Electromechanical system comprising two movable elements and capacitance measurement or actuation device

Abstract

The invention relates to an electromechanical system comprising two movable elements and a capacitance measurement or actuation device. An electromechanical system (2) comprises: a frame (10); a first element movable relative to the frame (10); and a capacitance measurement or actuation device (15 ') comprising a first electrode movable relative to the frame and at least one electrode fixed relative to the frame (10) and separated from the first movable electrode (151) by a first dielectric; a first motion transmission device connecting the first movable element (13a) to the first movable electrode (151), the first transmission device being rotatably movable relative to the frame (10) by a plurality of first pivot hinges (16a); a second element movable relative to the frame (10), the second movable element (13b) being connected to the capacitance measuring or actuating device (15 ').

Description

[0001] Cross - reference to related applications

[0002] This application claims the priority of French Patent Application No. FR2315317 filed on December 26, 2023, the disclosure of which is incorporated herein by reference in its entirety. Technical field

[0003] The technical field of the present invention is the field of electromechanical systems, in particular the field of electromechanical systems of the Microelectromechanical System (MEMS) or Nanoelectromechanical System (NEMS) type. The present invention more particularly relates to an electromechanical system comprising a movable element, capacitive measurement or actuation means, and a device for transmitting movement between the movable element and the capacitive measurement or actuation means. Such a system can be used as an electro - acoustic transducer (such as a microphone, a speaker, etc.) or a differential pressure sensor. Background art

[0004] Microelectromechanical microphones or nanoelectromechanical microphones represent a rapidly expanding market, particularly thanks to the development of portable devices (such as tablets, smartphones, and other connected objects, etc.), in which microelectromechanical microphones or nanoelectromechanical microphones are gradually replacing electret microphones.

[0005] A microphone measures rapid changes in atmospheric pressure (also called sound pressure). Thus, a microphone includes at least one part in contact with the outside.

[0006] Most of the currently manufactured MEMS or NEMS microphones are capacitive detection microphones. Figure 1 An example of a capacitive detection microphone 1 as described in Patent FR3114584B1 is shown.

[0007] The microphone 1 includes a frame (not shown) that at least partially defines a first region 11 and a second region 12, an element 13 movable relative to the frame, and a device 14 for transmitting movement between the first region 11 and the second region 12. The first region 11 and the second region 12 of the microphone 1 are sealed relative to each other.

[0008] The movable element 13 (also called a piston) is in contact with the first region 11 and includes a membrane 131 and a reinforcing structure 132 for reinforcing the membrane. The role of the membrane 131 of the piston 13 is to collect the pressure difference between its two sides over its entire surface, thereby inferring the change in atmospheric pressure. One side of the membrane 131 is subjected to atmospheric pressure (the change in which we wish to detect), and the opposite side of the membrane 131 is subjected to a reference pressure.

[0009] Furthermore, the microphone 1 includes capacitive detection means 15 arranged in the second region 12. These capacitive detection means 15 make it possible to measure the displacement of the piston 13 and thus the pressure difference between its two faces. These capacitive detection means preferably include a movable electrode 151 and at least one fixed electrode arranged opposite the movable electrode 151. These electrodes form the armatures of a capacitor, the capacitance of which varies according to the displacement of the piston 13.

[0010] The transmission device 14 is mounted so as to be rotatable relative to the frame by means of a number of pivot hinges 16. The transmission device 14 includes two first transmission arms 141 extending in the first region 11, two second transmission arms 142 extending in the second region 12, and two transmission shafts 143 extending partly in the first region 11 and partly in the second region 12. Each transmission shaft 143 connects a first transmission arm 141 to a second transmission arm 142.

[0011] Each first transmission arm 141 includes 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 includes 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.

[0012] Patent FR3059659B1 describes a capacitive detection microphone similar to Figure 1 a capacitive detection microphone. The capacitive detection means includes a movable electrode and two fixed electrodes, the movable electrode being arranged between the two fixed electrodes. The electrodes form the armatures of two capacitors, the capacitances of which vary in opposite directions according to the displacement of the piston. Thus, the measurement of the piston displacement is a differential measurement.

[0013] To achieve this differential measurement, the capacitor is first charged by applying a direct current (DC) bias voltage between the movable electrode and the fixed electrode via a high resistance. The movement of the piston causes a change in capacitance and thus a change in the voltage between the fixed electrodes (the charge of the capacitor being substantially constant at audible frequencies (usually greater than 100 Hz)), which voltage change can be read by an instrumentation amplifier.

[0014] These capacitive detection microphones may fail due to the collapse of the movable electrode (referred to as "pull-in"), which is common in all electromechanical systems including capacitive measurement or actuation devices. This collapse phenomenon is caused by electrostatic forces that tend to bring the movable electrode closer to the fixed electrode (or one of the fixed electrodes in a plurality of fixed electrodes) and depends on the square of the bias voltage. The electrostatic force also depends on the displacement of the movable electrode, and this electrostatic force can be approximated to the first order by a constant force plus the force exerted by a negative stiffness spring for small displacements.

[0015] To avoid this collapse phenomenon (up to a certain point), an elastic force opposite to the electrostatic force is applied. This elastic force can be generated by a spring that connects the frame of the movable electrode 151 to the frame of the microphone 1. The greater the stiffness of the spring, the greater the voltage value (the so-called "pull-in voltage") at which the electrostatic force overcomes the elastic force, and the higher the voltage at which the movable electrode 151 can be biased. This is advantageous because the sensitivity of the microphone 1 increases with the increase in the bias voltage.

[0016] A disadvantage of the above capacitive detection microphones is that energy is lost in the deformation of the piston 13, the transmission device 14, and the frame of the movable electrode 151, which means a useful signal is lost when detecting the dynamic change of pressure. One solution to reduce these energy losses and thus improve the microphone sensitivity is to strengthen the reinforcement structure 132 of the piston 13, the transmission device 14, and the frame of the movable electrode 151. However, this solution will greatly increase the mass of these moving parts and reduce the resonance frequency of the microphone. Summary of the Invention

[0017] Therefore, there is a need to provide an electromechanical system with capacitive detection or capacitive actuation that provides better performance, especially in terms of sensitivity and resonance frequency.

[0018] According to the present invention, this need tends to be met by providing an electromechanical system comprising:

[0019] - a frame;

[0020] - a first element capable of moving relative to the frame; and

[0021] - a capacitive measurement or actuation device comprising:

[0022] - a first electrode capable of moving relative to the frame; and

[0023] - at least one electrode fixed relative to the frame and separated from the first movable

[0024] electrode by a first dielectric;

[0025] - A first motion transmission device that connects the first movable element to the first movable electrode, and the first transmission device is capable of rotating relative to the frame through a plurality of first pivot hinges.

[0026] The remarkable feature of this electromechanical system is that the electromechanical system further includes a second element that is movable relative to the frame, and the second movable element is connected to the capacitance measurement or actuation device.

[0027] Preferably, the first motion transmission device also connects the second movable element to the first movable electrode.

