Micromechanical sensor for an environment containing water or moisture
The micromechanical sensor addresses humidity and water sensitivity by employing a hygromechanical material structure and additional layers to balance moisture-induced stresses, improving accuracy and resistance in moisture-containing environments.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- ROBERT BOSCH GMBH
- Filing Date
- 2025-12-03
- Publication Date
- 2026-06-11
Smart Images
Figure EP2025085330_11062026_PF_FP_ABST
Abstract
Description
[0001] R. 417016
[0002] - 1 -
[0003] Description
[0004] title
[0005] Micromechanical sensor for a water- or moisture-containing environment
[0006] The invention relates to a micromechanical sensor according to the preamble of claim 1.
[0007] State of the art
[0008] Micromechanical sensors comprise microelectromechanical structures that detect measured quantities through mechanical, electrical, and / or chemical interactions. However, in specific applications, micromechanical sensors can exhibit high cross-sensitivity to humidity or water, which can lead to unintended changes in the sensor signal.
[0009] Moisture or water affects micromechanical sensors through a variety of physical and / or chemical effects. For example, hydrophilic materials can have their physical properties altered by the adsorption or diffusion of water molecules. Surface adsorption, in turn, leads to changes in mechanical and electrical parameters. Additionally, water-bound layers can form on structures exposed to the environment, influencing their mechanical properties.
[0010] Disclosure of the invention
[0011] According to the present invention, a micromechanical sensor with the features of claim 1 is proposed. This reduces the cross-sensitivity of the micromechanical sensor to humidity and water. The micromechanical sensor can measure the quantity more accurately. R. 417016
[0012] - 2 - measure and be made more moisture-resistant. The micromechanical sensor can be designed to be compact and cost-effective.
[0013] The membrane is mechanically and electrically connected to the substrate via its edge, either conductively or non-conductively. The membrane surface can face away from the substrate in the normal direction.
[0014] The micromechanical sensor can be a microelectromechanical sensor. The micromechanical sensor can be a pressure sensor, a microphone, or an accelerometer. The pressure sensor can be an absolute pressure sensor or a differential pressure sensor. The pressure sensor can be a piezoresistive or capacitive sensor.
[0015] The hygromechanical material structure describes the entirety of the physical, chemical, and mechanical properties of a material that influence its mechanical behavior, particularly material stresses such as compressive and / or tensile stress, when exposed to moisture. The hygromechanical material structure thus indicates how the material behaves mechanically, for example, through material stresses or deformations, depending on the absorption, storage, or release of water or moisture.
[0016] In the preceding and following text, "lateral" is understood to mean a directional reference in a plane that has the normal direction as its normal.
[0017] If at least one additional layer on a locally limited first area of the membrane surface has a hygromechanical material structure that differs in a targeted manner from a second area offset laterally, moisture-induced tensile and compressive stresses in the membrane can be balanced or avoided, thus reducing deformation of the membrane due to the action of moisture or water on the membrane.
[0018] The second area can be offset from the first area in at least one lateral direction or in two mutually perpendicular lateral directions. The second area can be laterally offset from the first area by surrounding the first area. R. 417016
[0019] - 3 -
[0020] When an additional layer with a thickness of less than or equal to 1 pm is locally arranged on the membrane surface, limiting the absorption of water from the environment, it has been found that the moisture-related cross-sensitivity of the micromechanical sensor is significantly reduced.
[0021] Particularly on the surface of a membrane material facing the environment, an ice-like layer consisting of water molecules can form on a naturally occurring oxide, such as silicon dioxide, through the adsorption of water molecules onto the silicon dioxide surface. This ice-like layer arises from the interaction between the water molecules and immobilized hydroxyl groups on the silicon dioxide surface, which forces the water molecules into an ordered arrangement. This ice-like layer can form several molecular layers, for example, up to 15.
[0022] The additional layer can locally decouple the membrane surface from material stresses that would otherwise act on the top layer due to the ice-like layer. This reduces material stresses on the membrane surface caused by the ice-like layer.
