Micromechanical pressure sensor with a sensing capacitance for detecting foreign material

Abstract

The invention relates to a micromechanical pressure sensor (10) for measuring at least one environmental variable of a sensor environment (28), having a sensor unit (12) with at least one membrane (14) which can be deflected in a vertical direction (30) depending on the environmental variable, a first capacitor (16) with at least one first electrode (18) which is deflectably coupled to the membrane (14) and faces the sensor environment (28) and a first counter electrode (32) facing away from the sensor environment (28) and at least one second electrode (22) facing the sensor environment (28), an evaluation unit (36), wherein a sensing capacitor (26) which can be changed by an external material (46) above the membrane (14) is formed between the first and second electrodes (18, 22) and the pressure sensor (10) between a measuring circuit configuration (54),in which the environmental variable is measurable by the evaluation unit (36) depending on the deflection of the membrane (14) and thus at least depending on the first capacitance (16), and a sensor circuit configuration (98) in which an external material (46) above the membrane (14) is detectable by the evaluation unit (36) depending on the sensor capacitance (26), is switchable.

Description

[0001] The invention relates to a micromechanical pressure sensor according to the preamble of claim 1. State of the art

[0002] DE 10 2018 222 758 A1 describes a MEMS sensor with a membrane in which a base area of ​​the membrane is defined by a surrounding wall structure and has deflectable sections. A pair of electrodes is arranged within each section to form respective capacitances. Disclosure of the invention

[0003] According to the present invention, a micromechanical pressure sensor with the features of claim 1 is proposed. This allows foreign material present above the membrane to be detected. The pressure sensor can be constructed cost-effectively. The ambient variable can be measured more accurately and reliably.

[0004] The pressure sensor can be an absolute pressure sensor, in particular a barometric pressure sensor, or a differential pressure sensor. The pressure sensor is preferably a capacitive pressure sensor. The pressure sensor can be a microelectromechanical (MEMS) sensor.

[0005] The ambient variable can be a fluid pressure, in particular a water pressure and / or air pressure, in the sensor's environment. The ambient variable can be a sound pressure, which allows the pressure sensor to act as a microphone.

[0006] The membrane can at least partially span a cavity. The cavity can be sealed from the sensor environment. The cavity can have a fluid pressure that differs from the sensor environment. The fluid pressure in the cavity can be lower than the lowest fluid pressure of the ambient medium to be measured. The cavity can have a vacuum.

[0007] The membrane can be designed separately from the first electrode. The membrane can be designed as a single piece with the first electrode.

[0008] At least the membrane can be at least partially, or in particular completely, covered by a protective layer, in particular a gel layer. This can increase the media robustness of the pressure sensor.

[0009] Foreign material is an undesirable material present above the membrane. The foreign material can be a deposit directly or indirectly on the membrane. The foreign material can be present directly on the membrane or on a protective layer arranged on the membrane.

[0010] The foreign material can be a substance different from the substance that makes up the majority of the sensor environment. If the majority of the sensor environment is air, the foreign material can be water, especially a water droplet. The foreign material can be solid, liquid, or gaseous. The foreign material can be contamination and / or deposits above the membrane. The foreign material can be sand, dust, organic and / or inorganic material.

[0011] The evaluation unit can be implemented as an application-specific integrated circuit (ASIC). The evaluation unit can be electrically connected to at least the first and second capacitors, in particular via electrical bonding connections, for example, bond wires or flip-chip connections.

[0012] The input voltage can be a DC voltage, an AC voltage, or a pulsed voltage. The input voltage in the measuring switching configuration can be the same as or different from the input voltage in the sensing switching configuration. The input voltage in the sensing switching configuration can be a pulsed voltage, in particular a rectangular electrical pulse.

[0013] The second electrode, together with a second counter electrode opposite the second electrode, can form a second capacitance. The second counter electrode can face away from the sensor environment. The second electrode can be deflectably coupled to the membrane or another membrane. The second capacitance can be variable depending on the deflection of the membrane or another membrane. The second electrode can be spaced from the first electrode with respect to a plane having the vertical direction as the normal. The first and second electrodes can be arranged in the same plane.

[0014] The pressure sensor may have a first reference capacitance, comprising at least a first reference electrode and a first reference counter electrode. The first capacitance may be electrically connected in series with the first reference capacitance. The pressure sensor may have a second reference capacitance, comprising at least a second reference electrode and a second reference counter electrode. The second capacitance may be electrically connected in series with a second reference capacitance. The first capacitance, the first reference capacitance, the second capacitance, and the second reference capacitance may be electrically connected in a bridge circuit. The first capacitance may be electrically connected in parallel with the first reference capacitance, the second capacitance, and the second reference capacitance.