[0028] Preferably, the capacitance measurement or actuation device further includes:

[0029] - A second electrode that is capable of moving relative to the frame; and

[0030] - At least one additional electrode that is fixed relative to the frame and is separated from the second movable electrode by a second dielectric;

[0031] The system further includes a second motion transmission device that connects the first movable element and the second movable element to the second movable electrode, and the second transmission device is capable of rotating relative to the frame through a plurality of second pivot hinges.

[0032] In a preferred embodiment, the first transmission device includes:

[0033] - A first transmission shaft that has a first longitudinal rotation axis;

[0034] - At least one first transmission arm that includes a first end coupled to the first movable element and a second end integrated with the first transmission shaft; and

[0035] - At least one second transmission arm that includes a first end coupled to the second movable element and a second end integrated with the first transmission shaft.

[0036]

[0037]

[0038] Preferably, each of the first movable element and the second movable element includes a membrane and a membrane reinforcement structure.

[0039] In addition to the features just mentioned in the foregoing paragraphs, the electromechanical system according to the present invention may have one or several of the following additional features, and the one or several additional features are considered individually or in any technically possible combination:

[0040] - The second movable element is connected to the first movable electrode;

[0041] - The capacitance measuring or actuating device further comprises:

[0042] - A second electrode capable of moving relative to the frame; and

[0043] - At least one additional electrode fixed relative to the frame and separated from the second movable electrode by a second dielectric;

[0044] The second movable element is connected to the second movable electrode;

[0045]

[0046] - The first transmission device is located on the first side of the membrane of the first (respectively, second) movable element, and the reinforcing structure of the first (respectively, second) movable element includes a first beam located on the first side of the membrane, the first beam extending in the length direction of the first (respectively, second) movable element, preferably along the median line of the first (respectively, second)

[0047] movable element;

[0048] - The length of the first beam is greater than or equal to 50% of the length of the first (or second) movable element;

[0049] - The thickness of the first beam is between 5 μm and 800 μm;

[0050] - The reinforcing structure of the first (or second) movable element further includes a second beam located on the second opposite side of the membrane,

[0051] and superimposed on the first beam;

[0052] - The thickness of the second beam is strictly less than the thickness of the first beam, preferably between 5 μm and 50 μm;

[0053] - The reinforcing structure of the first (respectively, second) movable element further includes edges located on the second opposite

[0054] sides of the membrane and extending perpendicular to the first beam;

[0055] - The first movable element and the second movable element are the same;

[0056] - The first movable element and the second movable element are not the same;

[0057] ​- The capacitance measuring or actuating device is located between the first movable element and the second movable element;

[0058] - At least one first pivot hinge in the first pivot hinge is located at the level of the first movable electrode;

[0059] - The other first pivot hinge in the first pivot hinge is located at the first end of the first transmission device; and

[0060] - The other first pivot hinge in the first pivot hinge is located at the second opposite end of the first transmission device;

[0061] - At least one second pivot hinge in the second pivot hinge is located at the second movable electrode;

[0062] - The other second pivot hinge in the second pivot hinge is located at the first end of the second transmission device;

[0063] - The other second pivot hinge in the second pivot hinge is located at the second opposite end of the second transmission device;

[0064] - The first movable element and the second movable element are in contact with the first region, and the first movable electrode is located in the second region

[0065] where the second region is sealed from the first region;

[0066] - The first movable element and the second movable element translate relative to the frame;

[0067] - The first movable element and the second movable element rotate relative to the frame;

[0068] - The first movable electrode is connected to the first transmission shaft;

[0069] - The first movable electrode is integrated with the first transmission shaft such that the first movable electrode is mounted to be rotatable about the first longitudinal

[0070] axis of rotation;

[0071] - The second transmission device includes:

[0072] - A second transmission shaft having a second longitudinal axis of rotation;

[0073] - At least one third transmission arm including a first end coupled to the first movable element and a second end integrated with

[0074] the second transmission shaft;

[0075] - At least one fourth drive arm, the at least one fourth drive arm including a first end coupled to the second movable element and a second end integrated with

[0076] the second drive shaft;

[0077] - The second movable electrode is connected to the second drive shaft;

[0078] - The second movable electrode is integrated with the second drive shaft such that the second movable electrode is mounted to be rotatable about the second longitudinal rotation axis. Description of the Drawings

[0079] Other features and advantages of the present invention will become apparent from the following description given by way of illustration and not limitation with reference to the accompanying drawings, in which:

[0080] - Figure 1 is a partial perspective view of a capacitive detection microphone according to the prior art;

[0081] - Figure 2 is a partial bottom view of an electromechanical system according to a first embodiment, the electromechanical system including a capacitive detection or actuation device;

[0082] - Figure 3 is Figure 2 a partial top view of the capacitive detection or actuation device of the electromechanical system in

[0083] - Figure 4A is a sectional view of the electromechanical system taken along section line A-A in Figure 3 ;

[0084] - Figure 4B is Figure 3 a sectional view of the electromechanical system taken along section line C-C in

[0085] - Figure 5 is a partial bottom view of an electromechanical system according to a second embodiment;

[0086] - Figure 6 is Figure 5 a partial top view of the electromechanical system in

[0087] - Figure 7 is a partial bottom view of an electromechanical system according to a third embodiment;

[0088] For clarity, throughout the drawings, like or similar elements are denoted by the same reference numerals. Detailed Description

[0089] Figure 2 、 Figure 3 and Figures 4A to 4BShows a part of the electromechanical system 2 with capacitance detection or capacitance actuation according to the first embodiment. The electromechanical system 2 can form an electroacoustic transducer, for example, a microphone or a speaker, or a differential pressure sensor. In the following description, a microphone with capacitance detection will be taken as an example.

[0090] The electromechanical system 2 includes:

[0091] - A frame 10;

[0092] - A movable element 13 that contacts a first region 11;

[0093] - A capacitance detection (or measurement) device 15', which includes a first movable electrode 151 movable relative to the frame 10, a second movable electrode 152 movable relative to the frame 10. The first movable electrode 151 and the second movable electrode 152 are located in a second region 12 sealed relative to the first region 11; and

[0094] - A first device 14a for transmitting motion between the movable element 13 and the first movable electrode 151 (i.e., between the first region 11 and the second region 12); and

[0095] - A second device 14b for transmitting motion between the movable element 13 and the second movable electrode 152.

[0096] - A second device 14b for transmitting motion between the movable element 13 and the second movable electrode 152.

[0097] Figure 2 Is a top view of the electromechanical system 2, which shows a first part 101 of the frame 10, the movable element 13, the transmission devices 14a to 14b, and the movable electrodes 151 to 152 of the capacitance detection device 15'. Figure 3 Is a top view showing only a part of the capacitance detection device 15' (including the first movable electrode 151). Figures 4A to 4B Are respectively according to Figure 3 The different cross-sectional views of the electromechanical system 2 of the cross-sections A-A and C-C shown in. Figures 4A to 4B Partially shows the frame 10, the first transmission device 14a, and the capacitance detection device 15'.

