ELECTROMECHANICAL SYSTEM COMPRISING CAPABILITIES FOR MEASURING OR ACTUATING

Abstract

ELECTROMECHANICAL SYSTEM COMPRISING CAPACITIVE MEASUREMENT OR ACTUATION MEANS The invention relates to an electromechanical system (2) comprising: a frame (10); a movable element; capacitive measurement or actuation means (15') comprising a movable electrode (152) and at least one fixed electrode, called a counter electrode, the movable electrode (152) comprising a membrane (152a) and a membrane stiffening structure (152b); a motion transmission device (14') between the movable element and the movable electrode (152), the transmission device being rotationally mobile relative to the frame (10) by means of a plurality of pivot joints (16); and elastic means connected to the movable electrode (152) and configured to generate an elastic force that opposes the motion of the movable electrode (152);the stiffening structure (152b) of the mobile electrode (152) being integral with the transmission device (14') and anchored to the transmission device at least part of the pivot joints (16). Figure to be published with the abbreviation: Figure 2;

Description

Title of the invention: ELECTROMECHANICAL SYSTEM COMPRISING CAPACITIVE MEASURING MEANS OR ACTUATION 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 negative stiffness spring 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 to the microphone frame. 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 voltage the movable electrode can be polarized to (the sensitivity of the microphone increases with the polarization voltage).

[0015] The linear component (negative stiffness) of the electrostatic force, as well as the associated risk of collapse, are maximal in static mode, when the voltage applied to the terminals of the capacitor is constant. They impose a high stiffness in opposition. On the other hand, when detecting dynamic pressure variations (therefore in dynamic mode), the linear component of the electrostatic force exerted on the moving electrode is less, or even zero, and does not help to soften the system. The piston must then collect enough energy to compress the springs and move the moving electrode. The stiffness of the springs introduced to combat the collapse of the moving electrode therefore represents a loss of useful signal when detecting dynamic pressure variations.

[0016] Thus, increasing the collapse tension by increasing the stiffness of the springs and reducing energy losses in electromechanical systems with capacitive detection or capacitive actuation are contradictory. Summary of the invention

[0017] It is noted that there is a need to provide an electromechanical system with capacitive detection or capacitive actuation presenting a better compromise between collapse voltage and energy losses.

[0018] According to a first aspect of the invention, this need is tended to be satisfied by providing an electromechanical system comprising: • a frame; • an element movable relative to the frame, in contact with a first zone; • capacitive measuring or actuation means comprising an electrode movable relative to the frame, located in a second zone sealed from the first zone and at least one electrode fixed relative to the frame, called a counter-electrode, the movable electrode comprising a membrane and a structure for stiffening the membrane; • a device for transmitting a movement between the mobile element and the mobile electrode, the transmission device being mobile in rotation relative to the frame by means of a plurality of pivot joints; and • elastic means connected to the movable electrode and configured to generate an elastic force which opposes the movement of the movable electrode.

[0019] The electromechanical system is remarkable in that the stiffening structure of the mobile electrode is integral with the transmission device and anchored to the transmission device at least at part of the pivot joints.

[0020] The term "integral" means that there is no relative movement between the stiffening structure of the mobile electrode and the transmission device. More particularly, there is no transformation of the movement between the transmission device and the mobile electrode (for example, transition from a rotation of the transmission device to a translation of the mobile electrode) and therefore no energy loss associated with this transformation.

[0021] The chain of transmission of mechanical forces between the mobile element and the mobile electrode (this chain comprising the different elements of the transmission device) is reduced to a minimum, thanks to the anchoring of the mobile electrode at the pivot joints. The energy losses by (elastic) deformation of the transmission device are consequently reduced, which results, in the case of a microphone or a differential pressure sensor, in a higher useful signal at the output of the capacitive detection means (greater displacement of the mobile electrode).

[0022] The energy losses are thus restricted to the (useful) deformation of the elastic means intended to combat the collapse of the mobile electrode (so-called “anti-pull-in” means), by reducing the (useless) deformation of the transmission device.