[0023] The additional layer can locally prevent the membrane surface from absorbing water from the environment. The additional layer can be formed by atoms diffused into the membrane material, for example, from metals, metal oxides, and / or metal silicides. The additional layer can comprise a silicone gel, a hydrogel, aluminum oxide, a metal (gold, copper, platinum, chromium, nickel, or others), a metal alloy, oxides (silicon dioxide, aluminum oxide, zinc oxide, indium tin oxide, hafnium dioxide, titanium dioxide, niobium pentoxide, gallium oxide, zirconium dioxide, yttrium oxide, or others), metal silicides (titanium disilicide, tantalum disilicide, tungsten disilicide, cobalt disilicide, nickel disilicide, platinum silicide, palladium silicide, or others), and / or gold-silicon alloys. The additional layer can have a thickness of ≤ 100 nm, preferably ≤ 50 nm.
[0024] In a preferred embodiment of the invention, the additional layer has a material structure that reduces compressive stress and / or tensile stress. R. 417016
[0025] - 4 -
[0026] The membrane surface can have a surface roughness of less than or equal to 20 Ra.
[0027] The membrane can be rectangular, polygonal, round, oval, elliptical, or square with respect to a plane having the normal direction as its normal. The membrane can have a constant or variable thickness with respect to a plane having the normal direction as its normal in at least one lateral longitudinal direction and / or transverse direction.
[0028] The membrane material can be silicon, in particular monocrystalline, polycrystalline, and / or amorphous silicon. Alternatively, the membrane can be made of a dielectric membrane material such as silicon dioxide. The first or second region can have a hygro-mechanical material structure corresponding to the main part of the membrane material. The first region can be locally limited in that it spans at most a portion of the membrane surface. The first region can also be offset from the second region in a normal direction. The second region can be located on a rear surface of the membrane opposite the main surface. The first region can be hydrophobic or hydrophilic.
[0029] An elastic protective material, such as a protective gel, can be applied in the normal direction above the membrane or on an upper side of the membrane facing away from the substrate.
[0030] In a preferred embodiment of the invention, it is advantageous if the first region has a material structure that, compared to the second region, increases or decreases compressive stress due to hygromechanical factors. In the first case, this means that, assuming constant humidity, the first region develops a higher moisture-related compressive stress per unit volume or area than the second region, which develops no or a lower moisture-related compressive stress. In the second case, assuming constant humidity, this means that the first region develops a lower moisture-related compressive stress per unit volume or area than the second region, which develops a higher moisture-related compressive stress. R. 417016
[0031] - 5 -
[0032] Alternatively or additionally, the first area can have a material structure that increases or decreases tensile stress hygromechanically compared to the second area. In the first case, this means that, assuming constant humidity, the first area develops a higher moisture-related tensile stress per unit volume or area than the second area, which develops no or lower moisture-related tensile stress. In the second case, assuming constant humidity, this means that the first area develops a lower moisture-related tensile stress per unit volume or area than the second area, which develops a higher moisture-related tensile stress.
[0033] In a preferred embodiment of the invention, it is advantageous if the second region has a material structure that increases compressive stress hygromechanically compared to the first region. Given constant humidity, this means that the second region, compared to the first region, develops a higher moisture-induced compressive stress per unit volume or unit area than the first region, which develops no or a lower moisture-induced compressive stress.
[0034] Alternatively or additionally, the second area can have a material structure that increases tensile stress hygromechanically compared to the first area. Given constant humidity, this means that the second area develops a higher moisture-related tensile stress per unit volume or unit area than the first area, which develops no or a lower moisture-related tensile stress.
[0035] In a preferred embodiment of the invention, it is advantageous if the first and / or second region has a material structure that, compared to the majority of the membrane material, increases or decreases compressive stress hygromechanically. Alternatively or additionally, the first and / or second region can have a material structure that, compared to the majority of the membrane material, increases or decreases tensile stress hygromechanically. R. 417016
[0036] - 6 -
[0037] A preferred embodiment of the invention is advantageous in which the first region has a crystal structure and / or crystal orientation that differs from the second region and / or the predominant material structure of the membrane material. The first region can have a crystalline or at least partially crystalline material structure, and the second region can have an amorphous material structure, or vice versa. Alternatively or additionally, the second region can have a crystal structure and / or crystal orientation that differs from the predominant material structure of the membrane material.
