MEMS sensor with improved sensitivity and sensor device with such a MEMS sensor

Abstract

A microelectromechanical sensor (100) is described comprising a substrate (110), a stationary electrode arrangement (120) relative to the substrate (110) with several stationary finger electrodes (122, 124) arranged one behind the other in a detection direction (y), and a mass arrangement (130) with a first seismic mass (140) that is elastically deflectable relative to the substrate (110) in the detection direction (y) and that comprises a first movable electrode arrangement (150) of several movable finger electrodes (151), and a second seismic mass (160) that is elastically deflectable relative to the substrate (110) in the detection direction (y) and that comprises a second movable electrode arrangement (170) of several movable finger electrodes (171). wherein the finger electrodes (151) of the first movable electrode arrangement (150) and the finger electrodes (171) of the second movable electrode arrangement (170) are each alternately in combing engagement with the finger electrodes (122, 124) of the stationary electrode arrangement (120), wherein the mass arrangement (130) further comprises a coupling device (180) mechanically connecting the first seismic mass (140) with the second seismic mass (160) in a manner capable of movement, which is configured to cause a deflection of the first seismic mass (140) in a corresponding deflection of the second seismic mass (160) in the respective opposite direction.

Description

[0001] The invention relates to a MEMS sensor with two counter-rotating seismic masses. Furthermore, the invention relates to a sensor device with a correspondingly designed MEMS sensor.

[0002] Micromechanical electrical sensors (MEMS) are used in various applications. Among other things, micromechanical inertial sensors for measuring acceleration and rotation rate are mass-produced for various applications in the automotive and consumer sectors. These accelerometers consist of a seismic mass mechanically connected to a silicon substrate via elastic springs. The application of acceleration results in an inertial force and thus a displacement of the seismic mass. This displacement is measured by movable electrodes Em attached to the seismic mass, or by measuring the change in their distance and capacitance (E1-Em, E2-Em) relative to stationary electrodes. The resulting change in capacitance is a measure of the applied acceleration and is expressed as electrical sensitivity in fF / g.

[0003] For MEMS accelerometers, electrode types have become particularly established in which all movable finger electrodes of the ground electrodes Em, which are in intermeshing engagement with corresponding stationary finger electrodes Em, move simultaneously in one direction, so that one of the two electrode gaps between a movable finger electrode and an immediately adjacent stationary finger electrode (e.g. E1-Em) becomes smaller, while the other electrode gap (e.g. E2-Em) becomes larger.

[0004] The electrode arrangements described in the prior art have the disadvantage that the stationary detection electrodes E1 and E2 are directly adjacent, creating an electrostatic field and thus a parasitic capacitance E1-E2 between them. This parasitic capacitance, unlike all other parasitic capacitances, contributes twice as much to the noise performance of the accelerometer because the ASIC front end measures simultaneously at the E1 and E2 nodes. The higher signal-to-noise ratio results in lower sensor sensitivity. To improve this sensitivity, the parasitic capacitance between the moving ground electrodes and the stationary detection electrodes must be reduced as much as possible.

[0005] The object underlying the invention can therefore be seen as improving the sensitivity of a microelectromechanical inertial sensor. This object is achieved by means of the respective subject matter of the independent claims. Advantageous embodiments of the invention are the subject matter of the dependent claims.

[0006] The concept described here comprises a microelectromechanical sensor consisting of a substrate, a stationary electrode array with several stationary finger electrodes arranged sequentially in a detection direction, and a mass array. This mass array includes a first seismic mass that is elastically deflectable relative to the substrate in the detection direction and comprises a first movable electrode array consisting of several movable finger electrodes. The second seismic mass is also elastically deflectable relative to the substrate in the detection direction and comprises a second movable electrode array consisting of several movable finger electrodes. The finger electrodes of the first movable electrode array and the finger electrodes of the second movable electrode array are in alternating, intermeshing engagement with the finger electrodes of the stationary electrode array.Furthermore, the mass arrangement includes a coupling device that mechanically connects the first seismic mass to the second seismic mass in a movable manner. This coupling device is designed to cause a deflection of the first seismic mass in a corresponding deflection of the second seismic mass in the opposite direction. Since, in the arrangement described here, a movable finger electrode is located between two immediately adjacent stationary finger electrodes, the parasitic capacitance typically present between the stationary finger electrodes is significantly reduced. This improves the signal-to-noise ratio of the sensor signal and thus increases the sensitivity of the sensor.

