MICRO-ELECTRO-MECHANICAL DEVICE

Abstract

A micro-electromechanical device includes a frame; a proof mass connected to the frame through a first mechanical link which allows pivoting of the proof mass to relative to the frame about a first axis of rotation parallel to a mean plane of the frame; and a lever for detecting pivoting of the mass, connected to the proof mass through a second mechanical link allowing rotation of the lever relative to the proof mass about a second axis. The second link includes two walls connecting perpendicularly to each other, one to the lever and the other to the proof mass, one of the walls being parallel to the second axis of rotation.

Claims

1. A microelectromechanical device comprising: a frame, a proof mass, connected to the frame through a first mechanical link which allows pivoting of the proof mass to relative to the frame about a first axis of rotation parallel to a mean plane of the frame, and a lever for detecting pivoting of the mass, connected to the proof mass through a second mechanical link allowing rotation of the lever relative to the proof mass about a second axis parallel to the first axis, wherein the second link comprises: a first wall, perpendicular or virtually perpendicular to the second axis of rotation, and a second wall, perpendicular to the mean plane of the frame and in parallel or virtually in parallel to the second axis of rotation, the first wall and the second wall connecting to each other perpendicularly or virtually perpendicularly and connecting, as regards one, to the lever and, as regards the other, the proof mass, wherein the frame and the proof mass form a first frame and a first proof mass respectively, the device further comprising: a second frame, a second proof mass, connected to the second frame through a first additional link which allows pivoting of the second proof mass relative to the second frame about a first additional axis of rotation, parallel to the first axis of rotation, and wherein the second proof mass is also connected to the detection lever through a second additional link allowing rotation of the lever relative to the second proof mass about a second additional axis of rotation parallel to the first axis of rotation, the lever being connected on one side to the first proof mass and on the other side to the second proof mass.

2. The device according to claim 1, wherein the first wall and the second wall are connected to each other to form a T, the second wall corresponding to the vertical median bar of the T.

3. The device according to claim 1, wherein: the first wall extends: from a first end, connected to the lever, to a second end, also connected to the lever, and wherein the second wall extends: from a first end, through which the second wall connects to the first wall, in a median zone of the first wall, between the first end and the second end of the first wall, to a second end through which the second wall connects to the proof mass.

4. The device according to claim 3, wherein the first end of the first wall connects to the lever via a connecting wall, which extends from this first end to the lever, in parallel or virtually in parallel to the second wall.

5. The device according to claim 4, wherein the second end of the first wall is connected to the lever by means of another connecting wall which extends from this second end to the lever, in parallel or virtually in parallel to the second wall.

6. The device according to claim 1, wherein the first wall connects to the lever while the second wall connects to the proof mass, and wherein the first wall is connected to the proof mass only through said second wall.

7. The device according to claim 1, wherein the second link further comprises: a first additional wall, perpendicular or virtually perpendicular to the second axis of rotation, and a second additional wall, in parallel or virtually in parallel to the second axis of rotation, the first additional wall and the second additional wall connecting perpendicularly or virtually perpendicularly to each other and connecting, as regards one, to the lever and, as regards the other, to the proof mass, the second wall and the second additional wall being located as an extension of each other.

8. The device according to claim 1, wherein the first wall has, along a direction parallel to the lever, a length greater than twenty times a width that the first wall has along a direction perpendicular to the lever, or even greater than forty times the width of the first wall.

9. The device according to claim 1, wherein the second wall has, in parallel to the second axis of rotation, a length greater than twenty times a width that the second wall has in a direction perpendicular to the second axis of rotation, or even greater than forty times the width of the second wall.

10. The device according to claim 1, further comprising a support and wherein the first frame and the second frame are both translationally guided relative to the support along an axis of displacement which is parallel to a mean plane of the first frame and which is perpendicular to the first axis of rotation.

11. The device according to claim 10, further comprising an electromechanical actuation system configured to impose oscillation to each of the frames along said axis of displacement, the displacement of the first frame relative to the support and the displacement of the second frame relative to the support having a same amplitude and directions opposite to each other.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0080] The figures are set forth by way of indicating and in no way limiting purposes.

[0081] FIG. 1 schematically represents a gyrometer with two movable frames.

[0082] FIG. 2 is a top partial schematic view of a mechanical link of the gyrometer of FIG. 1, this link connecting one of the proof masses of the gyrometer to a detection lever.

