Patent Description:
Sensors with moving structures such as membranes are facing more or less the same issue. The membranes need to achieve a sufficient sensitivity to detect low signal levels, therefore have to be sufficiently moveable. On the other hand, it has to be sufficiently robust against forces exceeding the standard operation conditions, e.g., a drop or pressure burst.

<CIT> relates to a MEMS device that includes a flexible membrane disposed over a substrate, and a first backplate disposed over the flexible membrane.

<CIT> relates to a digital loudspeaker and a method for operating a digital loudspeaker.

<CIT> relates to a production method for a double-membrane MEMS component that includes: providing a layer arrangement on a carrier substrate.

<CIT> relates to a MEMS microphone that includes a first diaphragm element, a counter electrode element, and a low pressure region between the first diaphragm element and the counter electrode element.

There may be a need for sensitive and robust sensors.

According to an embodiment, a MEMS device comprises a first membrane structure, wherein the first membrane structure comprise a reinforcement region, wherein the reinforcement region has a larger thickness than an adjoining region of the first membrane structure. The MEMS device comprises an electrode structure, wherein the electrode structure is vertically spaced apart from the first membrane structure. The first membrane structure comprises a deflectable region and a clamped border region, wherein the clamped border region adjoins the deflectable region along a borderline of the deflectable region, wherein the reinforcement region of the first membrane structure is arranged at the borderline. Alternatively or in addition, the MEMS device comprises a second membrane structure, wherein the electrode structure is arranged between the first and second membrane structures, wherein the first and second membrane structures each comprise a deflectable portion, and wherein the deflectable portions of the first and second membrane structures are mechanically coupled by means of at least one mechanical connection element to each other and are mechanically decoupled from the electrode structure; wherein at least one of the first and second membrane structure comprises a reinforcement region at a coupling position with the at least one mechanical connection element.

A method for manufacturing such a MEMS device comprises manufacturing the reinforcement region of the first membrane structure using a local-Oxidation-of-Silicon, LOCOS, and arranging the electrode structure vertically spaced apart from the membrane structure. The method is executed such that the first membrane structure comprises a deflectable region and a clamped border region, such that the clamped border region adjoins the deflectable region along a borderline of the deflectable region, such that the reinforcement region of the first membrane structure is arranged at the borderline; or such that the MEMS device comprises a second membrane structure, wherein the electrode structure is arranged between the first and second membrane structures, such that the first and second membrane structures each comprise a deflectable portion, and wherein the deflectable portions of the first and second membrane structures are mechanically coupled by means of at least one mechanical connection element to each other and are mechanically decoupled from the electrode structure; and such that at least one of the first and second membrane structure comprises a reinforcement region at a coupling position with the at least one mechanical connection element.

Embodiments in accordance with the present disclosure are described herein whilst 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 embodiments of the present disclosure. However, it will be apparent to those skilled in the art that embodiments of the present disclosure may be practiced without these specific details. In other instances, well known structures and devices are shown in block diagram form rather than in detail in order to avoid obscuring embodiments of the present disclosure. In addition, features of the different embodiments described hereinafter may be combined with each other, unless specifically noted otherwise.

Embodiments described herein are related to microelectromechanical system (MEMS) devices. A MEMS device may comprise one or more semiconductor materials, for example an at least partially doped or undoped semiconductor material such as silicon, gallium arsenide or the like and/or combinations thereof. Materials derived therefrom such as silicon nitride (SiN, Si<NUM>N<NUM>, respectively), silicon oxide (SiOx, SiO<NUM>, respectively) or the like may be arranged alternatively or in addition. Alternatively or in addition, other materials such as a metal material, e.g., aluminum, copper, gold, silver, platinum or the like may be part of a MEMS structure.

