Inertial angular sensor with micro-machined electromechanical microsystem

Abstract

The invention relates to an angular sensor (1) comprising a support plate, an inner mass (10) suspended from the support plate at fixed anchor points (17) and suitable for vibrating in a plane (P), an outer mass (11) which encloses the inner mass (10), is coupled to the inner mass and is suitable for vibrating in the plane (P), and an outer frame (5) which is disposed above the support plate (5) in relation to an axis (Z) and encloses the inner mass (10) and the outer mass (11). The angular sensor (1) further comprises an inner frame (6) arranged between the outer mass (11) and the outer frame (5), fixed to the support plate by an electrically insulating element, the outer mass (11) being suspended at fixed anchoring points (15) of the inner frame (6) and being electrically connected to the inner frame (6) by first suspension elements (13).

Description

[0001] TITLE: Inertial angular sensor with micromachined microelectromechanical system

[0002] The present invention relates to a micromachined microelectromechanical system inertial angular sensor.

[0003] Such angular sensors are used to measure angular position or angular velocity. In the first case, these sensors function as gyroscopes, and in the second case, they function as gyrometers. These sensors are micromachined on silicon or quartz wafers, using techniques similar to integrated circuit manufacturing. This allows for low production costs and therefore varied application areas.

[0004] Inertial angular sensors generally comprise several vibrating moving masses, elastically connected to a support and elastically coupled together by means of elements functioning as springs. It is known to use silicon beams for these elements. The assembly formed by the masses and the elements functioning as springs forms a resonator which can advantageously be set into vibration on its natural modes by excitation systems, which can be electrical excitation systems. This excitation causes a vibration of the masses in the plane of the plate and perpendicular to a direction called the "sensitive axis" of the angular sensor, which is therefore perpendicular to the plane of the plate.

[0005] When the angular sensor has a certain rotation speed around the sensitive axis, the Coriolis effect generates a force that makes the masses vibrate in a direction perpendicular to the excitation direction, always in the plane of the plate. Measuring this vibration allows the rotation speed to be deduced.

[0006] As mentioned earlier, masses are excited by electrical excitation systems. For example, systems with two concentric masses, an internal mass and an external mass surrounding the internal mass, are known.

[0007] Electrical systems are, for example, electrodes, and in particular fixed electrodes associated with mobile electrodes, which are, for example, carried directly by the masses.

[0008] The masses are at the same electrical potential, because they are coupled together by coupling elements which are often made of electrically conductive material. This electrical potential can be non-zero, in the case where an electrical voltage is imposed on the moving electrodes, for example to facilitate the detection of vibrations.

[0009] The masses are generally elastically connected to a support via an insulating layer, for example silicon oxide. The outer mass is surrounded by an external frame which constitutes the exterior of the silicon chip. This frame is set to a fixed electrical potential to shield the sensitive part with lower and upper silicon layers (bulk and cap).

[0010] In this case, a potential difference is imposed between the external mass and the frame, which creates an electrostatic stiffness, which leads to a change in the apparent stiffness of a half-resonator formed by the external mass and the elements connecting it to the support. The change in the apparent stiffness of the half-resonator creates an unbalanced stiffness which changes the balancing of the resonator.

[0011] This phenomenon is also called "electrostatic trimming" and, while it can be used intentionally to compensate for defects in the masses, it creates an imbalance in the vibrating structure, making it particularly sensitive to external vibrations. Because of this change in the apparent stiffness of the half-resonator, the sensor no longer functions optimally for determining the rotation speed.

[0012] It is therefore necessary to optimize the operation of the sensors, including when an electrical potential difference exists between the masses and the frame surrounding the external mass.

[0013] The object of the present invention is to resolve this drawback by proposing an inertial angular sensor insensitive to the presence of an electrical potential difference between the masses and the external frame.

