Membrane structure, transducer device and method for manufacturing membrane structure

Abstract

A membrane structure (1) comprises a substrate (2) having a main surface (4) and a rear surface (24). A plurality of pillars (10) are arranged on the main surface (4) of the substrate (2) and have a support area (12) facing away from the main surface (4) of the substrate (2). A thin film structure (6) is arranged above the main surface (4) of the substrate (2) and the pillars (10), wherein the thin film structure (6) comprises a plurality of raised portions (15), the spacing between the raised portions and the substrate (2) being greater than the spacing between at least one lower portion (16) of the thin film structure and the substrate (2). The raised portions (15) each comprise at least one protrusion (13), the protrusion (13) being hollow and having a bottom portion (14) and a side wall (22), and the protrusion (13) extending toward the substrate (2). The bottom portion (14) of each protrusion (13) is respectively mechanically connected to the support area (12) of one of the pillars (10). The rear space (5) is formed by the space between the main surface (4) of the substrate (2) and the film structure (6).

Description

[0001] The present disclosure relates to a membrane structure, a transducer device and a method for producing a membrane structure.

[0002] For membrane-based transducer devices, the deflection of the membrane results in a spatial change in the space below the membrane. However, the reduction in the space below the membrane results in a compression of the gas in the space. This compression of the gas significantly affects the compliance of the membrane, especially in miniaturized systems. The compressed gas exerts a restoring force on the membrane, thereby preventing further displacement. However, in most cases, a large displacement of the membrane is required to achieve a good sensitivity of the underlying sensor system. This means that for conventional membrane structures, in addition to the membrane stiffness, the back-volume also limits the sensitivity of the system. For this reason, the back-volume must be chosen to be as large as possible, which prevents further miniaturization of the device.

[0003] One object is to provide a membrane structure which exhibits increased compliance. Another object is to provide a method of manufacturing a membrane structure which exhibits increased compliance.

[0004] This object is achieved with the independent claim. Further embodiments and variants result from the dependent claims.

[0005] In one embodiment, the membrane structure comprises a substrate, which may comprise a semiconductor material (eg silicon (Si)). The substrate may have a main extension plane. The substrate has a main surface and a rear surface. The rear surface faces away from the main surface.

[0006] A plurality of pillars are arranged at the main surface of the substrate. The pillars can comprise the same material as the substrate. The pillars can be formed by a portion of the substrate at its main surface. The pillars are physically connected to the main surface of the substrate via a base region. In a top view, the shape of the base region is arbitrary. A top view refers to a view of the membrane structure from the side of the pillar facing away from the substrate in a vertical direction. The vertical direction is perpendicular to the main extension plane of the substrate. In a top view, the pillars can be arranged at the main surface of the substrate along a circular line. The radius of the circle and the number of pillars depend on the application. Adjacent pillars can be arranged equidistant from each other.

[0007] For example, the number of pillars can be at least 3 and at most 200. Alternatively, the number of pillars can be at least 4 and at most 50.

[0008] The side surfaces of the pillars can be vertical or transverse relative to the main extension plane of the substrate. Each pillar also includes a support area facing away from the main surface of the substrate. This means that in the vertical direction, each support area is at a certain distance from the main surface of the substrate. The shape of the support area in the top view is arbitrary. The distance from the support area of ​​each pillar to the main surface of the substrate corresponds to the height of the respective pillar. The height can have any value, which is feasible in terms of the aspect ratio of the pillar. The aspect ratio of each pillar is defined by the ratio between its height and diameter. The diameter of the pillar refers to the lateral extent of the pillar, where the lateral direction extends parallel to the main extension plane of the substrate.

[0009] For example, the height of each pillar can be at least 1 μm and at most 100 μm. Alternatively, the height of each pillar can be at least 3 μm and at most 10 μm.

[0010] The membrane structure also includes a thin film structure arranged above the main surface of the substrate and above the pillar. The thin film structure may include a material compatible with semiconductor processes (e.g., silicon nitride (SiN) or polysilicon). The thin film structure can extend in a plane parallel to the main extension plane of the substrate. In a top view, the thin film structure can have any shape. In particular, in a top view, the shape of the thin film structure is circular or polygonal.

[0011] For example, the diameter of the thin film structure may be at least 100 μm and at most 10 mm. Alternatively, the diameter of the thin film structure may be at least 500 μm and at most 1 mm.

[0012] The membrane structure comprises a plurality of raised portions, the spacing of the plurality of raised portions from the substrate being greater than the spacing of at least one lower portion (16) of the membrane structure from the substrate. In the vertical direction, the raised portions and the lower portion do not overlap. In the transverse direction, the raised portions and the lower portion are arranged adjacent to each other. The raised portions are physically connected to the lower portion by a connecting portion of the membrane structure. The connecting portion can be vertical or transverse relative to the main extension plane of the substrate.

[0013] The lower portion is not in direct mechanical contact with the substrate. However, the lower portion is closer to the substrate than the elevated portion. The distance between the elevated portion and the lower portion in the vertical direction depends on the application and can vary from application to application.

[0014] For example, the distance between the raised portion and the lower portion can be at least 0.3 μm and at most 10 μm. Alternatively, the distance between the raised portion and the lower portion can be at least 0.6 μm and at most 4 μm.

[0015] The raised portions each comprise at least one protruding portion. The protruding portion extends in a vertical direction from the raised portion towards the substrate. The protruding portion is formed by a portion of the film structure. The protruding portion has at least one side wall and a bottom portion. The side wall is vertical or transverse relative to the main extension plane of the substrate. The bottom portion can extend parallel to the main extension plane of the substrate.

[0016] Each projection is arranged directly above the corresponding pillar. The projection mechanically connects the membrane structure to the support area of ​​the pillar via the bottom part. This means that the bottom part of each projection is in mechanical contact with one of the pillars via the support area of ​​the pillar, respectively. In top view, the projection can have any shape. The diameter refers to the lateral extent of the bottom part of the projection, which can be equal to or smaller than the lateral extent of the support area of ​​the corresponding pillar.

[0017] For example, the diameter of the bottom portion of the protruding portion can be at least 0.5 μm and at most 50 μm. Alternatively, the diameter of the bottom portion can be at least 2 μm and at most 15 μm.

[0018] The protrusion is hollow. This means that the protrusion forms a hollow profile. The space enclosed by the protrusion is bounded by the bottom part of the protrusion and at least one side wall. At the top side of the protrusion, the enclosed space is connected to the environment above the membrane structure. This means that the protrusion is open at the top side.

[0019] The back space is formed by the space between the main surface of the substrate and the thin film structure. This means that the space bounded on one side by the substrate and on the other side by the thin film structure forms the back space of the device. The back space can be filled with air or gas. The back space can be connected to the environment.

[0020] A plurality of pillars and projections can be arranged in a particular manner. For example, in a top view, the pillars and projections can be arranged along a circular line, and the film structure can also be a circular shape with a larger diameter, and the two circles are concentric. By this arrangement, the central part and the outer part of the film structure are defined. The central part of the film structure refers to the area of ​​the film structure located within the circular line of the pillars and projections in a top view. The outer part of the film structure refers to the outer ring of the film structure located outside the circular line of the pillars and projections in a top view. In addition, it is provided that the rear space is distributed into two rear chamber compartments. The inner rear chamber compartment is formed by the rear space between the central part of the film structure and the substrate. The outer rear chamber compartment is formed by the rear space between the outer part of the film structure and the substrate.

