Microsystem comprising a movable beam in bending and several stops

Abstract

Electromechanical microsystem (1), comprising: a beam (10), extending from a base (13) to an end (14), the beam being configured to oscillate about an equilibrium position; at least one strain gauge (11, 12), configured to deform when the angle of rotation of the diaphragm (θ) increases; a first stop extending to a first distance (e1) from the central axis, and configured to be in contact with the diaphragm when the end moves away from the central axis beyond a first displacement (y1); a second stop (202) extending to a second distance (e2) from the central axis, the second stop being configured to be in contact with the beam when the end moves away from the central axis by a second, greater displacement (y2), greater than the first displacement (y1). Fig. 3B.

Description

Title of the invention: Microsystem comprising a movable beam in bending and several stops. Technical field

[0001] The technical field of the invention relates to a microsystem comprising a beam bending in a plane, the bending movement being linked to a quantity of interest, for example a pressure differential, an acceleration or a displacement of the end of the beam. EARLIER ART

[0002] Sensors, such as accelerometers, microphones, or gyroscopes, use microsystems comprising a beam whose movement is linked to a quantity of interest to be measured, for example, acceleration, pressure, or the displacement of one end of the beam. This displacement can be generated by a component connected to the end of the beam. The amplitude of movement can be measured by piezoresistive or piezoelectric strain gauges, the latter converting a mechanical deformation into a usable electrical signal.

[0003] Patent EP2410767 describes, for example, a microphone in which the beam constitutes a diaphragm subjected to a pressure differential. The term diaphragm designates the element that delimits two portions of the acoustic array of said microphone: an upstream portion subjected to the pressure fluctuations of an incident sound wave and a downstream portion connected to a rear volume where the acoustic pressure fluctuations tend to cancel each other out in the audible frequency range. Strain gauges, suspended between a fixed substrate and the diaphragm, make it possible to measure the movement of the diaphragm produced by the pressure fluctuations of the incident sound wave. The measurement principle is based on a variation in the resistivity of the material forming each piezoresistive gauge, under the effect of compression or extension resulting from the bending movement of the diaphragm.

[0004] One limitation of strain gauges is their ability to withstand mechanical stresses that could reach excessive levels during significant diaphragm movement. To this end, in EP2410767, a mechanical stop device is described to limit the bending movement at the end of the movable diaphragm. In principle, as soon as the diaphragm comes into contact with the stop, the operating limit of the device is reached.

[0005] Patent EP3136052 describes a similar device for measuring the large-amplitude movement of a moving mechanical part. For this application, the beam is used as a rigid element between a base supported on a pivot and Its end is connected to the moving mechanical part by a flexible element. The beam's motion is a rigid body rotating around an axis of rotation fixed by the pivot. The elongation of the piezoresistive gauges is thus related to the displacement of the end of the slender structure by the ratio between the distance of the gauges from the axis of rotation and the length of the beam. In this device, the flexible link connecting the end of the slender structure to the moving mechanical part plays a crucial role, as it ensures the conversion of the large-amplitude motion of the moving part into a smaller-amplitude motion at the end of the slender structure. The gear ratio adopted is designed to reduce the mechanical stress on the gauges and must be adapted according to the amplitude of motion of the moving part being measured and the maximum elongation of the gauges.With the exception of the element mentioned above, nothing is mentioned in patent EP3136052 regarding the protection of strain gauges in the event of exceptional overload. It is feared that an impact along the direction of movement of the moving mechanical part being measured could lead to an excessive level of stress in the strain gauges.

[0006] However, a beam is never perfectly rigid. It can therefore continue to deform under excessive load and stress the strain gauges beyond the threshold deemed excessive, even when in contact with a stop device located at the end of the slender structure as mentioned in patent EP2410767. The invention described below allows for the design of robust electromechanical systems, preserving the integrity of strain gauges and providing a wider operating range. Description of the invention

[0007] A first object of the invention is a microelectromechanical system, comprising: - a beam, extending from a base to an end, the beam being configured to be mobile in bending in a bending plane, under the effect of a mechanical load, from an equilibrium position, the beam extending along a central axis when it occupies the equilibrium position, the beam being configured to drive, under the effect of bending, the base in rotation around an axis of rotation, according to an angle of rotation, in the bending plane, the angle of rotation, being defined with respect to the central axis; - at least one strain gauge, configured to deform when the angle of rotation increases, the strain gauge being configured to generate a detection signal dependent on the angle of rotation;

