METHOD FOR MANUFACTURING A VIBRATING MECHANICAL INERTIAL SENSOR, A SENSOR OBTAINED BY SUCH A METHOD, AND AN INERTIAL CONTROL UNIT INCLUDING SUCH A SENSOR

Abstract

Method for manufacturing a vibrating mechanical inertial sensor, sensor obtained by such a method and inertial unit including such a sensor. The invention relates to a method for manufacturing a vibrating inertial sensor (1), comprising a step of associating a sensing element (3) with a base (2), a step of assembling a cover (100) to said base (2) to form a housing in which said sensing element (3) is housed, a step of evacuating said housing or filling the latter with a dry gas, and a step of magnetically shielding said housing which includes a first operation of depositing, by electroplating, a first layer of a first ferromagnetic material on at least a part of said housing. Vibrating inertial sensors. Figure for the abstract: Fig. 3.

Description

Title of the invention: METHOD FOR MANUFACTURING A VIBRATING MECHANICAL INERTIAL SENSOR, A SENSOR OBTAINED BY SUCH A METHOD, AND AN INERTIAL CONTROL UNIT INCLUDING SUCH A SENSOR

[0001] The present invention relates to the general technical field of inertial motion and orientation measurement sensors, such as gyroscopic sensors based on Coriolis forces to measure rotational speeds and / or rotational angles, such as Coriolis vibratory gyroscopes (CVG), or vibrating beam accelerometers (VBA).

[0002] The present invention relates more particularly to a method for manufacturing a vibrating mechanical inertial sensor, comprising a step of associating a test body with a base, said test body being designed to vibrate and / or deform and / or move, said method further comprising a step of assembling a cover to said base so that said cover covers the test body and forms with the base a housing in which said test body is housed.

[0003] The present invention further relates to a vibrating mechanical inertial sensor comprising at least a base, a test body attached to said base and designed to vibrate and / or deform and / or move, and a cover which covers said test body and forms with the base a housing which delimits an interior space within which said test body is housed.

[0004] Finally, the present invention also relates to an inertial unit including at least one plate and at least one vibrating mechanical inertial sensor, said plate being provided with at least one support to which said inertial sensor is fixed in order to be immobilized relative to said plate, said inertial unit further including a cover which covers said vibrating mechanical inertial sensor and is attached to the plate to form with the latter a box in which said vibrating mechanical inertial sensor is housed.

[0005] Vibrating mechanical inertial sensors, which employ sensing bodies designed to vibrate, move, or deform, are well known. They are used to ensure measurements of movement and / or orientation.

[0006] In particular, vibrating structure gyrometers, designed to measure angular velocities, are known. These vibrating gyrometers are based on the Coriolis effect, which causes a vibrating structure, exhibiting a second-order resonance mode consisting of a primary mode and a secondary mode, modally orthogonal, to undergo a The force exerted by a structure rotating in order to continue vibrating in a fixed or partially driven plane with a known fixed coefficient, within the mode space defined by the primary and secondary modes, is called the angular velocity. Applying an opposing force causes the vibration plane to rotate with the vibrating structure. The vibration is then stationary relative to a rotating frame of reference attached to the vibrating structure. Measuring this force allows the angular velocity to be determined. In the absence of an opposing force to the Coriolis forces, measuring the position of the frame of reference attached to the mode space, rotating relative to the vibration (which is fixed or partially driven with a known fixed coefficient), directly provides the angle of rotation of the vibrating structure.This is referred to as gyroscope mode operation (or "Whole Angle (WA) mechanism" in English), as opposed to the previous operating mode, called gyrometer mode (or "Force to Rebalance (FTR) mechanism" in English).

[0007] For example, Coriolis effect gyroscopic sensors are known which employ a base to which a silica resonator, metallized on its surface, is attached by means of a central foot. Electrodes are arranged on an electrode holder, opposite the metallized wall of the resonator, both to set it into vibration (via the application of electrostatic forces) and to detect this vibration (via capacitive detection).

[0008] For example, Coriolis effect gyroscopic sensors of the MEMS type (for "Micro-Electro-Mechanical System") are also known, which employ a base to which is attached a quartz or silicon resonator made insulating on its surface by the creation of a layer of silicon dioxide SiO2. Electrodes are arranged on the walls of the resonator and on adjacent surfaces for the silicon version, opposite each other, to both excite it in vibrations (electrostatic forces) and detect these (capacitive detection).

[0009] Gyroscopic sensors are also known which employ a base to which a metallic resonator is attached by means of a central rod. Piezoelectric elements are arranged on and against the wall of the metallic resonator to both excite it into vibrations and detect these vibrations by indirect or direct piezoelectric effect.

[0010] We finally know, for example, vibrating beam accelerometers (VBAs) using a preferentially differential mechanical architecture with a structure made using MEMS technology, either in quartz, or even better, in silicon, to benefit from the high precision and low production cost of DRIE (Deep reactive-ion etching) techniques. The operating principle of these accelerometers is based on measuring the variations in resonance frequency of vibrating beams to which a seismic mass is attached, with, in response to An external acceleration is applied, with one beam placed in tension and the other in compression. This differential approach compensates for temperature variations and other environmental disturbances, thus improving the accuracy and stability of the measurement. Frequency variations are converted into electrical signals that are easily digitized.

[0011] These various known vibrating mechanical resonator sensors generally give satisfactory results, but nevertheless present certain disadvantages.

[0012] In particular, the resonator of the aforementioned vibrating gyroscopic sensors is generally made from materials with specific mechanical characteristics essential for achieving performance, especially in terms of damping, which must be as low as possible. However, this damping is disturbed by the electromagnetic force resulting from the interaction between the external magnetic field and the current induced on the surface of the resonator when its primary and secondary resonance modes are maintained, whether the resonator is intrinsically metallic, or whether it is made from an insulating material (for example, silica), or made insulating on its surface (silicon), and coated with conductive electrodes.Metallic resonators made of ferromagnetic materials (such as iron, nickel, and cobalt) generally exhibit magnetization that generates a magnetic field which adds to the overall magnetic field traversed by the conductive surfaces of the moving resonator. This adds an additional factor to the electromagnetic force mentioned above, disrupting the damping of the resonator's vibration. This additional internal field also interferes with the operation of any magnetically sensitive component located in close proximity to the metallic resonator. In such cases, it is known to use alternative non-magnetic or diamagnetic materials (e.g., copper alloys) and paramagnetic materials (e.g., aluminum), but this does not eliminate the presence of the disruptive electromagnetic force.Therefore, these known vibrating gyroscopic sensors are likely to interact unintentionally with any external magnetic field, which significantly degrades their performance, particularly when dealing with low-frequency electromagnetic fields (below 1 MHz).

[0013] The drawbacks described above apply in the same way to vibrating accelerometers since the vibrating beams they contain are necessarily coated with electrodes, are set in motion at the resonant frequency of these beams, and when the sensor passes through an external magnetic field, a disturbing electromagnetic force is created, resulting from the interaction of this external magnetic field with the electrodes moving in this field. The apparent damping and stiffness characteristics of these beams are then disrupted, leading to a significant degradation of their performance.

[0014] Therefore, in order to preserve the measurement performance of these vibrating mechanical resonator sensors, it is known to surround them with a magnetic shielding cage. It is known to form such shielding using a metallic foil of significant thickness (for example, 0.5 mm) made of a material exhibiting high magnetic permeability, such as the nickel-iron alloy called Permalloy®, or the alloy called Mu-metal®.

[0015] However, while such known shields can protect known vibrating mechanical resonator inertial sensors from external magnetic influences, they nevertheless present serious drawbacks. These known shields are, firstly, poorly suited to small sensors, because the ratio of the shielded area to the total area decreases (including fold areas and free spaces within these areas). These shields also prove to be particularly expensive. Furthermore, they contribute very significantly to increasing both the size and mass of the shielded vibrating mechanical resonator inertial sensor, since they have a considerable thickness in order to achieve effective shielding.The performance of these known shielding materials can also be sensitive to temperature (magnetic misalignment), making them unsuitable for certain applications involving, for example, subjecting the vibrating mechanical resonator inertial sensor to high temperatures. Furthermore, the metallic foils typically used to form the magnetic shielding cage experience a degradation in their magnetic shielding properties when subjected to the forming and assembly operations (bending, deformation, welding, machining, etc.) required to create the cage. This limits the possibility of implementing high-performance magnetic shielding in certain configurations and / or necessitates additional cage processing steps (such as annealing), which complicate manufacturing and increase costs.

[0016] However, specifically with regard to Permalloy®, less conventional approaches than machining or sheet forming could be considered, such as the use of thin-film Permalloy® deposition by direct current (DC) magnetron sputtering, where ionized gas molecules bombard a target material, releasing vaporized metal atoms into a plasma that ultimately physically coat the substrate surface. This process is inexpensive and can be carried out in series, but the sputtering speed is extremely slow, on the order of nm / min, and the substrate is exposed to potentially high temperatures. Thus, this method has been primarily explored for the production of thin shields that do not These methods do not allow for achieving optimal performance levels for vibrating mechanical resonator inertial sensors. Other methods have also been considered for shielding Permalloy®, such as laser powder bed fusion (LPBF), also known as direct metal laser sintering or selective laser melting. While this process is suitable for shielding complex-shaped objects, it is particularly expensive and slow, again exposing the substrate to high temperatures.

[0017] The objects assigned to the invention therefore aim to remedy the various drawbacks set out above, and to propose a new method of manufacturing a vibrating mechanical inertial sensor making it possible to obtain, at a lower cost and in a simple and rapid manner, a vibrating mechanical inertial sensor which, while being particularly light and compact, has a design which allows it, regardless of its size, to maintain its level of measurement performance even when subjected to strong external magnetic fields, in particular at low frequencies.

