Micromechanical pressure sensor

Abstract

A micromechanical pressure sensor (1) having two MEMS chips (2, 3) each having at least one pressure-sensitive diaphragm (4, 5), wherein the two MEMS chips (2, 3) are arranged in a stacked arrangement and the diaphragms (4, 5) are deflected in opposite directions as a result of the force to be measured. The effect of gravity on the diaphragms (4, 5) occurs in the same direction, so that the influence of the effect of gravity on the measurement result is at least partially compensated.

Description

Technical Field

[0001] This invention relates to a micromechanical pressure sensor for MEMS chips with different orientations. Background Technology

[0002] Micromechanical sensor devices, such as silicon-based micromechanical pressure sensor devices with ASIC chips and MEMS chips, are typically protected, for example, with gel to prevent corrosive environmental conditions and / or moisture or water. Here, the pressure to be measured is typically detected by a pressure-sensitive diaphragm of the MEMS chip. However, the protective gel on the diaphragm increases the total mass acting on the pressure sensor diaphragm of the sensor device, and thus also introduces interference effects on the pressure sensor diaphragm. In particular, any acceleration effect, especially gravity, acts as a interference variable on the sensor device.

[0003] Sensor assemblies with multiple MEMS chips are known in the prior art, which is usually intended to minimize the space requirements of the resulting total sensor device.

[0004] The arrangement of overlapping sensor substrates is known from document DE 10 2010 039 057 B4, which provides an improved solution for sensor modules with small space requirements. Summary of the Invention

[0005] The present invention is based on the objective of compensating for the acceleration effect on the diaphragm of a micromechanical pressure sensor device as an interference variable, and in particular, the effect of gravity.

[0006] This task is accomplished by a micromechanical pressure sensor having the features of the independent claim. Advantageous extensions are given in the dependent claims.

[0007] The micromechanical pressure sensor according to the present invention has at least two MEMS chips, each MEMS chip having at least one pressure-sensitive diaphragm, wherein the two MEMS chips are arranged in a stacked manner. The two MEMS chips are arranged such that the diaphragm is offset in opposite directions due to the force to be measured.

[0008] The definitions of each direction should be understood as follows: these directions are defined by a reference frame that is, in principle, arbitrary but fixed, relating to the entire micromechanical pressure sensor with the two MEMS chips. For example, a perpendicular line on the diaphragm plane could be such a direction.

[0009] In one embodiment, the MEMS chip is arranged such that the substrate of the MEMS chip is oriented outward and the diaphragm is located in a cavity between the substrates. The cavity is connected to the surrounding environment through an opening, and the force to be measured on the diaphragm occurs within the cavity.

[0010] The diaphragms of a MEMS chip are typically tensioned within a surrounding substrate, resulting in a substrate edge region in the plane containing the diaphragm and a vacuum cavity formed by the substrate beneath the diaphragm. In other words, if the diaphragm side of the MEMS chip is considered the upper side and the coherent substrate side of the MEMS chip is considered the lower side, then in this embodiment of the micromechanical pressure sensor, the two upper sides of the MEMS chip are adjacent to each other, while the lower side faces outwards. Through this opening, the pressure of any fluid medium to be measured, such as air, can enter the space between the diaphragms, and due to the diaphragms' facing arrangement, a reversal occurs. However, undesirable diaphragm shifts, such as those caused by acceleration acting on the entire assembly, act on both diaphragms in the same direction, allowing this effect to be compensated for. For this purpose, the sensitivity of the corresponding diaphragms to pressure should have only a small difference, preferably less than 10%, more preferably less than 1%.

[0011] In one embodiment, the cavity is filled with a protective layer, wherein the protective layer is configured to be incompressible and flexible. In particular, the protective layer may be composed of a silicon-based gel. To prevent corrosive environmental conditions, it may be necessary to provide a protective layer for the diaphragm of a MEMS chip, or for the entire MEMS chip including the chip containing readout circuitry. The protective layer is preferably constructed to be incompressible and sufficiently flexible to immediately transmit pressure to the diaphragm. The protective layer may be a gel or a liquid, but oil or oil foam are also considered. The material is preferably selected such that it does not damage the MEMS components and is robust against environmental corrosive factors.

