Stress and deformation monitoring in m&NEMS sensors

Abstract

The invention relates to a detection system. The detection system comprises : a microelectromechanical sensor (10) comprising a sensing element (12) anchored to a substrate (14); a first (16a) and a second pair of electrically resistive elements arranged to form a bridge circuit (18), wherein at least the electrically resistive elements of the first pair (16a) are strain gauges configured for differentially detecting a displacement or deformation of the sensing element (12); and an electronic readout device (20), configured for acquiring at least one electric signal by performing at least one electric measurement on the bridge circuit (18) and processing said signal or signals to extract therefrom information on said displacement or deformation of the sensing element (12); characterized in that the electronic readout device (20) is also configured for extracting from said electric signal or signals information on strain or deformation of the substrate (14).

Description

DESCRIPTIONStress and temperature monitoring in M&NEMS Sensors

[0001] The invention relates to MEMS and NEMS-based sensors (wherein “MEMS” and “NEMS” stand for “Micro Electro-Mechanical Systems” and “Nano ElectroMechanical Systems” respectively and to M&NEMS sensors which can be described as MEMS with nanoelectromechanical (NEMS) gauges. The invention more particularly relates to a detection system for correcting offsets and drifts in measurements made by a sensor based on MEMS technology.

[0002] MEMS (NEMS) are mechanical systems comprising at least one micro (nano) element using electricity as a power source. In the following description, the term “MEMS” refers equally to “MEMS” and “M&NEMS” based technologies.

[0003] MEMS and M&NEMS are frequently used in sensors or actuators. MEMS-based sensors can be used as gyroscopes, accelerometers, magnetometers, pressure sensors, capacitive sensors.

[0004] M&NEMS-based gyroscopes comprise for example Coriolis acceleration sensors using electrostatic actuators and nanoelectromechanical strain gauges.

[0005] In order to avoid common-mode disturbances and to strengthen the signal, which is usually quite weak, the strain gauges are usually embedded in a bridge circuit, usually a Wheatstone bridge.

[0006] Depending on the measurements made, one or more strain gauges are used in the Wheatstone bridge. In an “active full bridge” configuration, four nominally identical gauges form two parallel arms of the bridge, across which a voltage difference is applied as shown in [Fig. 1a]. A displacement or deformation of a sensing element (e.g. a moving mass) of the MEMS sensor induce opposite changes in opposite gauges - for instance, an increase AR in the “upper” gauge of the first arm and in the “lower” gauge of the second arm, and a decrease -AR in the “lower” gauge of the first arm and in the “upper” gauge of the second arm, or vice-versa. This induces a voltage difference between the midpoints of the arms, which constitutes a differential measurement of the displacement or deformation of the sensing element.

[0007] In many cases, only two “active” gauges - i.e. sensitive to the displacement or deformation of the sensing element - are used, one in each arm, and the bridgecircuit is completed by nominally constant resistors having a constant resistance value Rcas shown in [Fig. 1b], which can be either external to the MEMS (e.g. macroscopic resistors) or “dummy” gauges, i.e. gauges similar to the “active” one but not affected by a displacement or deformation of the sensing element. Usually, Rcis equal to R, the nominal resistance of the active gauges in the absence of stress.

[0008] MEMS are manufactured using usual microelectronics fabrication processes. Typically, a MEMS-based sensor comprises a MEMS device fabricated in a silicon substrate to which the MEMS devices is attached in specific regions known as anchor points. The substrate is in turn glued or soldered onto a carrier / interposer (made of ceramic, plastic, metal...), finally included in a plastic or ceramic package.

[0009] The output of several of most MEMS-based sensors is affected by deformation of the substrate, which causes relative displacements between different anchor points of the sensor, inducing displacement of the MEMS masses not related to the sensing quantity to measure.

[0010] This deformation can have different origins :

[0011] - when the user solders the sensor to the printed board, the package can be subject to permanent deformations which are transferred to the substrate and in turn as an output variation;

[0012] - if the package adsorbs / releases humidity, it deforms and transmits stress to the anchor points, and in turn as an output variation (in case there is any plastic material, this can induce hysteresis);

[0013] - if the system is subject to ambient temperature variations, also in operation, different coefficient of expansion of silicon, glue, carrier and package result in an overall stress on the silicon substrate and, once again, into an output variation;

[0014] - even under constant ambient temperature, other components on the electronic board, switching on or off, may induce local changes in temperature which again induce deformations and output changes.

[0015] Such deformations cause the output to differ from the expected value, resulting in offsets, offset drifts and scale factor drifts. Those errors are especially critical for the MEMS-based sensors (such as gyroscopes, accelerometers...) mentioned herein before, where the output needs to be integrated for navigationapplications. As a result, an integration of a constant offset corresponds to diverging results.

[0016] Several known methods have been developed to remedy deviations such as offsets and drifts.

