ELECTROMECHANICAL SYSTEM WITH CAPACITIVE MEASURING OR ACTUATORS AND A DRIVE SHAFT

Description

DOMAINE TECHNIQUE DE L'INVENTION

[0001] The technical field of the invention is that of electromechanical systems, particularly microelectromechanical systems (MEMS) or nanoelectromechanical systems (NEMS). More specifically, the invention relates to an electromechanical system comprising a moving element, capacitive means for measurement or actuation, and a device for transmitting motion between the moving element and the capacitive means for measurement or actuation. Such a system can be used as an electroacoustic transducer (e.g., microphone, loudspeaker) or a differential pressure sensor. ARRIERE-PLAN TECHNOLOGIQUE DE L'INVENTION

[0002] Microelectromechanical (MEM) and nanoelectromechanical (NEM) microphones represent a rapidly expanding market, driven in particular by the development of mobile devices such as tablets, smartphones, and other connected objects, in which they are gradually replacing electret microphones. Electromechanical systems such as micromirrors, like the one described in document WO2008 / 078182, also exist.

[0003] Microphones measure a rapid change in atmospheric pressure, also called acoustic pressure. They therefore have at least one part in contact with the outside.

[0004] Most MEMS or NEMS microphones manufactured today are capacitive sensing microphones. figure 1 represents an example of a capacitive sensing microphone 1, described in patent FR3114584B1.

[0005] The microphone 1 includes a frame (not shown) delimiting at least in part a first zone 11 and a second zone 12, a movable element 13 relative to the frame and a transmission device 14 of a movement between the first zone 11 and the second zone 12. The first and second zones 11-12 of the microphone 1 are isolated from each other in a sealed manner.

[0006] The moving element 13, also called the piston, is in contact with the first zone 11. It comprises a diaphragm 131 and a diaphragm stiffening structure 132. The diaphragm 131 of the piston 13 is designed to collect a pressure difference between its two faces across its entire surface, in order to deduce a change in atmospheric pressure. One face of the diaphragm 131 is subjected to atmospheric pressure (the change in which is to be detected), and the opposite face of the diaphragm 131 is subjected to a reference pressure.

[0007] Furthermore, the microphone 1 includes capacitive sensing means 15 arranged in the second zone 12. These capacitive sensing means 15 allow the displacement of the piston 13 to be measured, and therefore the pressure difference between its two faces. They preferably include a movable electrode 151 and at least one fixed electrode positioned opposite the movable electrode 151. The electrodes form the plates of a capacitor whose capacitance varies according to the displacement of the piston 13.

[0008] The transmission device 14 is mounted to rotate freely relative to the frame by means of several pivot joints 16. The transmission device 14 comprises two first transmission arms 141 extending into the first zone 11, two second transmission arms 142 extending into the second zone 12 and two transmission shafts 143 extending partly into the first zone 11 and partly into the second zone 12. Each transmission shaft 143 connects a first transmission arm 141 to a second transmission arm 142.

[0009] Each first transmission arm 141 comprises a first end coupled to the piston 13 and a second opposite end coupled to the associated transmission shaft 143. Each second transmission arm 142 comprises a first end coupled to the moving electrode 151 of the capacitive sensing means 15 and a second opposite end coupled to the associated transmission shaft 143.

[0010] French patent FR3059659B1 describes a capacitive sensing microphone similar to that of the figure 1 Capacitive sensing devices comprise a moving electrode and two fixed electrodes between which the moving electrode is positioned. The electrodes form the plates of two capacitors whose capacitances vary in opposite directions as a function of the piston's displacement. The measurement of the piston's displacement is thus a differential measurement.

[0011] To perform such a differential measurement, the capacitors are first charged by applying a DC bias voltage between the moving electrode and the fixed electrodes via a high resistance. The movement of the piston results in a change in capacitance, and therefore a change in the voltage between the fixed electrodes (the charge of the capacitors being essentially constant at audible frequencies, typically above 100 Hz), which can be read by an instrumentation amplifier.

[0012] One disadvantage of these capacitive sensing microphones is that energy is lost in the deformation of the transmission device 14 and the frame of the moving electrode 151, which represents a loss of useful signal when detecting dynamic pressure variations.

[0013] Furthermore, these capacitive sensing microphones can fail due to a phenomenon called "pull-in," a phenomenon common to all electromechanical systems incorporating capacitive measurement or actuation means. This pull-in is caused by electrostatic force, which tends to pull the moving electrode closer to the fixed electrode (or one of the fixed electrodes) and depends on the square of the bias voltage. The electrostatic force, which also depends on the displacement of the moving electrode, can be approximated to a first approximation by a constant force plus the force exerted by a spring with negative stiffness for small displacements.

[0014] To mitigate (to a certain extent) this collapse phenomenon, an elastic force is used to counteract the electrostatic force. This elastic force can be generated by springs connecting the frame of the moving electrode 151 to the microphone frame 1. The stiffer the springs, the higher the voltage at which the electrostatic force overcomes the elastic force (known as the collapse voltage or "pull-in voltage"), and the higher the voltage at which the moving electrode 151 can be biased. This is advantageous because the sensitivity of the microphone 1 increases with the bias voltage.

[0015] The sensitivity of the microphone 1 also increases with the displacement of the moving electrode 151. One solution to increase the displacement of the moving electrode 151 would be to increase the displacement of the piston 13 (also called compliance), but this is limited by the resonant frequency of the microphone 1 (which we want to be at least 35 kHz). Another solution is to reduce the length of the first transmission arms 141 and / or increase the length of the second transmission arms 142, thus increasing the lever arm effect. However, reducing the length of the first transmission arms 141 is difficult because there is a sealing zone around the capacitive sensing means 15 to enclose them within the second zone 12, and because this would require reducing the surface area of ​​the piston 13. Increasing the length of the second transmission arms 142 is easier, but considerably increases the microphone's overall size.In addition, simply increasing the length of the second transmission arms 142 makes them more easily deformable, which ultimately reduces the displacement of the moving electrode and decreases sensitivity. RESUME DE L'INVENTION

[0016] It is observed that there is a need to provide an electromechanical system with capacitive sensing or capacitive actuation that is both compact and has high sensitivity.

[0017] According to the invention, this need is met by providing an electromechanical system comprising: a frame; a movable element relative to the frame; capacitive means for measuring or actuation comprising: a first electrode movable relative to the frame; and at least one electrode fixed relative to the frame and separated from the first movable electrode by a first dielectric medium; a first device for transmitting a movement between the movable element and the first movable electrode, the first transmission device being rotationally movable relative to the frame by means of a plurality of first pivot joints; the first transmission device comprising: a first transmission shaft having a first longitudinal axis of rotation; and a plurality of first transmission arms, each of the first transmission arms comprising a first end coupled to a first half of the moving element and a second end attached to the first transmission shaft; the first moving electrode being connected to the first transmission shaft.

[0018] Thus, when the moving element moves, it rotates the first transmission device around the first longitudinal axis, which in turn sets the first moving electrode in motion. This arrangement allows for a greater displacement of the moving electrode for a given displacement of the moving element, without increasing the size of the electromechanical system, because the displacement of the moving electrode is now independent of the distance between the moving element and the moving electrode. It now depends on the distance between the first end of the first transmission arms and the first longitudinal axis of rotation. The electromechanical system according to the invention thus offers a better compromise between sensitivity and compactness than the prior art microphone.