Embodiments described herein relate to a membrane structure. Such a membrane structure may be a beam-like membrane or a more circular structure, e.g., a round or circular membrane, a quadratic membrane structure or a rectangular membrane structure. A beam-like membrane may differ from a conventional (e.g. circular) membrane with respect to its boundary conditions. For example, a circular membrane may be clamped at its edge or perimeter, whereas a beam-like membrane may comprise some free edges. A membrane structure described herein may be formed, for example, similar to a membrane structure being used in the MEMS microphones or MEMS loudspeakers. A membrane structure described herein is deflectable in a deflectable region or portion thereof.

Some of the embodiments described herein are explained in connection with MEMS devices that may implement at least a part of a MEMS microphone. However, embodiments described herein are not limited to MEMS microphones. The described principles may be applied, without limitations, to other MEMS sensors and/or actuators. For example, a MEMS sensor may be implemented as a pressure sensor or other type of sensor. An actuator may, for example, provide at least for a part of a loudspeaker, a pump or the like, comprising a membrane. That is, one aspect of embodiments described herein relate to sound transducers such as microphones or loudspeakers whilst other types of sensors and/or actuators using a membrane for operation may also benefit from the described principles.

<FIG> is a schematic side view of a MEMS device <NUM> according to an embodiment. The MEMS device <NUM> comprises a membrane structure <NUM> being configured for deflecting along a direction <NUM> which may be, at least within a tolerance range, be in parallel with a surface normal <NUM> of the membrane structure <NUM>, the surface normal <NUM> being perpendicular to one or both lateral extension directions. For example, the membrane structure <NUM> may be arranged so as to extend along lateral directions x and y whilst a thickness of the membrane structure may be arranged perpendicular hereto along a z-direction of an example Cartesian coordinate system. The direction <NUM> along with the membrane structure <NUM> may be flagged may, thus, be perpendicular to the z-direction as is the surface normal <NUM>.

The membrane structure <NUM> may comprise a reinforcement region <NUM> which may be understood as a part of the extension of the membrane structure <NUM> along the lateral directions x and/or y. In the reinforcement region <NUM> the membrane structure <NUM> may comprise a larger layer thickness <NUM><NUM> when compared to an adjoining region <NUM><NUM> and/or <NUM><NUM> of the membrane structure <NUM> having a layer thickness <NUM><NUM>.

An increase of the layer thickness <NUM><NUM> when compared to the layer thickness <NUM><NUM> may be larger or even significantly larger when compared to manufacturing tolerances that might provide for variances in the range of e.g., <NUM>%, <NUM>% or <NUM>%. For example, the layer thickness <NUM><NUM> may be in a range of at least <NUM> and at most <NUM>, at least <NUM> and at most <NUM> or at least <NUM> and at most <NUM>, for example, around <NUM>. Compared hereto, the layer thickness <NUM><NUM> may be increased by at least <NUM>%, at least <NUM>%, at least <NUM>% or even more. For example, the layer thickness of <NUM> may be increased to at least <NUM> and at most <NUM>, at least <NUM> and at most <NUM> or at least <NUM> and at most <NUM>, e.g., <NUM>.

The layer thickness <NUM><NUM> may relate to a maximum value of the layer thickness inside the reinforcement region <NUM>, e.g., in case a continuous variation of the layer thickness if increased along the x and/or y- direction. A shape of the membrane with regard to the increase may also be discontinuous, e.g., formed as a kind of square or brick wall or the like.

The reinforcement region <NUM> may be formed by material being same or different from a material of the membrane structure <NUM>. For example, it may be formed from one piece with the membrane structure <NUM>, i.e., it may be integrally formed with the membrane structure <NUM>. However, other ways of mechanically connecting additional reinforcing material <NUM> in the of the reinforcement region <NUM> to material of the membrane structure <NUM> during deposition of, e.g., the membrane structure onto the reinforcing material <NUM> or the reinforcing material <NUM> onto the membrane structure may be implemented, e.g., based on the used deposition process.

