Micromechanical pressure sensor

Abstract

The invention relates to a micromechanical pressure sensor (1) having two MEMS chips (2, 3) each having at least one pressure-sensitive membrane (4, 5), wherein the two MEMS chips (2, 3) are arranged in a stacked arrangement and the membranes (4, 5) are deflected in opposite directions by an action of force to be measured. The force of gravity acts on the membranes (4, 5) in the same direction such that an influence of the effect of gravity on the measurement result is at least partially compensated.

Description

[0001] Description

[0002] title

[0003] Micromechanical pressure sensor

[0004] The invention relates to a micromechanical pressure sensor with MEMS chips of different orientation.

[0005] State of the art

[0006] Micromechanical sensor devices, e.g., a silicon-based micromechanical pressure sensor device with an ASIC chip and a MEMS chip, are often protected against aggressive environmental conditions and / or moisture or water, for example, with a gel. The pressure to be measured is usually detected by a pressure-sensitive membrane of a MEMS chip. However, a protective gel on this membrane increases the total mass acting on the pressure sensor membrane of the sensor device and thus also causes interference. In particular, any acceleration effect, and especially gravity, acts as a disturbance on the sensor device.

[0007] Sensor arrangements with multiple MEMS chips are known in the state of the art, usually with the aim of minimizing the space required for the resulting overall sensor device.

[0008] From the publication DE 10 2010 039 057 B4, a stacked arrangement of sensor substrates is known, which provides an improved solution for a sensor module with a small footprint. Disclosure of the invention

[0009] The invention is based on the object of compensating for an acceleration effect and especially also the effect of gravity as a disturbance variable on the membrane of a micromechanical pressure sensor device.

[0010] This problem is solved with a micromechanical pressure sensor having the features of the independent patent claim. Advantageous further developments are specified in the dependent claims.

[0011] A micromechanical pressure sensor according to the invention comprises at least two MEMS chips, each with at least one pressure-sensitive membrane. The two MEMS chips are arranged in a stacked configuration. The two MEMS chips are arranged such that the membranes are deflected in opposite directions by the application of a force to be measured.

[0012] The definition of the respective directions should be understood as being defined by a reference system that is, in principle, arbitrary but fixed and refers to the entire micromechanical pressure sensor with the two MEMS chips. For example, a perpendicular to the plane of the membranes could be such a direction.

[0013] In one embodiment, the MEMS chips are arranged so that the substrates of the MEMS chips are oriented outward and the membranes are located in a cavity between the substrates. The cavity is connected to the environment via an opening, and the force to be measured on the membranes takes place within the cavity.

[0014] The membranes of MEMS chips are usually spanned within a surrounding substrate, so that a substrate edge region exists in the same plane as the membranes, and a vacuum cavity formed by the substrate is located below the membranes. In other words, if one considers the membrane side of the MEMS chip as the top side and the continuous substrate side of the MEMS chips as the bottom side, then in this embodiment of the micromechanical pressure sensor, the two top sides of the MEMS chips are assigned to each other and the bottom sides face outwards. The pressure to be measured from any fluid medium, such as air, can penetrate through the opening into the space between the membranes, and the deflection occurs in opposite directions due to the mutually facing arrangement of the membranes.However, an undesired deflection of the membranes, for example due to an acceleration acting on the entire assembly, acts on both membranes in the same direction, so this influence can be compensated. To achieve this, the sensitivity of the respective membranes with respect to the pressure effect should differ only slightly, preferably by less than 10%, more preferably by less than 1%.

[0015] In one embodiment, the cavity is filled with a protective layer, wherein the protective layer is incompressible and flexible. In particular, the protective layer can be formed from a silicon-based gel. To protect against aggressive environmental conditions, it may be necessary to provide the membranes of the MEMS chips or even the entire MEMS chips, including a chip containing the readout circuit, with a protective layer. The protective layer is preferably incompressible and sufficiently flexible to immediately conduct pressure to the membranes. The protective layer can be a gel or a liquid, but oils or oil foams are also conceivable. The material is preferably selected so that no MEMS components are damaged and that it is robust against occurring environmental aggressors.

