DEVICE WITH A STRESS DECOUPLING STRUCTURE

A MEMS device comprises a suspended membrane structure having an inner membrane section and an outer membrane section. The outer membrane section surrounds the inner membrane section. The membrane structure comprises an elastically deformable spring structure in the outer membrane section, such that the spring structure is arranged to convert a thermal-induced compressive stress in the suspended membrane structure into a spring displacement.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of European Patent Application No. 22208533, filed Nov. 21, 2022, each of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

Embodiments of the present disclosure relate to a device with a stress decoupling structure. In particular, embodiments relate to a micro-electro-mechanical system (MEMS) device for converting thermal-induced compressive stress into a local spring displacement of a spring structure.

BACKGROUND

Membrane structures are used in many devices that require, for example, measurement of a deflectable structure (e.g., a pressure sensor) or active deflection of a deflectable structure (e.g., a movable mirror mount for directing a mirror). Operation of such devices can cause or require heat generation (e.g. for generating infrared light or by illumination by a laser). Gas sensors with infrared sources often use a blackbody (or grey body) radiator as emitter of infrared light, wherein the temperature of the blackbody is about a few hundred degree Celsius.

Removal of heat can be challenging in particular in MEMS devices, which usually do not use fan devices and may even be hermetically closed. Excess heat can result in thermal expansion and thermal stress, which can cause a buckling or bulking mode if the stress becomes compressive due to thermal loading, which may impede operation and even damage the device. Furthermore, thermal stress can cause structural displacement to such a degree that the membrane structure comes in contact with other structures of the MEMS device, such as a backplate or a housing. The contact can cause damage to either structure and an uncontrolled heat flow from the membrane structure to the contacted other structure. Since the heat flow is uncontrolled, the membrane structure may exhibit excessive cooling and/or a highly asymmetric heat profile. In other words, the buckling or bulking mode may be larger than a thickness of the membrane structure itself, which is usually unwanted and hence may result in contact with other components such as electrodes. This may lead to local cooling due to conduction and/or fractures in the case of large compliance. This may affect operation of MEMS devices that requires a well-defined temperature distribution (e.g., an infrared light emitter).

One approach for addressing thermal stress is to increase a stiffness of the membrane structure in order to mitigate thermomechanical buckling, such as membrane structures with corrugations as well as the use of tensile materials with a higher stiffness. However, corrugations usually constitute additive structures, in which structures and materials are added to reduce a compliance of the heated membrane structure. The added thermal mass can lead to unwanted effects such as a lower modulation speed. Furthermore, corrugations require higher process complexity.

Another approach is to form perforations for ventilation or thermal isolation in the membrane structure (e.g., an infrared emitter). However, the perforations in highly tensile membrane structures may act as fracture initiation sites and affect the lifespan of the MEMS device.

Therefore, there is a need in the field of MEMS devices with membrane structures that have a better lifespan.

SUMMARY

According to an embodiment, a MEMS device is provided. MEMS device comprises a suspended membrane structure having an inner membrane section and an outer membrane section, wherein the outer membrane section surrounds the inner membrane section. The MEMS device further comprises an elastically deformable spring structure in the outer membrane region, wherein the spring structure is arranged to convert a thermal-induced compressive stress in the suspended membrane structure into a (local) spring displacement.

Thus, according to an embodiment, the spring structure is configured to convert thermal-induced compressive stress affecting the suspended membrane structure (and therefore affecting the inner and outer membrane sections) to displacement (and therefore to the outer membrane section). As a result, the thermal-induced compressive stress is reduced in the inner membrane section. Therefore, the risk of unintentional buckling and breaking of the inner membrane section is reduced. Furthermore, with thermal-induced compressive stress being converted to deformation of the spring structure instead to other components of the membrane structure, the spring structure has an increased chance of contacting other parts of the MEMS device (e.g. a housing of the MEMS device). As a result, direct heat dissipation directly from the inner membrane section is reduced, leading to a more homogenous temperature profile of the inner membrane section. Furthermore, heat dissipation is more predictable and controllable, as heat dissipation is rather expected to occur via the spring structure. The MEMS device is robust against mechanical stress has an improved lifespan. The MEMS device can be manufactured without requiring an additional mask or process.

According to an embodiment, a MEMS device is provided. The MEMS device comprises a suspended membrane structure having an inner membrane section and an outer membrane section, wherein the outer membrane section surrounds the inner membrane section. The MEMS device further comprises a strip-shaped intermediate region between the inner membrane section and the outer membrane section, wherein the intermediate region is thermally and mechanically connected to a heat sink by means of one or more connection structures which are mechanically and thermally coupled between the intermediate region structure and the heat sink.

Thus, according to an embodiment, the connection structures allow excess heat that may built up in the membrane to be diverted to the heat sink. As a result, thermal-induced stress and damage caused thereby can be reduced. Since the connection structures are coupled to the intermediate region and not the inner and outer membrane sections, deflection of the inner and outer membrane sections is not significantly inhibited by the connection structure. However, the inner and outer membrane sections benefit from the reduced thermal stress caused by the connection structures. The inner and outer membrane sections are therefore well suited for membrane applications while having reduced thermal stress. The MEMS device is robust against mechanical stress has an improved lifespan.

Further embodiments are described in the dependent claims.