[0098] The movable element 13 (hereinafter referred to as the piston) can translate relative to the frame 10 in a direction (Z) perpendicular to the Figure 2 plane (XY). The movable element preferably includes a membrane 131 and a reinforcing structure 132 for reinforcing the membrane 131, and the reinforcing structure is also called a skeleton or an armature. The function of the membrane 131 of the piston 13 is to collect the pressure difference between its two sides over its entire surface, thereby inferring the change in atmospheric pressure.

[0099] The membrane 131 of the piston 13 can partially delimit a closed reference volume in which a reference pressure prevails. The membrane separates this reference volume from a cavity that is open to the external environment. Thus, one face of the membrane 131 is subject to the reference pressure, and the opposite face of the membrane 131 is subject to the atmospheric pressure (the variations in which are to be detected in the case of a microphone). Alternatively, the reference volume can be quasi-closed, that is to say there is a groove around the piston (the groove is cut off). This groove allows the piston to move and allows air to leak between the reference volume and the outside. This leakage is small such that the pressure can equilibrate slowly, filtering out only the low-frequency pressure variations.

[0100] The first region 11 encompasses a cavity that is open to the external environment and subject to the atmospheric pressure and a reference volume that is subject to the reference pressure.

[0101] The capacitance detection device 15’ measures the displacement of the piston 13 and thus the pressure difference between its two faces. In addition to the first movable electrode 151 and the second movable electrode 152, the capacitance detection device also includes at least one fixed electrode (fixed relative to the frame 10) separated from the first movable electrode 151 by a first dielectric, and at least one additional fixed electrode separated from the second movable electrode 152 by a second dielectric.

[0102] Each movable electrode and the associated one or more fixed electrodes form the armatures of one or several capacitors, the capacitance of which varies according to the displacement of the piston 13. The fixed electrodes can also be referred to as “counter-electrodes”.

[0103] The first dielectric and the second dielectric are not solids (but are preferably constituted by a gas or a mixture of gases) so as not to impede the movement of the movable electrode 151. The second dielectric is the same as the first dielectric since both of the movable electrodes 151 to 152 are located in the second region 12.

[0104] Advantageously, the second region 12 is a controlled atmosphere cavity to reduce the phenomena of viscous friction and the associated acoustic noise. A “controlled atmosphere cavity” means a cavity at a reduced pressure, which is generally less than 1000 mbar, preferably less than 1 mbar. In this way, the second region 12 is subject to a pressure that is much lower than the atmospheric pressure or the reference pressure.

[0105] The first transmission device 14a is mounted so as to be rotatable relative to the frame 10 by means of a number of first pivot hinges 16a. The first transmission device includes a first transmission shaft 144a and one or several first transmission arms 145a (also called lever arms).

[0106] The first transmission shaft 144a has a first longitudinal axis of rotation Xa (hereinafter referred to as the first axis Xa) extending in the first direction X. In other words, the first transmission shaft 144a can pivot about the first axis Xa by itself. The first transmission shaft extends in the opposite direction to the piston 13, opposite to the region located between the piston 13 and the first movable electrode 151, and opposite to the first movable electrode 151.

[0107] Advantageously, the first movable electrode 151 is integrated 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. Therefore, the first movable electrode 151 is also mounted to be rotatable about the first axis Xa.

[0108] Therefore, the electromechanical system 2 has no motion conversion device (such as a torsion blade for switching from rotation to translation) between the first transmission device 14a and the first movable electrode 151. Therefore, there is no energy loss in these conversion members (for example, energy loss due to the deformation of the torsion blade).

[0109] The first transmission arm 145a (for example Figure 2 three of the first transmission arms) can extend perpendicular to the first axis Xa, in other words, in the second direction Y perpendicular to the first direction X. The first direction X and the second direction Y together with the perpendicular third direction Z form an orthogonal reference system.

[0110] Each first transmission arm 145a includes a first end coupled to the piston 13 and a second end integrated with the first transmission shaft 144a. One or several coupling elements 133 connect the reinforcement structure 132 of the piston 13 to the first end of each first transmission arm 145a. At least a part of the coupling element 133 (for example, a torsion blade) allows the transition from translational motion (piston 13) to rotational motion (first transmission shaft 144a and first movable electrode 151), while strongly coupling their displacements along the third direction Z. These coupling elements 133 can be elastically deformed.

[0111] The translational motion of the piston 13 causes the first transmission arm 145a and thus the first transmission shaft 144a to rotate about the first axis Xa. Then, this rotational motion is transmitted to the first movable electrode 151.

[0112] The first pivot hinge 16a (e.g., six first pivot hinges) is aligned in the first direction X here. Preferably, one of the plurality of first pivot hinges 16a is located at the end of the first transmission shaft 144a, on the piston 13 side (i.e., opposite to the first movable electrode 151), while the other first pivot hinges 16a are located on the first movable electrode 151 side. As will be described in detail below, the first movable electrode 151 is preferably connected to the first transmission shaft 144a at these other first pivot hinges 16a.

[0113] The second transmission device 14b is also mounted so as to be rotatable relative to the frame 10 via the second pivot hinge 16b. The second transmission device is constructed in the same manner as the first transmission device 14a. More particularly, the second transmission device includes a second transmission shaft 144b having a second longitudinal rotation axis Xb (hereinafter referred to as the second axis Xb) and second transmission arms 145b (e.g., three second transmission arms). Each second transmission arm 145b includes a first end coupled to the piston 13 (via one or several coupling elements 133) and a second end integrated with the second transmission shaft 144b. The second transmission arm 145b preferably extends perpendicular to the second axis Xb.

[0114] The second movable electrode 152 is advantageously integrated with the second transmission shaft 144b and thus rotates about the second axis Xb.

[0115] The second pivot hinge 16b is preferably distributed along the second axis Xb in the same manner as the first pivot hinge 16a is distributed along the first axis Xa (one of the second pivot hinges is located at the end of the second transmission shaft 144b, while the other second pivot hinges are located at the second movable electrode 152).

[0116] The first transmission arm 145a is coupled to the first half of the piston 13 ( Figure 2 the upper half in Figure 2 ), and the second transmission arm 145b is coupled to the second half of the piston 13 (

[0117] the lower half in Figure 2 ). In this way, the transmission devices 14a to 14b support the piston 13 and hold the piston in translation. Preferably, the piston 13 is held only by the first transmission arm 145a and the second transmission arm 145b. In this way, a larger proportion of the energy collected by the piston 13 is transmitted to the movable electrodes 151 to 152.

[0118] The first movable electrode 151 and the second movable electrode 152 can be the same and are symmetrically arranged with respect to the plane P of the first half and the second half of the separating piston 13. This symmetry enables the same reaction to be obtained for the two halves of the piston, thus enabling the piston to be held firmly during translation.

[0119] The first transmission device 14a and the second transmission device 14b can also be symmetric with respect to the plane P. Then, the first transmission shaft 144a and the first movable electrode 151 (about the first axis Xa) pivot in one direction, while the second transmission shaft 144b and the second movable electrode 152 (about the second axis Xb) pivot in the opposite direction.

