MEMS apparatus

Abstract

MEMS apparatus (10) having a movable displacement element (12) and a drive device (14) for driving the movable displacement element (12), the drive device (14) having at least one drive electrode (16), characterized in that the drive electrode (16) is segmented and at least one functional electrode (18) is provided for measuring the deflection of the displacement element (12).

Description

[0001] Description

[0002] title

[0003] MEMS device

[0004] The present invention relates to a MEMS device according to the preamble of claim 1.

[0005] State of the art

[0006] MEMS devices are micro-electromechanical devices, such as those used in MEMS sensor devices or MEMS loudspeakers. In such loudspeakers, sound pressure is generated by displacing a volume of air by deflecting a displacement element in the plane of a MEMS chip. A device and a method for deflecting the displacement element are known, for example, from WO 2022 / 117197 A1. This document describes a MEMS component comprising a plurality of MEMS layers, one of which is designed to be movable as a displacement element. Furthermore, a drive mechanism is provided, which has several drive electrodes in the form of a structured electrode arrangement and generates a driving force on the displacement element.

[0007] Disclosure of the invention

[0008] The invention provides a MEMS device according to claim 1 and a method for measuring the displacement of a displacement element according to claim 9. Preferred embodiments are the subject of the dependent claims. Advantages of the invention

[0009] One aspect of the invention is that the proposed MEMS device according to claim 1 comprises a movable displacement element and a drive unit for driving the displacement element. The drive unit includes at least one segmented drive electrode. A functional electrode is provided for measuring the displacement of the displacement element.

[0010] The measures listed in the dependent claims enable advantageous further developments and improvements of the MEMS device specified in independent claim 1.

[0011] For the purpose of simplifying the manufacture of the drive unit, the functional electrode can be provided as a segment in series with the drive electrode.

[0012] In another embodiment, the drive unit can be segmented and have a plurality of drive electrodes spaced apart from one another. At least one functional electrode is arranged as a segment in series with the drive electrodes. This segmentation allows for greater flexibility in controlling the displacement element. Furthermore, the functional electrode can be integrated into the arrangement of segments, enabling detection at the desired location.

[0013] In another embodiment, the MEMS device can have a plurality of functional electrodes. This enables more precise detection of the deflection at different positions of the displacement element, precisely at the desired locations.

[0014] In a further embodiment of the invention, the displacement element can be designed as a bending beam clamped at one or both sides. Clamping at both sides seals the pressure chambers separated by the displacement element from one another, thereby preventing an acoustic short circuit. Clamping at one side has the advantage that the force-displacement relationship is linear, and this embodiment is particularly suitable for applications where a connection between the adjacent pressure chambers, and thus an acoustic short circuit, can be avoided at the freely movable end. This is especially true for small displacements.

[0015] Furthermore, in the MEMS device, at least one of the functional electrodes can be designed so that it can be used either for force generation or for measuring the displacement. This is particularly advantageous when the force available from the drive electrodes alone is no longer sufficient for the required driving force or when an additional signal is to be superimposed.

[0016] In another embodiment, the MEMS device is designed such that one of the functional electrodes can generate a force to deflect the displacement element, which is significantly smaller than the force generated by the drive unit. This allows a test signal or test deflection of the displacement element to be generated, which can be used for self-testing or system identification of the MEMS device.

[0017] In another embodiment, the drive electrodes can be designed with a length of, for example, 1 to 10 mm, preferably 3 to 5 mm, and the functional electrodes with a length of, for example, 100 to 800 m, preferably 200 to 400 m. This ensures, on the one hand, a sufficiently high drive power and, on the other hand, a sufficiently accurate detection of the deflection.

[0018] A further aspect of the invention lies in the method for measuring the displacement of a movable displacement element in a MEMS device, wherein the MEMS device includes a drive unit for driving the displacement element, and the drive unit has at least one segmented drive electrode. Furthermore, at least one functional electrode is provided. The displacement of the displacement element is determined using the functional electrode, whereby a capacitive method can be used in particular. This allows the displacement to be determined contactlessly with high sensitivity, even for small changes in displacement.

[0019] In a further embodiment, at least two functional electrodes can be provided and arranged to form a functional electrode pair. The deflection of the displacement element can thus again be capacitive, and in particular, differential capacitance measurement can be applied. Here, proven electrical circuits made of MEMS-based inertial sensors for measuring very small capacitance changes can advantageously be used.

[0020] In another embodiment, the actual displacement of the displacement element can be measured simultaneously with the displacement caused by the drive unit. This allows the actual displacement of the displacement element, measured by the functional electrodes, to be used instantly for various purposes, such as continuous condition monitoring.