[0019] Advantageously, the first moving electrode is fixed to the first transmission shaft, from which it follows that the first moving electrode is mounted to rotate freely around the first longitudinal axis of rotation.

[0020] In a preferred embodiment: The capacitive means for measuring or actuation further include: a second electrode movable relative to the frame; and at least one additional electrode fixed relative to the frame and separated from the second movable electrode by a second dielectric medium; the system further includes a second device for transmitting motion between the movable element and the second movable electrode, the second transmission device being rotationally movable relative to the frame by means of a plurality of second pivot joints and comprising: a second transmission shaft having a second longitudinal axis of rotation; and a plurality of second transmission arms, each of the second transmission arms comprising a first end coupled to the movable element and a second end fixed to the second transmission shaft; the second movable electrode is connected to the second transmission shaft.

[0021] According to a development of this preferred embodiment, the second mobile electrode is fixed to the second transmission shaft, from which it follows that the second mobile electrode is mounted to rotate freely around the second longitudinal axis of rotation.

[0022] According to another development consistent with the previous one, the first longitudinal axis of rotation is parallel to the second longitudinal axis of rotation.

[0023] According to another development compatible with the previous ones, the first end of the first transmission arms is coupled to a first half of the moving element and the first end of the second transmission arms is coupled to a second half of the moving element.

[0024] Preferably, the moving element is in contact with a first zone and the first and second moving electrodes are located in a second zone hermetically isolated from the first zone.

[0025] In addition to the characteristics mentioned in the preceding paragraphs, the electromechanical system according to the invention may have one or more additional characteristics from among the following, considered individually or in all technically possible combinations: The moving element is in translation relative to the frame; the moving element is in rotation relative to the frame; at least one of the first pivot joints is located at the first moving electrode and another of the first pivot joints is located at one end of the first transmission shaft, opposite the first moving electrode; at least one of the second pivot joints is located at the second moving electrode and another of the second pivot joints is located at one end of the second transmission shaft, opposite the second moving electrode; the first transmission arms extend perpendicularly to the first longitudinal axis of rotation; the second transmission arms extend perpendicularly to the second longitudinal axis of rotation; the first longitudinal axis of rotation is parallel to the second longitudinal axis of rotation;the first moving electrode and the second moving electrode are symmetrical with respect to a plane separating the first and second halves of the moving element; the first transmission device and the second transmission device are symmetrical with respect to a plane separating the first and second halves of the moving element; the first end of each first transmission arm is located at a distance L pist1 from the first longitudinal axis of rotation such that: ; 1 2 × L elec 1 ≤ L pist 1 ≤ 2 × L elec 1 , Or L elec 1 is the distance between a longitudinal edge of the first moving electrode and the first longitudinal axis of rotation; the first end of each second transmission arm is located at a distance L pist2 from the second longitudinal axis of rotation such that: 1 2 × L elec 2 ≤ L pist 2 ≤ 2 × L elec 2 , Or L elec 2 is the distance between a longitudinal edge of the second moving electrode and the second longitudinal axis of rotation; at least a portion of the first transmission shaft located opposite the moving element is perforated; at least a portion of the second transmission shaft located opposite the moving element is perforated; the first transmission shaft and the first transmission arms extend into the first zone and the first transmission device further includes pillars extending partly into the first zone and partly into the second zone; the second transmission shaft and the second transmission arms extend into the first zone and the second transmission device further includes pillars extending partly into the first zone and partly into the second zone;the first transmission shaft and the first transmission arms have a thickness of between 5 µm and 800 µm, preferably between 50 µm and 200 µm; the second transmission shaft and the second transmission arms have a thickness of between 5 µm and 800 µm, preferably between 50 µm and 200 µm; the first moving electrode comprises a membrane and a membrane stiffening structure; the stiffening structure of the first moving electrode is anchored to the first transmission device at a portion of the first pivot joints; the stiffening structure of the first moving electrode comprises a plurality of beams extending parallel to each other and at least a portion of the beams are anchored to the first transmission device, each beam of said at least a portion being anchored at a first pivot joint corresponding to said beam;each first pivot joint of said at least one part includes a watertight insulating element capable of elastic deformation and ensuring a seal between the first zone and the second zone; the second movable electrode includes a membrane and a membrane stiffening structure; the stiffening structure of the second movable electrode is anchored to the second transmission device at a part of the second pivot joints; the stiffening structure of the second movable electrode includes a plurality of beams extending parallel to each other and at least a part of the beams are anchored to the second transmission device, each beam of said at least one part being anchored at a second pivot joint corresponding to said beam;each second pivot joint of said at least one part includes a watertight insulating element capable of elastic deformation and ensuring sealing between the first zone and the second zone; the capacitive measuring or actuation means include first and second fixed electrodes associated with the first movable electrode, the first movable electrode including a membrane disposed between the first and second fixed electrodes; each of the first and second fixed electrodes includes a first portion and a second portion situated on either side of the membrane and on either side of the first pivot joints, the first and second portions being electrically connected;The capacitive measuring or actuation means further comprise third and fourth fixed electrodes associated with the second movable electrode, the second movable electrode comprising a membrane disposed between the third and fourth fixed electrodes; and each of the third and fourth fixed electrodes comprises a first portion and a second portion situated on either side of the membrane and on either side of the second pivot joints, the first and second portions being electrically connected. BREVE DESCRIPTION DES FIGURES

[0026] Other features and advantages of the invention will become clear from the description given below, which is by way of example and not limitation, with reference to the accompanying figures, including: there figure 1 is a partial perspective view of a capacitive sensing microphone according to the prior art; the figure 2 is a partial bottom view of an electromechanical system according to a first embodiment of the invention, this electromechanical system comprising capacitive means for detection or actuation; the figure 3 is a partial top view of the capacitive means of sensing or actuation of the electromechanical system of the figure 2 ; there figure 4A is a cross-sectional view of the electromechanical system along section plane AA of the figure 3 ; there figure 4B is a cross-sectional view of the electromechanical system according to the BB section plane of the figure 3 ; there figure 4C is a cross-sectional view of the electromechanical system according to the CC cutting plane of the figure 3 ; there figure 5 is a partial bottom view of an electromechanical system according to a second embodiment of the invention; the figure 6 is a top view of the capacitive means of sensing or actuation of the electromechanical system of the figure 5 ; there figure 7 is a partial bottom view of an electromechanical system according to a third embodiment of the invention; the figure 8 is a partial bottom view of an electromechanical system according to a fourth embodiment of the invention; the figure 9 is a partial bottom view of an electromechanical system according to a fifth embodiment of the invention; and the figure 10 is a partial bottom view of an electromechanical system according to a sixth embodiment of the invention.

[0027] For clarity, identical or similar elements are identified by identical reference symbols across all figures. DESCRIPTION DETAILLEE

[0028] THE figures 2 , 3 And 4A à 4C represent a part of an electromechanical system 2 with capacitive sensing or capacitive actuation according to a first embodiment of the invention. This electromechanical system 2 can form an electroacoustic transducer, for example a microphone or a loudspeaker, or a differential pressure sensor. In the following description, the example of a capacitive sensing microphone will be used.

