Micromechanical inertial sensor and method for operating a micromechanical inertial sensor

Abstract

A micromechanical inertial sensor and a method for its operation are proposed, comprising at least the following: --- a sensor element, --- having a substrate, a substrate level, --- a detection device for detecting a mechanical deflection due to a tilting or deformation of the sensor element about an axis of rotation running essentially parallel to the substrate plane, wherein the mechanical deflection occurs due to tilting or deformation along a detection direction that is essentially perpendicular to the substrate plane, wherein the detection device has a first electrode structure and a second electrode structure firmly anchored to the substrate, wherein the detection device generates a measurement signal from the detected mechanical tilting or deformation of the sensor element about the axis of rotation.

Description

State of the art

[0001] The invention is based on a micromechanical inertial sensor according to the preamble of the main claim.

[0002] Micromechanical inertial sensors are now an integral part of many electronic devices. The problem of bending or the effects of mechanical stress on such a micromechanical inertial sensor or on individual components of such a micromechanical inertial sensor can arise. This problem can be exacerbated by a variety of defects; for example, soldering, assembly, and aging defects can have a significant impact on bending within the micromechanical inertial sensor. Furthermore, long-term aging of the circuit boards and changes in humidity are also crucial for bending and deformation within the micromechanical inertial sensor. All of this leads to a change in the sensor zero point or offset, severely limiting the accuracy and sensitivity of the sensor.

[0003] Within the detection device of the micromechanical inertial sensor, this leads to the detection, in particular a differential detection, of the measurement signal, which includes both the detection of the sensor element's deflection and the effects of mechanical stresses on the micromechanical inertial sensor or the detection device. Due to the effects of mechanical stresses on the detection device, the measurement signal also contains signal components resulting from such mechanical stresses, which cannot be compensated for, or can only be compensated for with difficulty. Disclosure of the invention

[0004] It is an object of the present invention to provide a micromechanical inertial sensor which detects bendings or effects of mechanical stresses within a detection device of the micromechanical inertial sensor by means of a suitable structure and adapts a measurement signal to a suitable extent effectively and efficiently.

[0005] The micromechanical inertial sensor according to the invention according to the main claim has the advantage over the prior art that the additional sensor element, which is firmly anchored to the substrate compared to the sensor element, reacts largely independently to external acceleration. Thus, by means of the electrode structures arranged opposite the additional sensor element, only bending or the effects of mechanical stress on the micromechanical inertial sensor or the detection device can be detected. This is used to efficiently and effectively compensate for possible interference signal components or offset signal components resulting from the bending or the effects of mechanical stress within the (detected) measurement signal or the faulty signal.

[0006] A further advantage is that, due to the (separate) ability to compensate for bending or mechanical stresses in the sensor arrangement, the size of the micromechanical inertial sensor according to the invention is not a limiting factor. Due to the efficient and effective compensation of bending or the effects of mechanical stresses, a two to five times more accurate offset and sensitivity specification can be achieved for a conventional size of the micromechanical inertial sensor. For a thinner design compared to conventional designs and a resulting higher susceptibility to the effects of mechanical stresses, the effective and efficient compensation ensures the same offset and sensitivity specifications as for conventional designs for the micromechanical inertial sensor according to the invention.Furthermore, micromechanical inertial sensors of larger design or with a higher restoring force can also be realized, since in this case too the bending or effects of mechanical stresses, for example with regard to the sensor housing, can be compensated.

[0007] According to the invention, a mechanical deflection due to a tilting of the sensor element about a rotation axis (torsion spring) running essentially parallel to the substrate plane is detected, wherein the mechanical deflection (due to the tilting) occurs along a detection direction running essentially perpendicular to the substrate plane. The stiffer this (torsion) spring is selected, the more susceptible the sensor is to offset errors due to bending. According to the invention, the bending can advantageously be measured separately and the useful signal can thus be corrected. Thus, the micromechanical inertial sensor according to the invention can also be realized with a spring, in particular a torsion spring, with high stiffness. Problematic bending or the effects of mechanical stresses can be compensated for particularly effectively and efficiently according to the invention because the additional sensor element for detecting the bending orThe effects of mechanical stress can be embedded or integrated directly into the detection device (and thus also into the arrangement of the first and second electrode structures) of the micromechanical inertial sensor. This advantageously allows, in particular, significantly better error correction than is possible, for example, with non-embedded, separate stress sensors (which are located elsewhere, i.e., outside the detection device, the component arrangement, for example, in the chip package). In particular, it is advantageous according to the invention that the bending of all fixed electrodes is measured, thus allowing all relevant false signals to be detected.

[0008] Advantageous embodiments and further developments of the invention can be found in the dependent claims and the description with reference to the drawings.

[0009] According to an advantageous embodiment of the invention, the micromechanical inertial sensor is configured such that the effects of mechanical stresses on the inertial sensor in the measurement signal of the sensor element detected from the variable capacitances are compensated by means of an additional measurement signal, wherein the additional measurement signal is generated by the differential detection of the additional variable capacitances. Thus, it is advantageously possible to effectively and efficiently compensate for the bending or effects of mechanical stresses within the detection device of the micromechanical inertial sensor using the additional sensor element and the additional measurement signal detected therefrom.