[0021] In another embodiment, the displacement of the displacement element can be effected by a force generated by one or more of the functional electrodes. It is particularly advantageous if the force for displacement is generated exclusively by one or more of the functional electrodes. The displacement of the displacement element can then be measured using one or more of the functional electrodes that do not generate a force for displacement. This makes it possible to generate a test signal or a test displacement of the displacement element, which can be much smaller than the displacement during normal operation. This displacement can be evaluated for purposes such as self-testing and / or system identification. It is advantageous if the force generated by the functional electrodes is significantly smaller than the force that can be generated by the drive unit.

[0022] Brief description of the figures: Further features and advantages of the present invention are explained below with reference to exemplary embodiments and the figures.

[0023] They show:

[0024] Fig. 1a, 1b shows a schematic cross-sectional view and a schematic top view of an EMS device according to the prior art;

[0025] Figs. 2a, 2b show a schematic cross-sectional view and a schematic top view of an EMS device according to a first embodiment of the present invention;

[0026] Fig. 3 shows a schematic top view of a MEMS device according to a further embodiment of the present invention;

[0027] Fig. 4 shows a schematic top view of a MEMS device according to a further embodiment of the present invention;

[0028] Fig. 5 shows a schematic top view of a MEMS device according to a further embodiment of the present invention;

[0029] Embodiments of the invention

[0030] In the figures, identical reference symbols denote identical or functionally equivalent elements.

[0031] Fig. 1a schematically shows a cross-sectional view (AA) and Fig. 1b a schematic top view of a prior art MEMS device configured as a loudspeaker. A movable or deformable displacement element 12 is provided in the chip plane of a MEMS chip 20. As shown in Fig. 1b, the displacement element 12 is clamped at both ends in the y-direction. Thus, the displacement element 12 forms a separation between two pressure regions 21, 23, which can, for example, be configured as pressure chambers, and seals them against each other. In this way, an acoustic short circuit in the x-direction is avoided. The clamping at both ends provides strain stiffening, which can result in a non-linear force-displacement relationship.If this leads to undesirable harmonic distortions in the generated sound pressure, this can be appropriately compensated in the design of the electronic control of the drive electrodes 15, 16.

[0032] The chip 20 is enclosed by an upper cover 22 and a lower cover 24. To generate sound pressure, the displacement element 12 is deflected in the x direction, thereby displacing a corresponding volume of air. The force required for this is generated by an electrostatic stray field drive. Drive electrodes 15, 16 are provided for this purpose. As shown in Fig. 1b, the drive electrodes 15, 16 extend over the length of the displacement element 12, with a chip frame 26 surrounding the MEMS chip. The cover 22 is omitted in Fig. 1b.

[0033] Fig. 2a schematically shows a cross-sectional view (AA) and Fig. 2b a schematic top view of a MEMS device according to an embodiment of the present invention. As shown in Fig. 2b, the drive electrodes 15, 16 are segmented, i.e., separated from each other by breaks. They have segments 15, 17 and 15a as well as segments 16, 18 and 16a. This allows at least one of the segments to be provided as a functional electrode 17, 18. The functional electrodes 17, 18 can be assigned a function other than simply generating force. In particular, they can be used to determine the deflection position of the displacement element 12. In the example shown, the two functional electrodes 17, 18 are arranged along the length of the displacement element 12. They can be used to determine the position and / or the magnitude of the deflection of the deflected displacement element 13.A capacitive measurement method can be used here. This can be achieved, for example, by appropriate electrical circuitry of the functional electrodes 17, 18.

[0034] This segmentation also makes it possible to provide a method for determining the displacement of the displacement element 12, particularly simultaneously with the current displacement. Depending on the application of the MEMS device 10, this offers a number of advantages. If the MEMS device 10 is operated as a MEMS loudspeaker, the displacement of the displacement element 12 can be compared with a final acoustic measurement of the loudspeaker. Depending on the application, a final acoustic measurement of the loudspeaker can be omitted entirely, or a subsequent comparison can be made on a production line at the customer's site or during field use.This may be particularly necessary if the MEMS device 10 is used in altered environmental conditions, such as different air pressure, different humidity or temperature, or if the MEMS device has been subject to an aging process.

[0035] Preventive shutdown of the MEMS loudspeaker is also possible, for example, if an undesirably large deflection of the displacement element 12 is detected; this applies both in the deflection direction x and perpendicular to it in the z direction. This can protect both the MEMS loudspeaker and the user from damage that could be caused by excessive volume. Furthermore, the method can also be used to perform a self-test of the MEMS device 10 or to implement continuous condition monitoring of the MEMS loudspeaker.