[0038] The first area can have a (100) crystal orientation and the second area can have a (110) crystal orientation or vice versa.
[0039] A preferred embodiment of the invention is advantageous in which the membrane material comprises or is polycrystalline silicon and the first and / or second region has an amorphous material structure. The amorphous material structure can be formed by depositing silicon at a lower temperature than the deposition temperature to form polycrystalline silicon. The amorphous material structure can be formed by laser treatment. Preferably, only one of the two regions of the first and second region can have an amorphous material structure.
[0040] The membrane material can alternatively or additionally contain or be monocrystalline silicon.
[0041] An embodiment of the invention is advantageous in which the first region has an additional layer on the surface of the membrane, in particular on the surface of the membrane material. The additional layer can be applied by physical or chemical vapor deposition, in particular plasma-enhanced chemical vapor deposition, electrochemical or galvanic deposition, electron beam evaporation, molecular beam epitaxy, atomic layer deposition, injection processes and / or sputtering.
[0042] A preferred embodiment of the invention is advantageous in which the second region at least partially encloses the membrane edge and / or the first region encompasses a membrane center of the membrane surface. The second region can also enclose the membrane center and / or the first region at least partially encloses the membrane edge. R. 417016
[0043] - 7 -
[0044] In a specific embodiment of the invention, it is advantageous if the additional layer is made of a layer material with greater elasticity than the membrane material. The additional layer can have a hydrophobic material property.
[0045] In a particular embodiment of the invention, it is advantageous if the additional layer, in particular at least on one surface of the additional layer, has a water diffusion barrier layer. This can reduce or prevent the diffusion of water from the environment to the membrane material.
[0046] Further advantages and advantageous embodiments of the invention will become apparent from the description of the figures and the illustrations.
[0047] Character description
[0048] The invention is described in detail below with reference to the illustrations. These show, in detail:
[0049] Figure 1: A cross-section of a micromechanical sensor in a special embodiment of the invention.
[0050] Figure 2: A cross-section of a micromechanical sensor in a special embodiment of the invention.
[0051] Figures 3 to 5: A top view of a membrane of a micromechanical sensor in each further specific embodiment of the invention.
[0052] Figure 6: A top view of a micromechanical sensor in a special embodiment of the invention.
[0053] Figures 7 to 9: A cross-section of a membrane of a micromechanical sensor in each further specific embodiment of the invention. R. 417016
[0054] - 8 -
[0055] Figure 1 shows a cross-section of a micromechanical sensor in a specific embodiment of the invention. The micromechanical sensor 10 is designed as a pressure sensor 12 for detecting a measured quantity, for example, ambient pressure, and comprises a substrate 14, preferably made of silicon, and a membrane 20, which is deflectable in a normal direction 16 into a free area 17 (cavern) depending on the measured quantity and is made of at least one membrane material 18, preferably polycrystalline silicon, and which is mechanically connected to the substrate 14 via a circumferential membrane edge 22 and whose membrane surface 24, here facing away from the substrate 14, is oriented towards a moisture-containing environment 26.wherein the membrane material 18 optionally additionally comprises a single dopant homogeneously distributed in a plane perpendicular to the normal direction 16. The membrane 20 is connected to the substrate 14 in a cantilevered manner in the normal direction above the free space 17, and the free space 17 can contain a gas or gas mixture and have an internal pressure lower than the ambient pressure 26.
[0056] Moisture can cause compressive stresses 28 in the membrane material 18, which can cause the membrane 20 to deflect downwards in the normal direction 16 (towards the substrate 14) in the region of the membrane edge 22, and upwards in the normal direction 16 (away from the substrate 14) in the membrane center 30. However, if the compressive stress 28 is applied across the entire membrane surface 24, the membrane 20 will deflect downwards, since the compressive stress in the region of the membrane edge 22 is greater than the compressive stress in the region of the membrane center 30.