[0010] According to an advantageous embodiment of the invention, the additional sensor element and the sensor element are mechanically coupled (but electrically separated). This advantageously results in a substantially similar effect of bending or the impact of mechanical stresses on the sensor element and on the additional sensor element. This leads to an increase in the accuracy of the compensation using the additional measurement signal.

[0011] According to an advantageous embodiment of the invention, it is provided that the sensor element comprises a first sensor element and a second sensor element, wherein the first sensor element is arranged along the detection direction relative to the first electrode structure and the second electrode structure in such a way that a first variable capacitance is formed between the first sensor element and the first electrode structure and between the first sensor element and the second electrode structure, wherein the second sensor element is arranged along the detection direction relative to the first electrode structure and the second electrode structure in such a way that a second variable capacitance is formed between the second sensor element and the first electrode structure and between the second sensor element and the second electrode structure,wherein the first sensor element, compared to the second sensor element, has a coupling in the detection direction that is at least a factor of 2 stronger, in particular a coupling in the detection direction that is at least a factor of 10 stronger, with the substrate. This advantageously makes it possible to achieve a very large measuring range for the micromechanical inertial sensor by switching between detecting a deflection of the first sensor element and the second sensor element. The compensation of the first and second measurement signals differentially detected from the first variable capacitances and the second variable capacitances, respectively, is ensured in both cases by the further measurement signal differentially detected from the further variable capacitances.

[0012] According to an advantageous embodiment of the invention, the additional sensor element has a coupling in the detection direction that is at least 50 times stronger than the sensor element, in particular a coupling in the detection direction that is at least 200 times stronger. This advantageously results in effective use of the additional sensor element, firstly, for compensating for the bending or effects of mechanical stresses on the micromechanical inertial sensor or the detection device and, secondly, in the case of high acceleration or maximum deflection of the sensor element, for detecting a measurement signal from the deflection of the additional sensor element at high acceleration.

[0013] According to an advantageous embodiment of the invention, an anchoring structure of the further sensor element differs from an anchoring structure of the first electrode structure and / or an anchoring structure of the second electrode structure. This advantageously allows the anchoring structure of the further sensor element to be implemented efficiently and in a space-saving manner in an existing detection device.

[0014] A further subject of the invention is a method for operating a micromechanical inertial sensor according to the independent method claim.

[0015] The inventive method for operating a micromechanical inertial sensor proves to be advantageous over the prior art in that the additional sensor element reacts largely independently to external acceleration and thus only reacts sensitively to the bending or effects of mechanical stresses on the micromechanical inertial sensor. Thus, possible offset signal components resulting from the bending or effects of mechanical stresses can be efficiently and effectively compensated within the measurement signal or the faulty signal.

[0016] In addition, the size of the micromechanical inertial sensor can be adapted or varied to a greater extent, as mechanical stresses are not a limiting factor due to their compensability, or at least only a minor one. By effectively compensating for the interference caused by bending or the effects of mechanical stresses, significantly improved offset and sensitivity specifications can be achieved with conventional sizes, particularly two to five times improved offset and sensitivity specifications. Alternatively, a thinner design can also be provided.Although this results in a higher susceptibility to mechanical stresses for the micromechanical inertial sensor in operation, the inventive design of the sensor and its operation ensure the same offset and sensitivity specifications as with conventional designs. Furthermore, the inventive method for operating the micromechanical inertial sensor also allows for larger designs or designs with a higher restoring force, since bending or the effects of mechanical stress on the housing can be compensated separately during operation of the micromechanical inertial sensor and are thus limited.

[0017] The same advantages and configurations that were described in connection with the embodiments of the micromechanical inertial sensor according to the invention can be applied to the method for operating a micromechanical inertial sensor.

[0018] Embodiments of the present invention are illustrated in the drawings and explained in more detail in the following description. Short description of the drawings: Fig. 1 shows a schematic representation of a micromechanical inertial sensor according to the prior art. Fig. 2 shows a schematic representation of a micromechanical inertial sensor according to the present invention. Fig. 3 a) to d) shows a schematic representation of the micromechanical inertial sensor according to the state of the art. Fig. 4 a) to d) shows an embodiment of the micromechanical inertial sensor according to the present invention. Fig. 5 to 9 show further embodiments of the micromechanical inertial sensor according to the present invention. Embodiments of the invention:

[0019] Fig. 1 shows a schematic representation of a micromechanical inertial sensor 100 according to the prior art in side view, i.e., the drawing plane is perpendicular to a substrate plane. Within a MEMS structure 101, a first electrode structure 200, 200' and a second electrode structure 210, 210' are shown, as well as a sensor element 220 that can be tilted about a rotation axis 102, such that a mechanical deflection due to this tilting occurs in a detection direction running substantially perpendicular to the substrate plane. Both the first electrode structure 200, 200' and the sensor element 220, as well as the second electrode structure 210, 210' and the sensor element 220, each form a variable capacitance.The variable capacitances are related in a manner known for MEMS structures; the arrangement enables a differential evaluation of the tilt of the sensor element 220 about the rotation axis 102 in a known manner. The capacitive signals are forwarded to an ASIC structure 101' and differentially detected there. Furthermore, a measurement signal 700 is generated by means of the differential detection. The measurement signal 700 represents an erroneous signal because, in addition to the useful signal component actually to be measured and resulting from the tilt of the sensor element 220 about the rotation axis 102, the measurement signal 700 also contains noise signal components or offset components, which result from bending or the effects of mechanical stresses on the micromechanical inertial sensor 100. Thus, the measurement signal 700 represents an erroneous signal 700 due to the effects of mechanical stresses.