[0017] An initial factory calibration, i.e. when the device is manufactured and subject to factory tests, makes it possible to correct offsets in the measurement, sometimes also as a function of temperature. However, this solution is not satisfactory because it does not allow account to be taken, for example, of offsets due to stresses created during the stage of soldering the substrate to the printed circuit, induced by variations in ambient humidity or by mounting and operating the sensor in a real system which includes other sub-components which may generate local temperature gradients.

[0018] Calibration during operation of the device does not fully address the technical problem raised. In fact, the accuracy of this method is affected by differences between the sensor temperature and the ambient temperature, as well as by all the other effects, other than temperature, which cause a offset in the output signal, and its drifts, as well as variations in the scale factor.

[0019] Another existing solution consists of adding additional stress sensors within the housing or outside the housing (Uzunoglu et al. 2022), (Tatar et al. 2016). However, this solution is only compatible with capacitive sensors and has a number of disadvantages.

[0020] Indeed, the number and size of the stress sensors are even greater than those of the main sensor, which implies a high silicon cost.

[0021] Moreover, the size of the stress sensors implies they measure stress at positions far from the main sensor.

[0022] Each stress sensor needs dedicated pads: this increases the routing complexity, overall number of pad, and in turn the required area, package and assembly cost.

[0023] Each stress sensor requires its own (or partly shared) sensing circuitry, thus increasing consumption.

[0024] In capacitive sensors, it is not possible to include capacitive stress sensors at the same readout nodes of the main sensor. Noise in capacitive sensors is highlydependent on parasitics and degrades when attaching multiple circuits to the same sensing node.

[0025] Consequently, there is a need to compensate efficiently deformations induced offsets and drifts of measurements in a MEMS-based sensor that is compatible with non-capacitive sensors and does not require additional stress sensors.

[0026] A subject of the invention is a detection system comprising:a microelectromechanical sensor comprising a sensing element anchored to a substrate;a first and a second pair of electrically resistive elements arranged to form a bridge circuit, wherein at least the electrically resistive elements of the first pair are strain gauges configured for differentially detecting a displacement or deformation of the sensing element; andan electronic readout device, configured for acquiring at least one electric signal by performing at least one electric measurement on the bridge circuit and processing said signal or signals to extract therefrom information on said displacement or deformation of the sensing element induced by a quantity to be sensed;characterized in that the electronic readout device is also configured for extracting from said electric signal or signals information on strain or deformation of the substrate.

[0027] Another subject of the invention is a method of operating such a detection system, comprising:- a first step of acquiring, from the detection system, said information on said displacement or deformation of the sensing element, representative of a physical quantity of interest, and said information on strain or deformation of the substrate; and- a second step of using said information on strain or deformation of the substrate for correcting said information on information on said displacement or deformation of the sensing element by compensating drifts of either offset, or scale factor, or both, of the microelectromechanical sensor.

[0028] Particular embodiments of the inventive detection system and of the method of operating it constitute the subject-matter of the dependent claims.

[0029] Other features, details and advantages of the invention will become apparent from the description made with reference to the appended drawings given by way of example and which represent, respectively:

[0030] [Fig.1a] is a block diagram of four strain gauges arranged to form a full active Wheatstone bridge;

[0031] [Fig.1b] is a block diagram of two strain gauges and two constant resistors arranged to form a full semi-active Wheatstone bridge;

[0032] [Fig.2] is a block diagram of a microelectromechanical sensor and its peripheral elements, used in a detection system according to the invention;

[0033] [Fig.3] is a block diagram of a detection system according to a first embodiment of the invention and incorporating the microelectromechanical sensor of [Fig.1];

[0034] [Fig.4] is a block diagram of a detection system according to a second embodiment of the invention in a first configuration and incorporating the microelectromechanical sensor of [Fig.2];

[0035] [Fig.5] is a block diagram of a detection system according to the second embodiment of the invention in a second configuration and incorporating the microelectromechanical sensor of [Fig.2];

[0036] [Fig.6] is a block diagram of a detection system according to a variant of the second embodiment of the invention and incorporating the microelectromechanical sensor of [Fig.2];

[0037] [Fig.7] is a block diagram of a detection system according to a third embodiment of the invention and incorporating the microelectromechanical sensor of [Fig.2];

[0038] [Fig.8] is a block diagram of a detection system according to a fourth embodiment of the invention and incorporating the microelectromechanical sensor of [Fig-2],

[0039] [Fig.2] is a block diagram of a microelectromechanical sensor 10 and its peripheral elements. The microelectromechanical sensor 10 comprises a sensing element 12. The lower face of the microelectromechanical sensor 10 is anchored to a first face of a substrate 14 by at least one anchor points 80. The microelectromechanical sensor 10 and the substrate 14 are integrated in a housing 82 and a second face of the substrate 14, opposite the first surface of the substrate 14, is fixed to a first face of a support 84, for example by bonding. A second face of the support 84, opposite the first surface of the support 84, is attached to a first face of an integrated circuit 86, for example by gluing or bonding. The detection system includes other peripheral elements, such as strain gauges (in the case of N&MEMS, nanogauges) and dummy gauges, which are not shown in [Fig. 2],

[0040] The microelectromechanical sensor 10 and its peripheral elements may be manufactured using usual microelectronics fabrication processes and may include: lithography steps, material deposition steps, etching steps.

