ELECTROMECHANICAL SYSTEM COMPRISING CAPABILITIES FOR MEASURING OR ACTUATING AND A TRANSMISSION SHAFT

Abstract

ELECTROMECHANICAL SYSTEM COMPRISING CAPACITIVE MEASUREMENT OR ACTUATION MEANS AND A TRANSMISSION SHAFT The invention relates to an electromechanical system (2) comprising: a frame (10); a movable element (13); capacitive measurement or actuation means (15') comprising: a first movable electrode (151); and at least one fixed electrode separated from the first movable electrode by a first dielectric medium; a first transmission device (14a) for a movement between the movable element (13) and the first movable electrode (151), the first transmission device (14a) being rotationally movable relative to the frame (10) by means of a plurality of first pivot joints (16a); the first transmission device (14a) comprising: 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 moving element (13) and a second end fixed to the first transmission shaft (144a); the first moving electrode (151) being connected to the first transmission shaft (144a). Figure to be published with the abbreviation: Figure 2;

Description

Title of the invention: ELECTROMECHANICAL SYSTEM COMPRISING CAPACITIVE MEASURING MEANS OR ACTUATING AND A TRANSMISSION SHAFT TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of electromechanical systems, in particular of the microelectromechanical system (MEMS) type. "microelectromechanical Systems" in English) or nanoelectromechanical system (NEMS, for "nanoelectromechanical System"). The invention relates more particularly to an electromechanical system comprising a mobile element, capacitive measuring or actuation means and a device for transmitting a movement between the mobile element and the capacitive measuring or actuation means. Such a system can be used as an electroacoustic transducer (e.g. microphone, loudspeaker, etc.) or differential pressure sensor. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] Microelectromechanical or nanoelectromechanical microphones represent a rapidly expanding market, particularly thanks to the development of portable devices, such as tablets, smart mobile phones (smartphones) and other connected objects, in which they are gradually replacing electret microphones.

[0003] Microphones measure a rapid variation 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 currently manufactured are capacitive sensing microphones. [Fig.l] shows an example of a capacitive sensing microphone 1, described in patent FR3114584B1.

[0005] The microphone 1 comprises 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 device 14 for transmitting 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 movable element 13, also called a piston, is in contact with the first zone 11. It comprises a membrane 131 and a stiffening structure 132 of the membrane. The membrane 131 of the piston 13 has the role of collecting over its entire surface a pressure difference between its two faces, to deduce therefrom a variation in atmospheric pressure. One face of the membrane 131 is subjected to atmospheric pressure (of which we wish to detect the variation) and an opposite face of the membrane 131 is subjected to a reference pressure.

[0007] Furthermore, the microphone 1 comprises capacitive detection means 15 arranged in the second zone 12. These capacitive detection means 15 make it possible to measure the displacement of the piston 13, and therefore the pressure difference between its two faces. They preferably comprise a movable electrode 151 and at least one fixed electrode arranged opposite the movable electrode 151. The electrodes form the armatures of a capacitor whose capacitance varies as a function of the displacement of the piston 13.

[0008] The transmission device 14 is mounted to be movable in rotation relative to the frame, by means of several pivot joints 16. The transmission device 14 comprises two first transmission arms 141 extending in the first zone 11, two second transmission arms 142 extending in the second zone 12 and two transmission shafts 143 extending partly in the first zone 11 and partly in 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 movable electrode 151 of the capacitive detection means 15 and a second opposite end, coupled to the associated transmission shaft 143.

[0010] Patent FR3059659B1 describes a capacitive detection microphone similar to that of [Fig.l]. The capacitive detection means comprise a movable electrode and two fixed electrodes between which the movable electrode is arranged. The electrodes form the armatures of two capacitors whose capacitances vary in opposite directions depending on the displacement of the piston. The measurement of the displacement of the piston is then a differential measurement.

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

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

[0013] Furthermore, these capacitive detection microphones can become faulty due to a phenomenon of collapse of the mobile electrode, called "pull-in" in English and common to all electromechanical systems comprising capacitive measuring or actuation means. This collapse phenomenon is caused by the electrostatic force, which tends to bring the mobile electrode closer to the fixed electrode (or one of the fixed electrodes) and which depends on the square of the polarization voltage. The electrostatic force, which also depends on the displacement of the mobile electrode, can be approximated to the first order by a constant force plus the force exerted by a spring of negative stiffness for small displacements.

[0014] To avoid (up to a certain extent) this collapse phenomenon, an elastic force is opposed to the electrostatic force. This elastic force can be generated by springs connecting the frame of the movable electrode 151 to the frame of the microphone 1. The greater the stiffness of the springs, the greater the voltage value at which the electrostatic force overcomes the elastic force (the so-called pull-in voltage) and the higher the movable electrode 151 can be biased to a high voltage. This is advantageous because the sensitivity of the microphone 1 increases with the bias voltage.

