Microsensor having a conductive layer on a protective coating and method for producing such a conductive layer

Abstract

The invention relates to a capacitive microsensor (10) for measuring a measurement variable of a sensor environment (30) of the microsensor (10), comprising a housing (12), a sensor element (16) which is accommodated in an interior (14) of the housing (12) and has a measuring element (18) having at least one measurement capacitance which can be changed depending on the measurement variable, and a connection device (20) which electrically connects the measuring element (18), a gel-like protective coating (32) which at least partially covers the sensor element (16) on the side facing the sensor environment (30), thereby separating it from the sensor environment (30), and which can transmit the measured variable between the sensor environment (30) and the sensor element (16), wherein an electrically conductive conductive layer (40) is applied directly to the side (38) of the protective coating (32) facing the sensor environment (30), at least partially spanning the sensor element (16). The invention further relates to a method for producing such a conductive layer of the capacitive microsensor (10).

Description

[0001] Description

[0002] title

[0003] Microsensor with a conductive layer on a protective coating and method for such a conductive layer

[0004] The invention relates to a capacitive microsensor according to the preamble of claim 1. The invention further relates to a method for producing such a conductive layer.

[0005] State of the art

[0006] In DE 10 2020 212 123 A1 a capacitive microsensor is described, comprising a housing, a sensor element in an interior of the housing and a protective coating covering the sensor element from a sensor environment.

[0007] Disclosure of the invention

[0008] According to the present invention, a capacitive microsensor with the features of claim 1 is proposed. This reduces the influence of interference, particularly stray fields from the sensor environment, on the measuring capacitance. The microsensor can exhibit improved media robustness. The microsensor can be designed to be less dependent on environmental influences. Investigations have shown that the conductive layer reduces the influence of foreign media on the microsensor's stray capacitance by approximately 90%.

[0009] The microsensor can be a pressure sensor and / or a microphone. The microsensor can be a microelectromechanical sensor. The measured quantity can be pressure, specifically absolute pressure or differential pressure. The pressure can be the ambient pressure of the sensor's environment.

[0010] The measuring element can have at least one membrane that can be deflected depending on the measured quantity, whereby the measuring capacity is variable depending on a deflection of the membrane.

[0011] The conductive layer can be located exclusively within the interior. It can also be positioned below a housing opening that connects the interior to the sensor environment, pointing towards the measuring element. Applying the conductive layer to the protective coating means that it lies flat against the coating. A gap between the conductive layer and the protective coating is not required. The conductive layer can be solid or structured. It can have a grid structure, allowing its mechanical properties to be specifically adjusted. The conductive layer can be made of metal and / or an electrically conductive plastic. It can also be an electrically conductive composite material. Finally, the conductive layer can completely cover the measuring element and / or the connection device.

[0012] The transmission of the measured quantity via the protective coating can be achieved through its elastic, particularly viscoelastic, structure. The measured quantity adjacent to the protective coating can be transmitted to the sensor element via the coating. The protective coating can be incompressible. The protective coating can be made of silicone gel, polyurethane gel, or fluorosilicone gel.

[0013] In a preferred embodiment of the invention, it is advantageous if the conductive layer has a topography adapted to that of the protective coating in the direction of the sensor environment. The topography of the conductive layer can correspond to the topography of the protective coating. The conductive layer can have a substantially constant thickness. This can mean that the thickness variation across the conductive layer is less than 10%. The topography of the protective coating, in turn, can result from the spatial dimensions of the sensor element and other components of the microsensor.

[0014] A preferred embodiment of the invention is advantageous in which the conductive layer is applied to the protective coating by a coating process. The conductive layer is designed as a coating of the protective coating. The conductive layer can be applied by physical vapor deposition (PVD), in particular sputtering, electron beam evaporation, or thermal evaporation. The conductive layer can be applied by autocatalytic metal deposition. The conductive layer can be applied by inkjet printing.

[0015] Accordingly, the invention also relates to a method for producing a conductive layer of the described capacitive microsensor, wherein the conductive layer is applied to the protective coating by inkjet printing as a coating method.

[0016] In an advantageous embodiment of the invention, the conductive layer is at least partially, and in particular completely, exposed to the sensor environment. The conductive layer can therefore be made of a material robust to the medium. The conductive layer can at least partially, and in particular completely, form a contact surface with the sensor environment.

[0017] In a particular embodiment of the invention, it is advantageous if at least one further gel-like protective coating is applied to the side of the conductive layer facing the sensor environment, at least partially, and in particular over the entire surface. This further protective coating can be made of the same or a different material as the protective coating. On the side of this further protective coating facing the sensor environment, an electrically conductive layer can be applied directly, at least partially spanning the sensor element. This further conductive layer can be made of the same or a different material as the conductive layer. This multilayer structure can extend arbitrarily in the direction of the sensor environment.In a specific embodiment of the invention, it is advantageous if the conductive layer has a common electrical ground potential with the housing. This allows the sensor element to be electrically shielded from the sensor environment as efficiently as possible. The conductive layer can be electrically connected to the housing.

