Anchor tracking device for in-plane accelerometers and related methods

Abstract

Microelectromechanical system accelerometer (MEMS), comprising: a multitude of anchors connected to a substrate, a test mass which is connected to at least one first and one second anchor of the plurality of anchors via one or more corresponding springs, a multitude of solid electrodes connected to the substrate, comprising a first solid electrode and another solid electrode, one or more scanning electrodes connected to the test mass and forming one or more scanning capacitors with at least one of the plurality of fixed electrodes, wherein the one or more scanning capacitors are configured to detect a lateral acceleration of the test mass, and a first and a second compensation structure, wherein the first compensation structure is rigidly connected to the first armature and the second compensation structure is rigidly connected to the second armature, wherein the first compensation structure has a first compensation electrode forming a first lateral compensation capacitor with the first fixed electrode, and wherein the second compensation structure has a second compensation electrode forming a second lateral compensation capacitor with the further fixed electrode.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation claiming priority to U.S. patent application Serial No. 15 / 228,229, filed August 4, 2016, with Attorney Docket No. G0766.70074US00 and entitled "ANCHOR TRACKING APPARATUS FOR IN-PLANE ACCELEROMETERS AND RELATED METHODS." AREA OF REVELATION

[0002] The present application relates to MEMS inertial sensors (MEMS: microelectromechanical system). BACKGROUND

[0003] Some capacitive MEMS (microelectromechanical system) sensors sense in-plane accelerations. Some such sensors have a fixed electrode and a movable electrode. The fixed electrode is anchored to a substrate, while the movable electrode is connected to a proof mass. The proof mass moves in response to accelerations in the plane of the proof mass. EP 1 640 726 A1 relates to a microelectromechanical structure (1; 30; 60; 70) in which a detection structure (19; 31) is formed from semiconductor material by a stator (5; 35; 61) and a rotor (4; 34) which are movable relative to one another in the presence of an external voltage and are subject to a thermal stress; a compensation structure (24; 46) of a microelectromechanical type, which is subject to a thermal stress and is invariant with respect to the external voltage, is connected to the detection structure (19; 31), whereby the microelectromechanical structure (1; 30; 60; 70) delivers an output signal (C, V OUT) correlated with the external voltage and temperature-compensated. US 2014 / 0 252 509 A1 relates to a micromechanical structure of a MEMS device integrated in a chip made of semiconductor material and provided with a substrate, said structure having at least one first axis of symmetry lying in a horizontal plane. The structure comprises a stator structure that is fixed with respect to the substrate, and a rotor structure with a suspended mass that is movable with respect to the substrate and the stator structure as a result of an external influence. The stator structure comprises fixed sensor electrodes that are capacitively coupled to the rotor structure; a compensation structure is integrated in the chip for compensating thermomechanical stresses. The compensation structure comprises stator compensation electrodes that are fixed with respect to the substrate, capacitively coupled to the rotor structure, and arranged symmetrically to the fixed sensor electrodes with respect to the first axis of symmetry. SUMMARY OF REVELATION

[0004] According to one aspect of the present application, a MEMS (microelectromechanical system) accelerometer is provided. The MEMS (microelectromechanical system) accelerometer may include: a plurality of armatures connected to a substrate; a proof mass connected to at least a first and a second armature of the plurality of armatures via one or more corresponding springs; a plurality of fixed electrodes connected to the substrate, each of which includes a first fixed electrode and another fixed electrode; one or more sensing electrodes connected to the proof mass and forming one or more sensing capacitors with at least one of the plurality of fixed electrodes, wherein the one or more sensing capacitors are configured to sense a lateral acceleration of the proof mass; and first and second compensation structures.wherein the first compensation structure is rigidly connected to the first armature and the second compensation structure is rigidly connected to the second armature, wherein the first compensation structure has a first compensation electrode forming a first lateral compensation capacitor with the first fixed electrode, and the second compensation structure has a second compensation electrode forming a second lateral compensation capacitor with the further fixed electrode.

[0005] According to another aspect of the present application, a MEMS (microelectromechanical system) accelerometer is provided.The MEMS (microelectromechanical system) accelerometer may include: a substrate, a first armature, a proof mass connected to the first armature via a spring and coupled to the substrate, a plurality of fixed electrodes coupled to the substrate and comprising a first fixed electrode, one or more sensing electrodes connected to the proof mass and forming one or more sensing capacitors with at least one of the plurality of fixed electrodes, the one or more sensing capacitors configured to sense a lateral acceleration of the proof mass, a second armature coupled to the substrate and not coupled to the proof mass, and a compensation structure rigidly connected to the second armature and comprising a compensation electrode forming a lateral compensation capacitor with the first fixed electrode.

[0006] According to yet another aspect of the present application, a method is provided. The method may comprise: sensing lateral accelerations of a proof mass using at least one sensing capacitor, wherein the at least one sensing capacitor comprises a first sensing electrode connected to the proof mass and a first fixed electrode connected to a substrate, wherein the proof mass is connected to a first armature via a first spring and to a second armature via a second spring, and the first and second armatures are connected to the substrate; detecting a first deflection of the first armature using a first lateral compensation capacitor, wherein the first lateral compensation capacitor comprises a first compensation electrode rigidly connected to the first armature and a second fixed electrode connected to the substrate;and detecting a second deflection of the second armature using a second lateral compensation capacitor, the second lateral compensation capacitor having a second compensation electrode rigidly connected to the second armature and a third fixed electrode connected to the substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Various aspects and embodiments of the application are described with reference to the following figures. It should be understood that the figures are not necessarily drawn to scale. Elements that appear in multiple figures are indicated using the same reference numeral in all figures in which they appear. Fig. 1 schematically shows a portion of a MEMS accelerometer having a proof mass connected to armatures and a plurality of compensation structures to detect deflection of the armatures, according to a non-limiting embodiment of the present application. Fig. 2A shows a detail of Fig. 1, which schematically illustrates a portion of a beam forming a pair of sampling capacitors with a pair of fixed electrodes, according to a non-limiting embodiment of the present application. Fig. Figure 2B shows an additional detail of Fig. 1, which schematically illustrates a portion of a beam forming a pair of compensation capacitors with a pair of fixed electrodes, according to a non-limiting embodiment of the present application. Fig. Figure 3 shows schematically a part of a MEMS accelerometer similar to that of Fig. 1 is alternative and which comprises a proof mass connected to armatures and a plurality of compensation structures for detecting deflection of armatures to which the compensation structures are coupled, according to a non-limiting embodiment of the present application. Fig. 4 schematically shows a MEMS accelerometer configured to sense accelerations along two different directions and including compensation structures to detect deflection of the armatures of the MEMS accelerometer, according to a non-limiting embodiment of the present application. Fig. 5 schematically shows an example spring connecting a proof mass to an armature, according to a non-limiting embodiment of the present application. Fig. 6 is a block diagram of a system including a MEMS accelerometer and a sampling circuit, according to a non-limiting embodiment of the present application. Fig. Figure 7 shows a vehicle in which the system of Fig. 6 can be used according to various embodiments of the present application. Fig. Figure 8 shows a tennis player wearing a portable device that incorporates the system of Fig. 6, according to a non-limiting embodiment of the present application. DETAILED DESCRIPTION

