Patent Description:
Microelectromechanical systems (MEMS) using a deflectable membrane may be implemented for a plurality of use cases such as microphones, loudspeakers, pressure sensors or the like. To prevent stiction between the membrane structure and a backplate structure, anti-stiction bumps may be arranged between the membrane structure and the backplate structure.

In <CIT> a condenser microphone array chip is described in which a plurality of structures of condenser microphones is fabricated in a single condenser microphone array chip.

In <CIT> an integrated MEMS microphone is described, including, a bonding wafer layer, a bonding layer, an aluminum layer, CMOS substrate layer, an N+ implant doped silicon layer, a field oxide (FOX) layer, a plurality of implant doped silicon areas forming CMOS wells, a two-tier polysilicon layer with selective ion implantation forming a diaphragm.

In <CIT> a production method for a double-membrane MEMS component is described. The method includes: providing a layer arrangement on a carrier substrate, wherein the layer arrangement comprises a first membrane structure, a sacrificial material layer adjoining the first membrane structure, and a counterelectrode structure in the sacrificial material layer and at a distance from the first membrane structure.

<CIT> discloses a capacity transducer with stoppers within a diaphragm and a plate.

<CIT> discloses a MEMs transducer with bumps.

<CIT> discloses a silicon capacitor microphone with a hole.

There is a request for robust MEMS devices. Further, there is a request for a method for producing robust MEMS devices.

The claimed invention is set out in claims <NUM> and <NUM>. According to claim <NUM>, the MEMS comprises inter alia a first electrode structure and a second electrode structure forming a capacitive sensing arrangement. The MEMS device comprises a plurality of anti-stiction bumps arranged between the first electrode structure and the second electrode structure at a corresponding plurality of locations. The plurality of locations is distributed so as to comprise a first distribution density in a first main surface region of a main surface into which the plurality of locations is projected. The plurality of locations comprises a second, different distribution density in a second main surface region of the main surface, the second main surface region being delimited from the first main surface region. Anti-stiction bumps provide for mechanical stress when the first and the second electrode structure abut to each other such that the anti-stiction bumps contact the other electrode structure, i.e., they form a mechanical contact or hit each other. By arranging the anti-stiction bumps with different distribution densities, the mechanical stress induced into the electrode structures may be adjusted so as to prevent mechanical overloads and may thus provide for robust MEMS devices.

Claim <NUM> provides a method for producing a MEMS device. The method comprises inter alia forming a capacitive sensing arrangement with a first electrode structure and a second electrode structure. The method comprises arranging a plurality of anti-stiction bumps between the first electrode structure and the second electrode structure at a corresponding plurality of locations. The method is executed such that the plurality of locations being projected into a main surface of the second electrode structure is distributed so as to comprise a first distribution density in a first main surface region of the main surface and so as to comprise a second, different distribution density in a second main surface region of the main surface, the second main surface region being delimited from the first main surface region.

Embodiments will be described in the following while making reference to the accompanying drawings in which:.

In the following description, a plurality of details is set forth to provide a more thorough explanation of the embodiments of the present invention. However, it will be apparent to those skilled in the art that embodiments of the present invention may be practiced without these specific details. In other instances, known structures and devices are shown in block diagram forms rather than in detail in order to avoid obscuring embodiments of the present invention. In addition, features of the different embodiments described in hereinafter may be combined with each other, unless specifically denoted otherwise.

Embodiments described herein relate to microelectromechanical structures (MEMS) having a capacitive sensing arrangement. Such capacitive sensing arrangements may comprise at least one backplate structure that may be referred to as a stator electrode or an electrode that is regarded as being essentially static or immobile. The MEMS further comprises at least one movable electrode structure, e.g., a membrane structure that is configured to be deflectable with regard to the backplate structure. Although both electrode structures may be formed deflectable with respect to each other, precise measurements may be obtained when forming one of the electrode structures as a fixed, static backplate structure. The deflection may lead to a varying distance between the electrode structures and thus to a varying capacitance between the electrodes, the varying capacitance being a parameter to be evaluated within the capacitive sensing arrangement. For example, such capacitive sensing arrangements may be used in microphone structures, in pressure sensor structures or in photoacoustic sensor structures.

MEMS devices may be manufactured in semiconductor-technology and/or may comprise semiconductor materials. Examples for such materials are layers or wafers comprising a silicon material, a gallium-arsenide-material and/or different semiconductor materials. MEMS devices may comprise one or more layer sequences or stacks of layers comprising conductive, semi-conductive and/or insulating layers so as to implement a respective MEMS functionality. In embodiments described hereinafter, one or more backplate electrodes or structures may form a stack together with at least one membrane structure or electrode. The backplate structure and the membrane structure may be held, fixed and/or clamped at respective outer regions with a substrate structure. The substrate structure may comprise, for example, amorphous, polycrystalline or crystalline semiconductor materials such as silicon.

Although the membrane structures are described hereinafter as comprising a conductive layer only, according to embodiments, one or both sides of the membrane structure is/are covered with an insulating material to increase robustness and/or to prevent short-circuits.