[0023] 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 transmission device comprises first elements extending in the first zone and second elements extending partly in the first zone and partly in the second zone, and the stiffening structure of the mobile electrode is connected to the first elements of the transmission device transmission by the second elements; • the first elements of the transmission device have a thickness of between 5 pm and 800 pm, preferably between 50 pm and 200 pm; • the first elements of the transmission device comprise two transmission arms and a transverse beam connecting the two transmission arms, each of the transmission arms comprising a first end coupled to the movable element and a second end secured to the transverse beam; • the first elements of the transmission device include: • a transmission shaft having a longitudinal axis of rotation; and • a plurality of transmission arms, each of the transmission arms comprising a first end coupled to the movable element and a second end secured to the transmission shaft; the stiffening structure of the mobile electrode being integral with the transmission shaft, from which it results that the mobile electrode is mounted mobile in rotation around the first longitudinal axis of rotation; • the stiffening structure of the mobile electrode comprises a plurality of beams extending parallel to each other and at least part of the beams are anchored to the transmission device, each beam of said at least one part being anchored at a pivot joint corresponding to said beam; • each beam of said at least one part is anchored to the transmission device at half its length; • each beam of said at least one part has a width which decreases as it moves away from the corresponding pivot joint; • the number of beams is greater than or equal to the number of pivot joints of said at least one part; • each pivot joint of said at least one part may comprise a sealed insulation element capable of deforming elastically and ensuring sealing between the first zone and the second zone, said elastic means comprising the sealed insulation element of said at least one part of the pivot joints; • each pivot joint of said at least one part further comprises two torsion blades each extending between a portion of the frame and the stiffening structure of the mobile electrode, said elastic means further comprising the torsion blades of said at least one part of the ar pivot joints; • the electromechanical system further comprises means for stopping a collapse of the movable electrode before it touches the fixed electrode and creates a short circuit, said means being located at one end or at the ends of one or more beams; • the capacitive measuring or actuation means comprise two counter-electrodes fixed relative to the frame, at least part of the membrane of the mobile electrode being located between the two counter-electrodes; • each counter-electrode comprises a first portion and a second portion located on either side of the membrane and on either side of the pivot joints of said at least one part, the first and second portions of each counter-electrode being electrically connected; • the first portion of each counter-electrode comprises a plurality of blocks separated by the stiffening structure of the mobile electrode and each block of the first portion is electrically connected to the second portion of the counter-electrode by a connector passing between two successive pivot joints of said at least one part; and • the pivot joints of said at least one part are aligned. BRIEF DESCRIPTION OF THE FIGURES

[0024] 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 perspective 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 top view of the electromechanical system of [Fig.2], showing part of the capacitive detection or actuation means; • [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 system along section plane CC of [Fig.3]; • [Fig.5] is a partial perspective view of an electromechanical system according to a second embodiment of the invention; • [Fig.6] is a top view of the electromechanical system of [Fig.5], showing part of the capacitive sensing or actuation means; and • [Fig.7] is a perspective view of means for preventing a dete improvement of the capacitive detection or actuation means in the electromechanical system of [Fig.2] or [Fig.5].

[0025] For clarity, identical or similar elements are identified by identical reference signs throughout the figures. DETAILED DESCRIPTION

[0026] 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.

[0027] Reference is made to [Fig. 1] for the elements of the electromechanical system 2 not shown in Figures 2, 3 and 4A to 4C.

[0028] Like the microphone 1 of [Fig.l], the electromechanical system 2 comprises: • a frame 10; • a movable element 13 relative to the frame 10, in contact with a first zone 11; • capacitive detection (or measurement) means 15' comprising a movable electrode 152 relative to the frame, the movable electrode 152 being located in a second zone 12 sealed from the first zone 11; and • a device 14' for transmitting a movement between the mobile element 13 and the mobile electrode 152 of the capacitive detection means 15', in other words between the first zone 11 and the second zone 12.

[0029] [Fig. 2] is a perspective view showing first portions 101 of the frame 10, only part of the transmission device 14' and the movable electrode 152 of the capacitive detection means 15'. [Fig. 3] is a top view showing only part of the capacitive detection means 15' (including the movable electrode 152). 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 transmission device 14' and the capacitive detection means 15'.