[0029] The electromechanical system 2 comprises: a frame 10; a movable element 13 in contact with a first zone 11; capacitive detection (or measurement) means 15' comprising a first electrode 151 movable relative to the frame 10, a second electrode 152 movable relative to the frame 10, the first and second movable electrodes 151-152 being located in a second zone 12 hermetically isolated from the first zone 11; and a first transmission device 14a of a movement between the movable element 13 and the first movable electrode 151 (in other words between the first zone 11 and the second zone 12); and a second transmission device 14b of a movement between the movable element 13 and the second movable electrode 152.

[0030] There figure 2 is a bottom view of the electromechanical system 2 showing the first portions 101 of the frame 10, the moving element 13, the transmission devices 14a-14b and the moving electrodes 151-152 of the capacitive sensing means 15'. The figure 3 is a top view showing only part of the capacitive sensing means 15' (including the first moving electrode 151). The figures 4A à 4C are different cross-sectional views of the electromechanical system 2, respectively according to the cross-sectional planes AA, BB and CC shown on the figure 3 They partly represent the frame 10, the first transmission device 14a and the capacitive detection means 15'.

[0031] The movable element 13, hereinafter referred to as the piston, is here movable in translation relative to the frame 10, along a direction (Z) perpendicular to the plane (XY) of the figure 2 It preferably comprises a membrane 131 and a stiffening structure 132 for the membrane 131, also called a skeleton or frame. The role of the membrane 131 of the piston 13 is to collect a pressure difference between its two faces across its entire surface, thereby deducing a variation in atmospheric pressure.

[0032] The diaphragm 131 of the piston 13 can partially define a closed volume, called the reference volume, where a reference pressure prevails. It separates this reference volume from a cavity open to the external environment, in this case, air. One face of the diaphragm 131 is therefore subjected to the reference pressure, and the opposite face of the diaphragm 131 is subjected to atmospheric pressure (the variation of which we wish to detect in the case of a microphone). Alternatively, the reference volume can be nearly closed, in the sense that there is a groove around the piston (which is outlined). This groove allows the piston to move and permits air to leak between the reference volume and the outside. This leakage is small so that the pressures can equalize slowly, thus filtering out only low-frequency pressure variations (< 100 Hz).

[0033] The first zone 11 encompasses the cavity open to the external environment, subject to atmospheric pressure, and reference volume subject to reference pressure.

[0034] The capacitive sensing means 15' allow the displacement of the piston 13 to be measured, and therefore the pressure difference between its two faces. In addition to the first and second moving electrodes 151-152, they include at least one fixed electrode (relative to the frame 10), separated from the first moving electrode 151 by a first dielectric medium, and at least one additional fixed electrode, separated from the second moving electrode 152 by a second dielectric medium.

[0035] Each moving electrode and associated fixed electrode(s) form the plates of one or more capacitors whose capacitance varies according to the displacement of the piston 13. The fixed electrodes can also be called "counter electrodes".

[0036] The first dielectric medium and the second dielectric medium are not solid (but preferably made up of a gas or a mixture of gases), so as not to hinder the movement of the mobile electrodes 151. The second dielectric medium is here identical to the first dielectric medium, because the mobile electrodes 151-152 are both located in the second zone 12.

[0037] The second zone 12 is advantageously a chamber under controlled atmosphere to reduce viscous friction and associated acoustic noise. A "chamber under controlled atmosphere" is defined as a chamber under reduced pressure, typically below 10 mbar, and preferably below 1 mbar. Thus, the second zone 12 is subjected to a pressure significantly lower than atmospheric pressure or the reference pressure.

[0038] The first transmission device 14a is mounted to rotate freely relative to the frame 10, by means of several first pivot joints 16a. It comprises a first transmission shaft 144a and first transmission arms 145a.

[0039] The first transmission shaft 144a has a first longitudinal axis of rotation Xa (hereinafter referred to as the first shaft Xa), which extends in a first direction X. In other words, the first transmission shaft 144a can pivot about itself, around the first axis Xa. It extends opposite the piston 13, opposite a zone located between the piston 13 and the first movable electrode 151, and opposite the first movable electrode 151.

[0040] The first movable electrode 151 is fixed to the first transmission shaft 144a, which means that there is no relative movement between the first movable electrode 151 and the first transmission shaft 144a. The first movable electrode 151 is therefore also mounted to rotate freely about the first axis Xa.

[0041] The electromechanical system 2 is thus devoid of motion transformation elements between the first transmission device 14a and the first moving electrode 151, such as torsion blades to convert rotation to translation. As a result, no energy is lost in these transformation elements (for example, through deformation of the torsion blades).

[0042] The first 145a transmission arms, for example two in number on the figure 2 , preferably extend perpendicularly to the first axis Xa, in other words in a second direction Y perpendicular to the first direction X. The first and second directions XY together with a third perpendicular direction Z form an orthogonal frame.

[0043] Each first transmission arm 145a comprises a first end coupled to the piston 13 and a second end fixed to the first transmission shaft 144a. One or more coupling elements 133 (for example, torsion blades) connect the stiffening structure 132 of the piston 13 to the first end of each first transmission arm 145a and allow the transition from a translational motion (piston 13) to a rotational motion (first transmission shaft 144a and first moving electrode 151) while strongly coupling their displacement along the third direction Z. These coupling elements 133 are capable of elastic deformation.

[0044] The translational movement of the piston 13 causes the rotation of the first transmission arms 145a, and therefore of the first transmission shaft 144a, around the first axis Xa. Then, this rotational movement is transmitted to the first moving electrode 151.

[0045] The first pivot joints 16a, for example six in number, are aligned, here in the first direction X. Preferably, one of the first pivot joints 16a is located at the end of the first transmission shaft 144a, on the side of the piston 13 (i.e. opposite the first movable electrode 151), while other first pivot joints 16a are located on the side of the first movable electrode 151. As will be described in detail later, the first movable electrode 151 is preferably connected to the first transmission shaft 144a at the level of these other first pivot joints 16a.

[0046] The second transmission device 14b is also mounted to rotate freely relative to the frame 10 by means of second pivot joints 16b. It is constructed in the same way as the first transmission device 14a. More specifically, it comprises a second transmission shaft 144b having a second longitudinal axis of rotation Xb (hereafter referred to as the second axis Xb) and second transmission arms 145b (for example, two). Each second transmission arm 145b has a first end coupled (via one or more coupling elements 133) to the piston 13 and a second end fixed to the second transmission shaft 144b. The second transmission arms 145b preferably extend perpendicularly to the second axis Xb.

[0047] The second mobile electrode 152 is fixed to the second transmission shaft 144b and therefore rotates around the second axis Xb.

[0048] The second pivot joints 16b are preferably distributed on the second axis Xb in the same way that the first pivot joints 16a are distributed on the first axis Xa (one of them is located at the end of the second transmission shaft 144b and others are located at the level of the second moving electrode 152).

[0049] The first 145a transmission arms are coupled to the first half of the piston 13 (the upper half on the figure 2 ) and the second transmission arms 145b are coupled to a second half of the piston 13 (the lower half on the figure 2 Thus, the transmission devices 14a-14b support the piston 13 and maintain it in translational motion. Preferably, the piston 13 is held only by the first and second transmission arms 145a-145b. Therefore, a greater proportion of the energy collected by the piston 13 is transmitted to the moving electrodes 151-152.

[0050] As illustrated by the figure 2 The first axis Xa and the second axis Xb are advantageously parallel. This helps to reduce the size of the electromechanical system 2 and allows the piston to be supported evenly.