[0036] To utilize the method for capacitive measurement of the displacement of the displacement element 12, it is possible to rely on the fact that an electrical capacitance C arises in the air gap 28, 30 between the functional electrodes 17, 18 and the displacement element 12. The displacement of the displacement element 12 relative to its rest position changes this capacitance by a value AC. The displacement of the displacement element 12 occurs primarily in the plane of the MEMS chip 20, i.e., in the direction x shown. However, an undesired displacement can also occur in a direction perpendicular to the MEMS chip plane, i.e., in the direction z. In principle, the functional electrodes 17, 18 can detect a displacement in both directions, so that the following generally applies to the capacitance C: C = f(x,z)

[0037] If one initially focuses on the deflection in the direction x, the change in capacitance AC can be measured by a corresponding electrical circuit of the functional electrodes 17, 18, whereby the functional electrodes 17, 18 form an electrode pair and the capacitance Csoam air gap 30 and the capacitance Czsam air gap 28 result in:

[0038] Cso = Co + AC(x) and C28 = Co~ AC(x)

[0039] Electrical circuits for measuring small changes in capacitance are known from EMS-based inertial sensors and can be used here. Furthermore, the same applies to the change in capacitance in the case of a deflection in the z-direction already described above, so this can also be measured. This is of particular importance because an unwanted deflection in the z-direction increases the risk of damaging the electrodes.

[0040] The number, size, position, and shape of the functional electrodes 17, 18 can be selected according to the specific requirements. The respective deformation and deflection amplitude of the displacement element 12 are crucial here, and the values ​​must be adjusted accordingly.

[0041] Figure 3 schematically shows an example of a MEMS device 10. The drive electrodes 15 and 16 are segmented multiple times, such that drive electrodes 16, 16a, 16b, 16c, 16d alternate with functional electrodes 18, 18a, 18b, 18c. The same applies to the drive electrodes 15, 15a, 15b, 15c, 15d and the functional electrodes 17, 17a, 17b, 17c. Both the functional electrodes and the drive electrodes can have different dimensions, allowing for adaptation to the specific application. The electrodes can also be arranged at different distances from each other.

[0042] Furthermore, it is also possible to generate the force for deflecting the displacement element 12 partially or exclusively via suitable control of one or more of the functional electrodes 18, 18a, 18b, 18c, 17, 17a, 17b, 17c. This makes it possible to generate a test signal or a test deflection of the displacement element 12. The test signal or test deflection can be significantly smaller than the deflection in normal operation, for example, in loudspeaker operation, and can be superimposed on the driving force generated by the drive electrodes 15, 15a, 15b, 15c, 15d, 16, 16a, 16b, 16c, 16d. This test deflection can then be measured with one or more of the functional electrodes 18, 18a, 18b, 18c, 17, 17a, 17b, 17c, which do not generate a deflection force. This enables self-testing and / or system identification of the MEMS device 10.This is especially true if the force generated by the at least one functional electrode 18, 18a, 18b, 18c, 17, 17a, 17b, 17c for a self-test or for system identification is the sole force acting on the displacement element 12.

[0043] Fig. 4 schematically shows an example of a MEMS device 10 in which the drive electrodes 16, 16a, 16b, 16c, 16d alternate with functional electrodes 18, 18a, 18b, 18c. The same applies to the drive electrodes 15, 15a, 15b, 15c, 15d and the functional electrodes 17, 17a, 17b, 17c. In the MEMS device 10, these are dimensioned such that a convex structure results along the length of the displacement element 12.

[0044] Fig. 5 schematically shows an example of a MEMS device 10 in which the drive electrodes 15 and 16 are segmented only once, so that in this embodiment one functional electrode 17 and one functional electrode 18 are provided, with both functional electrodes 17, 18 arranged at one edge of the chip frame 2. In the example shown here, the displacement element 12 is only fixed on one side. The displacement element 12 separates two pressure areas 21, 23 located on both sides of the displacement element 12 in the x-direction and seals them against each other in the non-displaced state. The one-sided clamping has the advantage that the force-displacement relationship is linear and the control of the drive electrodes 15, 16 can be simplified.When controlling the deflection of the displacement element 12, care must be taken to ensure that no connection is created between the adjacent pressure areas 21, 23 at the freely movable end of the deflected displacement element 13, as this would create an acoustic short circuit. This can be ensured particularly for small deflections of the deflected displacement element 13.

[0045] In general, for the described embodiments, the typical length of the functional electrodes is between 100 and 800 pm, particularly between 200 and 400 pm. The length of the drive electrodes is typically between 1 and 10 mm, preferably between 3 and 5 mm.