<FIG> shows a schematic side view of a MEMS device <NUM><NUM> according to an embodiment which is not part of the claimed invention. The MEMS device comprises an electrode structure <NUM> and a further electrode structure <NUM>, wherein at least one of the electrode structures <NUM> and/or <NUM> is deflectable with respect to each other. The electrode structures <NUM> and <NUM> form a capacitive sensing arrangement <NUM>. That is, a deflection of at least one of the electrode structures <NUM> and <NUM> with respect to the other electrode structure <NUM>, <NUM> respectively, may be detected, sensed or measured due to a varying capacitance between the electrode structures <NUM> and <NUM>.

Between the electrode structures <NUM> and <NUM>, a plurality of anti-stiction bumps <NUM><NUM> to <NUM><NUM> may be arranged. The anti-stiction bumps may be arranged at the electrode structure <NUM> and/or at the electrode structure <NUM>. A simple way for manufacturing MEMS devices with anti-stiction bumps is to form same by using recesses in a sacrificial layer, filling the recesses, followed by arranging an electrode structure on top of the sacrificial material. Whilst this does not exclude to form at least a subset of the anti-stiction bumps as stalagmite structures, forming the anti-stiction bumps as stalactite structures allows for simple processes. That is, the anti-stiction bumps <NUM><NUM> to <NUM><NUM> may be arranged at a mobile and/or immobile electrode structure.

A number of anti-stiction bumps <NUM><NUM> to <NUM><NUM> may at least be influenced from a side of the electrode structures <NUM> and/or <NUM>. Alternatively or in addition, the number of anti-stiction bumps may be at least influenced by a design of the MEMS device <NUM>,, e.g., a distance between the electrode structures <NUM> and <NUM> and/or a size of a possible abutting area in which the electrode structures <NUM> and <NUM> possibly form a mechanical contact when deflecting the at least one deflectable electrode structure.

Each of the anti-stiction bumps is arranged at a respective location <NUM><NUM> to <NUM><NUM>, e.g., at the electrode structure <NUM> or the electrode structure <NUM>. The locations <NUM><NUM> to <NUM><NUM> may be projected into a main surface 14A of the electrode structure <NUM>. The main surface 14A may be a surface of the membrane structure <NUM> facing the electrode structure <NUM> or facing away from the electrode structure <NUM> and having an opposing second main surface. Both main surfaces may be connected to each other by a side surface of the membrane structure, e.g., a lateral surface of a round, elliptical or polygon shaped cylinder having the main surfaces as top surface, bottom surface respectively. Locations <NUM><NUM> to <NUM><NUM> may be projected into the main surface 14A, for example, along a surface normal <NUM> of the main surface 14A or parallel to a surface normal of a stator electrode, a backplate structure respectively. Anti-stiction bumps <NUM><NUM> to <NUM><NUM> and <NUM><NUM> to <NUM><NUM> may define such projected locations by their real locations <NUM><NUM> to <NUM><NUM> and <NUM><NUM> to <NUM><NUM>, An anti-stiction bump being arranged at a different electrode structure such as the anti-stiction bump <NUM><NUM> may be projected such that a projected location <NUM>'<NUM> is considered when determining distribution densities <NUM><NUM> and <NUM><NUM> of the anti-stiction bumps <NUM><NUM> to <NUM><NUM>, their associated locations <NUM><NUM> to <NUM><NUM>, including the projected locations respectively.

The locations <NUM> and <NUM>' may comprise different distribution densities <NUM><NUM> and <NUM><NUM> in different, delimited surface regions <NUM><NUM>, <NUM><NUM> and <NUM><NUM>. For example, the surface region <NUM><NUM> may be sandwiched between the surface regions <NUM><NUM> and <NUM><NUM>. Although a number of anti-stiction bumps arranged in the respective surface region <NUM><NUM> and <NUM><NUM> may be different and although the density of the anti-stiction bumps <NUM> in those regions may differ from each other, the density including the projections <NUM>' of the locations <NUM> may be equal in the surface regions <NUM><NUM> and <NUM><NUM>. Alternatively, the distribution density <NUM><NUM> may differ from the distribution density <NUM><NUM>. In contrast, the distribution density <NUM><NUM> differs from the distribution density <NUM><NUM>. That is, between the delimited main surface <NUM><NUM> and <NUM><NUM>, a different density of anti-stiction bumps, including the projection thereof, is arranged, i.e., in a specific reference area, e.g., one square micrometer, two square micrometers, four square micrometers or the like, a different number of anti-stiction bumps, including the projection thereof, is arranged.

The distribution density <NUM><NUM> may be smaller than the distribution density <NUM><NUM>. For example, the main surface region <NUM><NUM> may be arranged in a center portion of the backplate structures <NUM> and/or <NUM>. The main surface region <NUM><NUM> may be arranged in a center portion of the electrode structure <NUM> and/or <NUM>. That is, the area covered by the main surface region <NUM><NUM> at the respective electrode structure and/or when being projected into the main surface 14A overlaps with a geometric center of the respective electrode structure. Possibly but not necessarily, a center of the main surface region <NUM><NUM> corresponds to the geometric center of the electrode structure within a tolerance range of <NUM> %, <NUM> % or <NUM> %. According to an example, the lower-valued or zero-valued bump density (distribution density) is located in the center of a membrane structure. This allows to consider that a deflection of a membrane structure may be high or even maximum in a center thereof, therefore having a comparatively high probability for abutment and thus a possibly high stress concentration at the bumps in this area.