[0051] The first mobile electrode 151 and the second mobile electrode 152 can be identical and arranged symmetrically with respect to a plane P separating the first and second halves of the piston 13. This symmetry makes it possible to obtain an identical reaction on the two halves of the piston so that it remains well in translation.

[0052] The first transmission device 14a and the second transmission device 14b can also be symmetrical with respect to the plane P. The first transmission shaft 144a and the first mobile electrode 151 then pivot in one direction (around the first axis Xa), while the second transmission shaft 144b and the second mobile electrode 152 pivot in the opposite direction (around the second axis Xb).

[0053] Piston 13 may also exhibit symmetry with respect to plane P.

[0054] The symmetries of the piston 13 and the transmission devices 14a-14b allow the energy collected by the piston 13 to be distributed equally between the first mobile electrode 151 and the second mobile electrode 152. Indeed, the mass of the piston 13 is distributed equally between the first and second halves, and therefore between the first and second transmission devices 14a-14b.

[0055] The rotational mounting of the first moving electrode 151 and the second moving electrode 152, respectively along the same axis of rotation as the first transmission device 14a and the second transmission device 14b, allows for a greater displacement of the moving electrodes 151-152 for a given displacement of the piston 13, without increasing the size of the electromechanical system 2. Indeed, the length of the transmission shafts 144a-144b does not affect the amplitude of the displacement of the moving electrodes 151-152. The moving electrodes 151-152 can therefore be positioned as close as possible to the piston 13.

[0056] The passage of a moving electrode ( Fig.1 ) with two mobile electrodes ( Fig.2 ) does not increase the size of the electromechanical system 2 significantly, because the two movable electrodes 151-152 can be arranged opposite each other in the extension of the piston 13. The distance d which separates the movable electrodes 151-152 is for example between 10 µm and 100 µm.

[0057] The displacement of each moving electrode 151, 152 relative to that of the piston 13 is a function of the distance Lpist1, Lpist2 between the first end of the transmission shafts 145a, 145b and the corresponding axis of rotation Xa, Xb. This distance can be of the same order of magnitude as the distance Lelec1, Lelec2 between a longitudinal edge (i.e., along X) of the moving electrode 151, 152 and the axis of rotation Xa, Xb.

[0058] More precisely, the Z-displacement of the longitudinal edge of the first mobile electrode 151 is given by the following relation: d Zelec 1 = L elec 1 L pist 1 × d Zpist Or d Zpist is the Z-displacement of piston 13 (and therefore of all the first ends of the first and second transmission arms 145a-145b), L elec 1 is the distance between the longitudinal edge of the first moving electrode 151 and the first axis Xa and L pist1 is the distance between the first end of each first transmission arm 145a and the first axis Xa.

[0059] The Z-displacement of the longitudinal edge of the second mobile electrode 152 is given by the following relation: d Zelec 2 = L elec 2 L pist 2 × d Zpist Or L elec 2 is the distance between the longitudinal edge of the second moving electrode 152 and the second axis Xb and L pist2 is the distance between the first end of each second transmission arm 14b and the second axis Xb.

[0060] Preferably, the distance L pist1 between the first end of each first transmission arm 145a and the first axis Xa is such that: 1 2 × L elec 1 ≤ l pist 1 ≤ 2 × l elec 1 and the distance L pist2 between the first end of each second transmission arm 14b and the second axis Xb is such that: 1 2 × L elec 2 ≤ L pist 2 ≤ 2 × L elec 2

[0061] The 144a-144b drive shafts and 145a-145b drive arms can be particularly rigid, and therefore relatively insensitive to deformations that result in energy losses. This rigidity of the 144a-144b drive shafts and 145a-145b drive arms can be achieved, in particular, by a significant thickness (measured in the third Z direction), preferably between 5 µm and 800 µm, and more preferably between 50 µm and 200 µm. The 144a-144b drive shafts and 145a-145b drive arms are advantageously formed by etching a silicon substrate. This substrate can be thinned to a thickness between 50 µm and 200 µm. Alternatively, the first elements of the transmission device 14' are formed by an epitaxial layer with a thickness between 5 µm and 40 µm.

[0062] Since the transmission shafts 144a-144b rotate on their own axis, their inertia remains low and does not negatively impact the resonant frequency of the electromechanical system 2. However, they can be perforated, as illustrated in the figure 2 , in order to optimize their stiffness-to-inertia ratio. The transmission shafts 144a-144b are preferably perforated at least in the portion facing piston 13. This also helps to limit damping with piston 13 (a phenomenon called "squeeze film damping"), which is a source of noise.

[0063] The width of the 145a-145b transmission arms (measured in the first X direction) is of the same order of magnitude as their thickness, in order to minimize their inertia. It is advantageously between 5 µm and 800 µm, preferably between 50 µm and 200 µm.

[0064] As illustrated on the figure 2 The transmission shafts 144a-144b can each include a portion offset from their axis of rotation Xa, Xb (and extending parallel to this axis), in order to provide space for the stiffening structure 132 of the piston 13. Part of the stiffening structure 132 can indeed be located on the same side of the diaphragm 131 as the transmission shafts 144a-144b (and formed in the same silicon substrate). The remaining part of the stiffening structure 132 is located on the opposite side of the diaphragm 131.

[0065] The capacitive sensing means 15' will now be described in more detail, referring only to the first moving electrode 151 (connected to the first transmission device 14a). Nevertheless, this description applies mutatis mutandis to the second mobile electrode 152 (connected to the second transmission device 14b), since it can be identical to the first electrode 151. Similarly, the description that will be made of the first pivot joints 16a applies to the second pivot joints 16b.

[0066] With reference to figures 2 And 3 The first electrode 151 may include a membrane 1511 and a stiffening structure 1512 for the membrane 1511. The stiffening structure 1512 preferably comprises a plurality of first beams 1512a extending parallel to each other. It may further include second beams 1512b connecting the first beams 1512a at their ends.

[0067] The first beams 1512a preferably extend in the second Y direction, advantageously from one edge to the opposite edge of the first movable electrode 151. They are advantageously spaced regularly from one another to uniformly stiffen the membrane 1511. The second beams 1512b preferably extend in the first X direction (i.e., perpendicular to the first beams 1512a).

[0068] The first mobile electrode 151 advantageously presents one or more planes of symmetry, for example a plane parallel to the XZ plane (therefore perpendicular to the first beams 1512a) and another plane parallel to the YZ plane.

[0069] The stiffening structure 1512 of the first moving electrode 151 is advantageously anchored, or fused, to the first transmission device 14a at a portion of the first pivot joints 16a. Compared to the microphone 1 of the figure 1 , the electrostatic system 2 is therefore devoid of the second transmission arms 142 extending into the second zone 12.

[0070] More specifically, the stiffening structure 1512 of the first mobile electrode 151 is connected to the first transmission device 14a, and more specifically to the first transmission shaft 144a, by pillars 146 visible on the figures 4A et 4C The pillars 146 of the first transmission device 14a are similar to the transmission shafts 143 of the figure 1 , because they extend partly into the first zone 11 and partly into the second zone 12. Indeed, the sealing between the first zone 11 and the second zone 12 is also carried out at the level of the first pivot joints 16a associated with the first mobile electrode 151.

[0071] The first transmission device 14a is thus reduced to initial elements extending exclusively within the first zone 11 (the first transmission shaft 144a and the first transmission arms 145a) and to secondary elements (the pillars 146) extending partly within the first zone 11 and partly within the second zone 12. This reduction of the first transmission device 14a limits energy losses. In particular, there are no longer any losses due to deformation of the second transmission arms 142.

