding electrode.

[0017] The corresponding electrode can be a substantially rigid and / or fixed structure of the device, which constitutes a measuring capacitance with the first and / or second film. The corresponding electrode can extend substantially parallel to the first and / or second film. The corresponding electrode thickness can be defined, for example, by the layer height of the corresponding electrode or by its extension perpendicular to the substrate surface, and the corresponding electrode thickness can be, for example, 1 to 10 microns. The spacing between the corresponding electrode and the first and / or second film can be, for example, 0.5 to 5 microns. The corresponding electrode can be coupled to the hollow space boundary by at least one, especially multiple support arms, wherein a support arm or multiple support arms can, for example, bridge or cross the free space channel. The corresponding electrode is maintained in the hollow space by at least one support arm and can be connected by the support arm electrical contact. The free space channel can be divided into free space channel segments by a support arm or multiple support arms, as explained in more detail later. The corresponding electrode can, for example, also be coupled to the hollow space boundary by two, three, four or more support arms. Thus, a uniform and stable support of the corresponding electrode is achieved. The support arms can, for example, be arranged in pairs, opposite to each other. The counter electrode can have a round, for example circular cross section, i.e., for example, a circular counter electrode surface is formed, which is opposite to the first membrane and the second membrane. The counter electrode can have a counter electrode edge on its circumference and a geometrically defined counter electrode center between two opposite points or sections of the counter electrode edge. The counter electrode edge can be a circumferential boundary of the counter electrode, to which the free space channel adjoins. The hollow space boundary, the free space channel and the counter electrode can be arranged concentrically with the counter electrode center as the center.

[0018] The hollow space and / or free space channel can be formed by a material recess in the device, for example by a partially removed material layer of the device. The free space channel can be delimited laterally, for example, by the hollow space boundary and by the counter electrode and directly transition into the wider hollow space region between the counter electrode and the membrane. The free space channel can extend at least in sections between a membrane edge section of the first membrane and a membrane edge section of the second membrane, which is opposite to the membrane edge section of the first membrane.

[0019] According to one embodiment, the free space channel can be connected to at least one etching inlet channel of the device extending through the first membrane by flow technology. Thus, in the manufacture of the device, it is achieved that the free space channel constitutes an etching medium distribution channel, which can help to accelerate and homogenize the etching process, for example, when etching at least one sacrificial layer to construct a hollow space. "Flow technology connection" can be understood as that the free space channel directly transitions into the etching inlet channel or leads to it, or, in other words, the etching inlet channel leads to the free space channel. The etching inlet channel can, for example, extend substantially vertically through the first membrane. The first membrane can have a plurality of etching inlet channels, wherein the free space channel can be connected to one, a plurality of or all etching inlet channels in the first membrane. The etching inlet channel can have a smaller channel cross section than the free space channel.

[0020] According to one configuration of the previously described embodiment, the etching inlet channel can extend through a membrane edge section of the first membrane, wherein the membrane edge section extends radially from the membrane edge in the direction of the membrane center of the first membrane over a section of up to 20% of the membrane diameter. As a result, the mechanical properties of the first membrane in its membrane main section can be maintained, so that despite the introduction of the etching inlet channel, the first membrane can be deflected uniformly and does not experience bending effects (for example due to thermal or mechanical pre-bending). As a result, the first membrane can be designed with high mechanical sensitivity. According to an embodiment, it can be additionally provided that no etching inlet channel extends through the membrane main section of the first membrane. As a result, rigidification of the membrane caused, for example, by the closure of the etching inlet channel in the region of its greater deflection can be avoided. According to another advantageous embodiment, the membrane edge section can extend radially from the membrane edge in the direction of the membrane center of the first membrane over a section of up to 15%, up to 10% or up to 5% of the membrane diameter, thereby further improving the mobility of the membrane. In order to illustrate the section ratio relationship in a 20% extension of the membrane edge section, for example, when the diameter of the membrane is 20 unit lengths, the membrane center is located at 10 unit lengths starting from a fixed point at the membrane edge, the membrane edge section extends 4 unit lengths, and after the membrane edge section, the membrane main section extends in the area of ​​4 to 16 unit lengths, and a 4 unit length membrane edge section of the opposite membrane edge is immediately followed by the membrane main section.