[0020] Fig. Figure 2 shows a schematic representation of a micromechanical inertial sensor 100 according to the present invention, also in a side view, ie, the drawing plane is to be understood perpendicular to a substrate plane. Shown within the MEMS structure 101 are again the first electrode structure 200, 200' and the second electrode structure 210, 210' as well as the sensor element 220, which is tiltable about the rotation axis 102, so that a mechanical deflection due to this tilting occurs in a detection direction running substantially perpendicular to the substrate plane. This detection direction corresponds in Fig. 2 a vertical direction, ie the tilting of the sensor element 220 corresponds to a movement (of parts) of the sensor element 220 (depending on their distance from the rotation axis 102) upwards or downwards as shown in Fig. 2. According to the present invention, the micromechanical inertial sensor comprises, in addition to the sensor element 220, a further sensor element 221, which is firmly (or more firmly) anchored to or on the substrate than the sensor element 220. The first electrode structure 200, 200' (hereinafter also referred to as C1 electrodes) and the sensor element 220, as well as the second electrode structure 210, 210' (hereinafter also referred to as C2 electrodes) and the sensor element 220, each form the variable capacitance or capacitances. Furthermore, the first electrode structure 200, 200' and the further sensor element 221, as well as the second electrode structure 210, 210' and the further sensor element 221, each form a further variable capacitance or capacitances.These are also related in a manner known for MEMS structures and are also read out differentially within the ASIC structure 101' - separately from the variable capacitances 300. The measurement signal 700 generated from the variable capacitances is compensated there by means of a further measurement signal differentially detected and generated from the further variable capacitances, thus generating a compensated measurement signal 700'. Using the information from the differential readout of the further variable capacitances, it is thus possible according to the invention to detect interference effects based in particular on bending or mechanical stresses by means of the further measurement signal in order to compensate for such interference effects or interference signal components in the measurement signal 700 as far as possible. The compensated measurement signal 700' therefore essentially contains the useful signal component and is free of the bending orEffects of mechanical stresses in the form of noise or offset components.

[0021] Fig. 3 a) to d) shows a schematic representation (of the MEMS element 101) of the micromechanical inertial sensor 100 according to the prior art. Fig. 3 a) shows schematically a top view of the micromechanical inertial sensor 100, while the Fig. 3 b) to 3 d) Side views according to section line 110 (in Fig. 3 a)) for different operating states or situations. By means of a two-sided torsion spring 103, the sensor element 220 is tiltable about the axis of rotation 102, which runs parallel to the substrate plane of the substrate 105. The torsion spring 103 and thus also the sensor element 220 are fixed or anchored relative to the substrate 105 via a substrate anchor 225. The mass distribution of the sensor element 220 is asymmetrical: The sensor element 220 has on one side of the axis of rotation 102 (in Fig. 3 shown on the right) due to a recess 240' (in its frame-like structure, hereinafter also referred to as box side) has a lower mass than on the other side of the rotation axis 102 (in Fig. 3 (left), on which the sensor element 220 comprises an additional mass element 240 (compared to the other side) (hereinafter also referred to as the mass side). Due to the elastic mounting and the asymmetric mass distribution of the sensor element 220 (due to its mass element 240 and the recess 240'), the seismic mass or the sensor element 220 is mechanically deflected or tilted by an angle (tilt angle) when subjected to an applied vertical acceleration; deflection and acceleration are largely proportional here - at least for small tilt angles. The frame-like part of the sensor element 220 (as well as the additional mass element 240) is realized in particular in a layer consisting of or comprising EpiPoly (EP) material.

[0022] Connected to the sensor element 220, the latter has its (associated) electrode 220' below (i.e., in a direction toward the substrate 105), hereinafter also referred to as the CM electrode 220', in particular in the form of an FP plate (i.e., realized in another layer of the inertial sensor 100). The FP plate (and thus also the CM electrode) 220' of the sensor element 220 is, in particular, largely planar.

[0023] When the sensor element 220 is tilted about the rotation axis 102, the CM electrode 220' moves along a detection direction that is substantially perpendicular to the substrate plane (this movement in the detection direction is more or less large, depending on the distance of the corresponding (observed) part of the CM electrode 220' from the rotation axis 102).