[0041] Lithography may include optical lithography and electronic lithography.

[0042] Material deposition techniques may include sputtering and epitaxy.

[0043] Etching techniques may include dry etching and wet etching.

[0044] [Fig.3] is a block diagram of a detection system according to a first embodiment of the invention and comprising the microelectromechanical sensor 10 of [Fig. 2] and its peripheral elements. In the embodiment shown in [Fig. 3], the detection system comprises a first pair of electrically resistive elements 16a and a second pair of electrically resistive elements 42, wherein the first pair of resistive elements 16a is a first pair of strain gauges 16a and the second pair of resistive elements 42 is a second pair of external resistors. The first pair of strain gauges 16a and the second pair of external resistors 42 are arranged to form a full semi-active Wheatstone bridge 18. The four arms of the full semi-active Wheatstone bridge 18 are formed by the resistances RNGof the two strain gauges 16a and the resistance Rext of the two external resistors 42. The strain gauges 16a are installed on the same side of the Wheatstone bridge 18. A first midpoint 91 connects the first gauge of the pair of strain gauges 16a to the first external resistor of the pair of external resistors 42. A second midpoint 92 connects the second gauge of the pair of strain gauges 16a to the second external resistor of the pair of external resistors 42.

[0045] The gauges of the first pair of strain gauges 16a are configured for differentially detecting a displacement or deformation of the sensing element 12: a displacement or deformation of the sensing element 12, induce a change AR of the resistance of the first strain gauge of the first pair of strain gauge 16a and an opposite change -AR of the resistance of the second strain gauge of the first pair of strain gauge 16a as shown by dashed arrows in [Fig. 3]. Another pair of dashed arrows shows that the resistance of strain gauges 16a also exhibits an (unwanted) dependence on deformations of the substrate 14.

[0046] The external resistors 42 are unaffected by strain or deformation of the substrate 14.

[0047] The detection system further comprises an electronic readout device 20 and processing means 60. The detection system further comprises a first Application-Specific Integrated Circuit (ASIC 1 in the following description) and a second ASIC 2. The first ASIC 1 is connected to the processing means 60, to the microelectromechanical sensor 10 and is configured to control the processing means 60 and the microelectromechanical sensor 10. The second ASIC 2 is connected to the full semi-active Wheatstone bridge 18, to the processing means 60 and to means 70. As shown in [Fig. 3], a first terminal of the second ASIC 2 is connected to the first midpoint 91 and a second terminal of the second ASIC 2 is connected to the second midpoint 92.

[0048] The detection system further comprises means 70 for actuating the sensing element 12 at a nonzero frequency f. The second ASIC 2 is configured to control the means 70. The actuating means 70 comprises transductors configured to transform electric signal into force, torque or displacement on the sensing element 12. The electronic readout device 20 is configured for extracting information on displacement or deformation of the sensing element 12 from a spectral component of said electric signal or signals at said frequency f. For instance, in a M&NEMS gyroscope, the actuating means 70 may induce an oscillation of a sensing element along a first direction, and the gauges 16a may detect an oscillation of the sensing element along a second direction perpendicular to the first direction, induced by Coriolis effect.

[0049] The electronic readout device 20 also comprises a first low-pass filter 22a and a second low-pass filter 22b. The first and the second low-pass filters (22a, 22b) areactive low-pass filters comprising three amplifiers, a first capacitance CSki and a second capacitance CSk2, a first impedance RSki and a second impedance RSk2 as shown in [Fig. 3]. The first low-pass filter 22a is connected to the first midpoint 91. The second low-pass filter 22b is connected to the second midpoint 92.

[0050] The electronic readout device 20 is configured for acquiring at least one electric signal by performing at least one electric measurement on the bridge circuit 18 and to extract therefrom information on said displacement or deformation of the sensing element 12.

[0051] The electronic readout device 20 is further configured for processing said signal or signals to extract information on strain or deformation of the substrate 14 by performing low-pass filtering of said electric signal or signals. The low-frequency component of the signal emitted by the first pair of strain gauges 16a is a direct or indirect measurement of the deformations affecting the substrate 14.

[0052] The electronic readout device 20 is connected to the first ASIC 1 which is configured to control the electronic readout device 20 and to manipulate said information on strain or deformation of the substrate 14. The first ASIC 1 is further configured to send said information to processing means 60.