[0016] In one embodiment, the MEMS chips can be at least partially covered with a protective layer (e.g. a gel) to protect the sensor and in particular a membrane of the sensor against aggressive environmental influences and / or moisture or water. This protective layer acts as an additional mass on the pressure sensor membrane. When at rest, the protective layer presses on the membrane. If the user turns the device with the pressure sensor by 180°, the protective layer pulls on the membrane, generating an interference signal. Due to the arrangement of the MEMS chips, the aforementioned effect of gravity on the two membranes occurs in the same direction. The protective layer presses on the membrane of the lower MEMS chip and pulls on the membrane of the upper MEMS chip, so that the influence of gravity on the measurement result is at least partially compensated. The protective layer can comprise a gel or be designed as a gel.The protective layers can completely cover the membranes.

[0017] Depending on the chosen design, the complete structure within the package, i.e. MEMS chips and evaluation circuit and bond wires and substrate, can be covered with a protective layer, in particular with a gel.

[0018] In one embodiment, the substrates of the MEMS chips are arranged facing each other, so that the membranes are oriented outward, and the membranes are at least partially coated with a protective layer against aggressive environmental conditions and / or against moisture and / or water. Preferably, the membranes are completely covered with a protective layer, in particular with a gel. In a view as described above, in which the continuous substrate side of the MEMS chips is considered the underside and the membrane side the top side, in this embodiment, the two undersides of the MEMS chips face each other, and the top sides with the membranes are oriented outward.

[0019] In one embodiment, spacers are arranged between the substrates of the MEMS chips in an edge region next to the membranes, such that the cavity between the membranes is enlarged. If the membranes of the MEMS chips are arranged in a plane with the substrate edge region, in the embodiment of the micromechanical pressure sensor in which the two upper sides of the MEMS chips face each other, the cavity between the two membranes can be very narrow or flat. In order to enlarge this cavity, spacers can be arranged in the substrate edge region. In one embodiment, the membranes are designed to be deeper in relation to an edge region of a surrounding substrate plane of the MEMS chips, such that the cavity between the membranes is enlarged.

[0020] In one embodiment, the MEMS chips are directly connected to each other; this connection of the MEMS chips can be formed as a wafer bond connection.

[0021] In one embodiment, electrical connecting lines are routed from at least one MEMS chip to an evaluation circuit, and the electrical connecting lines are covered with a protective layer. Advantageously, at least one, preferably both MEMS chips, are at least partially covered with the protective layer.

[0022] In one embodiment, one of the MEMS chips is arranged at least partially on a carrier. The carrier can have an evaluation circuit or be connected to an evaluation chip with an evaluation circuit. The evaluation circuit can be connected to at least one Wheatstone half-bridge, in particular one or two Wheatstone bridges. The two MEMS chips can be read in parallel or sequentially.

[0023] Embodiments of the invention are explained with reference to the following drawings. The drawings show:

[0024] Fig. 1 is a schematic representation of an embodiment of a micromechanical pressure sensor,

[0025] Fig. 2 is a schematic representation of another embodiment of a micromechanical pressure sensor,

[0026] Fig. 3 is a schematic diagram of a MEMS chip circuit, and

[0027] Fig. 4 is a schematic representation of a further MEMS chip circuit Fig. 1 schematically shows a micromechanical pressure sensor 1 with a first MEMS chip 2 with a pressure-sensitive membrane 4 and a surrounding substrate 6, and a second MEMS chip 3 with a pressure-sensitive membrane 5 and a surrounding substrate 7. The two MEMS chips 2, 3 are stacked so that the substrates 6, 7 are oriented outwards and the membranes 4, 5 are located in a cavity 8 between the substrates 6, 7. The cavity 8 is connected to the environment via an opening 9 such that a pressure of a fluid medium to be measured can pass through the opening 9 into the cavity 8 and act on the membranes 4, 5. The force to be measured due to the pressure and thus a deflection of the membranes 4, 5 occurs in opposite directions - in the example membrane 4 upwards and membrane 5 downwards.The effect of gravity on the membranes 4, 5 - or an accelerated movement of the micromechanical pressure sensor 1 - acts on the entire pressure sensor 1 in the same direction, so that an influence of gravity on the measurement result can be at least partially compensated.