[0072] The electromechanical system 2 is particularly compact, because several functions, namely the rotation of the first transmission device 14a, the sealing between the two zones 11-12 and the connection to the first moving electrode 151, are carried out in the same place.

[0073] The connection between the stiffening structure 1512 and the first transmission device 14a is preferably achieved using the first beams 1512a. At least some of these beams are fused to the first transmission device 14a, each at a corresponding first pivot joint 16a. The anchor point of each first beam 1512a is advantageously located at mid-length. Thus, the axis of rotation of the first movable electrode 151 lies in one of the planes of symmetry of the first movable electrode 151 (the one perpendicular to the first beams 1512a). The length of the first beams 1512a is measured in the second Y direction, while their width is measured in the first X direction.

[0074] Each first beam 1512a fused with the first transmission device 14a advantageously has a width that decreases with distance from the corresponding first pivot joint 16a. In other words, the width of the first beams 1512a is greatest at the first pivot joints 16a. Thus, the stiffening structure 1512 is most rigid where it is subjected to the greatest mechanical stress, i.e., near the axis of rotation. This helps to reduce energy losses due to deformation, limiting the negative impact on the inertia of the first moving electrode 151 and therefore the resonant frequency of the electromechanical system 2.

[0075] In this first embodiment of the electromechanical system 2, each of the first beams 1512a of the stiffening structure 1512 is fused to the first transmission device 14a. In other words, each first beam 1512a is associated with a first pivot joint 16a. The number of first pivot joints 16a on the side of the first moving electrode 151 is therefore equal to the number of first beams 1512a. This arrangement allows for a space 17 between two successive first pivot joints 16a.

[0076] The frame 10 can include, for each first pivot joint 16a, two distinct first portions 101 arranged on either side of the first beam 1512a associated with the first pivot joint. The first beam 1512a is preferably connected to each of the first portions 101 of the frame 10 by a torsion blade 162 (cf. Fig.3 ).

[0077] As represented by the figures 3 , 4A à 4C The capacitive sensing means 15' preferably comprise two counter electrodes 153-154 associated with the first mobile electrode 151: a first counter electrode 153 called positive and a second counter electrode 154 called negative. Preferably, at least a part of the membrane 1511 of the first mobile electrode 151 is located between the two counter electrodes 153-154 (cf. Figs.4A-4C The first moving electrode 151 and the counter electrodes 153-154 thus form the plates of two capacitors whose capacitances vary in opposite directions. A differential measurement of the displacement of the piston 13 can therefore be obtained. The surfaces of the counter electrodes 153-154 opposite the first moving electrode 151 are advantageously identical, thanks to a symmetry of the first moving electrode 151 and the counter electrodes 153-154 with respect to the first pivot joints 16a (the plane of symmetry coincides with the cutting plane CC).

[0078] Advantageously, each of the counter electrodes 153, 154 comprises a first portion 153a, 154a and a second portion 153b, 154b located on either side of the membrane 1511 and on either side of the first pivot joints 16a. The first portion 153a, 154a, referred to as the upper portion, and the second portion 153b, 154b, referred to as the lower portion, of the same counter electrode are electrically connected. This arrangement makes it possible to obtain a completely differential measurement, even if the distance between the membrane 1511 and the upper portions 153a-154a of the counter electrodes (called the upper air gap) is different from the distance between the membrane 1511 and the lower portions 153a-154a of the counter electrodes (the lower air gap).

[0079] The lower portions 153b-154b of the counter electrodes 153-154 extend under the first beams 1512a of the stiffening structure 1512, on each side of the first pivot joints 16a. In contrast, the upper portions 153a-154a of the counter electrodes 153-154 are preferably each divided into several blocks (or sub-portions) separated by the first beams 1512a, as illustrated by the figure 3 . The upper portions 153a-154a of the counter electrodes 153-154 being inscribed in the stiffening structure 1512, their surface facing the membrane 1511 is less than that of the lower portions 153b-154b.

[0080] Each block of the upper portion 153a of the first counter electrode 153 can be electrically connected to the lower portion 153b of the same counter electrode by a first connector 153c and a first via conductor 153d. Similarly, each block of the upper portion 154a of the second counter electrode 154 can be electrically connected to the lower portion 154b of the same counter electrode by a second connector 154c and a second via conductor 154d.

[0081] The first and second connectors 153c-154c extend advantageously into the space 17 located between two first pivot joints 16a. Thus, the electrical connection of the upper and lower portions of the same counter electrode is simplified and does not increase the size of the capacitive sensing means 15'.

[0082] Alternatively, the different blocks of an upper portion of the counter electrode can be connected directly to each other, for example at the periphery of the first moving electrode 151.

[0083] With reference to figures 4A et 4B The lower portions 153b-154b of the counter electrodes 153-154 are preferably secured to an annular portion 102 of the frame 10, located at the periphery of the first moving electrode 151, by means of annular seals 103, 105 made of an electrically insulating material (one annular seal per lower portion 153b, 154b). These annular seals 103, 105, for example made of silicon oxide, also provide a seal between the first zone 11 and the second zone 12.

[0084] Furthermore, each of the blocks of the upper portions 153a, 154a of the counter electrodes 153-154 can be secured to the underlying lower portion 154b, 153b by means of (at least) two electrically insulating pillars 104, preferably made of the same material as the annular seals 103, 105. The pillars 104 can be separated in pairs by a residual layer 104' made of the same material as the membrane 1511 of the first moving electrode 151, for example, silicon. The thickness of the pillars 104 is then equal to the upper and lower air gaps. Otherwise, there is only one "double" pillar, the thickness of which is equal to the sum of the upper air gap, the lower air gap and the thickness of the membrane 1511. The pillar(s) 104 and the residual layer 104' make it possible to reduce the parasitic capacitances between the upper portions 153a, 154a and the lower portions 153b-154b of the counter electrodes.

[0085] Alternatively, the capacitive detection means 15' may include (for each moving electrode) only one counter electrode (lower or upper), two upper and lower counter electrodes located on only one side of the pivot joints 16 (pseudo-differential detection) or two lower or upper counter electrodes arranged on either side of the pivot joints 16 (differential detection).

[0086] As previously mentioned, the seal between the first and second zones 11-12 of the electromechanical system 2 can be achieved at the first pivot joints 16a located on the side of the first moving electrode 151. As illustrated in the figures 4A et 4C , each first pivot joint 16a associated with the first mobile electrode 151 includes a watertight insulating element 161, capable of elastically deforming under the effect of the rotational displacement of the first transmission device 14a. The watertight insulating element 161 is preferably in the form of a sealing membrane.

[0087] Each watertight insulation element 161 is preferably traversed by an associated pillar 146 of the first transmission device 14a. The watertight insulation element 161 extends for example from the associated pillar 146 to the lower portions 153b-154b of the counter electrodes 153-154 (cf. Fig.4A ) and to the first portions 101 of the building 10 (cf. Fig.4C ), to which it is anchored by means of annular joints 103, 105 made of electrically insulating material.