[0053] This embodiment is suitable for detection systems used as frequency-modulated gyroscopes, magnetometers or accelerometers. In these detection systems, the measured variable is modulated around a certain resonance frequency, for example between 25 and 30 kHz. The signals emitted by the first pair 16a of strain gauges around this frequency are representative of the quantity to be measured.

[0054] Advantageously, the detection system according to the first embodiment allows local monitoring of the deformation of the substrate without requiring additional strain gauges or other detection systems. Consequently, the detection system does not require additional surface or additional pads.

[0055] Advantageously, the detection system also allows direct measurement of the stress, unlike capacitive sensors where the measurement is indirect since it can only measure deformations.

[0056] The processing means 60 comprise, for example, microprocessors configured for using said information on strain or deformation of the substrate 14 to correct saidinformation on information on said displacement or deformation of the sensing element 12 by compensating drifts of either offset, or scale factor, or both, of the microelectromechanical sensor 10. Said correction can be performed by first compensation algorithms that are simple and based on linear coefficients only. More advanced elaboration algorithms can be based on training the system and then applying suitable machine learning techniques.

[0057] Advantageously, the first embodiment does not lead to a reduction in noise performance due to the immunity of resistive detection to parasitic phenomena.

[0058] In a first variant of the first embodiment, the second pair of external resistors 42 is replaced by a second pair of strain gauges 16b. In this variant, the first 16a and the second pair 16b of strain gauges are configured for differentially detecting a displacement or deformation induced by the substrate on the sensing element 12.

[0059] In a second variant of the first embodiment, the second pair of external resistors 42 is replaced by a second pair of dummy gauges 16b. In this variant, dummy gauges are used for reasons of mechanical symmetry, but they are not used for stress monitoring.

[0060] In a fourth variant of the first embodiment, low-pass filtering is performed by digital low-pass filters. For performing digital filtering, the electronic readout device 20 comprises analogue to digital converters and digital to analogue converters.

[0061] [Fig.4] and [Fig. 5] are block diagrams of a detection system according to a second embodiment of the invention in a first configuration and in a second configuration respectively and comprising the microelectromechanical sensor 10 of [Fig. 2],

[0062] According to the second embodiment, the detection system comprises a first pair of electrically resistive elements 16a and a second pair of electrically resistive element 16b, wherein the first pair of electrically resistive element 16a is a first pair of strain gauges 16a and the second pair of electrically resistive element 16b is a second pair of strain gauge 16b. In the example shown in [Fig. 4] and [Fig. 5], the gauges of the first pair of strain gauges 16a are “active” strain gauges 16a, configured for differentially detecting a displacement or deformation of the sensing element 12: a displacement or deformation of the sensing element 12, induce a change AR of the resistance of the first strain gauge 16a and an opposite change -AR of the resistance of the second strain gauge. The gauges of the second pair of strain gauges 16b are instead dummy gauges formed on the substrate 14. A first gauge of the first pair of strain gauges 16a is connected to a first dummy gauge of the set of dummy gauges 16b by a first midpoint 91. A second gauge of the first pair of strain gauges 16a is connected to a second dummy gauge of the second pair of dummy gauges 16b by a second midpoint 92. The detection system further comprises a pair of external resistors 42. A first external resistor of the pair of external resistors 42 is connected to the midpoint 91 and a second external resistor of the pair of external resistors 42 is connected to the midpoint 92.

[0063] Dashed arrows show that the resistances of the active gauges 16a depend on both a displacement or deformation of the sensing element 12 and on deformations of the substrate 14, while the resistances of the dummy gauges 16b only depend on deformations of the substrate 14.

[0064] The detection system further comprises first switching means 40. The first switching means 40 comprise, for example, transistors. The first switching means 40 are configured for commuting between a first configuration, wherein the first pair of strain gauges 16a of and the second pair of dummy gauges 16b are connected to form a full semi-active Wheatstone bridge circuit 18, and a second configuration wherein the gauges of the second pair of dummy gauges 16b are disconnected and replaced by external resistor 42.

[0065] The detection system further comprises an electronic readout device 20 and processing means 60.

[0066] As shown in [Fig. 4] and [Fig. 5], the electronic readout device 20 comprises an Instrumentation Amplifier (INA in the following description) connected to an Analog-to-Digital Converter (ADC in the following description). The ADC is connected to a micro-controller (pC in the following description) or a Field-Programmable Gate Array (FPGA in the following description). The pC / FPGA is connected to the processing means 60 and to the microelectromechanical sensor 10 comprising the sensing element 12. The pC / FPGA is configured to control the processing means 60, the microelectromechanical sensor 10 and the sensing element 12.

[0067] According to the second embodiment, the electronic readout device 20 is configured for performing two separate electric measurements on the bridge circuit18. As shown in [Fig. 4] and [Fig. 5], a first terminal of the INA is connected to the midpoint 91 and a second terminal of the INA is connected to the midpoint 92.