[0046] The segmentation and the placement of the functional electrodes in the segments result in less power being available for the drive unit 14 16. Therefore, in cases where more drive power is required, the circuitry of the functional electrodes 17, 18 can be designed to allow dual operation, i.e., they can be used either for force generation, i.e., to drive the displacement element 12, or for measuring the displacement of the displacement element 12.

[0047] The described MEMS device 10 can be advantageously used for a variety of components. In addition to the application already described in the field of MEMS loudspeakers, the device can also be used in microphones or micropumps.

Claims

Claims 1. MEMS device (10) with a movable displacement element (12) and a drive device (14) for driving the movable displacement element (12), wherein the drive device (14) has at least one drive electrode (15, 16), characterized in that the at least one drive electrode (15, 16) is segmented and at least one functional electrode (17, 18) is provided for measuring the displacement of the displacement element (12).

2. MEMS device (10) according to claim 1 , characterized in that the at least one functional electrode (17, 18) is arranged as a segment in series with the drive electrode (15, 16).

3. MEMS device (10) according to claim 1 or 2, characterized in that the drive electrode (15, 16) is segmented and has a plurality of drive electrodes (15, 15a, 15b, 15c, 15d, 16, 16a, 16b, 16c, 16d) which are spaced apart from each other and the at least one functional electrode (17, 18) is arranged as a segment in series with the drive electrodes (15, 15a, 15b, 15c, 15d, 16, 16a, 16b, 16c, 16d).

4. MEMS device (10) according to one of claims 1 to 3, characterized in that the MEMS device (10) has a plurality of functional electrodes (18, 18a, 18b, 18c, 17, 17a, 17b, 17c).

5. MEMS device (10) according to one of claims 1 to 4, characterized in that the displacement element (12) is designed as a bending beam clamped on one or both sides.

6. MEMS device (10) according to one of claims 1 to 5, characterized in that at least one of the functional electrodes (18, 18a, 18b, 18c, 17, 17a, 17b, 17c) is designed and controllable in such a way that it can be used either for force generation or for measuring the deflection.

7. MEMS device (10) according to claim 6, characterized in that at least one functional electrode (18, 18a, 18b, 18c, 17, 17a, 17b, 17c) is configured such that it can generate a force which acts on the Displacement element (12) acts, which is in particular significantly smaller than the force generated by the drive device (14).

8. MEMS device (10) according to one of claims 1 to 7, characterized in that the drive electrodes (16, 16a, 16b, 16c, 15, 15a, 15b, 15c, 15d) are designed to have a length of 1 to 10 mm, preferably 3 to 5 mm, and the functional electrodes (18, 18a, 18b, 18c, 17, 17a, 17b, 17c) are designed to have a length of 100 to 800 pm, preferably 200 to 400 pm.

9. Method for measuring the displacement of a movable displacement element (12) in a MEMS device (10), wherein the MEMS device (10) provides a drive unit (14) for driving the displacement element (12) and the drive unit (14) has at least one drive electrode (15, 16), characterized in that the drive electrode (15, 16) is segmented, that at least one functional electrode (18, 18a, 18b, 18c, 17, 17a, 17b, 17c) is provided and the displacement of the displacement element (12) is determined with the functional electrode (18, 18a, 18b, 18c, 17, 17a, 17b, 17c), in particular capacitively determined.

10. Method according to claim 8 characterized in that at least two functional electrodes (17, 18) are provided and arranged in such a way that they form a functional electrode pair and the deflection of the displacement element (12) is determined capacitively, in particular by a differential capacitance measurement.

11. Method according to claim 9 or 10 characterized in that the measurement of the actual deflection of the displacement element (12) is carried out simultaneously with the deflection by the drive device (13, 14).

12. Method according to one of claims 9 to 11 characterized in that the displacement element (12) is deflected by a force generated by at least one of the functional electrodes (18, 18a, 18b, 18c, 17, 17a, 17b, 17c).

13. Method according to claim 13 characterized in that the force for deflecting the displacement element (12) is generated exclusively by one or more of the functional electrodes (18, 18a, 18b, 18c, 17, 17a, 17b, 17c) and is connected to one or more of the functional electrodes (18, 18a, 18b, 18c, 17, 17a, 17b, 17c), which do not generate a force to deflect, the deflection of the displacement element (12) is measured.

14. Method according to one of claims 12 or 13, characterized in that the force generated by the at least one functional electrode (18, 18a, 18b, 18c, 17, 17a, 17b, 17c) is significantly smaller than that generated by the The drive device (14) generates power.

Images