MOEMS device

Abstract

MOEMS device (10) comprising a substrate (12), a first boundary layer (14) anchored to the substrate (12), a second boundary layer (16) anchored to the substrate (12), wherein the first boundary layer (14) is spaced apart from the second boundary layer (16), and a cavity (18) located between the first boundary layer (14) and the second boundary layer (16), wherein a fiber optic system (22) is provided which extends at least partially into the cavity (18), which is spaced apart from the boundary layers (14, 16) and which is directly or indirectly connected at least at one point to one of the boundary layers (14, 16) via a coupling element (28).

Description

[0001] The present invention relates to a MOEMS device according to the preamble of claim 1. State of the art

[0002] MEMS devices are micro-electro-mechanical devices, such as those used in MEMS microphones or MEMS sensor devices. One such device is known, for example, from WO 2018134568 A1. This describes a MEMS microphone comprising a substrate with a substrate recess and a flexible membrane. Furthermore, WO 20141953721 A1 describes a MOEMS, i.e., a micro-opto-electro-mechanical device designed as an optical pressure sensor. It comprises a lower and an upper wafer that are connected to one another. An optical waveguide (FOC) that accommodates a distributed Bragg reflector is located on the lower wafer. Disclosure of the invention

[0003] The invention provides a MOEMS device according to claim 1. Preferred developments are the subject of the subclaims. Advantages of the invention

[0004] One aspect of the invention is that the proposed MOEMS device according to claim 1 comprises a first and a second confinement layer, each anchored to a substrate. The confinement layers are spaced apart from one another. Between them lies a cavity into which at least part of an optical fiber system extends. The optical fiber system is spaced apart from the confinement layers and is connected at least one point to one of the confinement layers directly or indirectly via a mechanical coupling element and / or a support membrane or beam. The optical fiber system can comprise one or more optical waveguides and preferably an optical coupling element such as a ring resonator and / or an interferometer. This ensures that a movement and / or the position of the coupled confinement layer can be transferred to properties of the optical fiber system, in particular to its optical conductivity or refractive index.These can then be used in various ways to detect a movement or position of at least one of the boundary layers. In this way, a movement or deformation of one of the boundary layers can be transferred as a property to the fiber optic system, making it measurable with high precision. For example, an optical fiber of the fiber optic system and / or an optical coupling element of the fiber optic system, such as a ring resonator and / or an interferometer, can be connected to at least one of the boundary layers via mechanical coupling elements. The boundary layers can be designed in the form of flexible membranes.

[0005] This creates a MOEMS device that can be used as a more sensitive component with a higher signal-to-noise ratio in a wide variety of applications. Conversely, a smaller component with the same signal-to-noise ratio could also be manufactured.

[0006] The measures listed in the dependent claims enable advantageous further developments and improvements of the MOEMS device specified in independent claim 1.

[0007] In one embodiment, the MOEMS device can be designed so that the cavity is hermetically sealed from the surrounding environment. This has the advantage of reducing sensitivity to moisture and dirt. The signal-to-noise ratio can also be further improved, especially if the cavity is at a lower pressure than the ambient pressure.

[0008] The two boundary layers can be coupled together in their moving area by one or more mechanical coupling elements. Mechanical coupling elements can be, for example, laterally bounding walls of the cavity, spring elements, and / or support columns. This ensures synchronous movement of the boundary layers in dynamic applications.

[0009] Mechanical coupling elements between the boundary layers can also prevent the boundary layers from collapsing at higher external ambient pressure.

[0010] In a further embodiment, the fiber optic system is coupled to at least one of the confinement layers in such a way that a movement of at least one of the confinement layers leads to a change in the optical properties of the waveguide. This offers the advantage that a plurality of different fiber optic systems can be used simultaneously in the same component or even in the same cavity, which can be selected depending on the given requirements.

[0011] Furthermore, at least part of the fiber optic system can be mounted on a support membrane or beam, particularly one that is slightly tensioned. This has the advantage of allowing for easier positioning.