[0021] Due to the materials used, its thickness and the specific arrangement, the thin film structure is a movable part. Therefore, the thin film structure forms a membrane, which is only connected to the substrate via the protrusions and the pillars. This means that the thin film structure can be deflected. The deflection of the membrane can be towards the substrate and / or away from the substrate in the vertical direction.

[0022] Each pair of pillars and protrusions forms a mechanical phase shifter during membrane deflection. This means that the mechanical phase shifters each include a pillar and a protrusion. The phase shift between the part of the membrane moving toward the substrate and the other part of the membrane moving away from the substrate is 180°. For example, when the central part of the membrane moves toward the substrate, the outer part of the membrane moves away from the substrate. Therefore, the membrane movement is driven in a push-pull mode, while one part of the membrane is directly coupled (0° phase shift) to the driving force and the other part is coupled to the driving force through a 180° phase shift. The driving force can be, for example, an acoustic pressure wave.

[0023] The effect of the mechanical phase shifter is that under deflection, the rear space below the membrane does not change much, or even remains equal. For example, when the central part of the membrane moves toward the substrate, the space below the central part becomes smaller. At the same time, the outer part of the membrane moves away from the substrate, which increases the space below the outer part. The movement can also be done in reverse. Depending on the deflection of the membrane, there is a net volume flow between the two rear chamber compartments. Since the net volume flow reduces gas compression, this in turn leads to increased system compliance. Due to the mechanical phase shifter, the rear space can be very small, which allows the system to be further miniaturized. In order to increase compliance and reduce the rear space, the membrane structure can include multiple mechanical phase shifters at user-defined positions (e.g., along a line within the contour of the membrane structure). The cross-section, number, and arrangement of these mechanical phase shifters can be selected to maximize compliance.

[0024] In another embodiment of the membrane structure, the pillars and the projections of the membrane structure are arranged at a predetermined distance from the outer edge of the membrane structure. All pillars and all projections can have the same predetermined distance from the outer edge of the membrane structure. For example, if the membrane structure is circular, each pillar and each projection can be arranged at a distance from the outer edge of the membrane structure that is one third of the radius of the membrane structure. In this way, in a top view, the pillars and projections are arranged along a circular line. However, the pillars and projections can also be arranged close to the outer edge of the membrane structure or the center of the membrane structure.

[0025] Certain predetermined distances of the pillars and the protrusions can enable operation of higher order eigenmodes of the membrane. In this way, the resonant frequency of the membrane can be shifted to higher values ​​and certain low order modes can be prevented.

[0026] In a further embodiment of the membrane structure, each raised portion is completely surrounded by at least one lower portion in a lateral direction. Thus, each raised portion is confined to a relatively small area within the thin film structure. The raised portions can be arranged above an area where pillars are present at the main surface of the substrate. In a top view, the diameter of each raised portion can be greater than the diameter of the corresponding pillar. Thus, the protrusion comprised by the raised portion can be mechanically connected to the pillar below. Each raised portion is connected to at least one lower portion at all lateral sides by connecting portions. The connecting portions can be vertical or lateral relative to the main extension plane of the substrate.

[0027] This construction allows the membrane to bend flexibly during deflection. The elevation and the projection provide a flexible connection so that the membrane can swing as freely as possible. The deformation of the membrane structure during deflection occurs mainly in the region of the side walls of the projection and in the region of the connection. The bending of the membrane at the projection dominates the sensitivity of the membrane. Thus, for example, the sensitivity can be increased by optimizing the projection in terms of shape and membrane thickness.

[0028] In a further embodiment of the membrane structure, each elevation extends to the outer edge of the membrane structure. Each elevation is connected to at least one lower portion by a connecting portion at all lateral sides except the side facing the outer edge of the membrane structure. The connecting portion can be vertical or lateral relative to the main extension plane of the substrate. In a top view, each elevation has an elongated shape extending from the outer edge of the membrane structure towards the corresponding pillar. In each elevation there is a protrusion connecting the membrane structure to the pillar.

[0029] With this arrangement, the bending of the membrane during deflection is flexible because the raised portions and protruding portions provide a flexible connection. The outer portion of the membrane is constructed more solidly. Lower portions and raised portions alternate in the outer portion of the membrane, thereby forming corrugations. The corrugations provide enhanced rigidity of the outer portion of the membrane and prevent the membrane from sinking.

[0030] In one embodiment of the membrane structure, at least one surrounding wall is arranged on the main surface of the substrate, at a distance from the outer edge of the membrane structure. The surrounding wall surrounds the membrane structure in a lateral direction. The surrounding wall can include the same material as the substrate. The surrounding wall can be formed by a portion of the substrate at its main surface. The surrounding wall is mechanically connected to the main surface of the substrate. The surrounding wall also includes a side surface. The side surface can be vertical or horizontal relative to the main extension plane of the substrate. The surrounding wall also includes a top surface. The top surface of the surrounding wall can extend on a plane extending parallel to the main extension plane of the substrate.

[0031] The top surface of the surrounding wall is at a distance from the main surface of the substrate, which distance corresponds to the height of the surrounding wall. The surrounding wall can be as high as the thin film structure. This means that in the vertical direction, the distance from the top surface of the surrounding wall to the main surface of the substrate can be the same as the distance from the lower part of the thin film structure to the main surface of the substrate. Alternatively, in the vertical direction, the distance from the top surface of the surrounding wall to the main surface of the substrate can be the same as the distance from the raised part of the thin film structure to the main surface of the substrate.

[0032] The surrounding wall surrounds the film structure in the transverse direction. This means that the surrounding wall can form a ring around the film structure in a top view. In the transverse direction, there is a gap between the surrounding wall and the film structure. This means that the inner diameter of the ring formed by the surrounding wall is larger than the diameter of the film structure.

[0033] The difference between these diameters, ie the size of the slit between the surrounding wall and the membrane structure, can be at least 0.1 μm and at most 5 μm. Alternatively, the slit size can be at least 0.5 μm and at most 1 μm.

[0034] By arranging a surrounding wall around the membrane structure, the rear space of the membrane structure is enclosed in the lateral direction. Therefore, the rear space of the membrane structure is connected to the environment only via the slit between the surrounding wall and the membrane structure. In this way, bypassing between the surrounding wall and the environment is prevented. In particular, if the membrane structure acts as a microphone or loudspeaker membrane of an acoustic device, an acoustic short circuit between the two sides of the membrane is avoided by the surrounding wall. In order to increase the acoustic impedance of the slit between the surrounding wall and the membrane, it is possible to select a slit that is as small as possible. Furthermore, a smaller slit results in an omnidirectional microphone device comprising the membrane structure, since the sound pressure waves can only affect the side of the membrane that is facing away from the substrate.

[0035] In another embodiment of the membrane structure, the membrane structure is connected to the surrounding wall by at least one elastic layer. The elastic layer can include any material with a lower Young's modulus value than the Young's modulus of the material used for the membrane structure and the surrounding wall. For example, the elastic layer can include polydimethylsiloxane (PDMS). The elastic layer can form a ring across the slit between the surrounding wall and the membrane structure. The elastic layer covers a portion of the membrane structure at a side away from the substrate and a portion of the top surface of the surrounding wall. Therefore, the elastic layer mechanically connects the membrane structure to the surrounding wall.