[0012] In one embodiment, the MEMS chip may be at least partially covered by a protective layer, such as a gel, to protect the sensor and, in particular, the sensor's diaphragm from corrosive environmental influences and / or moisture or water. This protective layer acts as an additional mass on the pressure sensor diaphragm. In a static state, the protective layer presses against the diaphragm. If the user rotates the device with the pressure sensor 180°, the protective layer pulls on the diaphragm, thereby generating interference signals. Due to the arrangement of the MEMS chips, the aforementioned effects of gravity on the two diaphragms occur in the same direction. The protective layer presses against the diaphragm of the lower MEMS chip and pulls on the diaphragm of the upper MEMS chip, such that the influence of gravity on the measurement results is at least partially compensated. The protective layer may be gel-based or constructed as a gel. The protective layer may completely cover the diaphragm.

[0013] Depending on the chosen implementation, the complete structure within the package, namely the MEMS chip and analysis and evaluation circuitry, as well as the bonding wires and substrate, can be covered by a protective layer, particularly by a gel.

[0014] In one embodiment, the substrates of the MEMS chip are arranged facing each other such that the diaphragm is oriented outwards, and the diaphragm is at least partially covered by a protective layer to protect against corrosive environmental conditions and / or moisture and / or water. Preferably, the diaphragm is completely covered by the protective layer, particularly by a gel. Following the viewing method described above, i.e., considering the continuous substrate side of the MEMS chip as the lower side and the diaphragm side as the upper side, in this embodiment, the two lower sides of the MEMS chip face each other, while the upper side of the diaphragm is oriented outwards.

[0015] In one embodiment, spacers are arranged between the substrates of the MEMS chip, in the edge region next to the diaphragms, thereby increasing the cavity between the diaphragms. If the diaphragms of the MEMS chip and the edge region of the substrate are arranged in a plane, then in an embodiment of a micromechanical pressure sensor where the two upper sides of the MEMS chip face each other, the cavity between the two diaphragms can be very narrow or flat. To increase this cavity, spacers can be arranged in the edge region of the substrate.

[0016] In one embodiment, the diaphragm is positioned lower relative to the edge region of the substrate plane surrounding the MEMS chip, thereby increasing the cavity between the diaphragms.

[0017] In one embodiment, the MEMS chips are directly interconnected, and such interconnection of the MEMS chips can be configured as wafer bonding interconnection.

[0018] In one embodiment, electrical connections are routed from at least one MEMS chip to analysis and evaluation circuitry, and these connections are covered by a protective layer. Advantageously, at least one, preferably two, MEMS chips are at least partially covered by the protective layer.

[0019] In one embodiment, one of the MEMS chips is at least partially disposed on a carrier. The carrier may have analysis and evaluation circuitry or be connected to an evaluation chip having analysis and evaluation circuitry. The analysis and evaluation circuitry may be connected to at least one Wheatstone half-bridge, particularly one or two Wheatstone bridges. The two MEMS chips can be read in parallel or sequentially. Attached Figure Description

[0020] Embodiments of the present invention are illustrated in the following figures. The figures show: Figure 1 A schematic diagram of one embodiment of a micromechanical pressure sensor. Figure 2 : A schematic diagram of another embodiment of the micromechanical pressure sensor, Figure 3 : A schematic diagram of MEMS chip interconnection, and Figure 4 : A schematic diagram of another MEMS chip interconnection. Detailed Implementation

[0021] Figure 1 A micromechanical pressure sensor 1 is schematically illustrated, comprising a first MEMS chip 2 and a second MEMS chip 3. The first MEMS chip 2 has a pressure-sensitive diaphragm 4 and a surrounding substrate 6, and the second MEMS chip 3 has a pressure-sensitive diaphragm 5 and a surrounding substrate 7. The two MEMS chips 2 and 3 are stacked such that the substrates 6 and 7 are oriented outwards and the diaphragms 4 and 5 are located in a cavity 8 between the substrates 6 and 7. The cavity 8 is connected to the surrounding environment through an opening 9, allowing the pressure of the fluid medium to be measured to reach the cavity 8 through the opening 9 and act on the diaphragms 4 and 5. The force exerted by this pressure and the resulting displacement of the diaphragms 4 and 5 occur in opposite directions; in this example, the diaphragm 4 is displaced upwards, while the diaphragm 5 is displaced downwards. The effect of gravity on the diaphragms 4 and 5, or the acceleration of the micromechanical pressure sensor 1, acts on the entire pressure sensor 1 in the same direction, such that the influence of gravity on the measurement results can be at least partially compensated.