The main surface region may have a lateral extension along one or more directions, e.g., as a polygon or circle of any suitable value, for example, of at least <NUM> and at most <NUM>, at least <NUM> and at most <NUM> or at least <NUM> and at most <NUM> and/or may cover an area of at least <NUM> % and at most <NUM> % or at least <NUM> % and at most <NUM> % or at least <NUM> % and at most <NUM> % of the respective electrode structure.

Alternatively to a center position, the main surface region <NUM><NUM> may be arranged at a different location with same or different size. For example, a location of the main surface region <NUM><NUM> may at least partially be influenced from a location from which a force or pressure is expected to arrive at the deflectable electrode structure <NUM> or <NUM>. Such a direction may be adjacent to a side of the electrode structure <NUM> so as to deflect the electrode structure <NUM> towards the electrode structure <NUM> or the electrode structure <NUM> towards the electrode structure <NUM>, e.g., in case of an under-pressure. Alternatively, the force may arise from a side of the electrode structure <NUM> so as to deflect the electrode structure <NUM> towards the electrode structure <NUM> or so as to deflect the electrode structure <NUM> towards the electrode structure <NUM>, e.g., in case of the under-pressure.

The electrode structure <NUM> may have any suitable cross-section, for example, with a round shape, a rounded rectangle shape, a polygon shape or the like. A diameter or a largest dimension between any two arbitrary points at a same main surface may be, for example, between at least <NUM> and at most <NUM>, between at least <NUM> and at most <NUM> or between at least <NUM> and at most <NUM>. A thickness of the silicon layer providing for the conductive layer of the electrode structure <NUM> and/or <NUM> may be at least <NUM> and at most <NUM>, at least <NUM> and at most <NUM> or at least <NUM> and at most <NUM>. The silicon material may provide for an elastic and electrically conductive property, e.g., when using mono or poly-silicon. The backplate structure may be implemented similarly. Nitride layers arranged between the electrode structures so as to prevent short-circuits and/or to provide for a high stiffness may be arranged. That is, one layer may ensure a high stiffness and also electrical insolation in case the membrane touches the backplate. A further layer may be used as an electrode.

The anti-stiction bumps may have a dimension along the surface normal <NUM> or parallel hereto between <NUM> and <NUM>, <NUM> and <NUM> or between <NUM> and <NUM>. A radius of curvature at an end facing the respective other electrode structure may vary within a range of at least <NUM> to <NUM>, <NUM> to <NUM> or <NUM> to <NUM>.

<FIG> shows a schematic side view of a MEMS <NUM><NUM> according to an embodiment. When compared to the MEMS device <NUM><NUM>, the main surface region <NUM><NUM> is out of a center <NUM> of the electrode structure <NUM>. Alternatively or in addition, the distribution density <NUM><NUM> may be zero, i.e., in the main surface region <NUM><NUM> there is in this example neither arranged an anti-stiction bump nor a projection thereof.

The MEMS device <NUM>, and the MEMS device <NUM><NUM> provide for a decreased amount of mechanical stress that is induced into the electrode structures <NUM> and <NUM> in the main surface region <NUM><NUM> when the electrode structures <NUM> and <NUM> abut each other such that mechanical contact is formed between the anti-stiction bumps <NUM> and both electrode structures <NUM> and <NUM>, when compared to the surface region <NUM><NUM>. By having a low mechanical stress, a high robustness may be obtained.

The high robustness may in particular be obtained in a case where strong forces lead to the contact between the electrode structures <NUM> and <NUM>. Such strong forces may, for example, occur in case the electrode structures <NUM> and <NUM> abut each other, thereby pressing one or more anti-stiction bumps <NUM>i against the opposing electrode structure. This pressing may lead to strong forces in the abutting and/or abutted electrode structure at the location of the anti-stiction bump <NUM>i. A source for such abutment may be, for example, a high pressure acting on the MEMS. The strong forces may encountered by use of a lower, possibly zero density, i.e., a lower number of anti-stiction bumps <NUM>i per area in the region that is exposed or susceptible to abutment, e.g., in a center area or the main surface region <NUM><NUM>. This allows to have a maximum of deflection in the center or main surface region 14A and/or a high stress concentration in the main surface region 14A.

In case of occurrence of a fast burst of pressure or pressure due to air flow, the pressure increase on the membrane may be at first concentrated in an area that corresponds to the projection of the port location which may be the center of the electrode structures. , the main surface region 14A may be in a center area and/or may be arranged corresponding to a location of a port as will be described in connection with <FIG>. That is, in case of a pressure burst or pressure, e.g., from air flow, the pressure is at first exerted on the membrane in an area corresponding to the port projection which may be considered when arranging the main surface region <NUM><NUM> correspondingly, at least within tolerance ranges.