[0008] Deflection of the armature(s) coupling the proof mass of a MEMS (microelectromechanical system) device to a substrate of the device can adversely affect the device's performance, as such deflection can produce a non-zero sensing signal due to armature deflection rather than the acceleration of the proof mass. Applicant has recognized that the accuracy of a MEMS inertial sensor, such as an accelerometer configured to sense in-plane accelerations, can be improved by detecting such armature deflection separately from the detection of proof mass movement.Furthermore, the applicant has recognized that when a proof mass is coupled to a substrate using multiple armatures, separately detecting the deflection of such armatures provides better performance than detecting the combined deflection of the armatures. Therefore, a MEMS inertial sensor can be provided with a plurality of compensation structures configured to separately detect and compensate for the deflection of multiple armatures of the inertial sensor, such as may result from stresses in the substrate. Reference to "in-plane acceleration" here refers to acceleration in a direction parallel to the plane of the proof mass.

[0009] Some conventional MEMS accelerometers are sensitive to stress that causes deflection of the armature to which the proof mass is connected. One example of stress is package stress, which can be caused by temperature fluctuations. Because they have different thermal expansion coefficients, the substrate and package can expand by different amounts in response to thermal fluctuations, and mechanical stress can occur as a result. Under some conditions, mechanical stress can lead to substrate warpage, causing the armatures to deflect from their intended positions.

[0010] Applicant has recognized that strain may be position-dependent, and armatures disposed at different portions of the substrate may be deflected by different amounts and / or along different directions. According to one aspect of the present application, a MEMS inertial sensor, such as an accelerometer, may be configured to reduce the susceptibility of its operation to strain by using a plurality of compensation structures, each compensation structure connected to a corresponding armature. In this way, the deflection of each armature may be accurately sensed. The compensation structures may comprise beams forming at least one compensation capacitor with a fixed electrode attached to the substrate.In response to the armature's deflection, the capacitance associated with such a compensation capacitor can vary, and thus the deflection can be sensed. The sensed deflection of the armature(s) can be removed from the sensed motion of the proof mass or used in another way to compensate for the acceleration sensed by the proof mass.

[0011] According to another aspect of the present application, a MEMS inertial sensor, such as an accelerometer, of the type described herein may include two or more compensation structures for a single sensing comb. A "sensing comb" refers to a group of sampling capacitors formed by interdigitated bars or fingers, wherein the sampling capacitors are configured to sample accelerations in a common direction. The sampling capacitors forming a sensing comb may, in some embodiments, be connected in parallel.

[0012] In some embodiments, a compensation structure and a proof mass may be connected to the same armature but in a different manner. The compensation structure may be rigidly attached to the armature, while the proof mass may be resiliently attached, allowing the proof mass to move relative to the armature. In other embodiments, a compensation structure may be connected to a first armature, and the proof mass may be connected to a second armature that is different from the first armature. The first and second armatures may be arranged in close proximity to each other. In such embodiments, the two armatures may experience similar deflection in response to a load.

[0013] According to another aspect of the present application, a MEMS accelerometer of the type described herein may be configured to sense accelerations in two directions. In some embodiments, such MEMS accelerometers may include one or more compensation structures configured to sense a deflection of an armature in one direction, such as the x-axis, and one or more compensation structures configured to sense a deflection of another armature in another direction, such as the y-axis.

[0014] The aspects and embodiments described above, as well as additional aspects and embodiments, are further described below. These aspects and / or embodiments may be used individually, all together, or in any combination of two or more, as the application is not limited in this regard.

[0015] Fig. Figure 1 schematically shows a portion of a MEMS accelerometer having a proof mass connected to armatures and a plurality of compensation structures for detecting armature deflection, according to a non-limiting embodiment of the present application. A MEMS accelerometer 100 may include a proof mass 102, compensation structures 120 and 122, armatures 104 and 108, springs 105, 106, 109, and 110, and fixed electrodes 114. A , 114 B , 114 C , 114 D , 114 E , 114 F , 114 G and 114 HThe MEMS accelerometer 100 may include additional features (not shown), such as additional fixed electrodes, compensation structures, armatures, and / or springs arranged in any suitable manner. The proof mass 102 may be formed of a conductive material, such as polysilicon. Only a portion of the proof mass 102 is shown, as indicated by the dashed lines at its ends. The solid-line circles in Fig. 1 represent anchors.

[0016] The proof mass 102 may be connected to the substrate of the MEMS accelerometer 100 via armatures 104 and 108. The proof mass 102 may be connected to the armature 104 via one or more springs, such as springs 105 and 106. In some embodiments, spring 105 may extend along the y-axis, while spring 106 may extend along the x-axis. The proof mass 102 may be connected to the armature 108 via one or more springs, such as springs 109 and 110. In some embodiments, spring 109 may extend along the y-axis, while spring 110 may extend along the x-axis. The proof mass 102 may be configured to move in response to accelerations in the xy plane. Being elastic, springs 105, 106, 109 and 110 may be configured to return proof mass 102 to its natural or rest position.