[0008] The microsystem being characterized in that it comprises a first-order stop and a second-order stop, each stop being intended to contact the beam, the microsystem being such that: - the first stop is positioned, parallel to the central axis, between the stop of rank 2 and the base; - the first rank stop extending to a first distance from the equilibrium position, the first rank stop being configured to be in contact with the beam when the end moves away from the equilibrium position beyond a first displacement; - the second row stop extends to a second distance, greater than the first distance, from the central axis, relative to the equilibrium position, the second row stop being configured to be in contact with the beam when the end moves away from the equilibrium position by a second displacement greater than the first displacement; - so that • when the end moves from the equilibrium position to the first displacement, the angle of rotation increases; • when the end moves from the first displacement to the second displacement, the angle of rotation decreases, under the effect of a deformation of the beam and a support of the beam against the first-order stop.

[0009] The microsystem may include several stops of rank n, n being an integer greater than or equal to 2, each stop of rank n being arranged: - along the central axis, at a distance from the base that is greater the higher the rank of the stop; - perpendicular to the central axis, at a distance, relative to the equilibrium position, which is all the greater as the rank of the stop is high; - the stop of rank n extends to an nth spacing, greater than the nth spacing relative to the equilibrium position, the stop of rank n being configured to be in contact with the beam when the end moves away from the equilibrium position by an nth displacement, greater than the nth displacement.

[0010] According to one possibility, the stops of rank greater than or equal to 2 are positioned so as to come simultaneously into contact with the beam, the stops being positioned according to a deformation profile of the beam.

[0011] According to one possibility, the stops of rank greater than or equal to 2 are positioned so as to come successively into contact with the beam, the stops being positioned according to a deformation profile of the beam.

[0012] According to one possibility, a stop, of rank greater than or equal to 2, is configured such that the distance between said stop and the equilibrium position increases as a function of a distance between the stop and the base, so that the shape of the stop corresponds to a deformation profile of the beam

[0013] According to one possibility, the strain gauge or each strain gauge is a piezoresistive or piezoelectric gauge.

[0014] According to one possibility: - the beam extends along a length between the base and the end; - the first distance is between 0.2 and 0.6 times the length.

[0015] The microsystem may include a processing unit, configured to: - receive the detection signal; - estimate the angle of rotation of the beam as a function of the detection signal.

[0016] According to one possibility, the processing unit is configured to calculate a bending amplitude of the beam as a function of the angle of rotation.

[0017] According to one possibility: - the beam is coupled to an actuator, configured to induce a bending of the beam; - the processing unit is configured to extract a variation of the detection signal in response to the bending induced by the actuator; - the processing unit can be configured to determine the beam's bending amplitude based on said variation of the detection signal.

[0018] The microsystem may include a detector of a contact between the beam and the rank 1 stop. The processing unit may be configured to determine the amplitude of bending of the beam as a function of a contact between the beam and the rank 1 stop.

[0019] According to one possibility, the microsystem comprises a chamber, the microsystem being such that the beam forms a diaphragm, delimiting the chamber, the beam being configured to flex according to a pressure differential on either side of the beam.

[0020] According to one possibility, the end of the beam forms a mass, so that the beam follows a bending movement under the effect of a displacement of the mass, so that the displacement of the mass causes the rotation of the base.

[0021] The displacements and spacings of each stop can be defined with respect to the central axis.

[0022] A second object of the invention is a measuring device, comprising a microsystem according to the first object of the invention, the measuring device being configured to measure the beam's flexural amplitude. The device can be an accelerometer, a gyroscope, or a microphone.

[0023] The invention will be better understood upon reading the description of the exemplary embodiments presented later in this description, in connection with the figures listed below. FIGURES

[0024] Figure 1 schematically illustrates an example of a photoacoustic detection device

[0025] Figure [Fig.2A] schematically represents a microsystem intended for photoacoustic detection.

[0026] [Fig.2B] is a detail of [Fig.2A].

[0027] Fig.2C illustrates a limitation of the microsystem described in relation to Fig.2A.

[0028] The [Fig.2D] is a curve representing the stresses exerted at the strain gauges as a function of a load applied to the beam.

[0029] Figures 3A and 3B schematically illustrate a first embodiment of a microsystem implementing the invention. In this example, it is a microsystem for photoacoustic detection similar to the microsystem of [Fig. 2A]. [Fig. 3A] illustrates the bending of the microsystem beam when it is supported against a first-order stop. [Fig. 3B] illustrates the bending of the microsystem beam, already supported against the first-order stop, when it is supported against a second-order stop.