[0018] Another object of the invention aims to propose a new manufacturing method for a vibrating mechanical inertial sensor whose magnetic sensitivity is particularly reduced over a relatively wide frequency spectrum.

[0019] Another object of the invention aims to propose a new manufacturing process for a vibrating mechanical inertial sensor which, while allowing optimization of the measurement performance of the sensor regardless of its environment, does not require the use of an annealing step.

[0020] Another object of the invention aims to propose a new manufacturing process for a vibrating mechanical inertial sensor which is particularly well suited to industrial implementation.

[0021] Another object of the invention aims to propose a new manufacturing method for a vibrating mechanical inertial sensor which presents an excellent compromise between its measurement accuracy on the one hand and its sensitivity to external magnetic fields on the other.

[0022] Another object of the invention aims to propose a new manufacturing process for a vibrating mechanical inertial sensor which makes it possible to obtain, in a simple and rapid way, a vibrating mechanical inertial sensor of particularly robust and durable construction.

[0023] Another object of the invention aims to provide a new vibrating mechanical inertial sensor which exhibits excellent measurement performance, even when subjected to strong external magnetic fields, particularly at low frequencies, while being particularly light, compact and inexpensive to manufacture.

[0024] Another object of the invention aims to propose a new inertial unit which has reduced magnetic sensitivity while being particularly light, robust and compact.

[0025] The objects assigned to the invention are achieved by means of a method for manufacturing a vibrating mechanical inertial sensor, comprising a step of associating a test body with a base, said test body being designed to vibrate and / or deform and / or move, said method further comprising a step of assembling a hood to said base so that said hood covers the test body and forms with the base a housing in which said test body is housed, a step of evacuating said housing or filling said housing with a dry gas, and a step of magnetically shielding said housing which includes a first operation of depositing, by electroplating, a first layer of a first ferromagnetic material on at least a part of said housing.

[0026] The objects assigned to the invention are also reached using a vibrating mechanical inertial sensor capable of being manufactured by the process according to the invention, said vibrating mechanical inertial sensor comprising at least a base, a test body attached to said base and designed to vibrate and / or deform and / or move, as well as a hood which covers said test body and forms with the base a housing which delimits an internal space within which said test body is housed, said internal space being placed under vacuum or being filled with a dry gas, said housing being at least partially coated by a first layer of a first ferromagnetic material deposited by electroplating, to form a magnetic shielding of said housing.

[0027] The objects assigned to the invention are finally reached using an inertial unit including at least one plate and at least one vibrating mechanical inertial sensor according to the invention, said plate being provided with at least one support to which said vibrating mechanical inertial sensor is fixed to be immobilized relative to said plate, said inertial unit further including a cover which covers said vibrating mechanical inertial sensor and is attached to the plate to form with the latter a box in which said vibrating mechanical inertial sensor is housed, said box being at least partially coated by a secondary layer of said first ferromagnetic material deposited by electroplating.

[0028] Other features and advantages of the invention will become apparent from the following detailed description, with reference to the accompanying drawings, given by way of purely illustrative and non-limiting examples, in which:

[0029] [Fig-1] illustrates, according to a schematic top perspective view, a first embodiment of a vibrating mechanical inertial sensor according to the invention, which is in this case a vibrating gyroscopic sensor of the CRG type (cylindrical resonator).

[0030] [Fig.2] illustrates, according to a schematic perspective view from below, the sensor vibrating gyroscopic of the [Fig.l].

[0031] [Fig.3] illustrates, according to a schematic cut-off perspective view, the sensor vibrating gyroscopic of figures 1 and 2.

[0032] [Fig.4] illustrates, according to a schematic top perspective view, a detail of realization of the vibrating gyroscopic sensor of figures 1 to 3, corresponding in this case to its base.

[0033] [Fig. 5] illustrates, according to a schematic perspective view from below, the base of the [Fig.4],

[0034] [Fig.6] illustrates, according to a schematic perspective view from below, a detail of realization of the vibrating gyroscopic sensor of figures 1 to 3, corresponding in this case to its cover.

[0035] [Fig.7] illustrates, according to a schematic cross-sectional view, the hood of the [Fig.6].

[0036] [Fig.8] illustrates, according to a schematic cross-sectional perspective view, a second embodiment of a vibrating mechanical inertial sensor according to the invention, which is in this case a vibrating gyroscopic sensor of type HRG (“Hemispherical Resonator Gyroscope”, or in French: vibrating gyroscope with hemispherical resonator).

[0037] [Fig.9] illustrates, according to a schematic perspective view, a third mode of realization of a vibrating mechanical inertial sensor according to the invention, which is in this case a vibrating beam accelerometer (VBA) of type MEMS (microelectromechanical system).

[0038] [Fig. 10] illustrates, according to a schematic perspective view from above, a detail of the embodiment of an inertial unit according to the invention, corresponding to a plate on which are intended to be mounted, according to the three directions of space respectively, three gyroscopic sensors according to the invention and / or three accelerometers according to the invention.

[0039] [Fig. 11] illustrates, according to a schematic perspective view from below, the plate of the [Fig. 10],

[0040] [Fig. 12] illustrates, according to a schematic perspective view from above, a detail of an embodiment of the inertial unit according to the invention, corresponding to a cover intended to cover the plate and the inertial sensors carried by the latter.

[0041] [Fig. 13] illustrates, according to a schematic perspective view from below, the lid of the [Fig. 12],

[0042] The invention relates to a method for manufacturing a vibrating mechanical inertial sensor 1, as well as a vibrating mechanical inertial sensor 1 capable of being manufactured by said method. Said vibrating mechanical inertial sensor 1 according to the invention is preferably obtained by the manufacturing method according to the invention, while the manufacturing method according to the invention is preferably a method for manufacturing the vibrating mechanical inertial sensor 1 according to the invention. However, it is perfectly conceivable, for example, that the vibrating mechanical inertial sensor 1 according to the invention could be obtained by a manufacturing method other than the method according to the invention, and conversely, that the manufacturing method according to the invention could make it possible to obtain a vibrating mechanical inertial sensor that differs from the vibrating mechanical inertial sensor 1 according to the invention.For the sake of brevity, the following description shall relate to both said process according to the invention and said vibrating mechanical inertial sensor 1 according to the invention, which means that the elements of the following description relating to said manufacturing process apply, mutatis mutandis, to said vibrating mechanical inertial sensor 1, and conversely that the elements of the following description relating to said vibrating mechanical inertial sensor 1 apply, mutatis mutandis, to said manufacturing process.

[0043] The manufacturing process according to the invention comprises a step of associating a test specimen 3 with a base 2. Said test specimen 3 is designed to vibrate and / or deform and / or move, for example globally or locally, so that its vibration and / or deformation and / or movement capabilities can be exploited to determine, for example, characteristics of a movement and / or orientation. Said base 2 is, for example, metallic (as in embodiments of Figures 1 to 8) or made of glass or silica (as in the embodiment of [Fig. 9]), and preferably provides, in particular, a support function. The base 2 thus constitutes, for example, a pedestal for the test specimen 3 to which it is attached.The base 2 is for example provided, as illustrated in figures 1 to 5, with fixing means 200, 210, 220, 230, which are in the form of a plurality of fixing lugs, each with an opening through it, to allow the inertial sensor 1 to be fixed by screwing it to a frame, for example to a plate 4 of an inertial measurement unit or any other equipment.

[0044] In accordance with the embodiments of Figures 1 to 8, said mechanical inertial sensor 1 is, for example, a vibrating gyroscopic sensor, preferably axisymmetric, with the Coriolis effect, that is to say, a vibration sensor based on Coriolis forces. Said vibrating gyroscopic sensor is thus a vibrating inertial sensor of the CVG type (Coriolis Vibratory Gyroscope). In this case, it advantageously forms a sensor designed (i) to measure a rotation angle (gyroscope operation, also called WA mode as mentioned above). (above), in which case it constitutes a vibrating gyroscope and / or (ii) to measure a rotational speed (gyroscope operation, also called FTR mode as mentioned above), in which case it constitutes a vibrating gyroscope, it being understood that said gyroscope can also determine an angle by integrating the angular velocity.

[0045] The invention is not limited to a specific type of vibrating gyroscopic sensor. The latter can, for example, form a cylindrical resonator gyroscopic sensor (or CRG for "Cylindrical Resonator Gyroscope") as in the embodiment of Figures 1 to 7, or a hemispherical resonator gyroscopic sensor (or HRG for "Hemispherical Resonator Gyroscope") as in the embodiment of [Fig. 8], or, for example, a MEMS gyroscopic sensor whose resonator takes the form of a ring generally made of silicon, or whose resonator consists of four oscillating masses forming two pairs vibrating at the same frequency but in opposite phase (in this case, we speak of a "double planar tuning fork").

[0046] The invention is not limited to a vibrating mechanical inertial sensor that forms a vibrating gyroscopic sensor. Thus, the vibrating mechanical inertial sensor 1 is, for example, a vibrating beam accelerometer, and in particular a VBA accelerometer of the MEMS (microelectromechanical system) type, silicon capacitive, or quartz, as in the embodiment of [Fig. 9].

[0047] In the embodiments of Figures 1 to 8, the test body 3 is formed by a resonator 3A, which is intended to vibrate in response to an excitation. Said resonator 3A has, for example, at least one second-order resonance mode consisting of a primary mode and a secondary mode that are modally orthogonal, with deformations that are, for example, elliptical (in the case of a resonator 3A having a shape of revolution, as illustrated in the figures), and in principle of the same frequencies.