[0021] According to one embodiment, the corresponding electrode can be arranged at least in sections, in particular completely, between the main membrane section of the first membrane and the main membrane section of the second membrane (which is opposite to the main membrane section of the first membrane). The corresponding electrode can be positioned, for example, between the first and second membranes so that it is aligned with the main membrane sections of the first and second membranes, that is, its corresponding electrode surface is respectively opposite to the main membrane section. As a result, the main membrane section and the corresponding electrode can construct a defined capacitance measurement area. Therefore, the accuracy of the capacitive fluid pressure measurement can be further improved. The main membrane section of the first membrane can be located between two mutually opposed membrane edge sections of the first membrane, wherein the membrane edge section can, for example, extend radially from the membrane edge toward the membrane center of the first membrane on a section of up to 20% of the membrane diameter. The main membrane section of the second membrane can be located between two mutually opposed membrane edge sections of the second membrane, wherein the membrane edge section can, for example, extend radially from the membrane edge toward the membrane center of the second membrane on a section of up to 20% of the membrane diameter.

[0022] According to one embodiment, the free space channel can be divided into a plurality of free space channel segments, and each free space channel segment can be connected to at least one etching inlet channel in a flow-technical manner. This can simplify the manufacture of the device, since the etching medium can be distributed more evenly and simultaneously via more inlets in the device, thereby achieving an acceleration and homogenization of the etching process. The free space channel can have a segmentation, for example, due to the support arms of the corresponding electrodes. For example, the free space channel can be divided into four free space channel segments by four support arms, wherein each free space channel segment can be connected to an etching inlet channel.

[0023] According to one embodiment, a gas volume can be enclosed in the hollow space, which has a gas pressure below the ambient air pressure. In this way, thermal noise and squeeze film attenuation effects are effectively prevented in capacitive fluid pressure measurement. For example, in the manufacture of the device, the gas volume can be enclosed, for example, in a simple and reliable manner via at least one etched inlet channel of the device and its closure. Here, the etched inlet channel can advantageously extend through the membrane edge section of the first membrane, so that the etched inlet channel and its closure do not hinder or hardly hinder the main membrane section, for example due to local stiffening (Aussteifung) or bending effects.

[0024] According to one embodiment of the previously described embodiment, the gas volume can be surrounded by a closure of at least one etched inlet channel. The closure can have, for example, a dielectric layer and / or a metal layer. If the closure has a dielectric layer and a metal layer, the metal layer can, for example, be applied to the dielectric layer. The metal layer can, for example, contain aluminum. The dielectric layer can, for example, consist of silicon dioxide or silicon nitride. The dielectric layer can be designed as a gas-tight encapsulation of the gas volume. The metal layer can provide a high service life and a reliable sealing guarantee. In principle, the closure can also be realized by local melting of the membrane material.

[0025] According to one embodiment, the first film, the second film and / or the corresponding electrode can be made of polysilicon. As a result, very favorable mechanical properties of the film and / or the corresponding electrode can be achieved while having good electrical conductivity. In addition, polysilicon can be easily structured. Polysilicon can be, for example, doped polysilicon. The first film and / or the second film and the corresponding electrode can be composed of a polysilicon layer, wherein the polysilicon layer of the film has a smaller layer thickness than the polysilicon layer of the corresponding electrode. The corresponding electrode can also be manufactured, for example, from a plurality of polysilicon layers applied one above the other. As a result, an elastically deflectable film and a substantially rigid, fixed corresponding electrode can be constructed with the same material.

[0026] The invention also relates to a micro-electromechanical microphone for capacitive sound pressure measurement, the micro-electromechanical microphone having a micro-electromechanical device according to the previously described features and a signal processing unit for applying and processing the signals of the micro-electromechanical device. A compact and high-performance microphone can thereby be provided, which has a sensitive, accurate and particle-sensitive sound pressure measurement, a very good signal-to-noise ratio and a reduced fluid squeeze film attenuation effect. The microphone can be a capacitive microphone, i.e. an electro-acoustic converter, which converts sound into a corresponding electrical signal in that it detects a change in capacitance caused by a change in the spacing between a first and / or second membrane and a corresponding electrode. The micro-electromechanical microphone can be implemented, for example, as a system on a chip (SoC).