To explanation of anti-stiction bumps: To avoid that the membrane sticks too strong with the backplate due to electrostatic forces when they enter in contact, anti-stiction bumps are made in order to maintain a certain distance between the two electrodes and to reduce contact forces per area.

<FIG> shows a schematic top view of an electrode structure <NUM> according to an embodiment which is not part of the claimed invention comprising a plurality of anti-stiction bumps <NUM> at a main side 12A of the electrode structure <NUM>. As the locations of the anti-stiction bumps <NUM> may be projected into the main surface 14A of the second or further electrode structure, explanations given in connection with the main surface regions <NUM><NUM>, <NUM><NUM>, respectively, the distribution density <NUM><NUM>, <NUM><NUM>, respectively may be transferred, without any limitations to the anti-stiction bumps arranged at the electrode structure <NUM>. For example, the main surface region <NUM><NUM> may be arranged in a center region of the electrode structure <NUM>. In the respective center region, a lower distribution density <NUM><NUM> may be implemented when compared to the distribution density <NUM><NUM> of the main surface region <NUM>, surrounding the main surface region <NUM><NUM>. Although the anti-stiction bumps <NUM> may be arranged in a regular manner or pattern in the main surface regions <NUM>, and/or <NUM><NUM>, the anti-stiction bumps may alternatively be arranged in an irregular or random way.

<FIG> shows a schematic top view of the electrode structure <NUM> according to an embodiment, wherein the distribution density <NUM><NUM> is zero, i.e., in the main surface region <NUM><NUM>, the number of anti-stiction bumps is zero.

In particular in connection with the distribution density <NUM><NUM> being zero, the respective electrode structure <NUM> and/or <NUM> is removed or absent.

<FIG> shows a schematic side view of a MEMS <NUM> according to an embodiment, wherein the anti-stiction bumps <NUM><NUM> to <NUM><NUM> are arranged at the electrode structure <NUM>, wherein the electrode structure <NUM>, being a backplate structure for example, comprises an opening <NUM> that forms at least a part of the main surface region <NUM><NUM>. According to an embodiment, the opening <NUM> completely forms the main surface region <NUM><NUM>.

According to an embodiment, the main surface region <NUM><NUM> is in encircled by the main surface region <NUM><NUM>, e.g., the opening <NUM> is encircled by the main surface region <NUM>, as described, for example, in connection with <FIG>.

The electrode structures <NUM> and <NUM> may be clamped, fixed or held by a substrate structure <NUM>. The arrangement comprising the substrate structure <NUM> and the electrode structures <NUM> and <NUM> may be arranged, fixed or connected to a bases <NUM>, e.g., comprising circuit structures or the like that are adapted to electrically contact the electrode structures <NUM> and/or <NUM>, e.g., by use of the substrate structure <NUM> having conductive traces. Such a connection between the bases <NUM> and the substrate structure <NUM> may be provided by use of a mechanical connection <NUM>, e.g., a solder material or a glue material. The bases <NUM> may at least partially be formed by conductive structures such as a printed circuit board (PCB). The substrate structure <NUM> and the electrode structures <NUM> and <NUM> may at least partially be covered by a housing lid <NUM>. The housing lid <NUM> and the bases <NUM> may together form a housing of the MEMS device <NUM>. An opening <NUM> of the housing may be arranged in the basis or in the housing lid so as to implement a bottom port configuration, a top port configuration respectively. That is, the opening <NUM> may be referred to as a port of the package. The opening <NUM> may be arranged such that a location of the opening <NUM> projected into the main surface 14A or the opposing side overlaps at least partially with the second main surface region.

A source <NUM> of forces leading to a deflection of at least one of the electrode structures, traveling through the opening <NUM> may lead to an abutment of the electrode structures <NUM> and <NUM>. For example, the source <NUM> may be a pressure that is part of an air flow travelling through the opening <NUM>. By arranging the opening <NUM> so as to at least partially overlap with the second main surface region <NUM><NUM>, to arrange the second main surface region <NUM><NUM> so as to at least partially overlap with the opening <NUM> respectively leads to a more mechanically robust MEMS device, especially in case of a mechanical contact between the electrode structure being pressed against an opposing electrode structure or abutting same. That is, the second main surface region <NUM><NUM> provides for a robust area of the capacitive sensing arrangement. In an area of abutment caused by source <NUM>, the mechanical load acting on the electrode structure being hit by or abutted by an anti-stiction bump may be reduced when compared to the main surface area <NUM><NUM> in accordance with the reduction of the number or density of anti-stiction bumps <NUM>.

According to an embodiment, a location of the second main surface region <NUM><NUM> and the location of the opening <NUM> of the housing correspond to each other within a tolerance range of ± <NUM>%, ± <NUM>%, ± <NUM>%. Alternatively or in addition, a size of the second main surface region <NUM><NUM> and a size of the opening <NUM> of the housing correspond to each other within a tolerance range of ± <NUM>%, ± <NUM>% or ± <NUM>%. According to an embodiment, one or both of the locations and/or the sizes correspond to each other within a tolerance range of ± <NUM>% or even exactly, i.e., within tolerance ranges of manufacturing. That is, the location of the opening <NUM> of the housing of the MEMS device <NUM> projected into the main surface 14A or 12A may form at least a part of the second main surface region <NUM><NUM>.