[0024] Furthermore, the micromechanical inertial sensor 100 also has, according to the prior art, the first electrode structure 200, 200' and the second electrode structure 210, 210'. The first electrode structure 200, 200' as well as the second electrode structure 210, 210' (hereinafter also referred to collectively as fixed electrodes) each comprise: -- an electrode on the one hand and on the other hand the rotation axis 102 and above (ie on the side facing away from the substrate 105) the CM electrode 220' of the sensor element 220 - for the first electrode structure designated by reference numeral 200 and for the second electrode structure by reference numeral 210 - and -- an electrode on the one hand and on the other hand the axis of rotation 102 and below (ie on the side facing the substrate 105) the CM electrode 220' of the sensor element 220 - for the first electrode structure with reference numeral 210' and for the second electrode structure with reference numeral 200'.

[0025] Both the electrodes 200, 200' of the first electrode structure and the electrodes 210, 210' of the second electrode structure are electrically connected to one another and, together with the CM electrode 220' of the sensor element 220, they form a variable capacitance 300 depending on the deflection (tilting) of the sensor element 220 in the detection direction. By means of this arrangement, it is possible, in a manner known for MEMS structures, to enable a differential evaluation of the tilting of the sensor element 220 about the rotation axis 102; the capacitive signals are transmitted to the ASIC structure 101' (in Fig. 3 not shown) and differentially detected there to generate the measurement signal 700. Thus, the first and second electrode structures 200, 200', 210, 210' form a differential capacitor that is divided into four separate quadrants (around the rotation axis 102).

[0026] The electrodes 200, 210 (of the first and second electrode structures), each arranged above the CM electrode 220' of the sensor element 220, are firmly connected to the substrate wafer 105 via separate anchors 200" (for the electrode 200) and 210" (for the electrode 210), respectively. The electrodes 200', 210' (of the first and second electrode structures), each arranged below the CM electrode 220' of the sensor element 220, lie directly on the substrate 105 and are firmly connected thereto. Fig. 3 b) shows the situation without a mechanical deflection of the sensor element 220, while Fig. 3 c) shows the situation with such a deflection. It can be seen that between the sensor element 220 (or between its CM electrode 220') and the first and second electrode structures 200, 200', 210, 210', the (portions of) the variable capacitance 300 is / are realized; by evaluating this variable capacitance 300, a deflection of the sensor element 220 (or the CM electrode 220' moving with it) can be measured, cf. Fig. 3c) wedge-shaped or trapezoidal (each with the same slope or inclination - due to the assumed (ideal) situation without any bending). In the case of deformations of the substrate 105, the electrode distance between the bottom electrodes (i.e., the electrodes 210', 200') and the CM electrode 220' of the sensor element 220 also changes (and likewise, distance changes and thus false signals can occur due to a bending of the top electrodes (i.e., the electrodes 200, 210)); this results in the erroneous measurement signal 700 in arrangements according to the prior art. Such a situation in the case of deformations is illustrated by the illustration in Fig. 3 d), in which the (portions of the) variable capacity 300 are also shown wedge-shaped or trapezoidal, but due to the deformation or bending not with the same (or at least with potentially different) gradient or inclination.

[0027] Fig. 4 a) to d) shows a schematic representation (of the MEMS element 101) of the micromechanical inertial sensor 100 according to a first embodiment of the present invention. Fig. 4 a) shows schematically a plan view of the micromechanical inertial sensor 100 according to the invention, while the Fig. 4 b) to 4 d) Side views according to section line 110 (in Fig. 4 a)) for various operating states or situations. Again, the sensor element 220 can be tilted or mechanically deflected about the rotation axis 102 by means of a two-sided torsion spring 103, and again, the rotation axis 102 runs parallel to the substrate plane or main extension plane of the substrate 105. The torsion spring 103 is fixed or anchored relative to the substrate 105 via a substrate anchor 225; thus, the sensor element 220 (connected by the torsion spring 103) is also fixed or anchored relative to the substrate 105, but is movably connected with respect to a mechanical deflection—in particular, with respect to the mechanical deflection or tilting about the rotation axis 102 (or around the torsion spring 103) primarily considered here.

[0028] Analogous to the representation according to Fig. 3, according to all embodiments of the present invention, the mass distribution of the sensor element 220 is asymmetrical, ie the sensor element 220 has on one side of the axis of rotation 102 (in Fig. 4 shown on the right) due to a recess 240' (in its frame-like structure, hereinafter also referred to as box side) has a lower mass than on the other side of the rotation axis 102 (in Fig. 4 (shown on the left), on which the sensor element 220 comprises an additional mass element 240 (compared to the other side) (hereinafter also referred to as the mass side). Due to the elastic mounting or suspension by means of the torsion spring 103 and the asymmetric mass distribution of the sensor element 220 (due to its mass element 240 on the one hand and the recess 240' on the other hand), the seismic mass or the sensor element 220 is mechanically deflected or tilted by an angle (tilt angle) when subjected to an applied vertical acceleration; deflection and acceleration are largely proportional here - at least for small tilt angles. The frame-like part of the sensor element 220 (as well as the additional mass element 240) is realized in particular in a layer consisting of or comprising EpiPoly (EP) material.

[0029] Connected to the sensor element 220, the latter has its (associated) electrode 220' below (i.e., in a direction from the EP layer to the substrate 105), hereinafter also referred to as the CM electrode 220', particularly realized in the form of an FP plate (i.e., realized in a different layer of the inertial sensor 100 than the EP layer). The FP plate (and thus also the CM electrode) 220' of the sensor element 220 is, in particular, largely planar.