[0014] To this end, the invention relates to an inertial angular sensor with a micro-machined electromechanical microsystem comprising:

[0015] - a support plate; an internal mass suspended from fixed anchor points of the support plate and adapted to vibrate in a plane substantially parallel to the support plate;

[0016] - an external mass framing the internal mass, coupled to the internal mass and adapted to vibrate in the plane substantially parallel to the support plate;

[0017] - an external frame arranged above the support plate relative to an axis and framing the internal mass and the external mass; characterized in that the sensor further comprises an internal frame arranged between the external mass and the external frame and fixed to the support plate by an electrically insulating element, the external mass being suspended from fixed anchor points of the internal frame and being electrically connected to the internal frame by first suspension elements. Thanks to the invention, the external mass is connected to a fixed internal frame which is electrically insulated from the external frame, and therefore which has the same electrical potential as the internal and external masses. Thus, there is no longer any electrical voltage applied between the external mass and the frame surrounding it.The apparent stiffness, i.e. the sum of the mechanical and electrostatic stiffnesses of an external half-resonator formed by the external mass and the first suspension elements, is therefore not modified when an electrical voltage is applied to the masses. The sensor is therefore not unbalanced and no energy coupling with the support is created during the vibration of the masses. In other words, the phenomenon of "electrostatic trimming" is minimized, or even eliminated. The operation of the sensor is therefore identical regardless of the voltage applied, and remains optimal regardless of the voltage applied to the masses.

[0018] The sensor may include one or more of the following features, taken individually or in any technically possible combination:

[0019] - The internal mass is suspended from the fixed anchor points of the support plate by second suspension elements and the external mass is coupled to the internal mass by coupling elements.

[0020] - The first and second suspension elements and the coupling elements are silicon beams.

[0021] - The outer frame is connected to an electrical ground.

[0022] - Mechanical and / or electrostatic forces applied to the internal mass are substantially equal to mechanical and / or electrostatic forces applied to the external mass.

[0023] - This sensor further comprises at least one mobile electrode carried by one of the internal mass and the external mass, and at least one fixed electrode, the or each fixed electrode being fixed relative to the support plate (4) and opposite one of the at least one mobile electrode.

[0024] - When the internal mass and the external mass are at rest, their centers of gravity are the same, and in which an assembly consisting of the internal and external masses and the or each mobile electrode is symmetrical with respect to a first axis parallel to the support plate, passing through the center of gravity of the two masses, and with respect to a second axis parallel to the support plate, perpendicular to the first axis (X) and passing through the center of gravity of the two masses.

[0025] - Mechanical and / or electrostatic forces applied to the internal mass along the first axis and along the second axis are substantially equal to mechanical and / or electrostatic forces applied to the external mass respectively along the first axis and along the second axis. - This sensor further comprises:

[0026] - four mobile excitation electrodes, two mobile excitation electrodes among the four being carried by the internal mass and the other two mobile excitation electrodes being carried by the external mass;

[0027] - four mobile detection electrodes, two mobile detection electrodes among the four being carried by the internal mass and the other two mobile detection electrodes being carried by the external mass; and

[0028] - eight fixed electrodes, each fixed electrode being fixed relative to the support plate, and opposite one of the eight mobile electrodes

[0029] - The four excitation electrodes and / or the four detection electrodes are configured to be traversed by a non-zero direct voltage and / or an alternating voltage of modulated amplitude.

[0030] - This sensor further includes a silicon cover, covering the outer frame, the inner frame, the outer ground and the inner ground.

[0031] - This sensor further comprises an electrically insulating layer arranged on faces of the external frame in contact respectively with the cover and the support plate.

[0032] The invention will be better understood on reading the description which follows, given solely as a non-limiting example and made with reference to the drawings in which:

[0033] - [Fig 1] Figure 1 is a schematic top view of the inertial angular sensor with micro-machined micro-electromechanical system, according to the invention;

[0034] - [Fig 2] Figure 2 is a sectional view of the micromachined microelectromechanical system inertial angular sensor of Figure 1;

[0035] - [Fig 3] Figure 3 is a view similar to that of Figure 1 where additional elements are visible.