[0120] The piston 13 can also be symmetric with respect to the plane P.

[0121] The symmetry of the piston 13 and the transmission devices 14a to 14b enables the energy collected by the piston 13 to be evenly distributed between the first movable electrode 151 and the second movable electrode 152. In fact, the mass of the piston 13 is evenly distributed between the first half and the second half, and thus evenly distributed between the first transmission device 14a and the second transmission device 14b.

[0122] Rotating the first movable electrode 151 and the second movable electrode 152 respectively along the same rotation axes as the first transmission device 14a and the second transmission device 14b enables a greater displacement of the movable electrodes 151 to 152 to be obtained for a given displacement of the piston 13 without increasing the overall size of the electromechanical system 2. Therefore, the movable electrodes 151 to 152 can be as close as possible to the piston 13.

[0123] From one movable electrode ( Figure 1 ) to two movable electrodes ( Figure 2 ) also does not significantly increase the overall size of the electromechanical system 2 because the two movable electrodes 151 to 152 can be arranged opposite to each other in the extension of the piston 13.

[0124] The displacement of each movable electrode 151, 152 relative to the piston 13 is a function of the distances L pist1 , L pist2 between the first ends of the transmission arms 145a, 145b and the respective rotation axes Xa, Xb. This distance can be of the same order of magnitude as the distances L elec1 , L elec2 between the longitudinal (i.e., along X) edges of the rotating electrodes 151, 152 and the rotation axes Xa, Xb.

[0125] More precisely, the Z-direction displacement of the longitudinal edge of the first movable electrode 151 is given by the following relation:

[0126] [Formula 1]

[0127]

[0128] where d zpist is the Z - displacement of the piston 13 (and thus the Z - displacement of all the first ends of the first drive arm 145a and the second drive arm 145b), L elec1 is the distance between the longitudinal edge of the first movable electrode 151 and the first axis Xa, L pist1 is the distance between the first end of each first drive arm 145a and the first axis Xa.

[0129] The Z - displacement of the longitudinal edge of the second movable electrode 152 is given by the following relation:

[0130] [Formula 2]

[0131]

[0132] where L elec2 is the distance between the longitudinal edge of the second movable electrode 152 and the second axis Xb, L pist2 is the distance between the first end of each second drive arm 145b and the second axis Xb.

[0133] The drive shafts 144a and 144b and the drive arms 145a to 145b can be particularly rigid and thus less sensitive to deformations equivalent to energy losses. This stiffness of the drive shafts 144a and 144b and the drive arms 145a to 145b can be determined in particular by a large thickness (measured in the third direction Z), which is preferably between 5 μm and 800 μm, more preferably between 50 μm and 200 μm. The drive shafts 144a and 144b and the drive arms 145a to 145b are advantageously formed by etching the substrate. The substrate can be thinned to a thickness of less than 200 μm.

[0134] When the drive shafts 144a and 144b rotate on their own, their inertia remains low and does not have a negative impact on the resonance frequency of the electromechanical system 2. However, the drive shafts can be perforated, as Figure 2 shown, to optimize the ratio of their stiffness to inertia. The drive shafts 144a and 144b are preferably perforated at least in the part facing the piston 13. This also makes it possible to limit the damping of the piston 13 (referred to as " squeeze - film damping"), which is a source of noise.

[0135] To minimize the inertia of the drive shafts 144a and 144b, the width (measured in the first direction Y) of these drive shafts is of the same order of magnitude as their thickness. Advantageously, it is between 5 μm and 800 μm.

[0136] The capacitive detection device 15' will now be described in more detail with reference only to the first movable electrode 151 (connected to the first drive device 14a). However, since the second movable electrode may be the same as the first movable electrode 151, this description applies, mutatis mutandis, to the second movable electrode 152 (connected to the second drive device 14b). Similarly, the description given for the first pivot hinge 16a applies to the second pivot hinge 16b.

[0137] Referring Figure 2 and Figure 3 , the first movable electrode 151 may include a membrane 1511 and a reinforcement structure 1512 for the membrane 1511. The reinforcement structure 1512 preferably includes a plurality of first beams 1512a extending parallel to each other. The reinforcement structure further includes second beams 1512b that are connected to the first beams 1512a at their ends.

[0138] The first beams 1512a preferably extend in the second direction Y, advantageously from a first edge of the first movable electrode 151 to an opposite second edge. These first beams are advantageously evenly spaced from each other to reinforce the membrane 1511 uniformly. The second beams 1512b preferably extend in the first direction X (i.e., perpendicular to the extension of the first beams 1512a).

[0139] The first movable electrode 151 advantageously has one or more planes of symmetry, for example, a plane parallel to the XZ plane (and thus perpendicular to the first beams 1512a) and another plane parallel to the YZ plane.

[0140] The reinforcement structure 1512 of the first movable electrode 151 is advantageously anchored or fused to the first drive device 14a at a part of the first pivot hinge 16a. Thus, compared with the microphone 1 of Figure 1 , the electromechanical system 2 lacks a second drive arm 142 extending into the second region 12.

[0141] More particularly, the reinforcement structure 1512 of the first movable electrode 151 is connected to the first drive device 14a, more particularly to the first drive shaft 144a, by columns 146 visible in Figure 4A and Figure 4B . The columns 146 of the first drive device 14a are similar to the drive shaft 143 of Figure 1 in that they partly extend into the first region 11 and partly extend into the second region 12. In fact, the seal between the first region 11 and the second region 12 is also made at the level of the first pivot hinge 16a associated with the first movable electrode 151.

[0142] Thus, the first drive device 14a is simplified to a first element (first drive shaft 144a and first drive arm 145a) extending only in the first region 11 and a second element (column 146) extending partly in the first region 11 and partly in the second region 12. This simplification of the first drive device 14a makes it possible to limit energy losses. In particular, there are no additional losses due to the deformation of the second drive arm 142.

[0143] The electromechanical system 2 is particularly compact because several functions (i.e., rotation of the first drive device 14a, sealing between the two regions 11 and 12, and connection to the first movable electrode 151) are performed at the same location.

[0144] Preferably, the anchoring between the reinforcement structure 1512 and the first drive device 14a is achieved by means of the first beams 1512a. At least some of these first beams merge into the first drive device 14a at respective first pivot hinges 16a. The anchoring points of each first beam 1512a are advantageously located in the middle along its length. Thus, the axis of rotation of the first movable electrode 151 lies in a plane of symmetry (perpendicular to the first beam 1512a) among the multiple planes of symmetry of the first movable electrode 151. The length of the first beam 1512a is measured in the second direction Y, while the width of the first beam is measured in the first direction X.

[0145] Each first beam 1512a merged with the first drive device 14a advantageously has a width that decreases away from the respective first pivot hinge 16a. In other words, the width of the first beam 1512a is maximum at the level of the first pivot hinge 16a.