In the following description, embodiments are discussed in further detail using the figures, wherein in the figures and the specification identical elements and elements having the same functionality and/or the same technical or physical effect are provided with the same reference numbers or are identified with the same name. Thus, the description of these elements and of the functionality thereof as illustrated in the different embodiments are mutually exchangeable or may be applied to one another in the different embodiments.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In the following description, embodiments are discussed in detail, however, it should be appreciated that the embodiments provide many applicable concepts that can be embodied in a wide variety of semiconductor devices. The specific embodiments discussed are merely illustrative of specific ways to make and use the present concept, and do not limit the scope of the embodiments. In the following description of embodiments, the same or similar elements having the same function have associated therewith the same reference signs or the same name, and a description of such elements will not be repeated for every embodiment. Moreover, features of the different embodiments described hereinafter may be combined with each other, unless specifically noted otherwise.

However, it will be apparent to one skilled in the art that other embodiments 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 examples described herein. In addition, features of the different embodiments described herein may be combined with each other, unless specifically noted otherwise.

In the description of the embodiments, terms and text passages placed in brackets are to be understood as further explanations, exemplary configurations, exemplary additions and/or exemplary alternatives.

It is understood that when an element is referred to as being “connected” or “coupled” to another element, it may be directly connected or coupled to the other element, or intermediate elements that may be present. Conversely, when an element is referred to as being “directly” connected to another element, “connected” or “coupled,” there are no intermediate elements. Other terms used to describe the relationship between elements should be construed in a similar fashion (e.g., “between” versus “directly between”, “adjacent” versus “directly adjacent”, and “on” versus “directly on”, etc.).

For facilitating the description of the different embodiments, some of the figures comprise a Cartesian coordinate system x, y, z, wherein the x-y-plane corresponds, i.e. is parallel, to a main surface region (e.g. a displaceable or deflectable structure) of a (suspended) MEMS membrane (=a reference plane=x-y-plane), wherein the direction vertically up with respect to the reference plane (x-y-plane) corresponds to the “+z” direction, and wherein the direction vertically down with respect to the reference plane (x-y-plane) corresponds to the “−z” direction. In the following description, the term “lateral” means a direction parallel to the x- and/or y-direction or a direction parallel to (or in) the x-y-plane, wherein the term “vertical” means a direction parallel to the z-direction.

Embodiments of the present disclosure relate to a device with a stress decoupling structure. In particular, embodiments relate to a MEMS device for converting thermal-induced compressive stress into a local spring displacement of a spring structure.

FIG.1shows a schematic top view of an example of a MEMS device100. The MEMS device comprises a suspended membrane structure no having an inner membrane section112and an outer membrane section114, wherein the outer membrane section114surrounds the inner membrane section112, and an elastically deformable spring structure116in the outer membrane region114, wherein the spring structure116is arranged to convert a thermal-induced compressive stress in the suspended membrane structure into a spring displacement.

In other words, at least some (or all) of thermal-induced compressive stress that would act on the suspended membrane structure no if it had no elastically deformable spring structure116is mitigated by being converted to thermal-induced compressive stress acting on the deformable spring structure116. As a result, at least some (or all) of deformation of the suspended membrane structure110that would have occurred if it had no elastically deformable spring structure116is mitigated and converted into deformation of the deformable spring structure116. For example, the elastically deformable spring structure116may comprise a region that is deflectable relative to an imaginary plane defined by the suspended membrane structure no, wherein a strain across the suspended membrane structure no causes the deformable spring structure116to exhibit a larger (e.g., per area size) deflection (e.g., in form of translation and/or torsion) than the inner membrane section112.

A membrane structure no with such a deformable spring structure116enables reduction of its displacement by transforming and controlling a thermo-mechanical energy into the deformable spring structure116, e.g. due to the deformable spring structure116being softer than the inner membrane section112and hence conducting the mechanical stress by transferring the energy towards displacement of the deformable spring structure116.

The MEMS device100may be used in a MEMS heater with a structure to decouple and adjust thermomechanical displacement and other areas where stress decoupling of membranes is important. The MEMS device100may be used in infrared emitters and in environmental sensors (e.g., gas sensors based on photoacoustic spectroscopy).

The membrane structure no may have at least essentially a shape of a circular, elliptical, rectangular, square, polygonal or regular polygonal structure. The inner membrane section112may have an at least essentially similar shape (but with smaller dimensions) as the membrane structure no. For example, if the membrane structure no has a circular shape, the inner membrane section112may also have a circular shape, but with a smaller outer diameter. Alternatively, the membrane structure no and the inner membrane section112may have different shapes. Geometric centers of the shapes (e.g., center of a circular structure) of the membrane structure110and the inner membrane section112may at least essentially coincide (e.g., two circular shaped forms may be arranged concentrically). The outer membrane section114may surround the inner membrane section112radially (e.g., within a plane of the membrane structure110).

A lateral surface area of the spring structure116may be less than 40%, e.g., less than 20%, e.g., less than 10%, e.g., less than 5% (or a value between any of these values) and at least 1%, for example, of a lateral surface area of the membrane structure no.

Since the spring structure116essentially absorbs thermal-induced compressive stress that could affect the inner membrane structure112, the inner membrane structure112is preferably used for operation of the MEMS device100. With the spring structure116occupying less than a maximum surface area (e.g., less than 40%), more of the membrane structure no can be used as inner membrane section112. Operation of the MEMS100device may therefore be improved.