[0030] Fig. 3C schematically illustrates different bendings of the beam in the microsystem described in relation to Fig. 3A.

[0031] Fig. 3D schematically illustrates the impact of beam bending, as described in relation to Fig. 3C, on the angle of rotation of a base connected to the beam.

[0032] The [Fig.3E] is a curve representing the stresses exerted at the strain gauges as a function of a load applied to the beam, in the case of the first embodiment.

[0033] Fig. 3F illustrates a configuration in which an actuator is configured to induce bending of the beam.

[0034] Fig. 4A illustrates a second embodiment of the invention, comprising two stops.

[0035] Figures 4B and 4C illustrate a third embodiment of the invention, comprising n stops, n being an integer greater than or equal to 4.

[0036] Figure 5 shows a third embodiment of the invention

[0037] Figure 6 illustrates a fourth embodiment of the invention. PRESENTATION OF SPECIFIC IMPLEMENTATION METHODS

[0038] Figure 1 represents a photoacoustic detection device 30. The device comprises a first and a second chamber 31, 32, intended to be occupied by a gas to be analyzed, at the same pressure. The first chamber 31 is configured to be exposed to a laser beam L modulated in amplitude according to a frequency of Modulation. The laser beam L is emitted at a wavelength corresponding to the absorption wavelength of a gaseous species likely to be present in the gas. Under the effect of absorption, the illuminated gas heats up, with the heating modulated according to the modulation frequency of the laser beam. This modulated heating causes a pressure variation, via the photoacoustic effect, in the first chamber 31, which acts as a measurement chamber. In the second chamber 32, the pressure is stable; this second chamber acts as a reference chamber.

[0039] The pressure variation within the first chamber 31 results in a pressure variation AP between the first chamber 31 and the second chamber 32. The pressure variation AP is modulated according to the modulation frequency of the laser beam.

[0040] The device includes a microsystem 1, described below, of the microphone type, intended to measure the pressure difference AP. In addition to the microsystem, the device includes a microfluidic network 33 allowing the supply of gas to the first chamber 31 and the second chamber 32, as well as the renewal of the gas.

[0041] The pressure variation within the first chamber 31 results in a pressure variation AP between the first chamber 31 and the second chamber 32, the latter being maintained at a constant pressure. The pressure variation AP is modulated according to the modulation frequency of the laser beam. The pressure variation AP is greater when the concentration of the gaseous species sought is higher.

[0042] Figures 2A and 2B illustrate an example of a microsystem Iaa according to the prior art. The microsystem comprises a beam 10, forming a diaphragm, the beam being suspended from a base 13, which is connected to a fixed substrate 15, forming a support. The beam is movable in bending in a plane designated the beam's bending plane. Under the effect of bending the beam, the base 13 is movable in rotation relative to the substrate 15. The base 13 is connected to two arms 16, 17 forming a hinge, allowing rotation of the base about an axis of rotation perpendicular to the beam's bending plane. The beam 10 separates the first chamber 31 from the second chamber 32. Under the effect of the pressure difference AP between the two chambers, the beam is configured to vibrate with a specific amplitude and frequency. Beam 10 extends from base 13 to a free end 14.A fixed stop 20 limits the displacement of the free end 14 on either side of an equilibrium position 10a. The equilibrium position 10a, shown in [Fig.2A] and [Fig.2C], corresponds to a pressure equilibrium between chamber 31 and chamber 32.

[0043] The pressure difference AP between chambers 31 and 32, modulated at the laser modulation frequency, causes the beam 10 to oscillate at the light frequency of the laser beam, on either side of the equilibrium position 10a. The amplitude of the oscillation depends on the concentration of the gaseous species sought in the illuminated gas.

[0044] Figure 2B shows a detail of the base 13 from which the beam 10 extends. Two strain gauges 11 and 12 are arranged between the base 13 and the fixed substrate 15. Under the effect of the beam's oscillation, the strain gauges undergo a deformation stress, either in compression or expansion. The strain gauges generate a detection signal that depends on their deformation. The detection signal is thus representative of the amplitude and frequency of the beam's oscillation relative to the fixed substrate 15. The detection signal is processed by a processing unit 19, of the electronic circuit or microprocessor type. Two arms 16 and 17 extend from the base and suspend it from the fixed substrate. The arms form a flexible hinge and define a pivot on which the base rests.The arms prevent translational movement of the base and allow rotational movement around an axis of rotation perpendicular to a plane along which the beam and the two arms extend. The axis of rotation can be considered as located at the intersection of two median planes, along which the two arms 16 and 17 extend respectively. In [Fig. 2B], each median plane has been represented by dashed lines.