[0088] Furthermore, each first pivot joint 16a (associated with the first movable electrode 151) advantageously comprises two torsion blades 162 (one per first portion 101 of the frame 10). The torsion blades 162 are dimensioned so as to be able to deform in torsion and allow the rotation of the first transmission device 14a and the first movable electrode 151, while limiting their translational movements, particularly along the third direction Z (so-called "out-of-plane" translation). The two torsion blades 162 connect the stiffening structure 1512 of the first movable electrode 151 (fused to the pillar 146 of the first transmission device 14a) to the first portions 101 of the frame 10 (see also Fig.4C ). They are preferably aligned and arranged diametrically opposite to the first beam 1512a associated with the first pivot joint 16a.

[0089] The first pivot joint 16a located at the end of the first transmission shaft 144a advantageously includes a sealing insulation element 161 (preferably in the form of a membrane) and two torsion blades 162, but does not participate in the sealing between the first and second zones 11-12 (being located only in the first zone 11).

[0090] The electromechanical system 2 includes elastic means connected to the first mobile electrode 151 and configured to generate an elastic force that opposes the movement of the first mobile electrode 151. The role of these elastic means is to counter the collapse phenomenon (called "pull-in" in English) of the first mobile electrode 151. Their stiffness influences the collapse voltage (or "pull-in voltage" of the system), therefore the ability to polarize the first mobile electrode 151, but also the energy losses.

[0091] The elastic "anti-pull-in" means mechanically connect the stiffening structure 1512 of the first moving electrode 151 to the frame 10 and / or to elements attached to the frame, such as the counter electrodes 153-154, possibly via the pillars 146 of the first transmission device 14a. Thus, the stiffness of the first transmission device 14a or the stiffness of the stiffening structure 1511 itself are not considered elastic "anti-pull-in" means.

[0092] The elastic "anti-pull-in" means here include the airtight insulation elements 161 and, where applicable, the torsion blades 162. The airtight insulation elements 161 and the torsion blades 162 thus fulfill several functions simultaneously.

[0093] The anti-pull-in elastic means are connected to the stiffening structure 1512 at its stiffest point, namely at the first pivot joints 16a. Thus, the stiffness of the anti-pull-in elastic means is not degraded by series elements with insufficient stiffness. This stiffness can also be easily controlled by adjusting the dimensions of the watertight insulating elements 161 and the torsion blades 162. The watertight insulating elements 161 can be delimited by anisotropic etching of a sacrificial layer (for example, SiO2) and are formed within a structural layer of controlled thickness. This type of etching allows for precise control of the dimensions of the watertight insulating elements 161. Consequently, the stiffness of the watertight insulating elements 161 exhibits low variability (primarily between different electromechanical systems manufactured on the same wafer or on different wafers).

[0094] The second movable electrode 152 is advantageously connected to the second transmission device 14b in the same way that the first movable electrode 151 is connected to the first transmission device 14a. Thus, the electromechanical system 2 also includes elastic "anti-pull-in" means connected to the second movable electrode 152, these elastic means preferably comprising the watertight insulation elements 161 and, where applicable, the torsion blades 162 of the second pivot joints 16b.

[0095] The sealed insulation elements 161 and, where applicable, the torsion blades 162, advantageously constitute the only "anti-pull-in" means of the electromechanical system 2. Thus, the electromechanical system 2 is particularly compact.

[0096] THE figures 5 And 6 represent a second embodiment of electromechanical system 2. The figure 5 is a bottom view of part of the electromechanical system 2, similar to that of the figure 2 The diaphragm and the stiffening structure of piston 13 are not shown. figure 6 is a top view, similar to that of the figure 3 showing the capacitive sensing means 15' (with the exception of the lower portions of the counter electrodes and the membranes of the moving electrodes under the counter electrodes).

[0097] This second embodiment differs from the first embodiment in the design of the transmission devices 14a-14b and in the design of the capacitive sensing means 15'. The pivot joints 16a-16b are constructed as described in relation to the figures 4A-4C (watertight insulation elements and torsion blades 162).

[0098] The transmission shafts 14a-14b are straight here. The number of first transmission arms 144a or second transmission arms 145b is equal to 3. They are preferably evenly spaced.

[0099] The stiffening structure 1512 of each moving electrode 151, 152 always includes first beams 1512a, but in a greater number than the number of pivot joints 16a, 16b used to anchor the moving electrode 151, 152. Thus, first beams 1512a are not fused with the transmission device 14a, 14b. They extend over the lateral edges (along the second direction Y) of the moving electrode 151, 152 or between two successive pivot joints 16a, 16b.

[0100] The second beams 1512b no longer connect the first beams 1512a at their ends, but closer to the pivot joints 16a, 16b, for example halfway between the axis of rotation Xa, Xb (passing through the torsion blades 162; cf. Fig.6 ) and the longitudinal edge of the mobile electrode 151, 152.

[0101] In addition to increasing the width of the first beams 1512a at the pivot joints 16a,16b (cf. Fig.6 ), or alternatively, oblique beams 1512c are added to the first beams 1512a fused with the transmission device 14a,14b to draw cross braces, which further increases the stiffness of the stiffening structure 1512a at the pivot joints 16 (where it is most stressed).

[0102] The space 17 between two successive joints 16a, 16b is occupied by one or more first beams 1512a (not fused with the transmission device 14a, 14b), which requires modifying the way in which the upper and lower portions of the counter electrodes are connected.

[0103] There figure 6 shows the first and second counter electrodes 153-154 associated with the first mobile electrode 151, and the third and fourth counter electrodes 155-156 associated with the second mobile electrode 152. The third and fourth counter electrodes 155-156 are advantageously arranged in the same way as the first and second counter electrodes 153-154, preferably in the manner described in relation to the figures 3 , 4A-4C In particular, each comprises an upper portion 155a, 156a, composed of different electrically connected blocks, and a lower portion (not visible on the figure 6 ) connected to the upper portion.

[0104] The various blocks of the upper portion 153a of the first counter electrode 153 are electrically connected to each other by a first conductive track 153c' which extends around the periphery of the first movable electrode 151. This first conductive track 153c', called the outer track, runs around the first movable electrode 151 to the first via conductor 153d to connect to the lower portion of the first counter electrode 153, located on the other side of the first pivot joints 16a. Similarly, the various blocks of the upper portion 154a of the second counter electrode 154 are electrically connected to each other by a second conductive track 154c' which extends around the periphery of the first movable electrode 151 to the second via conductor 154b.

[0105] Preferably, the third counter electrode 155 is electrically connected to the second counter electrode 154 so as to be subjected to the same electrical potential. The various blocks of the upper portion 155a of the third counter electrode 155 are advantageously connected to the various blocks of the upper portion 154a of the second counter electrode 154 via the second conductive track 154c'. The blocks of the upper portion 155a of the third counter electrode 155 are advantageously arranged opposite the blocks of the upper portion 154a of the second counter electrode 154. A third conductive track 155c is also connected to the second conductive track 154c' and bypasses the second movable electrode 152. This third conductive track 155c is connected to a third conductor 155d in electrical contact with the lower portion of the third counter electrode 155.

[0106] The fourth counter electrode 156 is preferably electrically connected to the first counter electrode 153 so as to be subjected to the same electrical potential. The various blocks of the upper portion 156a of the fourth counter electrode 156 are advantageously connected to the various blocks of the upper portion 153a of the first counter electrode 153 via the first conductive track 153c' and a fourth conductive track 156c. This fourth conductive track 156c bypasses the second movable electrode 152 and is connected to a fourth conductor 156d, which is in electrical contact with the lower portion of the fourth counter electrode 156.