[0030] The movable element 13, hereinafter called piston, can be movable (relative to the frame) in rotation or in translation. It can be identical to that described with reference to [Fig.l]. In particular, it may comprise a membrane 131 and a stiffening structure 132 of the membrane 131, also called a skeleton or frame.

[0031] 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).

[0032] The first zone 11 includes the cavity open to the external environment, subjected to atmospheric pressure, and the reference volume subjected to the reference pressure.

[0033] The capacitive detection means 15' make it possible to measure the movement of the piston 13, and therefore the pressure difference between its two faces. In addition to the movable electrode 152, they comprise at least one electrode fixed relative to the frame 10, called a “counter-electrode” and arranged opposite the movable electrode 152. The movable and fixed electrode(s) form the armatures of one or more capacitors whose capacitance varies as a function of the movement of the piston 13.

[0034] 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.

[0035] With reference to [Fig. 2], the mobile electrode 152 comprises a membrane 152a and a stiffening structure 152b of the membrane 152a. The stiffening structure 152b of the mobile electrode 152 preferably comprises a plurality of first beams 1521 extending parallel to each other. It may further comprise second beams 1522 connecting the first beams 1521 at their ends. The first beams 1521 extend in a first direction X, preferably from a first edge to a second opposite edge of the mobile electrode 152. They are advantageously regularly spaced from each other, to stiffen the membrane 152a uniformly. The second beams 1522 preferably extend in a second direction Y perpendicular to the first direction X. (therefore perpendicular to the first beams 1521). An orthogonal reference frame is thus defined, with a third Z direction perpendicular to the first and second XY directions.

[0036] The mobile electrode 152 advantageously has one or more planes of symmetry, for example a plane parallel to the YZ plane (therefore perpendicular to the first beams 1521) and another plane parallel to the XZ plane.

[0037] The transmission device 14' is mounted to be movable in rotation relative to the frame 10, by means of several pivot joints 16. It comprises first elements extending in the first zone 11, for example two transmission arms 141 and a transverse beam 144 connecting the two transmission arms 141. Preferably, the transmission arms 141 extend in the first direction X and the transverse beam 144 extends in the second direction Y. Each of the transmission arms 141 comprises a first end coupled to the piston 13 (see [Fig. 1]) and a second end secured to the transverse beam 144 (see [Fig. 2]).

[0038] The pivot joints 16, for example 5 in number in [Fig.2], are preferably aligned, here in the second direction Y. More particularly, they are located vertically to the transverse beam 144. They are advantageously spaced regularly from each other.

[0039] A particular feature of the electromechanical system 2 is that the stiffening structure 152b of the mobile electrode 152 is integral with the transmission device 14'. The mobile electrode 152 therefore moves relative to the frame 10 according to the same rotational movement as the transmission device 14'. It rotates here around an axis of rotation parallel to the second direction Y. The electromechanical system 2 is therefore devoid of members for transforming the movement between the transmission device 14' and the mobile electrode 152, 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).

[0040] Another particularity of the electromechanical system 2 is that the stiffening structure 152b of the mobile electrode 152 is anchored, or fused, to the transmission device 14' at the level of the pivot joints 16. 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.

[0041] More particularly, the stiffening structure 152b of the mobile electrode 152 is connected to the first elements of the transmission device 14', and more particularly to the transverse beam 144, by second elements 145 visible in FIGS. 4A and 4C. These second elements 145 of the transmission device 14', called pillars, 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 pivot joints 16.

[0042] The transmission device 14' is thus reduced to the first elements extending exclusively in the first zone 11 (here the transmission arms 141 and the transverse beam 144) and to the second elements 145 which extend partly in the first zone 11 and partly in the second zone 12. This reduction of the transmission device 14' makes it possible to limit energy losses. In particular, there are no longer any losses due to deformation of the second transmission arms 142.

[0043] Furthermore, the first elements of the transmission device 14' are relatively rigid (much more so than the second transmission arms 142 of the microphone 1), because they have a significant thickness, preferably between 5 pm and 800 pm, and more preferably between 50 pm and 200 pm. They are advantageously formed by anisotropic etching of a silicon substrate. This substrate can be thinned, down to a thickness of between 50 pm and 200 pm. 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.