[0028] The cavity 8 can be filled with a protective layer (not shown here, see Figure 2), whereby the protective layer can be incompressible and flexible so as not to distort the pressure effect on the membranes 4, 5. Such a protective layer increases the effective mass on which acceleration can act, thus preventing undesired influences on the pressure measurement result. Alternatively, the opening 9 can be sealed against environmental influences with a foam or a venting membrane (e.g., made of ePTFE), whereby the external pressure is still transmitted into the cavity 8.

[0029] The membranes 4, 5 can be configured to be lower relative to an edge region 11 of a surrounding substrate plane of the MEMS chips 2, 3, so that the cavity 8 between the membranes 4, 5 is enlarged, which is indicated in the figure by a curvature of the membranes 4, 5. Alternatively or additionally, spacers (not shown) can be arranged in the edge region 11 to enlarge the cavity 8. The connection of the MEMS chips 2, 3, in particular in the edge regions 11, can be formed as a wafer bond connection 17.

[0030] For electrically connecting the MEMS chips 2, 3 to an evaluation circuit 16, the first MEMS chip 2 can have first electrical sensor lines 13, wherein the first sensor lines 13 are routed to a surface of the first MEMS chip 2, wherein the first sensor lines 13 are connected to electrical lines 14 of the second MEMS chip 3, wherein the electrical lines 14 of the second MEMS chip 3 are provided for a connection 15 to an evaluation circuit 16. Advantageously, the MEMS chips 2, 3 can have a common supply of supply voltages and ground potential, for example, in the region where the first sensor lines 13 and the electrical lines 14 join.

[0031] The second MEMS chip 3 is mechanically mounted on a carrier 30—for example, by an adhesive bond 31. The carrier 30 can have the evaluation circuit 16 or be connected to an evaluation chip with an evaluation circuit. A thermally conductive silicone material can be used for the adhesive bond 31.

[0032] A common evaluation circuit 16, for example with an ASIC, can be provided for both MEMS chips 2, 3. The MEMS chip 2 and the second MEMS chip 3 can be alternately connected to the evaluation electronics via a switch. The evaluation circuit 16 can be connected to a Wheatstone bridge, with the analog output of the Wheatstone bridge being connected, for example, via a switch to an LNA (low noise amplifier), with the LNA being connected to a digital signal processor (DSP) via an analog-to-digital converter (ADC). By comparing the measurement results of the first MEMS chip 2 and the second MEMS chip 3, it is possible to conclude whether a measurement error due to an acceleration effect is present.

[0033] Fig. 2 shows a micromechanical pressure sensor 1 in which the substrates 6, 7 of the MEMS chips 2, 3 are arranged facing each other, so that the membranes 4, 5 are oriented outwards. The force to be measured due to the external pressure and thus a deflection of the membranes 4, 5 occurs in opposite directions - in the example, membrane 4 downwards and membrane 5 upwards. The effect of gravity on the membranes 4, 5 - or an accelerated movement of the micromechanical pressure sensor 1 - acts on the entire pressure sensor 1 in the same direction, as indicated by the black arrows on the left of the figure. By comparing the measurement results of the first MEMS chip 2 and the second MEMS chip 3, the influence of gravity on the measurement result can be at least partially compensated.

[0034] The membranes 4, 5 of the MEMS chips 2, 3 are coated with a protective layer 10 to protect them from aggressive environmental conditions. The electrical leads 26 and the electrical contacts 27, as well as parts of the evaluation circuit 16, are also coated with the protective layer 10. A sealing gasket 12 is arranged between the substrates 6, 7.

[0035] The second MEMS chip 3 is arranged at least partially on a carrier 30 via a connection 31, wherein the carrier 30 can have the evaluation circuit or is connected to an evaluation chip with evaluation circuit.