[0027] The invention also relates to a method for producing a micro-electromechanical device for capacitive fluid pressure measurement, the device having a first membrane and a second membrane, which can be elastically deflected by fluid pressure, wherein a hollow space is formed between the first membrane and the second membrane, in which a corresponding electrode is arranged, wherein the device is manufactured by gradually applying material layers on a substrate and structuring them, wherein the hollow space is formed by applying and subsequently etching at least one sacrificial layer, wherein during the manufacture, a corresponding electrode layer is applied to form the corresponding electrode, and the corresponding electrode layer and / or the sacrificial layer are structured so that a plurality of radial etching channels are generated in the corresponding electrode and / or in the sacrificial layer, wherein the radial etching channels in the corresponding electrode extend radially from the center of the corresponding electrode to the edge of the corresponding electrode and / or extend in the sacrificial layer. In particular, the radial etching channels in the sacrificial layer can extend radially from the center of the corresponding electrode to the edge of the corresponding electrode parallel to the extension of the corresponding electrode. In particular, the radial etching channels can extend in the sacrificial layer extending adjacent to the corresponding electrode layer, for example, directly below or directly above the corresponding electrode layer.

[0028] By constructing radial etching channels in the counter electrode and / or in at least one sacrificial layer, the manufacture of the device can be simplified and the etching process can be efficiently controlled, because the etching medium can be better distributed in the device, thereby accelerating and homogenizing the etching process. In order to produce the etching channel, a narrow groove can be etched in the counter electrode layer or in the sacrificial layer, and the narrow groove is closed with a second sacrificial layer. Here, due to the capillary effect, a groove hollow space appears in the narrow groove, and the groove hollow space can be used as an etching channel. Depending on the embodiment, a vertical etching channel can be set up in addition, wherein the vertical etching channel can extend substantially perpendicular to the main extension of the counter electrode layer.

[0029] According to one embodiment, an optional special layer can be applied between the first film layer (which can later form the second film of the device) and the substrate and optionally structured. The optional special layer can constitute, for example, a dielectric insulating layer or an etching stop layer. The optional special layer can be, for example, a silicon nitride layer. The etching stop layer can be used, for example, to better control the subsequent etching process for introducing the substrate recess into the substrate. The optional structuring can prepare the special layer for the production of electrical connections.

[0030] The first film layer can be applied on the special layer or directly on the substrate. The first film layer can be, for example, a doped polysilicon layer. According to one embodiment, the layer thickness of the first film layer can be up to 2 micrometers.

[0031] A first sacrificial layer can be applied to the first film layer and optionally structured. The optional structuring can prepare the first sacrificial layer, for example, for the production of electrical connections. The first sacrificial layer can be, for example, a silicon oxide layer.

[0032] A corresponding electrode layer can be applied to the first sacrificial layer. The corresponding electrode layer can, for example, later constitute the corresponding electrode of the device, the lateral hollow space boundary and the support arm. The corresponding electrode layer can be produced in a single layer or in a multilayer, for example by applying a plurality of polysilicon layers. According to one embodiment, the corresponding electrode layer can be deposited so that it is under tensile stress. As a result, a higher rigidity of the corresponding electrode relative to the first and second films can be achieved, and the corresponding electrode can be implemented very thinly. In addition, curvature effects can be reliably prevented, because the layer under compressive stress tends to deflect spontaneously and tensile stress can counteract this behavior.

[0033] According to one embodiment of the method, the counter-electrode layer is structured such that the counter-electrode is spaced apart from the lateral hollow space boundary of the hollow space by a free-space channel that surrounds it at least in sections and is anchored to the lateral hollow space boundary by means of at least one support arm. This makes it possible to produce a device with a defined capacitance measuring area of ​​the counter-electrode, thereby achieving a high measurement accuracy when performing capacitive fluid pressure measurement with the device. In addition, the free-space channel produced during production facilitates the distribution of the etching medium in the device, for example for producing cavities in the device, thereby simplifying the production of the device and making it possible to efficiently control the etching process of the production method.

[0034] In order to manufacture the free space channel, a portion of the corresponding electrode layer can be removed. To this end, for example, the channel opening can be etched into the second sacrificial layer so that the material of the corresponding electrode layer below the channel opening can then be removed, for example by means of an isotropic etching process. The channel opening can be closed by depositing a third sacrificial layer. The second sacrificial layer and / or the third sacrificial layer can be a silicon oxide layer. The second sacrificial layer and the third sacrificial layer can have a common layer thickness, which is substantially consistent with the layer thickness of the first sacrificial layer. It can be ensured that the hollow space region between the first membrane and the corresponding electrode later has a substantially the same height as the hollow space region between the second membrane and the corresponding electrode.