[0017] The test mass 102 may comprise one or more beams, such as beam 112 A , 112 B and 112 C The bars 112 A , 112 B and 112 C may also be referred to herein as "fingers" or "sensing electrodes." Each bar may extend along at least one fixed electrode, forming one or more sensing capacitors. For example, bar 112 A along the fixed electrodes 114 B and 114 C extend. Fig. Figure 2A shows a portion 124 of the MEMS accelerometer 100 in further detail. As shown, the beam 112 A a first sampling capacitor C S1 with the fixed electrode 114 B , and a second sampling capacitor C S2 with the fixed electrode 114 CThe sampling capacitors described here may also be referred to as "side sampling capacitors" because they are generally aligned in a plane parallel to the xy plane. The fixed electrodes may be formed from a conductive material, such as polysilicon. In some embodiments, the fixed electrode 114 B on the substrate via a rod 115 B anchored, and the fixed electrode 114 C can be attached to the substrate via a rod 115 C In response to accelerations in the x-axis, the beam can move 112 A sideways according to arrows A S1 and A S2 move. When the bar 112 A according to arrow A S1 moves, the distance between the beam and the fixed electrode 114 B reduce and the distance between the beam and the fixed electrode 114 Cmay increase. Accordingly, the capacitance measured with the sampling capacitor C S1 associated with the sampling capacitor C S2 associated capacity may decrease. In contrast, if the bar 112 A according to arrow A S2 moved, the distance between the beam and the fixed electrode 114 B increase and the distance between the beam and the fixed electrode 114 C may decrease. Accordingly, the capacitance measured with the sampling capacitor C S2 associated with the sampling capacitor C S1 associated capacitance. By sampling fluctuations in the capacitances measured with the sampling capacitors C S1 and C S2accelerations in a direction parallel to the x-axis can be sampled. In some embodiments, variations in capacitance associated with the sampling capacitor C S1 associated with the sampling capacitor C S2 associated with the first sampling signal may generate a second sampling signal. In some embodiments, the first sampling signal and the second sampling signal may be differential signals. Differential signals are those that have a phase shift of π or substantially π with respect to each other.

[0018] With further reference to Fig. 1 the bar can be 112 B a first sampling capacitor with the fixed electrode 114 D and a second sampling capacitor with the fixed electrode 114 E form. The bar 112 C may connect a first sampling capacitor to the fixed electrode 114 Fand a second sampling capacitor with the fixed electrode 114 G In some embodiments, the fixed electrodes 114 B , 114 D and 114 F be electrically connected to each other, for example, via metal or polysilicon interconnections arranged on a surface of the substrate. In some embodiments, the fixed electrodes 114 C , 114 F and 114 G be electrically connected to each other, for example via metal or polysilicon interconnections arranged on a surface of the substrate. As described with reference to Fig. 2A, the bars 112 B and 112 C be designed to move in response to accelerations in a direction parallel to the x-axis. Although Fig. 1 represents a test mass having three beams, any suitable number of beams may be used.

[0019] In addition to sensing accelerations along the x-axis, the sensing capacitors described herein may further, under some conditions, sense displacement of armature 104 and / or armature 108 along the x-axis that may arise in response to stress, such as packaging stress. Sampling the displacement of one or more armatures may be detrimental because it may distort the sensing signals. For example, a variation in the capacitance associated with one of the sensing electrodes due to armature displacement may be sensed even in the absence of accelerations along the x-axis. Under such circumstances, a user of MEMS accelerometer 100 may not be able to distinguish accelerations of interest from armature displacement.

[0020] According to one aspect of the present application, one or more compensation structures, such as compensation structures 120 and 122, may be used to compensate for armature deflection. In some embodiments, compensation structure 120 may be connected to armature 104, and compensation structure 122 may be connected to armature 108. Each compensation structure may be configured to track deflection of the armature to which it is connected. Unlike proof mass 102, compensation structures 120 and 122 may be rigidly connected to their respective armatures 104 and 108. Because they are rigidly connected to the respective armatures, compensation structures 120 and 122 may be insensitive to accelerations along the x-axis or the y-axis.

[0021] The compensation structure 120 may comprise one or more beams, such as beams 121 A and 121 BThe compensation structure 122 may comprise one or more beams, such as the beams 123 A and 123 B , The bars 121 A , 121 B , 123 A and 123 B may also be referred to herein as "fingers" or "compensation electrodes." Each bar may extend along at least one fixed electrode, forming one or more compensation capacitors. For example, bar 121 A along the fixed electrodes 114 A and 114 B extend. Fig. Figure 2B shows a portion 125 of the MEMS accelerometer 100 in further detail. As shown, the beam 121 A a first compensation capacitor C C1 with the fixed electrode 114 A and a second compensation capacitor C C2 with the fixed electrode 114 BThe compensation capacitors described here may also be referred to as "lateral compensation capacitors" because they are generally aligned in a plane parallel to the xy plane. The fixed electrodes may be formed from a conductive material, such as polysilicon. In some embodiments, the fixed electrode 114 A on the substrate via the rod 115 A anchored, and the fixed electrode 114 B can be attached to the substrate via the rod 115 B In response to a deflection of the armature 104 in the x-axis, the beam 121 A sideways according to arrows A C1 and A C2 move. When the bar is 121 A according to arrow A C1 moves, the distance between the beam and the fixed electrode 114 A reduce and the distance between the beam and the fixed electrode 114 Bmay increase. Accordingly, the capacitance that can be measured with the compensation capacitor C C1 associated with the sampling capacitor C C2 associated capacity may decrease. In contrast, if the bar 121 A according to arrow A C2 moved, the distance between the beam and the fixed electrode 114 A rise and the distance between the beam and the fixed electrode 114 B may decrease. Accordingly, the capacity measured with the compensation capacitor C C2 associated with the sampling capacitor C C1 associated capacitance may decrease. By sampling fluctuations in the capacitances associated with the compensation capacitors C C1 and C C2associated with the compensation capacitor C C1 associated with the capacitor C C2 associated with the first compensation signal may generate a second compensation signal. In some embodiments, the first compensation signal and the second compensation signal may be differential signals.

