Microelectromechanical inertial sensor and method for operating a microelectromechanical inertial sensor

Abstract

A microelectromechanical inertial sensor comprises a first measuring component with oscillating elements, wherein the first measuring component outputs a first measuring signal and a second measuring signal as a function of a movement about a rotational axis, and comprises a second measuring component with oscillating elements, wherein the second measuring component outputs a third measuring signal and a fourth measuring signal as a function of a movement about the rotational axis. An evaluation circuit generates a first difference signal of the first measuring signal and the second measuring signal and a second difference signal of the third measuring signal and the fourth measuring signal, amplifies the first difference signal, amplifies the second difference signal, and generates an output signal based on a sum of the amplified first difference signal and the amplified second difference signal. The first difference signal and the second difference signal are in phase at a first acceleration.The evaluation circuit amplifies the first difference signal and the second difference signal such that the output signal essentially disappears at a second acceleration. The first acceleration is a Coriolis acceleration and the second acceleration is a rotational acceleration, or the first acceleration is a rotational acceleration and the second acceleration is a Coriolis acceleration.

Description

[0001] The present invention relates to a microelectromechanical inertial sensor and a method for operating a microelectromechanical inertial sensor. State of the art

[0002] Microelectromechanical inertial sensors are used in various applications, for example in smartphones, game controllers, smart watches, drones or mobile devices.

[0003] In the automotive sector, inertial sensors and especially yaw rate sensors are used in the field of vehicle dynamics control as well as in other application areas such as roll-over sensing.

[0004] A key performance feature of inertial sensors is their robustness against external influences and, in particular, against vibrations caused by control interventions of systems or against external influences such as stone impacts or vibrating components in the interior or engine compartment.

[0005] From DE 10 2020 205 372 A1, a microelectromechanical component for a yaw rate sensor and a corresponding manufacturing method are known. Disclosure of the invention

[0006] The invention provides a microelectromechanical inertial sensor and a method for operating a microelectromechanical inertial sensor having the features of the independent patent claims.

[0007] Preferred embodiments are the subject of the respective subclaims.

[0008] According to a first aspect, the invention accordingly relates to a microelectromechanical inertial sensor comprising a first measuring component with oscillating elements, wherein the first measuring component outputs a first measuring signal and a second measuring signal as a function of a movement about a rotational axis, and comprising a second measuring component with oscillating elements, wherein the second measuring component outputs a third measuring signal and a fourth measuring signal as a function of a movement about the rotational axis. An evaluation circuit generates a first differential signal of the first measuring signal and the second measuring signal and a second differential signal of the third measuring signal and the fourth measuring signal, amplifies the first differential signal, amplifies the second differential signal, and generates an output signal based on a sum of the amplified first differential signal and the amplified second differential signal.The first difference signal and the second difference signal are in phase at a first acceleration. The evaluation circuit amplifies the first difference signal and the second difference signal such that the output signal essentially disappears at a second acceleration. The first acceleration is a Coriolis acceleration and the second acceleration is a rotational acceleration, or the first acceleration is a rotational acceleration and the second acceleration is a Coriolis acceleration.

[0009] According to a second aspect, the invention relates to a method for operating a microelectromechanical inertial sensor having a first measuring component with oscillating elements. The first measuring component outputs a first measuring signal and a second measuring signal as a function of a movement about a rotational axis. A second measuring component with oscillating elements outputs a third measuring signal and a fourth measuring signal as a function of a movement about the rotational axis. A first difference signal of the first measuring signal and the second measuring signal is generated, and a second difference signal of the third measuring signal and the fourth measuring signal is generated. The first difference signal and the second difference signal are each amplified. An output signal is generated based on a sum of the amplified first difference signal and the amplified second difference signal.The first difference signal and the second difference signal are in phase at a first acceleration. The first difference signal and the second difference signal are amplified such that the output signal essentially disappears at a second acceleration. The first acceleration is a Coriolis acceleration and the second acceleration is a rotational acceleration, or the first acceleration is a rotational acceleration and the second acceleration is a Coriolis acceleration. Advantages of the invention

[0010] The micromechanical inertial sensor can be configured to measure Coriolis accelerations (rotational rates). By providing two measuring components, rotational accelerations can be suppressed. Conversely, with modified signal processing, the micromechanical inertial sensor can measure rotational accelerations, while suppressing Coriolis accelerations.