The spring structure116may have a mechanical rigidity, which is at least two-times (e.g., or three, four, five, six, or more times) lower than the mechanical rigidity of the remaining membrane structure no. As a result, the spring structure116deflects easier than the remaining membrane structure no. It has been found that a mechanical rigidity that is two-times lower forms a good compromise between conversion of thermal-induced stress and stability of the membrane structure no.

The spring structure116may form a locally confined displacement region in the outer membrane region114of the membrane structure no. A confined displacement region results in a compact device. The spring structure116may be locally confined to a frame shaped area (e.g., a stripe shaped area framing an inner area that includes the inner membrane section112) or a segment thereof. The frame shaped area may have (at least partially) the shape of a ring, a rectangle, an oval, and a polygon. The frame shaped area may imitate a contour of the membrane structure (e.g., with smaller dimensions).

The spring structure116may comprise at least one of a trench structure, a slit structure and a lined-up hole structure in the outer membrane region116. Such structures form longitudinal openings that allow local deformations of the membrane structure116along the longitudinal opening. Furthermore, between two (or more) longitudinal openings one or more strips may be formed which have a lower rigidity than areas of the membrane structure110that has no spring structure116.

The trench or slit structure may comprise overlapped trenches or a meander-shaped trench. The trenches or meander-shaped trenches may overlap in a radial direction. For example, the trench structure may comprise two (or more trenches) in the shape of two concentrical rings with patterns comprising dashed lines (wherein each line is an opening and interruptions of the line therebetween do not form openings), wherein the two patterns are offset relative to each other in a circumferential direction.

According to an embodiment, a lateral surface area of the spring structure116may be less than 40% of a lateral surface area of the membrane structure. According to an embodiment, the spring structure116may have a mechanical rigidity which is at least two-times lower than the mechanical rigidity of the remaining membrane structure.

According to an embodiment, the spring structure116may form a locally confined displacement region in the outer membrane section of the membrane structure. According to an embodiment, the spring structure116may comprise at least one of a trench structure, a slit structure and a lined-up hole structure in the outer membrane section. According to a further embodiment, the trench structure116may comprise overlapped trenches or a meander-shaped trench.

According to an embodiment, the membrane structure110may comprise a perforation structure in the inner membrane section112to provide a higher mechanical rigidity of the inner membrane section112than the outer membrane section114and to use the outer membrane section as the spring structure.

According to an embodiment, the spring structure116may comprise at least one spring element which is formed by two neighboring and laterally spaced trenches or slits. According to a further embodiment, the spring element116may be formed as a strip or leaf spring in the outer membrane section, which partially surrounds the inner membrane section.

According to an embodiment, the spring element116may extend in the outer membrane section114parallel to a circumferential line of the membrane structure110or along a contour line of membrane deflection. According to an embodiment, the spring structure116may comprise a plurality of spring elements, which are respectively formed by two neighboring and laterally spaced trenches or slits. According to a further embodiment, the spring elements may be formed as parallel strips or leaf springs and partially surround the inner membrane section. According to an embodiment, the widths of the spring elements may be chosen to provide at least one of equal stiffness, equal electrical resistance and equal distance of the spring elements. According to an embodiment, the spring elements may be distributed in a pattern in the outer membrane section and extend parallel to a circumferential line of the membrane structure110or along a contour line of membrane deflection.

According to an embodiment, the suspended membrane structure110may be edge clamped to a support structure or substrate and may span across at least a cavity in the support structure or substrate. According to an embodiment, the suspended membrane structure110may comprise an integrated resistor which may be arranged to be heated by application of a voltage.

To summarize, a membrane structure110is provided having a spring structure116that may comprise trenches (or slits) that can compensate a displacement by transforming and controlling a thermo-mechanical energy into spring elements formed between the trenches; the spring elements are weaker and hence conduct the mechanical stress by transferring the energy towards displacement, as structures bend more where weaker. Additionally a thermal insulation towards an adjacent substrate (e.g., a housing and/or heatsink) can be adjusted by a trench width and number of trenches and as a result the remaining resistor is adjustable as well for a homogeneous temperature profile. Optimization allows focusing on constant stiffness (mechanical domain), constant electrical resistance (electrical and/or optical domain), constant gap size (symmetry), or and all of the above mentioned permutations.

The spring structure116may be designed to extend or to be formed along contour lines of a membrane deflection, for example, of a circular, elliptical or rectangular (square) membrane structure110. For example, in case of a rectangular (square) membrane structure110, the membrane deflection contour lines are no longer circles but have a more or less rounded-corner rectangular (or square) shape.

In contrast, the present disclosure is directed towards achieving a local deflection of a region of a component in the heating membrane structure (or the component subjected to strong heating—or mirror etc.), for example by forming a spring structure (e.g. cantilever), whereby only this locally deflected area comes (or can come) into contact with the housing and then cools (more strongly), so that the remaining surface area of the heated membrane structure (or the heated component) otherwise has a homogeneous heat distribution and can thus be operated, for example, at a maximum temperature. The ratio of the area (or mass) of the spring structure to the total area (total mass) of the membrane structure may be relatively small (e.g. <10%) as noted above.

Thus, the deflection of an area (of the spring structure) of the component can be achieved selectively, whereby this selective area (e.g., sacrificial area) is subjected to a selective temperature change (reduction).