[0015] The sensitivity of the microphone 1 further increases with the displacement of the movable electrode 151. One solution for increasing the displacement of the movable 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 is desired to be at least equal to 35 kHz). Another solution consists of reducing the length of the first transmission arms 141 and / or increasing the length of the second transmission arms 142, thus increasing the lever arm effect. However, it is difficult to reduce the length of the first transmission arms 141, because there is a sealing zone around the capacitive detection means 15 to enclose them in the second zone 12 and because this would involve reducing the surface area of ​​the piston 13. Increasing the length of the second transmission arms 142 is easier, but considerably increases the size of the microphone.Furthermore, simply increasing the length of the second transmission arms 142 makes them more easily deformable, which ultimately reduces the displacement of the movable electrode and decreases the sensitivity. Summary of the invention

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

[0017] According to the invention, this need is tended to be satisfied by providing an electro- mechanics including: • a frame; • a movable element relative to the frame; • capacitive measuring or actuation means 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 mobile element and the first mobile electrode, the first transmission device being mobile in rotation 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 movable element and a second end secured to the first transmission shaft; the first movable electrode being connected to the first transmission shaft.

[0018] Thus, when the mobile element moves, it rotates the first transmission device around the first longitudinal axis which itself sets the first mobile electrode in motion. This assembly makes it possible to obtain a greater displacement of the mobile electrode for a given displacement of the mobile element, without however increasing the size of the electromechanical system, because the displacement of the mobile electrode is now decorrelated from the distance between the mobile element and the mobile 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 presents a better compromise between sensitivity and compactness than the microphone of the prior art.

[0019] Advantageously, the first mobile electrode is integral with the first transmission shaft, from which it follows that the first mobile electrode is mounted mobile in rotation around the first longitudinal axis of rotation.

[0020] In a preferred embodiment: • the capacitive measuring or actuation means further comprise: • a second electrode movable relative to the frame; and • at least one additional electrode fixed relative to the frame and separated from the second mobile electrode by a second dielectric medium; • the system further comprises a second device for transmitting a movement between the mobile element and the second mobile electrode, the second transmission device being mobile in rotation 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 secured 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 movable electrode is integral with the second transmission shaft, from which it follows that the second movable electrode is mounted movable in rotation around the second longitudinal axis of rotation.

[0022] According to another development compatible 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 movable element and the first end of the second transmission arms is coupled to a second half of the movable element.

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

[0025] In addition to the characteristics which have just been mentioned in the preceding paragraphs, the electromechanical system according to the invention may have one or more complementary characteristics among the following, considered individually or according to all technically possible combinations: • the mobile element is in translation relative to the frame; • the moving element is rotating relative to the frame; • at least one of the first pivot joints is located at the first movable electrode and another of the first pivot joints is located at one end of the first transmission shaft, opposite the first movable electrode; • at least one of the second pivot joints is located at the second movable electrode and another of the second pivot joints is located at one end of the second transmission shaft, opposite the second movable electrode; the first transmission arms extend perpendicular to the first longitudinal axis of rotation; the second transmission arms extend perpendicular to the second longitudinal axis of rotation; the first longitudinal axis of rotation is parallel to the second longitudinal axis of rotation; the first movable electrode and the second movable electrode are symmetrical with respect to a plane separating the first and second halves of the movable 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 movable element; the first end of each first transmission arm is located at a distance Lpisti from the first longitudinal axis of rotation such that: 4 XL , , <L^i<2xL, ,, où est la distance entre un bord Ion- longitudinal axis of the first movable electrode and the first longitudinal axis of rotation; the first end of each second transmission arm is located at a distance Lpist2 from the second longitudinal axis of rotation such that: 2 v J , ,< / where L i 2 is the distance between a long edge- longitudinal axis of the second movable electrode and the second longitudinal axis of rotation; at least a portion of the first transmission shaft located opposite the mobile element is perforated; at least a portion of the second transmission shaft located opposite the mobile element is perforated; the first transmission shaft and the first transmission arms extend in the first area and the first transmission device further comprises pillars extending partly in the first area and partly in the second area; the second transmission shaft and the second transmission arms extend in the first zone and the second transmission device further comprises pillars extending partly in the first zone and partly in 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 pm and 200 pm; the second transmission shaft and the second transmission arms have a thickness of between 5 pm and 800 pm, preferably between 50 pm and 200 pm; the first movable electrode comprises a membrane and a membrane stiffening structure; the stiffening structure of the first mobile electrode is anchored to the first transmission device at a portion of the first pivot joints; the stiffening structure of the first mobile electrode comprises a plurality of beams extending parallel to each other and at least part of the beams are anchored to the first transmission device, each beam of said at least one part being anchored at a first pivot joint corresponding to said beam; each first pivot joint of said at least one part comprises a sealed insulation element capable of deforming elastically and ensuring sealing between the first zone and the second zone; the second movable electrode comprises a membrane and a membrane stiffening structure; the stiffening structure of the second mobile electrode is anchored to the second transmission device at a portion of the second pivot joints; the stiffening structure of the second mobile electrode comprises a plurality of beams extending parallel to each other and at least 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 comprises a sealed insulation element capable of deforming elastically and ensuring sealing between the first zone and the second zone; the capacitive measuring or actuation means comprise first and second fixed electrodes associated with the first mobile electrode, the first mobile electrode comprising a membrane arranged between the first and second fixed electrodes; each of the first and second fixed electrodes comprises a first portion and a second portion located 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 mobile electrode, the second mobile electrode comprising a membrane arranged between the third and fourth fixed electrodes; and • each of the third and fourth fixed electrodes comprises a first portion and a second portion located on either side of the membrane and on either side of the second pivot joints, the first and second portions being electrically connected. BRIEF DESCRIPTION OF THE FIGURES