[0036] The first MEMS chip 2 is arranged with a bottom side 22 on a first region 24 of a bottom side 23 of the second MEMS chip 3, wherein the first electrical sensor lines 13 are routed to the bottom side 22 of the first MEMS chip 2, wherein the electrical lines 14 of the second MEMS chip 3 are routed to the bottom side 23 of the further MEMS chip 3 in the first region 24. The first electrical sensor lines 13 are electrically conductively connected via contact surfaces to the electrical lines 14 in the first region 24 of the bottom side 23 of the second MEMS chip 3. A second region 25 is arranged laterally next to the first region 24 on the bottom side 23 of the second MEMS chip 3. In the second region 25, electrical contacts 27 are provided for connecting further electrical lines 26. The further electrical lines 26 are routed to the electrical contacts 27 and conductively connected to the electrical contacts 27.The first sensor lines 13 can have first vias 18, which are routed from a top side 20 of the first MEMS chip 2 to a bottom side 22 of the first MEMS chip 2. The electrical lines 14 can have second vias 19, which are routed from a top side 21 of the second MEMS chip 3 to a bottom side 23 of the second MEMS chip 3. The second MEMS chip 3 can have further vias 28, which are arranged laterally next to the first region 24 of the bottom side 23 of the second MEMS chip 3 and are routed from a bottom side 23 to a top side 21 of the second MEMS chip 3.The second MEMS chip 3 can have a rewiring 26 on its underside 23, which connects the second vias 19 to the further vias 28, and wherein the further vias 28 are connected to the electrical contacts on the top side 21 of the second MEMS chip 3 or represent the electrical contacts.

[0037] Fig. 3 shows a schematic representation of the internal circuitry of the MEMS chips, here in a configuration with two Wheatstone bridges. Two sensor membranes 4 and 34 are schematically arranged in one Wheatstone bridge, and two further sensor membranes 5 and 35 are arranged in another Wheatstone bridge. The Wheatstone bridges have sensor outputs 40, 42 and 41, 43. To evaluate the sensors, the signals from sensor outputs 40, 42 and sensor outputs 41, 43 are compared. Two to four membranes can be provided per MEMS chip, which can also be connected in a Wheatstone bridge.

[0038] The sensor membranes 4 and 34 can be integrated in the first MEMS chip 2, and the additional sensor membranes 5 and 35 can be integrated in the second MEMS chip 3. To increase sensitivity, two sensor membranes are used per MEMS chip, so that in this embodiment, two standard MEMS chips can be used. The MEMS chips are arranged as shown in Figs. 1 and 2, so that the representation as in Figs. 1 and 2 is used twice here, so to speak. This increases the accuracy of the measurement and reduces costs by using standard components. Advantageously, the stacked arrangement allows the supply voltage 32, 33 and the ground potential 36 to be used together. Fig. 4 shows a schematic representation of another evaluation circuit in which the sensor membranes 4 and 5 are arranged in a Wheatstone bridge 45.This results in an even more compact design of the micromechanical pressure sensor, but places greater demands on the similarity of the technical properties of the sensor membranes. Any covering with a protective layer must also be virtually identical in thickness and properties for both sensor membranes.

[0039] However, in this embodiment, the compensation of an undesirable effect of gravity or acceleration is advantageously already carried out on the analog level.

Claims

Claims 1. Micromechanical pressure sensor (1) with two MEMS chips (2, 3) each having at least one pressure-sensitive membrane (4, 5), wherein the two MEMS chips (2, 3) are arranged in a stacked arrangement and a deflection of the membranes (4, 5) occurs in opposite directions due to a force to be measured, wherein an effect of gravity on the membranes (4, 5) occurs in the same direction, so that an influence of the effect of gravity on the measurement result is at least partially compensated.

2. Micromechanical pressure sensor (1) according to claim 1, wherein the membranes (4, 5) of the MEMS chips (2, 3) are at least partially, in particular completely, covered with a protective layer (10), wherein the protective layer (10) is in particular incompressible and flexible, in particular comprising a gel.

3. Micromechanical pressure sensor (1) according to one of the preceding claims, wherein the MEMS chips (2, 3) are arranged such that substrates (6, 7) of the MEMS chips (2, 3) are oriented outwards and the membranes (4, 5) are located in a cavity (8) between the substrates (6, 7), wherein the cavity (8) is connected to the environment via an opening (9) and wherein the force to be measured on the membranes (4, 5) takes place within the cavity (8).

4. Micromechanical pressure sensor (1) according to claim 3, wherein the cavity (8) is filled with a protective layer (10), wherein the protective layer (10) is designed in particular to be incompressible and flexible, in particular being formed from a silicon-based gel.