For example, arranging the additional material <NUM> at the membrane structure <NUM> or vice versa may be obtained by arranging or depositing the additional material <NUM> to increase the layer thickness <NUM><NUM> in the reinforcement region when compared to the adjoining regions <NUM>. The additional material <NUM> may be arranged, e.g., by using an additional process or process step to attach the material <NUM> at the membrane structure <NUM>, such an additional step may be executed prior or after providing the membrane. Alternatively or in addition, material may be locally removed from the membrane structure <NUM>, e.g., in the adjoining regions <NUM><NUM> and/or <NUM><NUM> such that the material <NUM> may form, at least in parts, a remains of such a process. Alternatively or in addition, the membrane structure <NUM> may be formed so as to comprise the material <NUM> and the reinforcement region, e.g., by use of a deposition process or the like that deposits more material in the reinforcement region when compared to the adjoining regions <NUM><NUM> and/or <NUM><NUM>.

The MEMS device <NUM> comprises an electrode structure <NUM> that is vertically spaced apart from the membrane structure <NUM>. As a spacing vertically apart from the membrane structure <NUM> it may be understood to have a distance along the direction of deflection <NUM> between the membrane structure <NUM> and the electrode structure <NUM>. The membrane structure <NUM> and the electrode structure <NUM> may overlap, at least in part, when being projected into a plane parallel to the x/y-direction. The electrode structure <NUM> may be understood as a backplate structure, e.g., when the MEMS device <NUM> forms a part of a MEMS microphone. The electrode structure <NUM> may be of a same or a different size along the x, y and/or z- direction when compared to the membrane structure <NUM>.

The membrane structure <NUM> may be formed at least locally electrically conductive to allow application of an electrical potential between the membrane structure <NUM> and the electrode structure <NUM> that may provide for a basis for operating the MEMS device <NUM> as a sensor and/or an actuator.

The reinforcement region <NUM> may allow to combine different requirements being imposed on a membrane structure by using a single configuration. Whilst using a comparatively thin membrane in the adjoining region <NUM><NUM> and/or <NUM><NUM>, a high compliance may be achieved that may allow for small chip areas and/or small extensions of the membrane in the x/y-direction. At a same time, the reinforcement region may allow for a high compliance by providing a high robustness of the membrane structure. According to an embodiment, the reinforcement region is arranged at a location or position of the membrane structure <NUM> which is subjected to a locally increased mechanical stress during an operation condition of the MEMS device <NUM>, during an overload condition of the MEMS device and/or a misuse condition of the MEMS device. For example, where it is expected or possible to face high mechanical loads at the membrane structure <NUM>, the membrane may locally be reinforced to avoid damages.

Such locations may be arranged at areas where the membrane is configured or expected to abut other structures or to face high stresses due to bending and/or stretching.

The membrane structure <NUM> may comprise a single or a multitude of reinforcement areas <NUM>. Implementing a multitude of reinforcement regions <NUM> at the membrane structure <NUM> may allow for using a same layer thickness <NUM><NUM> for some or all of the reinforcement regions but may also to deviate with regard to the implemented layer thickness along different reinforcement regions.

Although being illustrated as facing the electrode structure <NUM>, the reinforcement region may also be arranged at a side of the membrane structure <NUM> facing away from the electrode structure <NUM>.

<FIG> shows a schematic side view of a MEMS device <NUM> according to an embodiment. The MEMS device <NUM> may comprise a layered electrode structure <NUM> that may have one or more insulating layers <NUM><NUM> and/or <NUM><NUM> and/or at least one conductive layer <NUM> that may be contacted by an electrical contact <NUM><NUM> to apply and/or receive an electrical potential.

The membrane structure <NUM> may comprise one or a plurality of n reinforcement regions <NUM><NUM> to <NUM>n. Parameter n may be a value of at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM> or even <NUM> or more. For example, reinforcement region <NUM><NUM> and/or <NUM><NUM> may be arranged in an area at which the membrane structure <NUM> is clamped or configured to abut a supporting structure <NUM>, e. , a substrate or the like. The membrane structure <NUM> may be electrically connected via an electrical contact <NUM><NUM> which may allow to obtain and/or sense a potential difference between electrical contacts <NUM><NUM> and <NUM><NUM>.