[0036] The elastic layer can further increase the acoustic impedance of the gap between the surrounding wall and the membrane structure. In this way, the back space below the membrane is completely surrounded and not connected to the environment above the membrane. Therefore, an acoustic short circuit between the two sides of the membrane is avoided. In addition, due to its low Young's modulus, the elastic layer can be stretched, allowing the membrane to move relatively freely.

[0037] In a further embodiment of the membrane structure, the elastic layer is gas permeable. This means that gas particles on both sides of the membrane (ie below the membrane and above the membrane in the vertical direction) can diffuse through the elastic layer.

[0038] Through the air permeability of the elastic layer, airflow is able to be established between the two sides of the membrane, although the back space below the membrane is enclosed. The airflow provides pressure equalization between the back space and the environment. This may be necessary because changes in gas density within the back space due to membrane deflection affect the system compliance and therefore the dynamic properties of the membrane structure.

[0039] In other embodiments, the membrane structure includes an opening in the substrate, which extends from the rear surface of the substrate toward the thin film structure. The opening is formed as a groove extending in the vertical direction in the substrate. The opening can have a smaller range than the thin film structure in the lateral direction. The opening can connect the rear space formed between the substrate and the thin film structure to the environment at the rear surface of the substrate. The opening can have any shape. The depth of the opening in the vertical direction is given by the thickness of the substrate.

[0040] By forming the opening, access is provided from the rear surface of the substrate to the main surface. Access may be necessary for processing reasons, for example to remove areas of a sacrificial layer. Furthermore, by forming the opening, the back space is increased. This is also important, for example for microphone applications, because the response of the membrane to sound waves, especially at audio frequencies, can be changed by increasing the back space. Due to the increased acoustic compliance given by the back space, the sensitivity can be improved as well as the signal-to-noise ratio. Furthermore, an optical readout of the membrane displacement becomes possible through the opening. In this case, light from the rear surface (for example from an attached photonic chip) can pass through the opening, reach the membrane, and be reflected towards a light sensor and / or photodetector.

[0041] In a further embodiment, the membrane structure comprises a vent hole within the membrane structure. The vent hole can be arranged in the center of the membrane structure relative to the lateral extent of the membrane structure. The vent hole connects two sides of the membrane structure to each other. This means that the vent hole connects the side of the membrane structure facing the substrate to the side of the membrane structure facing away from the substrate. The vent hole can have a smaller diameter compared to the diameter of the membrane structure.

[0042] Through the vents, airflow can be established between the two sides of the membrane. The airflow provides pressure equalization between the back space and the environment. This may be necessary because changes in gas density in the back space due to membrane deflection affect the system compliance and thus the dynamic properties of the membrane structure.

[0043] In another embodiment of the membrane structure, the membrane structure has a circular or polygonal shape in a top view. This means that the membrane structure has a center point. In the transverse direction, the membrane structure is point-symmetrical with respect to the center point. However, the shape of the membrane structure is not limited to a circle or a polygon, but can have any shape (e.g., a rectangular or elliptical shape).

[0044] The round or polygonal shape of the thin-film structure used as membrane is advantageous, for example, with regard to uniform deflection and uniform stress distribution in the transverse direction.

[0045] In a further embodiment, the membrane structure is incorporated into the transducer device. The transducer device can in particular be an omnidirectional optical microphone. An omnidirectional microphone can respond to sounds coming from all directions, even from the back side. The microphone can also be an optical microphone. An optical microphone evaluates the response of the membrane to the sound by using optical methods. When a reflector is integrated on the membrane, vibrations can be detected by using a laser beam and an interferometer. In this way, the movement of the membrane can be detected by changes in the optical path length of the reflected light beam. In this arrangement, a backplate as required for a conventional condenser microphone is advantageously not required. However, the transducer device can also be any other dynamic pressure sensing device.

[0046] In another embodiment, a plurality of membrane structures are incorporated into a transducer device (such as a microphone or a pressure sensor). A plurality of membrane structures can be arranged in a repeating configuration to form an array of membrane structures. In this way, the transducer device realizes array sensing.

[0047] In a further embodiment, the transducer device including the membrane structure is incorporated into an electronic device. The electronic device can be, for example, a smart speaker device, a smart watch, a phone, or a hearing aid device. Since the membrane structure can be manufactured by micro-electromechanical system (MEMS) technology and can have a reduced back space, the mobile device can have a smaller size.

[0048] Furthermore, a method for producing a membrane structure is provided. All features disclosed for the membrane structure are also disclosed for the method for producing the membrane structure, and vice versa.

[0049] The method for manufacturing the membrane structure includes providing a substrate. Pillars are formed at the top surface of the substrate by an etching step. The etching step can be, for example, deep reactive ion etching (DRIE). The etching step can be performed under time control to reach a specific height of the pillars. By forming the pillars, a rear space for the resulting membrane structure is generated. The pillars provide a support area for the thin film structure.

[0050] After forming the pillars, a sacrificial layer region is set in place at the main surface of the substrate and on the pillars. The sacrificial layer region can include, for example, tungsten-titanium (W-Ti) and can be deposited, for example, by a sputtering process. Patterning of the sacrificial layer region can be accomplished by etching. Several depositions of the sacrificial layer can then be performed, and an etching process can be performed after each deposition to pattern the corresponding sacrificial layer. Then, the stack of sacrificial layers forms a sacrificial layer region. The sacrificial layer region provides at least a first thickness level and a second thickness level. The first thickness level is greater than the second thickness level. A plurality of grooves are formed in a region having a first thickness level, wherein each groove extends to one of the pillars, respectively. In a top view, the diameter of the groove can be equal to or less than the diameter of the pillar.

[0051] The film is deposited on the sacrificial layer region and the plurality of grooves. The film can be deposited by chemical vapor deposition (CVD) or plasma enhanced CVD (PECVD). The film can be patterned by an etching process. The film is in mechanical contact with the support region of each pillar (i.e., at the bottom of the groove in the sacrificial layer region). In addition, the film covers the side surfaces of the grooves in the sacrificial layer region. The film also covers the edges of the grooves in the sacrificial layer region. The film also covers the top surface of the sacrificial layer region, i.e., the surface of the sacrificial layer region facing away from the substrate. Therefore, the sacrificial layer region is arranged between the substrate and the film.

[0052] After the film is deposited and patterned, the sacrificial layer region is removed. In this way, a thin film structure is formed by removing the sacrificial layer region. The removal of the sacrificial layer region can be accomplished by wet etching. The etchant can approach the sacrificial layer region through an opening in the substrate or the film or through an area not covered by the film. The removal of the sacrificial layer region releases the film. This means that the raised portion of the film is formed after removing the sacrificial layer region, wherein the film has been deposited at a first thickness level. The protruding portion is formed by a portion of the film deposited in one of the plurality of grooves in the sacrificial layer region. The connecting portion of the thin film structure is formed by a portion of the film deposited between the first thickness level and the second thickness level. The lower portion is formed by a portion of the film deposited on the second thickness level. The thin film structure is formed by the film, the pillar, the substrate, and the back space formed by the cavity left after removing the sacrificial layer region.

