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

Abstract

The invention relates to a micro-electromechanical sensor comprising a substrate, a stationary electrode assembly and a mass assembly having a plurality of successively arranged stationary finger electrodes in a detection direction relative to the substrate, the mass assembly having a first vibrating mass comprising a first movable electrode assembly of a plurality of movable finger electrodes elastically deflectable relative to the substrate in the detection direction, and a second vibrating mass comprising a second movable electrode assembly of a plurality of movable finger electrodes elastically deflectable relative to the substrate in the detection direction, the finger electrodes of the first movable electrode assembly and the finger electrodes of the second movable electrode assembly being respectively alternately comb-like interdigitated with the finger electrodes of the stationary electrode assembly, the mass assembly further comprising coupling means for movably mechanically connecting the first vibrating mass and the second vibrating mass, configured for causing a deflection of the first vibrating mass to induce a corresponding deflection of the second vibrating mass in a respectively opposite direction.

Description

Technical Field

[0001] This invention relates to a MEMS sensor having two vibrating masses arranged in opposite directions. Furthermore, this invention relates to a sensor device having a corresponding configuration for a MEMS sensor. Background Technology

[0002] Micromechanical sensors (MEMS) are used in a variety of applications. Additionally, micromechanical inertial sensors for measuring acceleration and rotational speed are mass-produced for different applications in the automotive and consumer sectors. An accelerometer consists of a vibrating mass mechanically deflected to a silicon substrate via an elastic spring. The action of acceleration results in an inertial force, which in turn causes the vibrating mass to deflect. This deflection is measured via a moving electrode Em arranged on the vibrating mass, or more specifically via the change in distance and capacitance (E1-Em, E2-Em) between the moving electrode and a fixed electrode. The resulting capacitance change is a measure of the applied acceleration and is given as electrosensitivity in fF / g.

[0003] For MEMS accelerometers, in particular, electrode types have been established in which all the movable finger electrodes Em, which are comb-interlocked with the corresponding fixed finger electrodes in the mass electrode, move simultaneously in one direction, such that one of the two electrode gaps (e.g., E1-Em) between the movable finger electrode and the directly adjacent fixed finger electrode becomes smaller, while the corresponding other electrode gap (e.g., E2-Em) becomes larger.

[0004] The electrode assembly described in the prior art has the following disadvantages: the stationary or fixed probe electrodes E1 and E2 are directly adjacent, resulting in an electrostatic field between them and thus a parasitic capacitance E1-E2. Unlike all other parasitic capacitances, this parasitic capacitance is weighted twice in the noise performance of the accelerometer because the ASIC front end performs measurements simultaneously at both the E1 and E2 nodes. The higher signal-to-noise ratio leads to lower sensor sensitivity. To improve this sensitivity, the parasitic capacitance between the moving mass electrode and the fixed probe electrode must be reduced as much as possible. Summary of the Invention

[0005] The objective upon which this invention is based can therefore be to improve the sensitivity of microelectromechanical inertial sensors. This objective is solved by means of the corresponding subject matter of this invention. An advantageous configuration of this invention extends the corresponding subject matter of the technical solution.

[0006] The scheme described herein provides a microelectromechanical sensor comprising a substrate, a fixed electrode assembly relative to the substrate, and a mass assembly. The electrode assembly has a plurality of fixed finger electrodes arranged sequentially in a detection direction. The mass assembly has a first vibrating mass elastically deflectable relative to the substrate in the detection direction and a second vibrating mass elastically deflectable relative to the substrate in the detection direction. The first vibrating mass comprises a first movable electrode assembly composed of a plurality of movable finger electrodes, and the second vibrating mass comprises a second movable electrode assembly composed of a plurality of movable finger electrodes. Here, the finger electrodes of the first and second movable electrode assemblies are alternately comb-interlocked with the finger electrodes of the fixed electrode assembly. Furthermore, the mass assembly includes a coupling device that movably and mechanically connects the first and second vibrating masses, the coupling device being configured such that deflection of the first vibrating mass causes a corresponding deflection of the second vibrating mass in opposite directions. Because in the arrangement described herein, each movable finger electrode is arranged between two directly adjacent fixed finger electrodes, the parasitic capacitance typically present between the fixed finger electrodes is significantly reduced. Therefore, the signal-to-noise ratio of the sensor signal can be improved, and thus the sensitivity of the sensor can be increased.