[0022] Cavity 8 may be filled with a protective layer (not shown here, see [link]). Figure 2 The protective layer can be configured to be incompressible and flexible to prevent distortion of the pressure applied to diaphragms 4 and 5. Such a protective layer increases the effective mass capable of withstanding acceleration, thereby increasing the undesirable impact on pressure measurements. Alternatively, opening 9 can be sealed with foam or a venting diaphragm (e.g., made of ePTFE) to prevent environmental influences, while external pressure is still transmitted to cavity 8.

[0023] Relative to the edge region 11 of the surrounding substrate plane of MEMS chips 2 and 3, diaphragms 4 and 5 can be configured to be positioned lower, thereby increasing the cavity 8 between diaphragms 4 and 5, as shown in the figures by the arching of diaphragms 4 and 5. Alternatively or additionally, spacers (not shown) for increasing the cavity 8 can be arranged in the edge region 11. The connection portion of MEMS chips 2 and 3, especially in the edge region 11, can be configured as a wafer bonding connection portion 17.

[0024] To electrically connect MEMS chips 2 and 3 to the analysis and evaluation circuit 16, the first MEMS chip 2 may have a first electrical sensor line 13, wherein the first sensor line 13 is directed onto the surface of the first MEMS chip 2, wherein the first sensor line 13 is connected to an electrical line 14 of the second MEMS chip 3, wherein the electrical line 14 of the second MEMS chip 3 is configured as a connection portion 15 for connection to the analysis and evaluation circuit 16. Advantageously, MEMS chips 2 and 3 may have a common feed line for supplying voltage and ground potential, for example, in the region where the first sensor line 13 and the electrical line 14 converge.

[0025] The second MEMS chip 3 is mechanically disposed on the carrier 30, for example, via an adhesive connection 31. The carrier 30 may have an analysis and evaluation circuit 16 or be connected to an analysis and evaluation chip having an analysis and evaluation circuit. For the adhesive connection 31, a thermally conductive silicone material may be used.

[0026] For the two MEMS chips 2 and 3, a common analysis and evaluation circuit 16 can be provided, for example, an ASIC. MEMS chip 2 and the second MEMS chip 3 can be alternately connected to the analysis and evaluation electronics via a switch. The analysis and evaluation circuit 16 can be connected to a Wheatstone bridge, wherein the analog output of the Wheatstone bridge is connected to an LNA (low-noise amplifier) ​​via a switch, and the LNA is connected to a digital signal processor (DSP) via an analog-to-digital converter (ADC). Measurement errors caused by acceleration can be inferred from the comparison of the measurement results of the first MEMS chip 2 and the second MEMS chip 3.

[0027] Figure 2 A micromechanical pressure sensor 1 is shown, in which the substrates 6 and 7 of MEMS chips 2 and 3 are arranged facing each other, such that diaphragms 4 and 5 are oriented outwards. The force to be measured caused by external pressure and the resulting offset of diaphragms 4 and 5 occur in opposite directions; in this example, diaphragm 4 is offset downwards, while diaphragm 5 is offset upwards. The effect of gravity on diaphragms 4 and 5, or the effect of the accelerating motion of the micromechanical pressure sensor 1, acts on the entire pressure sensor 1 in the same direction, as indicated by the black arrow on the left side of the figure. By comparing the measurement results of the first MEMS chip 2 and the second MEMS chip 3, the effect of gravity on the measurement results can be at least partially compensated.

[0028] The films 4 and 5 of MEMS chips 2 and 3 are covered by a protective layer 10 to protect them from corrosive environmental conditions. The electrical circuitry 26, electrical contacts 27, and portions of the analysis and evaluation circuitry 16 are also covered by the protective layer 10. A sealing element 12 is arranged between substrates 6 and 7 for sealing. The second MEMS chip 3 is at least partially disposed on a carrier 30 via a connection portion 31, wherein the carrier 30 may have analysis and evaluation circuitry or be connected to an evaluation chip having analysis and evaluation circuitry.