[0053] By using sacrificial layer regions, freestanding thin film structures can be fabricated in a simpler and more cost-effective process than equivalent structures fabricated using processes such as chemical mechanical polishing (CMP). Furthermore, by adding protrusions that mechanically contact the support regions of the underlying pillars, mechanical phase shifters can be introduced for push-pull mode operation during membrane deflection.

[0054] In one embodiment of the method for manufacturing the membrane structure, at least one surrounding wall is formed at the main surface of the substrate by an etching step. The etching step can be the same as the etching step for forming the pillar. However, the etching step can also be performed before or after the pillar is formed. Alternatively, several etching steps can be combined to form the pillar and the surrounding wall. For example, deep reactive ion etching (DRIE) can be used. Etching can be performed so that the pillar and the surrounding wall have the same height relative to the main surface of the substrate. However, the height of the pillar and the surrounding wall can also be different.

[0055] By forming the surrounding wall, the rear space of the membrane structure is enclosed in the lateral direction, which increases the acoustic impedance of the resulting membrane structure.

[0056] In one embodiment of the method for manufacturing the membrane structure, an elastic layer is deposited, which mechanically connects the thin film structure to the surrounding wall. For example, the elastic layer can include PDMS. The elastic layer can be deposited, for example, by coating or 3D printing. The deposition can be performed before or after removing the sacrificial layer area. The elastic layer covers the area on the top surface of the surrounding wall and the area on the side of the thin film structure facing away from the substrate. Therefore, the elastic layer can form a ring that spans the slit between the surrounding wall and the thin film structure.

[0057] The elastic layer can further increase the acoustic impedance of the gap between the surrounding wall and the membrane structure. In this way, the back space below the membrane is completely surrounded and not connected to the environment above the membrane. Therefore, an acoustic short circuit between the two sides of the membrane is avoided. In addition, due to its low Young's modulus, the elastic layer can be stretched, allowing the membrane to move relatively freely.

[0058] In one embodiment of the method for manufacturing the film structure, an opening is formed in the substrate. The opening can be formed by deep reactive ion etching (DRIE). The opening extends from the rear surface of the substrate toward the thin film structure. The etching process can be controlled by time or by using an etch stop layer. In the latter case, before the sacrificial layer region is deposited, the etch stop layer has been deposited at the position where the opening should be formed on the main surface of the substrate. The etch stop layer may include chromium (Cr) and can be removed, for example, by wet etching after the opening is formed. The lateral range of the opening can be less than the lateral range of the thin film structure.

[0059] By forming the opening, access is given from the rear surface of the substrate to the main surface. Access may be necessary for processing reasons, for example to remove areas of a sacrificial layer. Furthermore, by forming the opening, the back space between the substrate and the thin film structure can be increased. This means that the back space is increased in the vertical direction by the opening in the substrate. This is also important, for example for microphone applications, because the response of the membrane to sound waves can be changed in this way, especially at audio frequencies. Therefore, the sensitivity and the signal-to-noise ratio can be improved by increasing the back space. Furthermore, an optical readout of the membrane displacement becomes possible through the opening. In this case, light from the rear surface (for example from an attached photonic chip) can pass through the opening, reach the membrane, and be reflected towards the light sensor and / or photodetector.

[0060] In one embodiment of the method of manufacturing the membrane structure, the sacrificial layer region is removed after the opening is formed in the substrate. In some embodiments, the opening can provide the only access to the sacrificial layer region because the sacrificial layer region is covered by the thin film above the top surface of the substrate. The access can then be used to remove the sacrificial layer region, for example, by wet etching.

[0061] The following description of the drawings can further illustrate and explain the exemplary embodiments. Functionally identical or having the same function components are represented by the same reference numerals. The same or substantially identical components are described only for the first appearing drawing. The description thereof need not be repeated in the consecutive drawings.

[0062] 1a-1b show a cross section and an equivalent acoustic-electrical circuit of one example of a membrane-based acoustic device.

[0063] 2a-2b show a cross section and an equivalent acoustic-electrical circuit of one embodiment of a membrane structure.

[0064] Figure 3 Two cross sections of one embodiment of a membrane structure are shown.

[0065] Figure 4 Another embodiment of a membrane structure is shown in cross-section and in top view.

[0066] Figure 5 Another embodiment of a membrane structure is shown in cross-section and in top view.

[0067] Figure 6 Another embodiment of a membrane structure is shown in cross-section and in top view.

[0068] Figure 7 Another embodiment of a membrane structure is shown in cross-section and in top view.

[0069] Figure 8 A cross-sectional view of another embodiment of a membrane structure is shown.

[0070] Fig. 9 A schematic diagram of an exemplary embodiment of a transducer arrangement is shown, the transducer arrangement comprising a membrane structure.

[0071] 10a to 10f illustrate one embodiment of a method of manufacturing a membrane structure.

[0072] In FIG. 1a, a cross section of an example of a non-embodiment membrane structure 1 is shown. The membrane structure 1 is arranged in a conventional manner. The membrane structure 1 comprises a substrate 2. A surrounding wall 3 is arranged at a main surface 4 of the substrate 2. The surrounding wall 3 surrounds a rear space 5 in a transverse direction x, y, wherein the transverse direction extends parallel to the main extension plane of the substrate 2.

[0073] The membrane structure 1 also includes a thin film structure 6 attached to the surrounding wall 3 above the main surface 4 of the substrate 2. This means that the thin film structure 6 is in mechanical contact with the surrounding wall 3. The thin film structure 6 is spaced apart from the substrate 2 in the vertical direction z, wherein the vertical direction z is perpendicular to the main extension plane of the substrate 2. The thin film structure 6 spans the rear space 5. This means that the rear space 5 is surrounded by the substrate 2, the surrounding wall 3 and the thin film structure 6. The thin film structure 6 includes a vent 7. The vent 7 is an opening in the thin film structure 6, which connects the side of the thin film structure 6 facing the substrate 2 to the side of the thin film structure 6 facing away from the substrate 2. The vent 7 connects the rear space 5 to the environment above the thin film structure 6. The thin film structure 6 can act as a membrane that responds to sound pressure waves. In this way, the membrane structure 1 can be used for acoustic applications (such as microphone or speaker applications).

[0074] In Fig. 1 b, an equivalent acoustic-electrical circuit of the example of Fig. 1 a is shown. In the equivalent acoustic-electrical circuit, symbols are assigned to the acoustic components of the device, as in known electrical circuits.

[0075] The equivalent acoustic-electric circuit of FIG1b includes a common pressure level Pa and an external sound pressure source Pe, which serves as a driving force for the deflection of the membrane. The membrane is represented by the complex acoustic impedance Zm of the membrane in the equivalent acoustic-electric circuit of FIG1b, and the complex acoustic impedance includes the acoustic mass Lm of the membrane, the acoustic compliance Cm of the membrane, and the acoustic resistance Rs of the air film under the membrane. The acoustic mass Lm of the membrane corresponds to the inertia of the membrane deflected by the sound pressure Pe. The acoustic compliance Cm of the membrane corresponds to the stiffness of the membrane to provide a restoring force. The acoustic resistance Rs of the air film under the membrane corresponds to the gas film squeezed due to the movement of the membrane. In addition, FIG1b includes an additional acoustic resistance Rv representing the vent 7 of the membrane. Due to the limited diameter through which the sound pressure of the vent must pass, the vent 7 causes an additional acoustic resistance Rv. In addition, the equivalent acoustic-electric circuit includes the acoustic compliance Cv of the back space 5. The acoustic compliance Cv of the back space 5 represents the gas in the back space 5, which is compressed under the deflection of the membrane. Therefore, the compressed gas also acts as a restoring force.