Reinforcement regions <NUM><NUM>, <NUM><NUM> and/or <NUM>n may be arranged at a location of an elevation or bump <NUM><NUM> to <NUM><NUM> or other structures that are adapted to provide a mechanical contact or an abutting region for the membrane structure <NUM> so as to reinforce the mechanical structure of the membrane structure <NUM> at this location. That is, when projecting elevation or bumps <NUM><NUM> to <NUM><NUM>, they may overlap, partially or completely, with reinforcement regions <NUM><NUM>, <NUM><NUM>, <NUM>n, respectively. Although not necessarily implemented in such a way, at least one of elevation or bumps <NUM><NUM> to <NUM><NUM> may serve as an anti-stiction bump.

Clamping or abutting regions at the reinforcement regions <NUM><NUM> and <NUM><NUM> are examples for critical locations as are the reinforcement regions <NUM><NUM>, <NUM><NUM> and <NUM>n that are expected to be subjected to a locally increased mechanical stress. Such a locally increased mechanical stress may occur during an operation condition as well as an overload condition or a misuse condition, e.g., dropping the device or mechanically overloading the device. The MEMS device <NUM> shows a comparatively thick membrane at such critical locations to increase robustness at those regions and may show a comparatively thin membrane in other regions to increase sensitivity or maintain a high sensitivity. This may incorporate to skip a corrugation. Adjoining regions <NUM><NUM> to <NUM>j may be arranged adjacent to the reinforcement regions. However, the adjoining regions <NUM><NUM> to <NUM>j may be connected to one another at least partly or may form a common adjacent region, e.g., in a case where one or more of the reinforcement regions <NUM><NUM> to <NUM>m is formed as an island structure or the like.

<FIG> shows a schematic side view of an implementation of MEMS device <NUM>, in particular, a section <NUM><NUM> thereof. <FIG> shows insulating layers <NUM><NUM> and <NUM><NUM> sandwiching conductive layer <NUM> and anti-stiction bump <NUM><NUM>. As may be seen in <FIG>, the reinforcement region <NUM><NUM> of the membrane structure <NUM> may be arranged in a position aligned with respect to a bump or elevation arranged at the electrode structure <NUM>. Such a bump or elevation <NUM><NUM>, e.g., an anti-stiction bump, may in addition or as an alternative be arranged at the membrane structure <NUM>. For example, at a side opposing such a bump or elevation, the reinforcing material may be arranged so as to form the reinforcement region. This does not prevent to have the additional material of the reinforcement region at a same side as the bump or elevation. In the example shown in <FIG>, the bump or elevation, i.e., the anti-stiction bump <NUM><NUM> may be oriented towards the membrane structure <NUM>. As is also illustrated in <FIG>, the reinforcement region <NUM><NUM> may be arranged to comprise a gradual or stepless transition of the layer thickness <NUM> to the adjoining region <NUM><NUM> and/or <NUM><NUM>. According to other implementations the transition may comprise a step, i.e., a steep or transient transition.

When referring back again to <FIG>, a section <NUM><NUM> thereof is shown by way of a schematic side view of a realization of such a structure in <FIG>. whilst the section <NUM><NUM> represents at least a part of a deflectable region <NUM> of the membrane structure <NUM>, section <NUM><NUM> may be considered as a clamped border region <NUM> that adjoins the deflecting region <NUM><NUM>. Between the deflectable region <NUM> and clamped regions <NUM><NUM> and <NUM><NUM> there may be representable a borderline <NUM>. The clamped border region <NUM> may adjoin the deflectable region <NUM> along the borderline <NUM> of the deflectable region <NUM>. The reinforcement region <NUM><NUM> is arranged at the borderline, i.e., to overlap the borderline that indicates a region of increased mechanical stress. An optional layer <NUM> shown in <FIG> the bright layer in 2c may be at least a part of a sacrificial layer, e.g., comprising an oxide. The layer <NUM> may be arranged at a position possibly below the membrane <NUM>. In the region overlapping the moveable membrane <NUM> the layer <NUM> may be etched away. Alternatively or in addition, in a region where the membrane <NUM> is affixed, the layer <NUM> may remain.