[0007] In one embodiment, the finger electrodes of the fixed electrode assembly form two fixed detection electrodes loaded with different potentials. The finger electrodes of the first and second fixed detection electrodes are arranged alternately and successively in the detection direction. This results in a particularly advantageous arrangement in which the change in capacitance between the fixed finger electrode and the movable finger electrode of the first vibrating mass directly adjacent to the fixed finger electrode is structurally additive with the change in capacitance between the same fixed finger electrode and the movable finger electrode of the second vibrating mass directly adjacent to the fixed finger electrode. This significantly improves the sensitivity of the sensor.

[0008] In another embodiment, the finger electrodes of the two movable electrode assemblies have mass block potentials that deviate from the potentials of the two fixed detection electrodes. In this arrangement, the change in capacitance formed between the fixed finger electrode and the movable finger electrode of the first vibrating mass directly adjacent to the fixed finger electrode is structurally additive with the change in capacitance formed between the same fixed finger electrode and the movable finger electrode of the second vibrating mass directly adjacent to the fixed finger electrode. This significantly improves the sensitivity of the sensor.

[0009] In another embodiment, the first vibrating mass is constructed to be larger than the second vibrating mass. Due to the larger mass or weight of the first vibrating mass, it also has a larger moment of inertia. Therefore, when a corresponding acceleration is present, the first vibrating mass deflects in the opposite direction to the corresponding acceleration, while the second vibrating mass deflects in the direction of that acceleration. The sensitivity of the sensor can be adjusted by the mass difference between the two vibrating masses.

[0010] In another embodiment, the coupling device includes at least one carrier structure elastically deflectable about a rotation axis perpendicular to the base, the carrier structure having two arms arranged opposite each other relative to the rotation axis. A first vibrating mass and a second vibrating mass are respectively fixed to one of the two arms of the carrier structure. This allows the two vibrating masses to deflect in opposite directions in a particularly simple manner.

[0011] In another embodiment, the carrier structure is fixed to the base in the intermediate section via at least one elastic spring structure. This arrangement allows the carrier structure to rotate about a vertical axis of rotation arranged in its intermediate section. Furthermore, this arrangement has a particularly simple construction.

[0012] In another embodiment, the two vibrating masses are each fixed to the carrier structure via at least one elastic spring structure. The spring structure makes it particularly easy to convert the rotational motion of the carrier structure into the translational motion of the vibrating masses.

[0013] In another embodiment, the two vibrating masses are interconnected via at least two carrier structures, each capable of elastically deflecting about a rotation axis perpendicular to the base. This arrangement allows the rotational motion of the two carrier structures to be converted into translational motion of the two vibrating masses. The rotational torques acting on the vibrating masses by the rotational motion of the two carrier structures cancel each other out when the two carrier structures are properly arranged. Furthermore, the mechanical stability of the entire arrangement can be improved by using multiple carrier structures.

[0014] In another embodiment, the two carrier structures are arranged in a mirror-symmetrical manner so that they rotate in opposite directions when the vibrating masses deflect. This symmetrical arrangement allows for a particularly symmetrical force distribution on the two vibrating masses. This enables the opposite deflection of the vibrating masses to be achieved in a particularly advantageous way.

[0015] In another embodiment, the microelectromechanical sensor is constructed in the form of an accelerometer. Using the method described herein, a particularly sensitive and robust accelerometer can be produced.

[0016] According to another approach, the sensor device is equipped with a microelectromechanical (MEMS) sensor, wherein the MEMS sensor is constructed accordingly as described above. Such a sensor device yields the same advantages as the MEMS sensor. Attached Figure Description

[0017] Figure 1 The diagram schematically illustrates a detailed view of a known MEMS sensor with vibratory mass, in which parasitic capacitance is generated between directly adjacent finger electrodes of the sensing electrode. Figure 2 The diagram schematically illustrates a detail of another known MEMS sensor with vibratory mass, in which parasitic capacitance is generated between directly adjacent finger electrodes of the sensing electrode. Figure 3 The illustration schematically depicts an improved MEMS sensor with two vibrating masses in opposite directions. Figure 4 The illustration schematically shows a comparison between improved MEMS sensors and conventional MEMS sensors. Figure 5 This schematically illustrates an improved MEMS sensor with two vibrating masses interconnected via two carrier structures arranged in a mirror-symmetric manner. Figure 6 Schematic illustration, Figure 5 The improved MEMS sensor is in a deflection state, and Figure 7 The illustration schematically depicts a sensor device with improved MEMS sensors and an ASIC. Detailed Implementation