[0015] The sensing switching configuration and the measuring switching configuration can be switched alternately. In the sensing switching configuration, the first electrode can be electrically short-circuited to the first counter electrode. In the sensing switching configuration, the second electrode can be electrically short-circuited to the second counter electrode. This can reduce or eliminate the influence of capacitances that vary depending on the ambient size when detecting the foreign material.

[0016] In a preferred embodiment of the invention, it is advantageous if, in the measuring circuit configuration, an electrical input voltage is applied between the first and second electrodes. The input voltage can be applied via the first capacitance and the first reference capacitance electrically connected in series therewith. The input voltage can be applied via the second capacitance and the second reference capacitance electrically connected in series therewith.

[0017] In a specific embodiment of the invention, it is advantageous if at least one first switching element is arranged and configured to electrically isolate the second electrode from a potential of the input voltage in the sensing switching configuration. The electrical connection between the second electrode and the potential of the input voltage can be interrupted by the open first switching element. Regardless of the switching position of the first switching element, the counter potential of the input voltage can be applied to the first electrode.

[0018] In a specific embodiment of the invention, it is advantageous if, in the measurement circuit configuration, a first electrical output connection is established between the first counter electrode and the evaluation unit. The first output connection can output an electrical output signal to the evaluation unit. The output signal can be dependent at least on the input voltage and the first capacitance, in particular also on the second capacitance.

[0019] In a specific embodiment of the invention, it is advantageous if at least one second switching element is arranged and configured to electrically disconnect the first output connection in the sensing switching configuration. The first output connection can be interrupted when the second switching element is open. The second switching element can electrically disconnect the first counter electrode from the evaluation unit. Furthermore, the second switching element can electrically disconnect the first reference electrode from the evaluation unit.

[0020] In a preferred embodiment of the invention, the first output connection is electrically shielded from the sensor environment by the membrane, the first electrode, and / or the second electrode. The membrane can be constructed of a metal.

[0021] In a specific embodiment of the invention, it is advantageous if, in the sensing switching configuration, an excitation signal is applied to the first electrode, and an output signal generated by this signal and dependent on the sensing capacitance is detectable by the evaluation unit at the second electrode. The input voltage can be formed by the excitation signal or comprise the excitation signal.

[0022] A preferred embodiment of the invention is advantageous in which the first and second electrodes are arranged side by side with respect to a plane having the vertical direction as the normal. The first and second electrodes can have at least one identical or different dimension with respect to the plane.

[0023] In a specific embodiment of the invention, it is advantageous if the first counterelectrode is arranged vertically below the first electrode and / or the second counterelectrode is arranged vertically below the second electrode. The first electrode and the first counterelectrode can be completely spanned by the membrane. The second electrode and the second counterelectrode can be completely spanned by the membrane.

[0024] In a specific embodiment of the invention, it is advantageous if the sensing capacitance is directly electrically variable to a greater extent due to the foreign material than the first and / or second capacitance. This allows the foreign material to have a lesser direct electrical influence on the first and second capacitance when measuring the ambient variable. An indirect electrical influence of the foreign material on the first and second capacitance can arise via the deflection of the membrane influenced by the foreign material, which influences the capacitance of the first and second capacitance.

[0025] Further advantages and advantageous embodiments of the invention emerge from the description of the figures and the illustrations. Character description

[0026] The invention is described in detail below with reference to the figures. They show in detail: Fig. 1: A top view of a micromechanical pressure sensor in a specific embodiment of the invention. Fig. 2: A cross-section of a micromechanical pressure sensor in another specific embodiment of the invention. Fig. 3: A circuit diagram of a micromechanical pressure sensor in another specific embodiment of the invention in a measuring circuit configuration. Fig. 4: A circuit diagram of a micromechanical pressure sensor in another specific embodiment of the invention in a sensing switching configuration.

[0027] Fig. 1 shows a plan view of a micromechanical pressure sensor in a specific embodiment of the invention. The micromechanical pressure sensor 10 for measuring at least one ambient variable of a sensor environment comprises a sensor unit 12 with a membrane 14 that can be deflected in a vertical direction depending on the ambient variable, a first capacitor 16 having a first electrode 18 deflectably coupled to the membrane 14 and facing the sensor environment, a further membrane 15 that can be deflected in the vertical direction depending on the ambient variable, and a second capacitor 20 arranged next to the first capacitor 16 with respect to a plane having the vertical direction as a normal (here, the page plane), having a second electrode 22 facing the sensor environment.

[0028] The first and second capacitors 16, 20 can be electrically connected by connection surfaces 24, for example bond pads.

[0029] Between the first and second electrodes 18, 22, a sensing capacitance 26 is formed which is variable by a foreign material above the membrane 14.