<FIG> shows a schematic side view of an example MEMS device <NUM> according to an embodiment. Whilst the MEMS device <NUM> may realize, for example, a single backplate sound transducer with a single membrane structure, MEMS device <NUM> may implement a sealed dual membrane, SDM, device. Such a device may comprise a membrane structure <NUM><NUM> and an opposing membrane structure <NUM><NUM> that may be spaced apart by mechanical connection elements <NUM><NUM> to <NUM><NUM>, e.g., formed as pillar structures, and having the electrode structure <NUM> sandwiched therebetween. For example, the membrane structure <NUM><NUM> may be adapted to abut bump structures <NUM><NUM>, <NUM><NUM> and/or <NUM><NUM> which may be addressed by implementing reinforcement regions <NUM><NUM>, <NUM><NUM>, <NUM><NUM>, respectively. Alternatively or in addition, bump structures <NUM><NUM>, <NUM><NUM> and/or <NUM><NUM> may be adapted to abut the electrode structure <NUM>. Although not shown the membrane structure <NUM><NUM> may comprise reinforcement regions at corresponding locations on a side <NUM><NUM> and/or a side <NUM><NUM> thereof. Alternatively or in addition, reinforcement regions <NUM><NUM>, <NUM><NUM>, <NUM><NUM> and/or <NUM><NUM> may be arranged at membrane structure <NUM><NUM> and/or <NUM><NUM> at locations at which mechanical connection elements <NUM><NUM>, <NUM><NUM>, <NUM><NUM> and/or <NUM><NUM> are arranged on a same or opposing side of the respective electrode structure <NUM><NUM> and/or <NUM><NUM>. Alternatively or in addition, reinforcement regions <NUM><NUM> and <NUM><NUM> may be implemented together or independent from one another in a region of borderlines <NUM><NUM> and/or <NUM><NUM>.

Membrane structures <NUM><NUM> and <NUM><NUM> may be electrically connected to contacts <NUM><NUM> and/or <NUM><NUM>. In a similar way, the electrode structure <NUM> may be electrically connected via electrical contact <NUM><NUM>. Optionally, the MEMS device <NUM> may comprise one or more ventilation holes <NUM> to facilitate a movement of the membrane structures <NUM><NUM> and/or <NUM><NUM>. According to an embodiment, a MEMS device such as MEMS device <NUM> may comprise, beside the first membrane structure, a second membrane structure wherein the electrode structure <NUM> may be arranged between the first and the second membrane structures <NUM><NUM> and <NUM><NUM>. The membrane structures <NUM><NUM> and <NUM><NUM> may each comprise a deflectable portion or deflectable region <NUM><NUM>, <NUM><NUM>, respectively. The deflectable portions <NUM><NUM> and <NUM><NUM> may be mechanically connected or coupled by means of at least one mechanical connection element <NUM> to one another whilst being mechanically decoupled from the electrode structure <NUM>. The deflectable region <NUM><NUM> and a clamped region <NUM><NUM> of the membrane structure <NUM><NUM> may be arranged so as to adjoin one another along borderlines <NUM><NUM> and/or <NUM><NUM>.

Although not shown in <FIG>, the membrane structure <NUM><NUM> may comprise one or more reinforcement regions also being formed as a single piece of the membrane structure <NUM><NUM>. Such a reinforcement region may comprise a larger layer thickness than an adjoining region as was described in connection with membrane structure <NUM> in <FIG>. According to an embodiment, the reinforcement region of membrane structure <NUM><NUM> may comprise a gradual or stepless transition of the layer thickness to the adjoining region. As was described in connection with membrane structure <NUM><NUM>, the position of the membrane structure <NUM><NUM> is subjected to locally increased mechanical stress during an operation condition, an overload condition and/or a misuse condition of the MEMS device.