[0146] In this first embodiment of the electromechanical system 2, each first beam 1512a of the reinforcement structure 1512 is merged into the first drive device 14a. In other words, each first beam 1512a is associated with a first pivot hinge 16a. Thus, the number of first pivot hinges 16a on the side of the first movable electrode 151 is equal to the number of first beams 1512a. This arrangement makes it possible to create a space 17 between two consecutive first pivot hinges 16a.

[0147] For each first pivot hinge 16a, the frame 10 may include two different first parts 101 arranged on both sides of the first beam 1512a associated with this first pivot hinge. The first beam 1512a is preferably connected to each first part 101 of the frame 10 by means of a torsion bar 162 (see Figure 3 ).

[0148] As Figure 3 , Figure 4A and Figure 4BAs shown, the capacitance detection device 15’ preferably includes two counter electrodes 153 and 154 associated with the first movable electrode 151: the first counter electrode 153, which is referred to as the positive electrode, and the second counter electrode 154, which is referred to as the negative electrode. Preferably, at least a part of the membrane 1511 of the first movable electrode 151 is located between the two counter electrodes 153 and 154 (see Figures 4A to 4B ). Thus, the first movable electrode 151 and the counter electrodes 153 and 154 form the armatures of two capacitors whose capacitances vary in opposite directions. Therefore, a differential measurement of the displacement of the piston 13 can be obtained. Due to the symmetry of the first movable electrode 151 and the counter electrodes 153 and 154 with respect to the first pivot hinge 16a (the plane of symmetry coincides with the section C-C), advantageously, the surfaces of the counter electrodes 153 and 154 facing the first movable electrode 151 are identical.

[0149] Advantageously, each counter electrode 153, 154 includes a first part 153a, 154a and a second part 153b, 154b located on both sides of the membrane 1511 and on both sides of the first pivot hinge 16a. The first parts (referred to as the upper parts) 153a, 154a and the second parts (referred to as the lower parts) 153b, 154b of the same counter electrode are electrically connected. This arrangement enables a fully differential measurement to be obtained even if the distance (referred to as the upper air gap) between the membrane 1511 and the upper parts 153a and 154a of the counter electrodes is different from the distance (lower air gap) between the membrane 1511 and the lower parts 153b and 154b of the counter electrodes.

[0150] The lower parts 153b and 154b of the counter electrodes 153 and 154 extend on both sides of the first pivot hinge 16a and below the first beam 1512a of the reinforcement structure 1512. In contrast, as Figure 3 shown, the upper parts 153a and 154a of the counter electrodes 153 and 154 are each preferably divided into several blocks (or sub-parts) separated by the first beam 1512a. Since the upper parts 153a and 154a of the counter electrodes 153 and 154 are inscribed in the reinforcement structure 1512, the surface area of these upper parts facing the membrane 1511 is smaller than the surface area of the lower parts 153b and 154b.

[0151] Referring to Figure 4A , the lower parts 153b and 154b of the counter electrodes 153 and 154 are preferably fixed to the annular part 102 of the frame 10 by annular seals 103, 105 made of an electrically insulating material (one annular seal for each lower part 153b, 154b), which annular part is located at the periphery of the first movable electrode 151. These annular seals 103, 105 (made of, for example, silica) further ensure the seal between the first region 11 and the second region 12.

[0152] Alternatively, the capacitance detection device 15’ may include (for each movable electrode) only one counter electrode (lower electrode or upper electrode), two counter electrodes (upper electrode and lower electrode) (but these two counter electrodes are located on only one side of the pivot hinge 16 (pseudo-differential detection)), or even two lower counter electrodes or upper counter electrodes arranged on both sides of the pivot hinge 16 (differential detection).

[0153] As previously described, the seal between the first region 11 and the second region 12 of the electromechanical system 2 can be performed at the first pivot hinge 16a located on the side of the first movable electrode 151. As Figure 4A and Figure 4B shown, each first pivot hinge 16a associated with the first movable electrode 151 includes a sealing insulating element 161 that can be elastically deformed under the influence of the rotational displacement of the first transmission device 14a. The sealing insulating element 161 is preferably in the form of a sealing film.

[0154] Each sealing insulating element 161 is preferably traversed by a column 146 associated with the first transmission device 14a. The sealing insulating element 161 extends, for example, from the associated column 146 to the lower portions 153b and 154b of the counter electrodes 153 and 154 (see Figure 4A ) and the first portion 101 of the frame 10 (see Figure 4B ), and the sealing insulating element is anchored to the first portion by annular seals 103, 105 made of electrically insulating material.

[0155] In addition, each first pivot hinge 16a (associated with the first movable electrode 151) advantageously includes two torsion blades 162 (one torsion blade for each first portion 101 of the frame 10). The torsion blades 162 are sized to be deformable in torsion and allow the first transmission device 14a and the first movable electrode 151 to rotate while restricting their translational movement, particularly translational movement in the third Z direction (so-called "out-of-plane" translation). The two torsion blades 162 connect the reinforcement structure 1512 of the first movable electrode 151 (which is integrated into the column 146 of the first transmission device 14a) to the first portion 101 of the frame 10 (also see Figure 4B ). These torsion blades are preferably aligned and arranged to be opposite to the first beam 1512a associated with the first pivot hinge 16a in the radial direction.

[0156] The first pivot hinge 16a located at the end of the first transmission shaft 144a advantageously includes a sealing insulating element 161 (preferably in the form of a film) and two torsion blades 162, but does not participate in the seal between the first region 11 and the second region 12 (is only located in the first region 11).

[0157] The electromechanical system 2 includes an elastic device connected to the first movable electrode 151 and configured to generate an elastic force opposite to the movement of the first movable electrode 151. The function of these elastic devices is to counteract the pull-in phenomenon of the first movable electrode 151. The stiffness of these elastic devices affects the collapse voltage (or the "pull-in voltage" of the system), and thus affects the ability to bias the first movable electrode 151.

[0158] The "anti-pull-in" elastic device (possibly via the post 146 of the first transmission device 14a) mechanically connects the reinforcement structure 1512 of the first movable electrode 151 to the frame 10 and / or elements integrated with the frame, such as the counter electrodes 153 and 154. Therefore, the stiffness of the first transmission device 14a or the stiffness of the reinforcement structure 1512 itself is not considered as the "anti-pull-in" elastic device.

[0159] The "anti-pull-in" elastic device here includes the hermetic insulating element 161 and, in appropriate cases, the torsion blade 162. Therefore, the hermetic insulating element 161 and the torsion blade 162 perform several functions simultaneously.

[0160] At the place where the reinforcement structure 1512 is the most rigid (i.e., at the first pivot hinge 16a), the anti-pull-in elastic device is connected to the reinforcement structure 1512. In this way, the stiffness of the anti-pull-in spring device is not reduced by series elements with too low stiffness. This stiffness can also be easily controlled by adjusting the dimensions of the hermetic insulating element 161 and the torsion blade 162. The hermetic insulating element 161 can be defined by anisotropic etching of a sacrificial layer (e.g., SiO2) and produced in a structural layer with a controlled thickness. This type of etching provides good control over the dimensions of the hermetic insulating element 161. Therefore, the stiffness of the hermetic insulating element 161 exhibits little dispersion (mainly between different electromechanical systems manufactured on the same wafer or different wafers).