For example, the opening or port <NUM> may have a diameter of at least <NUM> to at most <NUM>, or at least <NUM> to at most <NUM> or of at least <NUM> to at most <NUM>. Alternatively or in addition, the dimension of the port <NUM> may be in range of at least <NUM> and at most <NUM>, of at least <NUM> and at most <NUM> or of at least <NUM> to at most <NUM> times smaller than the membrane. The main surface region <NUM><NUM> may be of a same size as the port but may also be smaller, e.g., slightly smaller or larger, e.g., slightly larger. A slight deviation may be understood as a variation of at most <NUM>%, at most <NUM>% or at most <NUM>%.

<FIG> shows as schematic side view of a known MEMS device <NUM> to provide a basis for a subsequent description of further embodiments. The MEMS device <NUM> may comprise the substrate structure <NUM> that carries a backplate structure <NUM> and a membrane structure <NUM>. The backplate structure <NUM> may comprise a conductive layer 52a that may provide for the functionality of an electrode. The conductive layer may comprise a doped semiconductor material, e.g., crystalline or polycrystalline silicon, and/or a metal material. The conductive layer 52a may be separated from the membrane structure <NUM> by an insulating layer 52b, e.g., comprising a silicon oxide material or a silicon nitride material.

The membrane structure <NUM> may also comprise a conductive material such as a doped polysilicon material. The membrane structure <NUM> may comprise a ventilation hole <NUM> allowing for a ventilation and/or pressure exchange between both sides of the membrane.

To further increase mechanical robustness, a further insulating layer 52c may be arranged such that the conductive layer 52a is sandwiched between the insulating layers 52b and 52c. By way of example, anti-stiction bumps <NUM> may be formed from the insulting layer 52b. The electrode structures <NUM> and <NUM> may be separated from each other and from the substrate structure <NUM> by use of an insulating material <NUM> such as silicon nitride or silicon oxide.

<FIG> shows a schematic side view of a MEMS device <NUM> according to an embodiment. When compared to the MEMS <NUM>, the electrode structure <NUM> which may be a layered structure with layers 12a, 12b and 12c that may correspond to the layers 52a, 52b and 52c of the structure <NUM> may comprise the opening <NUM> so as to implement the main surface region <NUM><NUM>. The opening <NUM> may have a size of at least <NUM>, <NUM> or <NUM>. The size may be understood as an in-plane dimension parallel to a position of the main surfaces of the electrode structures <NUM> and <NUM>. For example, the opening <NUM> may comprise a length of an edge or a diameter with such dimensions.

<FIG> shows a schematic side view of a MEMS device <NUM> according to an embodiment which is not part of the claimed invention. The electrode structure <NUM> may comprise an opening <NUM> having a size or diameter of at least <NUM>, at least <NUM> or at least <NUM> and is thus clearly larger when compared to ventilation holes <NUM> having a diameter of at most <NUM>, <NUM> or <NUM>.

One or more of the ventilation holes <NUM> contained in the electrode structure <NUM> may be arranged aside or beside the main surface area <NUM><NUM>. According to an embodiment, a portion <NUM> of the electrode structure <NUM> that faces or overlaps with the opening <NUM> is implemented so as to comprise a lower number or even no ventilation holes <NUM>. Such missing perforation allows to limit an acoustic vent to the other side of the electrode structure <NUM>, e.g., the back volume whilst allowing for pressure exchange through the ventilation hole <NUM>.

The electrode structure <NUM> may be formed so as to comprise the anti-stiction bumps in the region corresponding to the main surface region <NUM><NUM> whilst being implemented so as to have a distribution density <NUM><NUM> of zero in the area corresponding to the main surface region <NUM><NUM>. This may be referred to as the portion <NUM> of the electrode structure <NUM> being formed without anti-stiction bumps or with a lower amount thereof.

In the main surface region <NUM><NUM>, there is no overlap between electrode structures <NUM> and <NUM> such that capacitive measurement is independent or at least almost independent from a movement of the electrode structures in this area.

<FIG> shows a schematic side view of a MEMS device <NUM> according to an embodiment which is not part of the claimed invention. The anti-stiction bumps <NUM><NUM> to <NUM>i with i being any suitable number of larger than <NUM>, e.g., <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, or even a higher number, are arranged at the electrode structure <NUM>. The electrode structure <NUM> may be implemented as described for the electrode structure <NUM> of MEMS <NUM>. As described in connection with the MEMS device <NUM>, a portion <NUM>' of the electrode structure <NUM> may be formed so as the distribution density <NUM><NUM>. When compared to the MEMS device <NUM>, the portion <NUM>' may be electrically insulated from a remaining portion <NUM> of the electrode structure <NUM>. For example, the conductive layer 12a may be broken, cut, segmented or interrupted completely between the portion <NUM>' and the remaining portion <NUM>. The portion <NUM>' may be fixed or connected mechanically to the remaining portion <NUM> by use of a material used for the insulating layers 12b and/or 12c in a same, lower or higher layer thickness. For example, a segmentation of the portion <NUM>' with respect to the remaining portion <NUM> may be implemented as described in <CIT> or <CIT>. The remaining portion <NUM> may provide for a backplate area that is electrically insulated from the portion <NUM>' forming a further backplate area. The portion <NUM>' may form at least a part of the main surface region <NUM><NUM>.