According to the invention the membrane structure <NUM><NUM> and/or <NUM><NUM> comprises a reinforcement structure or local stiffening <NUM> that is arranged at a coupling position at which the membrane structure is connected to at least one mechanical connection element <NUM> and/or in a region where the membrane structure <NUM><NUM> is clamped, e.g., at the borderline <NUM><NUM>. The reinforcement structure <NUM><NUM>, <NUM><NUM>, <NUM><NUM> and/or <NUM><NUM> may comprise, for example, a material that has a higher stiffness when compared to a material of the membrane structure itself. For example, a material such as silicon nitride or the like may be used to reinforce a silicon-based membrane structure. Such a material may allow to use a material that is used for insulating one or more regions.

Respective reinforcement regions being not shown in <FIG> may, as was described in connection with MEMS device <NUM> and/or <NUM>, be arranged in a position aligned with respect to a bump or elevation arranged at the electrode structure and/or at the membrane structure <NUM><NUM>. Such a bump or elevation, e.g., an anti-stiction bump, on the electrode structure <NUM> may be orientated towards the membrane structure <NUM><NUM>.

Reinforcement regions <NUM><NUM> and/or <NUM><NUM> that may be adapted to abut supporting structure <NUM> may be formed according to a hill-like structure but may, as an alternative, be formed like a donut-like structure, e.g., having a reduced thickness or being even absent in a center region or inner section, e.g., so as to host therein an edge of the supporting structure <NUM> abutting the reinforcement region.

A reinforcement region <NUM><NUM> to <NUM><NUM> may have a larger extension along the x-direction and/or y-direction when compared to the structure forming the source of the stress to be compensated for. For example, an elevation or bump such as bump <NUM><NUM>, <NUM><NUM> and <NUM><NUM> may provide for a comparatively small surface abutting the membrane structure <NUM><NUM>. This may allow an extension or diameter of reinforcement regions <NUM><NUM>, <NUM><NUM> and/or <NUM><NUM> of, e.g., <NUM>, <NUM>, <NUM> or other suitable values to be sufficient, e.g., applying a factor of <NUM>, <NUM>, <NUM> or more to the extension of the source of stress.

An extension of coupling structures <NUM> being, for example, around <NUM> along the x-direction may be compensated by use of a reinforcement region <NUM><NUM>, <NUM><NUM> and/or <NUM><NUM> that has a same, two times, three times or four times or more of said dimension, e.g., in a range between <NUM> and <NUM>.

On the other hand, tolerances during manufacturing and/or operation may lead to uncertainties and/or larger areas of stress generation which may be addressed by implementing a large area of the respective reinforcement region. On the other hand, for example, an edge of a supporting structure <NUM> may be generated by use of an etching process such that an etched edge is inclined with regard to the z-direction. For example, this may come along with a tolerance of plus minus <NUM> and an extension of the reinforcement region <NUM><NUM> having, e.g., a double of said size or, e.g., <NUM>, may allow to compensate for such tolerances.

When considering the membrane structure <NUM><NUM> and/or <NUM><NUM> as a rectangular, round or oval structure, the reinforcement region <NUM><NUM> and <NUM><NUM> may also form a combined, segmented or uniform reinforcement region, e.g., having a circular or oval shape.

According to embodiments, the respective reinforcement region is at least of a same size when compared to the structure causing the stress to be compensated. According to other embodiments, the reinforcement region is larger, e.g., having a size of factor <NUM>, <NUM>, <NUM> or more.

One possible implementation to produce or obtain the varying layer thickness of the membrane structure <NUM> of a MEMS device <NUM> and/or <NUM> or the membrane structure <NUM><NUM> of MEMS device <NUM> is explained whilst making reference to a method being illustrated in <FIG>.