[0012] In a further embodiment, the fiber optic system can be designed such that it experiences a change in the refractive index upon mechanical deformation, which enables highly accurate measurement of the confinement layer's movement, particularly via a phase shift of the light. A fiber optic system with a Mach-Zehnder interferometer arrangement or a ring resonator arrangement is particularly suitable for this purpose, as it enables very precise measurements.

[0013] If the two boundary layers are mechanically coupled, a double cantilever beam or a double membrane can be created. This has the advantage that the device can be optimized depending on the application, for example, by adjusting the stiffness of the connection.

[0014] In a further embodiment, the substrate can be provided with a recess that is at least partially spanned by the boundary layers. This makes it possible to provide a back volume and create access to the MOEMS device from both sides.

[0015] In a further embodiment, it can advantageously be provided that one of the boundary layers, which is mechanically coupled to the movable part of the fiber optic system, is mechanically stiffened between the coupling points. In this way, the deformation of the boundary layer can be converted into a well-defined translation of the movable part of the fiber optic system. The stiffening can be achieved in the form of corrugation, a local material thickening, and / or a higher density of coupling elements.

[0016] In a further embodiment of the invention, one or both boundary layers can comprise a functional layer, which is applied such that the functional layer is exposed to the environment, toward the MOEMS device. This allows for additional sensitivities to environmental stimuli to be implemented, such as the detection of changes in environmental properties, such as temperature, humidity, or gases. These are detected by the functional layer, for example, through its shrinkage or expansion, and transferred to the boundary layer as deformation of the boundary layer. Short description of the drawings

[0017] Further features and advantages of the present invention are explained below using exemplary embodiments with reference to the figures.

[0018] They show: Fig. 1a, Fig. 1b is a schematic plan and cross-sectional view of a MOEMS device according to a first embodiment of the present invention; Fig. 2a, Fig. 2b is a schematic plan view and cross-sectional view of a MOEMS device according to a second embodiment of the present invention; Fig. 2c schematically shows the light path in a ring resonator application Fig. 3a, Fig. 3b is a schematic plan view and cross-sectional view of a MOEMS device according to a third embodiment of the invention; Fig. 4a, Fig. 4b is a schematic plan and cross-sectional view of a MOEMS device according to a fourth embodiment of the present invention; Fig. 5 is a schematic cross-sectional view of a MOEMS device according to an alternative first embodiment of the present invention. Embodiments of the invention

[0019] In the figures, the same reference symbols denote the same or functionally identical elements.

[0020] Fig. 1a shows a schematic plan view and Fig. 1b schematically shows a cross-sectional view of a MOEMS device. The MOEMS device 10 has a first flexible boundary layer 14 and a second boundary layer 16 spaced therefrom. As shown in Fig. As shown in Figure 5, the substrate 12 could also serve as a second confinement layer 16. A cavity 18 is provided between the confinement layers 14, 16, which are anchored to a substrate 12. The substrate 12 can be multilayered and is typically formed from a semiconductor material, such as silicon. One or more additional layers can be applied thereon, such as a dielectric such as silicon oxide. The confinement layers 14, 16 are typically layers of silicon and can represent membranes. The thickness is typically in the range of 1-10 µm.

[0021] A fiber optic system 22 is provided in the MOEMS device 10. It comprises fixed fiber optic cables 22a and a flexible, movable fiber optic cable 22b, wherein the movable fiber optic cable 22a and the flexible fiber optic cable 22b are each separated from one another by a gap 24. The fixed fiber optic cable 22a extends into the cavity 18, while the flexible fiber optic cable 22b is arranged entirely within the cavity 18. The flexible fiber optic cable 22b is mechanically coupled to the position and thus the movement of the first confinement layer 14 via coupling elements 28. A deformation of the confinement layer 14 is transmitted to the flexible fiber optic cable 22b, which is thereby deformed and / or moved. This changes the optical property of the fiber optic system 22—in this case, the amount of light that can be transmitted via the gap 24—because the optical coupling strength changes.