[0076] The acoustic mass Lm of the membrane, the acoustic compliance Cm of the membrane, and the acoustic resistance Rs of the air film under the membrane are connected in series to form the complex acoustic impedance Zm of the membrane. The additional acoustic resistance Rv of the vent 7 is connected in parallel to the complex acoustic impedance Zm of the membrane. The acoustic compliance Cv of the back space 5 is connected in series to the additional acoustic resistance Rv of the vent 7 and the complex acoustic impedance Zm of the membrane, and is further connected to a common pressure level Pa. The external sound pressure source Pe is connected in series to all these components and is further connected to a common pressure level Pa.

[0077] In this arrangement, the additional acoustic resistance Rv of the vent 7 and the acoustic compliance Cv of the back space 5 form a high pass filter. The acoustic compliance Cv of the back space 5 and the acoustic compliance Cm of the membrane form an acoustic compliance crossover.

[0078] This means that at low frequencies, the displacement of the membrane is limited by the high-pass filter. However, at audio frequencies, the displacement of the membrane is limited by the acoustic compliance crossover. In order to achieve the largest possible membrane displacement, the acoustic compliance Cv of the back space 5 must be large. Such a requirement requires a larger back space 5.

[0079] In FIG. 2a, a cross section of an embodiment of a membrane structure 1 is shown. Elements according to FIG. 2a corresponding to elements of the example according to FIG. 1a are indicated by the same reference numerals. The embodiment according to FIG. 2a includes a substrate 2 having a main surface 4. The substrate 2 has a main extension plane. As shown in FIG. 1a, a surrounding wall 3 is arranged at the main surface 4 of the substrate 2. The surrounding wall 3 can be formed by a portion of the substrate 2 and is in mechanical contact with the substrate 2. The surrounding wall 3 also includes a side surface 8 that can be perpendicular to the main extension plane of the substrate 2 and a top surface 9 extending parallel to the main extension plane of the substrate 2. In the vertical direction z perpendicular to the main extension plane of the substrate 2, the top surface 9 of the surrounding wall 3 is spaced apart from the main surface 4 of the substrate 2. The surrounding wall 3 surrounds the rear space 5 in the lateral directions x, y, which extend parallel to the main extension plane of the substrate 2.

[0080] Furthermore, a support post 10 is arranged at the main surface 4 in the space 5 behind the substrate 2. The support post 10 can be formed by a portion of the substrate 2 and is in mechanical contact with the substrate 2. The support post 10 includes a side surface 11 that can be perpendicular to the main extension plane of the substrate 2 and a support area 12 that extends parallel to the main extension plane of the substrate 2. In the vertical direction z, the support area 12 of the support post 10 is spaced apart from the main surface 4 of the substrate 2. However, in this embodiment, the distance from the support area 12 of the support post 10 to the main surface 4 of the substrate 2 is less than the distance from the top surface 9 of the surrounding wall 3 to the main surface 4 of the substrate 2. In the lateral directions x, y, the support post 10 is arranged at a distance from the surrounding wall 3.

[0081] The embodiment of Fig. 2a also includes a film structure 6 above the main surface 4 of the substrate 2 and above the pillars 10. The film structure 6 is spaced apart from the substrate 2. The film structure 6 extends in a plane extending parallel to the main extension plane of the substrate 2. The film structure 6 covers the rear space 5. However, the film structure 6 is not connected to the surrounding wall 3. Instead, the film structure 6 is connected to the pillars 10 by projections 13. This means that the bottom portion 14 of each projection 13 is in mechanical contact with the support area 12 of the corresponding pillar 10. The film structure 6 also includes a raised portion 15, each projection 13 extending from the raised portion toward the corresponding pillar 10. The spacing between the raised portion 15 of the film structure 6 and the substrate 2 is greater than the spacing between the lower portion 16 of the film structure 6 and the substrate 2. The raised portion 15 and the lower portion 16 are connected by a connecting portion 17 of the film structure 6. Because the film structure 6 is not connected to the surrounding wall 3, there is a slit 18 between the two components. This means that the slit 18 connects the rear space 5 to the environment above the film structure 6. However, the slit 18 can be very small.

[0082] As in the example of FIG. 1a, the thin film structure 6 can be used as a membrane that responds to sound pressure waves. In this case, the membrane can be considered to have a central portion 19 and an outer portion 20. The central portion 19 of the membrane is the portion that is located within the pillar 10 in a top view. The outer portion 20 of the membrane is the portion that is located between the surrounding wall 3 and the pillar 10 in a top view. The top view refers to a view of the membrane structure 1 from the side of the membrane facing away from the substrate 2 in the vertical direction z.

[0083] Due to this arrangement, the membrane is deflected by the sound pressure waves in the following manner. When the central part 19 of the membrane is moving towards the substrate 2, the outer part 20 of the membrane is moving away from the substrate 2, and vice versa. This means that when the back space 5 under the central part 19 of the membrane becomes smaller, the back space 5 under the outer part 20 of the membrane increases, and vice versa. This means that the support 10 and the protrusion 13 form a mechanical phase shifter 21, which provides a 180° phase shift between the outer part 20 and the central part 19 of the membrane.

[0084] In FIG. 2b , an equivalent acoustic-electrical circuit of an embodiment of the membrane structure 1 according to FIG. 2a is shown. FIG. 2b differs from FIG. 1b in that it shows two branches of the complex acoustic impedance Zm of the membrane. The first branch includes the complex acoustic impedance Zmc of the central portion 19 of the membrane. The complex acoustic impedance Zmc of the central portion 19 of the membrane includes the acoustic mass Lmc of the central portion 19 of the membrane, the acoustic compliance Cmc of the central portion 19 of the membrane, and the acoustic resistance Rsc of the air film squeezed by the central portion 19 of the membrane. The second branch includes the complex acoustic impedance Zmo of the outer portion 20 of the membrane. The complex acoustic impedance Zmo of the outer portion 20 of the membrane includes the acoustic mass Lmo of the outer portion 20 of the membrane, the acoustic compliance Cmo of the outer portion 20 of the membrane, and the acoustic resistance Rso of the air film squeezed by the outer portion 20 of the membrane. In addition, the second branch includes a phase shifter The phase shifter involves the fact that the central part 19 of the membrane and the outer part 20 of the membrane move in anti-phase.

[0085] The two branches are coupled by an acoustic resistance Rp, which corresponds to the acoustic resistance caused by the pillars 10 in the back space 5 and represents the damping of the membrane. The acoustic resistance Rv of the vent 7 in Figure 1b is replaced in Figure 2b by the acoustic resistance Rsl of the slit 18 between the surrounding wall 3 and the membrane. In addition, the equivalent acoustic-electrical circuit of Figure 2b includes the acoustic compliance Cvc of the back space 5 under the central part 19 of the membrane and the acoustic compliance Cvo of the back space 5 under the outer part 20 of the membrane.