[0048] The resonator 3A advantageously includes, as illustrated in Figures 3 and 8, a central foot 30 by which the resonator 3A is attached, directly ([Fig.3]) or indirectly ([Fig.8]) to said base 2, for example in a fixing zone ZI of the latter for the embodiment of Figures 3 and 4. Advantageously, said central foot 30 has a solid monolithic character, that is to say that it is formed by a single piece, in one piece, for example of metal or of silica or silicon. In the embodiments of Figures 3 and 8, said step of associating the test body 3 with the base 2 includes an operation of fixing the resonator 3A to the base 2 by fixing the central foot 30, for example by welding, brazing or gluing, either directly to the base 2, at the level of the fixing zone ZI (case of [Fig.3]), or to an intermediate plate 20 (embodiment of [Fig.8]) which is for example metallic or made of glass or ceramic.The said intermediate plate 20 is itself advantageously connected to the base 2, for example according to an arrangement on . pilings, via electrically conductive rods 60, 61 (and six others not shown but which can be deduced from the previous ones by symmetry). The vibrating gyroscopic sensor 1 according to the embodiments of Figures 1 to 8 thus advantageously includes mechanical linkage means which ensure direct or indirect attachment of the central foot 30 to the base 2, in order to establish preferably a fixed connection between the central foot 30 and the base 2, to immobilize the central foot 30 relative to the base 2. Preferably, the foot 30 has substantially a shape of revolution about a central axis ZZ' which corresponds, for example, to the sensitive axis about which the vibrating gyroscopic sensor of each [Fig. 3] and 8 is designed to measure an angular velocity and / or an angular displacement.In the embodiment of figures 1 to 7, the foot 30 extends, for example, along said central axis Z-Z', between an outer face 30A, which is preferably flat and is, for example, received in a housing provided in the base 2 and which forms the fixing zone Zl, and a free inner face 30B, which is also preferably flat.

[0049] In the embodiment shown in Figures 1 to 7, the resonator 3A comprises a vibrating cylinder 31, which is preferably attached to said foot 30, the latter advantageously supporting the vibrating cylinder 31. The vibrating cylinder 31 advantageously has a shape of revolution about said central axis ZZ. It rises, for example, between a lower edge connected to the foot 30, for example by arms 300, and a free upper edge 310 which defines an opening giving access to an internal volume V0. The vibrating cylinder 31 thus forms a lateral wall that surrounds the internal volume V0. Each arm 300 is, for example, formed by a rigid leg, which extends radially with respect to the central axis Z-Z', around and from the foot 30, to connect the latter to the vibrating cylinder 31.As illustrated in the figures, the vibrating cylinder 31 advantageously has a general shape of a straight circular cylinder, preferably extending between a lower circular edge connected to the foot 30 and a free upper circular edge. Advantageously, the central foot 30 and the vibrating cylinder 31 form a single, one-piece unit and are preferably made of the same material. In other words, the foot 30 and the side wall 31 form a single, one-piece unit, which is preferably entirely metallic. Advantageously, the vibrating cylinder 31 is made of martensitic steel, for example, X30Crl3 steel, or, for example, maraging steel.The use of one or the other of the aforementioned steels proves particularly advantageous because the steels in question have excellent mechanical damping properties, which allow a high quality factor (Q), guaranteeing an excellent level of measurement performance of the vibrating gyroscopic sensor 1.

[0050] In the embodiment of [Fig.8], the resonator 3A advantageously comprises a vibrating hemispherical shell 32 connected to the foot 30 at its center, said shell 32 being preferably made of quartz, or sapphire, or silica glass, preferably metallized on its surface, and advantageously forming a single piece with the base 30.

[0051] Advantageously, in embodiments of Figures 1 to 8, the method includes a step of associating at least one excitation device with said resonator 3A, to excite it into vibration, and more specifically to excite into vibration the vibrating cylinder 31 ([Fig. 3]) or the vibrating hemispherical shell 32 ([Fig. 8]), and in particular said primary and secondary modes of symmetrical vibration of the resonator 3A. Advantageously, the method also includes a step of associating at least one detection device with said resonator 3A, to detect vibrations of said resonator 3, and in particular the vibrations of the vibrating cylinder 31 or the vibrating hemispherical shell 32 excited by said at least one excitation device attached to said resonator 3A.Excitation and detection devices may be of similar or different natures, and may be based, for example, on an excitation principle of an electrostatic, electromagnetic and / or piezoelectric nature, or on a detection principle of an electrostatic, optical, electromagnetic and / or piezoelectric nature, without this list being exhaustive.

[0052] Preferably, as in the case of Figures 1 to 7, the vibrating gyroscopic sensor that advantageously forms the inertial sensor 1 comprises piezoelectric elements 14, 15, 16, 17, 18 (and three others not shown but which can be deduced from the preceding ones by symmetry) which form both the excitation and detection devices. Each of the piezoelectric elements is thus designed, on the one hand, to impart vibrations to the vibrating cylinder 31 ([Fig. 3]), in order to excite in particular the symmetrical primary and secondary resonance modes, and on the other hand, to detect the vibrations of said vibrating cylinder 31.The piezoelectric elements 14, 15, 16, 17, 18 (and three others not shown but which can be deduced from the preceding ones by symmetry) thus perform a dual function: vibrational excitation on the one hand and / or vibrational detection on the other, with a multitude of possible sub-variants using a variable number of piezoelectric elements for detection and excitation. In the embodiment illustrated in Figures 1 to 7, the aforementioned steps for associating the excitation and detection devices include, for example, an operation of fixing the piezoelectric elements 14, 15, 16, 17, 18 (and three others not shown but which can be deduced from the preceding ones by symmetry) respectively onto each of the arms 300 that provide the connection between the base 30 on the one hand and the vibrating cylinder 31 on the other.The piezoelectric elements 14, 15, 16, 17, 18 (and three others not shown but which can be deduced from the previous ones by symmetry) are for example fixed by gluing or by brazing on the upper surface of each of the said arms 300, which allows some of them to impart vibrations to the said. arms 300, so that these in turn transmit the vibrations in question to the vibrating cylinder 31 to which they are attached. Conversely, the vibrations of said cylinder 31 are transmitted to each of the arms 300 and thus detected by some of the piezoelectric elements 14, 15, 16, 17, 18 (and three others not shown but which can be deduced from the preceding ones by symmetry) fixed to said arms 300.

[0053] Preferably, in the case of [Fig.8], the vibrating gyroscopic sensor which advantageously forms the inertial sensor 1 comprises electrodes 14A, 15A, 16A, 17A, 18A (and three others not shown but which are deduced from the previous ones by symmetry), arranged on the surface of the intermediate plate 20 opposite the resonator 3A, which form both the said excitation devices and detection devices, in combination with the electrode deposited on the adjacent surface of the resonator 3A and which is connected by one or more conductive deposits, generally of the same nature as the adjacent electrode on the resonator, running along the walls of the resonator 3A, then along the foot 30, towards an electrical contact obtained by an elastic electrical connection with an electrically conductive rod 62, generally collinear with the axis of symmetry Z-Z'.and passing through the base 2 in the same way as rods 60, 61 (and six others not shown but which can be deduced from the previous ones by symmetry). Each of said electrodes is thus designed to, on the one hand, impart vibrations to the vibrating hemispherical shell 32 ([Fig. 8]), in order to excite in particular the symmetrical primary and secondary modes of resonance, and on the other hand, to detect the vibrations of said vibrating hemispherical shell 32. Electrodes 14A, 15A, 16A, 17A, 18A (and three others not shown but which can be deduced from the previous ones by symmetry) thus perform a dual function, of vibratory excitation on the one hand and / or of vibratory detection on the other. In the embodiment illustrated in [Fig.[8] The aforementioned steps for associating the excitation and detection devices include, for example, a deposition operation of electrodes 14A, 15A, 16A, 17A, 18A (and three others not shown but which can be deduced from the previous ones by symmetry) respectively on the intermediate platform 20 which provides the connection between the base 30 on the one hand and the vibrating hemispherical shell 32 on the other. The electrodes 14A, 15A, 16A, 17A, 18A (and three others not shown but which can be deduced from the previous ones by symmetry) are, for example, deposited using a physical vapor deposition (PVD) process, and impart vibrations to the vibrating hemispherical shell 32 under the effect of electrostatic forces as soon as a potential difference appears between these electrodes and the metallization opposite the resonator 3A.Conversely, the vibrations of said vibrating hemispherical shell 32 are detected by modulation of the capacitance between said electrodes and the metallization of the resonator, resulting from the modulation of the air gap between the vibrating hemispherical shell 32 and the intermediate plate 20 carrying these electrodes.