[0107] The electrical connections between the counter electrodes 153-156 are preferably arranged symmetrically to minimize the bulk of the capacitive sensing means 15'.

[0108] The electromechanical system 2 described above can be manufactured using the processes described in patents FR3059659B1 and FR3114584B1, notably by starting with a stack of layers comprising successively a substrate, a first sacrificial layer, and a first structural layer. The stack can, in particular, be a multilayer structure of the silicon-on-insulator (SOI) type, commonly referred to as an SOI substrate.

[0109] The substrate is used in particular to produce, by etching, the first elements of the transmission devices 14a-14b (transmission shafts 144a-144b and transmission arms 145a-145b), the lower portions of the counter electrodes 153-156 and part of the frame 10. The substrate can be made of a semiconductor material, for example silicon.

[0110] The first structural layer is used, in particular, to form the diaphragm 131 of the piston 13, the diaphragm 1511 of the moving electrodes 151-152, and the watertight insulating elements 161 (sealing membranes). It has a thickness less than that of the substrate, preferably between 100 nm and 10 µm, for example, 1 µm. It is preferably made of the same material as the substrate, for example, silicon.

[0111] The first sacrificial layer is designed to partially disappear during the fabrication of the electromechanical system 2 to free the diaphragm 131 from the piston 13, the diaphragm 1511 from the moving electrodes 151-152, and the sealed insulating elements 161. Its thickness defines, in particular, the distance between the diaphragm 1511 and the lower portions of the counter electrodes 153-156 (lower air gap). This layer also serves as a stop layer during the etching of the substrate, the diaphragm 152a, and the second structural layer (the so-called "MEMS" layer described later). The remaining portions of the first sacrificial layer form the annular seals 103, 105, and the lower pillars 104. The first sacrificial layer can be made of a dielectric material, preferably a silicon nitride or a silicon oxide, for example, silicon dioxide (SiO2). Its thickness, for example, is between 100 nm and 10 µm.

[0112] As described in the aforementioned patents, a second sacrificial layer is deposited on the first structural layer and a second structural layer is formed on the second sacrificial layer, preferably by epitaxy.

[0113] The second structural layer is etched to delineate the stiffening structure 132 of the piston 13, the stiffening structure 1512 of the moving electrodes 151-152, the torsion blades 162, the upper portions of the counter electrodes 153-156, the first portions 101 and the second annular portion 102 of the frame 10. It is advantageously formed of the same material as the first structural layer, for example, silicon. The thickness of the second structural layer is preferably between 5 µm and 50 µm, for example, 20 µm.

[0114] The stiffening structure 1512 of each mobile electrode 151, 152 is fused to the corresponding transmission device 14a, 14b by growing the second structural layer directly from the substrate at the pivot joints 16a, 16b (the first and second sacrificial layers having been opened beforehand). The pillars 146 of the transmission devices 14a, 14b are formed during this growth by epitaxy.

[0115] The second sacrificial layer serves, in particular, as a stop layer during the etching of the second structural layer. It is partially removed to free the diaphragm 131 from the piston 13, the diaphragm 1511 from the moving electrodes 151-152, and the airtight insulating elements 161. Its thickness defines the distance between the diaphragm 1511 and the upper portions of the counter electrodes 153-156 (upper air gap). The second sacrificial layer is advantageously made of the same dielectric material as the first sacrificial layer, for example, a silicon oxide. Its thickness can range from 100 nm to 10 µm.

[0116] The electromechanical system 2 does not necessarily include the two moving electrodes 151-152 and the two transmission devices 154a-154b. It may include a single moving electrode and a single transmission device (cf. Figs.7-9 ), or a single moving electrode and two transmission devices connected to this single moving electrode (cf. Fig.10 ).

[0117] There figure 7 represents a third embodiment in which the electromechanical system 2 comprises, in addition to the piston 13, a single movable electrode 151 (for example of the type represented by the figure 2 ) and a single transmission device 14a (for example of the type represented by the figure 2 ).

[0118] The piston 13 is again free to move in translation. It can be sufficiently balanced to be held in translation by the single transmission device 14a. The first ends of the transmission arms 145a of the transmission device 14a are preferably coupled to the piston 13 at points located on the midline of the piston 13 (i.e., the line separating the two halves of the piston). Alternatively, the piston 13 can be guided in translation by means other than the single transmission device 14a (particularly when it is not sufficiently balanced).

[0119] In a fourth embodiment represented by the figure 8 The electromechanical system 2 again comprises only one movable electrode 151 and only one transmission device 14a, but the piston 13 is movable in rotation around an axis Xp (and not in translation), thanks to pivot joints or hinges (not shown) distinct from the first pivot joints 16a. The rotational movement of the piston 13 (around the axis Xp) causes the transmission shaft 144a of the transmission device 14a to rotate (around its own axis Xa), via the transmission arms 145a, and the transmission shaft 144a sets the movable electrode 151 in motion (here in rotation around the axis Xa).

[0120] There figure 9 This illustrates a fifth embodiment of the electromechanical system 2, which differs from the fourth embodiment in that the single movable electrode 151 rotates about an axis Xe distinct from the longitudinal axis of rotation Xa of the transmission shaft. The rotational movement of the movable electrode 151 is therefore not the same as the rotational movement of the transmission shaft 144a, which is also not the same as the rotational movement of the piston 13. The axis of rotation Xp of the piston 13 and the axis of rotation Xe of the movable electrode 151 are not necessarily the same.

[0121] Thus, in this fifth embodiment (and unlike the previous embodiments), the movable electrode 151 is not rigidly connected to the transmission shaft 144a, but via coupling elements 147 (for example, torsion blades) allowing it to switch from one rotation to another. These coupling elements 147 connect, for example, beams 148 (similar to the first beams 1512a) fixed to the transmission shaft 144a to the stiffening structure of the movable electrode 151.

[0122] In a sixth embodiment represented by the figure 10 The electromechanical system 2 comprises only one moving electrode 151 but two transmission devices 14a-14b (for example, those represented by the figure 2 The piston 13 is in translation (along Z), as in the first, second, and third embodiments, and the movable electrode 151 is in translation (along Z), rather than in rotation. The transmission devices 14a-14b extend on either side of the movable electrode 151. The movable electrode 151 is connected to the transmission shaft 144a, 144b of each of the transmission devices 14a-14b via coupling elements 147 (for example, torsion blades) allowing the transition from rotation to translation and beams 148. The two transmission shafts 144a-144b rotate in opposite directions, so as to raise or lower the movable electrode 151.

[0123] The electromechanical system 2 according to the invention is not limited to the embodiments described in relation to the figures 2 à 10 and many variations and modifications of the electromechanical system will become apparent to the person skilled in the art.

[0124] The 144a-144b drive shafts can adopt other geometries. The number of 145a and 145b drive arms can be greater than 3.

[0125] The electromechanical system 2 may also include, for each transmission device 14a, 14b, one or more additional pivot joints, not shown in the figures, between the one located at the end of the transmission shaft 144a, 144b and those connecting the moving electrode 151, 152. These additional pivot joints are preferably located in the first zone 11 and therefore do not participate in the sealing between the two zones.

[0126] Conversely, it may only have two pivot joints per transmission device 14a, 14b, one at the level of the mobile electrode 151, 152, the other at the end of the transmission shaft 144a, 144b.