[0030] Fig. Figure 2 shows a cross-section of a micromechanical pressure sensor in another specific embodiment of the invention. In addition to the first electrode 18 facing the sensor environment 28, the first capacitance 16 comprises a first counter electrode 32 arranged vertically 30 below the first electrode 18. The first electrode 18 is movable relative to the fixed first counter electrode 32 depending on the deflection of the membrane 14, which is integral with the first electrode 18. As a result, the first capacitance 16 is variable depending on the deflection of the membrane 14.

[0031] In addition to the second electrode 22 facing the sensor environment 28, the second capacitance 20 comprises a second counter electrode 34 arranged in the vertical direction 30 below the second electrode 22. The second electrode 22 is movable relative to the fixed second counter electrode 34 depending on the deflection of the further membrane 15, which is integral with the second electrode 22. As a result, the second capacitance 20 is variable depending on the deflection of the further membrane 15.

[0032] The sensor unit 12 is arranged on an evaluation unit 36 ​​and surrounded by a protective layer 38, in particular gel. The evaluation unit 36 ​​is held on a substrate 42 by a connecting layer 40, in particular an adhesive layer, and, together with the sensor unit 12, is surrounded by a housing 44 attached to the substrate 42.

[0033] A foreign material 46 present above the membrane 14 and the further membrane 15, here for example water, influences the sensing capacity 26 between the first and second electrodes 18, 22.

[0034] The first electrode 18 and the first counter electrode 32, as well as the second electrode 22 and the second counter electrode 34, are each electrically connected via vertical vias 48. The first counter electrode 32 is electrically connected to the evaluation unit 36 ​​via a first output connection 50. The second counter electrode 34 is electrically connected to the evaluation unit 36 ​​via a second output connection 52. The first and second output connections 50, 52 are electrically shielded from the sensor environment 28 by the first electrode 18 and the second electrode 22 and are therefore less sensitive to external influences of the sensor environment 28.

[0035] Fig. Figure 3 shows a circuit diagram of a micromechanical pressure sensor in a further specific embodiment of the invention in a measuring circuit configuration. The pressure sensor 10 is depicted in a measuring circuit configuration 54, in which the ambient variable can be measured by the evaluation unit 36 ​​as a function of the deflection of the diaphragm and thus as a function of the first capacitance 16 and the second capacitance 20.

[0036] The first capacitor 16 is electrically connected in series with a first reference capacitor 56, comprising a first reference electrode 58 and a first reference counter electrode 60. The first reference electrode 58 and the first reference counter electrode 60 are fixed. The second capacitor 20 is electrically connected in series with a second reference capacitor 62, comprising a second reference electrode 64 and a second reference counter electrode 66. The second reference electrode 64 and the second reference counter electrode 66 are fixed.

[0037] The first capacitance 16 and the first reference capacitance 56 are electrically connected in parallel together with the second capacitance 20 and the second reference capacitance 62.

[0038] In the measuring circuit configuration 54, the first capacitance 16, the first reference capacitance 56, the second capacitance 20 and the second reference capacitance 62 are electrically connected in a bridge circuit 68, in which an electrical input voltage 72 is applied to the bridge circuit 68 by a closed first switching element 70, that is to say between the first electrode 18 of the first capacitance 16 and the first reference counter electrode 60 of the first reference capacitance 56, between the second reference counter electrode 66 of the second reference capacitance 62 and the second electrode 22 and by the parallel connection of the first capacitance 16 and the first reference capacitance 56 with the second capacitance 20 and the second reference capacitance 62 between the first and second electrodes 18, 22.

[0039] The electrical first output connection 50 is formed by a closed second switching element 76 between the first counter electrode 32 and the evaluation unit 36, and an electrical second output connection 52 is formed by a closed third switching element 80 between the second counter electrode 34 and the evaluation unit 36. The first and second output connections 50, 52 output the electrical output signal, which depends on the ambient variable due to the change in the first capacitance 16 and the second capacitance 20, to the evaluation unit 36, which comprises, for example, an amplifier 82, a downstream analog-to-digital converter 84, and a digital filter 86.

[0040] A direct electrical connection between a potential of the input voltage 72 and the evaluation unit 36 ​​is interrupted by a fourth switching element 88. Furthermore, a direct electrical connection between the first output connection 50 and an electrical ground connection 90 is interrupted by a fifth switching element 92, and a direct electrical connection between the second output connection 52 and an electrical ground connection 94 is interrupted by a sixth switching element 96.

[0041] Fig. Figure 4 shows a circuit diagram of a micromechanical pressure sensor in a further specific embodiment of the invention in a sensing switch configuration. The pressure sensor 10 is depicted in a sensing switch configuration 98, in which a foreign material above the membrane can be detected depending on the sensing capacitance 26.