[0054] In the particular embodiment of [Fig.9], in which the inertial sensor 1 is a vibrating accelerometer (VBA) of the MEMS (microelectromechanical system) type, the test body 3 is formed by a test mass which is, for example, produced by micromachining a silicon wafer 3B. The micromachining in question is, for example, carried out by a DRIE (“Deep Reactive Ion Etching”) etching process which makes it possible to cut in the silicon wafer 3B an element forming a test mass supported by elastic arms 3000 (visible in [Fig.9]), these arms being themselves connected to the two ends of a thin beam of this same wafer, and anchored to the rest of the silicon wafer 3B.The proof mass on these elastic arms forms a mass-spring system, causing, in the presence of acceleration in the plane of the 3B silicon wafer, compression or stretching of the beam, which leads to a change in its frequency. A system with two beams operating in opposite phase, one being compressed while the other is simultaneously stretched, advantageously benefits from a differential effect that eliminates common-mode errors and sensitivities ([Fig. 9]). The measurement of the frequency difference between the two beams is proportional to the external acceleration applied to the proof mass.Each beam is advantageously provided on its surface with one or more electrically conductive electrodes, performing detection functions, preferably arranged on the antinodes of vibration of said beam, opposite one or more stationary electrodes 70 attached to a fixed portion of the silicon wafer. The detection electrodes measure the modulation of the air gap between the vibrating beam and the fixed electrode 70, via the capacitance modulation between these electrodes, to deduce, by external electronic means, the frequency of this modulation carrying the acceleration information. In this particular embodiment, the base 2 is preferably formed by a first support piece 2000 made of glass or silicon, which advantageously has a concave inner face designed to face the silicon wafer 3B.Preferably, the silicon wafer 3B, which carries the test mass forming the test body 3, is joined by thermocompression to said first support piece 2000 on opposite metallized surfaces, said first support piece 2000 advantageously forming the base 2.

[0055] Advantageously, the method includes a step of supplying electronic processing and control means, which include for example an electronic card (not illustrated), during which said electronic processing and control means (electronic card) are housed at least in part in the base 2, or against the latter, or even in the vicinity of the latter.

[0056] In the embodiments of Figures 1 to 8, said electronic processing and control means are arranged in a housing 27 provided on the surface external to the base 2, on the opposite side to that on which the resonator 3A is mounted (figures 3 and 8). The base 2 thus advantageously extends, in the embodiments of figures 1 to 8, between the electronic board on one side and the resonator 3A on the other.

[0057] In the embodiments of figures 1 to 7, in order to electrically connect to the aforementioned electronic board the piezoelectric elements 14, 15, 16, 17, 18 (and three others not shown but which can be deduced from the preceding ones by symmetry), which preferentially form the excitation and detection devices, the manufacturing process advantageously includes a step of associating electrically conductive (metallic) rods 40, 41, 42, 43, 44, 45, 46, 47 with the base 2, by inserting said rods 40, 41, 42, 43, 44, 45, 46, 47 into orifices through said base 2 so that said rods protrude on either side of the base 2, as illustrated in the figures.The rods 40, 41, 42, 43, 44, 45, 46, 47 are intended to be electrically connected to the excitation and / or detection devices, that is to say, for example (as in the embodiment shown in Figures 1 to 7) to the piezoelectric elements 14, 15, 16, 17, 18 (and three others not shown but which can be deduced from the preceding ones by symmetry), preferably by means of microcables (visible in [Fig. 3]). Each conductive rod 40, 41, 42, 43, 44, 45, 46, 47 advantageously has a substantially rigid character, while the microcables have a flexible character and are, for example, made of metal (preferably aluminum or gold).More specifically, each conductive rod 41, 42, 43, 44, 45, 46, 47 preferably extends between a lower end, which is intended to be electrically connected to the electronic board arranged in the housing 27, and an upper end at the level of which is attached, for example, the microcable which connects the conductive rod concerned to one of the piezoelectric elements 14, 15, 16, 17, 18 (and three others not shown but which can be deduced from the previous ones by symmetry) mentioned above.The conductive rods 40, 41, 42, 43, 44, 45, 46, 47 each advantageously pass through a support wall of the base 2, via passages formed through said support wall and fitted with insulating channels (for example, made of glass, preferably with a coefficient of thermal expansion adapted to that of the base 2) locally forming an electrically insulating sheath that surrounds each conductive rod to prevent it from coming into contact with said support wall, which is, for example, metallic. The conductive rods 40, 41, 42, 43, 44, 45, 46, 47 thus pass through the base 2 until they emerge in the housing 27, where they are electrically connected to the aforementioned electronic board (not shown in [Fig. 3]).

[0058] In the embodiments of [Fig. 8], in order to electrically connect electrodes 14A, 15A, 16A, 17A, 18A (and three others) to the aforementioned electronic board not shown but which are deduced from the previous ones by symmetry), which preferentially form the excitation and detection devices, the manufacturing process advantageously includes a step of associating to the base 2 electrically conductive (metallic) rods 60, 61 (for example, 8 in number arranged symmetrically around the axis Z-Z'), as well as, for example, a central rod 62 advantageously aligned with the axis of the foot 30 and allowing the transmission of a high electrical voltage to the metallization of the resonator 3A, by inserting said rods into orifices through said base 2 so that said rods protrude on either side of the base 2, as illustrated in [Fig.8]. The said rods are intended to be electrically connected to the said excitation and / or detection devices, that is to say for example, as in the embodiment of [Fig.8], to electrodes 14A, 15A, 16A, 17A, 18A (and three others not shown but which can be deduced from the previous ones by symmetry), preferably by means of welds (visible in [Fig. 8]). Each conductive rod 60, 61 advantageously has a substantially rigid character. More precisely, each conductive rod 60, 61 preferably extends between a lower end, which is intended to be electrically connected to the electronic board located in the housing 27, and an upper end at which the weld to the intermediate plate 20 is made.The conductive rods 60, 61 each advantageously pass through a support wall of the base 2, via passages formed in said support wall and equipped with insulating channels (for example, made of glass) which locally form an electrically insulating sheath surrounding each conductive rod to prevent it from coming into contact with said support wall, which is, for example, metallic. The conductive rods 60, 61 thus pass through the base 2 until they emerge in the housing 27, where they are electrically connected to the aforementioned electronic board (not shown in [Fig. 8]).

[0059] As illustrated in the figures, the method further includes a step of assembling a cover 100 to said base 2, so that said cover 100 covers said test body 3 and forms with the base 2 a housing within which said test body 3 is housed. The subassembly formed by this housing and the test body 3 housed within it is generally designated by the term "sensing element" and constitutes the electromechanical part of the inertial sensor 1, which also requires known electronic means (not illustrated) for its implementation and which have been mentioned above. Said cover 100 is, for example, made of a metallic material (Figures 1 to 8) or of glass or silicon ([Fig.9]), and is advantageously designed to cooperate with the base 2 to delimit with the latter a closed internal space which houses the sensitive mechanical structure (test body 3 described above) of the inertial sensor 1, in order to isolate and protect it from the external environment. The housing thus formed. The base 2 and the hood 100 are advantageously gas-tight, thanks to the implementation of appropriate sealing means arranged at the interface between the hood 100 and the base 2, which allows control of the atmosphere within the dwelling in question.

[0060] For example, as in the embodiments of Figures 1 to 8, the hood 100 has a bell shape, with a cylindrical side wall 100A having a free edge 100B, and a bottom wall 100C extending from and around the periphery of said cylindrical side wall 100A. The hood 100 thus has a cap-like or container-like shape, which, together with the base 2, defines an enclosure, preferably airtight, within which the test specimen 3 is housed. The hood 100 advantageously has an inner face 110 facing the inside of the housing and an opposing outer face 120. Advantageously, the step of assembling the hood 100 to the base 2 includes a positioning operation so that the free edge 100B comes into contact with said base 2, along a contact interface that is, for example, continuous, and preferably circular.The said step of assembling the hood 100 to the base 2 also includes, after said docking operation, a welding or brazing operation to produce a weld or brazing bead, preferably substantially continuous, connecting the base 2 to a terminal zone Z2 of the cylindrical side wall 100A located in the vicinity of the free edge 100B, on the external face 120 of the hood 100. For example, as illustrated in figures 1 to 8, said terminal zone Z2 forms a circumferential band which extends, from the free edge 100B, over a fraction (for example at most 10%, even more preferably at most 5%, and particularly preferably at most 3%) of the height of the cylindrical side wall 100A (measured parallel to the central axis Z-Z').The said welding or brazing operation is thus carried out so that the weld bead adheres both to said terminal zone Z2 and to a circumferential zone of the base 2 which is adjacent to said terminal zone Z2, to attach the cover 100 to the base 2, while preferably forming a hermetic seal at the interface between the cover 100 and the base 2.

[0061] In the embodiment of [Fig. 9] (inertial sensor 1 forming a vibrating accelerometer (VBA) MEMS), the cover 100 is advantageously formed by a second support piece 1000 made of glass or silicon, which advantageously has a concave inner face intended to face the silicon wafer 3B in which the test mass forming the test body 3 is formed. Preferably, the silicon wafer 3B, which carries the test mass forming the test body 3, is bonded by thermocompression using metallized surfaces, with or without the addition of brazing metal, to said second support piece 1000 which advantageously forms the cover 100. In the particular embodiment of [Fig. 9], The said cap 100 and base 2 are thus formed respectively by the first support piece 2000 and the second support piece 1000, both made of glass or silicon. The silicon wafer 3B, which carries the test mass forming the test body 3, is advantageously interposed between the said first and second support pieces 2000, 1000 and secured to them by thermocompression at its periphery, so as to form a closed (preferably hermetic) housing delimiting a cavity that accommodates the test mass carried by the silicon wafer 3B. According to the embodiment of [Fig. 9], each internal electrode, such as for example the electrically conductive electrode 70, is advantageously connected to at least one metallized electrical connection well 71 provided in the second support piece 1000, which in this case forms the cap 100. Preferably, within the framework of the embodiment of [Fig.[9] The method includes a step of encapsulating the housing formed in this case by the first and second support pieces 2000, 1000 in an outer casing 80, formed, for example, by a support 80A, to which the housing is attached, and a cover 80B attached to the support 80A to cover the housing, as illustrated in [Fig. 9]. The support 80A and cover 80B are, for example, made of metallic or ceramic material. In this embodiment, the housing 27 for the electronic circuit board may be located inside the outer casing 80, or optionally outside of it. In the embodiment of [Fig. 9], the electronics associated with the housing 27 are located, for example, inside the outer casing 80 and may advantageously be an ASIC (Application-Specific Integrated Circuit).The electronics will be able to communicate with complementary electronic elements placed outside the outer casing 80, via an interconnection by connector (not shown in [Fig.9]) passing through the outer casing 80. It should be noted that each well 71 can also similarly be made in the first support piece 2000, by means of the placement of an air gap between the first support piece 2000 and the support 80A, for example by means of added risers or by design, to avoid short-circuiting these wells with the support 80A.