[0018] Figure 1 The schematic diagram illustrates the construction of a simple MEMS sensor 100, which has only one elastically deflectable vibrating mass 140. The MEMS sensor 100 includes a substrate 110 having a fixed electrode assembly 120 disposed thereon, the fixed electrode assembly having two detection electrodes 121, 123 loaded with different potentials, each detection electrode consisting of a plurality of fixed finger electrodes 122, 124. The finger electrodes 122, 124, mechanically rigidly connected to the substrate 110 via anchoring structures 125.1, 125.2, are arranged sequentially in the detection direction y, wherein the finger electrodes 122 of the first detection electrode 121 and the finger electrodes 124 of the second detection electrode 123 are arranged alternately and sequentially.

[0019] like Figure 1As shown, a corresponding movable electrode assembly 150, consisting of multiple finger electrodes 151, is disposed on the sidewall of the vibrating mass 140 facing the fixed electrode assembly 120. The finger electrodes are respectively comb-shaped and interposed between the fixed finger electrodes 122 and 124. In the current arrangement, the movable finger electrodes 151, the fixed finger electrodes 122 of the first detection electrode 121, and the fixed finger electrodes 124 of the second detection electrode 123 are alternately arranged sequentially in the detection direction y. Due to this arrangement, each finger electrode 122 of the first fixed detection electrode 121 is directly and successively paired with one finger electrode 124 of the second fixed detection electrode 123. Due to the different potentials of the two directly adjacent fixed finger electrodes 122 and 124, parasitic capacitances E1-E2 are generated in the electrode gap 128 arranged between the two fixed electrodes. Figure 1 The parasitic capacitances E1-E2, indicated by vertical lines, are weighted twice as much as all other parasitic capacitances in the noise performance of the accelerometer because the ASIC front end measures both E1 and E2 nodes simultaneously.

[0020] When the vibrating mass 140 deflects in the detection direction y as indicated by the two arrows in the current example, the electrode gap 127.1 (the gap between the corresponding finger electrodes 151, 121) between the movable finger electrode 151 and the fixed finger electrode 122 directly adjacent to the movable finger electrode of the first detection electrode 121 decreases, which is accompanied by a measurable increase in the capacitance (E1-Em) formed by the two associated finger electrodes 151, 121. Similarly, the deflection of the vibrating mass 140 in the detection direction y results in a decrease in the electrode gap 127.2 between the corresponding movable finger electrode 151 and the fixed finger electrode 124 directly adjacent to the movable finger electrode of the second detection electrode 121, which is accompanied by a measurable decrease in the capacitance (E2-Em) formed by the two associated finger electrodes 151, 124.

[0021] The vibrating mass 140 is preferably connected to the substrate 110 in a probe direction y by means of an elastic spring element (not shown here).

[0022] Figure 2 Shown in Figure 1A variation of the previous scheme shown, where the active finger electrode 151, unlike the arrangement described above, is now clamped between the two sidewalls of the vibrating mass 140. Pairs of finger electrodes 122 and 124 of the two fixed probe electrodes 121 and 123 are fixed to the sides of their respective anchoring structures 125.1 and 125.2, which extend in the intermediate space 128 between the associated fixed probe electrodes 121 and 123. Due to this arrangement, the aforementioned parasitic capacitances E1-E2 are generated between the directly adjacent finger electrodes 122 and 124 of the two fixed probe electrodes 121 and 123. These parasitic capacitances E1-E2 are weighted twice with respect to all other parasitic capacitances in the noise performance of the MEMS sensor because the ASIC front end measures the capacitances of the two nodes E1 and E2 separately.