The thermomechanical surface thus remains (except for the spring structure) in a basic deflection (e.g., no or reduced thermally induced deflection or deflection due to its intended operation) and can thus (except for the area with the target deflection) have a maximally homogeneous temperature distribution or, for example, in the case of a mirror element, a maximally homogeneous (flat or predefined) surface topography. That is, in the case of a mirror element, the structure can be maintained in an initial deflection. Therefore, according to some embodiments, a lot of effort (for example in pressure sensors or microphones) can be avoided on not transferring a package stress to component thereof (e.g., a membrane structure of a pressure sensor or microphone) or on not introducing it there.

In the present description of embodiments, the same or similar elements having the same structure and/or function are provided with the same reference numbers or the same name, wherein a detailed description of such elements will not be repeated for every embodiment. Thus, the above description with respect toFIG.1is equally applicable to the further embodiments as described below. In the following description, essentially different implementations or differences, e.g. additional elements, to the embodiment as shown inFIG.1and the technical effect(s) resulting therefrom are discussed in detail.

FIG.2shows a top view of an example of a MEMS device100with a spring structure116comprising a first and second slit (or trench)117a, b. A slit or trench may be realized as a longitudinal through hole (e.g., a through trench or through slit). Therefore, the spring structure116comprises a spring element119(e.g., a strip) which is formed by two neighboring and laterally spaced slits117a, b. The spring element119essentially forms a flat spring with two connection points120a, bto the rest of the membrane structure110. A stress applied between the two connection points120a, bcan be alleviated (at least partially) by a deflection (e.g., a buckling in an arch like shape and/or torsion around an extension axis of the spring element) of the spring element119. A thermal-induced stress acting on the membrane structure110can also causes a stress between the two connection points120a, b, which can be alleviated at least partially by deflection of the spring element119, thereby reducing the thermal-induced stress on the rest of the membrane structure110.

In other words, the slits or trenches117a, bmechanically weaken the membrane structure110for bending modes and allowing, for example, thermomechanical displacement of the spring structure116and therefore in a defined area where displacement may be less critical.

FIG.2shows a version of the spring structure116with two slits117a, b, which only extend over approximately a quarter of a circumference of the disc shaped membrane structure110. As will be explained in the following, the spring structure116can be realized in many different forms.

FIG.3Ashows a top view of an example of a MEMS device100with a spring structure116comprising a first and second slit (or trench)117a, b, which extend along almost the entire circumference (e.g., 350°) of the membrane structure110. Alternatively, at least one or more of the slits117a, b, extend along an are that covers different amounts of the circumference, such as at least essentially 45°, 60°, 90°, 120°, 135°, 180°, or 240° (or at least similar in a range of −5% and +5%).

The spring structure116may comprise a plurality of spring elements119, which are respectively formed by two neighboring and laterally spaced trenches or slits117. A plurality of spring elements119allows for a more homogenous distribution of the thermal-induced stress. Furthermore, when the thermal-induced stress is distributed amongst a plurality of spring elements119, the respective spring elements119require less deflection for the conversion of the thermal-induced stress. Therefore, the MEMS device100can be more compact.

The spring structure116may comprise a plurality of spring elements119, which are respectively formed by two neighboring and laterally spaced slits or trenches117. The spring structure116may comprise a plurality of spring elements119that are laterally spaced apart and/or spaced apart in a circumferential direction.

FIG.3Bshows a top view of an example of a MEMS device100with a spring structure116comprising a first and second slit117a, b, which each have a shape of segments of a common circle. In the example shown inFIG.3B, each circle has four segments. Therefore, the spring structure116ofFIG.3Bhas four spring elements119. Alternatively, a circle may have a different amount of segments, such as two, three, five, six, or more. Furthermore, the circles shown inFIG.3Bhave the same number of segments (e.g., four segments). Alternatively, the circles may have different numbers of segments, e.g., a multiple of each other (e.g., four segments and eight segments). In the example shown inFIG.3Bthe circle segments and gaps between the circle segments align in a circumferential direction. Therefore, the first and second slit117a, bdepicted inFIG.3Bboth have a gap at the top, right, bottom and left part (or 12, 3, 6, and 9 o'clock).

FIG.3Cshows a top view of an example of a MEMS device100with a slit structure that comprises overlapped slits. The spring structure116comprises a first and second slit117a, b, which each have a shape of segments of a common circle that are angularly offset relative to each other. Therefore, the first and second slit117a, bform overlapped slits (or overlapped trenches). In the example shown, the angular offset (e.g., 45°) is half an angle between two gaps (e.g., 90°). Alternatively, the angular offset can be any other value between zero and the angle between two gaps.

FIGS.3A-Cshow a spring structure116comprising holes in form of slits with a shape of one or more circle segments. Alternatively or additionally, the spring structure116may comprise holes with other shapes.

FIG.4Ashows a top view of an example of a MEMS device100with a spring structure116comprising a plurality of longitudinally shaped holes122arranged along an imaginary ring. In other words, the spring structure116comprises a lined-up hole structure. The membrane structure110forms radially extending bridges124between the longitudinally shaped holes122. The bridges124are configured to alleviate (at least partially) by a deflection (e.g., a buckling in an arch like shape and/or torsion around an extension axis the bridge124) of the bridge124.

FIG.4Bshows a top view of an example of a MEMS device100with a spring structure116comprising a ring shaped hole with multiple gaps in form of straight bridges. The examples of the spring structures116ofFIGS.4Aand B are similar, but the bridges inFIG.4Bhave straight bridges with at least essentially straight and parallel edges. The edges may extend radially, which still results in an essentially parallel orientation.