[0161] The second movable electrode 152 is advantageously connected to the second transmission device 14b in the same way as the first movable electrode 151 is connected to the first transmission device 14a. Therefore, the electromechanical system 2 also includes "anti-pull-in" elastic devices connected to the second movable electrode 152, and these elastic devices preferably include the hermetic insulating element 161 and, in appropriate cases, the torsion blade 162 of the second pivot hinge 16b.

[0162] The hermetic insulating element 161 and, in applicable cases, the torsion blade 162 advantageously constitute the only "anti-pull-in" device of the electromechanical system 2. Therefore, the electromechanical system 2 is particularly compact.

[0163] The above-mentioned electromechanical system 2 can be manufactured using the methods described in patents FR3059659B1 and FR3114584B1. In particular, it is manufactured starting from a stack of layers including a continuous substrate, a first sacrificial layer, and a first structural layer. This stack can in particular be a multi-layer structure of the SOI (silicon-on-insulator) type, commonly known as an SOI substrate.

[0164] This substrate is in particular used to manufacture, by etching, the first elements of the transmission devices 14a and 14b (the drive shafts 144a and 144b and the drive arms 145a and 145b), the lower parts of the counter electrodes 153 and 154, and a part of the frame 10. The substrate can be made of a semiconductor material (such as silicon).

[0165] The first structural layer is in particular used to manufacture the membrane 131 of the piston 13, the membranes 1511 of the movable electrodes 151 and 152, and the hermetic insulating element 161 (hermetic membrane). The thickness of this first structural layer is less than the thickness of the substrate, preferably between 100 nm and 10 μm. This first structural layer is preferably made of the same material as the substrate (such as silicon).

[0166] The first sacrificial layer is intended to partially disappear during the manufacture of the electromechanical system 2 in order to release the membrane 131 of the piston 13, the membranes 1511 of the movable electrodes 151 and 152, and the hermetic insulating element 161. In particular, the thickness of the first sacrificial layer defines the distance between the membrane 1511 and the lower parts of the counter electrodes 153 and 154 (lower air gap). This layer also acts as a barrier layer during the etching of the substrate, the membrane 152a, and the second structural layer (the "MEMS" layer described later). The remaining part of the first sacrificial layer forms the annular seals 103, 105, and the lower post 104. The first sacrificial layer can be made of a dielectric material, which is preferably silicon nitride or silicon oxide, for example, silicon dioxide (SiO2). For example, the thickness of this first sacrificial layer is between 100 nm and 10 μm.

[0167] As described in the above patents, a second sacrificial layer is preferably deposited on the first structural layer by epitaxy, and a second structural layer is formed on the second sacrificial layer.

[0168] The second structural layer is etched to define at least a part of the following: the reinforcement structure 132 of the piston 13, the reinforcement structures 1512 of the movable electrodes 151 and 152, the torsion blades 162, the upper parts of the counter electrodes 153 and 154, the first part 101 of the frame 10, and the second annular part 102. Advantageously, this second structural layer is made of the same material as the first structural layer (such as silicon). The thickness of the second structural layer is preferably between 5 μm and 50 μm.

[0169] By directly growing a second structural layer (the first and second sacrificial layers have been pre-opened) from the substrate at the positions of the pivot hinges 16a, 16b, the reinforcement structures 1512 of each movable electrode 151, 152 are fused to the corresponding transmission devices 14a, 14b. During this epitaxial growth, the columns 146 of the transmission devices 14a, 14b are formed.

[0170] During the etching of the second structural layer, the second sacrificial layer is specifically used as a barrier layer. The second sacrificial layer is partially removed to release the membranes 131 of the piston 13, the membranes 1511 of the movable electrodes 151 and 152, and the sealing insulating elements 161. The thickness of the second sacrificial layer defines the distance between the membrane 1511 and the upper part (upper air gap) of the counter electrodes 153 and 154. The second sacrificial layer is advantageously formed of the same dielectric material (e.g., silicon oxide) as the first sacrificial layer. The thickness of the second sacrificial layer can be between 100 nm and 10 μm.

[0171] Figure 5 and Figure 6 A second embodiment of the electromechanical system 2 is shown. Figure 5 is a top view of a part of the electromechanical system 2, similar to Figure 2 similar. Figure 6 is a top view of the same part of the electromechanical system 2.

[0172] The main difference between this second embodiment and the first embodiment is that the electromechanical system 2 includes two (instead of a single) movable elements or pistons.

[0173] Thus, in addition to the frame 10, the first transmission device 14a and the second transmission device 14b, and the capacitance detection device 15' including two movable electrodes 151 and 152, the electromechanical system 2 further includes a first piston 13a and a second piston 13b.

[0174] The first piston 13a is connected to the first movable electrode 151 through the first transmission device 14a on the one hand, and to the second movable electrode 152 through the second transmission device 14b on the other hand.

[0175] The second piston 13b is connected to the first movable electrode 151 through the first transmission device 14a on the one hand, and to the second movable electrode 152 through the second transmission device 14b on the other hand.

[0176] Thus, each transmission device 14a, 14b connects the two pistons 13a and 13b to the capacitance detection device 15', and more particularly, to the movable electrodes 151, 152 associated with the transmission devices 14a, 14b.

[0177] Previously, reference has been made to Figure 2 , Figure 3 andFigures 4A to 4B Describes how the movable electrodes 151 and 152 are constructed and how these movable electrodes are connected to the drive devices 14a and 14b. Figure 5 The movable electrodes 151 and 152 in Figure 2 are only smaller than the movable electrodes in

[0178] so as to best show the two pistons.

[0179] The pistons 13a and 13b are subject to the same pressure difference. These pistons are also mounted such that they can move in the same way relative to the frame 10, preferably translating along the third direction Z. Thus, the pistons 13a and 13b have the same displacement.

[0180] Each of the pistons 13a and 13b includes a membrane 131 and a membrane reinforcement structure 132. The effective surface area and mass of the first piston 13a are equal to or approximately equal to (within 5%) the effective surface area and mass of the second piston 13b. The effective surface area of the piston is defined as the surface area in contact with the first region 11 (in other words, the surface area where the pressure difference is obtained). Thus, the electromechanical system 2 is generally balanced.

[0181] Viewed from the front, the pistons 13a and 13b preferably have the same shape, such as a rectangle with rounded corners. The dimensions (length, width) of the first piston 13a are equal to or substantially equal to (within 5%) the dimensions of the second piston 13b. The width of the piston is measured in the first direction X, and the length of the piston is measured in the second direction Y.

[0182] For example, Figure 5 the two pistons 13a and 13b in Figure 2 have the same length (measured in Y) as the single piston 13 in

[0183] but the width (measured in X) is less than or equal to half of the piston 13. Figure 2 ) provides a better trade-off between stiffness and mass.