[0018] In a specific embodiment of the invention, it is advantageous if the conductive layer is electrically coupled to an electrically conductive coupling structure facing the sensor environment for the detection of foreign material on the microsensor. The conductive layer can form an additional electrical capacitance with the coupling structure. The foreign material can be detected by measuring the dielectric constant or by measuring a change in the dielectric constant of the surrounding medium in the sensor environment. The dielectric constant can influence the additional capacitance and thus be detected.

[0019] The coupling structure can be arranged directly on the protective coating. In a multi-layered structure consisting of a protective coating and a conductive layer, the coupling structure can be arranged in the same layer plane as the conductive layer or in a layer plane offset from it.

[0020] In a preferred embodiment of the invention, it is advantageous if the coupling structure is a further conductive layer spatially separated from the conductive layer and corresponding to the conductive layer. This allows the additional capacitance to be constructed simply and cost-effectively. The further conductive layer can be structured in the same way as the conductive layer.

[0021] In an advantageous embodiment of the invention, the maximum thickness of the protective coating is less than or equal to 25 pm, at least in a region spanning the sensor element, particularly the measuring element. The maximum thickness of the protective coating in this region can also be between 1 pm and 500 pm. In another advantageous embodiment, the average thickness of the conductive layer is less than the average thickness of the protective coating. The conductive layer can have a minimum thickness of 0.1 pm, at least in a region spanning the sensor element. The conductive layer can have a maximum thickness of 0.1 pm, at least in a region spanning the sensor element. The conductive layer can have an average thickness in a range between 0.01 pm and 1 pm.

[0022] Further advantages and advantageous embodiments of the invention will become apparent from the description of the figures and the illustrations.

[0023] Character description

[0024] The invention is described in detail below with reference to the illustrations. These show, in detail:

[0025] Figures 1 and 2: A cross-section of a microsensor in each of a specific embodiment of the invention.

[0026] Figures 3 to 6: A top view of a microsensor, each in a specific embodiment of the invention.

[0027] Figures 1 and 2 show a cross-section of a microsensor, each in a specific embodiment of the invention. Figure 1 shows a capacitive microsensor 10 for measuring a measurand in a sensor environment of the microsensor 10. The microsensor 10 comprises a housing 12 and a sensor element 16, the sensor element 16 being received in an interior 14 of the housing 12. The sensor element 16 has a measuring element 18, the measuring capacitance of which varies depending on the measurand, and a connection device 20 for electrically connecting the measuring element 18.

[0028] The measuring element 18 can have a diaphragm that can be deflected depending on the measured quantity, with the measuring capacitance varying depending on the deflection of the diaphragm. The connection device 20 comprises bond wires 22 between the measuring element 18 and an evaluation electronics unit 24, on which the sensor element 16 is arranged. The evaluation electronics unit 24 is in turn mounted on a substrate 26, on which the housing 12 is attached. The evaluation electronics unit 24 is electrically connected via further bond wires 28 to conductor layers within the substrate 26, which are not visible here.

[0029] The housing 12 can extend in an annular shape around the sensor element 16. A gel-like protective coating 32 is introduced into the interior 14. This coating covers the sensor element 16 on its surface relative to the sensor environment 30, separates it from the sensor environment 30, and mediates the measured quantity between the sensor environment 30 and the sensor element 16. The maximum thickness 34 of the protective coating 32 is less than or equal to 25 pm, at least in a region 36 spanning the measuring element 18.

[0030] On the side 38 of the protective coating 32 facing the sensor environment 30, an electrically conductive layer 40 is applied directly, completely spanning the sensor element 16 and the protective coating 32. This ensures that interference from the sensor environment 30 has as little effect as possible on the measurement of the measured quantity by the sensor element 16.

[0031] The conductive layer 40 is arranged within the housing 12 and is directly exposed to the sensor environment 30. The conductive layer 40 has a topography 44 that is adapted to, and in particular corresponds to, the topography 42 of the protective coating 32. The topography 42 of the protective coating 32 can in turn result from the spatial extent of the sensor element 16 and other components of the microsensor 10.

[0032] The electrical ground potential of the conductive layer 40 and the housing 12 is preferably the same, and the conductive layer 40 is in particular electrically connected to the housing 12.