FIG.4Cshows a top view of an example of a MEMS device100with a spring structure116comprising one or more holes126with a meandering shape. The meandering shape may define a shape extension path line, wherein the meandering shape is realized by a meandering path that repeatedly crosses the shape extension path line. In the example shown inFIG.4C, the shape extension path line is a ring circle (or four segments thereof) and the meandering path is the path of the hole126that repeatedly crosses the ring circle.

FIG.4Dshows a top view of an example of a MEMS device100with an inner membrane section112that comprises holes128configured to increase the rigidity of the inner membrane section112. As a result, the outer membrane section114forms a spring structure116that has a lower rigidity than the inner membrane section112.

In case of formation of the spring structure by means of perforations (as a stiffener inside the inner membrane section112—the heating membrane or the mirror element, etc.), the thermally induced deflection can be selectively relocated/shifted to the spring structure116(e.g., outer membrane section114) of the membrane structure110in order to obtain the above-mentioned sacrificial area at the spring element116. The perforations (formed by holes128) arranged in the inner membrane section112of the membrane structure no (for example, a heater membrane) can also be formed as plasmonic structures to possibly also perform a filtering function (in the case of a heater as an IR radiation source).

For example, the perforation (formed by the holes128) can be formed as corrugation rings in the inner membrane section112of the membrane structure no for thermomechanical stiffness. In such a case, the thermally induced bending can be shifted outward (towards the spring structure116). Thus, by providing a perforation in the inner membrane section112of the thermally loaded membrane structure no, a local spring structure116can be achieved in adjacent/adjacent outer regions of the membrane structure110.

A spring structure116with an adjustable spring constant can thus be formed as a spring segment and/or a spring area in the thermally loaded membrane structure110.

Any of the spring structures16described herein may be combined. The combination may be realized by arranged different types of spring structures116at different radial distances relative to a center point of the membrane structure110. Alternatively or additionally, different types of spring structures116may be arranged at the same of similar radial distances, e.g., by interweaving the different types of spring structures116.

FIG.5Ashows a top view of an example of a MEMS device100with a spring structure116comprising holes129arranged along an imaginary ring and holes126with a meandering shape interweaving between the holes129arranged along the imaginary ring. The holes129arranged in along an imaginary ring may be structurally so fragile that thermal stress can cause unintended fracturing. The holes129with a meandering shape126may reduce such stresses and therefore may reduce the risk of fractures between the holes129. The holes129with the meandering shape126may terminate outside an aggregation (or pattern or grid) of the holes129arranged along the imaginary ring (as exemplarily depicted at the bottom ofFIG.5A). Strain usually increases at an end of a longitudinal opening. With the meandering shape126terminating outside the aggregation, high strain is directed to a region of the membrane structure110that is less structurally weakened by the aggregation of the holes129arranged along the imaginary ring.

FIG.5Bshows a top view of an example of a MEMS device100with a spring structure116comprising three slits117a, b, cradially spaced apart. The three slits117a, b, cextend a long a circular circumference and each comprise two segments of the respective circle. However, any other shape of the circumference, any other number of segments and any other number of slits117may be used instead.

It is noted thatFIG.5Bshows that the outer membrane section114(surrounding the inner membrane section112) does not necessarily have to be arranged at an outmost area of the membrane structure no. For example, the membrane structure no inFIG.5Bcomprises a side region115that may surround the outer membrane section114or may comprise one or more portions that are arranged radially outside of the outer membrane section114. The side region115may comprise ventilation holes.

The widths of the spring elements may be chosen to provide at least one of equal stiffness, equal electrical resistance and equal distance of the spring elements. For example, radial distances between two slits117can be selected to emphasis constant stiffness (e.g., mechanical domain), constant electrical resistance (e.g., electrical and thermal domain) and constant gap size (e.g., symmetry), or different combinations thereof.

FIG.6Ashows a top view of a cutout A ofFIG.5B, wherein a ratio of radial distances of slits and a ratio strip widths (of the spring elements119a, b) may have a non-linear or polynomial relationship. A first slit117ahas a radius r1(to a center of a circle that the first slit117ais a part of) and a second slit117bhas a radius r2. A first spring element119abetween the first slit117aand a border of the inner membrane section112and the outer membrane section114has a first width w1. A second spring element119bbetween the first slit117aand the second slit117bhas a width w2. The ratios of the widths w1, w2may be adjusted based on the radii r1, r2.

FIG.6Bshows a top view of a cutout A ofFIG.5B, wherein a ratio of radial distances of slits and a ratio of strip widths (of strips between the corresponding spring elements119) have a different non-linear relationship compared to the one shown inFIG.6A.

FIG.7Ashows a top view of a cutout A ofFIG.5B, wherein spring element119between slits have equal widths.

As can be seen inFIGS.5B to7, the spring structure116may comprise at least one spring element119which is formed by two neighboring and laterally spaced slits (or trenches)117. The spring element119may be formed as a strip or leaf spring in the outer membrane region114, which partially surrounds the inner membrane region112. In the examples shown inFIGS.2and3B, the spring element119surrounds the inner membrane section112approximately (or exactly) by a quarter of a circumference around the inner membrane section112. However, the spring element119may surround the inner membrane112at a smaller or larger degree.FIG.3Ashows an example in which the spring element119surrounds the inner membrane section112by approximately 350°.FIG.5Bshows an example of spring elements119surrounding the inner membrane section112by (approximately or exactly) 120°.FIG.3Cshows an example of spring elements119forming between laterally overlapping slits117a, b, resulting in eight spring elements119that each surround the inner membrane section112by slightly less than an eighth of a circumference (e.g., 40°).