[0030] Again (ie analogous to the representation according to Fig. 3) When the sensor element 220 is tilted about the rotation axis 102, the CM electrode 220' moves along a detection direction that is substantially perpendicular to the substrate plane (this movement in the detection direction is more or less large, depending on the distance of the corresponding (observed) part of the CM electrode 220' from the rotation axis 102).

[0031] And again, the micromechanical inertial sensor 100 according to the invention (according to all embodiments of the invention) also has the first electrode structure 200, 200' and the second electrode structure 210, 210'. The first electrode structure 200, 200' as well as the second electrode structure 210, 210' (hereinafter also referred to collectively as fixed electrodes) each comprise: -- an electrode on the one hand and on the other hand (in plan view) of the rotation axis 102 and above (ie on the side facing away from the substrate 105) the CM electrode 220' of the sensor element 220 - designated by reference numeral 200 for the first electrode structure and by reference numeral 210 for the second electrode structure - and -- an electrode on the one hand and on the other hand (also in plan view) of the axis of rotation 102 and below (ie on the side facing the substrate 105) the CM electrode 220' of the sensor element 220 - for the first electrode structure with reference numeral 210' and for the second electrode structure with reference numeral 200'.

[0032] Again, the electrodes 200, 200' of the first electrode structure are electrically connected to one another, and furthermore (but separately from the first electrode structure) the electrodes 210, 210' of the second electrode structure are also electrically connected to one another. They form a variable capacitance 300 with the CM electrode 220' of the sensor element 220 depending on the deflection (tilting) of the sensor element 220 in the detection direction. By means of this arrangement, it is possible, in a manner known for MEMS structures - and in particular as in Fig. 3 - also according to all embodiments of the present invention (and in Fig. 4 schematically shown) to enable a differential evaluation of the tilting of the sensor element 220 about the rotation axis 102; the capacitive signals are transmitted to the ASIC structure 101' (in Fig. 4 not shown) and differentially detected there to generate the measurement signal 700. Thus, the first and second electrode structures 200, 200', 210, 210' form a differential capacitor that is divided into four separate quadrants (around the rotation axis 102).

[0033] Again, in Fig. 4 (but exclusively in Fig. 4 a) - and according to all embodiments of the invention - it is provided that the electrodes 200, 210 (of the first and second electrode structures) arranged above the CM electrode 220' of the sensor element 220 are firmly connected to the substrate wafer 105 via separate anchors 200" (for the electrode 200) and 210" (for the electrode 210); and likewise, the electrodes 200', 210' (of the first and second electrode structures) arranged below the CM electrode 220' of the sensor element 220 are located, in particular, directly on the substrate 105 and are firmly connected thereto.

[0034] In contrast to arrangements according to the prior art, however, it is provided according to the invention that in addition to the sensor element 220, a further sensor element 221 is present - preferably within the core of the inertial sensor 110, ie in particular directly adjacent (and in particular also arranged symmetrically with respect to the rotation axis 102) to the sensor element 220.

[0035] In plan view according to Fig. 4 a), the further sensor element 221 is fastened or connected by means of at least one further substrate anchor 211" (hereinafter also referred to as CMS anchor), which according to the invention is arranged as close as possible to the main anchor 225 (ie the substrate anchor 225 by means of which the torsion spring 103 is suspended relative to the substrate 105) - ie as centrally as possible. According to the invention, it is particularly provided that the further sensor element 221 is connected to the further substrate anchor 221" via at least one further connecting element 221'. According to the Fig. 4, four further substrate anchors 211" (i.e. additional substrate anchors or CMS anchors) are placed as centrally as possible and as close as possible to the main anchor (CM anchor 225) by way of example. The (exemplary) four further sensor elements 221 are guided on the CMS anchors 221" by means of EP structures (i.e. the connecting elements 221', which are formed in particular as part of the EP layer) up to the outer edge (in the example up to the corners) of the top electrodes (200, 210). At these outer edges, it is provided according to the invention that regions are cut out of the FP layer (i.e. from the layer of the CM electrode 220') (or are or are formed by means of recesses in this layer) electrically separable regions). Thus, it is possible according to the invention to have electrodes at the same location that are connected to CMS potential (CMS electrodes, i.e. the further sensor element 221 orthe electrodes of the further sensor element 221). This creates a second differential capacitor (i.e., the further variable capacitance) 310 in addition to the actual differential capacitor 300 of the sensor (or variable capacitance 300 between the sensor element 220 and the first and second electrode arrangement 200, 200', 210, 210'), which is used according to the invention for stress evaluation. The stiffness of the EP connections 211' to the CMS electrodes 221 is, according to the invention, significantly greater than the stiffness of the spring suspension of the sensor, i.e., the sensor element 220. The differential capacitor of the stress electrode (i.e.,The further variable capacitance 310 therefore does not react (or at least reacts considerably less) to external accelerations (along the sensitive direction of the sensor), but essentially only to a bending of the electrodes of the first and second electrode arrangement 200, 200', 210, 210' and the CMS electrodes 221. An example of such a situation is shown in . Fig. 4 d). For simplicity, Fig. 4 b) (analogous to Fig. 3 b)) the situation without a mechanical deflection of the sensor element 220 (and also without bending), while Fig. 4 c) shows the situation with such a deflection, but also without bending. It can be seen again that between the sensor element 220 (or between its CM electrode 220') and the first and second electrode structure 200, 200', 210, 210', the (portions of) the variable capacitance 300 is / are realized; by evaluating this variable capacitance 300, a deflection of the sensor element 220 (or of the CM electrode 220' moving with it) can be measured. Due to the fact that the (for the Fig. 4 b) to d) relevant) section line 110 in Fig. 4 a) cuts the CMS electrodes 221, is in the Fig. 4 b) to 4d) that the plane of the CM electrode 220' is interrupted at the locations of the illustrated CMS electrodes 221 and that the CMS electrodes 221 are located in this gap, which are held or connected to the substrate 105 by means of the connecting elements 221' (also produced by means of gaps or separating recesses in the EP plane) (and the further substrate anchors 211"); however, these connecting elements 221' are in the Fig. 4 b) to d) are not shown for the sake of simplicity.