[0057] A locally confined first region 32 of the membrane surface 24 has a different hygromechanical material structure compared to a second region 34 that is laterally offset from it. The first region 32 comprises the center of the membrane 30 and is arranged at a distance laterally from the membrane edge 22. The second region 34 includes, in particular, the area surrounding the first region 32, including the membrane edge 22. The first region 32 is composed of a material structure that increases hygromechanical compressive stress compared to the second region 34. This allows the moisture-induced compressive stress of the membrane edge 22 to be reduced by the R. 417016
[0058] - 9 - moisture-induced compressive stress of the first area 32 is balanced because of the material structure in the center of the membrane 30, which increases hygromechanical compressive stress compared to the membrane edge 22.
[0059] Figure 2 shows a cross-section of a micromechanical sensor in a specific embodiment of the invention. The micromechanical sensor 10 is identical to that of Figure 1 except for the following deviations. On the surface 38 of the membrane material 18 facing the environment 26, an additional layer 40 forming a hygromechanically compressive stress-increasing material structure is applied in the first region 32, forming the membrane surface 24 facing the environment 26 in this region. In the laterally adjacent second region 34, the surface 38 of the membrane material forms the membrane surface 24.
[0060] Figure 3 shows a micromechanical sensor 10 with a membrane 20. The membrane 20, made of membrane material 18, is connected to the substrate via the surrounding membrane edge 22, with the membrane surface 24 facing the moisture-containing environment.
[0061] The first region 32, which is locally confined and encloses the membrane center 30, is at least partially surrounded by the circumferential membrane edge 22 and arranged laterally at a distance from the membrane edge 22. The second region 34, which at least partially surrounds the first region 32 laterally and encloses the membrane edge 22, has a hygromechanical material structure that differs from that of the first region 32. In order to compensate for the moisture-induced material stresses in the membrane 20, the first region 32 has a material structure that increases hygromechanical compressive stress compared to the second region 34.
[0062] The micromechanical sensor 10 in Figure 4 is similar to that in Figure 3 with the following differences. The first region 32 spans the membrane edge 22 and, compared to the second region 34 which encloses the membrane center 30, has a preferably hygromechanical material structure that reduces compressive stress.
[0063] Figure 5 shows a micromechanical sensor 10 similar to that shown in Figure 3, however, several strip-shaped first regions 32 are arranged in a lateral direction. 417016
[0064] - 10 -
[0065] The longitudinal regions 42 are arranged offset from each other across the membrane surface 24. This allows the equalization of moisture-induced material stresses in the membrane 20 to preferably occur in a lateral longitudinal direction 42 and a transverse direction 44. The second region 34 is formed by the remaining area of the membrane surface 24 surrounding the first regions 32.
[0066] The length 46 of the individual first regions 32 in the longitudinal direction 42 can be up to 20% of the membrane length 48 in the longitudinal direction 42. It is also conceivable to extend the first regions 32 in the transverse direction 44 in at least one direction or in both directions beyond the membrane edge 20. Additionally or alternatively, the first regions 32 can be subdivided along the transverse direction 44.
[0067] Figure 6 shows a top view of a micromechanical sensor in a particular embodiment of the invention. The micromechanical sensor 10 is, for example, a capacitive pressure sensor 12 with a first diaphragm 50 and a second diaphragm 52 offset from it, spaced apart and adjacent to it, each of which is associated with a measuring capacitance and a reference capacitance. The micromechanical sensor 10 comprises a substrate 14 and several bond pads 54 for the electrical connection of the measuring capacitances and the reference capacitances.
[0068] A first covering layer 56, preferably less than or equal to 1 pm, is arranged on the membrane material of the entire membrane surface 24 of the first membrane 50. This covering layer at least restricts the absorption of water by the membrane surface 24 from the environment. A second covering layer 58, also at most 1 pm, is arranged on the membrane material of the entire membrane surface 24 of the second membrane 52. This covering layer at least restricts the absorption of water by the membrane surface 24 from the environment. The first and second covering layers 56, 58 are laterally spaced apart from each other and, in particular, span a respective membrane edge 22.