[0011] By amplifying the signal after determining the difference signal but before summing it to determine the output signal, it is possible to suppress signals caused by rotational accelerations even if the two measuring components are not perfectly symmetrical.

[0012] Such asymmetry can arise, for example, due to process inhomogeneities and is then stable over temperature or aging and can therefore be well compensated by amplification.

[0013] One cause of asymmetries can be an asymmetry in the spring width of the springs of the first and second measuring components. This asymmetry is not statistical; rather, depending on the position of the individual micromechanical inertial sensor on a wafer and the surrounding environment, a gradient arises across the chip due to bond pads or bond frames, which, for example, leads to the springs having different widths. This can be simplified by the different natural frequencies of the measuring components. The weaker the mechanical coupling between the measuring components, the greater the impact of this asymmetry.

[0014] The microelectromechanical inertial sensor can be provided in particular in a three-axis yaw rate sensor which is optimized with regard to robustness against rotational accelerations.

[0015] According to one embodiment of the microelectromechanical inertial sensor, the first measuring component has a first oscillating element and a second oscillating element. The second measuring component has a third oscillating element and a fourth oscillating element. The first oscillating element is arranged mirror-symmetrically to the third oscillating element with respect to a plane of symmetry. The second oscillating element is arranged mirror-symmetrically to the fourth oscillating element with respect to the plane of symmetry. Upon Coriolis acceleration, the first oscillating element and the fourth oscillating element are set into a first harmonic oscillating motion directed perpendicular to the plane of symmetry. The second oscillating element and the third oscillating element are set into a second harmonic oscillating motion directed perpendicular to the plane of symmetry. The first harmonic oscillating motion and the second harmonic oscillating motion are essentially in antiphase.

[0016] According to one embodiment of the microelectromechanical inertial sensor, upon rotational acceleration, the first oscillating element and the third oscillating element are set into a third harmonic oscillating motion directed perpendicular to the plane of symmetry. The second oscillating element and the fourth oscillating element are set into a fourth harmonic oscillating motion directed perpendicular to the plane of symmetry. The third harmonic oscillating motion and the fourth harmonic oscillating motion are essentially in antiphase.

[0017] According to one embodiment of the microelectromechanical inertial sensor, the first measurement signal is generated as a function of an oscillating movement of the first oscillating element. The second measurement signal is generated as a function of an oscillating movement of the second oscillating element. The third measurement signal is generated as a function of an oscillating movement of the third oscillating element. The fourth measurement signal is generated as a function of an oscillating movement of the fourth oscillating element.

[0018] According to one embodiment, the microelectromechanical inertial sensor comprises a microelectromechanical element (MEMS element) comprising the first measuring component and the second measuring component. Furthermore, the microelectromechanical inertial sensor comprises an application-oriented integrated circuit (ASIC) comprising the evaluation circuit. Thus, the summation to generate the output signal does not occur on the MEMS element, but rather the measurement signals of the two measuring components are transmitted individually, and the asymmetry can be compensated for individually in the ASIC (e.g., digitally).

[0019] According to one embodiment of the microelectromechanical inertial sensor, the evaluation circuit has a first digital amplifier stage configured to amplify the first differential signal. The microelectromechanical inertial sensor has a second digital amplifier stage configured to amplify the second differential signal. The gain factors can be set to constant values. However, it is also possible to dynamically adjust the gain factors based on additional input parameters, e.g., based on temperature sensor signals or stress sensor signals.

[0020] According to a further development, the method for operating the microelectromechanical inertial sensor is carried out with an evaluation circuit of the microelectromechanical inertial sensor arranged on an ASIC.

[0021] According to a further development of the method, the first differential signal is amplified by a first digital amplifier stage. The second differential signal is amplified by a second digital amplifier stage.

[0022] According to a further development of the method, the microelectromechanical inertial sensor is subjected to a predetermined Coriolis acceleration (or angular rate). The resulting first amplified differential signal and the resulting second amplified differential signal are determined. Gain factors for the first differential signal and the second differential signal are adjusted based on a comparison of the first amplified differential signal and the second amplified differential signal. In particular, corresponding first and second analog or digital amplifier stages can be trimmed.