[0007] In one embodiment, the finger electrodes of the stationary electrode arrangement form two stationary detection electrodes with different electrical potentials. The finger electrodes of the first stationary detection electrode and the finger electrodes of the second stationary detection electrode are arranged alternately one behind the other in the detection direction. This results in a particularly advantageous arrangement in which the change in capacitance between a stationary finger electrode and its immediately adjacent movable finger electrode of the first seismic mass and the change in capacitance between the same stationary finger electrode and its immediately adjacent movable finger electrode of the second seismic mass are additive. This significantly increases the sensitivity of the sensor.

[0008] In a further embodiment, the finger electrodes of the two movable electrode assemblies are provided to have an electrical ground potential that differs from the electrical potentials of the two stationary detection electrodes. In this arrangement, the change in capacitance between a stationary finger electrode and its immediately adjacent movable finger electrode of the first seismic mass and the change in capacitance between the same stationary finger electrode and its immediately adjacent movable finger electrode of the second seismic mass are additive. This significantly increases the sensitivity of the sensor.

[0009] In a further embodiment, the first seismic mass is larger than the second. Due to its greater mass, the first seismic mass also has a greater moment of inertia. This causes the first seismic mass to be deflected in the opposite direction to the acceleration when a corresponding acceleration is applied, while the second seismic mass is deflected in the direction of the acceleration. The sensitivity of the sensor can be adjusted by varying the mass difference between the two seismic masses.

[0010] In a further embodiment, the coupling device comprises at least one support structure elastically connected to the substrate and with two legs arranged opposite each other with respect to the axis of rotation. The support structure is elastically deflectable about an axis of rotation perpendicular to the substrate. The first seismic mass and the second seismic mass are each attached to one of the two legs of the support structure. This allows for a particularly simple deflection of the two seismic masses in opposite directions.

[0011] In a further embodiment, the support structure is attached to the substrate in a central section by means of at least one elastic spring structure. This arrangement allows the support structure to rotate about a vertical axis of rotation located in its central section. Furthermore, this arrangement has a particularly simple design.

[0012] In a further embodiment, the two seismic masses are each attached to the support structure via at least one elastic spring structure. The spring structures make it particularly easy to convert the rotational movement of the support structure into a translational movement of the seismic masses.

[0013] In a further embodiment, the two seismic masses are connected to each other via at least two support structures that are elastically deflectable about a rotational axis perpendicular to the substrate. This arrangement allows the rotational motion of the two support structures to be converted into a translational motion of the two seismic masses. With a suitable arrangement of the two support structures, the torques acting on the seismic masses from the rotational motion of the two support structures cancel each other out. Furthermore, the mechanical stability of the entire arrangement can be improved by using multiple support structures.

[0014] In a further embodiment, the two support structures are arranged in a mirror-symmetrical manner such that they rotate in opposite directions when the seismic masses are deflected. This symmetrical arrangement allows for a particularly symmetrical distribution of forces on the two seismic masses. This, in turn, allows for a particularly advantageous way of achieving opposite deflections of the seismic masses.

[0015] In another embodiment, the microelectromechanical sensor is designed as an accelerometer. Using the concept described here, particularly sensitive and robust accelerometers can be produced.

[0016] According to another aspect, a sensor device with a microelectromechanical sensor is provided, wherein the microelectromechanical sensor is designed according to the preceding description. Such a sensor device offers the same advantages as the microelectromechanical sensor. Fig. 1 schematically a detailed view of a known MEMS sensor with a seismic mass, in which parasitic capacitances arise between immediately adjacent finger electrodes of the detection electrodes, Fig. 2 schematically a detailed view of another known MEMS sensor with a seismic mass, in which parasitic capacitances arise between immediately adjacent finger electrodes of the detection electrodes, Fig. Figure 3 schematically shows an improved MEMS sensor with two counter-rotating seismic masses, Fig. Figure 4 schematically compares the improved MEMS sensor with a conventional MEMS sensor. Fig. 5 schematically an improved MEMS sensor with two seismic masses connected to each other via two support structures arranged in a mirror image to each other, Fig. 6 schematically the improved MEMS sensor Fig. 5 in a deflected state, and Fig. Figure 7 schematically shows a sensor device with an improved MEMS sensor and an ASIC.