[0044] The electromechanical system 2 is particularly compact, because several functions, namely the rotation of the transmission device 14', the sealing between the two zones 11-12 and the connection to the mobile electrode 152, are carried out at the same location.

[0045] The anchoring between the stiffening structure 152b and the transmission device 14' is preferably achieved by means of the first beams 1521. At least a portion of them are fused to the transmission device 14', each at a corresponding pivot joint 16. The anchoring point of each first beam 1521 is advantageously located at half its length. Thus, the axis of rotation is located in one of the planes of symmetry of the mobile electrode 152 (the one perpendicular to the first beams 1521). The length of the first beams 1521 is measured in the first direction X, while their width is measured in the second direction Y.

[0046] Each first beam 1521 merged with the transmission device 14' advantageously has a width which decreases as it moves away from the corresponding pivot joint 16. In other words, the width of the first beams 1521 is maximum at the pivot joints 16. Thus, the stiffening structure 152b 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, without negatively impacting the inertia of the mobile electrode 152 and therefore the resonant frequency of the electromechanical system 2.

[0047] In this first embodiment of the electromechanical system 2, each of the first beams 1521 of the stiffening structure 152b is merged with the transmission device 14'. In other words, each first beam 1521 is associated with a pivot joint 16. The number of pivot joints 16 is therefore at least equal to the number of first beams 1521. This arrangement makes it possible to provide a space 17 between two successive pivot joints 16.

[0048] The frame 10 may comprise, for each pivot joint 16, two distinct first portions 101 arranged on either side of the first beam 1521 associated with the pivot joint. The first beam 1521 is preferably connected to each of the first portions 101 of the frame 10 by a torsion blade 162.

[0049] As shown in Figures 3, 4A to 4C, the capacitive detection means 15' preferably comprise two counter-electrodes 153-154: a first counter-electrode 153 called positive and a second counter-electrode 154 called negative. Preferably, at least a portion of the membrane 152 of the movable electrode is located between the two counter-electrodes 153-154 (see Figs. 4A-4C). The movable electrode 152 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 mobile electrode 152 are advantageously identical, thanks to a symmetry of the capacitive detection means 15' relative to the pivot joints 16 (the plane of symmetry is merged with the section plane CC).

[0050] 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 152a of the movable electrode 152 and on either side of the pivot joints 16. 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 152a and the upper portions 153a-154a of the counter-electrodes (called upper air gap) is different from the distance between the membrane 152a and the lower portions 153a-154a of the counter-electrodes (lower air gap).

[0051] The lower portions 153b-154b of the counter-electrodes 153-154 may extend under the first beams 1521 of the stiffening structure 152b, on each side of the pivot joints 16. 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 1521, as illustrated by [Fig. 3]. The upper portions 153a-154a of the counter-electrodes 153-154 being inscribed in the stiffening structure 152b of the mobile electrode 152, their surface facing the membrane 152a is smaller than that of the lower portions 153b-154b.

[0052] 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.

[0053] The first and second connectors 153c-154c advantageously extend into the space 17 located between two pivot joints 16. 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'.

[0054] 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 mobile electrode 152.

[0055] 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 movable electrode 152, 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.

[0056] 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 152a of the mobile electrode 152, 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 152a. 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.

[0057] Alternatively, the capacitive detection means 15' may comprise 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).

[0058] As indicated previously, the sealing between the first and second zones 11-12 of the electromechanical system 2 can be achieved at the pivot joints 16. As illustrated in FIGS. 4A and 4C, each pivot joint 16 comprises a sealed insulation element 161, capable of elastically deforming under the effect of the rotational movement of the transmission device 14'. The sealed insulation element 161 is preferably in the form of a sealing membrane.

[0059] Each sealed insulation element 161 is preferably crossed by a second associated element 145 of the transmission device 14'. The sealed insulation element 161 extends for example from the second associated element 145 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.

[0060] Furthermore, each pivot joint 16 advantageously comprises the two torsion blades 162 described previously, with reference to [Fig. 2]. The torsion blades 162 are dimensioned so as to be able to deform in torsion and allow the rotation of the transmission device 14' and the mobile electrode 152, 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 152b of the mobile electrode 152 (fused to the second element 145 of the transmission device 14') 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 1521 associated with the pivot joint 16.