[0029] A first MEMS chip 2 is disposed on a first region 24 of a second MEMS chip 3 on its lower side 22. A first electrical sensor line 13 is guided to the lower side 22 of the first MEMS chip 2, and an electrical line 14 of the second MEMS chip 3 is guided to the lower side 23 of another MEMS chip 3 in the first region 24. The first electrical sensor line 13 is electrically connected to the electrical line 14 in the first region 24 of the second MEMS chip 3 via a contact surface. A second region 25 is laterally disposed beside the first region 24 on the lower side 23 of the second MEMS chip 3. An electrical contact 27 is provided in the second region 25 for connecting another electrical line 26. The other electrical line 26 is guided to the electrical contact 27 and electrically connected to the electrical contact 27.

[0030] The first sensor line 13 may have a first through contact 18 that extends from the upper side 20 of the first MEMS chip 2 to the lower side 22 of the first MEMS chip 2. The electrical line 14 may have a second through contact 19 that extends from the upper side 21 of the second MEMS chip 3 to the lower side 23 of the second MEMS chip 3. The second MEMS chip 3 may have an additional through contact 28 that is laterally arranged beside a first region 24 on the lower side 23 of the second MEMS chip 3 and extends from the lower side 23 to the upper side 21. The second MEMS chip 3 may have a wiring reconnection 26 on its lower side 23 that connects the second through contact 19 to the additional through contact 28, wherein the additional through contact 28 connects to or constitutes an electrical contact on the upper side 21 of the second MEMS chip 3.

[0031] Figure 3A schematic diagram of the internal interconnection of a MEMS chip is shown, illustrated here in a configuration with two Wheatstone bridges. Indicatively, two sensor diaphragms 4 and 34 are arranged in one Wheatstone bridge, and two other sensor diaphragms 5 and 35 are arranged in another Wheatstone bridge. The Wheatstone bridges have sensor output terminals 40, 42 and 41, 43. For sensor analysis and evaluation, the signals from sensor output terminals 40, 42 and sensor output terminals 41, 43 are compared. Two to four diaphragms can be provided for each MEMS chip, and these diaphragms are also interconnected in Wheatstone bridges.

[0032] Sensor diaphragms 4 and 34 can be integrated into the first MEMS chip 2, and additional sensor diaphragms 5 and 35 can be integrated into the second MEMS chip 3. To improve sensitivity, two sensor diaphragms are used for each MEMS chip, allowing the use of two standard MEMS chips in this embodiment. MEMS chips are as follows... Figure 1 and Figure 2 Arranged as shown, such that as in Figure 1 and Figure 2 The method shown here can be said to be used in double the amount. This improves measurement accuracy and reduces costs by using standard components.

[0033] Advantageously, the feeders supplying voltages 32 and 33 and the grounding potential 36 can be shared by stacking.

[0034] Figure 4 A schematic diagram of another analytical evaluation circuit is shown, in which sensor diaphragms 4 and 5 are arranged in a Wheatstone bridge 45. This results in a more compact structure for the micromechanical pressure sensor, but places higher demands on the similarity of the technical characteristics of the sensor diaphragms. The possible covering with a protective layer must also be nearly identical in thickness and characteristics for both sensor diaphragms.

[0035] However, advantageously in this embodiment, undesirable gravity or acceleration effects have already been compensated for at the simulation level.

Claims

1. A micromechanical pressure sensor (1) comprising two MEMS chips (2, 3), each of the two MEMS chips having at least one pressure-sensitive diaphragm (4, 5), wherein, The two MEMS chips (2, 3) are arranged in a stacked manner, and the diaphragms (4, 5) are offset in opposite directions due to the force to be measured, wherein the force of gravity on the diaphragms (4, 5) occurs in the same direction, so that the effect of gravity on the measurement results is at least partially compensated.

2. The micromechanical pressure sensor (1) according to claim 1, wherein, The membranes (4, 5) of the MEMS chips (2, 3) are at least partially, and especially completely, covered by a protective layer (10), wherein the protective layer (10) is particularly configured to be incompressible and flexible, and particularly has a gel.