[0026] Other characteristics and advantages of the invention will emerge clearly from the description given below, for information purposes only and in no way limiting, with reference to the appended figures, among which: • [Fig.l] is a partial perspective view of a capacitive detection microphone according to the prior art; • [Fig.2] is a partial bottom view of an electromechanical system according to a first embodiment of the invention, this electromechanical system comprising capacitive detection or actuation means; • [Fig.3] is a partial top view of the capacitive detection or actuation means of the electromechanical system of [Fig.2]; • [Fig.4A] is a sectional view of the electromechanical system according to section plane AA of [Fig.3]; • [Fig.4B] is a sectional view of the electromechanical system along section plane BB of [Fig.3]; • [Fig.4C] is a sectional view of the electromechanical system according to section plane CC of [Fig.3]; • [Fig.5] is a partial bottom view of an electromechanical system according to a second embodiment of the invention; • [Fig.6] is a top view of the capacitive means of detection or actuation of the electromechanical system of [Fig.5]; • [Fig.7] is a partial bottom view of an electromechanical system according to a third embodiment of the invention; • [Fig.8] is a partial bottom view of an electromechanical system according to a fourth embodiment of the invention; • [Fig.9] is a partial bottom view of an electromechanical system according to a fifth embodiment of the invention; and • [Fig. 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 signs throughout the figures. DETAILED DESCRIPTION

[0028] Figures 2, 3 and 4A to 4C represent a part of an electromechanical system 2 with capacitive detection 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 microphone with capacitive detection will be taken.

[0029] The electromechanical system 2 comprises: • a frame 10; • a mobile 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 sealed from the first zone 11; and • a first device 14a for transmitting a movement between the mobile element 13 and the first mobile electrode 151 (in other words between the first zone 11 and the second zone 12); and • a second device 14b for transmitting a movement between the mobile element 13 and the second mobile electrode 152.

[0030] [Fig. 2] is a bottom view of the electromechanical system 2 showing first portions 101 of the frame 10, the movable element 13, the transmission devices 14a-14b and the movable electrodes 151-152 of the capacitive detection means 15'. [Fig. 3] is a top view showing only a portion of the capacitive detection means 15' (including the first movable electrode 151). Figures 4A to 4C are different sectional views of the electromechanical system 2, respectively along the section planes AA, BB and CC shown in [Fig. 3]. They partly show the frame 10, the first transmission device 14a and the capacitive detection means 15'.

[0031] The movable element 13, hereinafter called the piston, is here movable in translation relative to the frame 10, in a direction (Z) perpendicular to the plane (XY) of [Fig.2]. It preferably comprises a membrane 131 and a stiffening structure 132 of the membrane 131, also called a skeleton or armature. The membrane 131 of the piston 13 here has the role of collecting over its entire surface a pressure difference between its two faces, to deduce therefrom a variation in atmospheric pressure.

[0032] The membrane 131 of the piston 13 may partly delimit a closed volume called a reference volume, where a reference pressure prevails. It separates this reference volume from a cavity open to the external environment, here the air. One face of the membrane 131 is therefore subjected to the reference pressure and an opposite face of the membrane 131 is subjected to atmospheric pressure (the variation of which is to be detected in the case of a microphone). Alternatively, the reference volume may be quasi-closed, in the sense that there is a trench around the piston (which is cut out). This trench allows the piston to move and allows air to leak between the reference volume and the outside. This leak is small so that the pressures can equalize slowly, so as to filter only low-frequency pressure variations (< 100 Hz).

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

[0034] The capacitive detection means 15' make it possible to measure the displacement of the piston 13, and therefore the pressure difference between its two faces. In addition to the first and second mobile electrodes 151-152, they comprise at least one fixed electrode (relative to the frame 10), separated from the first mobile electrode 151 by a first dielectric medium, and at least one additional fixed electrode, separated from the second mobile electrode 152 by a second dielectric medium.

[0035] Each mobile electrode and associated fixed electrode(s) form the armatures of one or more capacitors whose capacitance varies according to the movement 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 constituted by 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 a controlled atmosphere to reduce viscous friction phenomena and associated acoustic noise. By “chamber under a controlled atmosphere” is meant a chamber under a reduced pressure, typically less than 10 mbar, and preferably less than 1 mbar. Thus, the second zone 12 is here subjected to a pressure well below atmospheric pressure or the reference pressure.

[0038] The first transmission device 14a is mounted to be able to rotate 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 on itself, around the first axis Xa. It extends opposite the piston 13, opposite an area 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 integral with 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 be movable in rotation about the first axis Xa.

[0041] The electromechanical system 2 is thus devoid of members for transforming the movement between the first transmission device 14a and the first mobile electrode 151, such as torsion blades for switching from rotation to translation. As a result, no energy is lost in these transformation members (for example, by deformation of the torsion blades).

[0042] The first transmission arms 145a, for example two in number in [Fig.2], preferably extend perpendicular 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 constitute with a third perpendicular direction Z an orthogonal reference frame.

[0043] Each first transmission arm 145a comprises a first end coupled to the piston 13 and a second end secured 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 movement (piston 13) to a rotational movement (first transmission shaft 144a and first mobile electrode 151) while strongly coupling their movement in the third direction Z. These coupling elements 133 are capable of deforming elastically.

[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 mobile 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 mobile electrode 151), while other first pivot joints 16a are located on the side of the first mobile electrode 151. As will be described in detail later, the first mobile electrode 151 is preferably connected to the first transmission shaft 144a at these other first pivot joints 16a.