[0083] FIG. 3 schematically represents the link of FIG. 2, in a situation where the proof mass has moved along the axis X with respect to its rest position.

[0084] FIG. 4 schematically represents a flexible wall connecting two elements, in a top view.

[0085] FIG. 5 schematically represents how the wall in FIG. 4 purely flexurally deforms.

[0086] FIG. 6 is a representation of the principle of a link implementing the present technology, this link connecting the proof mass of a micro-electromechanical device to a lever for detecting pivoting of this mass.

[0087] FIG. 7 schematically represents the link of FIG. 6, in a situation where the proof mass has moved relative to its rest position, along an axis of displacement X.

[0088] FIG. 8 is a schematic perspective representation of a gyrometer with two movable frames implementing the present technology.

[0089] FIG. 9 schematically represents part of the gyrometer of FIG. 8, in a side view.

[0090] FIG. 10 is a detail perspective view of a central zone of the gyrometer of FIG. 8.

[0091] FIG. 11 schematically represents a cross-section side view of a detection lever and strain gauges of the gyrometer of FIG. 8.

[0092] FIG. 12 is a detail cross-sectional and side view of these strain gauges.

[0093] FIG. 13 schematically represents a first embodiment of a mechanical link which, in the gyrometer of FIG. 8, connects one of the proof masses to the detection lever, in a top view.

[0094] FIG. 14 again represents the first embodiment of this link, in a partial top view.

[0095] FIG. 15 schematically and partially represents a second embodiment of the mechanical link in question, in a top view.

[0096] FIG. 16 schematically and partially represents a third embodiment of the mechanical link in question, in a top view.

[0097] FIG. 17 schematically and partially represents a fourth embodiment of the mechanical link in question, in a top view;

[0098] FIG. 18 schematically and partially represents a fifth embodiment of the mechanical link in question, in a top view;

[0099] FIG. 19 schematically and partially represents a sixth embodiment of the mechanical link in question, in a top view;

[0100] FIG. 20 schematically and partially represents a seventh embodiment of the mechanical link in question, in a top view;

[0101] FIG. 21 schematically and partially represents an eighth embodiment of the mechanical link in question, in a top view.

DETAILED DESCRIPTION

[0102] FIGS. 8, 9 and 10 show a gyrometer-type device 1 implementing the present technology. This gyrometer 1 is a double-frame gyrometer with out-of-plane movement, which makes it possible to measure a speed of rotation about an axis Y parallel to the mean plane of the substrate from which the gyrometer 1 is made.

[0103] Most of this substrate forms a thick layer that serves as a support 2.

[0104] The gyrometer 1 comprises two movable frames 3 and 3, each guided for displacement, relative to this support 2, along an axis X which is parallel to the mean plane of the support. Each frame 3; 3 is parallel to the support 2. Stated differently, for each frame 3, 3, the mean plane P of the frame is parallel to the mean plane of the support 2. In the following, the orientation of different axes and walls are referred to the mean plane P of the frame 3, 3, or, indifferently, to the mean plane of the support 2 (since these two mean planes are parallel to each other).

[0105] The axis of displacement of the frames, X, is perpendicular to the axis of measurement of the angular speed of rotation, Y. The axis of displacement of the frames, X, and the axis of measurement of the angular speed, Y, are shown in the different figures, as is an axis Z, perpendicular to the mean plane of the support (perpendicular to X and Y).

[0106] For each frame, guidance of the frame relative to the support is achieved by virtue of four springs 20, for example, disposed at four points of the frame remote from each other, each spring 20 connecting the frame to the support and allowing relative movement parallel to the axis X. In this case, the springs 20 comprise leaves working in flexion, which connect the support 2 to the frame 3, 3 considered. The frames 3 and 3 herein have an overall rectangular shape.

[0107] During operation of the gyrometer, the two frames are moved, for example by electrostatic actuation using interdigital combs (not represented), so that they oscillate in parallel to the axis X, in phase opposition to each other (symmetrically). The two frames then have the same speed, but their directions of movement, relative to the support 2, are opposite to each other.

[0108] The two frames 3 and 3 are arranged opposite to each other, on either side of a fixed central portion 8 (i.e. without movement relative to the support 2) of the gyrometer. In FIGS. 8 and 10, the detail of this central portion 8 is not represented, for the sake of clarity of the figure. Stated differently, FIGS. 8 and 10 are partial views. The boundary between non-represented parts and represented parts is marked on each of these figures by three thick, wavy lines.