FIG.5Bshows slits17that are formed in the shape of three rings that are segmented into two ring segments. However, the slits of may be formed in any other number of rings (or other circumferential form such as a rectangle, an ellipsis or a polygon) such as three, four, five, six, or more rings. Furthermore, each ring (or other circumferential form) may be segmented in a different number of segments such as three, four, five six, or more.

FIG.7Bshows a top view of an example of a membrane structure110, wherein slits are formed in the shape of rings that are separated into four segments.

FIG.7Cshows a top view of an example of a membrane structure no, wherein slits are formed in the shape of rings that are separated into six segments.

While all rings inFIGS.7B, C are separated into the same amount of segments, at least two rings may be separated into different numbers of segments (e.g., four and eight).

The spring elements119may extend in the outer membrane region114parallel to a circumferential line of the membrane structure no or along a contour line of membrane deflection. As thermal stress may originate and/or distributes according to a contour of the membrane structure110, spring elements119extending parallel to the contour line may reduce stress efficiently.

FIG.8Ashows a top view of an example of a membrane structure110with a circular circumferential contour line. Spring elements119in the outer membrane region114also extend in a (e.g., partial) circular circumferential line and therefore extend parallel to the circumferential line of the membrane structure110. In the example shown inFIG.8A, the spring elements119extend along a path with the shape of a quarter circle.

FIG.8Bshows a top view of an example of a membrane structure110with a rectangular (e.g., in the shape of an oblong rectangle or a square) circumferential contour line. Spring elements119in the outer membrane region114also extend in a (e.g., partial) rectangular circumferential line. In the example shown inFIG.8B, the spring element119extends along an L-shaped path that is arranged parallel to the rectangular circumferential line of the membrane structure110.

The spring structure116may be designed to extend or to be formed along contour lines of a membrane deflection, for example, of a circular, elliptical or rectangular (square) membrane structure no. For example, in case of a rectangular (square) membrane structure no inFIG.8B, the membrane deflection contour lines are no longer circles but have a more or less rounded rectangular (square) shape.

As can be seen inFIG.8B, the spring element119is formed by two slits that each have an L-shape with a rounded corner. Alternatively, the corner may be formed angular-shaped (i.e. without a rounded corner).

FIG.8Cshows a top view of an example of a membrane structure110with an elliptical circumferential contour line. Spring elements119in the outer membrane region114also extend in a (e.g., partial) elliptical circumferential line. In the example shown inFIG.8A, the spring elements119extend along a path with the shape of a quarter ellipse.

FIG.8Dshows a top view of an example of a membrane structure110with an octagonal circumferential contour line. Spring elements119in the outer membrane region114also extend in a (e.g., partial) octagonal circumferential line. In the example shown inFIG.8D, the spring element extends along a path of two lines at an angle of 135°, wherein the path is arranged parallel to the octagonal circumferential line of the membrane structure110. The two lines may meet at a round corner (as depicted inFIG.8D) or at an angular-shaped corner.

The spring elements119may be formed as parallel strips or leaf springs and partially surround the inner membrane region112. InFIG.8A, the spring elements119are formed as a plurality of strips that extends in parallel in an arch like path around the inner membrane region112. InFIG.8B, the spring elements119are formed as strips that extend in in parallel along straight path that bend in a900angle.

The suspended membrane structure110may be edge clamped to a support structure or substrate and the suspended membrane structure110may span at least across a cavity in the support structure or substrate. The membrane structure110can be deflected relative to the clamped edge, wherein the spring structure116can alleviate thermal-induced stress between clamped edges.

FIG.9shows an example of a MEMS device100with an edge clamped membrane structure110. A support structure150has a clamping structure152and a cavity154. The membrane structure no is edge clamped by the clamping structure152. The clamping structure152may, for example, be a support plate and a top plate that was been fabricated on top of the support plate and the membrane structure no after the membrane structure no has been arranged on top of the support plate. Alternatively or additionally, the clamping structure152may be formed by material deposition into openings of a sacrificial layer and subsequent removal of the sacrificial layer.

The support structure150further comprises a cavity154. The cavity154can be hermetically closed (e.g., for a microphone) or can have one or more openings (e.g., for emission or reception of electromagnetic radiation and/or fluid connection to a pressure to be measured). The edge clamped membrane structure no spans across the cavity154of the support structure150.

The suspended membrane structure110may comprise an integrated resistor which is arranged to be heated by application of a voltage. The integrated resistor may be the membrane structure110or a part thereof. Therefore, application of a voltage causes a current to travel through the membrane structure no (or the part thereof), which results in heat generation by the membrane structure no. Alternatively, the integrated resistor may be a separate electrical component that is thermally coupled to the membrane structure no. Possible thermal stress induced by the heating can be alleviated at least partially by the spring structure116.

In an embodiment, a MEMS device100comprises a suspended membrane structure clamped at one or more edges, with an integrated resistor, which can be heated by application of a voltage, in which a selective segmentation of the said membrane structure into (at least) an inner and outer membrane section112,114results in two or more subsections thereof, used to control the heat generation and deformation of the membrane structure no.