[0022] With further reference to Fig. 1 the bar can be 121 B a first compensation capacitor with the fixed electrode 114 C and a second compensation capacitor with the fixed electrode 114 D form. The bar 123 A can connect a first compensation capacitor to the fixed electrode 114 Eand a second sampling capacitor with the fixed electrode 114 F form. The bar 123 B can connect a first compensation capacitor to the fixed electrode 114 G and a second sampling capacitor with the fixed electrode 114 H In some embodiments, the fixed electrode 114 A with the fixed electrode 114 C be electrically connected, the fixed electrode 114 B can be used with the fixed electrode 114 D be electrically connected, the fixed electrode 114 E can be used with the fixed electrode 114 G be electrically connected and the fixed electrode 114 F can be used with the fixed electrode 114 H be electrically connected. As described with reference to Fig. 2B, the bar 121 Bbe designed such that it moves in response to a deflection of the armature 104 in a direction parallel to the x-axis, while the beams 123 A and 123 B may be configured to move in response to a deflection of the armature 108 in a direction parallel to the x-axis. Although Fig. 1 illustrates compensation structures, each having two beams, any suitable number of beams may be used. As described below, the sampling signals obtained via the sampling capacitors can be combined with compensation signals obtained via the compensation capacitors to generate compensated sampling signals.

[0023] In some embodiments, at least two compensation structures may be used in combination with a single scanning comb. Fig. 1, a sampling comb may be formed from the sampling capacitors connected to the bars 112 A , 112 B and 112 C As shown, the compensation structures 120 and 122 may be associated with such a scanning comb.

[0024] In the Fig. In the non-limiting example illustrated in Figure 1, the proof mass and at least one compensation structure are connected to the same armature. For example, proof mass 102 and compensation structure 120 are coupled to armature 104. However, the application is not limited in this regard, and the proof mass may be connected to one or more armatures, and at least one compensation structure may be connected to a separate armature. Fig. 3 shows a portion of an alternative MEMS accelerometer including at least two compensation structures, according to some non-limiting embodiments. The MEMS accelerometer 300 may include a proof mass 302, compensation structures 320 and 322, armatures 304, 308, 318, and 319, and springs 305, 306, 309, and 310. The MEMS accelerometer 300 may include additional features (not shown), such as additional fixed electrodes, compensation structures, armatures, and / or springs arranged in any suitable manner. The proof mass 302 may be formed from a conductive material, such as polysilicon.

[0025] The proof mass 302 may be connected to the armature 304 via the springs 305 and 306 and may be connected to the armature 308 via the springs 309 and 310. The proof mass 302 may be one or more beams, such as the beams 312 A , 312 B and 312 C, each of which may form one or more sampling capacitors with corresponding fixed electrodes. For example, the bar 312 A Sampling capacitors with fixed electrodes 314 B and 314 C form, the beam 312 B can sample capacitors with the fixed electrodes 314 D and 314 E form, and the beam 312 C can sample capacitors with the fixed electrodes 314 F and 314 G As explained with reference to Fig. 1, the sampling capacitors can be designed to sample accelerations along the x-axis. Although Fig. 3 represents a test mass comprising three beams, any suitable number of beams may be used. The beams 312 A , 312 B and 312 C can also be referred to here as “fingers” or “sensing electrodes”.

[0026] Compensation structures 320 and 322 may be connected to armatures 318 and 319, respectively. Armature 318 may be disposed on the substrate of MEMS accelerometer 300 at a distance from armature 304 such that the two armatures experience similar deflection in terms of direction and intensity. For example, in some embodiments, the distance between armature 304 and armature 318 may be less than 20 µm, in some embodiments, less than 15 µm, in some embodiments, less than 10 µm, in some embodiments, less than 5 µm, in some embodiments, less than 3 µm, in some embodiments, less than 2 µm, in some embodiments, less than 1 µm, or any value within such ranges.Armature 319 may be disposed on the substrate of MEMS accelerometer 300 at a distance from armature 308 such that the two armatures experience similar deflection in terms of direction and intensity. For example, the distance between armature 308 and armature 319 may be any of those listed above with respect to the distance between armature 304 and armature 318.

[0027] Analogous to the compensation structures 120 and 122 of Fig. 1, the compensation structures 320 and 322 can be configured to track a deflection along the x-axis of the armatures 318 and 319, respectively. Furthermore, since they are rigidly connected to the respective armatures, the compensation structures 320 and 322 can be insensitive to accelerations along the x-axis or the y-axis. The compensation structure 320 can comprise beams 321. A and 321 Band the compensation structure 322 may have beams 323 A and 323 B The bars 321 A , 321 B , 323 A and 321 B can also be referred to here as finger or compensation electrodes. Each compensation electrode can form one or more compensation capacitors with one or more corresponding fixed electrodes. For example, the bar 321 A Compensation capacitors with fixed electrodes 314 A and 314 B form, the beam 321 B can compensation capacitors with the fixed electrodes 314 C and 314 D form, the beam 323 A can compensation capacitors with the fixed electrodes 314 E and 314 F form, the beam 323 B can compensation capacitors with the fixed electrodes 314 G and 314 H Although Fig. 3 represents compensation structures, each having two beams, any suitable number of beams may be used. As described below, sampling signals obtained via the sampling capacitors can be combined with compensation signals obtained via the compensation capacitors to generate excursion-free sampling signals.

[0028] In some embodiments, at least two compensation structures may be used in combination with a single scanning comb. Fig. 3, a sampling comb may be formed from the sampling capacitors connected to the bars 312 A , 312 B and 312 C As shown, the compensation structures 320 and 322 may be associated with such a scanning comb.