[0086] Since the deflection of the membrane causes the space between the back space 5 under the central part 19 of the membrane and the back space 5 under the outer part 20 of the membrane to flow, the gas compression is reduced. Therefore, the restoring force on the membrane is small. Therefore, even if the back space 5 is small, the acoustic compliance Cvc, Cvo of the back space 5 is large.

[0087] At low frequencies, the time constant of the acoustic device based on the membrane structure 1 of Figures 2a and 2b is determined by the acoustic resistances Rsl and Rp and the acoustic compliances Cvc and Cvo. In order to achieve a low high-pass cut-off frequency, the acoustic resistance Rsl of the slit 18 must be as large as possible. In this way, pressure drops are avoided and the noise level of the acoustic device can be reduced. The acoustic resistance Rsl of the slit 18 can be increased, for example, by reducing the size of the slit 18 (i.e. the distance from the membrane to the surrounding wall 3).

[0088] exist Figure 3 , a cross section of another embodiment of a membrane structure 1 is shown. Figure 3 2 a is that the surrounding wall 3 is not shown at the main surface 4 of the base 2 . Furthermore, the side surfaces 11 s of the struts 10 are transverse to the main extension plane of the base 2 .

[0089] Figure 3Two states of membrane deflection caused by, for example, sound pressure waves are shown. In the first case, the central part 19 of the membrane is deflected towards the substrate 2, while the outer part 20 of the membrane is deflected away from the substrate 2. In the second case, the central part 19 of the membrane is deflected away from the substrate 2, while the outer part 20 of the membrane is deflected towards the substrate 2. Each pair of pillars 10 and protrusions 13 forms a mechanical phase shifter 21, which causes a phase reversal between the movement of the central part 19 of the membrane and the movement of the outer part 20 of the membrane. The raised part 15 and the protrusion 13 provide a flexible connection so that the membrane can swing as freely as possible. The deformation of the membrane during the deflection mainly occurs in the area of ​​the side walls 22 of the protrusion 13 and in the area of ​​the connecting part 17.

[0090] exist Figure 4 , a cross section and a top view of another embodiment of a membrane structure 1 are shown. The cross section shows the membrane structure along section AA as shown in the top view. The measurements in the cross section correspond to the measurements in the top view, indicated by the vertical dashed lines.

[0091] Figure 4 The cross section in FIG. 2a differs from the cross section in FIG. 2b in that it shows an opening 23 in the substrate 2. The opening 23 extends in the vertical direction z from the rear surface 24 of the substrate 2 towards the membrane structure 6. The extent of the opening 23 in the lateral directions x, y is smaller than the central part 19 of the membrane structure 6. Furthermore, the top surface 9 of the surrounding wall 3 and the supporting area 12 of the pillar 10 have the same height, where the height is the distance to the main surface 4 of the substrate 2 in the vertical direction z. Compared with FIG. 2a, Figure 4 The raised portions 15 of the film structure 6 of FIG. 1 have a smaller extent in the transverse directions x, y. This means that each raised portion 15 is completely surrounded by the lower portion 16, as in Figure 4 The lower part 16 of the membrane structure 6 extends to the outer edge 25 of the membrane structure 6. Therefore, at the outer edge 25 of the membrane structure 6, the membrane structure 6 has the same height as the top surface 9 of the surrounding wall 3. Figure 4 In the embodiment of the invention, the membrane structure 6 has a circular shape in a top view. A plurality of pillars 10 are arranged along a circular line at a predetermined distance from the outer edge 25 of the membrane structure 6. This means that the circular line on which the pillars 10 are arranged is concentric with the circular membrane structure 6, but has a smaller diameter. The elevations 15 are arranged above the pillars 10, but have a greater extent than the pillars 10 in the transverse directions x and y. Each elevation 15 comprises a protruding portion 13, which extends toward the corresponding pillar 10 and is mechanically connected to the support area 12 of the pillar 10 via a bottom portion 14.

[0092] exist Figure 5, a cross section and a top view of another embodiment of a membrane structure 1 are shown. The cross section shows the membrane structure along section AA as shown in the top view. The measurements in the cross section correspond to the measurements in the top view, indicated by the vertical dashed lines.

[0093] Figure 5 and Figure 4 The difference of FIG. 1 is that it shows an additional elastic layer 26 connecting the membrane structure 6 to the surrounding wall 3. This means that the elastic layer 26 is mechanically connected to a portion of the top surface 9 of the surrounding wall 3 and to a portion of the membrane structure 6 at its outer edge 25. Thus, the elastic layer 26 covers the gap 18 between the membrane structure 6 and the surrounding wall 3. The elastic layer 26 increases the acoustic resistance Rsl of the slit. The elastic layer 26 can be stretched so that the membrane structure 6 can still be used as a membrane, i.e. can be deflected, for example by sound pressure waves.

[0094] Figure 5 The membrane structure 6 of the embodiment further comprises a vent hole 7 in the center of the membrane structure 6. The vent hole 7 is provided for pressure balance between the environment above the membrane structure 6 and the rear space 5. In the case where the elastic layer 26 is breathable, the vent hole 7 can be omitted.

[0095] exist Figure 6 , a cross section and a top view of another embodiment of a membrane structure 1 are shown. The cross section shows the membrane structure along section AA as shown in the top view. The measurements in the cross section correspond to the measurements in the top view, indicated by the vertical dashed lines.

[0096] Figure 6 and Figure 4 The difference is that it comprises raised portions 15 extending to the outer edge 25 of the membrane structure 6. Each raised portion 15 is connected to the lower portion 16 by a connecting portion 17 at all lateral sides except the side facing the outer edge 25 of the membrane structure 6. This means that the lateral extent of the raised portions 15 in this embodiment is greater than that according to Figure 4 The lateral extent of the raised portion 15 in the embodiment of FIG. The raised portion 15 has an elongated shape extending from the outer edge 25 of the membrane structure 6 towards the corresponding pillar 10 .

[0097] exist Figure 7 , a cross section and a top view of another embodiment of a membrane structure 1 are shown. The cross section shows the membrane structure 1 along the section AA as shown in the top view. The measurements in the cross section correspond to the measurements in the top view, indicated by the vertical dashed lines.

[0098] Figure 7 and Figure 6The difference of FIG. 1 is that it shows an additional elastic layer 26 connecting the membrane structure 6 to the surrounding wall 3. This means that the elastic layer 26 is mechanically connected to a portion of the top surface 9 of the surrounding wall 3 and to a portion of the membrane structure 6 at its outer edge 25. Thus, the elastic layer 26 spans the gap 18 between the membrane structure 6 and the surrounding wall 3. The elastic layer 26 increases the acoustic resistance Rsl of the slit. The elastic layer 26 can be stretched so that the membrane structure 6 can still act as a membrane, i.e. can be deflected, for example by sound pressure waves.

[0099] Figure 7 The membrane structure 6 of the embodiment further comprises a vent hole 7 in the center of the membrane structure 6. The vent hole 7 is provided for pressure balance between the environment above the membrane structure 6 and the rear space 5. In the case where the elastic layer 26 is breathable, the vent hole 7 can be omitted.

[0100] Figure 8 Two cross-sectional views of another embodiment of the membrane structure 1 are shown. Figure 3 , two deflection states of the membrane deflection caused by, for example, sound pressure waves are shown. Figure 8 An embodiment similar to Figure 6 but includes fewer elevations 15, protrusions 13 and struts 10. The membrane deflection is shown in a stereoscopic view (i.e., a three-dimensional view). It must be noted that in Figure 8 The support 10 , the elevation 15 and the projection 13 shown in the center are located on the side of the membrane facing away from the observer.