According to an embodiment, the MEMS device100(e.g., the spring structure116) is manufactured using a subtractive method (e.g., using at least one of laser cutting, dry etching, wet etching, and optical lithography). The spring structure116may be detected and/or verified optically, e.g., by detecting slits or holes that for a spring structure116, e.g., using a light microscope or electron scanning microscope.

According to an embodiment at least a portion of the membrane structure may comprise or be made of a semiconductor material. The semiconductor material of the membrane structure no (e.g., the inner membrane section112and/or the outer membrane section114) may comprise poly-silicon or monocrystalline silicon. Further materials may be used. The semiconductor material may comprise, for example, silicon (Si), such as poly-silicon (poly-Si), amorphous silicon (a-Si), or monocrystalline silicon, gallium nitride (GaN), gallium arsenide (GaAs) or aluminum nitride (AlN). However, this list of materials for the semiconductor material is not to be regarded as exhaustive. In some embodiments, the semiconductor material may be a conductive semiconductor material.

FIG.10Ashows a top view of an example of MEMS device200. The MEMS device200comprises a suspended membrane structure210having an inner membrane section212and an outer membrane section214, wherein the outer membrane section214surrounds the inner membrane section212. The MEMS device200further comprises a strip-shaped intermediate region216between the inner membrane section212and the outer membrane section214, wherein the intermediate region216is thermally and mechanically connected to a heat sink (not shown inFIG.10A) by means of one or more connection structures218(indicated in dashed lines inFIG.10A) which are mechanically and thermally coupled between the intermediate region216and the heat sink.

FIG.10Ashows a top view of an example of a connection structure218with the shape of a wall that extends in a ring shaped path extending in circumferential direction in parallel to a shape of the strip-shaped intermediate region. In other words, the connection structure218has the shape of a (very short) circumferential or ring-shaped wall that extends perpendicular to the membrane structure210. The ring shaped connection structure218provides an improved heat transfer. However, the connection structure218may have other shapes, e.g. arc-shaped or shaped as segments of a circle.

FIG.10Bshows a top view of an example of a MEMS device100connection structure218that comprises two pillars. The solid or hollow pillars may have a cylindrical shape and may extend perpendicular or non-perpendicular relative to the membrane structure110. Alternatively, the connection structure218may comprise any other number of pillars such as one, three, four, five, six, or more (e.g. equally spaced) pillars. The spaced pillars may improve air circulation to the inner membrane section212and may improve deflectability of the membrane structure110.

FIG.10Cshows a schematic cross sectional view of a plane B through the MEMS device100depicted inFIG.10A(as well asFIG.10Bits pillars also cross plane B).

The connection structure218is mechanically coupled to both, the intermediate region216and a heat sink220. At least one of the mechanical couplings may comprise at least one of an adhesive and a welding connection. The connection structure218may be fabricated (at least partially) by deposition of material in openings of a sacrificial layer and subsequent removing (e.g., dry or wet etching) of the sacrificial layer). The connection structure218may additionally or alternatively, be fabricated using any other MEMS fabrication process.

InFIG.10C, the heat sink spans across the membrane structure110. Alternatively, the heat sink may have at least one opening (e.g., at the inner membrane section212). Such an opening allows optical communication (e.g., emission of infrared radiation) and/or fluid communication of a fluid for a pressure measurement.

The heat sink inFIG.10Cmay comprise no other mechanical connection to the membrane structure no. However, the heat sink may comprise other mechanical connections such as a support structure that edge clamps the membrane structure no.

A lateral surface area of the strip-shaped intermediate region116may be less than 40%, e.g., less than 20%, e.g., less than 10%, e.g., less than 5% of a lateral surface area of the remaining membrane structure. For example, the lateral surface area of the strip-shaped intermediate region116depicted inFIG.10Cis approximately 20% of a lateral surface area of the remaining membrane structure.

The strip-shaped intermediate region216may be laterally separated from the remaining membrane structure no by two neighboring and laterally spaced segmentation structures, wherein each segmentation structure may comprise a trench, overlapped trenches, a meander-shaped trench, a lined-up hole structure or a combination thereof.

FIG.11Ashows a top view of an example of a MEMS device100with laterally spaced segmentation structures217. The segmentation structures217depicted inFIG.11comprise a plurality of slits (or trenches) arranged along two concentrical rings. The strip-shaped intermediate region216is formed between the two rings of slits. The segmentation structure217may have any other shape such as the spring structure as described herein.

FIG.11Bshows a cross sectional view of a plane C depicted inFIG.11A.

The strip-shaped intermediate region216forms one or more spring elements219between the slits. The spring elements219are therefore movable relative to the inner and/or outer membrane sections212,214. As a result, the inner and/or outer membrane sections212,214may have improved deflectability relative to the spring elements219, which are mechanically coupled to the heat sink. The membrane structure210may therefore be less rigid.

The strip-shaped intermediate region216may form a locally confined heat-sink region between the inner and outer membrane region of the membrane structure. In the examples shown inFIGS.10A to11B, the connection structures218are mechanically connected to the strip-shaped intermediate region216. The inner and/or outer membrane sections212,214do not comprise a connection structure for thermally coupling to the heat sink220. As a result, heat transfer between the inner and/or outer membrane sections212,214and the heat sink may occur in form of thermal convection and/or thermal radiation, but not in form of thermal conduction. As a result, a temperature distribution across the inner and/or outer membrane sections212,214is more homogenous than across the strip-shaped intermediate region216(which is cooler due to heat transfer via the connection structures218). A homogenous temperature distribution may reduce thermal stress and improves accuracy of applications that may require a homogenous temperature distribution (e.g., for infrared emission). Alternatively, the inner and/or outer membrane sections212,214may comprise one or more connection structures that mechanically and thermally couple the inner and/or outer membrane sections212,214to the heat sink220.