[0029] MEMS accelerometers 100 and 300 may be configured to sense accelerations in one direction, such as along the x-axis. However, some embodiments provide MEMS accelerometers configured to sense accelerations in more than one direction. Fig. Figure 4 schematically shows a MEMS accelerometer configured to sense accelerations along two different directions and having compensation structures for detecting deflection of the MEMS accelerometer's armatures, according to a non-limiting embodiment of the present application. The MEMS accelerometer 400 may include a proof mass 402, compensation structures 420, and a magnetic field strength sensor 422. A , 420 B , 420 C and 420 D Anchor 403 A , 403 B , 403 C and 403 D , springs 404 A , 404 B , 405 A , 405 B , 406 A, 406 B , 407 A and 407 B and fixed beams 414 A , 414 B , 414 C , 414 D , 415 A , 415 B , 415 C , 415 D , 416 A , 416 B , 416 C , 416 D , 417 A , 417 B , 417 C and 417 D have.

[0030] The test mass 402 can be connected to the armature 403 A about the springs 404 A and 404 B can be connected to the anchor 403 B about the springs 405 A and 405 B can be connected to the anchor 403 C about the springs 406 A and 406 B and can be connected to the anchor 403 D about the springs 407 A and 407 B The proof mass 402 may be configured to move in response to accelerations in the xy plane. The proof mass 402 may support the beams 412A , 412 B , 412 C and 412 D Each such bar, also referred to herein as fingers or sensing electrodes, may form at least one sensing capacitor with one or more corresponding fixed electrodes. In some embodiments, the bar 412 A Sampling capacitors with fixed electrodes 414 B and 414 C form, and the beam 412 C can sample capacitors with the fixed electrodes 416 B and 416 C The capacities, which are indicated by the bars 412 A and 412 C associated with the beam 412 may be configured to vary in response to accelerations in a direction parallel to the x-axis. In some embodiments, the beam 412 B Sampling capacitors with fixed electrodes 415 B and 415 C form, and the beam 412 Dcan sample capacitors with the fixed electrodes 417 B and 417 C The capacities, which are indicated by the bars 412 B and 412 D associated with the y-axis can be designed to vary in response to accelerations in a direction parallel to the y-axis. Although Fig. 4 represents a proof mass having four beams, any other suitable number of beams may be used, including one or more beams configured to form capacitances responsive to acceleration in the x and / or y directions.

[0031] The compensation structure 420 A can be used with the anchor 403 A be rigidly connected and can have one or more beams, such as beams 421 A and 421 B , The bar 421 A can compensation capacitors with the fixed electrodes 417 A and 417 BSuch compensation capacitors can be designed to compensate for a deflection of the armature 403 A in a direction parallel to the y-axis. The bar 421 B can compensation capacitors with the fixed electrodes 414 A and 414 B Such compensation capacitors can be designed to compensate for a deflection of the armature 403 A in a direction parallel to the x-axis. The compensation structure 420 A is not necessarily limited to two beams. In some embodiments, a compensation structure may include at least two compensation electrodes for sensing armature deflection along the x-axis and / or at least two compensation electrodes for sensing armature deflection along the y-axis.

[0032] The compensation structure 420 B can be used with the anchor 403 Bbe rigidly connected and can have one or more beams, such as the beams 422 A and 422 B , The bar 422 A can compensation capacitors with the fixed electrodes 415 A and 415 B Such compensation capacitors can be designed to compensate for a deflection of the armature 403 B in a direction parallel to the y-axis. The bar 422 B can compensation capacitors with the fixed electrodes 414 C and 414 D Such compensation capacitors can be designed to compensate for a deflection of the armature 403 B in a direction parallel to the x-axis. The compensation structure 420 Bis not necessarily limited to two beams. In some embodiments, a compensation structure may include at least two compensation electrodes for sensing armature deflection along the x-axis and / or at least two compensation electrodes for sensing armature deflection along the y-axis.

[0033] The compensation structure 420 C can be used with the anchor 403 C be rigidly connected, and can have one or more beams, such as beams 423 A and 423 B , The bar 423 A can compensation capacitors with the fixed electrodes 415 C and 415 D Such compensation capacitors can be designed to compensate for a deflection of the armature 403 C in a direction parallel to the y-axis. The bar 423 B can compensation capacitors with the fixed electrodes 416 C and 416 DSuch compensation capacitors can be configured to sense a deflection of the armature 403c in a direction parallel to the x-axis. The compensation structure 420 C is not necessarily limited to two beams. In some embodiments, a compensation structure may include at least two compensation electrodes for sensing an armature deflection along the x-axis and / or at least two compensation electrodes for sensing an armature deflection along the x-axis.

[0034] The compensation structure 420 D can be used with the anchor 403 D be rigidly connected, and can have one or more beams, such as beams 424 A and 424 B , The bar 424 A can compensation capacitors with the fixed electrodes 417 C and 417 D Such compensation capacitors can be designed to compensate for a deflection of the armature 403 Din a direction parallel to the y-axis. The bar 424 B can compensation capacitors with the fixed electrodes 416 A and 416 B Such compensation capacitors can be designed to compensate for a deflection of the armature 403 D in a direction parallel to the x-axis. The compensation structure 420 D is not necessarily limited to two beams. In some embodiments, a compensation structure may include at least two compensation electrodes for sensing armature deflection along the x-axis and / or at least two compensation electrodes for sensing armature deflection along the y-axis.

[0035] As will be described below, sampling signals obtained via the sampling capacitors can be combined with compensation signals obtained via the compensation capacitors to generate compensated sampling signals.

[0036] According to one aspect of the present application, the proof mass of a MEMS accelerometer of the type described herein is connected to an armature via one or more springs. Because of the elastic connection to the armature, the proof mass can move freely in response to accelerations in the xy plane. A non-limiting example of a spring for connecting the proof mass to an armature is described in Fig. 5. As shown, the armature 504 may be connected to the proof mass 502 via the spring 507. The spring 507 may include one or more beams 508 oriented parallel to the y-axis and one or more beams 509 oriented parallel to the x-axis. In some embodiments, the beams may have equal lengths. However, the application is not limited in this regard, and beams having different lengths may be used. The beams may be configured to flex in response to accelerations in the x-axis and / or the y-axis, thereby allowing the proof mass to move. The spring 507 may serve as any of the springs of the MEMS accelerometers 100, 300, and 400.Springs that have one or more beams oriented in a first direction and one or more beams oriented in a second direction may be referred to as “multi-segment springs.”