[0036] Figures 1 to 3 show an inertial angular sensor with a micro-machined electromechanical microsystem 1, hereinafter called angular sensor 1.

[0037] Since the angular sensor 1 is micro-machined, it forms a micro-electromechanical system, also called MEMS, from the English acronym “Micro-Electromechanical Systems”.

[0038] The angular sensor 1 is, for example, a gyrometer configured to measure an angular velocity. Alternatively or additionally, the angular sensor 1 is a gyroscope configured to measure an angular position.

[0039] The angular sensor 1 is intended in particular to be embedded in a vehicle, not shown, which is for example an aircraft, a drone or a ship, more particularly in a navigation, piloting or guidance unit of the vehicle. The angular sensor 1 is here a tuning fork type gyrometer, more specifically a tuning fork type gyrometer with two vibrating masses. According to an alternative not shown, the angular sensor can comprise more than two vibrating masses.

[0040] By "vibrating mass" we mean that the two masses are capable of oscillating, whether following excitation, or by the Coriolis effect during rotation of the angular sensor 1.

[0041] The angle sensor 1 comprises a support plate 4, an outer frame 5, an inner frame 6, a cover 7, an internal mass 10 and an external mass 11.

[0042] The support plate 4 extends parallel to a plane P defined by a first axis X and a second axis Y perpendicular to the first axis X, linked to the support plate 4. The support plate 4 is typically made of silicon, but may optionally be made of glass.

[0043] Above the support 4 relative to an axis Z, perpendicular to the first axis X and to the second axis Y, therefore perpendicular to the plane P, are arranged the external frame 5 and the internal frame 6.

[0044] An electrical potential of the outer frame 5 is kept fixed. Advantageously, the electrical potential of the outer frame 5 is kept zero, that is to say that the outer frame is electrically connected to an electrical ground. The outer 5 and inner 6 frames are typically made of electrically conductive material, for example doped silicon.

[0045] The cover 7 covers the external frame 5, the internal frame 6, the internal mass 10 and the external mass 11. Advantageously, the cover 7 is made of silicon, but it can optionally be made of glass.

[0046] The external frame 5 is separated from the support 4 and the cover 7 by an electrically insulating layer 8, for example made of silicon oxide. This electrically insulating layer 8 is arranged on one face of the external frame 5 in contact with the support plate 4 on the one hand, and on one face of the external frame 5 in contact with the cover 7 on the other hand. This makes it possible to provide electrical shielding, and thus to protect the angular sensor 1 from parasitic electromagnetic waves which could impair its operation, or even damage it.

[0047] The inner frame 6 is framed by the outer frame 5 and is fixed to the support plate 4 by an electrically insulating element 9. Alternatively, the inner frame 6 is fixed to both the support plate 4 and the cover 7. This electrically insulating element 9 may be identical to the electrically insulating layer 8, in particular the electrically insulating element 9 is of a material and a thickness, measured along the Z axis, identical to those of the electrically insulating layer 8. Advantageously, the electrically insulating layer 8 and the electrically insulating element 9 are both made of silicon oxide. Thanks to this electrically insulating element 9, the inner frame 6 can be at a different electrical potential than the support 4.

[0048] The internal 10 and external 11 masses are the vibrating masses of the angular sensor 1. The external mass 11 is arranged around the internal mass 10. The internal and external masses 10 and 11 are framed by the internal frame 6, therefore also framed by the external frame 5. The internal 10 and external 11 masses are for example made of silicon, and are movable relative to the support plate 4, and movable relative to each other.

[0049] The internal 10 and external 11 masses each have a center of gravity, which, when the angular sensor 1 is at rest, that is to say when the internal 10 and external 11 masses are not vibrating, are substantially coincident at point O. Point O is also the point of intersection of the X and Y axes.