Optionally, the conductive layer 12a of the portion or segment <NUM>' may be electrically connected or may be subjected to a same potential as the electrode structure <NUM>, the conductive layer thereof respectively by connecting both elements to a same optional power supply <NUM>. Thereby, a capacitive effect between the layer 12a in the portion <NUM>' and the electrode structure <NUM> is reduced or even eliminated such that a similar effect when compared to the MEMS device <NUM> may be obtained without providing for the opening <NUM>. A capacitance C between the layer 12a in the remaining portion <NUM> and the conductive layer of the electrode structure <NUM> may be evaluated, for example, using a readout circuit <NUM>.

<FIG> shows a schematic side view of a MEMS device <NUM> according to an embodiment which is not part of the claimed invention. When compared to the MEMS device <NUM>, an anchor structure <NUM> may be arranged between the electrode structures <NUM> and <NUM> providing for a permanent fixation or mechanical contact between the electrode structure <NUM> and the anchor structure <NUM> and between the anchor structure <NUM> and the electrode structure <NUM>. The anchor structure <NUM> may be of any suitable material, in particular, a conductive or insulating material. A simple manufacturing may be obtained by implementing the anchor structure <NUM> as part of a layer of the insulating material <NUM><NUM>. For example, the anchoring structure <NUM> may be a remaining portion of a deposited layer. The anchor structure <NUM> allows to shift regions <NUM><NUM> and <NUM><NUM> of maximum displacement of the electrode structure <NUM> from a center of the electrode structure <NUM> closer to the substrate structure <NUM>.

As described in connection with the MEMS device <NUM>, the portion <NUM>' and the electrode structure <NUM> may be connected to a same potential or voltage. This allows suppressing anti-stiction bumps without risk of electrostatic stiction. Anchoring of the membrane in the center allows a maximum displacement being shifted to the side of the electrode structure <NUM>, e.g., the membrane structure.

<FIG> shows a schematic side view of a MEMS device <NUM> according to an embodiment which is not part of the claimed invention. The anti-stiction bumps <NUM><NUM> to <NUM>i are arranged at least partially at the electrode structure <NUM> so as to face the electrode structure <NUM>. The electrode structure <NUM> may be, for example, a backplate structure. The electrode structure <NUM> may comprise the remaining portions <NUM> as described, for example, in connection with the MEMS device <NUM>. When compared to the MEMS device <NUM> or the MEMS device <NUM>, the electrode structure <NUM> may comprise an insulating material portion <NUM>, e.g., comprising insulating materials only. That is, when compared to the portion <NUM> or <NUM>', the conductive layer 12a may be absent. The remaining portion <NUM> may provide for a backplate area being electrically conductive. The insulating portion <NUM> may provide for a backplate area being electrically non-conductive, insulating respectively. The backplate area or insulating portion <NUM> may at least partially form the main surface region <NUM><NUM>. That is, an area adjacent to the insulating portion <NUM> of the remaining portion <NUM> may optionally be formed as a part of the surface region <NUM><NUM>. Arranging only the insulating material, e.g., nitride, may allow to ensure mechanical stability of the electrode structure <NUM> whilst avoiding electrostatic forces caused by conductive materials such that an arrangement of anti-stiction bumps may be omitted.

<FIG> shows a schematic side view of a MEMS device <NUM> according to an embodiment which is not part of the claimed invention. The MEMS device <NUM> may comprise two backplate structures <NUM><NUM> and <NUM><NUM> sandwiching the electrode structure <NUM> being formed as a membrane structure. The electrode structures <NUM><NUM> and <NUM><NUM> may each comprise an opening <NUM> of same or different sizes. For example, the openings <NUM><NUM> and <NUM><NUM> may be arranged at locations corresponding to the main surface area <NUM><NUM>. This allows for a high robustness of the electrode structure <NUM> with respect to mechanical context to both of the electrode structures <NUM><NUM> and <NUM><NUM>.