[0046] The second transmission device 14b is also mounted to be able to rotate 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 particularly, it comprises a second transmission shaft 144b having a second longitudinal axis of rotation Xb (hereinafter referred to as the second axis Xb) and second transmission arms 145b (for example two). Each second transmission arm 145b comprises a first end coupled (via one or more coupling elements 133) to the piston 13 and a second end secured to the second transmission shaft 144b. The second transmission arms 145b preferably extend perpendicular to the second axis Xb.

[0047] The second mobile electrode 152 is integral with 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 as 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 mobile electrode 152).

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

[0050] As illustrated by [Fig.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 makes it possible to support the piston in a homogeneous manner.

[0051] The first mobile electrode 151 and the second mobile electrode 152 may 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 the latter 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 movable electrode 151 then pivot in one direction (around the first axis Xa), while the second transmission shaft 144b and the second movable electrode 152 pivot in the opposite direction (around the second axis Xb).

[0053] The piston 13 may also have symmetry with respect to the plane P.

[0054] The symmetries of the piston 13 and the transmission devices 14a-14b make it possible to distribute the energy collected by the piston 13 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 movable electrode 151 and the second movable electrode 152, respectively along the same axis of rotation as the first transmission device 14a and the second transmission device 14b, makes it possible to obtain a greater displacement of the movable electrodes 151-152 for a given displacement of the piston 13, without however increasing the size of the electromechanical system 2. Indeed, the length of the transmission shafts 144a-144b does not influence the amplitude of the displacement of the movable electrodes 151-152. The movable electrodes 151-152 can therefore be brought as close as possible to the piston 13.

[0056] The transition from one mobile electrode ([Fig.l]) to two mobile electrodes ([Fig.2]) also does not significantly increase the size of the electromechanical system 2, since the two mobile electrodes 151-152 can be arranged opposite each other in the extension of the piston 13. The distance d which separates the mobile electrodes 151-152 is for example between 10 μm and 100 μm.

[0057] The displacement of each movable electrode 151, 152 relative to that of the piston 13 is a function of the distance Lpisti, Lpist2 between the first end of the transmission shafts 145a, 145b and the corresponding axis of rotation Xa, Xb. This distance may be of the same order of magnitude as the distance Leieci, Leiec2 between a longitudinal edge (i.e. along X) of the movable electrode 151, 152 and the axis of rotation Xa, Xb.

[0058] More precisely, the displacement in Z of the longitudinal edge of the first mobile electrode 151 is given by the following relation:

[0059] [Math.l]

[0060] where d^pist is the Z displacement of the piston 13 (and therefore of all the first ends of the first and second transmission arms 145a-145b), Leleci is the distance between the longitudinal edge of the first mobile electrode 151 and the first axis Xa and Lpisti is the distance between the first end of each first transmission arm 145a and the first axis Xa.

[0061] The displacement in Z of the longitudinal edge of the second mobile electrode 152 is given by the following relation:

[0062] [Math.2] dzelecl = X dZpût

[0063] where Lelec2 is the distance between the longitudinal edge of the second movable electrode 152 and the second axis Xb and Lpist2 is the distance between the first end of each second transmission arm 14b and the second axis Xb.

[0064] Preferably, the distance Lpisti between the first end of each first transmission arm 145a and the first axis Xa is such that:

[0065] [Math.3] 2 X ^eleci — ^pisti 4 2 X leicc\

[0066] and the distance Lpist2 between the first end of each second transmission arm 14b and the second axis Xb is such that:

[0067] [Math.4] i X ^elec2 - Lpistl

[0068] The transmission shafts 144a-144b and the transmission arms 145a-145b may be particularly rigid, and therefore not very sensitive to deformations which are equivalent to energy losses. This rigidity of the transmission shafts 144a-144b and the transmission arms 145a-145b may in particular be provided by a significant thickness (measured in the third direction Z), preferably between 5 μm and 800 μm, and more preferably between 50 μm and 200 μm. The transmission shafts 144a-144b and the transmission arms 145a-145b are advantageously formed by etching a silicon substrate. This substrate may 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 of between 5 pm and 40 pm.

[0069] As the transmission shafts 144a-144b rotate on themselves, their inertia remains low and does not negatively impact the resonance frequency of the electromechanical system 2. However, they can be perforated, as illustrated in [Fig.2], in order to optimize their stiffness to inertia ratio. The transmission shafts 144a-144b are preferably perforated at least in the portion located opposite the piston 13. This also makes it possible to limit the damping with the piston 13 (a phenomenon called “squeeze film damping” in English), which is a source of noise.

[0070] The width of the transmission arms 145a-145b (measured in the first direction X) 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 pm.

[0071] As illustrated in [Fig.2], the transmission shafts 144a-144b may each comprise a portion offset from their axis of rotation Xa, Xb (and which extends parallel to this axis), in order to provide space for the stiffening structure 132 of the piston 13. A portion of the stiffening structure 132 may in fact be located on the same side of the membrane 131 as the transmission shafts 144a-144b (and formed in the same silicon substrate). The remaining portion of the stiffening structure 132 is located on the opposite side of the membrane 131.

[0072] The capacitive detection means 15' will now be described in more detail, with reference only to the first movable electrode 151 (connected to the first transmission device 14a). However, this description applies mutatis mutandis to the second movable electrode 152 (connected to the second transmission device 14b), since it may 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.