[0022] As in Fig. 1b, the flexible optical fiber 22b can optionally be arranged on a carrier membrane 30. This is advantageous because the carrier membrane 30 can be coupled to the first boundary layer 14 via the coupling elements 28. This makes it possible to couple the flexible optical fiber 22b to the boundary layer 14 indirectly, rather than directly. This enables a significantly simpler and more secure coupling of the flexible optical fiber 22b to the first boundary layer 14; this increases the robustness of the sensor with respect to external vibrations or overload conditions. Fig. Figure 1a shows that the coupling elements 28 are arranged on both sides of the flexible optical fiber 22b and are connected to each other via coupling struts 32 located beneath the flexible optical fiber 22b. The first boundary layer 14 can have a stiffener, a structure, a fold, or an anvil in the area where the coupling elements 28 are attached. This ensures that it remains as flat as possible and does not create undesirable bending of the flexible optical fiber 22b due to flexion.

[0023] Common materials and dimensions can be used for the optical fibers, such as silicon or silicon nitride, for example with a rectangular cross-section of 200 nm thickness and 500 nm width for monomode Si and 200 nm thickness and <1 µm width for monomode SiN waveguides.

[0024] In one embodiment, it is advantageous if the cavity 18 is hermetically sealed from the environment 20, which can be achieved by suitable layer processes, in particular by deposition or etching. A pressure of 1 mbar to 700 mbar can be advantageously provided in the cavity 18 compared to a pressure of the environment 20 of typically 1 bar, since a lower gas pressure in the cavity 18 dampens the mobility of the boundary layer 14 less.

[0025] The boundary layer 14 can also be designed with tensile stress to avoid compressive stress, which can lead to undesirable wave formation in the first boundary layer 14. The tensile stress can preferably be in the range of 10 MPa to 50 MPa.

[0026] In the example shown, the light is transmitted across two slits 24. However, the fiber optic system 22a, b can also be configured so that the light only needs to be coupled across one slit 24.

[0027] As in Fig. 2a, Fig. 2b in a schematic top view and a cross-sectional view, in one embodiment of the MOEMS device 10, the substrate 12 can have a substrate recess 26 that is at least partially spanned, or, as in the illustrated embodiment, completely spanned, by the boundary layers 14, 16 and the cavity 18. Thus, a back volume can be provided so that component variants can be realized that allow access from both sides of the environment 20 to the MOEMS device 10. The substrate recess can alternatively comprise only a portion of the thickness of the substrate, as shown. The environment 20 can also be configured as an ambient fluid.

[0028] Furthermore, an alternative fiber optic system 22 is shown. This has two fixed bus fiber optic cables 32 that are not coupled to the boundary layers, as well as a ring resonator 38 located partially above them.

[0029] Mechanical coupling elements 28 couple the first confinement layer 14 to the second confinement layer 16 and ensure synchronous movement. The ring resonator 38 is connected to at least two of the coupling elements 28 via at least two coupling webs 34, so that a deflection of the first confinement layer 14 and / or the second confinement layer 16 leads to a change in the distance of the ring resonator 38 relative to the fixed bus fiber optic cables 32 and thus to a change in the optical properties of the fiber optic system 22.

[0030] As in Fig. As shown schematically in Figure 2c, one of the fixed bus optical fibers 32 has an input light quantity i, a through-line light quantity t, and a drop-line light quantity d. Changing the position of the ring resonator 38 relative to the fixed bus optical fibers 32 changes the ratio of the through-line light quantity t to the drop-line light quantity d. This can serve as a measure of the distance of the ring resonator 38 from the fixed bus optical fibers 32 and thus as a measure of the deflection of the boundary layers 14, 16. This embodiment allows for a very sensitive measurement of the deflection of the boundary layers 14, 16.