[0023] To eliminate or reduce the parasitic capacitances E1-E2 and improve the sensitivity of the MEMS sensor, a new electrode assembly with additional movable finger electrodes is proposed. These additional movable finger electrodes are arranged in the electrode gap 128 between two fixed finger electrodes 122 and 123, and are respectively positioned relative to the electrode gap 128 between the two fixed finger electrodes 122 and 123. Figure 1 The existing active finger electrodes 151 move in the opposite direction. Figure 3 The image shows an improved electrode assembly of a MEMS sensor 100. As can be seen here, the MEMS sensor 100 has a modified mass assembly 130 with an additional second vibrating mass 160. This second vibrating mass 160 is mechanically connected to the first vibrating mass 140 via a suitable coupling device (not shown) such that when the first vibrating mass 140 deflects in the detection direction y, the second vibrating mass 160 deflects in the opposite direction. A second active electrode assembly 170 corresponding to the first active electrode assembly 150 is arranged on the electrode-facing side of the second vibrating mass 160. The second active electrode assembly includes a plurality of finger electrodes 171, which are respectively comb-shaped and embedded in the intermediate space 128 between previously directly adjacent fixed finger electrodes 122, 124. Here, the fixed finger electrodes 122, 124 are distinguished from those in… Figure 1 and 2 The arrangement shown is preferably evenly spaced apart from each other. In the present embodiment, the fixed finger electrodes 122 of the first detection electrode 121 and the fixed finger electrodes 124 of the second detection electrode 123 are electrically connected separately to two electrical conductor structures 111 and 112 extending below them via their respective anchoring structures 125.1 and 125.2, respectively, which have different potentials.

[0024] When the first vibrating mass 140 deflects in the detection direction y and the second vibrating mass 160 deflects in the opposite detection direction y, the first electrode gap 127.1, formed by the spacing between the finger electrode 122 of the first fixed detection electrode 121 and the finger electrode 151 of the first movable electrode assembly 150 directly adjacent to the finger electrode, increases, and the second electrode gap 127.2, formed by the spacing between the corresponding fixed finger electrode 122 and the finger electrode 171 of the second movable electrode assembly 170 directly adjacent to the finger electrode, increases. Conversely, the corresponding opposite deflections of the vibrating masses 140 and 160 result in a decrease in the third electrode gap 127.3, formed by the spacing between the finger electrode 124 of the second detection electrode 123 and the finger electrode 151 of the first movable electrode assembly 150 directly adjacent to the finger electrode, and a decrease in the fourth electrode gap 127.4, formed by the spacing between the corresponding fixed finger electrode 124 and the finger electrode 171 of the second movable electrode assembly 170 directly adjacent to the finger electrode.

[0025] exist Figure 4 The image shows, side-by-side, the electrode assembly of a conventional MEMS sensor and the electrode assembly of a MEMS sensor improved according to the scheme described herein. As can be seen here, the new electrode assembly (left) compared to the old electrode assembly (right) shows that each probe element (pitch) has more than twice the probe capacitance E1-Em and E2-Em, thereby doubling the electrosensitivity and halving most of the ASIC noise components. Compared to the previous electrode assembly, the new scheme has a significantly reduced E1-E2 parasitic capacitance (parasitic capacitance between the directly adjacent finger electrodes 151 and 171 of the two fixed probe electrodes 150 and 170), and therefore also a significantly improved noise performance. Furthermore, it shows doubled electrosensitivity in the case of equal area or a significant reduction in area for the same performance.

[0026] exist Figure 5The diagram illustrates the construction of a micromechanical sensor 100 constructed according to a novel scheme. The sensor 100 has a mass assembly 130 movably connected to a substrate 110 via four elastic spring structures 132.1, 132.2, 132.3, 132.4 and anchoring structures 131.1, 131.2, 131.3, 131.4. This mass assembly consists of a frame-shaped first vibrating mass 140 with a central opening 142, a second vibrating mass 160 disposed within the central opening 142 of the first vibrating mass 140, and a coupling device 180. The two vibrating masses 140 and 160 are movably mechanically connected to each other via this coupling device. The coupling device 180 includes two carrier structures 190.1 and 190.2 constructed in a mirror-symmetrical configuration. Each carrier structure has a central region 192, and the corresponding carrier structure is connected to the elastic spring structures 131.1, 131.2, 131.3, 131.4 in the central region. The carrier structures 190.1 and 190.2 also have two arms 193 and 194 extending in opposite directions, respectively. At the ends of these arms are respectively arranged elastic spring structures 141.1, 141.2, 141.3, and 141.4 for elastically suspending the first vibrating mass 140 and elastic spring structures 161.1, 161.2, 161.3, and 161.4 for elastically suspending the second vibrating mass 160. (As shown by...) Figure 5 As can be seen, the two carrier structures 190.1 and 190.2 are positioned in the central notch 135 of the mass assembly 130, which in this example divides the second vibrating mass 160 into two parts 160.1 and 160.2. However, in principle, it is also possible to implement the second vibrating mass 160 as a single unit.