[0073] With reference to Figures 2 and 3, the first electrode 151 may comprise a membrane 1511 and a stiffening structure 1512 of the membrane 1511. The stiffening structure 1512 preferably comprises a plurality of first beams 1512a extending parallel to each other. It may further comprise second beams 1512b connecting the first beams 1512a at their ends.

[0074] The first beams 1512a preferably extend in the second direction Y, advantageously from a first edge to a second opposite edge of the first mobile electrode 151. They are advantageously spaced regularly from each other, to stiffen the membrane 1511 uniformly. The second beams 1512b preferably extend in the first direction X (therefore perpendicular to the first beams 1512a).

[0075] The first mobile electrode 151 advantageously has 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.

[0076] The stiffening structure 1512 of the first mobile 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 [Fig.l], the electrostatic system 2 is therefore devoid of the second transmission arms 142 extending in the second zone 12.

[0077] More particularly, the stiffening structure 1512 of the first mobile electrode 151 is connected to the first transmission device 14a, and more particularly to the first transmission shaft 144a, by pillars 146 visible on the Figures 4A and 4C. The pillars 146 of the first transmission device 14a are similar to the transmission shafts 143 of [Fig.l], because they extend partly in the first zone 11 and partly in 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.

[0078] The first transmission device 14a is thus reduced to first elements extending exclusively in the first zone 11 (the first transmission shaft 144a and the first transmission arms 145a) and to second elements (the pillars 146) which extend partly in the first zone 11 and partly in the second zone 12. This reduction of the first transmission device 14a makes it possible to limit energy losses. In particular, there are no longer any losses due to deformation of the second transmission arms 142.

[0079] 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 mobile electrode 151, are carried out at the same location.

[0080] The anchoring between the stiffening structure 1512 and the first transmission device 14a is preferably achieved by means of the first beams 1512a. At least a portion of them are fused to the first transmission device 14a, each at a corresponding first pivot joint 16a. The anchoring point of each first beam 1512a is advantageously located at half its length. Thus, the axis of rotation of the first mobile electrode 151 is located in one of the planes of symmetry of the first mobile electrode 151 (the one perpendicular to the first beams 1512a). The length of the first beams 1512a is measured in the second direction Y, while their width is measured in the first direction X.

[0081] Each first beam 1512a merged with the first transmission device 14a advantageously has a width which decreases away from the corresponding first pivot joint 16a. In other words, the width of the first beams 1512a is maximum at the first pivot joints 16a. Thus, the stiffening structure 1512 is the most rigid at the locations where it is most mechanically stressed, that is to say near the axis of rotation. This contributes to reducing energy losses by deformation, by limiting the negative impact on the inertia of the first mobile electrode 151 and therefore the resonance frequency of the electromechanical system 2.

[0082] 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 joints pivot 16a on the side of the first mobile electrode 151 is therefore equal to the number of first beams 1512a. This arrangement makes it possible to provide a space 17 between two successive first pivot joints 16a.

[0083] The frame 10 may comprise, 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 (see [Fig.3]).

[0084] As shown in Figures 3, 4A to 4C, the capacitive detection 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 portion of the membrane 1511 of the first mobile electrode 151 is located between the two counter-electrodes 153-154 (see Figs. 4A-4C). The first mobile electrode 151 and the counter-electrodes 153-154 thus form the armatures of two capacitors whose capacitances vary in opposite directions. A differential measurement of the displacement of the piston 13 can thus be obtained.The surfaces of the counter-electrodes 153-154 opposite the first mobile electrode 151 are advantageously identical, thanks to a symmetry of the first mobile electrode 151 and the counter-electrodes 153-154 relative to the first pivot joints 16a (the plane of symmetry is coincident with the section plane CC).

[0085] 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, called upper, and the second portion 153b, 154b, called lower, of the same counter-electrode are electrically connected. This arrangement makes it possible to obtain a totally differential measurement, even if the distance between the membrane 1511 and the upper portions 153a-154a of the counter-electrodes (called upper air gap) is different from the distance between the membrane 1511 and the lower portions 153a-154a of the counter-electrodes (lower air gap).

[0086] 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. On the other hand, 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 [Fig. 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 smaller than that of the lower portions 153b-154b.

[0087] Each block of the upper portion 153a of the first counter-electrode 153 can be electrically connected to the lower portion 153b of this same counter-electrode by a first connector 153c and a first conductive via 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 this same counter-electrode by a second connector 154c and a second conductive via 154d.

[0088] The first and second connectors 153c-154c advantageously extend 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 detection means 15'.

[0089] Alternatively, the different blocks of an upper portion of counter-electrode can be connected directly to each other, for example at the periphery of the first mobile electrode 151.

[0090] With reference to Figures 4A and 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 movable 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 ensure sealing between the first zone 11 and the second zone 12.

[0091] 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 formed from the same material as that of the annular seals 103, 105. The pillars 104 can be separated two by two by a residual layer 104' formed from the same material as that of the membrane 1511 of the first mobile electrode 151, for example silicon. The thickness of the pillars 104 is then equal to the upper air gap and the lower air gap. 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.

[0092] Alternatively, the capacitive detection means 15' may comprise (for each mobile electrode) only one counter-electrode (lower or upper), two upper and lower counter-electrodes but located on one side only of the pivot joints 16 (pseudo-differential detection) or even two lower or upper counter-electrodes arranged on either side of the pivot joints 16 (differential detection).