[0035] A second film layer can be applied and structured on the third sacrificial layer, which second film layer can later form the first film of the device. The second film layer can be a doped polysilicon layer. According to one embodiment, the layer thickness of the second film layer can be up to 2 micrometers.

[0036] According to one embodiment, a first film layer can be applied to manufacture a second film, and a second film layer can be applied to manufacture the first film and structured so that at least one etching inlet channel is generated in the edge section of the first film. It is achieved that the etching inlet channel and its closure do not hinder or hardly hinder the main film section of the first film during the subsequent operation of the device. For example, a narrow groove can be designed in the second film layer as an inlet, which can constitute the etching inlet channel. In particular, an inlet can be generated in the region of the second film layer, which later constitutes the film edge section of the first film. Optionally, an electrically insulating layer can be introduced into the second film layer in order to structurally separate the subsequent main film section from the adjacent film edge section and to concentrate the capacitance measurement area on the main film section.

[0037] After forming the etching inlet channel, a sacrificial layer etching can be performed, in which the first sacrificial layer, the second sacrificial layer and the third sacrificial layer are removed, so that a hollow space appears in the device. The sacrificial layer etching can be performed, for example, by means of an etching method based on hydrogen fluoride. Then, a negative pressure can be generated in the hollow space, and the hollow space can be fluid-tightly closed, for example, by plasma deposition and deposition of a dielectric layer. Then, a metal layer can be deposited and structured to ensure that the etching inlet channel is particularly firmly and hermetically sealed over a long period of time. In addition, the metal layer can be used as a contact layer. The dielectric layer and the metal layer can be removed in all areas above the second film layer except the closure, at least in the area of ​​the later film main section of the first film.

[0038] Subsequently, a substrate recess can be produced in order to construct, for example, a front volume and / or a rear volume of the device. This can be done, for example, by backside etching, wherein the backside etching can advantageously stop on the optional special layer if the optional special layer is designed as an etching stop layer. In this case, the special layer can then be removed after the backside etching in order to ensure optimal mobility of the second membrane at least in its main membrane section.

[0039] Generally speaking, in connection with the present application, unless explicitly defined otherwise, the terms “a” and “an” are not to be understood as numerals but as indefinite articles having the meaning of “at least one”. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention allows for different embodiments and is explained in more detail below based on an embodiment with accompanying drawings. It is shown in a schematic diagram:

[0041] Figure 1a-1d - a microelectromechanical device according to one embodiment in a cross-sectional top view and in a lateral cross-sectional view;

[0042] Figure 2a-2h - According to the Figure 1a A method for manufacturing a micro-electromechanical device according to a lateral cross-sectional view of a section line II shown in FIG.

[0043] Figure 3a-3g - According to the Figure 1a A method for manufacturing a micro-electromechanical device according to a lateral cross-sectional view of the section line II-II shown in FIG.

[0044] Figure 4a-4b - Schematic sketch for making radial etched channels in the sacrificial layer;

[0045] Figure 5 - Schematic sketch of a MEMS microphone with a MEMS device. DETAILED DESCRIPTION

[0046] Figure 1a , 1b, 1c and 1d show a micro-electromechanical device 1 according to one embodiment, wherein Figure 1a A cross-sectional top view is shown in FIG. Figure 1b In the figure, Figure 1a A lateral cross-sectional view of the section line II shown in FIG. Figure 1c In the figure, Figure 1a A lateral cross-sectional view of the section line II-II shown in FIG. Figure 1d In the figure, Figure 1a A lateral cross-sectional view along the section line III-III is shown in FIG.