[0109] Each frame 3, 3 drives a proof mass 4, 4 (also known as a Coriolis mass) therewith, which is connected to the frame through a first link 5, 5 which allows pivoting of the proof mass to about a first axis of rotation ?.sub.1, ?.sub.1 parallel to the axis Y. This link partly resembles a pivot link or, stated differently, a hinge. The first link 5, 5 is rigid with respect to relative displacements between the mass and the frame along the axis X (whereas the second links 9, 9 shown below are instead flexible along the axis X). As a result of this strong coupling, for the oscillating movement of each massframe assembly, relative to the support, in parallel to the axis X, virtually a single resonance frequency is obtained, typically between 1 and 100 kHz (or even between 5 and 50 kHz).

[0110] As can be seen in FIG. 8, each proof mass 4, 4 here has an overall shape which is that of a plate (approximately parallelepipedal), parallel to the mean plane P of the frame 3, 3 when the mass is at rest. This plate is surrounded by the corresponding frame over most of its perimeter. Each mass 4, 4 extends from a first end 41, 41 to a second end 42, 42. The mean axis of the proof mass 4, 4, which connects its first end to its second end, is parallel to the axis of displacement, X.

[0111] The first end 41, 41 is connected to the frame 3, 3 through the first link 5, 5 mentioned above, while the second end 42, 42 of the mass can move out of plane, along a direction parallel to the axis Z, when the mass 4, 4 pivots about its axis of rotation ?.sub.1, ?.sub.1.

[0112] For each mass 4, 4, the first end 41, 41 is located, relative to the rest of the proof mass 4, 4, opposite to the other proof mass 4, 4 (and therefore opposite to the other frame 3). Stated differently, each proof mass 4, 4 is instead connected to its frame 3, 3 (through the first link 5, 5) on the somewhat outer side of the frame, on a side of this mass opposite to the other proof mass 4, 4.

[0113] Each proof mass 4, 4 is connected, on the side of its second end 42, 42, to a common rotation detection lever, 7, through a mechanical link 9, 9. This lever 7 pivots about a detection axis ?.sub.3, which is parallel to the axis Y and which is fixed (or at least essentially fixed) with respect to the support 2. The lever 7 is here connected to the support 2 through a link acting as a hinge (translationally stiff along X and Z, and relatively flexible with respect to rotation about the detection axis ?.sub.3). Lever 7 is located in the central zone of the gyrometer, between the two proof masses. Lever 7 has the shape of a beam, centred on the mean axis of the gyrometer (the mean axis which is parallel to X), when the gyrometer is at rest.

[0114] When the gyrometer 1 rotates (i.e.: when the support 2 rotates) with respect to an inertial reference frame, for example with respect to the Galilean reference frame, about the axis Y, with an angular velocity {right arrow over (?)}=?{right arrow over (y)}, each mass 4, 4 then experiences a Coriolis force, which is expressed as {right arrow over (F)}.sub.cor=2 m.sub.cor(v{right arrow over (x)})?(??) where m.sub.cor represents the mass of any one of the proof masses 4, 4 and where v is its speed of displacement (along the axis X). This force is therefore directed along the axis Z and is of the same amplitude but in the opposite direction for the two proof masses 4 and 4 (since the two masses are driven in opposite directions). For each of these two masses, this force therefore causes a displacement of its second end 42, 42, along the axis Z (or, stated differently, a pivoting of the mass about the first axis of rotation ?.sub.1, ?.sub.1), in an opposite direction for the two masses 4, 4, which then causes the detection lever 7 to rotate about the detection axis ?.sub.3 (see FIG. 9). This rotation of the lever is measured, here by virtue of piezoresistive strain gauges 21, 22 (FIGS. 11 and 12), to deduce the angular velocity ? thereof. In FIGS. 8 to 10, the amplitude of displacement along the axis Z is exaggerated (i.e. this displacement is not represented to scale), to make it clearly visible. In practice, the amplitude of oscillation of the frames, along the axis X, is in the order of about ten microns (which is very high, for a MEMS), while the displacement, along the axis Z, of the second ends of the masses is, for example, in the order of 0.1 micron. In these figures, the displacement of the frames and masses along the axis X is schematically represented by the double arrows M1 and M1, while the displacement along the axis Z of the second ends of the masses is depicted by the double arrows M2 and M2.