[0036] For this reason, in the Fig. 4 b) to d) the regions of the variable capacitance 300 are interrupted by regions of the further variable capacitance 310 (which correspond to those regions of the first and second electrode structures 200, 200', 210, 210' that are arranged opposite the CMS electrode 221 and opposite the plurality of CMS electrodes 221, respectively).

[0037] As already mentioned, Fig. 4 b) the situation without a mechanical deflection of the sensor element 220 (and without bending), while Fig. 4 c) shows the situation with such a deflection, cf. Fig. 4c) wedge-shaped and trapezoidal (each with the same gradient or slope - due to the assumed (ideal) situation without any bending) represented capacitance portions of the variable capacitance 300 and the further variable capacitance 310.

[0038] According to the invention it is therefore true - as in the prior art, cf. Fig. 3 - also such that in the event of deformations or bending of the substrate 105, the electrode spacing between the bottom electrodes (i.e., the electrodes 210', 200') and the CM electrode 220' of the sensor element 220 (and likewise the spacings due to a bending of the top electrodes, i.e., the electrodes 200, 210) change and thus erroneous measurement signals 700 arise; however, it is advantageously possible according to the invention to be able to compensate for this erroneous measurement signal due to the measurement of the further variable capacitance 310, because according to the invention the influence of such deformations or bendings of the substrate 105 can be detected separately (from the signal 700 caused by the acceleration to be measured) by means of the CMS electrode(s) 221 arranged locally in the (lateral) region of the CM electrode 220' (i.e., in a recess or gap thereof). Such a situation of deformation is in Fig. 4 d) indicated - the (portions of) the variable capacitance(s) 300 or the further variable capacitance(s) 310 is / are shown wedge-shaped or trapezoidal, but due to the deformation or bending not with the same (or at least with potentially different) gradient or inclination.

[0039] The position and shape of the CMS electrodes along the stress sensor suspension (ie the connecting elements 221') are generally freely selectable. Fig. In the variant or embodiment shown in Figure 4, the CMS electrodes 221 are square and placed in the outermost corners of the top electrodes 200, 210. Elongated CMS electrodes 221, which are inserted along the vertical bars, are also conceivable. This design freedom facilitates, according to the invention, the actual design of the stress sensor (i.e., the design and placement of the CMS electrode or the additional sensor element 221) and its integration into the inertial sensor, i.e., the arrangement of the additional sensor elements 221 in the region of the CM electrode 220'.

[0040] The CMS electrode 221 and the CM electrode 220' of the seismic mass are electrically and mechanically separated from each other; however, they can also be mechanically coupled (at least to some extent) and electrically separated. In particular, they are connected to the ASIC structure 101' with separate bond pads (see Fig. 2). The first electrode structures 200, 200' and the second electrode structures 210, 210' are each connected together to the MEMS bond pads (sensor pads C1 and C2). No electrical separation is necessary between the differential capacitor of the stress electrodes (additional variable capacitance 310) and the measuring electrodes (variable capacitance 300); thus, the first and second electrode structures 200, 200', 210, 210' are used simultaneously for acceleration and stress measurement.

[0041] In the "normal" Acc measurement mode (i.e., acceleration measurement mode), the ASIC (ASIC structure 101') evaluates the MEMS element (or acceleration sensor) via the CM / C1 / C2 electrodes. In contrast, in "correction mode," the sensor is evaluated via the CMS / C1 / C2 electrodes. By switching the CM to the CMS electrode at the ASIC input, it is possible to switch between these two modes or operating modes.

[0042] The capacitance value measured by the stress sensor can be used directly to compensate for the offset and sensitivity errors in the ACC sensor signal 700 – in the simplest case, for example, using linear scaling. However, by measuring the sensor deformation, more complex evaluation logic can also be implemented in the ASIC. Furthermore, it is possible to permanently compensate the error signals using a multiplexing method.