[0027] As by Figure 5 As can also be seen, the fixed electrodes 122, 124 and the movable electrodes 151, 171 used to detect deflection are arranged in a total of four horizontally extending intermediate spaces between the two vibrating masses 140, 160 in this example. The local area marked by dashed lines here essentially corresponds to the one in... Figure 3 The arrangement shown.

[0028] Figure 6 As shown, Figure 5The MEMS sensor 100 is in a deflected state. It can be seen that, with acceleration in the detection direction y, the first vibrating mass 140, due to its greater inertia, undergoes a deflection relative to the substrate 110 in the opposite detection direction y. This deflection of the first vibrating mass 140 causes the two carrier structures 190.1 and 190.2 to rotate about their respective rotation axes 195.1 and 195.2, with the first carrier structure 190.1 rotating counterclockwise and the second carrier structure 190.2 rotating clockwise. Through the rotation of the two carrier structures 190.1 and 190.2, the smaller second vibrating mass 160 undergoes a corresponding deflection in the detection direction y. Because the two carrier structures 190.1 and 190.2 preferably have arms 193 and 194 of the same length, and the spring structures 141 and 161 serving as the elastic suspension devices for the vibrating masses 140 and 160 are preferably of the same size and at the same distance from the respective axis of rotation 195 of the carrier structure, a substantially symmetrical suspension of the two vibrating masses 140 and 160 is achieved. Therefore, the two vibrating masses 140 and 160 deflect by the same distance in substantially opposite directions under corresponding accelerations. Figure 6 In the example shown, the spacing between the finger electrode 122 of the first fixed detection electrode 121 and the directly adjacent finger electrodes 151, 171 of the two movable electrode assemblies 150, 170 increases by the same amount for all finger electrodes 122 of the corresponding second fixed detection electrode 121. Similarly, the spacing between the finger electrode 124 of the second fixed detection electrode 123 and the directly adjacent finger electrodes 151, 171 of the two movable electrode assemblies 150, 170 decreases by the same amount for all finger electrodes 124 of the corresponding second fixed detection electrode 123 under the corresponding acceleration.

[0029] As by Figure 6 As can be seen, the deflection of the two masses 140 and 160 causes corresponding bending of the elastic spring elements 132.1, 132.2, 132.3, and 132.4 used to suspend the entire mass assembly 130, and corresponding bending of the elastic spring elements 141.1, 141.2, 141.3, 141.4 and 161.1, 161.2, 161.3, and 161.4 used to fix the vibrating masses 140 and 160 to the carrier structures 190.1 and 190.2. The symmetrical construction and arrangement of these elastic spring elements advantageously results in a uniform distribution of forces and mechanical stresses acting on the participating structures. Therefore, the bending of each spring element results in a restoring force reacting to the deflection of the two vibrating masses 140 and 160.

[0030] Figure 7A sensor device 200 is schematically illustrated, comprising a MEMS sensor 100 constructed according to the scheme described herein, and a control and analysis evaluation facility 210 associated with the MEMS sensor 100 for controlling the MEMS sensor 100 and / or for analyzing, evaluating, or converting its sensor signals. The control and analysis evaluation facility 210 may be constructed herein, for example, in the form of an ASIC and includes one or more integrated switching circuits. The MEMS sensor 100 may be, for example, an inertial sensor, such as an accelerometer sensor for various applications in the automotive and consumer sectors.