[0093] As indicated previously, the sealing 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 mobile electrode 151. As illustrated in FIGS. 4A and 4C, each first pivot joint 16a associated with the first mobile electrode 151 comprises a sealed insulation element 161, capable of elastically deforming under the effect of the rotational movement of the first transmission device 14a. The sealed insulation element 161 is preferably in the form of a sealing membrane.

[0094] Each sealed insulation element 161 is preferably crossed by an associated pillar 146 of the first transmission device 14a. The sealed insulation element 161 extends for example from the associated pillar 146 to the lower portions 153b-154b of the counter-electrodes 153-154 (see [Fig.4A]) and to the first portions 101 of the frame 10 (see [Fig.4C]), to which it is anchored by means of the annular seals 103, 105 made of electrically insulating material.

[0095] Furthermore, each first pivot joint 16a (associated with the first mobile 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 mobile electrode 151, while limiting their translational movements, in particular in the third direction Z (so-called “out-of-plane” translation). The two torsion blades 162 connect the stiffening structure 1512 of the first mobile 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 relative to the first beam 1512a associated with the first pivot joint 16a.

[0096] The first pivot joint 16a located at the end of the first transmission shaft 144a advantageously comprises a sealed 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).

[0097] The electromechanical system 2 comprises elastic means connected to the first mobile electrode 151 and configured to generate an elastic force which opposes the movement of the first mobile electrode 151. The role of these elastic means is to combat 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.

[0098] The elastic “anti-pull-in” means connect (mechanically) the stiffening structure- attachment 1512 of the first mobile electrode 151 to the frame 10 and / or to elements integral with 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 to be elastic “anti-pull-in” means.

[0099] The elastic “anti-pull-in” means here comprise the sealed insulation elements 161 and, where appropriate, the torsion blades 162. The sealed insulation elements 161 and the torsion blades 162 thus fulfill several functions simultaneously.

[0100] The “anti-pull-in” elastic means are connected to the stiffening structure 1512 where it is most rigid, namely at the first pivot joints 16a. Thus, the stiffness of the “anti-pull-in” elastic means is not degraded by series elements of too low stiffness. This stiffness can also be easily controlled, by varying the dimensions of the sealed insulation elements 161 and the torsion blades 162. The sealed insulation elements 161 can be delimited by anisotropic etching of a sacrificial layer (for example in SiO2) and are produced in a structural layer whose thickness is controlled. This type of etching allows good control of the dimensions of the sealed insulation elements 161. The stiffness of the sealed insulation elements 161 consequently has a low dispersion (mainly between the different electromechanical systems manufactured on the same wafer or on different wafers).

[0101] The second mobile electrode 152 is advantageously connected to the second transmission device 14b in the same way as the first mobile electrode 151 is connected to the first transmission device 14a. Thus, the electromechanical system 2 also comprises elastic “anti-pull-in” means connected to the second mobile electrode 152, these elastic means preferably comprising the sealed insulation elements 161 and, where appropriate, the torsion blades 162 of the second pivot joints 16b.

[0102] The sealed insulation elements 161 and, where appropriate, 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.

[0103] Figures 5 and 6 show a second embodiment of the electromechanical system 2. [Fig.5] is a bottom view of a part of the electromechanical system 2, similar to that of [Fig.2]. The membrane and the stiffening structure of the piston 13 are not shown. [Fig.6] is a top view, similar to that of [Fig.3], showing the capacitive detection means 15' (with the exception of the lower portions of the counter-electrodes and the membranes of the mobile electrodes under the counter-electrodes).

[0104] This second embodiment differs from the first embodiment in the design of the transmission devices 14a-14b and in the design of the capacitive detection means 15'. The pivot joints 16a-16b are constructed in the manner described in relation to FIGS. 4A-4C (sealed isolation elements and torsion blades 162).

[0105] The transmission shafts 14a-14b are here rectilinear. The number of first transmission arms 144a or second transmission arms 145b is equal to 3. They are preferably regularly spaced.

[0106] The stiffening structure 1512 of each mobile electrode 151, 152 still comprises first beams 1512a, but in a number greater than the number of pivot joints 16a, 16b used for anchoring the mobile electrode 151, 152. Thus, first beams 1512a are not merged with the transmission device 14a, 14b. They extend on the lateral edges (in the second direction Y) of the mobile electrode 151, 152 or between two successive pivot joints 16a, 16b.

[0107] 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; see [Fig.6]) and the longitudinal edge of the mobile electrode 151, 152.

[0108] In addition to increasing the width of the first beams 1512a at the pivot joints 16a, 16b (see [Fig.6]), or alternatively, oblique beams 1512c are added to the first beams 1512a merged with the transmission device 14a, 14b to form crosspieces, which further increases the rigidity of the stiffening structure 1512a at the pivot joints 16 (where it is most stressed).

[0109] The space 17 between two successive articulations 16a, 16b is occupied by one or more first beams 1512a (not merged with the transmission device 14a, 14b), which requires modifying the way in which the upper and lower portions of the counter-electrodes are connected.

[0110] [Fig. 6] shows the first and second counter-electrodes 153-154 associated with the first movable electrode 151, and third and fourth counter-electrodes 155-156 associated with the second movable 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 FIGS. 3, 4A-4C. In particular, they each comprise an upper portion 155a, 156a, composed of different blocks electrically connected to each other, and a lower portion (not visible in [Fig. 6]) connected to the upper portion.