[0031] In the example shown, the ring resonator 38 is located on a plane that is different from the plane on which the fixed bus fiber optic cables 32 are located. However, the ring resonator 38 can also be located on the plane of the fixed bus fiber optic cables 32. Furthermore, other coupling or attenuation elements can be used, the position changes of which influence the light transmission into the fixed bus fiber optic cables.

[0032] In a further embodiment, the boundary layers 14, 16 can be provided with a functional layer 40. Fig. Figure 2b shows an exemplary and schematic representation of such a functional layer 40 on the boundary layer 14. The functional layer 40 is exposed to the environment 20 of the MOEMS device 10. Its task is to convert an external stimulus, e.g., via a longitudinal expansion or stress change, into a deformation of the boundary layer 14, which can then be optically detected. Examples of the functional layer 40 include a moisture-absorbing polyimide or a heat-absorbing metal layer.

[0033] As in Fig. As shown in Figure 2a, in a further embodiment, the MOEMS device 10 can have a connection 42, sealed against the cavity 18, to the environment 20 between the substrate recess 26 and a side of the cavity opposite the substrate recess 26. Quasi-static pressure equalization can then occur via this connection 42, so that the sensor signal becomes independent of the ambient pressure. This is particularly advantageous when the environment 20 is a fluidic environment with variable hydrostatic fluid pressure. The connection 42 can, for example, be designed as a sleeve leading through the cavity 18. The sleeve is designed to be sealed against the cavity 18 and thus has no connection to the cavity 18.

[0034] Fig. 3a shows a top view and Fig. 3b shows a cross-section of another embodiment. The first boundary layer 14 is connected to the second boundary layer 16 via a plurality of mechanical coupling elements 28. Thus, the boundary layers 14, 16 are spaced apart from one another and coupled to one another in their movement. This configuration counteracts the external ambient pressure and allows synchronous movement of the boundary layers 14, 16. For this purpose, the coupling elements 28 preferably have high rigidity in a vertical direction and low rigidity in a horizontal direction. In this way, the coupled first and second boundary layers 14, 16 form a double bending beam or a double membrane. Depending on the application, the component can thus be optimized for various applications.

[0035] A substrate recess 26 is provided in the substrate 12, which is covered by the boundary layers 14, 16 and the cavity 18 located between them, except for a slot 48. This results in a double bending beam that is fixed in the substrate 12 on at least one side. On the opposite side, however, it can oscillate freely. This can be achieved by exposing the cavity 18 to the surroundings 20 by the slot 48, for example, in a U- or Ω-shape. A U-shaped end element 50 ensures the sealing of the cavity 18 on the freely oscillating side.

[0036] Also shown is another example of a fiber optic system 22 in a Mach-Zehnder interferometer arrangement. This comprises a movable U-shaped fiber optic arm 22b and a fixed, immobile fiber optic arm 22a. The movable fiber optic arm 22b is coupled to the first confinement layer 14 and / or the second confinement layer 16 via coupling webs 34 and coupling elements 28. The resulting transmission of a movement of the first confinement layer 14 and / or the second confinement layer 16 to the movable fiber optic system 22b generates a mechanical stress therein, which results in a corresponding change in the refractive index in the strained regions of the fiber optic system 22b. The refractive index in the parallel-connected, fixed fiber optic arm 22a, however, does not change. In this way, the phase of the light in the two optical fibers 22a, b shifts relative to each other, which leads to a detectable intensity modulation at the output of the optical fiber system 22.

[0037] Fig. 4a, Fig. 4b schematically shows a top view and a cross-section of an embodiment in which the fiber optic system 22 again comprises a Mach-Zehnder interferometer. A coupled interferometer arm 46 is coupled to the first confinement layer 14 and / or the second confinement layer 16 via a coupling element 28 and a coupling web 34. The rigid interferometer arm 44, in contrast, is not coupled. Movement of the confinement layers 14, 16 generates a mechanical stress in the coupled interferometer arm 46, which leads to a stress-induced change in the refractive index and thus a relative phase shift of the light in this interferometer arm. Thus, the light intensity detectable in the Mach-Zehnder interferometer changes depending on the phase shift of the light in the two interferometer arms. However, the light intensity signal is not unambiguous because the intensity modulation repeats periodically, which makes absolute measurements difficult.However, this homodyne detection principle enables particularly accurate and low-noise relative measurements.