[0062] Advantageously, the manufacturing process includes a step of evacuating said housing formed by assembling the cover 100 to the base 2, in order to place the interior of said housing under vacuum, and for example under coarse vacuum (pressure between atmospheric pressure and 100 Pa), or under primary vacuum (atmospheric pressure between 100 Pa and 0.1 Pa), or even under secondary vacuum (pressure between 0.1 Pa and 10⁶ Pa), or even under ultra-high vacuum (pressures between 10⁶ Pa and 10⁹ Pa), or possibly even under ultra-ultra-high vacuum (pressure less than 10⁹ Pa). Alternatively, said process includes a step of The enclosure is filled with a dry gas so that its interior is filled with said dry gas. This dry gas contains essentially no liquids or condensates. It is, for example, composed of nitrogen (N2) or an inert gas such as argon (Ar). In general, evacuating the enclosure containing the vibrating test body, or filling it with a dry gas, helps to minimize external disturbances, improves measurement stability, and extends the sensor's lifespan, particularly by reducing damping that affects, for example, the amplitude and stability of vibrations, especially when the test body includes a resonator (Figures 1 to 8) or a vibrating beam ([Fig. 9]). In the case of the variant in [Fig. 9], filling the internal volume of the enclosure with a dry gas may be preferable to a vacuum for damping the movements of the test mass.

[0063] For example, in the embodiment of Figures 1 to 7, the vacuuming step is carried out by means of an air suction tube introduced inside the housing, preferably through a suction port formed through said bottom wall 100C (in a vacuuming zone Z3), which is then (once the vacuuming operation is complete) sealed. A vacuuming method of a principle similar to that described above can be implemented, with the necessary adaptations, for the embodiment of [Fig. 8], for example using the principle of a metal pin passing through the base 2 and pinched under vacuum to obtain the desired airtightness. This is then referred to as "pinning." Regarding the embodiment of [Fig. 9], the assembly of the base 2 to the cover 100, both made of glass or silicon, will advantageously be carried out by vacuum thermocompression.

[0064] The manufacturing process according to the invention further comprises a step of magnetically shielding the housing formed by the base 2 and the cover 100. This shielding step includes a first electroplating operation (which can also be referred to as "electrodescoping") of a first layer of a first ferromagnetic material onto at least a portion of said housing, in order to reduce the sensitivity of the vibrating mechanical inertial sensor 1 to external magnetic fields, particularly low frequencies, which could affect measurement performance. The first electroplating operation of said first layer thus consists of an electrodeposition operation of the first layer, which is based on an electrolytic deposition technique for applying a metallic deposit (in this case, said first ferromagnetic material) to the surface of an object (in this case, at least a portion of the housing).The said electrodeposition (galvanoplating) operation is advantageously an electroplating operation ("electroplating" in English), which may possibly be a composite electroplating operation ("electro-clad" in English).

[0065] Electroplating generally consists of uniformly depositing a metal onto a conductive surface in a salt bath (sulfate-based electrolyte, or citrate electrolyte for greater efficiency, or chloride electrolyte for special applications, etc.) using an electric current. Electrodeposition (electroplating) is based more specifically on the following general principle:

[0066] - the target object to be coated (for example, in this case, the casing, or a part thereof) such as the hood 100 and / or the base 2) is placed in a bath containing an electrolyte solution;

[0067] - the target object forms a cathode connected to the negative terminal of a source of direct current, while an anode made of the material to be deposited is connected to the positive terminal and also immersed in said bath;

[0068] - the application of an electric current causes the migration of metal ions from from the anode towards the cathode where they are deposited and form a uniform metallic layer.

[0069] Electroplating makes it possible to obtain high deposition rates (for example, which can be nearly 100 times higher than those implemented by the cathodic sputtering technique mentioned above).

[0070] The implementation of a deposit by such an electrolytic technique makes it possible to form a magnetic shield as close as possible to the test body 3, in the form of a magnetic shielding layer which can faithfully follow the shape of the sensitive element, and more precisely of the housing, thus making it possible to obtain a particularly effective magnetic shield, without having to resort as in the prior art to a shielding cage which may increase the size and mass of the inertial sensor 1, with in addition a risk of degradation of the shielding properties of the cage during its manufacture by shaping and assembling thick metal sheets.The use of shielding formed by a layer of ferromagnetic material directly electrodeposited on at least part of the surface of the sensitive element, and more specifically of the housing, offers, in addition to magnetic shielding, particularly interesting technical effects and advantages, such as in particular: .

[0071] - Improvement of structural integrity and sealing: by electrodeposition Applying a layer of ferromagnetic material directly to the surface of the sensing element, and more specifically to the housing, particularly the wall of cover 100, improves the robustness and durability of the sensing element, and especially of cover 100. This is a synergistic effect: in addition to providing electromagnetic shielding, the electroplating of the ferromagnetic material layer mechanically reinforces the sensing element, and more specifically the housing, and particularly cover 100. Furthermore, the application of an electrodeposited magnetic shielding layer provides an additional sealing barrier, thus improving the integrity of the internal vacuum within the sensing element.

[0072] - Reduction of manufacturing complexity and costs: the use of Electroplating to deposit a layer of ferromagnetic material simplifies the manufacturing process by eliminating the need to manufacture and assemble separate shielding cages. This reduces production costs and speeds up the assembly process.

[0073] - Minimizing size: by incorporating electromagnetic protection By placing the shielding directly at the sensitive element, in this case the casing, the space required for external shielding is reduced, which is particularly advantageous for applications where space is limited.

[0074] - Improved shielding efficiency: electroplating allows for the deposition of a uniform and continuous coating, provided that the part to be coated does not have excessively sharp radii (less than 0.2 mm for example - this requirement can be taken into account when designing the sensitive element), thus potentially offering particularly homogeneous and effective coverage against electromagnetic interference.

[0075] - Reduction of thermal gradients: temperature differences and gradients Thermal variations in and around said sensitive element, and more specifically said housing in which the test body 3 is housed, can cause anisotropies of the physical parameters degrading the performance of the vibrating mechanical inertial sensor due to the non-uniform expansion or contraction of the test body 3. A shielding coating deposited by electroplating can, in addition to its function of protection against electromagnetic interference, help to homogenize the thermal response of the housing, improving the thermal stability of the vibrating mechanical inertial sensor.

[0076] In conclusion, the direct deposition of a ferromagnetic shielding material onto at least part of the housing (i.e., onto at least part of the cover 100 and the base 2) that encompasses the sensing element 3 allows, in particular, for a minimization of mass and size compared to conventional shielding solutions, an increase in robustness and durability, as well as a significantly improved and more stable measurement performance. Furthermore, using such an electroplating operation directly on the housing allows the manufacturing process to be particularly fast and inexpensive, as this initial electroplating operation can also be cleverly integrated into the overall manufacturing process of the sensing element, as will become apparent from the following.

[0077] Optionally, the method includes a preliminary surface treatment operation on the sensitive element, and more specifically on the housing, to be coated by electroplating, before the first electroplating operation of the first layer. This preliminary treatment operation includes, for example, the deposition on said surface of the housing to be coated, with an adhesion layer (for example, containing copper). In the case where the wall of the sensing element, and more specifically of the housing, coated by the first layer of the first ferromagnetic material, is metallic, said first layer can be deposited directly by electroplating onto the metallic wall of the housing (embodiments of Figures 1 to 8), without first depositing an adhesion layer. The use of such an adhesion layer may nevertheless prove preferable even in this case where the surface to be coated is metallic. In the case where the wall of the housing to be coated by electroplating is not metallic, and is for example made of glass or silicon as in the embodiment of [Fig.[9], the process preferably includes said preliminary operation of treating the surface of the sensitive element (and more specifically of the housing) to be coated by electroplating, before deposition by electroplating of the first layer, in the form, for example, of a deposit, on said surface of the housing to be coated, of said adhesion layer (for example a nickel-gold alloy containing copper) which adheres to the glass or silicon wall of the housing and on which the first layer of the first ferromagnetic material is then deposited by electroplating.

[0078] Advantageously, said first ferromagnetic material of the first layer is a material with a nanocrystalline structure. Said nanocrystalline structure has, for example, an average grain size of between 5 and 100 nm, preferably between 5 and 50 nm, and even more preferably between 10 and 30 nm. The use of such a nanocrystalline structure allows the first layer to have high magnetic permeability, resulting in excellent magnetic shielding, particularly against low-frequency external magnetic fields (e.g., below 1 MHz), while also providing broad-spectrum shielding. This minimizes the thickness of the first layer while maintaining optimal shielding performance. Furthermore, the use of a nanocrystalline material gives the first layer exceptionally high hardness and mechanical strength, making it particularly robust, reliable, and durable.

[0079] Advantageously, said first ferromagnetic material of the first layer has a low coercivity, preferably less than 80 A / m, even more preferably less than 70 A / m, for example between 20 and 70 A / m, preferably less than 10 A / m, and even more preferably less than 3 A / m. The corollary of this relatively low level of coercivity is a relatively high level of magnetic permeability. Thus, the first ferromagnetic material advantageously has a maximum relative magnetic permeability of at least 4,500, preferably at least 5,000 or even 8,000, for example between 5,000 and 50,000, even more preferably at least equal to 40,000, and possibly even exceeding 90,000, so that the first ferromagnetic material exhibits excellent low-frequency magnetic shielding characteristics.