[0031] The improved design features a new electrode assembly based on a "reverse motion" accelerometer. In this configuration, instead of just one, but two masses 140 and 160 deflect in opposite directions depending on the acceleration. This results in two active electrode groups (Em1 and Em2), or electrode assemblies 150 and 170, which, despite having the same potential (node ​​Em), deflect in opposite directions. This has the advantage that the stationary probe electrodes E1 and E2 are always separated from or shielded from each other by the mass electrodes Em1 or Em2. Therefore, in this arrangement, no or almost no parasitic capacitance (E1-E2 parasitic capacitance) is generated between the directly adjacent finger electrodes of the two probe electrodes.

[0032] The novel solution is further illustrated and described in detail according to preferred embodiments, but is not limited to the disclosed examples. Instead, those skilled in the art can derive other variations of the MEMS sensor based on the full disclosure herein, without departing from the scope of protection defined by the technical solution.

Claims

1. A microelectromechanical sensor (100) comprising a substrate (110), a fixed electrode assembly (120) relative to the substrate (110), and a mass assembly (130), the fixed electrode assembly having a plurality of fixed finger electrodes (122, 124) arranged sequentially in a detection direction (y), the mass assembly having a first vibrating mass (140) elastically deflectable relative to the substrate (110) in the detection direction (y) and a second vibrating mass (160) elastically deflectable relative to the substrate (110) in the detection direction (y), the first vibrating mass comprising a first movable electrode assembly (150) composed of a plurality of movable finger electrodes (151), and the second vibrating mass comprising a second movable electrode assembly (170) composed of a plurality of movable finger electrodes (171). in, The finger electrodes (151) of the first movable electrode assembly (150) and the finger electrodes (171) of the second movable electrode assembly (170) are alternately comb-shapedly engaged with the finger electrodes (122, 124) of the fixed electrode assembly (120). The mass assembly (130) further includes a coupling device (180) that enables the first vibrating mass (140) and the second vibrating mass (160) to be mechanically connected movably. The coupling device is configured such that deflection of the first vibrating mass (140) causes a corresponding deflection of the second vibrating mass (160) in opposite directions.

2. The microelectromechanical sensor (100) according to claim 1. in, The finger electrodes (122, 124) of the fixed electrode assembly (120) form two fixed detection electrodes (121, 123) loaded with different potentials. The finger electrodes (122) of the first fixed detection electrode (121) and the finger electrodes (124) of the second fixed detection electrode (123) are alternately arranged in the detection direction (y).

3. The microelectromechanical sensor (100) according to claim 2. in, The finger electrodes (151, 171) of the two active electrode assemblies (150, 170) have mass block potentials that deviate from the potentials of the two fixed probe electrodes (121, 123).

4. The microelectromechanical sensor (100) according to any one of the preceding claims. in, The first vibrating mass (140) is constructed to be larger than the second vibrating mass (160).

5. The microelectromechanical sensor (100) according to any one of the preceding claims. in, The coupling device (180) has at least one carrier structure (190) that is elastically deflectable to the base (110) about a rotation axis (195) perpendicular to the base (110), the carrier structure comprising two arms (193, 194) arranged opposite to each other relative to the rotation axis (195), and The first vibrating mass (140) and the second vibrating mass (160) are respectively fixed to one of the two arms (193, 194) of the carrier structure (190).

6. The microelectromechanical sensor (100) according to claim 5. in, The carrier structure (190) is fixed to the base (123) in the intermediate section (192) via at least one elastic spring structure (132).

7. The microelectromechanical sensor (100) according to any one of the preceding claims. in, The two vibrating masses (140) are respectively fixed to the carrier structure (190) via at least one elastic spring structure (141).

8. The microelectromechanical sensor (100) according to any one of claims 5 to 7. in, The two vibrating masses (140, 160) are interconnected via at least two carrier structures (190) that are elastically deflectable about a rotation axis (195) perpendicular to the base (110).

9. The microelectromechanical sensor (100) according to claim 8. in, The two carrier structures (190) are arranged so as to be mirror images of each other that they rotate in opposite directions as the vibrating masses (140, 160) deflect.

10. The microelectromechanical sensor (100) according to any one of the preceding claims. in, The microelectromechanical sensor (100) is constructed in the form of an accelerometer.

11. A sensor device (200) including a microelectromechanical sensor (100), wherein, The microelectromechanical sensor (100) is a microelectromechanical sensor (100) according to any one of claims 1 to 10.

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