[0038] Fig. 5 shows an alternative first embodiment of the Fig. 1b in a schematic cross-sectional view of a MOEMS device. The MOEMS device 10 has a first flexible boundary layer 14 and a second boundary layer 16 spaced therefrom, which, in contrast to Fig. 1b is formed by the substrate 12.

[0039] In general, depending on the application, several optical fiber systems and various optical converter principles can be implemented in the MOEMS device 10. In particular, absolute and relative measurements can be combined. This allows for absolute measurements with simultaneously high accuracy. The coupling of the light into the fiber optic system 22 can be performed as shown in the Fig. 1 to 3 via grating couplers 52 or with a laser integrated on the substrate 12, such as an edge-emitting laser 54, as in Fig. 4b. To detect the change in the optical properties of the fiber optic system 22, as also shown in Fig. As shown in Figure 4b, a detector structure 56 for measuring the light intensity after passing through the fiber optic system 22, for example a pn photodiode, can be integrated into the substrate 12. Alternatively, the light can be coupled out of the fiber optic system 22, for example, via a Bragg grating coupler, and detected in a separate detector.

[0040] With the MOEMS device, microphones, pressure sensors, acceleration sensors, humidity sensors or temperature sensors can be implemented both as relative and absolute measuring sensors. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] WO 2018134568 A1

[0002] WO 20141953721 A1

[0002]

Claims

[1] MOEMS device (10) comprising a substrate (12), a first confinement layer (14) anchored to the substrate (12), a second confinement layer (16) anchored to the substrate (12), the first confinement layer (14) being spaced from the second confinement layer (16), and a cavity (18) located between the first confinement layer (14) and the second confinement layer (16), characterized by that an optical fiber system (22) is provided which extends at least partially into the cavity (18), which is spaced from the boundary layers (14, 16) and which is directly or indirectly connected at least at one point to one of the boundary layers (14, 16) via a coupling element (28). [2] MOEMS device (10) according to claim 1, characterized by that the cavity (18) is hermetically sealed from an environment (20). [3] MOEMS device (10) according to claim 1 or 2, characterized bythat the optical fiber system (22) is connected to at least one of the boundary layers (14, 16) in such a way that a movement of one of the boundary layers (14, 16) leads to a change in the optical properties of the optical fiber system (22), in particular the light conductivity or the refractive index. [4] MOEMS device (10) according to claims 1 to 3, characterized by that at least a part (22b) of the optical fiber system (22) is arranged on a carrier membrane (30), in particular a tensile-stressed carrier membrane (30). [5] MOEMS device (10) according to one of claims 1 to 4, characterized by that the optical fiber system (22) comprises at least two optical fibers (22a, 22b) with a gap coupling (24). [6] MOEMS device (10) according to one of claims 1 to 5 characterized by that the optical fiber system (22) comprises a waveguide (22b) whose refractive index changes as a result of mechanical action. [7] MOEMS device (10) according to one of claims 1 to 6 characterized bythat the optical fiber system (22) comprises a Mach-Zehnder interferometer (36) and / or a ring resonator (38). [8] MOEMS device (10) according to one of claims 1 to 7 characterized by that the first boundary layer (14) is connected to the second boundary layer (16), in particular such that the boundary layers (14, 16) form a double bending beam or a double membrane. [9] MOEMS device (10) according to one of claims 1 to 8 characterized by that the substrate (12) has a partial or continuous substrate recess (26) which is at least partially spanned by the first boundary layer (14) and the second boundary layer (16). [10] MOEMS device (10) according to one of claims 1 to 9 characterized bythat at least one of the boundary layers (14, 16) has a functional layer (24) facing the environment (20) which changes one of its mechanical properties depending on the properties of the environment (20).

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