[0115] Each first link 5, 5 has some stiffness, opposing to rotation of the corresponding proof mass 4, 4 about the first axis of rotation ?.sub.1, or ?.sub.1. To this rotational stiffness are added: [0116] stiffness of the strain gauges, [0117] stiffness of the hinge which connects lever 7 to support 2, [0118] and rotational stiffness of the second link 9, 9, which connects the mass 4, 4 and the lever 7.

[0119] The rotational movement of the mass 4, 4 about its axis of rotation ?.sub.1, ?.sub.1 is associated with a resonance frequency, chosen for example so as to be close to (slightly higher, for example by 1 to 10%) the resonance frequency of the frame-mass assembly in its oscillation in parallel to X (frequency at which the system is excited to obtain large displacements). This results in a larger angular velocity measurement signal Q.

[0120] In any case, the overall architecture of the gyrometer, with two proof masses 4 and 4 oscillating symmetrically and actuating the same rotation detection lever 7, is particularly interesting because it allows differential detection of the angular speed of rotation ?, which greatly improves the signal-to-noise ratio of this gyrometer 1 while greatly attenuating effect of vibrations on the movable parts.

[0121] FIGS. 11 and 12 show how the gauges 21 and 22 are arranged. Each of these gauges 21, 22 is connected, on one side to the lever 7, and on the other side to a gauge anchoring stud, 23, 24. Each anchoring stud is integral with the support 2. Here, the anchoring studs are at least partly housed in openings or housings provided in the lever 7, with sufficient spacing between the studs and the lever to allow the lever to pivot about the detection axis ?.sub.3. The two anchoring studs are located on either side of the detection axis ?.sub.3.

[0122] The two strain gauges 21, 22 are located in the lower part of the lever. They extend from a lower face of the lever (lower face which is the face of the lever on the side of the support).

[0123] The strain gauges 21, 22 may, as here, each be formed by a portion of a thin silicon top layer of an SOI, silicon-on-insulator, substrate from which the gyrometer is manufactured.

[0124] Such an SOI substrate comprises a thick support layer (generally at least 100 microns thick, generally more), covered with an insulating layer, generally of silicon oxide, itself covered by the thin silicon top layer, often called the Si-top layer. This Si-top layer, when manufactured, has a reduced t.sub.NEMS thickness (for example 250 nm) and is very well controlled. It is also essentially monocrystalline, and therefore suitable for producing the piezoresistive gauges 21, 22. During manufacture of the gyrometer, an additional layer of silicon (or possibly another material), which is fairly thick (thickness h=t.sub.MEMS?t.sub.NEMS), is deposited on the Si-top layer, to form the bulk of the proof masses and frames (total thickness t.sub.MEMS). This additional layer is polycrystalline or monocrystalline, and its thickness h is typically a few microns or tens of microns. During manufacture of the gyrometer, the Si-top layer and this additional layer are etched to define the different elements of the gyrometer. The silicon oxide layer mentioned above, located under the Si-top layer, is removed (by chemical etching) especially under the parts of the gyrometer that are movable in relation to the support (frames and proof mass in particular), to release these movable parts. Once manufactured, the thick support layer of the SOI substrate forms the support 2 of the gyrometer. In such a device, the Si-top layer, or the elements derived from this layer, are sometimes referred to as the NEMS (nano-electromechanical system) layer.

[0125] The two strain gauges 21, 22 are located on either side of the detection axis 3. In addition, the detection axis ?.sub.3 is offset with respect to the strain gages (due to the positioning and configuration of the hinge mentioned above, which connects lever 7 to support 2), in that it is not located as an extension of the strain gages (in practice, the axis ?.sub.3 is located at a different z coordinate from those of the strain gages). Thus, when the lever is rotated about this axis, one of the gauges is stretched, while the other is compressed, which contributes to the differential nature of the angular velocity measurement. In FIGS. 11 and 12, lever 7 is represented in a position which is slightly tilted (about the axis ?.sub.3) with respect to the reference position which it occupies when the angular velocity ? is zero. In the situation represented, strain gauge 22 is compressed while strain gauge 21 is stretched (FIG. 12).

[0126] Here, each strain gauge takes the form of a beam or membrane extending parallel to the axis X.

[0127] Clearances 25, 26, 71 and 72 are provided, both in the anchoring studs and in the lever, around the zone occupied by each strain gauge 21, 22 (this results from the way the gauges are manufactured, and enables the gauges to be clearly delimited).

[0128] The second links 9 and 9, which connect lever 7 to proof mass 4 and proof mass 4 respectively, are now set forth in more detail.