Between the electrode structure <NUM>, and the electrode structure <NUM>, there may be arranged a plurality of anti-stiction bumps <NUM><NUM> to <NUM>i. between the electrode structure <NUM> and the electrode structure <NUM><NUM> there may be arranged a further plurality of anti-stiction bumps <NUM>i+<NUM> to <NUM>j, wherein the pluralities may be of a same number of a different number. As described in connection with the MEMS devices <NUM>, and <NUM><NUM>, each of the anti-stiction bumps <NUM><NUM> to <NUM>j is arranged at a respective location. Both, the first plurality of <NUM>, to <NUM>i and the second plurality <NUM>i+<NUM> to <NUM>j may comprise a respective distribution density <NUM><NUM> or <NUM><NUM> in the main surface region <NUM><NUM>, <NUM><NUM> and <NUM><NUM> respectively aside thereof, e.g., in the main surface region <NUM><NUM>. The distribution densities <NUM><NUM> of the first plurality <NUM><NUM> to <NUM>i in the main surface region <NUM><NUM> and the distribution density <NUM><NUM> of the second plurality <NUM>i+<NUM> to <NUM>j in the main surface region <NUM><NUM> of the locations of anti-stiction bumps, the projections thereof respectively, may be same or different. For example, the distribution densities <NUM><NUM> and <NUM><NUM> are equal within a tolerance range of ± <NUM>%, ± <NUM>%, ± <NUM>% or less. <FIG> shows a configuration in which both distribution densities <NUM><NUM> and <NUM><NUM> are equal, in particular, they may be zero in absence of the electrode structure <NUM><NUM> and <NUM><NUM> in a region of the main surface region <NUM><NUM> along a direction of the surface normal <NUM> or opposing hereto.

In other words, MEMS device <NUM> implements a version with a double backplate structure having no backplate in the center.

<FIG> shows a schematic side view of a MEMS device <NUM> according to an embodiment which is not part of the claimed invention that may be referred to as a version with a double backplate having no membrane in the center. For example, the electrode structures <NUM><NUM> and <NUM><NUM> may each be implemented similar to the electrode structure <NUM> described in connection with the MEMS device <NUM>, alternatively <NUM> or <NUM> with exception of the anti-stiction bumps <NUM>. For example, the electrode structure <NUM> may be formed without anti-stiction bumps like the electrode structure <NUM><NUM> of MEMS device <NUM>. Alternatively, one or more of the plurality of anti-stiction bumps <NUM>i+<NUM> to <NUM>j may be formed at the electrode structure <NUM><NUM>, for example, directed towards the electrode structure <NUM>.

Complementary to the MEMS device <NUM>, the electrode structure <NUM> may comprise the opening in the main surface region <NUM><NUM>. Although the openings <NUM><NUM>, <NUM><NUM> and <NUM> of MEMS devices <NUM> and <NUM> may be combined, having at least one electrode structure <NUM><NUM>, <NUM> or <NUM><NUM> having at most the ventilation holes, allows to prevent an acoustic short-circuit or a low sensitivity of the MEMS device.

In other words, <FIG> shows a version with a double backplate structure having no membrane in the center.

<FIG> shows a schematic side view of a MEMS device <NUM> according to an embodiment which is not part of the claimed invention. When compared to the MEMS devices <NUM> and <NUM>, the MEMS device <NUM> may be formed as a so-called double membrane structure having electrode structures <NUM><NUM> and <NUM><NUM> formed as flexible membrane structures sandwiching the electrode structure <NUM> providing for a backplate structure. That is, the electrode structure <NUM> is arranged between the electrode structures <NUM><NUM> and <NUM><NUM>. For example, anti-stiction bumps <NUM><NUM> to <NUM>i and <NUM>i+<NUM> to <NUM>j are arranged at the electrode structure <NUM><NUM>, <NUM> respectively facing the electrode structure <NUM>, <NUM><NUM> respectively. A distribution density <NUM><NUM> of the anti-stiction bumps <NUM>i+<NUM> to <NUM>j may be different or at least within a tolerance range of ± <NUM>%, ± <NUM>% or ± <NUM>% same as the distribution density <NUM><NUM>. Alternatively or in addition, a distribution density <NUM><NUM> in the main surface region <NUM><NUM> may be different or at least within a tolerance range of ± <NUM>%, ± <NUM>% or ± <NUM>% equal when compared to the distribution density <NUM><NUM>.

A connecting structure <NUM> may provide for a mechanical and optionally an electrical connection between the electrode structures <NUM>, and <NUM><NUM>. This allows to house a volume <NUM> between the electrode structures <NUM><NUM> and <NUM><NUM> which allows to provide for pressures or environments being different when compared to an outside world in the volume <NUM>. For example, in the volume <NUM>, there may be a low pressure or even a pressure close to a vacuum so as to minimize mechanical work by transporting a fluid between both sides of the electrode structure <NUM>.

It may be sufficient to have only one of the electrode structures <NUM><NUM> and <NUM><NUM> being implemented in the main surface region <NUM><NUM>. , optionally, one of the electrode structures <NUM><NUM> and <NUM><NUM> may be absent in the main surface region <NUM><NUM>. Optionally, one or more ventilation holes <NUM> may be arranged in the remaining electrode structure <NUM>, and/or <NUM><NUM> in the main surface region <NUM><NUM>. <FIG> shows a schematic side view of a MEMS device <NUM> according to an embodiment which is not part of the claimed invention. When compared to the MEMS device <NUM>, the electrode structure <NUM>, is present in the main surface region <NUM><NUM>, wherein the electrode structure <NUM><NUM> is removed in at least <NUM>%, <NUM>% or <NUM>% of the main surface region <NUM><NUM>, for example, completely removed.