[0047] The device 1 is configured to perform capacitive fluid pressure measurement. Figure 1b As can be seen in 1c and 1d, the device 1 has a first membrane 2 and a second membrane 3, which can be elastically deflected by fluid pressure. The fluid pressure can be, for example, static, quasi-static or dynamic fluid pressure, and in particular can also be sound pressure. The second membrane 3 extends essentially parallel to the first membrane 2. The device 1 is made of a material layer applied to a substrate 13 and structured. The second membrane 3 is arranged closer to the substrate 13 than the first membrane 2. A substrate cavity 14 is introduced into the substrate 13, and the substrate cavity can constitute the front volume and / or the rear volume of the device 1. The second membrane 3 spans the substrate cavity 14. The first membrane 2 and the second membrane 3 have a circular cross-section. As shown in Figure 1bAs shown in the figure, the first membrane 2 is delimited in its circumferential direction by a film edge 2b. The first membrane 2 has a geometric membrane center 2c. The first membrane 2 has a circumferential membrane edge section 2a, which extends radially from the membrane edge 2b in the direction of the membrane center 2c, but here occupies a section of up to 20% of the membrane diameter 2e from each point of the membrane edge 2b. Adjacent to the membrane edge section 2a, the first membrane 2 has a membrane main section 2d, and when the fluid pressure acts on the first membrane 2, a greater deflection of the first membrane 2 occurs in the region of the membrane main section than in the membrane edge section 2a. According to the illustration, the membrane edge section 2a and the membrane main section 2d transition directly into each other.

[0048] Despite Figures 1a to 1d In the figure, for reasons of simplicity, no more detailed reference numerals are provided, the second film 3 also has a film edge, a film center and a film diameter. In addition, the second film 3 has Figure 1d The membrane edge section 3a and the membrane main section 3d are marked in FIG.

[0049] A hollow space 4 is formed and delimited between the first film 2 and the second film 3. A lateral hollow space boundary 7 extends circumferentially between the first film 2 and the second film 3.

[0050] Arranged in the hollow space 4 is a Figure 1a 5 is shown in a cross-sectional top view. According to the figure, the counter electrode 5 has a circular cross section with a counter electrode edge 5a and a counter electrode center 5b. Figure 1a The cross sections I, II and III are shown in Figure 1b , 1c and 1d can understand other configurations of the corresponding electrode 5. The corresponding electrode 5 can constitute a substantially rigid and / or fixed structure of the device 1, which forms a measuring capacitance with the first membrane 2 and / or with the second membrane 3. The corresponding electrode 5 is separated from the lateral hollow space boundary 7 of the hollow space 4 by a free space channel 6 that surrounds it at least in sections. According to the embodiment shown, the corresponding electrode 5 has four support arms 8, which are used to anchor the corresponding electrode on the lateral hollow space boundary 7 and can be electrically contacted via the terminal contacts 12. The support arms 8 are arranged in pairs opposite to each other. Figure 1d, it is shown that the support arm 8 can be formed by the corresponding electrode layer G of the device. In other words, the corresponding electrode 5 can be guided to the lateral hollow space boundary 7 in the area of ​​the support arm 8 and transition therein. The free space channel 6 forms a gap and thus an electrical insulation of the corresponding electrode 5, through which the parasitic capacitance can be reduced and a defined capacitance measurement area is provided for detecting the capacitance change between the membrane 2, 3 and the corresponding electrode 5. In addition, the free space channel 6 can form an etching medium distribution channel, which can contribute to a better distribution of the etching medium in the device 1, as will be explained in more detail later in connection with the manufacturing method of the device 1 described. According to Figure 1a In the illustration in FIG. 5 , the lateral hollow space boundary 7, the free space channel 6 and the counter electrode 5 are arranged concentrically with the counter electrode center 5 b as the center. Figure 1b As can be seen in the figure, the free space channel 6 is laterally delimited by the hollow space boundary 7 and the counter electrode 5 and directly transitions into the further hollow space region between the counter electrode 5 and the membranes 2, 3. The free space channel 6 extends at least in sections between the membrane edge section 2a of the first membrane 2 and the membrane edge section of the second membrane 3, which is opposite to the membrane edge section 2a of the first membrane 2. According to the illustrated embodiment, the counter electrode 5 is completely arranged between the membrane main section 2d of the first membrane 2 and the membrane main section 3d of the second membrane 3, so that a very accurate measurement signal can be provided.

[0051] As in Figure 1a and 1c As can be seen in FIG. 5 , the counter electrode 5 has a plurality of etching channels 10, which extend radially from the counter electrode center 5 b to the counter electrode edge 5 a and open into the free space channel 6. This simplifies the production of the device 1, since the etching medium can be better distributed in the device 1 via the etching channels 10.