[0068] The first electric measurement is performed in the first configuration shown in [Fig. 4] for acquiring a first electric signal representative of resistance changes in the gauges of both the first pair of strain gauges 16a and the second pair of dummy gauges 16b. The second measurement is performed in the second configuration shown in [Fig. 5] for acquiring a second electric signal representative of resistance changes in the gauges of the first pair of strain gauges 16a. So to speak, the first electric signal is acquired with the first switching means 40 in the first configuration and the second electric signal is acquired with the first switching means 40 in the second configuration.

[0069] The electronic readout device 20 is configured for extracting information on displacement or deformation of the sensing element 12 and on said displacement or deformation of the substrate 14 by combining said first and second electric signals.

[0070] As recited hereinbefore, the first signal is representative of the quantity to be measured but is also influenced by the deformations of the substrate.

[0071] In contrast, the quasi-stationary, low-frequency content of the second signal is directly representative of the deformations occurring through the substrate 14.

[0072] A signal compensating for the deformations of the substrate can therefore advantageously be extracted from the first signal and the second signal.

[0073] The processing means 60 comprise, for example, microprocessors configured for using said information on strain or deformation of the substrate 14 to correct said information on information on said displacement or deformation of the sensing element 12 by compensating drifts of either offset, or scale factor, or both, of the microelectromechanical sensor 10. Said correction can be performed by first compensation algorithms that are simple and based on linear coefficients only. More advanced elaboration algorithms can be based on training the system and then applying suitable machine learning techniques.

[0074] The second embodiment is suitable for detection systems which are not frequency modulated around a certain resonance frequency as in the first embodiment.

[0075] In a first variant of the second embodiment of the invention shown in [Fig. 6], the electronic readout device 20 is configured for performing two separate electric measurements on the bridge circuit 18. A third measurement is performed for acquiring a third electric signal representative of resistance changes in the gauges of either one of the first 16a and second pair 16b. A fourth measurement is performed for acquiring a fourth electric signal representative of resistance changes in the gauges of the other one the first 16a or the second pair 16b. The electronic readout device 20 is further configured for extracting information on said displacement or deformation of the sensing element 12 and on said displacement or deformation of the substrate 14 by combining said third and fourth electric signals. The detection system further comprises second switching means 44 configured for commuting between a third configuration, wherein the gauges of the first pair 16a are connected to the bridge circuit 18 while the gauges of the second pair 16b are disconnected from it and replaced by external resistors 42, and a fourth configuration, wherein the gauges of the second pair 16b are connected to the bridge circuit 18 while the gauges of the first pair 16a are disconnected from it and replaced by external resistors 42. The second switching means 44 comprise, for example, transistors.

[0076] In a second variant of the second embodiment of the invention, the first pair 16a and the second pair 16b are strain gauges.

[0077] In a third variant of the second embodiment of the invention, the switching means 40 are configured for, in the second configuration, disconnecting the gauges of the first pair 16a and replacing them by external resistors 42.

[0078] In alternative variants of the second embodiment (not illustrated), the switching means are used to connect / disconnect active gauges 16a, while dummy gauges are permanently part of the circuit.

[0079] [Fig.7] is a block diagram of a detection system according to a third embodiment of the invention.

[0080] The third embodiment corresponds to the combination of the first embodiment and the second embodiment.

[0081] According to the third embodiment, the detection system comprises the microelectromechanical sensor 10, a first pair of strain gauges 16a and a second pair of strain gauges 16b. In the example shown in [Fig. 7], the gauges of the first pair ofstrain gauges 16a are “active” strain gauges 16a, configured for differentially detecting a displacement or deformation of the sensing element 12: a displacement or deformation of the sensing element 12, induce a change AR of the resistance of the first strain gauge 16a and an opposite change -AR of the resistance of the second strain gauge. The gauges of the second pair of strain gauges 16b are instead dummy gauges. A first gauge of the first pair of strain gauges 16a is connected to a first dummy gauge of the set of dummy gauges 16b by a first midpoint 91. A second gauge of the first pair of strain gauges 16a is connected to a second dummy gauge of the second pair of dummy gauges 16b by a second midpoint 92. The detection system further comprises a pair of external resistors 42. A first external resistor of the pair of external resistors 42 is connected to the midpoint 91 and a second external resistor of the pair of external resistors 42 is connected to the midpoint 92.

[0082] Dashed arrows show that the resistances of the active gauges 16a depend on both a displacement or deformation of the sensing element 12 and on deformations of the substrate 14, while the resistances of the dummy gauges 16b only depend on deformations of the substrate 14.

[0083] The detection system further comprises first switching means 40. The first switching means comprise, for example, transistors. The first switching means 40 are configured for commuting between a first configuration, wherein the first pair of strain gauges 16a and the second pair of dummy gauges 16b are connected to form a full semi-active Wheatstone bridge circuit 18, and a second configuration wherein the gauges the second pair of dummy gauges 16b are disconnected and replaced by external resistor 42.