[0080] Advantageously, said first ferromagnetic material of said first layer has a saturation magnetization of between 0.6 and 1.5 T, preferably between 0.9 and 1.1 T. Thanks to this level of saturation magnetization, the first layer ensures optimal electromagnetic shielding, it being understood that a high saturation magnetization is generally associated with a high magnetic permeability, which allows the material to conduct magnetic field lines more easily, thus improving its shielding efficiency, including in the presence of intense external magnetic fields.

[0081] Advantageously, said first ferromagnetic material exhibits a remanence of between 0.1 and 1 T, preferably between 0.3 and 0.8 T. Such a level of remanence again optimizes electromagnetic shielding, ensuring that the first layer does not itself become a significant source of magnetic disturbance once the external field is removed. Thus, thanks to the aforementioned preferential level of remanence, it is possible to benefit from particularly stable shielding properties, even after exposure to intense external magnetic fields.

[0082] The values ​​of the aforementioned parameters (magnetic permeability, saturation magnetization, coercivity, remanence...) are determined by standard measurements, carried out for example according to the ASTM A773 standard of 2021, from for example BH hysteresis loop plots.

[0083] Advantageously, said first ferromagnetic material includes nickel, and preferably is a nickel-iron alloy, with, for example, a mass percentage of between 45 and 80% for nickel and between 15 and 55% for iron. The use of a nickel-iron alloy makes it possible, in particular, to achieve excellent magnetic properties, preferably when a nanocrystalline structure is implemented, corresponding to the various parameter ranges mentioned above, which allows for very effective electromagnetic shielding, even when the first layer has a thickness much less than the thickness of the shielding sheets used in the prior art to form shielding cages. Preferably, said Ni-Fe alloy further includes molybdenum Mo (for example, up to 5% by mass) and manganese Mn (for example, less than 1% by mass).

[0084] For example, the first layer has a thickness of less than 350 pm, preferably less than 300 pm, and even more preferably between 50 and 250 pm, for example between 100 and 200 pm. Using such a thickness advantageously leads, in combination with the other aforementioned characteristics, to a particularly effective shielding effect, without adding too much weight to the vibrating mechanical inertial sensor 1.

[0085] Advantageously, the ferromagnetic material has a density of between 8 and 9 g / cm3, preferably between 8.4 and 8.8 g / cm3, which places it at the level of that of the alloys classically used in sheets to form shielding cages.

[0086] Advantageously, during said first deposition operation, said first layer of the first ferromagnetic material is electrodeposited on at least a portion of said hood 100 and / or on at least a portion of said base 2. In other words, the first deposition operation may consist of:

[0087] - to electrodeposit the first layer on at least part of the hood 100, during of a first sub-operation of electroplating the first layer onto the hood 100; and / or

[0088] - to electrodeposit the first layer on at least a part of the base 2, during of a second sub-operation of electroplating the first layer onto the base 2,

[0089] said first and second sub-operations of depositing the first layer can be carried out together or separately.

[0090] Advantageously, during said first deposition operation, and more specifically during said first sub-deposition operation, said first layer is electrodeposited onto the cover 100, preferably on only one of the inner 110 and outer 120 faces of the cover 100. Preferably, said first layer of the first ferromagnetic material is electrodeposited on at least a portion of the outer face 120 during said first deposition operation. Preferably, said first layer is deposited on the outer face 120 but not on the inner face 110. It turns out that depositing the first layer on only one of the faces of the cover 100 is sufficient to obtain the desired shielding effect.Furthermore, it is sufficient to place a masking cover on and against the edge 100B (embodiments of figures 1 to 8) to prevent the electrodeposition of a layer of ferromagnetic material on the inner face 110, which facilitates the implementation of the first deposition operation, compared to a coating only of the inner face and not of the outer face.

[0091] For example, the first deposition operation is carried out before the assembly step of the hood 100 to the base 2, so that the first deposition of the first layer is performed on the hood 100 and / or the base 2 while the hood 100 is separated from the base 2, which facilitates the first deposition operation and optimizes its quality. However, it is perfectly conceivable that the first operation of The deposit is made after the housing is formed by assembling the cover 100 and the base 2.

[0092] According to the embodiments of Figures 1 to 8, the first layer of the first ferromagnetic material is electrodeposited, during said first deposition operation, over the entire cylindrical side wall 100A of the cover 100, on the external face 120, except in said terminal zone Z2, by means, for example, of a temporary masking deposited on the terminal zone Z2 to prevent the deposition of the first layer of the ferromagnetic material on the terminal zone Z2. In the embodiments of Figures 1 to 8, the absence of the first layer at the level of the terminal zone Z2 makes it easier and more reliable to say the welding or brazing operation, thus allowing said weld or braze bead connecting the base 2 to the terminal zone Z2 to adhere directly to the material forming the cover 100, without interposing the first layer between the bead and said cover 100, which could impair the adhesion and reliability of said weld or braze bead.For a similar reason, the first layer is advantageously electrodeposited, during the first deposition operation, over the entire bottom wall 100C of the hood 100, on the external face 120, except in a vacuum zone Z3 where the suction orifice is intended to be made through the bottom wall 100C. This vacuum zone Z3 is intended to subsequently receive the weld or braze pad that seals the suction orifice. Thus, the weld or braze pad adheres directly to the material forming the hood 100, without the interposition of the first layer, which could impair the adhesion and robustness of the weld or braze pad.

[0093] Advantageously, during said first deposition operation, and more specifically during said second deposition sub-operation, said first layer is electrodeposited on at least part of said base 2. Preferably, the first layer is uniform, that is to say that the characteristics of the first layer are constant over the entire coated surface, whether it is the surface of the base 2 or that of the cover 100. This means that the composition, the physico-chemical properties (in particular magnetic), the structure and the thickness of the first layer are advantageously everywhere the same on the surface of the sensitive element, and more specifically of the housing.

[0094] Advantageously, said second sub-operation of depositing the first layer onto the base 2 is carried out before said step of assembling the hood 100 to said base 2. Thus, the first layer of said first ferromagnetic material can be electrodeposited onto the base 2 separately, before its assembly with the hood 100, which can facilitate the implementation of the manufacturing process. Optionally, said second deposition sub-operation is carried out before the step of associating the test body 3 at base 2, which can allow, particularly in the embodiments of figures 1 to 8, to simplify and make the manufacturing process more reliable.

[0095] For example, said first layer is electrodeposited, during said first deposition operation, over the entire base 2, except for at least a portion of the latter intended to be inside the housing and which includes said fixing area ZI (embodiments of Figures 1 to 8). For example, said portion which includes said fixing area ZI is covered with a temporary mask during said second electroplating sub-operation of the first layer, so as not to be covered by said first layer. The temporary mask may simply consist of an adhesive protective film, which prevents electroplating of the area concerned, and can then be removed after the second deposition sub-operation is completed. This makes it possible to promote a particularly reliable and durable attachment of the test body 3 to the base 2, for example by welding or brazing (Figures 1 to 8), or thermocompression ([Fig.9]), avoiding the interposition between the material of the base 2 and that of the central foot 30 or the silicon wafer 3B, of the first layer of the first ferromagnetic material, which could disrupt the assembly by brazing or welding of the foot 30 to the base 2 (figures 1 to 8), or by thermocompression of the silicon wafer 3B to the base 2 ([Fig.9]). .

[0096] Advantageously, the first layer of ferromagnetic material does not cover the electrically conductive rods 40, 41, 42, 43, 44, 45, 46, 47, 60, 61, 62 (as well as those not shown in the figures but which can be deduced from those mentioned above by symmetry) precisely so as not to alter the performance of subsequent welding operations of these rods to electronic elements or connectors. To this end, the said rods 40, 41, 42, 43, 44, 45, 46, 47, 60, 61, 62 (as well as those not shown in the figures but which are derived from those mentioned above by symmetry) are preferentially covered with a temporary mask during the said first deposition operation (and more precisely during the said second sub-deposition operation), so as not to be covered by the said first layer of ferromagnetic material.The temporary mask can, for example, take the form of a peelable adhesive element that prevents electroplating of the conductive rods during the first electroplating operation, both with regard to the portion of the rods that is intended to protrude inside the housing and that which is intended to protrude outside the housing.

[0097] In the particular embodiments of Figures 1 to 8, the first operation of depositing the first layer of the first ferromagnetic material thus includes, for example:

[0098] - the first sub-operation of deposition, by electroplating, of the first layer of the first ferromagnetic material on substantially the entire external face 120 of the hood 100, with the exception of the terminal area Z2 and the vacuum drawing area Z3;

[0099] - the second sub-operation of depositing, by electroplating, the first layer said first ferromagnetic material on the base 2, with the exception of said portion including the fixing zone Zl, while ensuring that the electrically conductive rods 40, 41, 42, 43, 44, 45, 46, 47, 60, 61, 62 (as well as those not shown in the figures but which are derived from those mentioned above by symmetry) are not covered by said first layer, if said rods have been previously associated with the base 2, before the second deposition sub-operation; preferably, the first layer has a uniform thickness, identical on the hood 100 and the base 2, for example between 50 and 250 pm, and uses the same first ferromagnetic material everywhere, which is preferably a nickel-iron alloy, for example with a nanocrystalline structure.