[0050] By "significantly" here and in the rest of the text, we mean that a deviation of 10% from the announced value is permitted.

[0051] Advantageously, the internal 10 and external 11 masses have substantially the same mass.

[0052] The internal 10 and external 11 masses are adapted to vibrate in the plane P defined by the X and Y axes. Thus, the angular sensor 1 has the Z axis as its sensitive axis. In other words, the angular sensor 1 is adapted to measure a rotation or a rotation speed around the Z axis.

[0053] The angular sensor 1 further comprises first suspension elements 13 and second suspension elements 14.

[0054] The first suspension elements 13 connect the external mass 11 to the internal frame 6, more particularly to fixed anchor points 15 of the internal frame 6.

[0055] These first suspension elements 13 are advantageously 4 in number, as shown in Figures 1 and 3.

[0056] These first suspension elements 13 are similar to springs, and can be either springs or, preferably, beams, in particular made of silicon. In the case where the first suspension elements 13 are beams made of silicon, the external mass 11 and the internal frame 6 are connected to each other mechanically and electrically. They are in particular at the same electrical potential.

[0057] The second suspension elements 14 connect the internal mass 10 to the support plate 4, by fixed anchoring points 17 of the support plate 4. These second suspension elements 14 are advantageously four in number, are advantageously similar to the first suspension elements 13, and are in particular silicon beams. A layer of an electrically insulating material, not shown, is interposed along the Z axis between the fixed anchoring points 17 and the support plate 4. It is advantageously similar to the electrically insulating element 9.

[0058] Advantageously, the first and second suspension elements 13 and 14 have substantially equal stiffnesses.

[0059] The internal 10 and external 11 masses are also connected to each other by coupling elements 19. These coupling elements 19 are advantageously four in number, and are advantageously silicon beams, adapted to behave like springs. In the latter case, the internal 10 and external 11 masses are electrically and mechanically coupled to each other. They are therefore in particular at the same electrical potential. An electrostatic stiffness additional to a mechanical stiffness of the suspension elements 13, 14 can be generated if two surfaces movable relative to each other and connected to one of the suspension elements 13 or 14 are placed in an electrical potential field, for example created by two parts having a potential difference.

[0060] In the present case, the internal 10 and external 11 masses are coupled together, the external mass 11 is connected to the internal frame 6 which is electrically insulated from the support plate 4 and the external frame 5. Thus the internal 10, external 11 masses and the internal frame 6 are at the same electrical potential. The electrical voltage between a periphery of the external mass 11 and an interior of the internal frame 6 is therefore zero, and the first suspension elements 13 do not undergo the appearance of electrostatic stiffness.

[0061] The angular sensor 1, as shown in Figure 3, further comprises electrodes. In Figure 3, eight movable electrodes are shown, four electrodes on the internal mass 10 and four on the external mass 11.

[0062] In Figure 3 are shown mobile excitation electrodes 31 along the X axis, mobile excitation electrodes 32 along the Y axis, mobile detection electrodes 33 along the X axis and mobile detection electrodes 34 along the Y axis. The positioning of the mobile electrodes 31, 32, 33 and 34 can vary, and in particular, according to a variant not shown, one or the electrodes 31 can be at the location of one or more electrodes 34.

[0063] The mobile electrodes 31, 32, 33 and 34 are not shown in Figure 1, but they are advantageously present as in Figure 3. Eight fixed electrodes are opposite the mobile electrodes, but are not shown. The fixed and mobile electrodes are formed for example by interdigitated combs. A fixed electrode-mobile electrode pair forms an electromechanical transducer.

[0064] The electromechanical transducers of which the mobile electrodes 31, 32, 33, 34 are part are capable of converting an electrical voltage into movement and / or vice versa. In particular, the mobile excitation electrodes 31 and 32 are capable of generating the vibration of the internal 10 and external 11 masses, along the X and Y axes respectively, by applying electrostatic forces to the mass on which the electrode is arranged.