[0017] The Fig. Figure 1 schematically shows the structure of a simple MEMS sensor 100, which comprises only an elastically deflectable seismic mass 140. The MEMS sensor 100 includes a substrate 110 with a stationary electrode arrangement 120 mounted on it, comprising two detection electrodes 121, 123 each operating at different electrical potentials and consisting of several stationary finger electrodes 122, 124. The finger electrodes 122, 124, which are rigidly connected to the substrate 110 via anchor structures 125.1, 125.2, are arranged one behind the other in the detection direction y, with the finger electrodes 122 of the first detection electrode 121 and the finger electrodes 124 of the second detection electrode 123 being arranged alternately one behind the other.

[0018] As from the Fig. As can be seen in Figure 1, a corresponding movable electrode arrangement 150 consisting of several finger electrodes 151 is provided on the side wall of the seismic mass 140 facing the stationary electrode arrangement 120. These movable electrodes engage in a combing manner between the stationary finger electrodes 122 and 124. In the present arrangement, the movable finger electrodes 151, the stationary finger electrodes 122 of the first detection electrode 121, and the stationary finger electrodes 124 of the second detection electrode 123 are arranged alternately one behind the other in the detection direction y. Due to this arrangement, a finger electrode 122 of the first stationary detection electrode 121 and a finger electrode 124 of the second stationary detection electrode 123 are arranged in pairs directly one behind the other.Due to the different electrical potentials of the two immediately adjacent stationary finger electrodes 122, 124, a parasitic capacitance E1-E2 arises in the electrode gap 128 arranged between the two stationary electrodes. This in the . Fig. The parasitic capacitance E1-E2, indicated by vertical lines, is weighted twice as heavily in the noise performance of the accelerometer, unlike all other parasitic capacitances, because the ASIC frontend measures at the E1 and E2 nodes simultaneously.

[0019] In the present example, a deflection of the seismic mass 140 in the detection device y, indicated by two arrows, reduces the electrode gap 127.1 (gap between the respective finger electrodes 151, 121) arranged between a movable finger electrode 151 and the stationary finger electrode 122 of the first detection electrode 121 immediately adjacent to it, which is accompanied by a measurable increase in the capacitance (E1-Em) formed by the two finger electrodes 151, 121. Similarly, a deflection of the seismic mass 140 in the detection device y leads to a reduction of the electrode gap 127.2 arranged between the respective movable finger electrode 151 and the stationary finger electrode 124 of the second detection electrode 121 immediately adjacent to it, which is accompanied by a measurable reduction of the capacitance (E2-Em) formed by the two finger electrodes 151, 124 in question.

[0020] The seismic mass 140 is preferably connected to the substrate 110 in the detection device y by means of elastic spring elements (not shown here) so that they can be deflected elastically.

[0021] The Fig. 2 shows a variant of the one in the Fig. The previously shown concept differs from the previously shown concept, in that the movable finger electrodes 151 are now clamped between two side walls of the seismic mass 140, unlike the arrangement described above. The paired finger electrodes 122, 124 of the two stationary detection electrodes 121, 123 are each laterally attached to the associated anchor structures 125.1, 125.2, with the anchor structures 125.1, 125.2 extending into the space 128 between the respective stationary detection electrodes 121, 123. Due to this arrangement, the parasitic capacitance E1 - E2 described above arises between the immediately adjacent finger electrodes 122 and 124 of the two stationary detection electrodes 121, 123. Unlike all other parasitic capacitances, this E1-E2 parasite is weighted twice in the noise performance of the MEMS sensor because the ASIC front end measures the capacitances of the two E1 and E2 nodes separately.