[0061] The electromechanical system 2 comprises elastic means connected to the mobile electrode 152 and configured to generate an elastic force which opposes the movement of the mobile electrode 152. The role of these elastic means is to combat the collapse phenomenon (called “pull-in” in English) of the mobile electrode 152. Their stiffness influences the collapse voltage (or “pull-in voltage” of the system), therefore the ability to polarize the mobile electrode 152, but also the energy losses.

[0062] The elastic “anti-pull-in” means connect (mechanically) the stiffening structure 152b of the mobile electrode 152 to the frame 10 and / or to elements integral with the frame, such as the counter-electrodes 153-154, possibly via the second elements 145 of the transmission device 14'. Thus, the stiffness of the transmission device 14' or the stiffness of the stiffening structure 152b itself are not considered to be elastic “anti-pull-in” means.

[0063] 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.

[0064] The elastic “anti-pull-in” means are connected to the stiffening structure 152b where it is most rigid, namely at the pivot joints 16. Thus, the stiffness of the elastic “anti-pull-in” means is not degraded by series elements of too low stiffness. This stiffness can also be easily controlled, by adjusting 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 made 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).

[0065] 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.

[0066] Figures 5 and 6 show a second embodiment of the electromechanical system 2. [Fig. 5] is a perspective view of a part of the electromechanical system 2, similar to that of [Fig. 2]. [Fig. 5] 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).

[0067] This second embodiment differs from the first embodiment essentially in the design of the capacitive detection means 15'. The transmission device 14' is notably identical to that of [Fig.2] (transmission arm 141 and transverse beam 144) and the pivot joints 16 are constructed in the manner described in relation to FIGS. 4A-4C (sealed isolation elements and torsion blades 162).

[0068] The stiffening structure 152b of the mobile electrode 152 still comprises first beams 1521, but in a number greater than the number of pivot joints 16 used for anchoring the mobile electrode 152. Thus, first beams 1521 are not merged with the transmission device 14'. They extend on the longitudinal edges (in the lengthwise direction, i.e. along the first direction X) of the mobile electrode 152 or between two successive pivot joints 16.

[0069] The second beams 1522 no longer connect the first beams 1521 at their ends, but closer to the pivot joints 16, for example halfway between the axis of rotation (passing through the torsion blades 162) and the transverse edge of the mobile electrode 152.

[0070] In addition to increasing the width of the first beams 1521 at the pivot joints 16 (see [Fig.6]), or alternatively, oblique beams 1533 are added to the first beams 1521 merged with the transmission device 14' to draw crosspieces, which further increases the rigidity of the stiffening structure 152b at the pivot joints 16 (where it is most stressed).

[0071] The space 17 between two successive articulations 16 is occupied by one or more first beams 1521 (not merged with the transmission device 14'), which requires modifying the way in which the upper and lower portions of the counter-electrodes 153-154 are connected.

[0072] With reference to [Fig. 6], 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 mobile electrode 152. This first conductive track 153c', called external, goes around the mobile electrode 152 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 pivot joints 16. 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 mobile electrode 152 to the second conductive via 154b.

[0073] In a manner common to both embodiments (see Figs. 3 and 6), the electromechanical system 2 may comprise means 18 for stopping the collapse of the membrane 152a of the movable electrode 152, before it sticks to one of the counter-electrodes, when the polarization voltage of the movable electrode 152 is such that the electrostatic force becomes greater than the elastic force (in other words, in the event of a “pull-in”). These means 18 are located at one end or at the ends of one or more first beams 1521, preferably of all the first beams 1521, and comprise, for example, stops. They essentially aim to prevent damage to the movable electrode 152 due to a case of short-circuit with a counter-electrode.

[0074] [Fig. 7] shows an exemplary embodiment of the means 18 for preventing the collapse of the mobile electrode 152. The stiffening structure 152b of the mobile electrode 152 comprises at the end of the first beam 1521 two fingers 181 and a membrane 182 connecting the two fingers 181 at one of their ends. The frame 10 comprises two cavities 183, delimited laterally by two outer fingers 184a and an inner finger 184b (arranged between the outer fingers 184a), and two membranes 185 forming the bottom of the cavities 183. The fingers 181 of the stiffening structure 152b are arranged inside the cavities 183 of the frame 10.