[0023] Further advantages, features and details of the invention will become apparent from the following description, in which various embodiments are described in detail with reference to the drawings. Short description of the drawings

[0024] They show: Fig. 1 is a schematic block diagram of a microelectromechanical inertial sensor according to an embodiment of the invention for Coriolis acceleration; Fig. 2 a schematic block diagram of the microelectromechanical inertial sensor at rotational acceleration; Fig. 3 a schematic representation of transfer functions; and Fig. 4 a flowchart of a method for operating a microelectromechanical inertial sensor according to an embodiment of the invention.

[0025] In all figures, identical or functionally equivalent elements and devices are provided with the same reference numerals. The numbering of process steps serves the purpose of clarity and is generally not intended to imply a specific chronological order. In particular, several process steps can be performed simultaneously. Description of the embodiments

[0026] Fig. Figure 1 shows a schematic block diagram of a microelectromechanical inertial sensor 1 for a Coriolis acceleration 7. The microelectromechanical inertial sensor 1 has a MEMS element 2, which includes a first measuring component 4 and a second measuring component 5. Furthermore, the microelectromechanical inertial sensor has an ASIC, which represents or includes an evaluation circuit 3.

[0027] The microelectromechanical inertial sensor 1 is designed to measure Coriolis accelerations 7 about a rotation axis perpendicular to a substrate of the MEMS element 2.

[0028] The first measuring component 4 comprises a first measuring element 41 with a first oscillating element and a first drive structure, and a second measuring element 42 with a second oscillating element and a second drive structure. The second measuring component 5 has a third measuring element 51 with a third oscillating element and a third drive structure, and a fourth measuring element 52 with a fourth oscillating element and a fourth drive structure. The first measuring element 41 is arranged mirror-symmetrically to the third measuring element 51 with respect to a plane of symmetry A. The second measuring element 42 is arranged mirror-symmetrically to the fourth measuring element 52 with respect to the plane of symmetry A.

[0029] The first to fourth drive structures are deflected by a drive signal (e.g., by applying an electrical voltage) parallel to the symmetry plane A. For this purpose, the first and fourth drive structures are set into an in-phase harmonic oscillation motion 61 and 67, respectively, and the second and third drive structures are set into an anti-phase (i.e., offset by 180°) harmonic oscillation motion 63 and 65, respectively.

[0030] The structure of the microelectromechanical inertial sensor 1 can essentially correspond to the sensor described in DE 10 2020 205 372 A1.

[0031] During a Coriolis acceleration 7, the first oscillating element and the fourth oscillating element are set into a first harmonic oscillating motion 62 and 68, respectively, directed perpendicular to the plane of symmetry. The second oscillating element and the third oscillating element are set into a second harmonic oscillating motion 64 and 66, respectively, directed perpendicular to the plane of symmetry. The first harmonic oscillating motion 62, 68 and the second harmonic oscillating motion 64, 66 are essentially in antiphase (opposite), i.e., offset by 180° from each other.

[0032] As in Fig. As shown in Figure 2, upon rotational acceleration, the first oscillating element and the third oscillating element are set into a third harmonic oscillating motion 91 and 93, respectively, directed perpendicular to the plane of symmetry. The second oscillating element and the fourth oscillating element are set into a fourth harmonic oscillating motion 92 and 94, respectively, directed perpendicular to the plane of symmetry. The third harmonic oscillating motion 91, 93 and the fourth harmonic oscillating motion 92, 94 are essentially in antiphase.

[0033] The first measuring component 4 outputs a first measuring signal and a second measuring signal depending on a movement around the axis of rotation. The second measuring component 5 outputs a third measuring signal and a fourth measuring signal depending on a movement around the axis of rotation. The first measuring signal is generated depending on an oscillating movement of the first oscillating element. The second measuring signal is generated depending on an oscillating movement of the second oscillating element. The third measuring signal is generated depending on an oscillating movement of the third oscillating element. The fourth measuring signal is generated depending on an oscillating movement of the fourth oscillating element.