[0069] The membrane 20 in Figure 7 comprises the membrane material 18, which consists, for example, of polycrystalline silicon, and a further membrane material 62 made of silicon oxide arranged in the normal direction 16 on the side of the membrane material 18 facing away from the substrate. A cover layer 64 made of a layer material 66 is additionally applied to the further membrane material 62, R. 417016
[0070] - 11 - which exhibits greater elasticity compared to the membrane material 18 and the further membrane material 62. The layer thickness 68 of the cover layer 64 is in particular less than or equal to 1 pm, preferably less than or equal to 100 nm.
[0071] In contrast to the membrane in Figure 7, the membrane 20 in Figure 8 comprises only the membrane material 18, which consists of polycrystalline silicon, and the cover layer 64 on it.
[0072] The membrane 20 in Figure 9 comprises the surface layer 64 on the side of the membrane material 18 facing away from the substrate, which forms the membrane surface 24 and is created by diffusion of metals, metal oxides and / or metal silicides into the membrane material 18. A water diffusion barrier layer 70 can in turn be applied to this surface layer 64 to limit or prevent the diffusion of water molecules to the membrane surface 24.
Claims
R. 417016 - 12 - Patent claims 1. Micromechanical sensor (10) for detecting a measured quantity, comprising a substrate (14), a substantially media-tight membrane (20) which is deflectable in a normal direction (16) depending on the measured quantity and which has at least one membrane material (18), which connects to the substrate (14) via a membrane edge (22) and which faces a moisture-containing environment (26) with a membrane surface (24), characterized in that the membrane surface (24) facing the environment (26) has at least one locally limited first region (32) and a second region (34) laterally offset thereto within the membrane edge (22), wherein an additional layer (40) is arranged in the at least one first region (32) on the membrane surface (24) which has a different hygromechanical material structure than the second region (34).
2. Micromechanical sensor (10) according to claim 1 , characterized in that the membrane material (18) forming the membrane (20) additionally comprises a single, homogeneously distributed dopant.
3. Micromechanical sensor (10) according to one of the preceding claims, characterized in that the additional layer (40) has a thickness of less than or equal to 1 pm.
4. Micromechanical sensor (10) according to one of the preceding claims, characterized in that the first area (32) has a material structure that is hygromechanically increasing or decreasing pressure stress compared to the second area (34).
5. Micromechanical sensor (10) according to one of the preceding claims, characterized in that the second area (34) has a material structure that increases or decreases compressive stress compared to the first area (32). R. 417016 - 13 - 6. Micromechanical sensor (10) according to one of the preceding claims, characterized in that the first and / or second area (32, 34) has a material structure that is hygromechanically increasing or decreasing pressure stress compared to the majority material structure of the membrane material (18).
7. Micromechanical sensor (10) according to one of the preceding claims, characterized in that the first region (32) has a crystal structure and / or crystal orientation that differs from the second region (34) and / or the majority material structure of the membrane material (18).
8. Micromechanical sensor (10) according to one of the preceding claims, characterized in that the membrane material (18) comprises or is polycrystalline silicon and the first and / or second region (32, 34) has an amorphous material structure.
9. Micromechanical sensor (10) according to one of the preceding claims, characterized in that the second area (34) at least partially encloses the membrane edge (22) and / or the first area (32) encompasses a membrane center (30) of the membrane surface (24) over a flat area.
10. Micromechanical sensor (10) according to one of the preceding claims, characterized in that the additional layer (40) is made of a layer material (66) with a greater elasticity than the membrane material (18).
11. Micromechanical sensor (10) according to one of the preceding claims, characterized in that the additional layer 40 has a hygromechanically compressive stress-reducing and / or tensile stress-reducing material structure.
12. Micromechanical sensor (10) according to one of the preceding claims, characterized in that the additional layer (40) is at least partially surrounded by a water diffusion barrier layer (70).