[0042] An electrical connection between the second electrode 22 and a potential of the input voltage 72 is interrupted by the open first switching element 70. The first reference counter electrode 60 and the second electrode 22 are electrically connected directly to the evaluation unit 36 ​​by the closed fourth switching element 88.

[0043] The first output connection 50 is electrically isolated by the open second switching element 76, thus interrupting a direct electrical connection between the first counter electrode 32 and the evaluation unit 36, as well as between the first reference electrode 58 and the evaluation unit 36. The second output connection 52 is electrically isolated by the open third switching element 80, thus interrupting a direct electrical connection between the second counter electrode 34 and the evaluation unit 36, as well as between the second reference electrode 64 and the evaluation unit 36.

[0044] The first counter electrode 32 and the first reference electrode 58 are electrically connected to the ground terminal 90 by the closed fifth switching element 92. The second counter electrode 34 and the second reference electrode 64 are electrically connected to the ground terminal 94 by the closed sixth switching element 96.

[0045] The input voltage 72 can be an excitation signal 100, in particular a pulsed voltage, in particular a rectangular electrical pulse, which is applied to the first electrode 18. An output signal generated therefrom and dependent on the sensing capacitance 26 can be detected at the second electrode 22 by the closed fourth switching element 88 by the evaluation unit 36.

[0046] The sensing capacitance 26 is more variable due to the foreign material than the first and second capacitances 16, 20, whereby the foreign material can be detected more accurately in the sensing switching configuration 98 and the direct electrical influence of the foreign material on the first and second capacitances 16, 20 can be reduced in the measuring switching configuration. 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] DE 10 2018 222 758 A1

[0002]

Claims

[1] Micromechanical pressure sensor (10) for measuring at least one environmental variable of a sensor environment (28), comprising a sensor unit (12) with at least one membrane (14) which can be deflected in a vertical direction (30) depending on the environmental variable, a first capacitor (16) comprising at least one first electrode (18) which is deflectably coupled to the membrane (14) and faces the sensor environment (28), and a first counter electrode (32) facing away from the sensor environment (28), and at least one second electrode (22) facing the sensor environment (28), an evaluation unit (36), characterized by , that a sensing capacitance (26) which is variable and is formed by a foreign material (46) above the membrane (14) is formed between the first and second electrodes (18, 22) and the pressure sensor (10) can be switched between a measuring switching configuration (54), in which the ambient variable can be measured by the evaluation unit (36) depending on the deflection of the membrane (14) and thus at least depending on the first capacitance (16), and a sensing switching configuration (98), in which a foreign material (46) above the membrane (14) can be detected by the evaluation unit (36) depending on the sensing capacitance (26). [2] Micromechanical pressure sensor (10) according to claim 1, characterized by that in the measuring switching configuration (54) an electrical input voltage (72) is applied between the first and second electrodes (18, 22). [3] Micromechanical pressure sensor (10) according to claim 2, characterized by that at least one first switching element (70) is arranged and configured to electrically separate the second electrode (22) from a potential of the input voltage (72) in the sensing switching configuration (98). [4] Micromechanical pressure sensor (10) according to one of the preceding claims, characterized by that in the measuring switching configuration (54) an electrical first output connection (50) is established between the first counter electrode (32) and the evaluation unit (36). [5] Micromechanical pressure sensor (10) according to claims 3 and 4, characterized by that at least one second switching element (76) is arranged and configured to electrically disconnect the first output connection (50) in the sensing switching configuration (98). [6] Micromechanical pressure sensor (10) according to claim 4 or 5, characterized by that the first output connection (50) is electrically shielded from the sensor environment (28) by the membrane (14), the first electrode (18) and / or the second electrode (22). [7] Micromechanical pressure sensor (10) according to one of the preceding claims, characterized bythat in the sensing switching configuration (98) an excitation signal (100) is applied to the first electrode (18) and an output signal generated thereabove and dependent on the sensing capacitance (26) can be detected at the second electrode (22) by the evaluation unit (36). [8] Micromechanical pressure sensor (10) according to one of the preceding claims, characterized by that the first and second electrodes (18, 22) are arranged next to one another with respect to a plane having the vertical direction (30) as a normal. [9] Micromechanical pressure sensor (10) according to one of the preceding claims, characterized by that the first counter electrode (32) is arranged below the first electrode (18) with respect to the vertical direction (30) and / or the second counter electrode (34) is arranged below the second electrode (22) with respect to the vertical direction (30). [10] Micromechanical pressure sensor (10) according to one of the preceding claims, characterized bythat the sensing capacitance (26) is electrically directly more variable due to the foreign material (46) than the first and / or second capacitance (16, 20).

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