[0043] The Fig. 5 to 9 show further embodiments (of the MEMS element) of the micromechanical inertial sensor according to the present invention.

[0044] Fig. 5 shows a variant (or embodiment) in which the EP suspension 221' of the CMS electrode 221 is formed as a closed frame: As shown in Fig. 4, two additional substrate anchors 221" (for the EP suspensions 221') are provided on both sides of the rotation axis 102; these two additional substrate anchors are connected by an additional connecting element 221''' to close the frame. This increases the overall rigidity of the stress sensor while slightly increasing the space requirement. In addition, the stability of these anchors can be increased by an optional mechanical connection (another connecting element 221"') of the additional substrate anchors 221'' belonging to each other, thereby increasing the robustness of the stress sensor.

[0045] Fig. Figure 6 shows a variant (or embodiment) in which the anchors of the top electrodes (C1 a / C2a) - ie the separate anchors 200" (for the electrode 200) and 210" (for the electrode 210) - are divided. Furthermore, the respective CMS anchors (further substrate anchors 221") are connected by means of an EP bridge (similar to the further connecting element 221''' according to Fig. 5). An EP suspension is constructed on this bridge, which extends through the resulting gap between the split anchors (of the top electrodes (C1a / C2a)). At the end of the suspension, the CMS electrode 221 with stiffening structures is inserted vertically and centrally. This variant requires less space overall and achieves a significantly smaller overhang of the CMS suspension. Furthermore, the suspension only extends in one direction. Both of these increase the stiffness of the stress sensor structure. Furthermore, it simplifies the overall less complex EP suspension in the stress sensor, thus meeting robustness requirements for the stress sensor.

[0046] Fig. Figure 7 shows a variant (or embodiment) in which the design features according to Fig. 5 and Fig. 6 are combined: While the design of the stress sensor becomes more complex overall, the larger suspension surface provides significantly more possibilities for using the CMS electrodes 221. As a result, the sensitivity of the stress sensor can be increased, for example.

[0047] Fig. Figure 8 shows a variant (or embodiment) in which the CMS electrodes 221 are used on the inner sides of the top electrodes (C1a / C2a) with respect to the rotation axis 102. Thus, only individual EP beams 221' are required for their suspension (the CMS electrodes 221). While detecting the deformation close to the center reduces the sensitivity of the stress sensor, it enables maximum rigidity in the CMS suspension with minimal interference with the basic structure of the sensor.

[0048] Fig. 9 shows a variant (or embodiment) in which a modified anchoring of the stress sensor and the seismic mass is realized: In the previously described embodiments, the seismic mass (at CM potential) is suspended completely centrally (by means of the substrate anchor 225) and the anchors for the CMS electrodes 221 are arranged as close as possible to it, but slightly eccentrically placed; in the variant according to Fig. 9, the central anchor supports the CMS stress electrodes 221 and the seismic mass is suspended via two separate, vertically distributed anchors 225.

[0049] The central suspension and the exclusively vertical offset of all anchors minimizes the deviation between the deformation measured by the stress sensor and the deformation that actually induces error signals in the inertial sensor. This increases the accuracy of the measured offset signal. Furthermore, this variant requires fewer anchors overall, saving space.

[0050] The described anchor variation is exemplary and can be transferred with the mentioned advantages to the constructions of the previously mentioned embodiments.

[0051] The embodiments of the invention described so far largely assume that the additional sensor element is largely mechanically separated from the sensor element (in addition to their electrical separation); however, the invention also provides for the additional sensor element (despite its electrical separation from the sensor element) to be mechanically coupled at least to a certain extent. Such a mechanical connection of the CM and CMS anchors effectively transfers problematic deformations of the CM electrode to the CMS electrodes. This leads to a largely equal stress input to both the CM electrodes and the CMS electrodes. This increases the accuracy of the stress measurement / compensation.

[0052] Furthermore, it is advantageously possible according to the invention for the sensor element to have a first and a second sensor element, so that additional electrodes (hereinafter also referred to as CMX electrodes) are present opposite the fixed electrodes C1 and C2. This arrangement is advantageous, for example, for a sensor with a very large measuring range. For this purpose, a very softly suspended mass (CM; first sensor element) and a harder suspended mass (CMX; second sensor element) are used. By switching between CM and CMX, the sensitivity range can be switched. By switching to CMS, the offset, i.e. the bending effect, can be compensated for simultaneously for both measuring channels.

[0053] Furthermore, it can advantageously be provided that the mass of the CMS channel (i.e., the additional sensor element) is not rigidly connected to the substrate 105, but rather more rigidly than the mass of the CM channel (i.e., the sensor element). This allows the CMS channel to continue to be used to correct the CM channel for an offset. At the same time, when the CM channel reaches its limit, the CMS channel can be used as an acceleration sensor for very high accelerations. This advantageously allows the sensor's measuring range to be expanded very easily and cost-effectively.