[0045] The oscillation of the beam 10 causes, at the base 13, a change in the angle of rotation 0. The angle of rotation 0 corresponds to an angle, formed at the base 13, between: - a central axis A, around which the beam 10 extends to the equilibrium position, at which the pressures in chambers 31 and 32 are equal; - the axis around which the beam 10 extends, deflected by the pressure variation AP between the two chambers 31 and 32.

[0046] The central axis A is symbolized by a dashed line. The larger the rotation angle 0, the greater the stress exerted on the strain gauges 11 and 12.

[0047] Figure 2C shows a view of the microsystem Iaa in the beam's bending plane. In Figure 2C, the beam 10 is shown in the equilibrium position 10a and in a butted position 10b, in which the beam is supported by the abutment 20. When the beam is butted, due to an increase in pressure in chamber 31, the beam continues to bend while remaining supported against the abutment, which increases the angle of rotation θ measured at the base 13, relative to the equilibrium position. In Figure 2C, the bending is indicated by an arrow F. Under the effect of bending, the angle of rotation θ increases, which leads to an increase in the strain stress exerted on the strain gauges, potentially causing them to break. Thus, due to the flexibility of the beam, after the latter has reached the stop 20, the angle of rotation 0 can continue to increase, under the effect of an increase in the pressure variation AP on either side of the beam.

[0048] In [Fig.2C], the bending has been shown in an exaggerated manner.

[0049] In this type of application, strain gauges are sized to measure very small pressure fluctuations, on the order of IPa. However, at equilibrium, the pressure in each chamber reaches, for example, 1 bar, or 100,000 Pa, which is 100,000 times the pressure difference that one wishes to be able to measure using the strain gauges. Consequently, an imbalance of a few percent in the filling pressure of chambers 31 and 32, for example due to incorrect sizing or improper use of the microfluidic circuit 33, can cause deflection of the beam leading to the rupture of the strain gauges.

[0050] Figure 2D shows the axial stress acting on the strain gauges (ordinate axis: unit MPa) as a function of the pressure variation AP on either side of beam 10 (abscissa axis: unit Pa). Curves 1a and 11b correspond to the axial stress acting on the first gauge 11 in extension, respectively: - between the equilibrium position and contact with the stop 20; - after beam 10 has reached the abutment 20, under the effect of the bending described related to [Fig.2C].

[0051] Axial stress is understood to mean a stress exerted along the axis of each gauge. In the example shown, gauges 11 and 12 are coaxial, along an axis shown in dashed lines on [Fig.2B].

[0052] Curves 12a and 12b correspond to the axial stress exerted in the second gauge 12 in compression, respectively: - between the equilibrium position and contact with the stop 20; - after beam 10 has reached the stop 20, under the effect of bending.

[0053] The stop 20 limits the displacement of the end 14 of the beam 10. However, it does not prevent an increase in the stress exerted on the strain gauges after the beam 10 is in contact with the stop. The operating ranges of the strain gauges corresponding to curves 11b and 12b are not usable. Indeed, the stress level can be such that it can lead to damage to the strain gauges. Thus, the microsystem Iaa described in connection with Figures 2A to 2D is not optimal. In [Fig. 2D], the operating range of the microsystem, which extends from 0 to approximately 60 Pa, is indicated by a double arrow.

[0054] Figure 3A represents a microsystem 1 according to a first embodiment. The microsystem comprises a first stop 20i, a second stop 202, and a The third abutment 203 is designed to contact beam 10 in order to limit its rotation. Each abutment is assigned a rank n, the rank being higher the greater the distance dn the abutment is, parallel to the central axis, from the base 13 from which beam 10 extends. N is a strictly positive natural number. The first abutment 20i is positioned, parallel to the central axis, between the second abutment 202 and the base 13. In [Fig. 3A], the distances db, d2, d3 between the first abutment 20i, the second abutment 202, and the third abutment 203 and the base 13 are shown.