[0075] Depending on the direction of movement (rotation) of the mobile electrode 152, either the fingers 181 of the stiffening structure 152b come into abutment against the membranes 185 of the frame 10, or the membrane 182 of the stiffening structure 152b comes into abutment against the inner finger 184b of the frame 10.

[0076] 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, commonly called an SOI substrate.

[0077] The substrate is used in particular to produce, by etching, the first elements of the transmission device 14' (transmission arm 141 and transverse beam 144), the lower portions 153b-154b of the counter-electrodes 153-154 and a part of the frame 10. The substrate may be made of a semiconductor material, for example silicon.

[0078] The first structural layer serves in particular to produce the membrane 131 of the piston 13, the membrane 152a of the mobile electrode 152, the sealed insulation elements 161 (sealing membranes) and the membranes 182 and 185 of the means 18 for preventing the collapse of the mobile electrode 152. 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.

[0079] The first sacrificial layer is intended to disappear in part during the manufacture of the electromechanical system 2 to release the membrane 131 of the piston 13, the membrane 152a of the mobile electrode 152 and the sealed insulation elements 161. Its thickness defines in particular the distance between the membrane 152a of the mobile electrode 152 and the lower portions 153b-154b of the counter-electrodes 153-154 (lower air gap). This layer also serves as a stop layer during 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.

[0080] 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.

[0081] The second structural layer is etched to delimit the stiffening structure 132 of the piston 13, the stiffening structure 152b of the movable electrode 152, the torsion blades 162, the upper portions 153a-153b of the counter-electrodes 153-154, 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 pm and 50 pm, for example equal to 20 pm.

[0082] The stiffening structure 152b of the mobile electrode 152 is fused to the transmission device 14', by growing the second structural layer directly from the substrate, at the location of the pivot joints 16 (the first and second sacrificial layers having been opened beforehand). The second elements 145 of the transmission device 14' are formed during this growth by epitaxy.

[0083] 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 152a of the mobile electrode 152 and the sealed insulation elements 161. Its thickness defines the distance between the membrane 152a of the mobile electrode 152 and the upper portions 153a-154a of the counter-electrodes 153-154 (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 may be between 100 nm and 10 μm.

[0084] The electromechanical system according to the invention is not limited to the embodiments described in relation to Figures 2 to 7 and numerous variants and modifications of the electromechanical system will appear to those skilled in the art.

[0085] The transmission device 14' may in particular adopt other configurations than that described in relation to [Fig.2]. For example, the transmission device 14' may comprise a transmission shaft having a longitudinal axis of rotation and a plurality of transmission arms, each of the transmission arms comprising a first end coupled to the piston and a second end secured to the transmission shaft. The stiffening structure of the movable electrode is secured to the transmission shaft (in the same way as with the transverse beam 144). The movable electrode is then mounted to be movable in rotation about the first longitudinal axis of rotation. The transmission arms preferably extend perpendicular to the transmission shaft. The piston may be movable (relative to the frame) in rotation or in translation.

[0086] The electromechanical system 2 may comprise one or more additional pivot joints, not shown in the figures, which are not merged with the stiffening structure 152b of the mobile electrode 152 (for example pivot joints located at the end of the transmission arms 141, as shown in [Fig.l]).

[0087] The electromechanical system 2 has been described by taking as an example a capacitive detection microphone 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 capacitive detection transducer, in particular a loudspeaker (sound transmitter) or an ultrasonic transmitter (which are electroacoustic transducers), or even a differential pressure sensor.

[0088] 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.

[0089] 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 a movable electrode and at least one counter-electrode. The movable electrode is set in motion by an electrostatic force and this movement is transmitted by the transmission device 14' to the piston 13. The movement of the membrane 131 of the piston 13 makes it possible to emit a sound (or ultrasound).

[0090] 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 mobile electrode of the capacitive means (detection or actuation) is placed in the second zone 12 to protect it from this aggressive environment (in addition to reducing viscous friction, and therefore acoustic noise).