[0065] For this, an alternating voltage is advantageously applied between the electrodes 31 and 32 and the fixed electrodes to which they are respectively opposite. The frequency of this voltage is substantially equal to the mechanical resonance frequency of the internal 10 and external 11 masses, called the tuning fork frequency. This causes the internal 10 and external 11 masses to vibrate at this frequency.

[0066] The electromechanical transducers of which the mobile detection electrodes 33 and 34 are part are capable of detecting the vibration of the internal 10 and external 11 masses along the X and Y axes respectively. For this, a direct voltage, called a polarization voltage, is advantageously applied between each mobile detection electrode.

[0067] 33 and 34 and the fixed electrodes to which they are respectively opposite. Charge variations between the mobile and fixed electrodes, due to the movement of the internal 10 and external 1 1 masses are measured and make it possible to deduce the movement of the internal 10 and external 1 1 masses.

[0068] Of course, other electrodes than those shown in Figure 3 can be added to the internal 10 and external 11 grounds, such as for example electrodes for compensating a quadrature or frequency bias.

[0069] In practice, the electrodes and transducers used in micromachined microelectromechanical system inertial angular sensors are known per se and are not limiting. In particular, other positions of the electrodes and other excitation and detection principles can be used. For example, the movable electrodes 31 to

[0070] 34 can be traversed by an alternating voltage whose amplitude is modulated, in order to facilitate the detection of vibrations by the detection electrodes 33 and 34.

[0071] The angular sensor 1 shown in Figures 1 to 3 has symmetry along the X and Y axes when it is at rest. In particular, an assembly consisting of the internal 10, external 11 masses and the fixed and mobile electrodes 31 to 34 is symmetrical with respect to the X and Y axes, in the absence of vibration of the masses 10 and 11. However, according to a variant not shown, this assembly is not symmetrical with respect to the X and Y axes.

[0072] The operation of angle sensor 1 will now be explained.

[0073] The angular sensor is excited, that is to say that an excitation voltage is applied between the electrodes 31 and 32 and the fixed electrodes to which they are opposite. The excitation voltage generates electrostatic forces which set in motion the internal 10 and external 11 masses, which begin to vibrate. As mentioned previously, this vibration takes place in the plane P. We note: xï

[0074] - Xi = the translational displacement of the internal mass 10, of mass Mi yi. in the plane P; rxe-i

[0075] - Xe = j the translational displacement of the external mass 11, of mass Me in the P plane;

[0076] Kxi Kxyi

[0077] - Kl = the sum of the stiffnesses associated with a half-resonator

[0078] Kxyi Kyi internal formed by the second suspension elements 14 and the internal mass 10 on the resonance modes in translation in the plane P, that is to say the sum of the mechanical stiffnesses and the electrostatic stiffnesses applying to the mass Mi.;

[0079] Kxi is the sum of the stiffnesses on the X axis of the second suspension elements 14 connecting the internal mass 10 to the support 4, the same for Kyi but for the Y axis;

[0080] Kxyi represents a coupling stiffness between the X axis and the Y axis. The coupling stiffness is associated with a force in quadrature with the motion of the internal 10 and external 1 1 masses.

[0081] Kxe Kxye the sum of the stiffnesses associated with a half-resonator

[0082] External Kxye Kye formed by the first suspension elements 13 and the external mass 1 1 on the resonance modes in translation in the plane P, that is to say the sum of the mechanical stiffnesses and the electrostatic stiffnesses applying to the mass Me;

[0083] F the excitation forces. In practice, other forces may apply, including forces due to the Coriolis effect, when the angle sensor is rotating around the Z axis, or damping forces.