[0129] Here, these two links are identical. Therefore, only one of these two links, 9, will be described in detail here. This link 9, as represented in FIGS. 13 and 14, corresponds to a first contemplatable embodiment for the link between the lever and the proof mass considered. A second, third and fourth embodiment of such a connection, well adapted to connect the lever 7 to the proof mass 4, are represented respectively in FIGS. 15, 16 and 17, and are marked respectively by the references 19, 29 and 39. The link 19; 29; 39 according to any one of these three embodiments could thus replace the link 9, 9 in the gyrometer 1 of FIG. 8.

[0130] From one embodiment to the next, identical (or, at least, corresponding) elements are marked by the same reference as far as possible.

[0131] In these four embodiments, the second link 9; 19; 29; 39 comprises two half-links, located respectively on one side and the other side of lever 7, on either side of a plane of symmetry of the link, Ps (plane of symmetry which is perpendicular to axis Y). Here, the plane of symmetry PS is also a plane of symmetry for the mass-lever assembly. The two half-links in question are facing each other. They are symmetrical to each other with respect to the plane of symmetry PS. FIG. 13 shows the two half-links, 90 and 90s, which together form the link 9 in the first embodiment. FIGS. 14 to 17 then show, for each of these four embodiments, one of the two half-links forming the link in question, 9; 19; 29; 39 (the other half-link being symmetrical).

[0132] In these four embodiments, the half-link in question comprises: [0133] a first wall 91; 391, perpendicular to a second axis of rotation ?.sub.2, and [0134] a second wall 97, perpendicular to the mean plane P of the frame 3 (strictly speaking, perpendicular to the mean plane of the frame when the mass is in its rest position), and parallel to the second axis of rotation ?.sub.2, [0135] the first wall 91; 391 and the second wall 97 connecting perpendicularly to each other and connecting, as regards one, to the lever 7 and, as regards the other, to the proof mass 4.

[0136] The second axis of rotation ?.sub.2, which is the axis of rotation of the second link, is parallel to the first axis of rotation ?.sub.1. When the frames 3, 3 oscillate, the positions of the first axes of rotation ?.sub.1, ?.sub.1 vary (these axes are translated), as the frames move relative to the support 2. It should be noted that the X position of the second axes of rotation ?.sub.2, ?2 does not necessarily vary by the same amount as the X position of the first axes ?.sub.1, ?.sub.1.

[0137] As explained in detail in the summary section, by virtue of this particular arrangement, the second link 9; 19; 29; 39: [0138] a) is able to transmit a force in parallel to the axis Z, with little deformation in this direction (i.e.: high stiffness of the link along the axis Z, by virtue of the significant t.sub.MEMS extension of the walls 91; 391 and 97 along the axis Z); this enables the proof mass 4 to drive the lever 7 therewith along a direction parallel to the axis Z, effectively, when the proof mass pivots; [0139] b) allows a large relative displacement of the mass 4 with respect to the lever 7, along the direction X, with a low stiffness with respect to this displacement (by virtue of the flexural deformation possibilities of the second wall 97), and with a low non-linearity (by virtue of the addition of the first wall 91; 391 which allows displacements along Y of the end 98 of the second wall 97, at the junction between these two walls), and [0140] c) has a low rotational stiffness with respect to a rotation of the lever 7 relative to the mass 4, about the axis of the link, which is the second axis of rotation ?.sub.2 (by virtue of the possibility of torsional deformation of the second wall 97 about this axis).

[0141] In the exemplary embodiments represented, the first wall 91; 391 connects (directly, or via one or two connecting walls 94, 95) to the lever 7, while the second wall 97 connects (directly) to the proof mass 4, the first and second walls also connecting to each other at right angles, for example forming an (inverted) T, as in FIGS. 13 to 16, or forming an L (FIG. 17). Alternatively, the first wall could connect to the proof mass while the second wall connects to the lever (stated differently, for the different embodiments set forth here, the configuration of each half-link could be reversed).

[0142] In any case, here, the first wall 91; 391 is connected to the proof mass only through the second wall 97 in question (and not by several flexible walls located side by side, as is the case in the link 9aa of prior art set forth above with reference to FIG. 2), which contributes to the flexibility of the link in terms of rotation about the second axis ?.sub.2.