5. Micromechanical pressure sensor (1) according to claim 1 or 2, wherein the substrates (6, 7) of the MEMS chips (2, 3) are arranged facing each other, so that the membranes (4, 5) are oriented outwards and the membranes (4, 5) are at least partially covered with a protective layer (10).

6. Micromechanical pressure sensor (1) according to claim 3 or 4, wherein spacers are arranged between the substrates (6, 7) of the MEMS chips (2, 3) in an edge region (11) next to the membranes (4, 5), so that the cavity (8) between the membranes (4, 5) is enlarged.

7. Micromechanical pressure sensor (1) according to one of claims 3 or 4, wherein the membranes (4, 5) are designed to be lower in relation to an edge region (11) of a surrounding substrate plane of the MEMS chips (2, 3), so that the cavity (8) between the membranes (4, 5) is enlarged.

8. Micromechanical pressure sensor (1) according to one of the preceding claims, wherein the connection of the MEMS chips (2, 3) is formed as a wafer bond connection.

9. Micromechanical pressure sensor (1) according to claim 5, wherein a sealing gasket (12) is arranged between the substrates (6, 7).

10. Micromechanical pressure sensor (1) according to one of the preceding claims, wherein the first MEMS chip (2) has first electrical sensor lines (13), wherein the first sensor lines (13) are guided to a surface of the first MEMS chip (2), wherein the first sensor lines (13) are connected to electrical lines (14) of the second MEMS chip (3), wherein the electrical lines (14) of the second MEMS chip (3) are provided for a connection (15) to an evaluation circuit (16).

11. Micromechanical pressure sensor (1) according to claim 5, wherein the first MEMS chip (2) is arranged with a bottom side (22) on a first region (24) of a bottom side (23) of the second MEMS chip (3), wherein the first electrical sensor lines (13) are led to the bottom side (22) of the first MEMS chip (2) wherein the electrical lines (14) of the second MEMS chip (3) are guided to the underside (23) of the second MEMS chip (3) in the first region (24), wherein the first electrical sensor lines (13) are electrically conductively connected via contact surfaces to the electrical lines (14) in the first region (24) of the underside (23) of the second MEMS chip (3), wherein a second region (25) of the underside of the second MEMS chip (3) is arranged laterally next to the first region (24), wherein electrical contacts (27) for connecting further electrical lines (26) are provided in the second region (25), and wherein the further electrical lines (26) are guided to the electrical contacts (27) and are conductively connected to the electrical contacts (27).

12. The micromechanical pressure sensor (1) according to claim 11, wherein the first sensor lines (13) have vias that are routed from a top side (20) of the first MEMS chip (2) to a bottom side (22) of the first MEMS chip, wherein the electrical lines (14) have second vias that are routed from a top side (21) of the second MEMS chip (3) to a bottom side (23) of the second MEMS chip (3), wherein the second MEMS chip (3) has further vias (28) that are arranged laterally next to the first region (24) of the bottom side (23) of the second MEMS chip (3) and are routed from a bottom side (23) to a top side (21) of the second MEMS chip (3), wherein the second MEMS chip (3) has a rewiring (26) on a bottom side (23) that connects the second vias to the further vias,and wherein the further vias (28) are connected to the electrical contacts on the top side (21) of the second MEMS chip (3) or represent the electrical contacts., 13. Micromechanical pressure sensor (1) according to one of the preceding claims, wherein one of the MEMS chips (2, 3) is arranged at least partially, in particular completely, on a carrier (30), and wherein the carrier (30) has the evaluation circuit or is connected to an evaluation chip with evaluation circuit.

14. Micromechanical pressure sensor (1) according to one of claims 12 or 13, wherein electrical connecting lines (26) are led from a MEMS chip to the evaluation circuit, wherein the electrical connecting lines are covered with a protective layer, and wherein in particular at least one, preferably both MEMS chips (2, 3) are at least partially connected to the protective layer.

15. Micromechanical pressure sensor (1) according to one of the preceding claims, with an evaluation circuit, wherein the evaluation circuit is provided with at least one Wheatstone half bridge, in particular one or two Wheatstone bridges.

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