[0084] Applying the fundamental principle of dynamics to the system, we obtain:

[0085] Mi. Xi + Ki.Xi = Fi

[0086] Me. Xe + Ke. Xe = Fe

[0087] Then by combining the first terms Mi. Xi and Me. Xe:

[0088] . .. , , ,y .. .. . (Xi+Xe), Mi+Me,y.

[0089] Mi. Xi - Me. Xe = (Mi - Me) 1 2 J + — - — (Xi - Xe).

[0090] This equation presents an in-phase acceleration (Xl+Xe associated with the mass difference between the internal 10 and external 1 1 masses, and an acceleration in phase opposition, called tuning fork (Xi - Xe) which is associated with an average mass Mt+Me . Combining the second terms, we obtain:

[0091] This equation presents an in-phase motion > ^ Xl+ ^ Xe associated with the difference in stiffness of the external and internal half-resonators, and an anti-phase movement (Xi - Xe), which is associated with an average stiffness Kl+Xe .

[0092] Or, by combining the two previous equations:

[0093] In the case where the mass of the internal 10 and external 11 masses is not substantially the same or in the case where the mechanical stiffness of the first suspension elements 13 and the second suspension elements 14 is not substantially the same, or again, in the case where the electrostatic stiffnesses which are applied to the internal mass 10 and to the external mass 11 are not equal, the angular sensor 1 is unbalanced. In this case, when the angular sensor 1 is subjected to external vibrations whose frequency is substantially equal to the tuning fork frequency, in-phase and out-of-phase modes, associated with the described in-phase and out-of-phase movement and acceleration are excited at the same time, which degrades the operation of the angular sensor 1.

[0094] The sum of the stiffnesses Ke associated with the external half-resonator depends on the mechanical stiffness of the first suspension elements 13, but also on the electrical voltages applied between the external half-resonator and the fixed electrodes or the internal frame 6. Similarly, the sum of the stiffnesses Ki associated with the internal half-resonator depends on the mechanical stiffness of the second suspension elements 14, but also on the electrical voltages applied between the external half-resonator and the fixed electrodes.

[0095] It has been seen previously that advantageously, the first and second suspension elements 13 and 14 have substantially equal mechanical stiffnesses. On the other hand, according to the invention, the suspension elements 13 and 14, the internal 10, external 11 masses, the internal frame 6 and the coupling elements 19 are all substantially at the same electrical potential, as explained previously. In this case, the sum of the stiffnesses associated with the two half-resonators are therefore substantially equal, thus making the operation of the angular sensor 1 optimal. In other words, the terms Ki and Ke are substantially equal, therefore the term associated with the movement in phase disappears.

[0096] Thus, in the angular sensor 1 described above, mechanical and / or electrostatic forces linked to the mechanical and / or electrostatic stiffnesses applied to the internal mass 10 along the first and second axes X and Y are substantially equal to mechanical and / or electrostatic forces linked to the mechanical and / or electrostatic stiffnesses applied along the first and second axes X and Y respectively on the external mass 11.

[0097] In the case where the angular sensor 1 does not have symmetry along the first and second axes X and Y, the mechanical and / or electrostatic forces applied to the internal mass 10 are substantially equal to the mechanical and / or electrostatic forces applied to the external mass 11.

[0098] The internal frame 6 thus makes it possible not to create additional electrostatic stiffness which would have to be corrected by adding additional electrodes which generate electrostatic forces to counter this electrostatic stiffness.

[0099] When a rotation of the angular sensor 1 takes place around the Z axis, the Coriolis effect induces additional forces which generate an additional vibration of the internal 10 and external 11 masses in the X and Y directions. The amplitude of this vibration is proportional to the speed of rotation of the angular sensor 1 around the Z axis. The overall movement of the internal 10 and external 11 masses is detected by the transducers which include the detection electrodes 33 and 34. The processing of the signal thus received subsequently makes it possible to deduce the angular speed or the angular position of the angular sensor 1.