[0052] For reasons of simplicity, support struts are not shown further, which extend substantially vertically between the membranes 2, 3 and mechanically couple them and stabilize them with respect to the ambient pressure of the device 1. For example, the support struts can be inserted through the membranes 2, 3. Figure 1c The etching channel 10 shown in FIG. 1 and explained below extends through the etch channel 10 .

[0053] like Figure 1a , 1b and 1c, the etching inlet channel 9 leading to the free space channel 6 extends in the membrane edge section 2a of the first membrane 2. Thus, in the manufacture of the device 1, the free space channel 6 can be used as an etching medium distribution channel. Since the etching inlet channel 9 is arranged in the membrane edge section 2a of the first membrane 2, the mechanical properties of the first membrane 2 can be maintained in its membrane main section 2d and the bending effect can be avoided.

[0054] exist Figure 1a As can be seen in the figure, the free space channel 6 is divided into a plurality of (here four) free space channel segments 6a by the support arm 8. Each free space channel segment 6a is connected to the etching inlet channel 9 in terms of flow technology. The free space channel segment 6a can be supplied with etching medium uniformly and smoothly through the etching inlet channel 9.

[0055] According to the embodiment shown, a gas volume is enclosed in the hollow space 4, which has a gas pressure below the ambient air pressure in order to reduce thermal noise and squeeze film damping effects. During the production of the device 1, the negative pressure in the hollow space 4 is generated by etching the inlet channel 9, which is closed in a fluid-tight manner by the closure 11 during operation of the device 1. The closure 11 has a dielectric layer 11a and a metal layer 11b applied thereon.

[0056] Subsequently, according to Figures 2a to 2h and 3a-3g explain a method for manufacturing the device 1.

[0057] According to Figure 2a and 3a , first, an optional special layer S can be applied to the substrate 13 and optionally structured. The optional special layer S can constitute, for example, a dielectric insulating layer or an etching stop layer. With the help of the etching stop layer, for example, a subsequent etching process for introducing the substrate recess 14 into the substrate 13 can be better controlled. The special layer S can be prepared for, for example, the manufacture of electrical terminals by optional structuring. Following the optional application and optional structuring of the special layer S, the first film layer M1 is applied to the special layer S. Alternatively, the first film M1 can also be applied directly to the substrate 13. The first film M1 can be, for example, a doped polysilicon layer. According to one embodiment, the layer thickness of the first film M1 can be up to 2 microns. The first film layer M1 can then constitute the second film 3 of the device 1. The first sacrificial layer O1 can be applied to the first film layer M1 and optionally structured. The first sacrificial layer O1 can be prepared for, for example, the manufacture of electrical terminals by optional structuring. The first sacrificial layer O1 can be, for example, a silicon oxide layer. The first sacrificial layer O1 can then constitute the hollow space region of the device 1.

[0058] According to Figure 2b and 3b, a corresponding electrode layer G can be applied to the first sacrificial layer O1. According to the embodiment shown, the corresponding electrode layer G can subsequently form the corresponding electrode 5, the lateral hollow space boundary 7 and the support arm 8 of the device 1. The corresponding electrode layer G can be produced in a single layer or in multiple layers, for example by applying a plurality of polysilicon layers. According to one embodiment, the corresponding electrode layer G can be deposited so that it is under tensile stress. In order to prepare for the production of the etching channel 10, a narrow groove G1 is etched into the corresponding electrode layer G.

[0059] According to Figure 2c and 3c , the narrow trench G1 is closed with a second sacrificial layer O2. Here, due to the capillary effect, a trench hollow space G2 appears in the narrow trench G1, which can be used as an etching channel 10. Depending on the embodiment, a vertical etching channel 10 can be set up in addition. The etching channel 10 can, for example, be composed of a hollow volume in at least one material layer of the device 1. Alternatively or additionally, it can be that the etching channel 10 is constructed by the following structure: the structure has an etching rate that is several times higher than the surrounding sacrificial layer material. For example, it is advantageous to arrange a highly doped oxide region next to an undoped oxide region, which can be removed, for example, by a gaseous, hydrogen fluoride-based etching method.