[0034] The evaluation circuit 3 comprises a first differential stage 31, which generates a first differential signal from the first measurement signal and the second measurement signal. The evaluation circuit 3 further comprises a second differential stage 32, which generates a second differential signal from the third measurement signal and the fourth measurement signal.

[0035] The evaluation circuit 3 has a first digital amplifier stage 33, which amplifies the first differential signal. The evaluation circuit 3 further has a second digital amplifier stage 34, which amplifies the second differential signal.

[0036] The evaluation circuit 3 further comprises a summing element 35, which adds the amplified first difference signal and the amplified second difference signal, thereby generating an output signal. The first difference signal and the second difference signal are in phase during Coriolis accelerations. The evaluation circuit amplifies the first difference signal and the second difference signal such that the output signal essentially disappears during rotational accelerations. This is explained in more detail below.

[0037] The first to fourth measurement signals are generated based on capacitance values ​​at measuring electrodes.

[0038] It denotes CP z1 the capacitance at the first measuring element and dC cor,1 the capacity change due to the Coriolis acceleration a cor for the first measuring component 4. Then the first measuring signal is given by CPz1+dCcor,1=CPz1+acor⋅Hz1, where H z1refers to the frequency-dependent transfer function of detection and includes, in addition to the mechanical transfer function, also the capacitive sensitivity of the detection electrodes, ie dC / dx.

[0039] The transfer function is given by: Hz1=∂C∂x⋅1(2πf1)2⋅1(1−f2f12)+i⋅fQ1⋅f1

[0040] Here, f1 describes the natural frequency of the first measuring element, Q1 denotes the quality of the first measuring element and f the exciting frequency.

[0041] Analogously, CN z1 , CP z2 and CN z2 the capacitance at the second to fourth measuring element and dC cor,2 the capacity change due to the Coriolis acceleration a cor for the second measuring component 5.

[0042] Then the second measurement signal is given by CNz1+dCcor,1=CNz1+acor⋅Hz1.

[0043] The third measurement signal is given by CNz2+dCcor,2=CNz2+acor⋅Hz2.

[0044] The fourth measurement signal is given by CNz2+dCcor,2=CNz2+acor⋅Hz2.

[0045] The first difference signal is then proportional to acor⋅Hz1.

[0046] The second difference signal is proportional to acor⋅Hz2.

[0047] DigGain1 and DigGain2 now denote the gain of the first amplifier stage 33 and the second amplifier stage 34, respectively. The output signal of the summing element 35 is then proportional to: acor⋅(Hz1⋅DigGain1+Hz2⋅DigGain2).

[0048] At a rotational acceleration a dreh the first measurement signal is given by: CPz1+adreh⋅Hz1.

[0049] The second measurement signal is given by: CPz1−adreh⋅Hz1.

[0050] The third measurement signal is given by: CNz2+adreh⋅Hz2.

[0051] The fourth measurement signal is given by: CPz2−adreh⋅Hz2.

[0052] The output signal of the summing element 35 is then proportional to: adreh⋅(Hz1⋅DigGain1−Hz2⋅DigGain2).

[0053] In the symmetric case Hz1=Hz2 The signal generated by rotational acceleration is perfectly suppressed even without amplification. In the case of asymmetries Hz1≠Hz2 However, this would degrade the performance, which could not be compensated for by a later correction without amplification before the signals are added.

[0054] When it comes to the susceptibility of a yaw rate sensor, the frequency range around the drive frequency is particularly relevant. This range results from the output bandwidth of the microelectromechanical inertial sensor 1, typically 80 to 500 Hz. The drive frequency is typically 10 to 50 kHz, for example, 35 kHz.

[0055] The microelectromechanical inertial sensor 1 can be operated partially resonantly, ie the resonance frequency of the oscillating elements is above or below the drive frequency with a distance of typically 1000 to 5000 Hz, for example -3000 Hz. An asymmetry can now exist between the two measuring components 4, 5, for example of 100 Hz.