<FIG> shows a step of local oxidation, e.g., performing a local oxidation of a substrate <NUM> which may comprise, for example, a silicon material. Such a step may be considered as local oxidation of silicon (LOCOS) to obtain an oxide material <NUM> by at least partly oxidizing the substrate <NUM>, e.g., using a mask <NUM>.

By removing the oxide material <NUM> as shown in <FIG>, a recess <NUM> may be obtained that may have a depth of, for example, at most or in a range of <NUM>, , e.g., at least <NUM>, at least <NUM> or at least <NUM>, e.g., <NUM> or a different value below <NUM> or about <NUM>.

<FIG> shows an example of further processing the substrate <NUM> of <FIG> by performing a deposition of Tetraethylorthosilicate (TEOS - e.g., C<NUM>H<NUM>O<NUM>Si) and a deposition of, e.g., an oxide layer <NUM>, e.g., silicon-oxide SiO<NUM>, followed by a deposition of a semiconductor layer <NUM> such as a silicon layer, in particular, a poly-silicon layer.

As shown <FIG>, a planar surface may be obtained, for example, by using a chemical-mechanical polishing, CMP, process e.g., to remove at least a part of the layer <NUM> outside region <NUM> that may later form the reinforcement region <NUM>. Using this planarized surface, a same material as layer <NUM> may be deposited again to increase the layer thickness homogeneously to obtain a varying thickness in the region <NUM> and outside thereof.

The step illustrated in <FIG> may be used to deposit again polysilicon and may allow to afterwards continue with standard processes to mount or use the obtained membrane structure. A process containing the steps as illustrated in <FIG> may be referred to as a locally thicker membrane (LTM) process. Such a process may be used for single backplate devices as well as sealed dual membrane devices. Although describing the membrane structure <NUM>, <NUM><NUM> and/or <NUM><NUM> as being deflectable, such a feature is not mandatory. Also undeflected structures may benefit from a reinforcement region. A locally reinforcement may provide for an improvement of robustness whilst providing for a high sensitivity. By using a locally thicker membrane, a stress being introduced in the reinforced structure may be distributed so as to allow for a uniform stress distribution or at least a more uniform stress distribution.

As shown by <FIG>, a method for manufacturing a MEMS device in accordance with embodiments described herein comprises manufacturing the reinforcement region of the membrane structure using a LOCOS process. Alternatively or even in combination, an etching process to obtain tapered edges of an etched recess at the reinforcement region may be used for manufacturing the reinforcement region. Such edges may be inclined with respect to a surface normal of a main surface of the membrane structure <NUM><NUM> and/or <NUM><NUM>. For example, such an etching process may comprise a wet silicon oxide (SiO) etching with tapered edges, e.g. by damaging an implant and/or by using a doped oxide. Such an etching process may be implemented with low effort when compared to the LOCOS process, e.g., in a case where a structure such as membrane structure <NUM><NUM> of MEMS device <NUM> is hard or even unable to be processed with the LOCOS process. Further, not shown in <FIG>, a method may comprise arranging the electrode structure <NUM> vertically spaced apart from the membrane structure. As shown in <FIG>, a method may additionally comprise a step of oxide etching, <FIG>, a deposition of reinforcement material (TEOS, SiON/silicon oxide/silicon nitride, poly-Si), <FIG>, a planarization (CMP), <FIG> and/or a standard deposition of a membrane material, <FIG>.