[0184] In fact, since the two pistons 13a and 13b are smaller than a single piston, they are more rigid under all other equal conditions (thickness, reinforcement structure, etc.), and thus are subject to less deformation. For the same (cumulative) mass, they can be more rigid, or for the same stiffness level, they can be lighter, or even lighter while being more rigid. In addition, the parts of the transmission devices 14a and 14b for holding the pistons 13a and 13b (each piston is located between two pivot hinges 16a, 16b positioned on both sides of the piston) are shorter (due to the smaller width of the pistons), so the weight of these parts can be reduced without reducing the stiffness of the pistons.

[0185] Advantageously, the pistons 13a and 13b are identical. These pistons can be arranged symmetrically with respect to the plane passing through the movable electrodes 151 and 152. Similarly, the transmission devices 14a, 14b are preferably symmetric with respect to this plane.

[0186] As in the first embodiment (see Figure 2 ), the first transmission device 14a is mounted to rotate relative to the frame 10 through a plurality of first pivot hinges 16a. In Figure 5 the illustrated embodiment, at least one of the first pivot hinges 16a is located at the first movable electrode 151, another first pivot hinge 16a is located at the first end of the first transmission device 14a (beyond the first piston 13a), and another first pivot hinge 16a is located at the second opposite end of the first transmission device 14a (beyond the second piston 13b).

[0187] The second transmission device 14b is rotatably mounted relative to the frame 10 through the second pivot hinge 16b. Preferably, the second pivot hinge 16b is arranged in the same manner as the first pivot hinge 16a.

[0188] In this second embodiment, each of the transmission devices 14a, 14b includes:

[0189] - Drive shafts 144a, 144b that rotate about their longitudinal axes Xa, Xb, to which the movable electrodes 151, 152 are connected;

[0190]

[0191] - One or more transmission arms (or lever arms) 145a, 145b that have a first end integrated with the drive shafts 144a, 144b and a second end coupled to the first piston 13a;

[0192]

[0193] - one or more additional drive arms (or lever arms) 145c, 145d, the one or more additional drive arms having a first end integrated with the drive shafts 144a, 144b and a second end coupled to the second piston 13b.

[0194] Advantageously, the drive devices 14a and 14b have a lattice structure that enables these drive devices to transmit motion with as little deformation as possible while minimizing inertia.

[0195] The first piston 13a and the manner in which it is connected to the drive devices 14a and 14b will now be described in more detail. This description applies, mutatis mutandis, to the second piston 13b.

[0196] Thus, the reinforcement structure 132 of the first piston 13a advantageously includes a first beam 1321 on the side of the membrane 131 where the drive devices 14a and 14b are located, the first beam extending along the length of the first piston 13a. As Figure 5 shown, the first beam 1321 may extend along the midline M of the first piston 13a or parallel to the midline M at a distance less than one quarter of the width of the first piston 13a. The first beam 1321 advantageously has the same thickness as the drive shafts 144a, 144b and the drive arms 145a, 145b, i.e., a thickness between 5 μm and 800 μm. The first beam is formed simultaneously with the drive shafts and the drive arms by etching the substrate.

[0197] Due to the large thickness of the first beam, the first beam 1321 greatly contributes to strengthening the first piston 13a in its largest dimension (length), thereby reducing the deformation of the first piston 13a. Thus, the first beam significantly improves the sensitivity.

[0198] The first beam 1321 preferably extends over more than 50% of the length of the first piston 13a.

[0199] Preferably, on this side of the membrane 131, the reinforcement structure 132 includes only the first beam 1321.

[0200] On the other side of the membrane 131, as Figure 6 shown, the reinforcement structure 132 for the first piston 13a advantageously includes a second beam 1322 superimposed on the first beam 1321. The thickness of the second beam 1322 is strictly less than the thickness of the first beam 1321. The second beam may be formed in the second structural layer having a thickness between 5 μm and 50 μm. The length of the second beam 1322 may be equal to the length of the first beam 1321.

[0201] Thus, the second beam 1322 extends at least a portion of the first beam 1321 in the third direction Z to achieve a greater thickness. This second beam only slightly increases the mass of the first piston 13a (the increase is less significant because the second beam has a smaller thickness compared to the first beam 1321), but significantly increases the stiffness of the piston (since the stiffness varies as a function of the cube thickness).

[0202] On the same side as the second beam 1322, the reinforcement structure 132 may also include edges 1323 that are perpendicularly oriented to the first beam 1321 (and thus preferably parallel to the first axis Xa). These ridges 1323 reinforce the first piston 13a over its entire width. Since the width is the smallest side of the first piston 13a, the ridges 1323 do not need to be thick (unlike the first beam 1321). The edges 1323 preferably have the same thickness as the second beam 1322 (between 5 μm and 50 μm). In this way, these ridges do not significantly increase the mass of the first piston 13a. These ridges are also formed by etching the second structural layer. These ridges may extend from one edge of the first piston 13a to the other edge.

[0203] At least a portion of the edges 1323 may abut against a stop element belonging to the frame of the electromechanical system 2. These stop elements are provided, for example, in the form of beams that extend opposite to the edges 1323 to prevent the first piston 13a and the movable electrodes 151, 152 from being damaged when the first piston 13a is subjected to a very large pressure difference (e.g., during a reliability test).

[0204] Finally, the reinforcement structure 132 may include a frame 1324 located at the periphery of the first piston 13a. The frame 1324 preferably has the same thickness as the second beam 1322. This frame can also be formed by etching the second structural layer.

[0205] The multiplication of the number of pistons greatly simplifies their reinforcement structure. Compared to the piston 13 in Figure 2 , the mass of the two pistons 13a and 13b is reduced while their stiffness is increased. This represents a twofold improvement in performance.

[0206] The electromechanical system 2 does not necessarily include two movable electrodes 151 and 152 and two transmission devices 14a and 14b. The electromechanical system may include a single movable electrode and a single transmission device (see Figure 7 ), or may include a single movable electrode and two transmission devices connected to the single movable electrode.

[0207] Figure 7 A third embodiment is shown in which, in addition to the two pistons 13a and 13b, the electromechanical system 2 further includes a single movable electrode 151 (e.g.,Figure 5 of the type shown) and a single transmission device 14a (e.g., Figure 5 of the type shown).

[0208] Pistons 13a and 13b can here be rotatably moved (and not translatable) about axis Xp by a pivot hinge or hinges (not shown) different from the first pivot hinge 16a. The rotational movement of pistons 13a and 13b (about axis Xp) causes the transmission shaft 144a of transmission device 14a to rotate (about its own axis Xa) via transmission arms 145a, 145c, and the transmission shaft 144a (here in rotation about axis Xa) moves the movable electrode 151.

[0209] The electromechanical system 2 is not limited to the Figures 2 to 7 described embodiment, and many alternatives and modifications of the electromechanical system will be apparent to those skilled in the art.

[0210] In particular, the first piston 13a and the second piston 13b can be connected to the capacitance detection device 15' by two (four) separate transmission devices, in particular, to the first movable electrode 151 (or the first movable electrode 151 and the second movable electrode 152).