[0033] The structure in Figure 2 is identical to that in Figure 1 except for the following differences. A gel-like protective coating 48 is applied to the side 46 of the conductive layer 40 facing the sensor environment 30. This additional protective coating 48 is made of the same material as the protective coating 32. The additional protective coating 48 is directly exposed to the sensor environment 30 and forms a contact surface with it.

[0034] Figures 3 to 6 show a top view of a microsensor, each in a specific embodiment of the invention. Figure 3 shows the microsensor 10 with an annular housing 12 and the sensor element 16 located in the interior 14 of the housing 12. The measuring element 18 is electrically connected to the evaluation electronics 24 via the connection device 20, which has bond wires 22. The evaluation electronics 24 are in turn electrically connected to conductor layers within the substrate 26 via further bond wires 28. The conductive layer 40 completely covers an inner surface of the interior 14. The conductive layer 40 and the protective coating located beneath the conductive layer 40 are shown transparently, making the components arranged below, such as the sensor element 16, the substrate 26, the evaluation electronics 24, and the further bond wires 28, visible. The conductive layer 40 is, in particular, designed to cover the entire surface.

[0035] The microsensor 10 in Figure 4 is identical to that in Figure 3 except for the following differences. The conductive layer 40 is structured in strips 50, with the protective coating 32 forming the contact surface to the sensor environment between the strips 50 of the conductive layer 40. This adapted structure of the conductive layer 40 allows the mechanical behavior of the conductive layer 40, particularly with regard to the transmission of the measured quantity from the sensor environment to the sensor element 16, to be adjusted.

[0036] The microsensor 10 from Figure 5 is identical to that from Figure 3 except for the following differences. Here, the conductive layer 40 only covers the sensor element 16 with the measuring element 18 and the connection device 20. This means that in this area 52, the conductive layer 40 forms the contact surface with the sensor environment, while the protective coating 32 located underneath it forms the adjacent contact surface with the sensor environment.

[0037] Figure 6 shows a microsensor 10 identical to that in Figure 5, with the following differences. The connection device 20 is spanned by the conductive layer 40, and the additional bond wires 28 are spanned by a coupling structure 60 designed as a further conductive layer 62. The conductive layer 40 and the further conductive layer 62 can be electrically coupled to detect foreign material on the microsensor 10. For example, the conductive layer 40 and the further conductive layer 62 can form an additional electrical capacitance 58 for detecting foreign material on the surface.

Claims

Patent claims 1. Capacitive microsensor (10) for measuring a measured quantity of a sensor environment (30) of the microsensor (10), comprising a housing (12), a sensor element (16) received in an interior (14) of the housing (12) with a measuring element (18) having at least one measuring capacitance that can be varied depending on the measured quantity and with a connecting device (20) electrically connecting the measuring element (18), a gel-like protective coating (32) which at least partially covers the sensor element (16) with respect to the sensor environment (30) and thereby demarcates it from the sensor environment (30) and allows the measured quantity to be mediated between the sensor environment (30) and the sensor element (16), characterized in that an electrically conductive conductive layer (40) spanning at least partially over the sensor element (16) is applied directly to the side (38) of the protective coating (32) facing the sensor environment (30).

2. Capacitive microsensor (10) according to claim 1 , characterized in that the conductive layer (40) has a topography (44) adapted to the topography (42) of the protective coating (32) in the direction of the sensor environment (30).

3. Capacitive microsensor (10) according to claim 1 or 2, characterized in that the conductive layer (40) is applied to the protective coating (32) by a coating process.

4. Capacitive microsensor (10) according to one of the preceding claims, characterized in that the conductive layer (40) is at least partially directly exposed to the sensor environment (30).

5. Capacitive microsensor (10) according to one of the preceding claims, characterized in that at least one further gel-like protective coating (48) is applied at least sectionally to the side (46) of the conductive layer (40) facing the sensor environment (30).

6. Capacitive microsensor (10) according to one of the preceding claims, characterized in that the conductive layer (40) has a common electrical ground potential with the housing (12).

7. Capacitive microsensor (10) according to one of the preceding claims, characterized in that the conductive layer (40) is electrically coupled to an electrically conductive coupling structure (60) facing the sensor environment (30) for the detection of a foreign material on the microsensor (10).

8. Capacitive microsensor (10) according to claim 7, characterized in that the coupling structure (60) is a further conductive layer (62) corresponding to the conductive layer (40) and spatially separated from the conductive layer (40).

9. Capacitive microsensor (10) according to one of the preceding claims, characterized in that a maximum layer thickness (34) of the protective coating (32) is less than or equal to 25 pm at least in a region (36) spanning the sensor element (16).

10. Method for producing a conductive layer (40) of a capacitive microsensor (10) according to one of the preceding claims, characterized in that the conductive layer (40) is applied to the protective coating (32) by inkjet printing as a coating method.

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