[0111] The different 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 to the periphery of the first mobile electrode 151. This first conductive track 153c', called external, goes around the first mobile electrode 151 to the first conductive via 153d to connect to the lower portion of the first counter-electrode 153, located on the other side of the first pivot joints 16a. In the same way, the different 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 to the periphery of the first mobile electrode 151 to the second conductive via 154b.

[0112] 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 different blocks of the upper portion 155a of the third counter-electrode 155 are advantageously connected to the different 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 furthermore connected to the second conductive track 154c' and bypasses the second movable electrode 152. This third conductive track 155c is connected to a third conductive via 155d in electrical contact with the lower portion of the third counter-electrode 155.

[0113] 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 different blocks of the upper portion 156a of the fourth counter-electrode 156 are advantageously connected to the different 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 conductive via 156d in electrical contact with the lower portion of the fourth counter-electrode 156.

[0114] The electrical connections between the counter-electrodes 153-156 are preferably arranged symmetrically to minimize the size of the capacitive detection means 15'.

[0115] The electromechanical system 2 described above can be manufactured using the methods described in patents FR3059659B1 and FR3114584B1, in particular starting from a stack of layers successively comprising 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 or SOI type. in English), commonly called SOI substrate.

[0116] 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 a part of the frame 10. The substrate may be made of a semiconductor material, for example silicon.

[0117] The first structural layer is used in particular to produce the membrane 131 of the piston 13, the membrane 1511 of the mobile electrodes 151-152 and the sealed insulation elements 161 (sealing membranes). It has a thickness less than that of the substrate, preferably between 100 nm and 10 μm, for example equal to 1 μm. It is preferably made of the same material as the substrate, for example silicon.

[0118] The first sacrificial layer is intended to disappear in part during the manufacture of the electromechanical system 2 to release the membrane 131 from the piston 13, the membrane 1511 from the mobile electrodes 151-152 and the sealed insulation elements 161. Its thickness defines in particular the distance between the membrane 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 membrane 152a and the second structural layer (so-called “MEMS” layer described later). The remaining parts of the first sacrificial layer form the annular seals 103, 105 and the lower pillars 104. The first sacrificial layer may be made of a dielectric material, preferably a silicon nitride or a silicon oxide, for example silicon dioxide (SiO2). Its thickness is for example between 100 nm and 10 pm.

[0119] 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.

[0120] The second structural layer is etched to delimit the stiffening structure 132 of the piston 13, the stiffening structure 1512 of the mobile 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 from 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 equal to 20 μm.

[0121] 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 location of the pivot joints 16a, 16b (the first and second sacrificial layers having been opened at the The pillars 146 of the transmission devices 14a, 14b are formed during this epitaxial growth.

[0122] The second sacrificial layer serves in particular as a stop layer during the etching of the second structural layer. It is partially removed to release the membrane 131 of the piston 13, the membrane 1511 of the mobile electrodes 151-152 and the sealed insulation elements 161. Its thickness defines the distance between the membrane 1511 and the upper portions of the counter-electrodes 153-156 (upper air gap). The second sacrificial layer is advantageously formed from the same dielectric material as the first sacrificial layer, for example a silicon oxide. Its thickness can be between 100 nm and 10 μm.

[0123] The electromechanical system 2 does not necessarily comprise the two movable electrodes 151-152 and the two transmission devices 154a-154b. It may comprise a single movable electrode and a single transmission device (see Figs. 7-9), or a single movable electrode and two transmission devices connected to this single movable electrode (see [Fig. 10]).

[0124] [Fig.7] represents a third embodiment in which the electromechanical system 2 comprises, in addition to the piston 13, a single mobile electrode 151 (for example of the type represented by [Fig.2]) and a single transmission device 14a (for example of the type represented by [Fig.2]).

[0125] The piston 13 is here again movable in translation. It can be sufficiently balanced to be maintained 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 center line of the piston 13 (i.e. the line which separates the two halves of the piston). Alternatively, the piston 13 can be guided in translation by means other than the single transmission device 14a (in particular when it is not sufficiently well balanced).

[0126] In a fourth embodiment represented by [Fig.8], the electromechanical system 2 again comprises only one mobile electrode 151 and only one transmission device 14a, but the piston 13 is mobile 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) drives the transmission shaft 144a of the transmission device 14a in rotation (around its own axis Xa), via the transmission arms 145a, and the transmission shaft 144a sets the mobile electrode 151 in motion (here in rotation around the axis Xa).

[0127] [Fig.9] illustrates a fifth embodiment of the electromechanical system 2, which differs from the fourth embodiment in that the single mobile electrode 151 is rotating around 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.

[0128] Thus, in this fifth embodiment (and unlike the previous embodiments), the mobile electrode 151 is not connected to the transmission shaft 144a in a fixed manner, but by means of coupling elements 147 (for example torsion blades) allowing the transition from one rotation to another rotation. 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 mobile electrode 151.

[0129] In a sixth embodiment shown in [Fig. 10], the electromechanical system 2 comprises only one movable electrode 151 but two transmission devices 14a-14b (for example those shown in [Fig.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 the coupling elements 147 (for example torsion blades) allowing the transition from rotation to translation and the beams 148. The two transmission shafts 144a-144b rotate in opposite directions, so as to raise or lower the movable electrode 151.

[0130] The electromechanical system 2 according to the invention is not limited to the embodiments described in relation to figures 2 to 10 and numerous variants and modifications of the electromechanical system will appear to those skilled in the art.