[0060] According to Figure 2d , a portion of the counter electrode layer G is removed to form the subsequent free space channel 6 of the device 1. For this purpose, for example, a channel opening O2-1 can be etched into the second sacrificial layer O2, so that the material of the counter electrode layer G below the channel opening O2-1 can then be removed, for example by means of an isotropic etching process.

[0061] According to Figure 2e and Figure 3d , the channel opening O2-1 can be closed by the deposition of a third sacrificial layer O3. Optionally, the second sacrificial layer O2 and / or the third sacrificial layer O3 can be structured. The second sacrificial layer O2 and / or the third sacrificial layer O3 can be a silicon oxide layer. The second sacrificial layer O2 and the third sacrificial layer O3 can have a common layer thickness, which corresponds essentially to the layer thickness of the first sacrificial layer O1. It can be ensured that the hollow space region between the first membrane 2 and the corresponding electrode 5 later has essentially the same height as the hollow intermediate region between the second membrane 3 and the corresponding electrode 5.

[0062] According to Figure 2f and 3e, a second film layer M2 is applied to the third sacrificial layer O3 and structured, and the second film layer can later constitute the first film 2 of the device 1. The second film layer M2 can be a doped polysilicon layer. According to one embodiment, the layer thickness of the second film layer M2 can be up to 2 microns. In the second film layer M2, a narrow groove is established as an inlet M2-1, which can constitute an etching inlet channel 9. The inlet M2-1 is generated in the following area of ​​the second film layer M2: the area later constitutes the film edge segment 2a of the first film 2. Optionally, an electrically insulating layer is introduced into the second film layer M2 so as to structurally separate the subsequent film main segment 2b from the adjacent film edge segment 2d and concentrate the capacitance measurement area on the film main segment 2b.

[0063] After forming the etching access channel 9, a sacrificial layer etching is performed, in which the first sacrificial layer O1, the second sacrificial layer O2 and the third sacrificial layer O3 are removed, so that a cavity 4 is formed in the device 1. The sacrificial layer etching can be performed, for example, by means of a hydrogen fluoride-based etching method.

[0064] According to Figure 2g and 3f , a negative pressure can then be generated in the hollow space 4, and the hollow space 4 can be closed in a fluid-tight manner, for example, by plasma deposition and deposition of the dielectric layer 11a. Subsequently, the metal layer 11b can be deposited and structured to ensure a particularly strong and sealed closure 11 of the etching inlet channel 9 over a long period of time. In addition, the metal layer 11b can be used as a contact layer. The dielectric layer 11a and the metal layer 11b are removed in all areas above the second membrane layer M2 except for the closure 11, at least in the area of ​​the later membrane main section 2d of the first membrane 2.

[0065] According to Figure 2h and 3g , a substrate recess 14 can then be produced, for example to form a front volume and / or a rear volume of the device 1. This can be done, for example, by backside etching, wherein, if the special layer is configured as an etching stop layer, the backside etching can be stopped on the special layer S. In this case, the special layer S can then be removed after the backside etching in order to ensure optimal mobility of the second membrane 3 at least in its membrane main section 3 d.

[0066] Figure 2h and 3g The device 1 produced by means of the previously described method is illustrated schematically and therefore corresponds to the method discussed in connection with the device 1. Figure 1b and 1c .

[0067] Figure 4a and 4bThe schematic diagram schematically illustrates the production of radial etching channels 10 in the first sacrificial layer O1 according to one exemplary embodiment. Figure 4a As shown in FIG, firstly, a first sacrificial layer O1 can be deposited, for example, onto a substrate 13 or substantially also onto other material layers of a layer system applied onto the substrate 13 and locally structured by etching so that radial etching channels 10 extending through the sacrificial layer O1 are formed. Figure 4b As shown in FIG. 1 , a further second sacrificial layer O2 can then be deposited, for example, in order to close the etching channels 10 on the surface and thus form buried etching channels 10. With the aid of radial etching channels 10, a uniform and smoothly running etching process can be achieved.

[0068] Figure 5 Schematically shown is a micro-electromechanical microphone 16 for capacitive sound pressure measurement, which has a device 1 according to the features described above and a signal processing unit 17 which is connected to the device 1 via a signal connection 18 and is designed to apply and process signals of the micro-electromechanical device 1. The micro-electromechanical microphone 16 can be implemented, for example, as a system on a chip.