[0211] Furthermore, the second piston 13b does not necessarily have to be connected to the same movable electrode (or the same plurality of movable electrodes) as the first piston 13a. Thus, the first piston 13a can be connected to the first movable electrode 151 by a first transmission device, while the second piston 13b is connected to the second movable electrode 152 by a second transmission device.

[0212] The transmission devices 14a and 14b (more particularly, the transmission shafts 144a and 144b) can have other geometries. The number of transmission arms 145a, 145b can be greater than 3.

[0213] For each transmission device 14a, 14b, the electromechanical system 2 can also include one or several additional pivot hinges (not shown in the figures), which are between the pivot hinges at each end of the transmission shafts 144a, 144b and the pivot hinges connecting the movable electrodes 151, 152. These additional pivot hinges are preferably located in the first region 11 and thus do not contribute to the sealing between the two regions.

[0214] Conversely, Figures 5 to 7 the electromechanical system (two pistons) can include only three pivot hinges for each transmission device 14a, 14b, one pivot hinge at the movable electrodes 151, 152 and one pivot hinge at each end of the transmission shafts 144a, 144b.

[0215] The electromechanical system 2 has been described by way of example with a microphone having capacitance detection, the microphone including one or several pistons 13, 13a and 13b, each piston being equipped with a membrane 131 subjected on the one hand to atmospheric pressure and on the other hand to a reference pressure. However, the electromechanical system may form other types of capacitance detection transducers, in particular loudspeakers (sound emitters) or ultrasonic emitters (which are electroacoustic transducers), or even differential pressure sensors.

[0216] In the case of a differential pressure sensor, the first face of the membrane 131 (of each piston) 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 capacitance detection means 15’. The membrane 131 of the piston is integrated with the frame 10 so as to be sealed, and the reinforcement structure 132 of the piston is absent or reduced so as not to anchor the piston to the frame.

[0217] In the case of a loudspeaker or an ultrasonic emitter, capacitance actuation means replace the capacitance detection means 15’. These capacitance actuation means also include two movable electrodes and at least one counter electrode for each movable electrode. These movable electrodes are moved by electrostatic force, and this movement is transmitted by transmission means 14a, 14b to the piston 13 or the pistons 13a and 13b. The movement of the membrane 131 of one or several pistons 13, 13a and 13b makes it possible to emit sound (or ultrasound).

[0218] The second region 12 may include two chambers in a controlled atmosphere, one chamber containing the first movable electrode 151 and the other chamber containing the second movable electrode 152.

[0219] The sealed first region 11 and the sealed second region 12 are not necessarily subjected to different pressures. The first region 11 may also be an invasive environment, and the movable electrodes of the capacitance means (detection means or actuation means) are placed in the second region 12 so as to protect these movable electrodes from this invasive environment in addition to reducing viscous friction and thus reducing acoustic noise.

[0220] The electromechanical system 2 may even have no sealing means between the first region 11 and the second region 12 (which amounts to considering only one region). More particularly, the pivot hinge 16 may not have any sealing and insulating element 161. In fact, the torsion blade 162 may be sufficient for the rotation of the transmission means 14a, 14b and may act as a “pull-in prevention” elastic means.

Claims

1. An electromechanical system (2), comprising: - a frame (10); - a first movable element (13a) movable relative to the frame (10); as well as - a capacitance measuring or actuating device (15'), comprising: o a first movable electrode (151) movable relative to the frame (10); and o at least one electrode (153, 154), the at least one electrode being fixed relative to the frame (10) and separated from the first movable electrode (151) by a first dielectric; a first motion transmission device (14a) connecting the first movable element (13a) to the first movable electrode (151), the first motion transmission device (14a) being rotatably movable relative to the frame (10) via a plurality of first pivot hinges (16a); Characterized in that the electromechanical system further comprises a second movable element (13b), which is movable relative to the frame (10) and which is connected to the capacitance measuring or actuating device (15').

2. The system (2) according to claim 1, wherein: The first motion transmission device (14a) also connects the second movable element (13b) to the first movable electrode (151).

3. The system (2) according to claim 2, wherein: The capacitance measuring or actuating device (15') further comprises: - a second movable electrode (152) movable relative to the frame (10); and - at least one additional electrode, fixed relative to the frame (10) and separated from the second movable electrode (152) by a second dielectric; The system also includes a second motion transmission device (14b), which connects the first movable element (13a) and the second movable element (13b) to the second movable electrode (152), and the second motion transmission device (14b) is capable of rotatably moving relative to the frame (10) through a plurality of second pivot hinges (16b).

4. System (2) according to one of claims 2 and 3, wherein: The first motion transmission device (14a) comprises: - a first transmission shaft (144a) having a first longitudinal axis of rotation (Xa); - at least one first transmission arm (145a), comprising a first end coupled to the first movable element (13a) and a second end integrated with the first transmission shaft (144a); and - at least one second transmission arm (145c), comprising a first end coupled to the second movable element (13b) and a second end integral with the first transmission shaft (144a).

5. The system (2) according to any one of claims 1 to 4, wherein: Each of the first movable element (13a) and the second movable element (13b) includes a membrane (131) and a reinforcing structure (132) for reinforcing the membrane.

6. The system (2) according to claim 5, wherein: The first motion transmission device (14a) is located on the first side of the membrane (131) of the first movable element (13a), and wherein the reinforcement structure (132) of the first movable element includes a first beam (1321), the first beam is located on the first side of the membrane (131), and the first beam (1321) extends in the length direction of the first movable element (13a), preferably, extends along the center line (M) of the first movable element (13a).

7. The system (2) according to claim 6, wherein: The length of the first beam (1321) is greater than or equal to 50% of the length of the first movable element (13a).

8. System (2) according to one of claims 6 and 7, wherein: The reinforcement structure (132) of the first movable element (13a) further comprises a second beam (1322) which is located at a second opposite side of the membrane (131) and is superimposed on the first beam (1321).

9. The system (2) according to any one of claims 6 to 8, wherein: The reinforcement structure (132) of the first movable element (13a) further comprises a ridge (1323) located on a second opposite side of the membrane (131) and extending perpendicularly to the first beam (1321).

10. The system (2) according to any one of claims 1 to 9, wherein: The first movable element (13a) and the second movable element (13b) are identical.

11. The system (2) according to any one of claims 1 to 10, wherein: The capacitance measuring or actuating device (15') is located between the first movable element (13a) and the second movable element (13b).

12. The system (2) according to claim 11, wherein: - at least one of the first pivot hinges (16a) is located at the first movable electrode (151), - another of the first pivot hinges (16a) is located at a first end of the first motion transmission device (14a); - Another of said first pivot hinges (16a) is located at a second opposite end of said first motion transmission device (14a).

13. The system (2) according to any one of claims 1 to 12, wherein: The first movable element (13a) and the second movable element (13b) are in contact with a first region (11), and the first movable electrode (151) is located in a second region (12) which is sealed and isolated from the first region (11).

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