A method in accordance with embodiments may be implemented to comprise arranging a second membrane structure in such a way that the electrode structure is arranged between the membrane structures <NUM><NUM> and <NUM><NUM> as shown in <FIG>. Such a method may comprise manufacturing a reinforcement region of the second membrane structure <NUM><NUM> using a LOCOS process that may also be used to then insert material of a reinforcement structure <NUM>. As an alternative or even in combination, an etching process that provides for edges of the obtained recess that are tapered or inclined with respect to a surface normal of the etched structure, may be used. According to an embodiment, different MEMS devices may be manufactured differently. For example, the MEMS device <NUM> may be manufactured using the LOCOS process or a described etching process. Although not precluding to use the LOCOS process for both membrane structures <NUM><NUM> and <NUM><NUM>, a MEMS device having a double membrane structure such as MEMS device <NUM> may be manufactured by use of an etching process, e.g., at least for membrane structure <NUM><NUM> allowing a combination with the LOCOS process when using same for membrane structure <NUM><NUM> and/or allowing to use the etching process also for manufacturing the membrane structure <NUM><NUM>. The reinforcement region <NUM> may be generated according to both options.

Embodiments provide, among other things, a membrane of a sensor that has a locally different thickness in order to achieve high robustness whilst maintaining sensitivity. Using the LOCOS process in the process flow for manufacturing a MEMS device such as a silicon microphone these different thicknesses can be achieved using standard CMOS (complementary metal oxide semiconductor) processes. Such a process flow may create a thickened structure with smooth transitions from the thicker to the thinner region and therefore may avoid high stress concentration at these points. This may be of relevance as for a membrane it may be at least to a certain extent or even mostly the thickness which determines together with the stress and the structure the sensitivity. Therefore, a thicker structure may be an aim to achieve robustness whilst a contradicting requirement may lead to a thin membrane to achieve high sensitivity. Embodiments allow to combine both aims whilst providing a solution.

Embodiments allow to provide for a reinforcement at regions where stress, e.g., due to an overload, that is not equally present in all positions of the membrane concentrates to avoid a failure of the device at those locations. A sensor membrane may be structured, according to an embodiment, in a way that it has locally a higher thickness to gain high robustness in the critical areas, where in the larger area of the membrane the thickness may be reduced or kept low to gain the wanted high sensitivity.

Claim 1:
A MEMS device comprising:
a first membrane structure (<NUM>; <NUM><NUM>), wherein the first membrane structure (<NUM>; <NUM><NUM>) comprises a reinforcement region (<NUM>; <NUM><NUM>-<NUM><NUM>), wherein the reinforcement region (<NUM>; <NUM><NUM>-<NUM><NUM>) has a larger layer thickness (<NUM><NUM>) than an adjoining region (<NUM>; <NUM><NUM>-<NUM><NUM>) of the first membrane structure (<NUM>; <NUM><NUM>), and
an electrode structure (<NUM>), wherein the electrode structure (<NUM>) is vertically spaced apart from the first membrane structure (<NUM>; <NUM><NUM>);
characterized in that:
the first membrane structure (<NUM>; <NUM><NUM>) comprises a deflectable region (<NUM>; <NUM><NUM>) and a clamped border region, wherein the clamped border region adjoins the deflectable region (<NUM>; <NUM><NUM>) along a borderline of the deflectable region (<NUM>; <NUM><NUM>), wherein the reinforcement region (<NUM>; <NUM><NUM>-<NUM><NUM>) of the first membrane structure (<NUM>; <NUM><NUM>) is arranged at the borderline; or
the MEMS device comprises a second membrane structure (<NUM><NUM>), wherein the electrode structure (<NUM>) is arranged between the first and second membrane structures(<NUM><NUM>-<NUM><NUM>), wherein the first and second membrane structures (<NUM><NUM>-<NUM><NUM>) each comprise a deflectable portion (<NUM><NUM>-<NUM><NUM>), and wherein the deflectable portions (<NUM><NUM>-<NUM><NUM>) of the first and second membrane structures (<NUM><NUM>-<NUM><NUM>) are mechanically coupled by means of at least one mechanical connection element (<NUM><NUM>-<NUM><NUM>) to each other and are mechanically decoupled from the electrode structure (<NUM>); wherein at least one of the first and second membrane structure (<NUM><NUM>-<NUM><NUM>) comprises a reinforcement region (<NUM>; <NUM><NUM>-<NUM><NUM>) at a coupling position with the at least one mechanical connection element.