[0055] In a direction perpendicular to the central axis: - the first stop 20i extends to a first distance ei from the equilibrium position 10a, the first stop being configured to be in contact with the beam 10 when the end 14 moves away from the equilibrium position 10a beyond a first displacement yb In this example, by displacement, we mean a displacement of the end 14 of the beam relative to the equilibrium position 10a. - the second stop 202 extends to a second distance e2, greater than the first distance eb from the equilibrium position 10a, the second stop being configured to be in contact with the beam 10 when the end 14 moves away from the equilibrium position 10a by a second displacement y2 greater than the first displacement yb - the third stop 203 extends to a third distance e3, greater than the second distance e2, from the central axis A, the third stop being configured to be in contact with the beam 10 when the end 14 moves away from the equilibrium position 10a according to a third displacement y3 greater than or equal to the second displacement y2.

[0056] Thus, in general, and regardless of the embodiment, for n > 2: - each stop of rank n is disposed at a distance in de from the equilibrium position greater than or equal to the distance in i of the stop of rank lower; - each stop is configured to be in contact with the beam 10 when the end 14 moves away from the equilibrium position 10a according to an nth displacement yn greater than or equal to the n-1st displacement y„ idc the end 14 at which the beam 10 reaches the stop of rank n-1.

[0057] Equivalently, the spacing of each stop and each displacement of the end can be defined with respect to the central axis A.

[0058] The rank n of each abutment corresponds to a chronological order in which the beam is supported as it deforms, when the end gradually moves away from the equilibrium position. A abutment designates a zone, point or extent, against which the beam rests for a given displacement of the end 14.

[0059] In Figures 3A and 3B, the displacement of the end 14, perpendicular to the central axis A, is represented by a grayscale scale (unit pm). Figure 3A corresponds to a configuration in which the beam 10 contacts the first abutment 20i. The displacement yi of the end 14 is approximately 2.5 pm. Figure 3B corresponds to a configuration in which the beam 10 contacts the second and third abutments 202, 203. The displacement y2 of the end 14 is approximately 8.5 pm.

[0060] In the embodiment shown in Figures 3A to 3F, the microsystem comprises a total of N stops, N being equal to 3. The invention applies for N>2.

[0061] When the end 14 moves, from the equilibrium position 10a, to the first displacement yb the angle of rotation 0 increases.

[0062] When the end 14 moves from the first displacement yi to the second displacement y2, the beam rests on the first abutment 20i. Figure 3B corresponds to this configuration. If, due to an increase in the pressure difference AP, the end 14 moves beyond the displacement yl, the beam 10 deflects while resting on the first abutment 201, as shown in Figures 3B and 3C. The deformation results in a decrease in the angle of rotation 0.

[0063] This represents a significant difference from the configuration using a single abutment in each direction of displacement, described in connection with Figures 2A and 2D. In the configuration shown in Figures 3A and 3B, at the strain gauges, the maximum stress is observed when the beam 10 reaches the first abutment 20i. If the pressure difference AP increases while the beam 10 is supported against the first abutment 20i, the deflection of the beam between the first abutment 20i and the end 14 results in a deflection of the beam 10 between the base 13 and the first abutment 20i, this latter deflection tending to bring the beam closer to the central axis A in the vicinity of the base 13. This effect is detailed in Figures 3C and 3D.

[0064] Figure 3C shows four configurations 100, 10i, 102, and 103 of the beam 10, for four load values, i.e., four pressure difference values ​​AP: 10 Pa, 16 Pa, 400 Pa, and 800 Pa. The x-axis corresponds to a position along the central axis (unit pm), with the base located at x = 0 pm. The y-axis corresponds to the displacement y of the end 14 of the beam. The first abutment 20i is positioned at a distance ei from the equilibrium position 10a equal to 1 pm and at a distance di of 350 pm from the base 10. The length 1 of the beam 10, parallel to the central axis A, is equal to 750 pm.

[0065] When the load AP < 16 Pa (configuration 100), the beam moves freely towards the first abutment 20i, which is reached when AP = 16 Pa (configuration 10i). The value AP = 16 Pa corresponds to a so-called full-scale value APp; this corresponds to the value of AP at which the stress (or mechanical load) exerted on the strain gauges 11, 12 is maximum. The displacement y of the end 14 is approximately 1.5 pm.