Claims

1. A micro-electromechanical device (1) for capacitive fluid pressure measurement, comprising a first membrane (2) and a second membrane (3), wherein the first membrane and the second membrane can be elastically deflected by fluid pressure, wherein: A hollow space (4) is formed between the first membrane (2) and the second membrane (3), in which a counter electrode (5) is arranged. The invention is characterized in that the counter electrode (5) has a plurality of radial etching channels (10), which extend radially from the counter electrode center (5b) to the counter electrode edge (5a).

2. The device (1) according to claim 1, wherein: The counter electrode (5) is separated from a lateral hollow space boundary (7) of the hollow space (4) by a free space channel (6) which surrounds the hollow space at least in sections, wherein the counter electrode (5) has at least one supporting arm (8) by means of which the counter electrode can be anchored to the lateral hollow space boundary (7) and can be electrically contacted.

3. The device (1) according to claim 2, wherein: The free-space channel (6) is fluidically connected to at least one etched inlet channel (9) of the device (1) extending through the first membrane (2).

4. The device (1) according to claim 3, wherein: The etching inlet channel (9) extends through a membrane edge section (2a) of the first membrane (2), wherein the membrane edge section (2a) extends radially from the membrane edge (2b) in the direction of the membrane center (2c) of the first membrane (2) over a section of at most 20% of the membrane diameter (2e).

5. The device (1) according to any one of the preceding claims, wherein: The counter electrode (5) is arranged at least in sections, in particular completely, between a membrane main section (2d) of the first membrane (2) and a membrane main section (3d) of the second membrane (3) which is opposite the membrane main section (2d) of the first membrane (2).

6. The device (1) according to any one of the preceding claims, wherein: The free-space channel (6) is divided into a plurality of free-space channel sections (6a), and each free-space channel section (6a) is connected in a flow-related manner to at least one etching inlet channel (9).

7. The device (1) according to any one of the preceding claims, wherein: A gas volume is enclosed in the hollow space (4), which has a gas pressure below the ambient air pressure.

8. The device (1) according to claim 7, wherein: The gas volume can be enclosed by a closure (11) of the at least one etching inlet channel (9).

9. The device according to claim 8, wherein: The closing portion (11) comprises a dielectric layer (11a) and / or a metal layer (11b).

10. The device (1) according to any one of the preceding claims, wherein: The first film (2), the second film (3) and / or the counter electrode (5) are made of polysilicon.

11. A microelectromechanical microphone (16) for capacitive sound pressure measurement, comprising a microelectromechanical device (1) according to any one of claims 1 to 10 and a signal processing device (17) for applying and processing signals of the microelectromechanical device (1).

12. A method for producing a micro-electromechanical device (1) for capacitive fluid pressure measurement, the micro-electromechanical device having a first membrane (2) and a second membrane (3), the first membrane and the second membrane being elastically deflectable by fluid pressure, wherein: A hollow space (4) is formed between the first film (2) and the second film (3), in which a corresponding electrode (5) is arranged, wherein the device (1) is manufactured by gradually applying material layers (G, M1, M2, O1, O2, O3, S) to a substrate (13) and structuring them, wherein the cavity (4) is formed by applying and subsequently etching at least one sacrificial layer (O1, O2, O3), wherein in the manufacturing, a corresponding electrode layer (G) is applied with A corresponding electrode (5) is formed and the corresponding electrode layer (G) and / or the sacrificial layer (O1, O2, O3) are structured so that a plurality of radial etching channels (10) are generated in the corresponding electrode (5) and / or in the sacrificial layer (O1, O2, O3), wherein the radial etching channels (10) in the corresponding electrode (5) extend radially from the corresponding electrode center (5b) to the corresponding electrode edge (5a) and / or the sacrificial layer (O1, O2, O3).

13. The method according to claim 12, wherein: The corresponding electrode layer (G) is structured so that the corresponding electrode (5) is separated from a lateral hollow space boundary (7) of the hollow space (4) by a free space channel (6) that surrounds it at least in sections and is anchored to the lateral hollow space boundary (7) by means of at least one supporting arm (8).

14. The method according to any one of claims 12 or 13, wherein: A first film layer (M1) is applied to produce the second film (3), and a second film layer (M2) is applied to produce the first film (2) and structured so that at least one etching inlet channel (9) is produced in a film edge section (2a) of the first film (2).

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