[0084] The detection system further comprises an electronic readout device 20 and processing means 60. The detection system further comprises a first ASIC 1 and a second ASIC 2. The first ASIC 1 is connected to the processing means 60, to the microelectromechanical sensor 10 and is configured to control the processing means 60 and the microelectromechanical sensor 10. The second ASIC 2 is connected to the full semi-active Wheatstone bridge 18, to the processing means 60 and to means 70. As shown in [Fig. 7], a first terminal of the second ASIC 2 is connected to the first midpoint 91 and a second terminal of the second ASIC 2 is connected to the second midpoint 92.

[0085] The detection system further comprises means 70 for actuating the sensing element 12 at a nonzero frequency f. The second ASIC 2 is configured to control the means 70.

[0086] The electronic readout device 20 comprises a first low-pass filter 22a and a second low-pass filter 22b. The first and the second low-pass filters (22a, 22b) are active low-pass filters comprising three amplifiers, a first capacitance CSki and a second capacitance CSk2, a first impedance RSki and a second impedance RSk2 as shown in [Fig. 7], The first low-pass filter 22a is connected to the first midpoint 91. The second low-pass filter 22b is connected to the second midpoint 92.

[0087] The electronic readout device 20 is configured for acquiring at least one electric signal by performing at least one electric measurement on the bridge circuit 18 and to extract therefrom information on said displacement or deformation of the sensing element 12.

[0088] The electronic readout device 20 is further configured for processing said signal or signals to extract information on strain or deformation of the substrate 14 by performing low-pass filtering of said electric signal or signals. The low-frequency component of the signal emitted by the first pair of strain gauges 16a and of the second pair of dummy gauges 16b in the first configuration, or of the first pair of strain gauges 16a in the second configuration, is a direct or indirect measurement of the deformations affecting the substrate 14.

[0089] The electronic readout device 20 is connected to the first ASIC 1 which is configured to control the electronic readout device 20 and to manipulate said information on strain or deformation of the substrate 14. The first ASIC 1 is further configured to send said information to processing means 60.

[0090] The means 70 comprises transductors configured to transform electric signal into force, torque or displacement on the sensing element 12. The electronic readout device 20 is configured for extracting information on displacement or deformation of the sensing element 12 from a spectral component of said electric signal or signals at said frequency f.

[0091] The processing means 60 comprise, for example, microprocessors configured for using said information on strain or deformation of the substrate 14 to correct said information on information on said displacement or deformation of the sensingelement 12 by compensating drifts of either offset, or scale factor, or both, of the microelectromechanical sensor 10. Said correction can be performed by first compensation algorithms that are simple and based on linear coefficients only. More advanced elaboration algorithms can be based on training the system and then applying suitable machine learning techniques.

[0092] The variants of the first and second embodiments of the invention may be applied to the third embodiment of the invention.

[0093] Advantageously, the invention according to the three embodiments described herein above allows local monitoring of the deformation of the substrate without needing to add stress sensors with dedicated electronics, allowing savings in space or pads, and saving in energy for implementing the invention. This implementation does not therefore require any additional feature in the design of the microelectromechanical sensor.

[0094] Advantageously, the invention does not lead to any worsening of performance in terms of noise because of the immunity of the resistive detection to interference.

[0095] Advantageously, and as described above, it is possible to combine several gauges configured to measure stress in different directions. Such a configuration is advantageous in multi-sensor applications.

[0096] Advantageously, the stress measurement is direct, unlike capacitive sensors where the measurement is carried out by means of a pressure sensor.

[0097] [Fig.8] is a block diagram of a detection system according to a fourth embodiment of the invention.

[0098] The fourth embodiment is equivalent to the first embodiment but comprises a first full semi-active Wheatstone bridge 18a and a second full semi-active Wheatstone bridge 18b.

[0099] The first full semi-active Wheatstone bridge 18a comprises a first pair of strain gauges 16a and a second pair of external resistors 42a arranged to form the first full semi-active Wheatstone bridge 18a. The four arms of the first full semi-active Wheatstone bridge 18a are formed by the resistances RNGof the two strain gauges 16a and the resistance Rext of the two external resistors 42a. The strain nanogauges 16a are installed on the same side of the first full semi-active Wheatstone bridge 18a.A first midpoint 91a connects the first gauge of the pair of strain gauges 16a to the first external resistor 42a. A second midpoint 92a connects the second gauge of the pair of strain gauges 16a to the second external resistor of the second pair of external resistor 42a.

[0100] The gauges of the first pair of strain gauges 16a are “active” strain gauges 16a, configured for differentially detecting a displacement or deformation of the sensing element 12: a displacement or deformation of the sensing element 12, induce a change AR of the resistance of the first strain gauge 16a and an opposite change -AR of the resistance of the second strain gauge.