[0056] By transmitting the signals separately, the error caused by rotational accelerations can be reduced by specifically trimming DigGain1 / DigGain2 according to: Hz1⋅DigGain1=Hz2⋅DigGain2

[0057] Both the Coriolis acceleration and the critical angular accelerations act at the drive frequency f. Now (e.g., during a standard adjustment of the angular rate sensitivity) DigGain1 and DigGain2 can be determined, since the output signal for a Coriolis acceleration also has exactly this transfer function as gain. For this purpose, the microelectromechanical inertial sensor 1 can be rotated, and both angular rate channels can be evaluated before adding the final output signal. Thus, at the applied angular rate 2⋅acor⋅Hz1⋅DigGain1 and 2⋅acor⋅Hz2⋅DigGain2 If both yaw rate channels are trimmed to the same sensitivity, angular accelerations are suppressed as best as possible.

[0058] If gain differences result not from mechanics but from electrostatics, these can also be corrected via individual gain adjustment.

[0059] With modified signal processing, the micromechanical inertial sensor 1 can be configured to measure rotational accelerations while suppressing Coriolis accelerations. For this purpose, a differential stage can be used instead of summing element 35 to subtract the signals.

[0060] According to further embodiments, it can also be provided that the relative sign in component 35 can be changed. In the case of a dynamic change, for example, both measured variables (rotational accelerations and Coriolis accelerations) can be separated and measured separately, while the other variable is suppressed.

[0061] Fig. Figure 3 shows a schematic representation of exemplary transfer function curves. Shown is a curve 100 of H z1 , a course 200 of H z2 , a course 300 from H z1 - H z2without correction, ie without amplification, and a course 400 of H z1 - H z2 with correction.

[0062] Fig. 4 shows a flowchart of a method for operating a microelectromechanical inertial sensor, in particular the microelectromechanical inertial sensor 1 described above.

[0063] The microelectromechanical inertial sensor 1 has a first measuring component 4 with oscillating elements. The first measuring component outputs a first measuring signal and a second measuring signal depending on a movement about a rotational axis.

[0064] A second measuring component 5 with oscillating elements outputs a third measuring signal and a fourth measuring signal depending on a movement around the axis of rotation.

[0065] In a first step S1, a first differential signal of the first measurement signal and the second measurement signal is generated. A second differential signal of the third measurement signal and the fourth measurement signal is then generated.

[0066] In a second step S2, the first difference signal and the second difference signal are each amplified.

[0067] In a step S3, an output signal is generated based on a sum of the amplified first difference signal and the amplified second difference signal.

[0068] The first difference signal and the second difference signal are in phase at Coriolis accelerations. The first difference signal and the second difference signal are amplified such that the output signal essentially disappears at angular accelerations.

[0069] The described method for operating the microelectromechanical inertial sensor 1 can be carried out with an evaluation circuit 3 of the microelectromechanical inertial sensor 1 arranged on an ASIC.

[0070] The first difference signal can be amplified with a first digital amplifier stage 33. The second difference signal is then amplified with a second digital amplifier stage 34.

[0071] To determine the amplification factors of the amplifier stages 33, 34, the microelectromechanical inertial sensor 1 can be subjected to a predetermined Coriolis acceleration. The resulting first amplified differential signal and the resulting second amplified differential signal are determined. The amplification factors for the first differential signal and the second differential signal are adjusted based on a comparison of the first amplified differential signal and the second amplified differential signal. In particular, the first and second amplifier stages can be trimmed. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2020 205 372 A1 [0005, 0030]