[0100] Thus, the internal frame 6 and the external mass 11 being substantially at the same electrical potential, there is no creation of electrostatic stiffness which is added to the mechanical stiffness of the first suspension elements 13. The sum of the stiffnesses associated with the internal mass 10 and the sum of the stiffnesses associated with the external mass 11 are therefore substantially equal. The angular sensor 1 presented above does not see its operation disturbed by an imbalance caused by a difference in stiffness. The angular sensor 1 thus has a reliable operation, independent of the electrical voltage applied to the electrodes 31 to 34.

Claims

CLAIMS 1. Inertial angular sensor with micro-machined micro-electromechanical system (1) comprising: - a support plate (4); an internal mass (10) suspended from fixed anchor points (17) of the support plate (4) and adapted to vibrate in a plane (P) substantially parallel to the support plate (4); - an external mass (11) framing the internal mass (10), coupled to the internal mass (10) and adapted to vibrate in the plane (P) substantially parallel to the support plate (4); - an external frame (5) arranged above the support plate (4) relative to an axis (Z), perpendicular to the plane (P) and framing the internal mass (10) and the external mass (11); characterized in that the angular sensor (1) further comprises an internal frame (6) arranged between the external mass (11) and the external frame (5) and fixed to the support plate (4) by an electrically insulating element (9), the external mass (11) being suspended from fixed anchoring points (15) of the internal frame (6) and being electrically connected to the internal frame (6) by first suspension elements (13).

2. Angular sensor (1) according to claim 1, wherein the internal mass (10) is suspended from the fixed anchor points (17) of the support plate (4) by second suspension elements (14) and the external mass (11) is coupled to the internal mass (10) by coupling elements (19).

3. Angular sensor (1) according to claim 2, wherein the first and second suspension elements (13, 14) and the coupling elements (19) are silicon beams.

4. Angular sensor (1) according to any one of the preceding claims, wherein the external frame (5) is connected to an electrical ground.

5. Angular sensor (1) according to any one of the preceding claims, further comprising at least one movable electrode (31, 32, 33, 34) carried by one of the internal mass (10) and the external mass (11), and at least one fixed electrode, the or each fixed electrode being fixed relative to the support plate (4) and opposite one of the at least one movable electrode (31, 32, 33, 34).

6. Angular sensor (1) according to any one of the preceding claims, wherein, when the internal mass (10) and the external mass (11) are at rest, their centers of gravity are merged, and in which an assembly constituted by the internal (10) and external (11) masses and the or each mobile electrode (31, 32, 33, 34) is symmetrical with respect to a first axis (X) parallel to the support plate (4), passing through the center of gravity of the two masses (10,1 1), and with respect to a second axis (Y) parallel to the support plate (4), perpendicular to the first axis (X) and passing through the center of gravity of the two masses (10,1 1).

7. Angular sensor (1) according to any one of the preceding claims, further comprising: - four mobile excitation electrodes (31, 32), two mobile excitation electrodes among the four being carried by the internal mass (10) and the other two mobile excitation electrodes being carried by the external mass (11); - four mobile detection electrodes (33, 34), two mobile detection electrodes among the four being carried by the internal mass (10) and the other two mobile detection electrodes being carried by the external mass (11); and - eight fixed electrodes, each fixed electrode being fixed relative to the support plate (4), and opposite one of the eight mobile electrodes (31, 32, 33, 34).

8. Angular sensor (1) according to claim 7, wherein the four excitation electrodes (31, 32) and / or the four detection electrodes (33, 34) are configured to be traversed by a non-zero direct voltage and / or an alternating voltage of modulated amplitude.

9. Angular sensor (1) according to any one of the preceding claims, further comprising a silicon cover (7), covering the external frame (5), the internal frame (6), the external mass (11) and the internal mass (10).

10. Angular sensor (1) according to claim 9, further comprising an electrically insulating layer (8) arranged on faces of the external frame (5) in contact respectively with the cover (7) and the support plate (4).

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