[0101] Fig. 9 A schematic diagram of an exemplary embodiment of a transducer arrangement 27 is shown, the transducer arrangement comprising a membrane structure 1 as described above. The transducer arrangement 27 can be, for example, an optical omnidirectional microphone or any other dynamic pressure sensing device.

[0102] 10 a to 10 f show an exemplary embodiment of a method of manufacturing a membrane structure 1 .

[0103] The method comprises providing a substrate 2, as shown in FIG10 a. The substrate 2 has a rear surface 24 and a main surface 4. The substrate 2 can include Si. Etching is performed on the main surface 4 to form a surrounding wall 3 and a pillar 10. This can be done by a single etching step or by several subsequent etching steps. The surrounding wall 3 can be higher than the pillar 10 relative to the main surface 4 of the substrate 2. This means that the spacing between the top surface 9 of the surrounding wall 3 and the main surface 4 of the substrate 2 is greater than the distance between the top surface 9 of the surrounding wall 3 and the support area 12 of the pillar 10. The pillar 10 is arranged in the surrounding wall 3 at a certain distance from the surrounding wall 3.

[0104] In the next step, a first sacrificial layer 28 is deposited in the region within the surrounding wall 3 on the main surface 4 of the substrate 2 ( FIG. 10 b ). For example, the first sacrificial layer 28 can include W—Ti. The first sacrificial layer 28 partially fills the region within the surrounding wall 3. Thus, the first sacrificial layer 28 can cover the side surface 11s of the pillar 10. However, the first sacrificial layer 28 can leave the support region 12 of the pillar 10 uncovered.

[0105] The second sacrificial layer 29 is deposited on the first sacrificial layer 28. The second sacrificial layer 29 can also include W—Ti. The second sacrificial layer 29 is formed in the area above the pillar 10, however, the lateral extent of the second sacrificial layer 29 after formation is greater than the lateral extent of the pillar 10. In the lateral directions x, y, the second sacrificial layer 29 is removed in the area adjacent to the surrounding wall 3. This means that there is a gap between the second sacrificial layer 29 and the surrounding wall 3. A groove 30 is formed in the second sacrificial layer 29 above the pillar 10. The groove 30 can be formed by the same etching step as other areas where the second sacrificial layer 29 is formed. The groove 30 extends toward the pillar 10. The groove 30 can have the same lateral extent as the pillar 10.

[0106] The stack of sacrificial layers 28, 29 forms a sacrificial layer region 33. The sacrificial layer region 33 can locally have the same height as the surrounding wall 3 relative to the main surface 4 of the substrate 2. This means that the top surface 31 of the second sacrificial layer 29 and the top surface 9 of the surrounding wall 3 are located in a plane extending parallel to the main extension plane of the substrate 2. The sacrificial layers 28, 29 form a region providing a first thickness level and a second thickness level of the sacrificial layer region 33. The first thickness level is greater than the second thickness level.

[0107] In the next step, the thin film 32 is deposited in the area within the surrounding wall 3 (FIG. 10c). This means that the thin film 32 is deposited on the second sacrificial layer 29, on the first sacrificial layer 28, in the groove 30 and on the support area 12 of the pillar 10. The thin film 32 may include SiN. The thin film 32 is removed in the area adjacent to the surrounding wall 3. For example, the thin film 32 is removed by etching. Therefore, the thin film 32 is not in mechanical contact with the surrounding wall 3.

[0108] In Fig. 10d, the deposition of an elastic layer 26 is shown. The elastic layer 26 may comprise PDMS. The elastic layer 26 covers a portion of the top surface 9 of the surrounding wall 3 and a portion of the membrane. Thus, the elastic layer 26 spans the gap 18 between the surrounding wall 3 and the membrane.

[0109] An opening 23 is formed from the rear surface 24 of the substrate 2 to the main surface 4 towards the sacrificial layer region 33 (FIG. 10e). However, the lateral extent of the opening 23 may be smaller than the lateral extent of the sacrificial layer region 33. To form the opening 23, the substrate 2 can be turned over and back-side processed.

[0110] In a subsequent step, the sacrificial layers 28, 29 are removed in order to release the thin film 32 and form a thin film structure 6 (FIG. 10f). The raised portion 15 of the thin film structure 6 is formed by a thin film which has been deposited at a first thickness level. The protruding portion 13 is formed by a portion of the thin film 32 deposited in one of the plurality of grooves 30 in the sacrificial layer region 33. The connecting portion 17 of the thin film 32 structure 6 is formed by a portion of the thin film 32 deposited between the first thickness level and the second thickness level. The lower portion 16 is formed by a portion of the thin film 32 deposited at the second thickness level. The resulting membrane structure 1 is equivalent to Figure 7 The membrane structure 1 is formed by a substrate 2, a surrounding wall 3, pillars 10, an elastic layer 26, a membrane structure 6 and a rear space 5 formed by a cavity left after removing the sacrificial layer area 33. The membrane structure 6 can form a membrane for use in a transducer device 27.

[0111] The embodiments disclosed herein have been discussed for the purpose of familiarizing the reader with the novel aspects of the concept. Although preferred embodiments have been shown and described, many changes, modifications, equivalents and substitutions may be made to the disclosed concepts by those skilled in the art without unnecessarily departing from the scope of the claims.

[0112] It should be understood that the present disclosure is not limited to the disclosed embodiments and the contents specifically shown and described above. On the contrary, the features described in the individual dependent claims or the specification may be advantageously combined. In addition, the scope of the present disclosure includes those changes and modifications that are obvious to those skilled in the art and fall within the scope of the appended claims.

[0113] The term "comprising" used in the claims or in the description does not exclude other elements or steps of the corresponding features or processes. Where the terms "a" or "an" are used in conjunction with a feature, they do not exclude a plurality of such features. Furthermore, any reference signs in the claims should not be construed as limiting the scope.

[0114] This application is a national phase entry application of International Patent Application No. PCT / EP2020 / 074365 filed on September 1, 2020, claiming priority to European Patent Application No. 19197358.5 filed on September 13, 2019, which are incorporated herein by reference in their entirety for all purposes.