[0066] When AP > 16 Pa, the beam bears on the first abutment 20i and bends, such that the displacement y of the end 14 increases: see configurations 102 and 103. The deformation of the beam causes a deflection, towards the central axis A, of the portion of the beam adjacent to the base, located between the base (x = 0) and a distance of approximately 100 pm from the base. This portion is represented by a bracket in [Fig. 3C]. This results in a decrease in the angle of rotation 0. Thus, when the load, i.e., AP, applied to the beam exceeds the full-scale load APB, the portion of the beam adjacent to the base tends to return to the equilibrium configuration, under the combined effects of the curvature of the beam 10 and its bearing on the first abutment 20i. When the load AP = APmax = 800 Pa, the beam reaches the second and third abutments 202 and 203: configuration 103. It is then blocked.The value of APmax = 800 Pa corresponds to the maximum applicable load. The displacement of end 14 reaches a maximum value of 8.5 pm. This is the load for which the part of the beam adjacent to the base returns towards the central axis under the effect of deflection and reaches a rotation angle of zero or that can be considered as such.

[0067] Figure 3D schematically represents the configurations 10i and 102, during which the beam reaches and passes respectively the first abutment 20i. The maximum angle of rotation, denoted 0b, is reached in the configuration 10i. When, from this configuration, the load increases, the angle of rotation decreases: in the configuration 102, the angle of rotation is 02 with 02 < 0b. In Figure 3D, the beam in the state of equilibrium has been represented by a solid line.

[0068] Figure 3E represents, for the two strain gauges 11 and 12, the stress level (ordinate axis - unit MPa) as a function of the load exerted on the beam (abscissa axis - unit Pa). The positive axial stress curve corresponds to strain gauge 11 in extension on Figure 3D. The negative axial stress curve is recorded in the opposite strain gauge (gauge 12 in compression on Figure 3D). Until contact with the abutment is reached, the load applied to gauge 11 increases rapidly, up to a full-scale API load, which is equal to 16 Pa in this example. Upon reaching configuration 101 described in connection with Figures 3C and 3D, the stress level exerted on the The strain on gauges 11 and 12 is at its maximum. As the load increases and progresses to the maximum load APmax, the stress level decreases due to the decreasing angle of rotation. Thus, when AP varies between 0 and APmax, the maximum stress level is exerted on the strain gauges when AP = API.

[0069] Such an embodiment has several advantages: - the maximum stress exerted on the strain gauges, when the beam reaches the first stop 20i (AP = APi ), ​​is controlled: this allows the integrity of the strain gauges to be preserved. When the load applied to the beam is between the full-scale value APi and the maximum value APmax, the stress exerted on the strain gauges decreases and becomes close to 0 when AP = APmax. The operating range of the microsystem is improved, as indicated by a double arrow in [Fig. 3E]. It should be noted that load values ​​AP close to the full-scale value APi may not be precisely quantifiable due to the reversal of the rotation angle on either side of the full-scale value APb.

[0070] The curve shown in [Fig.3E] illustrates the fact that the beam can be used according to two operating regimes: - a first regime, for 0 < AP < APB according to which an increase in load results in an increase in the stress exerted on the strain gauges. - a second regime, for API < AP < APmax, according to which an increase in load results in a reduction of the stress exerted on the strain gauges.

[0071] The microsystem can only be used, in its entire measurement range, if the operating regime is known. For this purpose, the beam can be coupled to an actuator, for example, an electrostatic actuator 21 as shown in [Fig. 3F]. When actuated, the actuator generates a deflection of the beam, this deflection being reflected by a signal detected by the strain gauges. The operating regime can be identified based on the signal induced by the actuator; the most direct way to distinguish between the two regimes is by observing the change in sign in the response when the beam is at its limit. The processing unit 19 can determine the beam's deflection amplitude or the load applied to the beam and / or the angle of rotation based on the signal detected as a result of the beam's deflection induced by the actuator 21.

[0072] The electrostatic actuator 21 preferably extends along the beam 10, for example between the first stop 20i and the second stop 202. The actuator The electrostatic actuator 21 is configured to be polarized, which generates an attractive force. It is positioned to avoid contact with the beam. Placing the electrostatic actuator between two stops prevents contact between it and the beam following beam deflection. Under the effect of the attractive force exerted by the actuator, the beam undergoes deflection in a known direction. Measuring the change in the angle of rotation under the effect of deflection determines the operating regime: if the change in the angle of rotation is positive, the beam deflects according to the first operating regime. If the change in the angle of rotation is negative, the beam deflects according to the second operating regime.

[0073] According to one possibility, the electrostatic actuator is activated at a modulation frequency different from the beam's displacement frequency. The signal from each strain gauge can be demodulated at the modulation frequency to extract a component representative of the beam's deflection under the actuator's influence. This allows the change in the rotation angle resulting from the actuator's activation to be determined, thus identifying the beam's operating regime.