[0100] - the step of fixing the resonator 3 A to the base 2, for example by welding or brazing;

[0101] - the step of assembling the cover 100 to the base 2, for example by brazing or welding;

[0102] - the step of creating a vacuum by suction of the air contained in the housing, via an orifice made through hood 100, which is then immediately sealed, for example by a weld or brazing pin.

[0103] At the end of the process, a vibrating mechanical inertial sensor 1 is obtained with particularly effective electromagnetic shielding, especially with regard to external low-frequency electromagnetic fields.

[0104] In the embodiment of [Fig. 9], where the housing is contained within a closed outer casing 80, beyond the preceding electroplating steps of the base 2 and the cover 100, the magnetic shielding step of the housing advantageously includes a primary electroplating operation of depositing a primary layer of said first ferromagnetic material on at least a portion of said outer casing 80, and for example on the entire external surface of the outer casing 80, formed by the assembly of the support 80A and the cover 80B. This makes it possible to obtain optimal magnetic shielding, by combination of the first layer of ferromagnetic material deposited on the housing formed by the assembly of the base 2 and the cover 100, and the primary layer of ferromagnetic material deposited on the outer casing 80.The said primary operation of depositing by electroplating the primary layer on the outer envelope 80 may be preceded by an operation of depositing a bonding layer on the surface to be coated. of the outer envelope 80, especially if the latter is made of a ceramic material as previously envisaged.

[0105] In order to further improve shielding performance, while preserving the compactness and lightness of the inertial sensor 1, said magnetic shielding step advantageously includes:

[0106] - a second deposition operation, preferably by electroplating, of a second layer of a second diamagnetic or paramagnetic material, for example copper-based, which also allows for better heat conduction and optimizes the reduction of temperature gradients at the sensitive element, on said first layer of the first ferromagnetic material, and

[0107] - a third electroplating operation of depositing a third layer of a third ferromagnetic material, on said second layer of the second diamagnetic or paramagnetic material.

[0108] In this preferred embodiment, the process according to the invention leads to the realization of a multilayer shield, formed by the stacking of at least the first layer, the second layer and the third layer.

[0109] Such an arrangement proves particularly advantageous because it results in more effective magnetic shielding than that obtained with a layer of the same thickness made solely of the first ferromagnetic material. It has been observed that when a homogeneous layer of ferromagnetic material of a given thickness is used to magnetically shield the sensing element of the vibrating mechanical inertial sensor 1, only a portion of the layer's thickness actually deflects the magnetic field lines effectively. It is therefore more advantageous to use a plurality of thinner layers of ferromagnetic material separated from each other by a layer of diamagnetic or paramagnetic material. Preferably, the second layer of the second diamagnetic or paramagnetic material has a thickness between 50 and 400 pm, more preferably between 50 and 300 pm, for example, approximately 100 pm.

[0110] For example, said second and third deposition operations are carried out before said step of assembling said hood 100 to said base 2 (as for example in the embodiments of figures 1 to 8).

[0111] The third ferromagnetic material is advantageously identical to the first ferromagnetic material, so that the third deposition operation in this case consists of depositing a third layer of the first ferromagnetic material onto said second layer. Advantageously, the third layer has a thickness of less than 350 pm, preferably less than 300 pm, and even more preferably between 50 and 250 pm, for example between 100 and 200 pm. In a particularly advantageous embodiment, The first layer is made of a ferromagnetic material consisting of a nickel-iron alloy with, for example, a nickel mass percentage between 45 and 79% and an iron mass percentage between 15 and 55%, and also includes molybdenum (Mo) (at most 5% by mass) and manganese (Mn) (less than 1% by mass). The thickness of the first layer is, for example, approximately 150 µm. The third layer is essentially identical to the first layer, that is, it is made of the same ferromagnetic material mentioned above and has a similar thickness of 150 µm. Finally, the second layer is preferably made of a diamagnetic material, for example, copper or a copper alloy, which also allows for better heat conduction and optimizes the reduction of temperature gradients at the sensing element.This results in a three-layer shield with a total thickness of approximately 0.5 mm, whose shielding performance is superior to that of a single layer made entirely of the same ferromagnetic material as the first and third layers, and having the same total thickness of 0.5 mm. In this particular embodiment, it is therefore possible to optimize the shielding effectiveness for a given maximum thickness.

[0112] Advantageously, the second and third deposition operations are repeated alternately to form a stack of alternating layers of ferromagnetic and diamagnetic or paramagnetic material, thus forming a stack of electrodeposited layers of ferromagnetic material separated from each other by electrodeposited layers of diamagnetic or paramagnetic material. The invention thus advantageously implements a uniform surface coating of the housing, which can be either a single layer (monolayer) of a ferromagnetic material, deposited by electroplating, or a stack of alternating layers of ferromagnetic and diamagnetic (or paramagnetic) material, all deposited by electroplating, in order to form a multilayer shield.

[0113] As previously mentioned, the invention also relates as such to a vibrating mechanical inertial sensor 1 capable of being manufactured by a process according to the preceding description, said vibrating mechanical inertial sensor 1 comprising at least a base 2, a test body 3 attached to the base 2 and designed to vibrate and / or deform and / or move, for example globally or locally, as well as a hood 100 which covers the test body 3 and forms with the base 2 a housing which delimits an internal space within which the test body 3 is housed, said internal space being placed under vacuum or being filled with a dry gas, said housing being at least partly coated by a first layer of a first ferromagnetic material deposited by electroplating, to form a magnetic shielding of said housing.

[0114] As previously stated, the vibrating mechanical inertial sensor 1 advantageously forms a vibrating gyroscopic sensor ([Fig.1] to 8), said test body 3 being in this case formed by a resonator 3A, which includes for example a vibrating cylinder 31 ([Fig.1] to 7) or a vibrating hemispherical shell 32 ([Fig.8]).

[0115] In another embodiment, the vibrating mechanical inertial sensor 1 forms a vibrating beam accelerometer (VBA) of the microelectronic system (MEMS) type, in which case the test body 3 is advantageously formed by a test mass which is, for example, produced by micromachining a silicon or quartz wafer 3B. In this latter embodiment, the vibrating mechanical inertial sensor 1 preferably comprises, as previously described in relation to the method, an outer casing 80 within which the housing is encapsulated, as illustrated in [Fig. 9].The outer casing 80 is at least partially coated in this case by a primary layer of the first ferromagnetic material deposited by electroplating, to optimize magnetic shielding, possibly with an interposed adhesion layer between the outer casing 80 and the primary layer to promote the adhesion of the latter to the outer casing 80, particularly if the latter is made of a ceramic material, for example. Thus, in the particular embodiment of [Fig. 9], the vibrating mechanical inertial sensor 1 preferably comprises a housing at least partially coated by a first layer of a first ferromagnetic material deposited by electroplating, and an outer casing 80 within which the housing is encapsulated, which outer casing 80 is also advantageously coated by the first ferromagnetic material deposited by electroplating.

[0116] The invention also relates as such to an inertial unit which includes at least one plate 4 and at least one vibrating mechanical inertial sensor 1 according to the invention. The plate 4 is provided with at least one support 50 to which the vibrating mechanical inertial sensor 1 is fixed in order to be immobilized relative to the plate 4. For example, in the embodiment illustrated in the figures, the support 50 is in the form of a monolithic part extending from the plate 4 or of a ring attached to the plate 4 and into which the cover 100 of a vibrating mechanical inertial sensor 1 is threaded. The ring forming the support 50 may, for example, further include fixing holes 500, 501, 502, 503 corresponding respectively to the holes provided by the fixing lugs 200, 210, 220, 230 (embodiment of figures 1 to 7), to allow, for example, fixing of the base 2 to the support 50 by screwing.Advantageously, the plate is provided, in addition to the support 50, with two other supports 51, 52 which are similar to it and to which are attached respectively two other vibrating mechanical inertial sensors according to the invention. Said supports 50, 51, 52 are arranged. perpendicular to each other along the three spatial directions respectively, such that the three vibrating mechanical inertial sensors according to the invention, integrated into the inertial unit, are arranged so that their respective central axis ZZ' extends along a spatial direction perpendicular to the other two spatial directions. Preferably, the inertial unit according to the invention incorporates, in addition to three vibrating gyroscopic sensors according to the invention, for example, in embodiments of Figures 1 to 7, three vibrating beam accelerometers (VBA) according to the invention, for example, in embodiment [Fig. 9], said accelerometers being arranged respectively along the three spatial directions.

[0117] The inertial measurement unit further includes a cover 5 which covers said at least one vibrating mechanical inertial sensor 1 (and for a navigation system, at least six vibrating mechanical inertial sensors arranged perpendicularly to each other and providing accelerometric and gyroscopic measurement functions according to an orthogonal trihedron) and is attached to the plate 4, for example by screwing, to form with the latter a housing in which said at least one vibrating mechanical inertial sensor 1 (in this case, the six vibrating mechanical inertial sensors) is housed. Said housing is at least partially coated by a secondary layer of said first ferromagnetic material deposited by electroplating. Preferably, the secondary layer is deposited by electroplating in the same manner and according to a process identical to that used to deposit the first and / or said third layer.This secondary layer is preferably substantially similar to said first and / or third layer, both in its thickness and in its microstructure and physico-chemical characteristics, and in particular its magnetic characteristics. Thus, the invention makes it possible to combine double shielding, namely that directly deposited on each vibrating mechanical inertial sensor 1 of the inertial measurement unit, and that directly deposited on the inertial measurement unit housing, which makes it possible to obtain excellent shielding performance while maintaining controlled size and mass, as well as an easy, fast and inexpensive manufacturing and assembly process.