Regarding the embodiment ofFIGS.11A-B, the segmentation structures217can be designed as prestressed (e.g., fixed) springs which form a thermal connection to a heat sink (e.g., a solid structure) by means of connection structures218(e.g., columns) in order to obtain a bypass (=temperature dissipation) specifically from a small section of the surface area of the temperature-impacted area element (of the membrane structure210) via the thermally highly conductive connection structures218to the heat sink220. In this way, a maximally homogeneous temperature distribution (except for the “sacrificial areas” where the membrane structure210is coupled to the connection structures218) can be obtained in the membrane structure210. The heat sink220can be, for example, another membrane opposite the (e.g., heating) membrane structure210(above the Bosch cavity) or can extend to an oxide layer of a bulk silicon of the MEMS device200or a system comprising the MEMS device200.

Additional embodiments and aspects are described which may be used alone or in combination with the features and functionalities described herein.

According to an embodiment, a MEMS device comprises a suspended membrane structure having an inner membrane section and an outer membrane section, wherein the outer membrane section surrounds the inner membrane section, and an elastically deformable spring structure in the outer membrane section, wherein the spring structure is arranged to convert a thermal-induced compressive stress in the suspended membrane structure into a (local) spring displacement.

According to an embodiment, at least a lateral surface area of the spring structure is less than 40% of a lateral surface area of the membrane structure.

According to an embodiment, the spring structure has a mechanical rigidity which is at least two-times lower than the mechanical rigidity of the remaining membrane structure.

According to an embodiment, the spring structure forms a locally confined displacement region in the outer membrane section of the membrane structure.

According to an embodiment, the spring structure comprises at least one of a trench structure, a slit structure and a lined-up hole structure in the outer membrane section.

According to an embodiment, the trench structure comprises overlapped trenches or a meander-shaped trench.

According to an embodiment, the membrane structure comprises a perforation structure in the inner membrane section to provide a higher mechanical rigidity of the inner membrane section than the outer membrane section and to form the outer membrane section as the spring structure.

According to an embodiment, the spring structure comprises at least one spring element which is formed by two neighboring and laterally spaced trenches or slits.

According to an embodiment, the spring element is formed as a strip or leaf spring in the outer membrane section, which partially surrounds the inner membrane section.

According to an embodiment, the spring element extends in the outer membrane section parallel to a circumferential line of the membrane structure or along a contour line of membrane deflection.

According to an embodiment, the spring structure comprises a plurality of spring elements, which are respectively formed by two neighboring and laterally spaced trenches or slits.

According to an embodiment, the spring elements are formed as parallel strips or leaf springs and partially surround the inner membrane section.

According to an embodiment, the widths of the spring elements are chosen to provide at least one of equal stiffness, equal electrical resistance and equal distance of the spring elements.

According to an embodiment, the spring elements are distributed in a pattern in the outer membrane section and extend parallel to a circumferential line of the membrane structure or along a contour line of membrane deflection.

According to an embodiment, the suspended membrane structure is edge clamped to a support structure or substrate and spans at least a cavity in the support structure or substrate.

According to an embodiment, the suspended membrane structure comprises an integrated resistor which is arranged to be heated by application of a voltage.

According to an embodiment, a MEMS device comprises a suspended membrane structure having an inner membrane section and an outer membrane section, wherein the outer membrane section surrounds the inner membrane section, and a strip-shaped intermediate region between the inner membrane section and the outer membrane section, wherein the intermediate region is thermally and mechanically connected to a heat sink by means of one or more connection structures which are mechanically and thermally coupled between the intermediate region structure and the heat sink.

According to an embodiment, a lateral surface area of the strip-shaped intermediate region is less than 40% of a lateral surface area of the remaining membrane structure.

According to an embodiment, the strip-shaped intermediate region is laterally separated from the remaining membrane structure by two neighboring and laterally spaced segmentation structures, wherein each segmentation structure comprises a trench, overlapped trenches, a meander-shaped trench, a lined-up hole structure or a combination thereof.

According to an embodiment, the strip-shaped intermediate region forms a locally confined heat-sink region between the inner and outer membrane region of the membrane structure.

Although some aspects have been described as features in the context of an apparatus it is clear that such a description may also be regarded as a description of corresponding features of a method. Although some aspects have been described as features in the context of a method, it is clear that such a description may also be regarded as a description of corresponding features concerning the functionality of an apparatus.

In the foregoing Detailed Description, it can be seen that various features are grouped together in examples for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed examples require more features than are expressly recited in each claim. Rather, as the following claims reflect, subject matter may lie in less than all features of a single disclosed example. Thus the following claims are hereby incorporated into the Detailed Description, where each claim may stand on its own as a separate example. While each claim may stand on its own as a separate example, it is to be noted that, although a dependent claim may refer in the claims to a specific combination with one or more other claims, other examples may also include a combination of the dependent claim with the subject matter of each other dependent claim or a combination of each feature with other dependent or independent claims. Such combinations are proposed herein unless it is stated that a specific combination is not intended. Furthermore, it is intended to include also features of a claim to any other independent claim even if this claim is not directly made dependent to the independent claim.