[0037] As mentioned with reference to Fig. 1, Fig. 2 and Fig. 4, compensation signals obtained via compensation capacitors can be used to compensate for deflection of one or more armatures. In some embodiments, a MEMS inertial sensor, such as an accelerometer, of the type described herein can be connected to a circuit configured to compensate sensing signals with compensation signals. Fig. 6 is a block diagram showing a system 600 including a MEMS accelerometer 602, a power supply 604, a sensing circuit 606, and an input / output (I / O) interface 608. The MEMS accelerometer 602 may function as a MEMS accelerometer 100, 200, or 400. In some embodiments, the sensing circuit 606 and the MEMS accelerometer 602 may be disposed on the same substrate, such as a silicon substrate. In other embodiments, the sensing circuit 606 and the MEMS accelerometer 602 may be disposed on separate substrates that may be bonded together and / or packaged within a common housing. In some embodiments, the MEMS accelerometer 602 may further include an accelerometer configured to sense out-of-plane accelerations, e.g., in a direction perpendicular to the xy plane.Such out-of-plane accelerometers may include one or more compensation structures configured to sense a deflection of one or more armatures. In some embodiments, MEMS accelerometer 602 may further include one or more angular accelerometers configured to sense angular acceleration about one, two, or three axes.

[0038] The sampling circuit 606 may be configured to receive sampling signals acquired via one or more sampling capacitors and compensation signals acquired via one or more compensation capacitors. For example, in response to accelerations in a direction parallel to the x-axis, the sampling circuit 606 may be configured to generate a signal S S1 which leads to the fluctuation ΔC S1 the capacitance that is measured with the sampling capacitor C S1 associated, is proportional, and a signal SS2 which leads to the fluctuation ΔC S2 the capacitance that is measured with the sampling capacitor C S2 associated with the armature 104. In response to a deflection of the armature 104 in a direction parallel to the x-axis, the sampling circuit 606 may also be configured to generate a signal S C1 which leads to the fluctuation ΔC C1 the capacity that is connected to the compensation capacitor C C1 associated, is proportional, and a signal S C2 which leads to the fluctuation ΔC C2 the capacity that is connected to the compensation capacitor C C2 associated with the signal. In some embodiments, the sampling circuit 606 may be configured to generate a compensated sampling signal S comp to generate by S S1 , S S2 , S C1 and S C2 be combined according to the following expression: Scomp=SS1+SC2−(SS2+SC1)

[0039] In some embodiments, the compensated signal may be configured to be proportional to the acceleration experienced by the MEMS accelerometer and to be insensitive to deflection of the armatures.

[0040] In some embodiments, the sampling capacitors and the compensation capacitors may be connected to provide a capacitor that absorbs a fluctuation (a change in total capacitance) C T which is expressed as follows: CT=CS1+CC2−(CS2+CC1).

[0041] C S1 , C S2 , C C1 and C C2 can be designed in such a way that in the absence of acceleration C T = 0. If a deflection occurs at a given acceleration, the forces associated with C S1 and C S2associated capacitances vary by an equal amount dC with opposite polarities, while those with C C1 and C C2 associated capacitances remain largely unchanged due to the fact that the stiffness of the compensation structure is much greater than the stiffness of the sensing structure. As a consequence, the resulting deflection of the compensation structure can be much smaller than the deflection of the sensing structure. In the presence of acceleration, C T provided as follows: CT=CS1+dC+CC2−(CS2−dC+CC1)=2dC

[0042] In some embodiments, C S1 = C S2 ≈ C C1 = C C2 In such embodiments, when an armature deflection occurs, the C S1 , C S2 , C C1 and C C2associated capacities vary by an equal amount δC. Under such conditions, C T provided as follows: CT=CS1+δC+CC2−δC−(CS2−δC+CC1+δC)=0

[0043] Consequently, in some embodiments, C T equal to zero, providing a compensated sampling signal that does not reflect armature deflections.

[0044] For comparison, consider a MEMS accelerometer that is not equipped with a compensation structure of the type described here. In such a case, the sampling capacitors can be connected to provide a capacitor that compensates for a change in capacitance C TT which is provided as follows: CTT=CS1−CS2

[0045] If a deflection occurs at a given acceleration, the forces associated with C S1 and C S2associated capacitances vary by an equal amount dC, with different polarities, resulting in: CTT=CS1+dC−(CS2−dC)=2dC In this case, if an armature deflection occurs at a given stress or chip deformation, which is expressed as C S1 and C S2 associated capacities vary by an equal amount δC, which gives: CTT=CS1+δC−(CS2−δC)=2δC

[0046] Due to the sensitivity to acceleration and armature deflection, misalignment errors may occur.

[0047] The system 600 can periodically send a compensated sampling signal to an external monitoring system, such as a computer, smartphone, tablet, smartwatch, smart glasses, or any other suitable receiving device, via wired connections or wirelessly. The I / O interface 608 can be configured to send and / or receive data via WiFi, Bluetooth, Bluetooth Low Energy (BLE), Zigbee, Thread, ANT, ANT+, IEEE 802.15.4, IEEE 802.11.ah, or any other suitable wireless communication protocol. Alternatively or additionally, the I / O interface 608 can be configured to send and / or receive data using proprietary connection protocols. The I / O interface 608 can include one or more antennas, such as a microstrip antenna.In some embodiments, the I / O interface 608 may be connected to a cable and may be configured to send and / or receive signals over the cable.