[0118] It is also entirely feasible to deposit a tertiary layer of a diamagnetic or paramagnetic material onto the secondary layer, for example by electroplating, and then to deposit on this tertiary layer, again preferably by electroplating, a quaternary layer of a fourth ferromagnetic material, which is, for example, identical to the first ferromagnetic material. This forms a stack of layers that offer the same advantages as those already described above in relation to the manufacturing process.

[0119] Advantageously, the plate 4 has an inner face 4A which carries the support 50 and is located opposite the inside of the enclosure, as well as an opposing outer face 4B, while the cover 5 has an inner face 5A located opposite the inside of the enclosure, and therefore opposite the inner face 4A of the plate 4, and an opposing outer face 5B. Advantageously, said secondary layer is electrodeposited on the inner face of the plate 4, and preferably on each support 50, 51, 52, in order to form a shield located as close as possible to each inertial sensor 1 mounted inside the enclosure. This secondary layer is not, however, deposited on the outer face 4B of the plate 4, in order to avoid exposure to a risk of mechanical, chemical, or thermal degradation from the external environment.Similarly, said secondary layer is advantageously deposited on the inner face 5A of the cover 5, but not on its outer face 5B, which again allows the shielding layer to be placed as close as possible to each vibrating mechanical inertial sensor 1 contained in the box, preventing the secondary layer from being directly exposed to the external environment and the resulting risks of degradation.

Claims

Demands

1. A method for manufacturing a vibrating mechanical inertial sensor (1), comprising a step of associating a test body (3) with a base (2), said test body (3) being designed to vibrate and / or deform and / or move, said method further comprising a step of assembling a hood (100) to said base (2) so that said hood (100) covers the test body (3) and forms with the base (2) a housing in which said test body (3) is housed, a step of evacuating said housing or filling said housing with a dry gas, and a step of magnetically shielding said housing which includes a first operation of depositing, by electroplating, a first layer of a first ferromagnetic material on at least a part of said housing.

2. A method according to the preceding claim characterized in that said first ferromagnetic material is a material with a nanocrystalline structure.

3. A method according to the preceding claim, characterized in that said nanocrystalline structure has an average grain size of between 5 and 100 nm, preferably between 5 and 50 nm, even more preferably between 10 and 30 nm.

4. A method according to any one of the preceding claims characterized in that said first ferromagnetic material includes nickel.

5. A process according to the preceding claim characterized in that said first ferromagnetic material is a nickel-iron alloy, with, for example, a mass percentage of between 45 and 80% for nickel and between 15 and 55% for iron.

6. A method according to any one of the preceding claims characterized in that said first layer has a thickness of less than 350 pm, preferably less than 300 pm, even more preferably between 50 and 250 pm, for example between 100 and 200 pm.

7. A method according to any one of the preceding claims characterized in that said first ferromagnetic material has a density of between 8 and 9 g / cm3, preferably between 8.4 and 8.8 g / cm3.

8. A method according to any one of the preceding claims characterized in that said first ferromagnetic material has a maximum relative magnetic permeability of at least 4,500, preferably at least 5,000, even more preferably at least 8,000, for example at least 40,000.

9. A method according to any one of the preceding claims characterized in that said first ferromagnetic material has a saturation magnetization of between 0.6 and 1.5 T, preferably between 0.9 and 1.1 T.

10. A method according to any one of the preceding claims characterized in that said first ferromagnetic material has a coercivity of less than 80 A / m, preferably less than 70 A / m, even more preferably less than 10 A / m, advantageously less than 3 A / m.

11. A method according to any one of the preceding claims characterized in that said first ferromagnetic material has a remanence of between 0.1 and 1 T, preferably between 0.3 and 0.8 T.

12. A method according to any one of the preceding claims characterized in that during said first deposition operation, said first layer of the first ferromagnetic material is electrodeposited on at least a part of said hood (100) and / or on at least a part of said base (2).

13. A method according to any one of the preceding claims characterized in that said first deposition operation is carried out before said step of assembling said hood (100) to said base (2).

14. A method according to any one of the preceding claims characterized in that said hood (100) has an inner face (110) intended to be located opposite the inside of the housing and an opposite outer face (120), said first layer of the first ferromagnetic material being electrodeposited on at least a portion of said outer face (120) during said first deposition operation.

15. The method according to the preceding claim characterized in that during said first deposition operation, said first layer is electrodeposited on said external face (120) but not on said internal face (110).

16. The method according to the preceding claim, characterized in that said hood (100) has a bell shape with a cylindrical side wall (100A) having a free edge (100B), said step of assembling the hood (100) to the base (2) including a docking operation so that said free edge (100B) comes into contact with said base (2) and a welding or brazing operation to produce a weld or brazing bead connecting the base (2) to a terminal area (Z2) of the cylindrical side wall (100A) located in the vicinity of the free edge (100B) on the external face (120), said first layer being electrodeposited, during said first deposition operation, over the entire cylindrical side wall (100A), on the external face (120), except in said terminal area (Z2).

17. A method according to any one of the preceding claims characterized in that said vibrating mechanical inertial sensor (1) is a vibrating gyroscopic sensor, said test body being formed by a resonator (3A), said resonator (3A) comprising for example a vibrating cylinder (31) or a vibrating hemispherical shell (32).

18. Method according to the preceding claim characterized in that it comprises a step of associating at least one excitation device with said resonator (3A) to excite it into vibration, as well as a step of associating at least one detection device with said resonator (3A) to detect vibrations of said resonator (3A).

19. A method according to any one of claims 1 to 16 characterized in that said vibrating mechanical inertial sensor (1) is a vibrating beam accelerometer (VBA), for example of the microelectromechanical system (MEMS) type, said test body (3) being formed by a test mass which is for example produced by micromachining a silicon wafer (3B).

20. Method according to the preceding claim characterized in that said base (2) and hood (100) are formed respectively by a first and a second support piece (2000, 1000) made of glass or silicon.

21. A method according to any one of claims 19 and 20 characterized in that it comprises a step of encapsulating the housing in an outer casing (80), said step of magnetically shielding said housing including a primary deposition operation, by electroplating, of a primary layer of said first ferromagnetic material on at least part of said outer envelope (80).

22. A method according to any one of the preceding claims characterized in that said magnetic shielding step includes: - a second deposition operation, preferably by electroplating, of a second layer of a second diamagnetic or paramagnetic material, for example copper-based, on said first layer of the first ferromagnetic material, and - a third deposition operation, by electroplating, of a third layer of a third ferromagnetic material, on said second layer of the second diamagnetic or paramagnetic material.

23. Method according to the preceding claim characterized in that said second and third deposition operations are carried out before said step of assembling said hood (100) to said base (2).

24. A method according to any one of claims 22 and 23, characterized in that said second layer of the second diamagnetic or paramagnetic material has a thickness of between 50 and 400 pm, preferably between 50 and 300 pm.

25. A method according to any one of claims 22 to 24 characterized in that said third ferromagnetic material is identical to said first ferromagnetic material.

26. A method according to any one of claims 22 to 25 characterized in that said third layer has a thickness of less than 350 pm, preferably less than 300 pm, even more preferably between 50 and 250 pm, for example between 100 and 200 pm.

27. ​​A method according to any one of claims 22 to 26 characterized in that said second and third deposition operations are repeated alternately to form a stack of alternating layers of ferromagnetic material and diamagnetic or paramagnetic material.

28. A vibrating mechanical inertial sensor (1) capable of being manufactured by a process according to any one of the preceding claims, said vibrating mechanical inertial sensor (1) comprising at least one base (2), a test body (3) attached to said base (2) and designed to vibrate and / or deform and / or move, thus that a hood (100) which covers said test body (3) and forms with the base (2) a housing which delimits an interior space within which said test body (3) is housed, said interior space being placed under vacuum or being filled with a dry gas, said housing being at least partly coated by a first layer of a first ferromagnetic material deposited by electroplating, to form a magnetic shielding of said housing.

29. Vibrating mechanical inertial sensor (1) according to the preceding claim, characterized in that it forms a vibrating gyroscopic sensor, said test body (3) being formed by a resonator (3A), said resonator (3A) comprising for example a vibrating cylinder (31) or a vibrating hemispherical shell (32).

30. Vibrating mechanical inertial sensor (1) according to claim 28 characterized in that it forms a vibrating accelerometer, for example of the microelectromechanical system (MEMS) type, said test body (3) being formed by a test mass which is for example produced by micromachining a silicon wafer (3B).

31. Vibrating mechanical inertial sensor (1) according to the preceding claim characterized in that it comprises an outer casing (80) within which said casing is encapsulated, said outer casing (80) being at least partly coated by a primary layer of said first ferromagnetic material deposited by electroplating.

32. Inertial unit comprising at least one plate (4) and at least one vibrating mechanical inertial sensor (1) according to any one of claims 28 to 31, said plate (4) being provided with at least one support (50) to which said vibrating mechanical inertial sensor (1) is fixed for immobilization relative to said plate (4), said inertial unit further comprising a cover (5) which covers said vibrating mechanical inertial sensor (1) and is attached to the plate (4) to form with the latter a housing in which said vibrating mechanical inertial sensor (1) is housed, said housing being at least partially coated by a secondary layer of said first ferromagnetic material deposited by electroplating.

33. Inertial measurement unit according to the preceding claim, characterized in that said plate (4) has an inner face (4A) which carries the support (50) and is located opposite the interior of the housing and a opposite outer face (4B), while the cover (5) has an inner face (5A) facing the inside of the box and an opposite outer face (5B), said secondary layer being deposited on said inner faces (4A, 5A) of the plate (4) and the cover (5), but not on their outer faces (4B, 5B).

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