Claims

[1] Microelectromechanical inertial sensor (1), with: a first measuring component (4) with oscillating elements, wherein the first measuring component (4) outputs a first measuring signal and a second measuring signal as a function of a movement about a rotation axis; a second measuring component (5) with oscillating elements, wherein the second measuring component (5) outputs a third measuring signal and a fourth measuring signal depending on a movement about the axis of rotation; and an evaluation circuit (3) which is designed to generate a first difference signal of the first measurement signal and the second measurement signal and to generate a second difference signal of the third measurement signal and the fourth measurement signal, to amplify the first difference signal and the second difference signal and to generate an output signal based on a sum of the amplified first difference signal and the amplified second difference signal; wherein the first difference signal and the second difference signal are in phase at a first acceleration, and wherein the evaluation circuit (3) is designed to amplify the first difference signal and the second difference signal such that the output signal substantially disappears at a second acceleration; wherein the first acceleration is a Coriolis acceleration and the second acceleration is a rotational acceleration, or wherein the first acceleration is a rotational acceleration and the second acceleration is a Coriolis acceleration. [2] Microelectromechanical inertial sensor (1) according to claim 1, wherein the first measuring component (4) has a first oscillating element and a second oscillating element, and wherein the second measuring component (5) has a third oscillating element and a fourth oscillating element, wherein the first oscillating element is arranged mirror-symmetrically to the third oscillating element with respect to a plane of symmetry (A), and wherein the second oscillating element is arranged mirror-symmetrically to the fourth oscillating element with respect to the plane of symmetry (A), wherein, upon a Coriolis acceleration, the first oscillating element and the fourth oscillating element are set into a first harmonic oscillating motion directed perpendicular to the plane of symmetry (A), and the second oscillating element and the third oscillating element are set into a second harmonic oscillating motion directed perpendicular to the plane of symmetry (A),wherein the first harmonic oscillation motion and the second harmonic oscillation motion are substantially in antiphase., [3] Microelectromechanical inertial sensor (1) according to claim 2, wherein, upon rotational acceleration, the first oscillating element and the third oscillating element are set into a third harmonic oscillating motion directed perpendicular to the plane of symmetry (A) and the second oscillating element and the fourth oscillating element are set into a fourth harmonic oscillating motion directed perpendicular to the plane of symmetry (A), wherein the third harmonic oscillating motion and the fourth harmonic oscillating motion are substantially in antiphase. [4] Microelectromechanical inertial sensor (1) according to claim 3, wherein the first measurement signal is generated as a function of an oscillating movement of the first oscillating element, wherein the second measurement signal is generated as a function of an oscillating movement of the second oscillating element, wherein the third measurement signal is generated as a function of an oscillating movement of the third oscillating element, and wherein the fourth measurement signal is generated as a function of an oscillating movement of the fourth oscillating element. [5] Microelectromechanical inertial sensor (1) according to one of the preceding claims, comprising: a microelectromechanical element comprising the first measuring component (4) and the second measuring component (5); and an application-oriented integrated circuit comprising the evaluation circuit (3). [6] Microelectromechanical inertial sensor (1) according to one of the preceding claims, wherein the evaluation circuit (3) has a first digital amplifier stage (33) which is designed to amplify the first difference signal, and a second digital amplifier stage (34) which is designed to amplify the second difference signal. [7] A method for operating a microelectromechanical inertial sensor (1) which has a first measuring component (4) with oscillating elements, wherein the first measuring component outputs a first measuring signal and a second measuring signal as a function of a movement about an axis of rotation, and which has a second measuring component (5) with oscillating elements, wherein the second measuring component outputs a third measuring signal and a fourth measuring signal as a function of a movement about the axis of rotation; comprising the steps: a) generating (S1) a first difference signal of the first measurement signal and the second measurement signal, and a second difference signal of the third measurement signal and the fourth measurement signal; b) amplifying (S2) the first difference signal and the second difference signal; and c) generating (S3) an output signal based on a sum of the amplified first difference signal and the amplified second difference signal; wherein the first difference signal and the second difference signal are in phase at a first acceleration, and wherein the first difference signal and the second difference signal are amplified such that the output signal substantially disappears at a second acceleration; wherein the first acceleration is a Coriolis acceleration and the second acceleration is a rotational acceleration, or wherein the first acceleration is a rotational acceleration and the second acceleration is a Coriolis acceleration. [8] Method according to claim 7, wherein steps a) to c) are carried out with an evaluation circuit (3) of the microelectromechanical inertial sensor (1) arranged on an application-oriented integrated circuit. [9] A method according to claim 7 or 8, further comprising the steps of: Applying a predetermined Coriolis acceleration to the microelectromechanical inertial sensor (1); Determining the resulting first amplified difference signal and the resulting second amplified difference signal; and Setting gain factors for the first difference signal and the second difference signal based on a comparison of the first amplified difference signal and the second amplified difference signal. [10] Method according to one of claims 7 to 9, wherein the first difference signal is amplified with a first digital amplifier stage, and wherein the second difference signal is amplified with a second digital amplifier stage.

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