[0022] To eliminate or reduce the parasitic capacitances E1-E2 described above and to improve the sensitivity of the MEMS sensor, a new electrode arrangement with additional movable finger electrodes is proposed. These are arranged in the electrode gaps 128 between the two stationary finger electrodes 122, 123 and are positioned opposite to those shown in the Fig. 1 existing movable finger electrodes 151 move. In the Fig. Figure 3 shows such an electrode arrangement of the improved MEMS sensor 100. As can be seen here, the MEMS sensor 100 has a modified mass arrangement 130 with an additional second seismic mass 160. This second seismic mass 160 is mechanically connected to the first seismic mass 140 via a suitable coupling device (not shown here) such that a deflection of the first seismic mass 140 in the detection direction y causes a deflection of the second seismic mass 160 in the opposite direction. A second movable electrode arrangement 170, corresponding to the first movable electrode arrangement 150, is arranged on the side of the second seismic mass 160 facing the electrodes.The second movable electrode arrangement comprises several finger electrodes 171, each of which combs into a space 128 between the previously immediately adjacent stationary finger electrodes 122, 124. In contrast to the arrangement described in the... Fig. 1 and Fig. The arrangements shown in Figure 2 are preferably arranged uniformly. In the present embodiment, the stationary finger electrodes 122 of the first detection electrode 121 and the stationary finger electrodes 124 of the second detection electrode 123 are electrically connected separately via their respective anchor structures 125.1, 125.2 to two underlying electrical conductor structures 111, 112, each of which has a different electrical potential.

[0023] When the first seismic mass 140 is deflected in the detection direction y and the second seismic mass 160 is deflected in the opposite detection direction y, the first electrode gap 127.1, formed by the distance between a finger electrode 122 of the first stationary detection electrode 121 and the finger electrode 151 of the first movable electrode arrangements 150 immediately adjacent to it, and the second electrode gap 127.2, formed by the distance between the respective stationary finger electrode 122 and the finger electrode 171 of the second movable electrode arrangements 170 immediately adjacent to it, increase.In contrast, corresponding opposite deflections of the seismic masses 140, 160 lead to a reduction of the third electrode gap 127.3 formed by the distance between a finger electrode 124 of the second detection electrode 123 and the finger electrode 151 of the first movable electrode arrangements 150 immediately adjacent to it, as well as of the fourth electrode gap 127.4 formed by the distance between the respective stationary finger electrode 124 and the finger electrode 171 of the second movable electrode arrangements 170 immediately adjacent to it.

[0024] In the Fig. Figure 4 shows the electrode arrangement of a conventional MEMS sensor and the electrode arrangement of a MEMS sensor improved according to the concept described here, side by side. As can be seen, the new electrode arrangement (left) results in twice as many detection capacitances E1-Em and E2-Em per detection cell (pitch) compared to the old electrode arrangement (right), thereby doubling the electrical sensitivity and halving most ASIC noise components. Compared to the previous electrode arrangement, the new concept has a significantly reduced E1-E2 parasite (parasitic capacitance between the immediately adjacent finger electrodes 151, 171 of the two stationary detection electrodes 150, 170) and thus also a significantly improved noise performance. Furthermore, the electrical sensitivity is almost doubled for the same area, or a significant reduction in area is achieved for the same performance.

[0025] In the Fig. Figure 5 shows an exemplary construction of a micromechanical sensor 100 built according to the new concept. The sensor 100 has a mass arrangement 130 movably connected to the substrate 110 via four elastic spring structures 132.1, 132.2, 132.3, 132.4 and anchor structures 131.1, 131.2, 131.3, 131.4. The arrangement consists of a frame-shaped first seismic mass 140 with a central opening 142, a second seismic mass 160 arranged in the central opening 142 of the first seismic mass 140, and a coupling device 180 by which the two seismic masses 140 and 160 are mechanically movably connected to each other. The coupling device 180 comprises two mirror-image support structures 190.1, 190.2, each with a central area 192 where the respective support structures are connected to the elastic spring structures 132.1, 132.2, 132.3, 132.4. The support structures 190.1, 190.2 each have two legs 193, 194 extending in opposite directions, at the ends of which elastic spring structures 141.1, 141.2, 141.3, 141.4 for the elastic suspension of the first seismic mass 140 and elastic spring structures 161.1, 161.2, 161.3, 161.4 for the elastic suspension of the second seismic mass 160 are arranged. As can be seen from the . Fig. As can be seen in Figure 5, the two support structures 190.1, 190.2 are housed in a central recess 135 of the mass arrangement 130, which in the present example divides the second seismic mass 160 into two parts 160.1, 160.2. However, embodiments in which the second seismic mass 160 is formed in one piece are also possible.