[0048] The system 600 may be powered using a power supply 604. The power supply may be configured to power the sampling circuit 606, the I / O interface 608, the MEMS accelerometer 602, or any suitable combination thereof. In some embodiments, the power supply 604 may include one or more batteries. The system 600 may, in at least some embodiments, consume sufficiently low power to enable operation for extended periods based solely on battery power. The battery or batteries may, in some embodiments, be rechargeable.The power supply unit 604 may include one or more lithium-ion batteries, lithium polymer (LiPo) batteries, supercapacitor-based batteries, alkaline batteries, aluminum-ion batteries, mercury batteries, dry cell batteries, zinc-carbon batteries, nickel-cadmium batteries, graphene batteries, or any other suitable battery types. In some embodiments, the power supply unit 604 may include circuitry for converting AC power to DC power. For example, the power supply unit 604 may receive AC power from a power source external to the system 600, such as via the I / O interface 608, and may supply DC power to some or all of the components of the system 600.In such cases, the supply unit 604 may comprise a rectifier, a voltage regulator, a DC-DC converter, or any other suitable power conversion device.

[0049] The supply unit 604 may, in some embodiments, include energy harvesting components and / or energy storage components. Energy may be harvested from the environment and stored to power the system 600 when needed, which may include a periodic, random, or continuous supply. The type of energy harvesting components implemented may be chosen based on the expected environment of the system 600, for example, based on, among other possible considerations, the expected magnitude and frequency of movement the system 600 is likely to undergo, the amount of stress the system is likely to be subjected to, the amount of light the system is likely to be exposed to, and / or the temperature(s) the system is likely to be exposed to.Examples of suitable energy harvesting technologies include thermoelectric energy harvesting, magnetic vibration harvesting, electrical overload harvesting, photovoltaic harvesting, radio frequency harvesting, and kinetic energy harvesting. The energy storage components may include supercapacitors in some embodiments.

[0050] System 600 can be used to detect acceleration in various situations, including, but not limited to, sports, healthcare, military, and industrial applications. Some non-limiting examples will now be described. System 600 can be a wearable sensor used in monitoring sports-related physical activities and performance, patient health, military personnel activity, or other applications of interest to a user.

[0051] Such a situation occurs with passenger cars or other means of transport, such as boats and aircraft. Fig. Figure 7 shows an example in which a sensor system of the type described here is used in a vehicle. In the example of Fig. 7, a vehicle 700 includes a control unit 701 coupled to an on-board computer 704 of the vehicle through a wired or wireless connection. The control unit 701 may control the system 600 of Fig. 6. The system 600 may comprise a housing or enclosure attached to a suitable part of the vehicle 700 and may include a MEMS accelerometer of the type described herein. The MEMS accelerometer may, as one example, sense accelerations along the direction of travel and / or perpendicular to the direction of travel. Additionally or alternatively, the MEMS accelerometer may be configured to sense vertical accelerations, thereby monitoring, for example, the status of the suspensions. The control unit 701 may receive power and control signals from the on-board computer 704 and may provide sense signals, such as compensated sense signals of the type described herein, to the on-board computer 704. In some situations, temperature fluctuations within the control unit 701 may induce stress on the MEMS accelerometer disposed therein. The operation of the system 600 in the manner described with reference to Fig. The manner described in paragraph 6 may mitigate or eliminate the effect of such stress.

[0052] Another situation is represented by portable devices for sports applications, such as tennis. Fig.8 shows a tennis player 801 holding a racket 802 and wearing a wristband 830 and a leg band 832. The racket 802 may have one or more devices attached thereto, such as devices 804 and 806. Such devices may each include a system 600 and may be configured to detect angular accelerations and / or linear accelerations. For example, the device 804 mounted on the handle of the racket 802 may be configured to sense accelerations associated with the racket handle. The device 806 mounted on the racket head may be configured to sense accelerations associated with any suitable part of the racket head, such as the racket tip. The devices 804 and 806 may, in some embodiments, be embedded within the racket frame or body.In some embodiments, data associated with accelerations experienced by the racket 802 may provide an indication of the player's ability to play tennis. For example, information concerning a forehand movement or a backhand movement may be obtained. The player 801 may wear one or more wearable devices, such as a wristband 830 and / or a leg band 832. Such wearable devices may each be equipped with a system 600 and may be configured to sense angular and / or linear accelerations. For example, a system 600 disposed on a wristband may be configured to provide information about the movement of the player's arm, while a system 600 disposed on a leg band may be configured to provide information about the movement of the player's leg.

[0053] Although compensation structures are described with respect to accelerometers, the application is not limited in this respect. Compensation structures of the types described herein may be used in conjunction with gyroscopes, resonators, switches, or any other suitable MEMS device to sense a deflection of one or more armatures.

[0054] Aspects of the present application may provide one or more of the advantages described above. Some non-limiting examples of such advantages will now be described. It should be understood that not all aspects and embodiments necessarily provide all of the advantages described. Furthermore, it should be understood that aspects of the present application may provide advantages in addition to those described.

[0055] Aspects of the present application provide MEMS accelerometers that have reduced sensitivity to stress, such as packaging stress. Under some conditions, stress may not be uniform across the substrate of a MEMS accelerometer, causing different armatures to experience different deflections. Some embodiments provide a MEMS inertial sensor, such as an accelerometer, that has a plurality of armatures, where each armature may be connected to a compensation structure. In this way, the deflection of each armature may be sensed independently.

[0056] The terms "approximately" and "about" may be used to mean, in some embodiments, within ±20% of a target value, in some embodiments, within ±10% of a target value, in some embodiments, within ±5% of a target value, and in some embodiments, within ±2% of a target value. The terms "approximately" and "about" may include the target value.