[0091] 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), in contact with a first zone (11); - capacitive measuring or actuation means (15') comprising a movable electrode (152) relative to the frame, located in a second zone (12) sealed from the first zone (11), and at least one fixed electrode (153, 154) relative to the frame (10), called a counter-electrode, the movable electrode (152) comprising a membrane (152a) and a stiffening structure (152b) of the membrane; - a device (14') for transmitting a movement between the movable element (13) and the movable electrode (152), the transmission device being movable in rotation relative to the frame (10) by means of a plurality of pivot joints (16);and - elastic means connected to the mobile electrode (152) and configured to generate an elastic force which opposes the movement of the mobile electrode (152); characterized in that the stiffening structure (152b) of the mobile electrode (152) is integral with the transmission device (14') and anchored to the transmission device at least at part of the pivot joints (16).;

2. System (2) according to claim 1, wherein the transmission device (14') comprises first elements extending in the first zone (11) and second elements (145) extending partly in the first zone (11) and partly in the second zone (12), and wherein the stiffening structure (152b) of the mobile electrode (152) is connected to the first elements of the transmission device by the second elements (145).

3. System (2) according to claim 2, in which the first elements of the transmission device (14') have a thickness of between 5 pm and 800 pm, preferably between 50 pm and 200 pm.

4. System (2) according to one of claims 2 and 3, in which the first elements of the transmission device (14') comprise two transmission arm (141) and a transverse beam (144) connecting the two transmission arms (141), each of the transmission arms comprising a first end coupled to the movable element (13) and a second end secured to the transverse beam (144).

5. System (2) according to any one of claims 1 to 4, wherein the stiffening structure (152b) of the mobile electrode (152) comprises a plurality of beams (1521) extending parallel to each other and wherein at least a portion of the beams (1521) are anchored to the transmission device (14'), each beam of said at least one portion being anchored at a pivot joint (16) corresponding to said beam.

6. System (2) according to claim 5, wherein each beam (1521) of said at least one part is anchored to the transmission device (14') at half its length.

7. System (2) according to one of claims 5 and 6, in which each beam (1521) of said at least one part has a width which decreases away from the corresponding pivot joint (16).

8. System (2) according to any one of claims 5 to 7, wherein the number of beams (1521) is greater than or equal to the number of pivot joints (16) of said at least one part.

9. System (2) according to any one of claims 5 to 8, further comprising means (18) for stopping a collapse of the movable electrode (152) before it touches the fixed electrode (153, 154) and creates a short circuit, said means (18) being located at one end or at the ends of one or more beams (1521).

10. System (2) according to any one of claims 1 to 9, wherein each pivot joint (16) of said at least one part comprises a sealed insulation element (161) capable of elastically deforming and ensuring sealing between the first zone (11) and the second zone (12), said elastic means comprising the sealed insulation element (161) of said at least one part of the pivot joints (16).

11. System (2) according to claim 10, wherein each pivot joint (16) of said at least one part further comprises two torsion blades (162) each extending between a portion (101) of the frame (10) and the stiffening structure (152b) of the movable electrode (152), said elastic means further comprising the torsion blades (162) of said at least one part of the pivot joints (16).

12. System (2) according to any one of claims 1 to 11, in which the capacitive measuring or actuation means (15') comprise two counter-electrodes (153, 154) fixed relative to the frame (10), at least part of the membrane (152a) of the mobile electrode (152) being located between the two counter-electrodes (153, 154).

13. System (2) according to claim 12, in which each counter-electrode (153, 154) comprises a first portion (153a, 154a) and a second portion (153b, 154b) located on either side of the membrane (152a) and on either side of the pivot joints (16) of said at least one part, the first and second portions of each counter-electrode being electrically connected.

14. System (2) according to claim 13, in which the first portion (153a, 154a) of each counter-electrode (153, 154) comprises a plurality of blocks separated by the stiffening structure (152b) of the movable electrode (152) and in which each block of the first portion is electrically connected to the second portion (153b, 154b) of the counter-electrode (153, 154) by a connector (153c, 154c) passing between two successive pivot joints (16) of said at least one part.

15. System (2) according to any one of claims 1 to 14, wherein the pivot joints (16) of said at least one part are aligned.

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