[0101] The second full semi-active Wheatstone bridge 18b comprises a first pair of dummy gauges 16b and a second pair of external resistors 42b arranged to form the second full semi-active Wheatstone bridge 18b. The four arms of the second full semi-active Wheatstone bridge 18b are formed by the resistances RNG, dummy of the two dummy gauges 16b and the resistance Rext of the two external resistors 42b. The dummy gauges 16b are installed on the same side of the second full-semi-active Wheatstone bridge 18b. A third midpoint 91b connects the first dummy gauge of the pair of dummy gauges 16b to the first external resistor of the second pair of external resistor 42b. A fourth midpoint 92b connects the second dummy gauge of the pair of dummy gauges 16b to the second external resistor of the second pair of external resistor 42b.

[0102] Dashed arrows show that the resistances of the active gauges 16a depend on both a displacement or deformation of the sensing element 12 and on deformations of the substrate 14, while the resistances of the dummy gauges 16b only depend on deformations of the substrate 14.

[0103] The detection system further comprises an electronic readout device 20 and processing means 60. The detection system further comprises a first ASIC 1 and a second ASIC 2. The first ASIC 1 is connected to the processing means 60, to the microelectromechanical sensor 10 and is configured to control the processing means 60, the microelectromechanical sensor 10. The second ASIC 2 is connected to the first full semi-active Wheatstone bridge 18a, to the processing means 60 and to means 70. As shown in [Fig. 8], a first terminal of the second ASIC 2 is connected tothe first midpoint 91a and a second terminal of the second ASIC 2 is connected to the second midpoint 92a.

[0104] The detection system further comprises means 70 for actuating the sensing element 12 at a nonzero frequency f. The second ASIC 2 is configured to control the means 70. The means 70 comprises transductors configured to transform electric signal into force, torque or displacement on the sensing element 12. The electronic readout device 20 is configured for extracting information on displacement or deformation of the sensing element 12 from a spectral component of said electric signal or signals at said frequency f.

[0105] The electronic readout device 20 comprises a first low-pass filter 22a and a second low-pass filter 22b. The first and the second low-pass filters (22a, 22b) are active low-pass filters comprising three amplifiers, a first capacitance CSki and a second capacitance CSk2, a first impedance RSki and a second impedance RSk2 as shown in [Fig. 3]. The first low-pass filter 22a is connected to the third midpoint 91b. The second low-pass filter 22b is connected to the fourth midpoint 92b.

[0106] The electronic readout device 20 is configured for acquiring at least one electric signal by performing at least one electric measurement on the second bridge circuit 18b and to extract therefrom information on said displacement or deformation of the sensing element 12.

[0107] The electronic readout device 20 is further configured for processing said signal or signals to extract information on strain or deformation of the substrate 14 by performing low-pass filtering of said electric signal or signals. The low-frequency component of the signal emitted by the second pair of dummy gauges 16b is a direct or indirect measurement of the deformations affecting the substrate 14.

[0108] The electronic readout device 20 is connected to the first ASIC 1 which is configured to control the electronic readout device 20 and to manipulate said information on strain or deformation of the substrate 14. The first ASIC 1 is further configured to send said information to processing means 60.

[0109] The processing means 60 comprise, for example, microprocessors configured for using said information on strain or deformation of the substrate 14 to correct said information on information on said displacement or deformation of the sensing element 12 by compensating drifts of either offset, or scale factor, or both, of themicroelectromechanical sensor 10. Said correction can be performed by first compensation algorithms that are simple and based on linear coefficients only. More advanced elaboration algorithms can be based on training the system and then applying suitable machine learning techniques.

[0110] Using the processing means 60, the detection system according to the fourth embodiment therefore makes it possible to calibrate the measurement made by the first pair of strain gauges 16a by correcting it with the low frequency component of the measurement made on the signal emitted by the second pair of dummy gauge 16b.

[0111] In all the embodiments of the invention, the processing means 60 are not necessary to the implementation of the invention. Indeed, the invention relates to a detection system which is configured for extracting deformation or stress information from the substrate directly from the gauges. Compensation of deformation or stress using the extracted information is optional.

[0112] In all the embodiments of the invention, the gauges (both “actives” and “dummy”) may be nanogauges or microgauges.

[0113] The invention also relates to a method of operating a detection system according to the invention.

[0114] The method comprises:- a first step S10 of acquiring, from the detection system, said information on said displacement or deformation of the sensing element 12, representative of a physical quantity of interest, and said information on strain or deformation of the substrate 14; and- a second step S20 of using said information on strain or deformation of the substrate 14 for correcting said information on information on said displacement or deformation of the sensing element 12 by compensating drifts of either offset, or scale factor, or both, of the microelectromechanical sensor 10.