[0026] As from the Fig. As can also be seen in Figure 5, the stationary electrodes 122, 124 and movable electrodes 151, 171 used to detect the displacement are arranged in a total of four horizontally running spaces between the two seismic masses 140, 160 in the present example. The section marked by a dashed line corresponds essentially to that shown in the Fig. 3 shown arrangement.

[0027] The Fig. Figure 6 shows the MEMS sensor 100. Fig. 5 in a deflected state. It can be seen that when there is an acceleration in the detection direction y, the first seismic mass 140, due to its greater inertia compared to the substrate 110, experiences a deflection in the opposite detection direction y. The deflection of the first seismic mass 140 causes a rotation of the two support structures 190.1, 190.2 about their respective axes of rotation 195.1, 195.2, whereby the first support structure 190.1 rotates counterclockwise and the second support structure 190.2 rotates clockwise. Due to the rotation of the two support structures 190.1, 190.2, the smaller second seismic mass 160 experiences a corresponding deflection in the detection direction y. Since the two support structures 190.1, 190.Since the two preferably equal-length legs 193, 194 have spring structures 141, 161 serving as elastic suspensions for the seismic masses 140, 160, and the spring structures 141, 161 serving as elastic suspensions for the seismic masses 140, 160 are preferably of the same size and equidistant from the respective axis of rotation 195 of the respective support structure, a substantially symmetrical suspension of the two seismic masses 140, 160 results. Consequently, in the case of a corresponding acceleration, both seismic masses 140, 160 are deflected by substantially the same distance in opposite directions. In the [reference to the diagram] Fig. In the example shown in Figure 6, the distance between a finger electrode 122 of the first stationary detection electrode 121 and the immediately adjacent finger electrodes 151, 171 of the two movable electrode arrangements 150, 170 increases by the same amount for all finger electrodes 122 of the respective second stationary detection electrode 121. Similarly, the distance between a finger electrode 124 of the second stationary detection electrode 123 and the immediately adjacent finger electrodes 151, 171 of the two movable electrode arrangements 150, 170 decreases by the same amount for all finger electrodes 124 of the respective second stationary detection electrode 123 upon corresponding acceleration.

[0028] As from the Fig. As can be seen in Figure 6, the deflection of the two masses 140, 160 leads to a corresponding bending of the elastic spring elements 132.1, 132.2, 132.3, 132.4, which serve to suspend the entire mass arrangement 130, as well as of the elastic spring elements 141.1, 141.2, 141.3, 141.4 and 161.1, 161.2, 161.3, 161.4, which serve to attach the seismic masses 140, 160 to the support structures 190.1, 190.2. The symmetrical design and arrangement of these elastic spring elements advantageously results in a uniform distribution of the forces and mechanical stresses acting on the structures involved. Consequently, the bending of the respective spring elements leads to a restoring force that counteracts the deflections of the two seismic masses 140, 160.

[0029] The Fig.Figure 7 schematically shows a sensor device 200 with a MEMS sensor 100 designed according to the concept described here, and a control and evaluation unit 210 associated with the MEMS sensor 100 for controlling the MEMS sensor 100 and / or for evaluating or converting its sensor signals. The control and evaluation unit 210 can, for example, be designed as an ASIC and comprise one or more integrated circuits. The MEMS sensor 100 can, for example, be an inertial sensor, such as an accelerometer for various applications in the automotive and consumer sectors.