[0127] The electromechanical system 2 was described using as an example a capacitive sensing microphone comprising a piston 13 with a diaphragm 131 subjected on one side to atmospheric pressure and on the other to a reference pressure. However, the electromechanical system can form other types of capacitive sensing transducers, notably a loudspeaker (sound emitter) or an ultrasonic emitter (which are electroacoustic transducers), or even a differential pressure sensor.

[0128] In the case of a differential pressure sensor, the first face of the diaphragm 131 is subjected to a first pressure (not necessarily atmospheric pressure), and the second face of the diaphragm 131 is subjected to a second pressure, different from the first. The displacement of the diaphragm 131, under the effect of the pressure difference, is measured by the capacitive sensing means 15'. The diaphragm 131 of the piston is fixed to the frame 10 so as to be sealed, and the piston stiffening structure 132 is absent or reduced so as not to anchor it to the frame.

[0129] In the case of a loudspeaker or ultrasonic transmitter, capacitive actuation means replace the capacitive sensing means 15'. These capacitive actuation means also include two movable electrodes and at least one counter electrode per movable electrode. The movable electrodes are set in motion by an electrostatic force, and this motion is transmitted by the transmission devices 14a, 14b to the piston 13. The movement of the diaphragm 131 of the piston 13 enables the emission of sound (or ultrasound).

[0130] The second zone 12 may include two chambers under controlled atmosphere, one containing the first mobile electrode 151, the other containing the second mobile electrode 152.

[0131] The first and second zones 11-12, which are hermetically sealed, are not necessarily subjected to different pressures. The first zone 11 can also be an aggressive environment, and the moving electrodes of the capacitive means (for sensing or actuation) are placed in the second zone 12 to protect them from this aggressive environment (in addition to reducing viscous friction, and therefore acoustic noise).

[0132] The electromechanical system 2 may even lack sealing means between the first and second zones 11-12 (which amounts to considering only a single zone). More specifically, the pivot joints 16 may lack a watertight insulating element 161. Indeed, the torsion blades 162 may suffice for the rotation of the transmission device 14' and as elastic "anti-pull-in" means.

Claims

1. Electromechanical system (2) comprising: - a frame (10); - an element (13) movable relative to the frame (10); - capacitive measurement or actuation means (15') comprising: ∘ a first electrode (151) movable relative to the frame (10); and ∘ at least one electrode (153, 154) fixed relative to the frame (10) and separated from the first movable electrode (151) by a first dielectric medium; - a first transmission device (14a) for transmitting movement between the movable element (13) and the first movable electrode (151), the first transmission device (14a) being rotatably movable relative to the frame (10) by means of a plurality of first pivot hinges (16a); wherein the first transmission device (14a) comprises: - a first transmission shaft (144a) having a first longitudinal axis of rotation (Xa); and - a plurality of first transmission arms (145a), each of the first transmission arms (145a) comprising a first end coupled to the movable element (13) and a second end secured to the first transmission shaft (144a); and wherein the first movable electrode (151) is connected to the first transmission shaft (144a).

2. System (2) according to claim 1, wherein the first movable electrode (151) is secured to the first transmission shaft (144a), whereby the first movable electrode (151) is rotatably mounted about the first longitudinal axis of rotation (Xa).

3. System (2) according to one of claims 1 and 2, wherein the capacitive measurement or actuation means (15') further comprise: - a second electrode (152) movable relative to the frame (10); and - at least one additional electrode (155, 156) fixed relative to the frame (10) and separated from the second movable electrode (152) by a second dielectric medium; the system further comprising a second transmission device (14b) for transmitting movement between the movable element (13) and the second movable electrode (152), the second transmission device (14b) being rotatably movable relative to the frame (10) by means of a plurality of second pivot hinges (16b) and comprising: - a second transmission shaft (144b) having a second longitudinal axis of rotation (Xb); and - a plurality of second transmission arms (145b), each of the second transmission arms (145) comprising a first end coupled to the movable element (13) and a second end secured to the second transmission shaft (144b); in which system the second movable electrode (152) is connected to the second transmission shaft (144b).

4. System (2) according to claim 3, wherein the second movable electrode (152) is secured to the second transmission shaft (144b), whereby the second movable electrode (152) is rotatably movably mounted about the second longitudinal axis of rotation (Xb).

5. System (2) according to one of claims 3 and 4, wherein the first longitudinal axis of rotation (Xa) is parallel to the second longitudinal axis of rotation (Xb).

6. System (2) according to any of claims 3 to 5, wherein the first end of the first transmission arms (145a) is coupled to a first half of the movable element (13) and wherein the first end of the second transmission arms (145b) is coupled to a second half of the movable element (13).

7. System (2) according to claim 6, wherein the first movable electrode (151) and the second movable electrode (152) are symmetrical with respect to a plane (P) separating the first and second halves of the movable element (13).

8. System (2) according to claim 7, wherein the first transmission device (14a) and the second transmission device (14b) are symmetrical with respect to the plane (P) separating the first and second halves of the movable element (13).

9. System (2) according to any of claims 1 to 8, wherein at least one of the first pivot hinges (16a) is located at the first movable electrode (151) and another of the first pivot hinges (16a) is located at an end of the first transmission shaft (145a), opposite to the first movable electrode (151).

10. System (2) according to any of claims 1 to 9, wherein the first transmission arms (145a) extend perpendicularly to the first longitudinal axis of rotation (Xa).

11. System (2) according to any of claims 1 to 10, wherein the first end of each first transmission arm (145a) is located at a distance Lpist1 from the first longitudinal axis of rotation (Xa) such that: 1 2 × L elec 1 ≤ L pist 1 ≤ 2 × L elec where Lelec1 is the distance between a longitudinal edge of the first movable electrode (151) and the first longitudinal axis of rotation (Xa).

12. System (2) according to any of claims 1 to 11, wherein at least one part of the first transmission shaft (144a) located facing the movable element (13) is perforated.

13. System (2) according to any of claims 1 to 12, wherein the movable element (13) is in contact with a first zone (11) and the first movable electrode (151) is located in a second zone (12) sealingly insulated from the first zone (11).

14. System (2) according to claim 13, wherein the first transmission shaft (144a) and the first transmission arms (145a) extend into the first zone (11) and wherein the first transmission device (14a) further comprises pillars (146) extending partly into the first zone (11) and partly into the second zone (12).

15. System (2) according to any of claims 1 to 14, wherein the first transmission shaft (144a) and the first transmission arms (145a) have a thickness between 5 µm and 800 µm, preferably between 50 µm and 200 µm.

16. System (2) according to any of claims 1 to 15, wherein: - the first movable electrode (151) comprises a membrane (1511) and a membrane rigidifying structure (1512); - the rigidifying structure (1512) of the first movable electrode (151) is anchored to the first transmission device (14a) at a part of the first pivot hinges (16a).

17. System (2) according to claim 16, wherein the rigidifying structure (1512) of the first movable electrode (151) comprises a plurality of beams (1512a) extending in parallel to each other and wherein at least one part of the beams (1512a) are anchored to the first transmission device (14a), each beam of said at least one part being anchored to a first pivot hinge (16a) corresponding to said beam.

18. System (2) according to any of claims 1 to 17, wherein the capacitive measurement or actuation means (15') comprise first and second fixed electrodes (153, 154) associated with the first movable electrode (151), the first movable electrode (151) comprising a membrane (1511) disposed between the first and second fixed electrodes (153, 154).