3. The micromechanical pressure sensor (1) according to any one of the preceding claims, wherein, The MEMS chips (2, 3) are arranged such that the substrates (6, 7) of the MEMS chips (2, 3) are oriented outward and the diaphragms (4, 5) are located in a cavity (8) between the substrates (6, 7), wherein the cavity (8) is connected to the surrounding environment through an opening (9), and wherein the force to be measured on the diaphragms (4, 5) is applied within the cavity (8).

4. The 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 configured to be incompressible and flexible, and is made of silicone gel.

5. The 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, such that the films (4, 5) are oriented outward and the films (4, 5) are at least partially covered by the protective layer (10).

6. The 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) and in the edge region (11) next to the diaphragms (4, 5), thereby increasing the cavity (8) between the diaphragms (4, 5).

7. The micromechanical pressure sensor (1) according to claim 3 or 4, wherein, The diaphragms (4, 5) are positioned lower relative to the edge region (11) of the substrate plane surrounding the MEMS chips (2, 3), thereby increasing the cavity (8) between the diaphragms (4, 5).

8. The micromechanical pressure sensor (1) according to any one of the preceding claims, wherein, The connection portion of the MEMS chips (2, 3) is constructed as a wafer bonding connection portion.

9. The micromechanical pressure sensor (1) according to claim 5, wherein, A sealing element (12) is arranged between the substrates (6, 7) for sealing.

10. The micromechanical pressure sensor (1) according to any one of the preceding claims, wherein, The first MEMS chip (2) has a first electrical sensor line (13), wherein the first sensor line (13) is guided to the surface of the first MEMS chip (2), wherein the first sensor line (13) is connected to the electrical line (14) of the second MEMS chip (3), wherein the electrical line (14) of the second MEMS chip (3) is configured to be connected to the connection portion (15) on the analysis and evaluation circuit (16).

11. The micromechanical pressure sensor (1) according to claim 5, wherein, The first MEMS chip (2) is arranged on the lower side (22) of the second MEMS chip (3) in a first region (24) on the lower side (23). The first electrical sensor line (13) is guided to the lower side (22) of the first MEMS chip (2). The electrical line (14) of the second MEMS chip (3) is guided to the lower side (23) of the second MEMS chip (3) in the first region (24). The first electrical sensor line (13) is electrically connected to the electrical line (14) in the first region (24) of the lower side (23) of the second MEMS chip (3) through a contact surface. The second region (25) on the lower side of the second MEMS chip (3) is laterally arranged next to the first region (24). An electrical contact (27) is provided in the second region (25) for connecting another electrical line (26). The other electrical line (26) is guided to the electrical contact (27) and electrically connected to the electrical contact (27).

12. The micromechanical pressure sensor (1) according to claim 11, wherein, The first sensor line (13) has a through contact portion leading from the upper side (20) of the first MEMS chip (2) to the lower side (22) of the first MEMS chip, wherein the line (14) has a second through contact portion leading from the upper side (21) of the second MEMS chip (3) to the lower side (23) of the second MEMS chip (3), wherein the second MEMS chip (3) has an additional through contact portion (28), the additional through contact portion being laterally arranged on the second The second MEMS chip (3) is located next to a first region (24) on the lower side (23) of the MEMS chip (3) and extends from the lower side (23) to the upper side (21), wherein the second MEMS chip (3) has a line reconnection portion (26) on the lower side (23) that connects the second through contact portion to the other through contact portion, and wherein the other through contact portion (28) is connected to or constitutes an electrical contact on the upper side (21) of the second MEMS chip (3).

13. The micromechanical pressure sensor (1) according to any one of the preceding claims, wherein, One of the MEMS chips (2, 3) is at least partially, and especially completely, arranged on the carrier (30), wherein the carrier (30) has the analysis and evaluation circuit or is connected to the analysis and evaluation chip having the analysis and evaluation circuit.

14. The micromechanical pressure sensor (1) according to claim 12 or 13, wherein, Electrical connection lines (26) are guided from a MEMS chip to the analysis and evaluation circuit, wherein the electrical connection lines are covered by a protective layer, and wherein, in particular, at least one, preferably two, MEMS chips (2, 3) are at least partially covered by the protective layer.

15. The micromechanical pressure sensor (1) according to any one of the preceding claims, comprising an analysis and evaluation circuit, wherein, The analysis and evaluation circuit is connected to at least one Wheatstone half-bridge, particularly one or two Wheatstone bridges.

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