[0143] More generally, the only mechanical link which directly connects the second end 42 of the proof mass 4 to the lever 7 (that is which connects them without passing through another element, such as the frame 3) is the second link 9; 19; 29; 39 in question. And, in the second link, only the second wall 97 (as well as another second wall 97s, symmetrical to the second wall 97 and belonging to the other half-link, 90s) connects directly to the proof mass 4.

[0144] As indicated above, in the different embodiments represented, the second link 9; 19; 29; 39 comprises two half-links 90, 90s. The first half-link (90, in FIG. 13) comprises the first wall 91; 391, and the second wall 97 mentioned above. The second half-link (90s, in FIG. 13) comprises: [0145] a first additional wall 91s, perpendicular to the second of rotation, ?.sub.2, and [0146] a second additional wall 97s, parallel to the second axis of rotation, ?.sub.2, [0147] the first additional wall 91s and the second additional wall 97s connecting perpendicularly to each other and connecting, as regards one, to the lever 7 and, as regards the other, to the proof mass 4, [0148] the second wall 97 and the second additional wall 97s being located as an extension of each other.

[0149] Here, the second wall 97 and the second additional wall 97s are aligned with each other, and each extend along the second axis of rotation ?.sub.2.

[0150] In the different embodiments represented, the second wall 97 extends, in parallel to the axis Y: [0151] from a first end 98, through which the second wall connects directly and rigidly to the first wall 91; 391 (forming an embedment, from a mechanical point of view), [0152] to a second end 99 through which the second wall 97 connects directly and rigidly to the proof mass 4.

[0153] As for the first wall 91, in the first three embodiments (FIGS. 13 to 16), it extends: [0154] from a first end 92, connected to the lever 7 either directly and rigidly (FIGS. and 16), or connected to the lever via a first connecting wall 94 (FIGS. 13, 14), [0155] to a second end 93, also connected to the lever 7, either directly and rigidly (FIG. 16), or via a second connecting wall 95 (FIGS. 13, 14 and 15).

[0156] The axis which connects the first end 92 to the second end 93 is parallel to the lever 7.

[0157] In these first three embodiments, the first end 98 of the second wall connects (directly and rigidly) to the first wall 91 in a median zone of the first wall 91, between the first and second ends 92, 93 of the first wall. As indicated above, the first and second walls together are then shaped like an (inverted) T.

[0158] In the fourth embodiment (FIG. 17), the first wall 391 extends: [0159] from a first end 392, connected directly and rigidly to the lever 7, [0160] to a second end 393, connected (directly and rigidly) to the first end 98 of the second wall 97.

[0161] The axis which connects the first end 392 to the second end 393 is again parallel to the axis X (strictly speaking, parallel to the axis X when the lever is at rest, aligned with the axis X).

[0162] In the different embodiments considered here, the first and second walls are thin.

[0163] In this respect, it will be noted that FIGS. 13 to 17 are top views (the plane of the figure being parallel to the axes X and Y on each occasion), so that the extension along the axis Z of the first and second walls, t.sub.MEMS, is not visible in these figures (which extension is, in this case, significantly greater than the width of these walls). These figs additionally show the links 9; 19; 29; 39 in a rest position, in which the proof masses, the frames and the lever are stationary, occupying their rest position.

[0164] In these different embodiments, the second wall 97 has, in parallel to the second axis of rotation ?.sub.2, between its two ends 98 and 99, a length b greater than twenty times its width a (i.e. greater than twenty times its extension along the direction X), or even greater than forty times its width a. Furthermore, along the direction Z, it extends over a thickness t.sub.MEMS greater than four times its width a, or even greater than ten times its width a.

[0165] By way of example, the length b of the second wall may be between 30 and 150 microns. Its width a can be between 0.5 and 5 microns, and its thickness t.sub.MEMS can be between 5 and 100 microns.

[0166] In the different embodiments considered here, the first wall 91; 391 has, between its first end 92; 392 connected to the lever and the junction with the second wall 97, a length greater than twenty times its width c (i.e.: greater than twenty times its extension along the direction Y), or even greater than forty times its width c. In the case of the first, second and third embodiments, the first wall 91 thus has, between its two ends 92 and 93, a total length d greater than forty times, or even eighty times, its width c.

[0167] By way of example, the total length d of the first wall may be between 50 and 200 microns. Its width c can be between 0.5 and 5 microns.

[0168] Furthermore, along the direction Z, the first wall 91; 391 also extends over a thickness t.sub.MEMS greater than four times its width c or even greater than ten times its width c. This thickness may, again, be between 5 and 100 microns, for example.