Claims

[1] Micromechanical inertial sensor (100) comprising at least: --- a sensor element (220), --- a substrate (105) having a substrate plane, --- a detection device for detecting a mechanical deflection due to a tilting of the sensor element (220) about a rotational axis (102) running substantially parallel to the substrate plane, wherein the mechanical deflection due to the tilting occurs along a detection direction running substantially perpendicular to the substrate plane, wherein the detection device comprises a first electrode structure (200, 200') and a second electrode structure (210, 210') firmly anchored to the substrate (105), wherein the detection device generates a measurement signal (700) from the detected mechanical deflection of the sensor element (222) along the detection direction characterized by , that the micromechanical inertial sensor (100) comprises a further sensor element (221), wherein the further sensor element (221) is firmly anchored to the substrate (105) in comparison with the sensor element (220), wherein the first electrode structure (200, 200') and the second electrode structure (210, 210') are arranged along the detection direction relative to the further sensor element (221) and the sensor element (220) in such a way that a variable capacitance (300) is formed between the sensor element (220) and the first electrode structure (200, 200') and between the sensor element (220) and the second electrode structure (210, 210'), and a further variable capacitance (310) is formed between the further sensor element (221) and the first electrode structure (200, 200') and between the further sensor element (221) and the second electrode structure (210, 210'), wherein the detection device is provided for differential detection of the variable capacitances (300) and the further variable capacitances (310), wherein the micromechanical inertial sensor (100) is configured such that the effects of mechanical stresses on the inertial sensor (100) affect both the first electrode structure (200, 200') and the second electrode structure (210, 210') as well as the sensor element (220) and the further sensor element (221). [2] Micromechanical inertial sensor (100) according to claim 1, characterized byin that the micromechanical inertial sensor (100) is configured such that the effects of mechanical stresses on the inertial sensor (100) in the measurement signal (700) detected from the variable capacitances (300) are compensated by means of a further measurement signal, wherein the further measurement signal is generated by the differential detection of the further variable capacitances (310), so that it is particularly possible to compensate the effects of mechanical stresses on the inertial sensor (100) in the measurement signal (700) detected from the variable capacitances (300, 300') and to generate a compensated measurement signal (700'). [3] Micromechanical inertial sensor according to one of the preceding claims, characterized by that the further sensor element (221) and the sensor element (220) are mechanically coupled. [4] Micromechanical inertial sensor (100) according to one of the preceding claims, characterized bythat the sensor element (220) comprises a first sensor element and a second sensor element, wherein the first sensor element is arranged along the detection direction relative to the first electrode structure (200, 200') and the second electrode structure (210, 210') such that a first variable capacitance is formed between the first sensor element and the first electrode structure (200, 200') and between the first sensor element and the second electrode structure (210, 210'), wherein the second sensor element is arranged along the detection direction relative to the first electrode structure (200, 200') and the second electrode structure (210, 210') such that a second variable capacitance is formed between the second sensor element and the first electrode structure (200, 200') and between the second sensor element and the second electrode structure (210, 210'), wherein the first sensor element has a coupling in the detection direction (102) with the substrate (105) that is at least a factor of 2 stronger than the second sensor element, in particular a coupling in the detection direction (102) that is at least a factor of 10 stronger. [5] Micromechanical inertial sensor (100) according to one of the preceding claims, characterized by that the further sensor element (221) has a coupling in the detection direction (102) with the substrate (105) that is at least 50 times stronger than the sensor element (220), in particular a coupling in the detection direction (102) that is 200 times stronger. [6] Micromechanical inertial sensor (100) according to one of the preceding claims, characterized bythat an anchoring structure (621', 621'') of the further sensor element (221) differs from an anchoring structure of the first electrode structure (200, 200') and / or an anchoring structure of the second electrode structure (210, 210'). [7] Method for operating a micromechanical inertial sensor (100) at least comprising: --- a sensor element (220), --- a substrate (105) having a substrate plane, --- a detection device for detecting a mechanical deflection due to a tilting of the sensor element (220) about an axis of rotation (102) running substantially parallel to the substrate plane, wherein the mechanical deflection occurs due to the tilting along a detection direction running substantially perpendicular to the substrate plane, wherein the detection device comprises a first electrode structure (200, 200') and a second electrode structure (210, 210') firmly anchored to the substrate (105), wherein the detection device generates a measurement signal (700) from the detected mechanical deflection of the sensor element (220) along the detection direction (102) characterized by , that the micromechanical inertial sensor (100) comprises a further sensor element (221), wherein the further sensor element (221) is firmly anchored to the substrate (105) in comparison with the sensor element (220), wherein the first electrode structure (200, 200') and the second electrode structure (210, 210') are arranged along the detection direction relative to the further sensor element (221) and the sensor element (220) such that a variable capacitance (300) is formed between the sensor element (220) and the first electrode structure (200, 200') and between the sensor element (220) and the second electrode structure (210, 210'), and a further variable capacitance (310) is formed between the further sensor element (221') and the first electrode structure (200, 200') and between the further sensor element (221) and the second electrode structure (210, 210'), wherein the detection device is provided for differential detection of the variable capacitances (300) and the further variable capacitances (310), wherein the effects of mechanical stresses on the inertial sensor (100) affect both the first electrode structure (200, 200') and the second electrode structure (210, 210') as well as the sensor element (220) and the further sensor element (221).

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