[0074] According to another possibility, the microsystem includes a contact detector, configured to detect contact between the beam and the first-order stop 20i. This may be, but is not limited to, a mechanical, electrical, electrostatic, capacitive, or magnetic detector. The type of detector depends on the properties of the material forming the beam, in particular its conductivity. The processing unit 19 can determine the beam's bending amplitude or the load applied to the beam and / or the angle of rotation as a function of the detected contact between the beam and the first-order stop.

[0075] When the operating regime cannot be known, the microsystem remains usable in the first operating regime, with the advantage of not risking a rupture of the strain gauges in case of overpressure.

[0076] In the embodiment described in connection with Figures 3A to 3F, the bending load acting on the beam results from a pressure differential on either side of the beam. This load can be considered as a linear force density assumed to be homogeneous along the entire length of the beam. The distance di between the first abutment 20i and the base 13 is preferably less than 58%, between 10% and 75%, or between 10% and 60% of the length 1 of the beam 10, between the base 13 and the end 14. The spacing ei between the first abutment 20i and the central axis A is determined according to the maximum stress level that is agreed to be applied to the strain gauges. The minimum spacing emin that can be obtained with the manufacturing or assembly process of the device limits the minimum distance di that can be adopted: by noting 0max the maximum angle which should not be exceeded, for a first stop close to the base, we can write within the framework of an approximation for small angles: di0max = ei > emin so that necessarily di > (emin / 0max).

[0077] The minimum spacing emin corresponds, for example, to the thickness of the substrate from which the device is made, divided by 20. 0max can be on the order of 1° or 2°

[0078] With regard to the abutment(s) of rank n greater than 1, their respective positions depend on the deformation profile of the beam. The adopted deviations preferentially ensure that the base 13 returns to the zero rotation configuration, i.e., zero rotation angle, when the beam contacts the higher-rank abutment.

[0079] In the embodiment described with reference to Figures 3A and 3F, a number N of stops equal to 3 is used. However, N can be equal to 2, as shown in [Fig. 4A], or be greater than 3, as shown in Figures 4B and 4C. When using a number of stops greater than or equal to 3, it can be advantageous for the position of the stops beyond rank 1 to be defined according to the beam's deformation profile. This allows the stops of rank above 2 to be simultaneously in contact with the beam. This is considered advantageous.

[0080] However, it is possible that the stops of rank higher than 1 are successively brought into contact with the beam when the load increases, a stop of rank n being brought into contact for a load value lower than that for which the beam contacts a stop of rank n+1.

[0081] A high number of rows of stops introduces a damping effect by compressing a gas film extending between each stop and the beam prior to contact. Adding damping is not recommended for microphone-type applications where the thermomechanical noise associated with viscous damping negatively impacts the signal-to-noise ratio. Adding damping may be suitable in microsystem applications within accelerometer-type devices.

[0082] Figure 5 shows an embodiment in which the second-order stop extends, facing the beam, over a significant length, while conforming to the beam's deformation profile. The second gap, which corresponds to the distance between the second-order stop and the equilibrium position, increases with the distance from the base. The spatial variation of the second gap corresponds to the beam's deformation profile. According to this embodiment, after the beam has been brought into contact with the first-order stop, the beam rests on the first-order stop and deforms as it approaches the second-order stop. This results in a decrease in the angle of rotation, as explained in connection with the previous embodiments. Because the shape of the second-order stop conforms to the beam's deformation profile, the beam simultaneously presses against the surface of the stop. The dimension of the stop, along the beam, can lead to a crushing of the gas film extending between the beam and the second-order stop: this can generate a damping effect, as described in connection with figures 4B and 4C.

[0083] The invention makes it possible both to secure the operation of a microsystem, while allowing an increase in the measurement dynamics.

[0084] Although described in connection with the manufacture of a microphone, the invention can be applied to other types of devices, for example, a gyroscope or an accelerometer. In the embodiments described above, the linear force density exerted on the beam, inducing bending, can be considered homogeneous. This is also the case when the device is an accelerometer, in which the beam is used as a test mass.

[0085] According to another possibility, described in connection with [Fig. 6], the end 14 of the beam forms a movable mass. The beam 10 operates via a lever arm that converts the force transmitted by the movable mass onto the beam into a rotational moment on the base: the rotation of the base is linked to the movement of the movable mass at the end of the beam. The end 14 can be connected to a restoring means, exerting a restoring force to return the beam to the equilibrium position.