[0169] Whatever embodiment is considered, the first and second walls are delimited by a lower edge (on the support side), and, opposite to this, by an upper edge, both of which are free edges (i.e. free to move, as they are not linked, at least not directly, to any other element of the gyrometer).

[0170] As indicated above, in the first embodiment (FIGS. 13 and 14), the first and second ends 92 and 93 of the first wall 91 connect to the lever 7 via the first connecting wall 94 and the second connecting wall 95 respectively. These two connecting walls are each parallel to the second wall 97. They are shorter, for example at least two or three times shorter than the second wall (i.e.: of extension f, in parallel to the axis Y, at least two or three times smaller than the length b of the second wall). They each connect to the first wall perpendicularly to this wall, and, opposite to this, they each connect rigidly to the lever 7. As explained in the summary section, these connecting walls make it possible to improve linearity of the spring force-displacement relationship along X, for link 9. The width e and thickness of the connecting walls are comparable (for example identical) to the width c and thickness of the first wall. In the same way, the first additional wall 91s extends, in parallel to X, from a first end to a second end, these two ends connecting to the lever 7 by means of a first additional connecting wall 94s and a second additional connecting wall 95s respectively. These two connecting walls 94s, 95s are each parallel to the second additional wall 97s, and are shorter, for example at least two or three times shorter than the second additional wall.

[0171] The second embodiment of the second link (FIG. 15) is identical to the first embodiment, except that the first end 92 of the first wall 91 connects directly and rigidly to the lever 7, instead of connecting thereto via a connecting wall.

[0172] The third embodiment of the second link (FIG. 16) is identical to the first embodiment, except that the first and second ends 92, 93 of the first wall 91 each connect directly and rigidly to the lever, instead of connecting thereto via a connecting wall.

[0173] A complete numerical example is now set forth, byway of illustration, for the first embodiment of link 9 (FIGS. 13 and 14). The dimensions of the different elements of link 9 are shown in FIG. 14. The values of these dimensions are given in Table 1, in microns.

[0174] A numerical example corresponding to link of prior art in FIG. 2 is also set forth by way of comparison. The dimensions of the different elements of this link are shown in FIG. 2. The values of these dimensions are also given in Table 1, in microns.

[0175] The values of the stiffness coefficients k.sub.X, k.sub.Z and C.sub.Y corresponding to these dimensions are given in Table 2, both for the present link, 9, and for that of prior art, 9aa. The values of these stiffness coefficients have been obtained by numerical simulation.

[0176] The stiffness coefficient k.sub.X is the stiffness coefficient of the link (expressed, for example, in Newtons per metre) with respect to a relative displacement, between the mass and the lever, along the axis X. The stiffness coefficient k.sub.Z is the stiffness coefficient of the link with respect to a relative displacement, between the mass and the lever, along the axis Z. And the stiffness coefficient C.sub.Y is the rotational stiffness coefficient of the link (expressed, for example, in Newtons.Math.metres per radian), with respect to a rotation of the mass relative to the lever about the axis ?.sub.2.

[0177] Table 2 also indicates the value of a non-linearity coefficient NL. This coefficient is equal to the relative difference (in %) between: on the one hand, the spring force (directed along the axis X) corresponding to a stretch of 5 microns in the direction X, and, on the other hand, the value kX?5 microns (i.e.: deviation between the spring force and the straight line which, for small stretches, best describes the force-stretch relationship along the axis X, for a link stretch of 5 microns).

TABLE-US-00001 TABLE 1 a b c d e f g l m n t.sub.MEMS Prior art 4.8 176 12 12 13 17.8 400 100 2 20 (link 9aa) link 9 1 55 1 82 1 11 20 10 10 100 20

TABLE-US-00002 TABLE 2 Prior art link 9 (parameters stiffness (link 9aa) from table 1) ratio k.sub.X (N/m) 52 13 4 times smaller k.sub.Z (N/m) 780 1211 1.5 times greater C.sub.Y (Nm/rad) 5.2E?7 1.06E?8 58 times smaller NL (% F(@5 ?m) 0.15% 17% 113 times greater k.sub.X ? NL (N/m) 0.08 2.2 28 times greater

[0178] As can be seen from this example, the link 9 effectively provides a low stiffness coefficient k.sub.X, a high stiffness coefficient k.sub.Z and a low stiffness coefficient C.sub.Y. In particular, the value of the stiffness coefficient C.sub.Y is significantly lower than for the link 9aa of prior art, which substantially increases sensitivity of the gyrometer.