Claims

[1] Microelectromechanical system (MEMS) accelerometer, comprising: a plurality of anchors connected to a substrate, a proof mass connected to at least a first and a second armature of the plurality of armatures via one or more corresponding springs, a plurality of fixed electrodes connected to the substrate, comprising a first fixed electrode and another fixed electrode, one or more sensing electrodes connected to the proof mass and forming one or more sensing capacitors with at least one of the plurality of fixed electrodes, wherein the one or more sensing capacitors are configured to sense a lateral acceleration of the proof mass, and a first and a second compensation structure, wherein the first compensation structure is rigidly connected to the first armature and the second compensation structure is rigidly connected to the second armature, wherein the first compensation structure has a first compensation electrode forming a first lateral compensation capacitor with the first fixed electrode, and wherein the second compensation structure has a second compensation electrode forming a second lateral compensation capacitor with the further fixed electrode. [2] The MEMS accelerometer of claim 1, further comprising a third compensation structure rigidly connected to the first armature and comprising a third compensation electrode forming a third lateral compensation capacitor with a third fixed electrode of the plurality of fixed electrodes, the first lateral compensation capacitor responsive to a deflection of the first armature in a first lateral direction, and the third lateral compensation capacitor responsive to a deflection of the first armature in a second lateral direction different from the first lateral direction. [3] The MEMS accelerometer of claim 2, wherein the first lateral direction and the second lateral direction are perpendicular. [4] The MEMS accelerometer of claim 1, wherein each of the first and further fixed electrodes is connected to the substrate via one or more rods. [5] The MEMS accelerometer of claim 1, wherein the one or more sensing electrodes comprise a first sensing electrode and a second sensing electrode, and wherein the first sensing electrode forms a first sensing capacitor with the further fixed electrode and the second sensing electrode forms a second sensing capacitor with a further fixed electrode. [6] The MEMS accelerometer of claim 1, wherein the one or more sampling capacitors are a first sampling capacitor, and the one or more sampling electrodes form a second sampling capacitor with a third fixed electrode of the plurality of fixed electrodes, and wherein the first sampling capacitor and the second sampling capacitor are configured to generate a pair of differential signals. [7] The MEMS accelerometer of claim 1, wherein the first compensation electrode forms a third lateral compensation capacitor with a third fixed electrode of the plurality of fixed electrodes, and wherein the first and third lateral compensation capacitors are configured to generate a pair of differential signals. [8] The MEMS accelerometer of claim 1, wherein the first lateral compensation capacitor responds to a deflection of the first armature in a first lateral direction and the second lateral compensation capacitor responds to a deflection of the second armature in the first lateral direction. [9] The MEMS accelerometer of claim 1, further comprising a sampling circuit disposed within the substrate, the sampling circuit configured to compensate a sampling signal representing a variation in the capacitance of the one or more sampling capacitors for a deflection of the first armature by combining the sampling signal with a compensation signal obtained via the first lateral compensation capacitor. [10] Microelectromechanical system (MEMS) accelerometer, comprising: a substrate, a first anchor, a proof mass connected to the first armature via a spring and connected to the substrate, a plurality of fixed electrodes connected to the substrate, each having a first fixed electrode, one or more sensing electrodes connected to the proof mass and forming one or more sensing capacitors with at least one of the plurality of fixed electrodes, wherein the one or more sensing capacitors are configured to sense a lateral acceleration of the proof mass, a second anchor coupled to the substrate and not coupled to the proof mass, and a compensation structure rigidly connected to the second armature and having a compensation electrode having a lateral compensation capacitor connected to the first solid electrode. [11] The MEMS accelerometer of claim 10, wherein the first armature is electrically connected to the second armature. [12] The MEMS accelerometer of claim 10, wherein the first armature is spaced from the second armature by a distance of less than 20 µm. [13] The MEMS accelerometer of claim 10, wherein the compensation structure is a first compensation structure, wherein the lateral compensation capacitor is a first lateral compensation capacitor, the MEMS accelerometer further comprising: a second compensation structure rigidly connected to the second armature and having a further compensation electrode forming a second lateral compensation capacitor with another fixed electrode of the plurality of fixed electrodes, wherein the first lateral compensation capacitor responds to a deflection of the second armature in a first lateral direction, and the second lateral compensation capacitor responds to a deflection of the second armature in a second lateral direction different from the first lateral direction. [14] The MEMS accelerometer of claim 10, wherein the one or more sampling capacitors are a first sampling capacitor, and the one or more sampling electrodes form a second sampling capacitor with another fixed electrode of the plurality of fixed electrodes, and wherein the first sampling capacitor and the second sampling capacitor are configured to generate a pair of differential signals. [15] The MEMS accelerometer of claim 10, wherein the lateral compensation capacitor is a first lateral compensation capacitor, and wherein: the compensation electrode forms a second lateral compensation capacitor with another fixed electrode of the plurality of fixed electrodes, and wherein the first and second lateral compensation capacitors are configured to generate a pair of differential signals. [16] The MEMS accelerometer of claim 10, further comprising a sampling circuit disposed within the substrate, the sampling circuit configured to compensate a sampling signal representing a variation in the capacitance of the one or more sampling capacitors for a deflection of the second armature by combining the sampling signal with a compensation signal obtained via the lateral compensation capacitor. [17] Method comprising: Sensing lateral accelerations of a proof mass using at least one sensing capacitor, wherein the at least one sensing capacitor has a first sensing electrode connected to the proof mass and a fixed electrode connected to a substrate, wherein the proof mass is connected to a first armature via a first spring and to a second armature via a second spring, and the first and second armatures are connected to the substrate, Detecting a first deflection of the first armature using a first lateral compensation capacitor, the first lateral compensation capacitor having a first compensation electrode rigidly connected to the first armature and a further fixed electrode connected to the substrate; and Detecting a second deflection of the second armature using a second lateral compensation capacitor, the second lateral compensation capacitor having a second compensation electrode rigidly connected to the second armature and another fixed electrode connected to the substrate. [18] The method of claim 17, wherein the first compensation electrode is not connected to the second armature and the second compensation electrode is not connected to the first armature. [19] The method of claim 17, wherein the first deflection of the first armature is along a first lateral direction, the method further comprising: Detecting a third deflection of the first armature along a second lateral direction different from the first lateral direction using a third lateral compensation capacitor, the third lateral compensation capacitor comprising a third compensation electrode rigidly connected to the first armature and a third fixed electrode connected to the substrate. [20] The method of claim 17, further comprising: Compensating a sampling signal using a sampling circuit, wherein the sampling signal represents a variation in the capacitance of the at least one sampling capacitor for a deflection of the first armature by combining the sampling signal with a compensation signal obtained by the first lateral compensation capacitor.

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