[0115] References

[0116] (Uzunoglu et al. 2022): B.E. Uzunoglu , D. Erkan , E. Tatar, A Ring Gyroscope With On-Chip Capacitive Stress Compensation, IEEE, Volume 341, Issue 5, 2022, Pages 741-752.

[0117] (Tatar et al. 2016) : E. Tatar; T. Mukherjee; G. K. edder, On-chip stress compensation on the ZRO of a mode-matched MEMS gyroscope, 2016 IEEE International Symposium on Inertial Sensors and Systems, Laguna Beach, CA, USA, 2016, pp. 128-131.

Claims

CLAIMS1. A detection system comprising:- a microelectromechanical sensor (10) comprising a sensing element (12) anchored to a substrate (14);- a first (16a) and a second pair (16b) of electrically resistive elements arranged to form a bridge circuit (18), wherein at least the electrically resistive elements of the first pair (16a) are strain gauges configured for differentially detecting a displacement or deformation of the sensing element (12); and- an electronic readout device (20), configured for acquiring at least one electric signal by performing at least one electric measurement on the bridge circuit (18) and processing said signal or signals to extract therefrom information on said displacement or deformation of the sensing element induced by a quantity to be sensed (12);characterized in that the electronic readout device (20) is also configured for extracting from said electric signal or signals information on strain or deformation of the substrate (14).

2. The detection system of claim 1 wherein the electrically resistive elements of the second pair (16b) are external resistors (42), unaffected by strain or deformation of the substrate (14).

3. The detection system of any one of the preceding claims wherein the electronic readout device (20) is configured for extracting said information on strain or deformation of the substrate (14) by performing low-pass filtering of said electric signal or signals.

4. The detection system of claim 3 wherein the microelectromechanical sensor (10) comprises means for actuating the sensing element (12) at a nonzero frequency f, and the electronic readout device (20) is configured for extracting information on said displacement or deformation of the sensing element (12) from a spectral component of said electric signal or signals at said frequency f.

5. The detection system of claim 1 , wherein the electrically resistive elements of the second pair are dummy gauges formed on the substrate (14) and wherein the electronic readout device (20) is configured for performing two separate electric measurements on the bridge circuit (18) for acquiring:- a first electric signal representative of resistance changes in the gauges of both the first (16a) and second pair (16b); and- a second electric signal representative of resistance changes in the gauges of either the first (16a) or the second pair (16b);and for extracting information on said displacement or deformation of the sensing element (12) and on said displacement or deformation of the substrate (14) by combining said first and second electric signals.

6. The detection system of claim 5 further comprising first switching means (40) configured for commuting between a first configuration, wherein the first (16a) and second pairs (16b) of gauges are connected to form said bridge circuit (18), and a second configuration wherein the gauges of either the first (16a) or the second pair (16b) are disconnected and replaced by external resistor (42), the first electric signal being acquired with the first switching means (40) in the first configuration and the second electric signal being acquired with the first switching means (40) in the second configuration.

7. The detection system of claim 6, wherein the switching means (40) are configured for, in said second configuration, disconnecting the dummy gauges of the second pair (16b) and replacing them by said external resistors (42).

8. The detection system of claim 1 , wherein the electrically resistive elements of the second pair are dummy gauges formed on the substrate (14) and wherein the electronic readout device (20) is configured for performing two separate electric measurements on the bridge circuit (18) for acquiring:- a third electric signal representative of resistance changes in the gauges of either one of the first (16a) and second pair (16b); and- a fourth electric signal representative of resistance changes in the gauges of the other one the first (16a) or the second pair (16b); andand for extracting information on said displacement or deformation of the sensing element (12) and on said displacement or deformation of the sensing element (12) by combining said third and fourth electric signals.

9. The detection system of claim 8 further comprising second switching means (44) configured for commuting between a third configuration, wherein the gauges of the first pair (16a) are connected to the bridge circuit (18) while the gauges of thesecond pair (16b) are disconnected from it and replaced by external resistors (42), and a fourth configuration, wherein the gauges of the second pair (16b) are connected to the bridge circuit (18) while the gauges of the first pair (16a) are disconnected from it and replaced by external resistors (42).

10. The detection system of any one of the preceding claims wherein the gauges are nanogauges.

11. The detection system of any one of the preceding claims further comprising processing means (60) configured for using said information on strain or deformation of the substrate (14) to correct said information on information on said displacement or deformation of the sensing element (12) by compensating drifts of either offset, or scale factor, or both, of the microelectromechanical sensor (10).

12. A method of operating a detection system according to any one of the preceding claims, comprising:- a first step (S10) of acquiring, from the detection system, said information on said displacement or deformation of the sensing element (12), representative of a physical quantity of interest, and said information on strain or deformation of the substrate (14); and- a second step (S20) of using said information on strain or deformation of the substrate (14) for correcting said information on information on said displacement or deformation of the sensing element (12) by compensating drifts of either offset, or scale factor, or both, of the microelectromechanical sensor (10).

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