Claims

1. Demands Electromechanical microsystem (1), comprising: - a beam (10), extending from a base (13), to an end (14), the beam being configured to be mobile in bending in a bending plane, under the effect of a mechanical load, from an equilibrium position, the beam extending along a central axis (A) when it occupies the equilibrium position, the beam being configured to cause, under the effect of bending, the base to rotate about an axis of rotation, according to an angle of rotation (0), in the bending plane, the angle of rotation being defined with respect to the central axis; - at least one strain gauge (11, 12), configured to deform when the angle of rotation (0) increases, the strain gauge being configured to generate a detection signal dependent on the angle of rotation; The microsystem is characterized in that it comprises a first-order stop and a second-order stop, each stop being intended to contact the beam, the microsystem being such that: the first stop (20i) is arranged, parallel to the central axis, between the stop of rank 2 and the base; the first rank stop extending to a first distance (ej from the equilibrium position, the first rank stop being configured to be in contact with the beam when the end moves away from the equilibrium position beyond a first displacement (y J; the rank 2 stop (202) extends to a second distance (e2), greater than the first distance, from the central axis, relative to the equilibrium position, the rank 2 stop being configured to be in contact with the beam when the end moves away from the equilibrium position by a second greater displacement (y2), greater than the first displacement (yi); so that • when the end (14) moves from the equilibrium position to the first displacement (yj, the angle of rotation increases; • when the end moves from the first displacement (yi), to the second displacement (y2), the angle of rotation decreases, under the effect of a deformation of the beam and a support of the beam against the rank 1 stop.

2. A microsystem according to claim 1, comprising several stops of rank n, n being an integer greater than or equal to 2, each stop of rank n being disposed: - along the central axis, at a distance (dn) from the base that is greater the higher the rank of the stop; - perpendicular to the central axis, at a distance (en) from the equilibrium position that is greater the higher the rank of the stop; - the stop of rank n (20n) extends to an nth distance (en), greater than the nth distance from the equilibrium position, the stop of rank n being configured to be in contact with the beam when the end deviates from the equilibrium position by an nth displacement (yn), greater than the nth displacement (y„ i)

3. Microsystem according to claim 2, wherein the stops of rank greater than or equal to 2 are positioned so as to come simultaneously into contact with the beam, the stops being positioned according to a deformation profile of the beam.

4. Microsystem according to claim 2, wherein stops of rank greater than or equal to 2 are positioned so as to come successively into contact with the beam, the stops being positioned according to a deformation profile of the beam.

5. A microsystem according to any one of the preceding claims, wherein a stop, of rank greater than or equal to 2, is configured such that the distance between said stop and the equilibrium position increases as a function of the distance between the stop and the base, such that the shape of the stop corresponds to a beam deformation profile

6. Microsystem according to any one of the preceding claims, wherein the strain gauge is a piezoresistive or piezoelectric gauge.

7. Microsystem according to any one of the preceding claims, wherein: - the beam extends over a length (;) between the base and the end; - the first distance is between 0.2 and 0.6 times the length.

8. Microsystem according to any one of the preceding claims, comprising a processing unit (19), configured to - receive the detection signal; - estimate the angle of rotation of the beam as a function of the detection signal.

9. Microsystem according to claim 8, wherein the processing unit is configured to calculate a beam bending amplitude as a function of the rotation angle.

10. Microsystem according to claim 8 or claim 9, wherein: - the beam is coupled to an actuator (21), configured to induce a bending of the beam; - the processing unit is configured to extract a variation of the detection signal in response to the bending induced by the actuator and to determine the angle of rotation and / or the amplitude of bending of the beam as a function of said variation of the detection signal.

11. Microsystem according to claim 8 or claim 9, comprising a detector of a contact between the beam and the stop of rank 1.

12. Microsystem according to claim 11, wherein the processing unit is configured to determine the angle of rotation and / or the amplitude of bending of the beam as a function of a contact between the beam and the rank 1 stop.

13. Microsystem according to any one of the preceding claims, comprising a chamber, the microsystem being such that the beam forms a diaphragm, delimiting the chamber, the beam being configured to flex according to a pressure differential on either side of the beam.

14. 20 Microsystem according to any one of the preceding claims, wherein the end of the beam forms a mass, such that the beam follows a bending motion under the effect of a displacement of the mass, such that the displacement of the mass causes the base to rotate.

15. Measuring device, comprising a microsystem according to any one of the preceding claims, the measuring device being configured to measure an amplitude of beam bending.

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