[0131] The transmission shafts 144a-144b may adopt other geometries. The number of transmission arms 145a, 145b may be greater than 3.

[0132] The electromechanical system 2 may also comprise, for each transmission device 14a, 14b, one or more additional pivot joints, not shown in the figures, between that located at the end of the transmission shaft 144a, 144b and those connecting the mobile electrode 151, 152. These additional pivot joints are preferably located in the first zone 11 and therefore do not contribute to the sealing between the two zones.

[0133] Conversely, it may comprise only 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.

[0134] The electromechanical system 2 has been described using a microphone as an example. with capacitive detection comprising a piston 13 provided with a membrane 131 subjected on the one hand to atmospheric pressure and on the other hand to a reference pressure. The electromechanical system can however form other types of transducer with capacitive detection, in particular a loudspeaker (sound transmitter) or an ultrasonic transmitter (which are electroacoustic transducers), or even a differential pressure sensor.

[0135] In the case of a differential pressure sensor, the first face of the membrane 131 is subjected to a first pressure (not necessarily atmospheric pressure) and the second face of the membrane 131 is subjected to a second pressure, different from the first pressure. The displacement of the membrane 131, under the effect of the pressure difference, is measured by the capacitive detection means 15'. The membrane 131 of the piston is integral with the frame 10 so as to be sealed and the stiffening structure 132 of the piston is absent or reduced so as not to anchor it to the frame.

[0136] In the case of a loudspeaker or an ultrasonic transmitter, capacitive actuation means replace the capacitive detection means 15'. These capacitive actuation means also comprise 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 movement is transmitted by the transmission devices 14a, 14b to the piston 13. The movement of the membrane 131 of the piston 13 makes it possible to emit a sound (or ultrasound).

[0137] The second zone 12 may comprise two chambers under controlled atmosphere, one containing the first mobile electrode 151, the other containing the second mobile electrode 152.

[0138] The first and second sealed zones 11-12 are not necessarily subjected to different pressures. The first zone 11 may also be an aggressive environment and the movable electrodes of the capacitive means (detection 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).

[0139] The electromechanical system 2 may even be devoid of sealing means between the first and second zones 11-12 (which amounts to considering only one zone). More particularly, the pivot joints 16 may be devoid of a sealed insulating element 161. Indeed, the torsion blades 162 may be sufficient for the rotation of the transmission device 14' and as elastic "anti-pull-in" means.

Claims

Claims

1. Electromechanical system (2) comprising: - a frame (10); - a movable element (13) relative to the frame (10); - capacitive measuring or actuating means (15') comprising: • a first movable electrode (151) relative to the frame (10); and • at least one fixed electrode (153, 154) 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 a movement between the movable element (13) and the first movable electrode (151), the first transmission device (14a) being movable in rotation relative to the frame (10) by means of a plurality of first pivot joints (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, in which the first movable electrode (151) is integral with the first transmission shaft (144a), from which it follows that the first movable electrode (151) is mounted movable in rotation around the first longitudinal axis of rotation (Xa).

3. System (2) according to one of claims 1 and 2, in which the capacitive measuring or actuation means (15') further comprise: a second movable electrode (152) relative to the frame (10); and - at least one additional electrode fixed (155, 156) relative to the frame (10) and separated from the second mobile electrode (152) by a second dielectric medium; the system further comprising a second device (14b) for transmitting a movement between the mobile element (13) and the second mobile electrode (152), the second transmission device (14b) being rotatable relative to the frame (10) by means of a plurality of second pivot joints (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 mobile element (13) and a second end secured to the second transmission shaft (144b); system in which the second mobile electrode (152) is connected to the second transmission shaft (144b).

4. System (2) according to claim 3, in which the second movable electrode (152) is integral with the second transmission shaft (144b), from which it follows that the second movable electrode (152) is mounted movable in rotation around the second longitudinal axis of rotation (Xb).

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

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

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

11. System (2) according to any one of claims 1 to 10, in which the first end of each first transmission arm (145a) is located at a distance Lpisti from the first longitudinal axis of rotation (Xa) such that: 2 x L^eiec\ 4 s 2 x Lgigf-i where Leîecl is the distance between a longitudinal edge of the first mobile electrode (151) and the first longitudinal axis of rotation (Xa).

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

13. System (2) according to any one of claims 1 to 12, in which 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) sealed 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 in the first zone (11) and wherein the first transmission device (14a) further comprises pillars (146) extending partly in the first zone (11) and partly in the second zone (12).

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

16.

17.

18. System (2) according to any one of claims 1 to 15, in which: - the first mobile electrode (151) comprises a membrane (1511) and a stiffening structure (1512) of the membrane; - the stiffening structure (1512) of the first mobile electrode (151) is anchored to the first transmission device (14a) at a portion of the first pivot joints (16a). System (2) according to claim 16, wherein the stiffening structure (1512) of the first mobile electrode (151) comprises a plurality of beams (1512a) extending parallel to each other and wherein at least a portion of the beams (1512a) are anchored to the first transmission device (14a), each beam of said at least one portion being anchored at a first pivot joint (16a) corresponding to said beam. System (2) according to any one of claims 1 to 17, wherein the capacitive measuring or actuating means (15') comprise first and second fixed electrodes (153, 154) associated with the first mobile electrode (151), the first mobile electrode (151) comprising a membrane (1511) arranged between the first and second fixed electrodes (153, 154).

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