[0030] The improved concept features a new electrode arrangement based on a counter-motion accelerometer concept. Here, depending on the acceleration, not just one, but two masses 140, 160 are deflected in opposite directions. This results in two movable electrode groups (Em1 and Em2) or electrode arrangements 150, 170, which, although possessing the same electrical potential (node ​​Em), are deflected in opposite directions. This has the advantage that the stationary detection electrodes E1 and E2 are always separated or shielded from each other by the ground electrodes Em1 or Em2. Therefore, with this arrangement, no or virtually no parasitic capacitance (E1-E2 parasite) can occur between the immediately adjacent finger electrodes of the two detection electrodes.

[0031] The new concept has been illustrated and described in detail using preferred embodiments, without being limited to the disclosed examples. Rather, other variations of the MEMS sensor can also be derived by a person skilled in the art from the entirety of the present disclosure without departing from the scope of protection defined by the patent claims.

Claims

[1] Microelectromechanical sensor (100) comprising a substrate (110), an electrode arrangement (120) stationary relative to the substrate (110) with several stationary finger electrodes (122, 124) arranged one behind the other in a detection direction (y), and a mass arrangement (130) comprising a first seismic mass (140) elastically deflectable relative to the substrate (110) in the detection direction (y), which includes a first movable electrode arrangement (150) of several movable finger electrodes (151), and a second seismic mass (160) elastically deflectable relative to the substrate (110) in the detection direction (y), which includes a second movable electrode arrangement (170) of several movable finger electrodes (171), wherein the finger electrodes (151) of the first movable electrode arrangement (150) and the finger electrodes (171) of the second movable electrode arrangement (170) are each alternately in combing engagement with the finger electrodes (122, 124) of the stationary electrode arrangement (120), wherein the mass arrangement (130) further comprises a coupling device (180) mechanically connecting the first seismic mass (140) with the second seismic mass (160) in a manner capable of movement, which is configured to cause a deflection of the first seismic mass (140) in a corresponding deflection of the second seismic mass (160) in the respective opposite direction. [2] Microelectromechanical sensor (100) according to claim 1, wherein the finger electrodes (122, 124) of the stationary electrode arrangement (120) form two stationary detection electrodes (121, 123) exposed to different electrical potentials, wherein the finger electrodes (122) of the first stationary detection electrode (121) and the finger electrodes (124) of the second stationary detection electrode (123) are arranged alternately one behind the other in the detection direction (y). [3] Microelectromechanical sensor (100) according to claim 2, wherein the finger electrodes (151, 171) of the two movable electrode arrangements (150, 170) have an electrical ground potential that differs from the electrical potentials of the two stationary detection electrodes (121, 123). [4] Microelectromechanical sensor (100) according to one of the preceding claims, wherein the first seismic mass (140) is larger than the second seismic mass (160). [5] Microelectromechanical sensor (100) according to any one of the preceding claims, wherein the coupling device (180) comprises at least one support structure (190) connected to the substrate (110) in a manner elastically deflectable about an axis of rotation (195) perpendicular to the substrate (110) and having two legs (193, 194) arranged opposite each other with respect to the axis of rotation (195), and wherein the first seismic mass (140) and the second seismic mass (160) are each attached to one of the two legs (193, 194) of the support structure (190). [6] Microelectromechanical sensor (100) according to claim 5, wherein the support structure (190) is attached to the substrate (123) in a central section (192) via at least one elastic spring structure (132). [7] Microelectromechanical sensor (100) according to one of the preceding claims, wherein the two seismic masses (140) are each attached to the support structure (190) via at least one elastic spring structure (141). [8] Microelectromechanical sensor (100) according to one of claims 5 to 7, wherein the two seismic masses (140, 160) are connected to each other via at least two support structures (190) which are elastically deflectable about a rotation axis (195) perpendicular to the substrate (110). [9] Microelectromechanical sensor (100) according to claim 8, wherein the two support structures (190) are arranged in a mirror-symmetrical manner such that they rotate in opposite directions when the seismic masses (140, 160) are deflected. [10] Microelectromechanical sensor (100) according to one of the preceding claims, wherein the microelectromechanical sensor (100) is designed in the form of an accelerometer. [11] Sensor device (200) comprising a microelectromechanical sensor (100), wherein the microelectromechanical sensor (100) is configured according to any one of claims 1 to 10.

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