[0115] Reference numerals

[0116] 1 Membrane structure

[0117] 2 Base

[0118] 3 Enclosing wall

[0119] 4 Main surface of substrate

[0120] 5 Back Space

[0121] 6 Thin film structure

[0122] 7 Ventilation holes

[0123] 8 Side surfaces of the surrounding wall

[0124] 9 Top surface of the surrounding wall

[0125] 10 Pillars

[0126] 11 Side surface of the pillar

[0127] 12 Pillar support area

[0128] 13 Protrusions of membrane structures

[0129] 14 Bottom part of the protrusion

[0130] 15. Elevated part of membrane structure

[0131] 16 Lower part of the membrane structure

[0132] 17 Connection parts of membrane structures

[0133] 18 Slit between surrounding wall and membrane structure

[0134] 19 Central part of the membrane

[0135] 20 External part of the membrane

[0136] 21 Mechanical Phase Shifter

[0137] 22 Side wall of protruding part

[0138] 23 Opening in the base

[0139] 24 Rear surface of base

[0140] 25 Outer edge of membrane structure

[0141] 26 Elastic Layer

[0142] 27 Transducer device

[0143] 28 First Sacrificial Layer

[0144] 29 Second Sacrificial Layer

[0145] 30 Grooves in the sacrificial layer area

[0146] 31 Top surface of the second sacrificial layer

[0147] 32 films

[0148] 33 Sacrificial layer area

[0149] x, y horizontal direction

[0150] z vertical direction

[0151] Pa Common pressure level

[0152] Pe External sound pressure source

[0153] Complex acoustic impedance of Zm membrane

[0154] Lm is the acoustic mass of the membrane

[0155] Acoustic compliance of Cm membrane

[0156] Rs Acoustic resistance of compressed air film

[0157] Rv Acoustic resistance of the vent

[0158] Cv Compliance of the back space

[0159] Complex acoustic impedance of the central part of the Zmc membrane

[0160] Lmc The acoustic mass of the central part of the membrane

[0161] Acoustic compliance of the central part of the Cmc membrane

[0162] Rsc Acoustic resistance of the compressed air film beneath the central part of the membrane

[0163] Complex acoustic impedance of the outer part of the Zmo membrane

[0164] The acoustic mass of the outer part of the Lmo membrane

[0165] Acoustic compliance of the outer part of the Cmo membrane

[0166] Rso The acoustic resistance of the compressed air film beneath the outer part of the membrane

[0167] Phase Shifter

[0168] Rp Acoustic resistance of the pillar

[0169] Rsl acoustic resistance of the slit

[0170] Acoustic compliance of the back space below the center part of the Cvc membrane

[0171] Acoustic compliance of the back space beneath the outer part of the CVO membrane

Claims

1. A membrane structure (1), comprising: - a substrate (2) having a main surface (4) and a rear surface (24), a plurality of struts (10) arranged on the main surface (4) of the substrate (2) and having a support area (12) facing away from the main surface (4) of the substrate (2), and a thin film structure (6) arranged above the main surface (4) of the substrate (2) and the pillars (10), the thin film structure (6) forming a membrane, in - the membrane structure (6) comprises a plurality of raised portions (15), the spacing between the raised portions and the base (2) being greater than the spacing between at least one lower portion (16) of the membrane structure and the base (2); - each of the elevations (15) comprises at least one protruding portion (13), the protruding portion (13) being hollow and having a bottom portion (14) and a side wall (22), and the protruding portion (13) extending towards the base (2), - the bottom portion (14) of each protrusion (13) is mechanically connected to the support area (12) of one of the pillars (10), respectively, wherein each pair of pillars (10) and protrusions (13) forms a mechanical phase shifter during membrane deflection, - the rear space (5) is formed by the space between the main surface (4) of the substrate (2) and the film structure (6), - wherein the support (10) and the protruding portion (13) of the membrane structure (6) are arranged at a predetermined distance from the outer edge of the membrane structure (6); and - wherein the mechanical phase shifter provides a phase shift of 180 degrees between the outer portion (20) and the central portion (19) of the membrane.

2. The membrane structure (1) according to claim 1, wherein: The raised portions and protruding portions provide a flexible connection during deflection of the membrane.

3. The membrane structure (1) according to claim 1 or 2, wherein: Each raised portion (15) is completely surrounded by the at least one lower portion (16) in a transverse direction (x, y) extending parallel to the main extension plane of the base (2), and each raised portion (15) is connected to the at least one lower portion (16) via a connecting portion (17).

4. The membrane structure (1) according to claim 1 or 2, wherein: Each raised portion (15) extends to the outer edge of the membrane structure (6) and is connected to the at least one lower portion (16) via a connecting portion (17).

5. The membrane structure (1) according to claim 1 or 2, further comprising: At least one surrounding wall (3) is arranged on the main surface (4) of the substrate (2) at a certain distance from the outer edge of the film structure (6), and the surrounding wall (3) surrounds the film structure (6) in a lateral direction (x, y) extending parallel to the main extension plane of the substrate (2).

6. The membrane structure (1) according to claim 5, further comprising: At least one elastic layer (26) mechanically connects the membrane structure (6) to the surrounding wall (3).

7. The membrane structure (1) according to claim 6, wherein: The elastic layer (26) is breathable.

8. The membrane structure (1) according to claim 1 or 2, further comprising: An opening (23) is located in the substrate (2), the opening extending from the rear surface (24) towards the thin film structure (6) at the main surface (4) of the substrate (2).

9. The membrane structure (1) according to claim 1 or 2, wherein The membrane structure (1) comprises ventilation holes (7) within the thin film structure (6).

10. The membrane structure (1) according to claim 1 or 2, in The film structure (6) has a circular or polygonal shape in a plan view.

11. A transducer device (27) comprising a membrane structure (1) according to any one of claims 1 to 10, wherein The transducer device (27) is in particular an optical omnidirectional microphone or any other dynamic pressure sensing device.

12. A method for producing a membrane structure (1), the method comprising: - providing a substrate (2), - forming a plurality of pillars (10) at the main surface (4) of the substrate (2), - forming a sacrificial layer region (33) at the main surface (4) of the substrate (2) and on the pillars (10), providing at least a first thickness level and a second thickness level of the sacrificial layer region (33), the first thickness level being greater than the second thickness level, - forming a plurality of grooves (30) in the sacrificial layer region (33) having a first thickness level, wherein each groove (30) extends towards one of the pillars (10), - depositing a thin film (32) on the sacrificial layer region (33) and in the plurality of trenches (30), and - forming a thin film structure (6) from the thin film (32) by removing the sacrificial layer region (33), the thin film structure (6) forming a membrane, wherein the thin film structure (6) comprises an elevation (15), wherein the elevation (15) is formed by a portion of the thin film (32) deposited on the sacrificial layer region (33) having the first thickness level, - each elevation (15) comprises at least one protrusion (13) formed by a portion of the thin film (32) deposited within the plurality of grooves (30), wherein each pair of pillars (10) and protrusions (13) forms a mechanical phase shifter during membrane deflection, - the rear space (5) is formed by the cavity left after removing the sacrificial layer area (33), - the membrane structure (1) comprises a thin film structure (6), a substrate (2) and a rear space (5) between the thin film structure (6) and the substrate (2), - wherein the support (10) and the protruding portion (13) of the membrane structure (6) are arranged at a predetermined distance from the outer edge of the membrane structure (6); and - wherein the mechanical phase shifter provides a phase shift of 180 degrees between the outer portion (20) and the central portion (19) of the membrane.

13. The method according to claim 12, further comprising: At least one surrounding wall (3) is formed on the main surface (4) of the substrate (2) at a certain distance from the outer edge of the film structure (6), and the surrounding wall (3) surrounds the film structure (6) in a lateral direction (x, y) extending parallel to the main extension plane of the substrate (2).

14. The method according to claim 13, further comprising: An elastic layer (26) is deposited, which mechanically connects the membrane structure (6) to the surrounding wall (3).

15. The method according to any one of claims 12 to 14, further comprising: - forming an opening (23) in the substrate (2), the opening (23) extending from a rear surface (24) of the substrate (2) towards the thin film structure (6), wherein the rear surface (24) faces away from the main surface (4), - Removing the sacrificial layer region (33) after forming the opening (23) in the substrate (2).

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