[0179] In terms of non-linearity, however, the performance of link 9 is less good than that of the link 9aa of prior art. However, this performance is still much better than what would be obtained with a single flexible wall (parallel to the plane Y,Z) embedded at its two ends. In addition, for link 9, the fairly high value of the coefficient NL finally does not have as great an impact as it might appear at first sight, as the coefficient k.sub.X is lower than in prior art. Indeed, for the oscillation dynamics of the mass 4-frame 3 assembly, the total X stiffness, due not only to the link 9 (or 9aa), but also, and above all, due to the springs 10 which link the frame to the support should be taken into account. It is therefore in relation to this total stiffness that the non-linearity introduced by link 9 (or 9aa) should be evaluated. And as the coefficient k.sub.X is low, for link 9 (lower than for link 9aa), the non-linear term k.sub.X?NL(%), to be compared with the total stiffness along X, is not as high as the value of NL(%) would suggest.

[0180] For dimensioning the link 9 corresponding to the values in Table 1, the non-linearity of the spring force along the axis X nevertheless remains relatively high. This non-linearity can be decreased by increasing the length of the walls 91, 97 of link 9, as can be seen in Table 3, which gathers the values of the coefficients k.sub.X, k.sub.Z, C.sub.Y and NL for three different dimensioning items of link (configurations 1 to 3). In Table 3, the values for dimensions a to f are again given in microns. The values for the other dimensions are the same as for Table 1.

[0181] The main difference between configurations 2 and 3 is the length f of the connecting walls 94 and 95 (15 microns for configuration 2 and 30 microns for configuration 3). This difference enables the NL coefficient to be reduced from 8% to 5%, which clearly shows that the flexibility of the connecting walls 94, 95 effectively helps to reduce non-linearity of the link, which has already been made acceptable (compared to a single flexible wall such as the second wall) by virtue of the addition of the first wall 91. It is also noted that, for the example corresponding to configuration 3, the kX x NL(%) term is only 2 to 3 times greater than for the link 9aa of prior art, while the rotational stiffness coefficient C.sub.Y is approximately 60 times lower than for the link 9aa.

TABLE-US-00003 TABLE 3 Config. k.sub.x k.sub.z C.sub.y NL k.sub.x ? NL no b d f a, c, e (N/m) (N/m) (Nm/rd) (% F(@5 ?m)) (N/m) 1 55 82 11 1 13 1211 1.06E?8 17% 2.2 2 70 120 15 1 6 557 0.81E?8 8% 0.5 3 80 120 30 1 4 398 0.70E?8 5% 0.2

[0182] Different alternatives can be made to the gyrometer just described, in particular as regards the second link connecting the lever to the proof mass. Thus, in the examples set forth above, for embodiments 1 to 3, the first wall connects to the lever while the second wall (central bar of the T, providing flexibility along X) connects to the proof mass. However, as already indicated, as an alternative, the first wall could be connected to the proof mass while the second wall would be connected to the lever (instead of vice versa). Thus, as illustrated in FIG. 18, there is a first wall 491 which connects to the proof mass 4 (here via two connecting walls 495 and 494) while the second wall 497 connects directly to the lever 7, the first and second walls additionally connecting to each other at right angles, for example forming a T. FIG. 19 illustrates an alternative to FIG. 18 in which the first wall is connected directly to the proof mass 4 at one end and via a connecting wall 494 at the other end.

[0183] FIG. 20 illustrates an alternative to FIG. 14 in which the first wall 91 connects via a connecting wall 95 to one end to the lever 7 and directly to the other end, while the second wall 97 connects directly to the proof mass 4, the first and second walls additionally connecting to each other at right angles.

[0184] FIG. 21 illustrates an alternative to FIG. 17 in which the first wall 591 connects directly to the lever 7 while the second wall 597 connects directly to the proof mass 4, the first and second walls also connecting to each other at right angles and forming an inverted L.

[0185] The articles a and an may be employed in connection with various elements and components, processes or structures described herein. This is merely for convenience and to give a general sense of the processes or structures. Such a description includes one or at least one of the elements or components. Moreover, as used herein, the singular articles also include a description of a plurality of elements or components, unless it is apparent from a specific context that the plural is excluded.

[0186] It will be appreciated that the various embodiments and aspects of the inventions described previously are combinable according to any technically permissible combinations.