In other words, MEMS devices <NUM> and <NUM> provide for versions with a dual membrane whilst having only the top or the bottom membrane in the main surface region <NUM><NUM>.

Embodiments described herein allow to increase the mechanical robustness of a MEMS microphone. In particular, embodiments allow for withstand high forces leading to abutments between electrode structures which may lead to a highly destructive stress generated on the membrane due to anti-stiction bumps. This allows to prevent damages as a membrane may be sensitive for such forces induced when the MEMS faces high loads, e.g., high pressures. Such effects may be reduced or even be prevented with the embodiments described herein.

Embodiments provide for a MEMS, for example, a MEMS microphone having at least one membrane and at least one backplate for a capacitive measurement of motion of the membrane due to sound pressure or other forces. Anti-stiction bumps may be arranged between the electrodes. The MEMS may have a possibly central are that may correspond to the position of the port hole in the package, wherein no or at least a reduced number of anti-stiction bumps is present between the electrodes in this region. Alternatively or in addition, no backplate(s) may be arranged in the respective region, e.g., the center of the area. Alternatively or in addition, no membrane may be arranged in the respective region. In both cases, the backplate structure may have a low perforation rate in the central part or even just few holes or no holes, to control the ventilation between the outside pressure and the back volume of the package.

Alternatively or in addition, the at least one backplate structure may be present in the center area, but the central part is connected to a same potential as the membrane so that bumps can be removed but no force is existing between the central part of the membrane and the one of the backplate structure. For example, the membrane and the central part of the backplate structure may be connected to a constant voltage in a range of at least <NUM> volts and at most <NUM> volts, while the readout is done on the peripheral part of the backplate, i.e., the remaining portion <NUM>. In this case, one option is to have a central anchor, e.g., the anchor structure <NUM> of the membrane to the backplate so that the maximum motion of the membrane occurs aside of the center in an area closer to the border, i.e., the substrate structure <NUM>.

Alternatively or in addition, only the insulating material, e.g., nitride material, of the backplate is present in the center, whilst conductive material is missing. This allows that no electrostatic force is present and bumps can be suppressed without risk of stiction.

Alternatively or in addition, a dual membrane structure may be implemented as illustrated in <FIG> and in <FIG>, this allows to have only the bottom membrane or the top membrane present in the main surface region <NUM><NUM>. According to a further embodiment, both membrane structures may be absent. According to an embodiment that is compatible with such a structure, the backplate may be present in the main surface area. In this case, the backplate may have a low perforation rate in the central part, or even just few holes or no holes, to control the ventilation between the outside pressure and the pressure in the back volume of the package.

<FIG> shows a schematic flowchart of a method <NUM> according to an embodiment. At <NUM>, a capacitive sensing arrangement with a first electrode structure and a second electrode structure is formed. At <NUM>, a plurality of anti-stiction bumps is arranged between the first electrode structure and the second electrode structure at a corresponding plurality of locations such that the plurality of locations being projected into a main surface of the second electrode structure is distributed so as to comprise a first distribution density in a first main surface region of the main surface and so as to comprise a second, different distribution density in a second main surface region of the main surface, the second main surface region being delimited from the first main surface region.

Claim 1:
MEMS device comprising:
a first electrode structure (<NUM>) and a second electrode structure (<NUM>) forming a capacitive sensing arrangement (<NUM>);
a plurality of anti-stiction bumps (<NUM>) arranged between the first electrode structure (<NUM>) and the second electrode structure (<NUM>) at a corresponding plurality of locations (<NUM>);
wherein the plurality of locations (<NUM>) being projected into a main surface (14A) of the second electrode structure (<NUM>) is distributed so as to comprise a first distribution density (<NUM><NUM>) in a first main surface region (<NUM><NUM>) of the main surface (14A) and so as to comprise a second, different distribution density (<NUM><NUM>) in a second main surface region (<NUM><NUM>) of the main surface (14A), the second main surface region (<NUM><NUM>) being delimited from the first main surface region (<NUM><NUM>);
wherein the second distribution density (<NUM><NUM>) is zero;
wherein the second main surface region (<NUM><NUM>) is encircled by the first main surface region (<NUM><NUM>),
characterized in that the first electrode structure (<NUM>) and/or the second electrode structure (<NUM>) comprises an opening (<NUM>) that completely forms the second main surface region (<NUM><NUM>),
and in that the MEMS device further comprises a housing, the housing comprising an opening (<NUM>) between an inner volume of the MEMS device and an outside of the housing of the MEMS device, wherein the opening (<NUM>) is arranged such that a location of the opening (<NUM>) of the housing projected into the main surface (14A) on the one hand and the second main surface region (<NUM><NUM>) on the other hand overlap at least partially, wherein a location of the second main surface region (<NUM><NUM>) and the location of the opening (<NUM>) of the housing correspond to each other within a tolerance range of ± <NUM>% and/or wherein a size of the second main surface region (<NUM><NUM>) and a size of the opening (<NUM>) of the housing correspond to each other within a tolerance range of ± <NUM>%.