Thermal regulation system for micro-electro-mechanical system

Abstract

One aspect of the invention relates to a regulation system (100) comprising: - a micro-electro-mechanical system (200) or "MEMS", comprising a base (210); - at least one thermal micromachine (300) configured to operate according to a Stirling cycle, comprising: - an expansion volume (310) delimited in part by a first deformable membrane (130); - a rear volume (330) separated from the expansion volume (310) by means of the first deformable membrane (130); wherein the base (210) of the MEMS (200) partially delimits the rear volume (330).

Description

DESCRIPTION TITLE: THERMAL CONTROL SYSTEM FOR MICROSYSTEM ELECTROMECHANICAL SYSTEM TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of the thermal regulation of micro-electromechanical systems (called "MEMS" for "micro-electromechanical systems" in English) to function as a sensor (for example thermal sensor or inertial sensor) and / or actuator (for example to carry out micrometric positioning). TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] A microelectromechanical system, or MEMS, comprises one or more elements capable of performing a sensor and / or actuator function. For example, a MEMS comprises a microstructure (i.e., a structure with dimensions of the order of a micrometer) whose function is partly ensured by the shape of this microstructure.

[0003] It is known that MEMS performance (e.g. sensor sensitivity or actuator position accuracy) is sensitive to ambient temperature variations. Ensuring good temperature stability therefore helps achieve optimal performance.

[0004] Document FR 3 078 694 discloses a system for regulating the temperature of a MEMS. The system comprises a MEMS encapsulated in a vacuum-sealed package designed to thermally isolate the MEMS from the environment. The system also comprises a Peltier module thermally coupled to the MEMS and a controller. The controller is used to control the Peltier module to change the temperature of the MEMS.

[0005] However, it is known that the energy efficiency of heat transfers by thermoelectricity (such as the Peltier effect or the Seebeck effect) is limited.

[0006] Document US 6,385,973 B1 describes a thermal micromachine operating according to a Stirling cycle. It comprises a closed fluid circuit including in particular a first chamber, called "expansion", a second chamber, called "compression", and a porous medium (regenerator), putting the two chambers in contact with each other. Each chamber comprises a wall deformable allowing its volume to be modulated. Thus, a controlled deflection of the walls makes it possible to carry out compression / expansion sequences of a gas enclosed in the fluid circuit and to carry out a heat transfer from the compression chamber to the expansion chamber or vice versa.

[0007] Although thermal micromachines allow for much better energy efficiency than that achievable by thermoelectricity, they nevertheless pose integration problems because they include, in particular, deformable moving elements.

[0008] Document US 10,927,001 B2 also describes a thermal micromachine operating according to a Stirling cycle. Unlike the previous micromachine, the compression-related mechanisms form a macroscopic-sized compressor assembly and communicate with a matrix of expansion chambers via a pipe. The integration of the expansion matrix with a macroscopic element, such as an infrared detector, is thus facilitated.

[0009] However, given the macroscopic size of the compressor assembly, this thermal machine cannot be easily integrated or efficiently coupled with an independent and small system, such as on-board electronics.

[0010] Therefore, there is a need to provide a thermal control system for MEMS with good energy efficiency and small size. SUMMARY OF THE INVENTION

[0011] The invention provides a solution to the problems mentioned above by improving the interface between the microelectromechanical system and the thermal micromachine. The system thus offers better energy efficiency than a Peltier module while maintaining a reduced footprint.

[0012] For this purpose, the invention relates to a regulation system comprising: a microelectromechanical system called "MEMS", comprising a base; at least one first thermal micromachine configured to operate according to a Stirling cycle called "Stirling micromachine", the first Stirling micromachine comprising a fluidic circuit comprising: a first volume, called the “expansion volume”, delimited in part by a first deformable membrane; a second volume, called the “compression volume”, delimited in part by a second deformable membrane; a third volume, called the “rear expansion volume”, separated from the expansion volume by the first deformable membrane; a fourth volume, called the “rear compression volume”, separated from the compression volume by the second deformable membrane; a regenerative volume relating the compression volume to the expansion volume, the regulation system being remarkable in that the base of the MEMS partly delimits the rear expansion volume of the first Stirling micromachine.

[0013] By "MEMS base" is meant a portion of the MEMS such as a backing or bottom layer.

[0014] The deformation of the first and second membranes allows the expansion and compression volumes to be varied and thus a gas enclosed in the fluid circuit to be compressed / expanded, thereby transferring heat from the expansion volume to the compression volume. The rear expansion volume allows the first membrane to deform and oscillate freely. Thus, the first Stirling micromachine can then operate according to a Stirling cycle.

[0015] The implementation of a Stirling micromachine, rather than a Peltier module, allows for good energy efficiency. First, the energy efficiency of the Stirling micromachine alone can significantly exceed that of the Peltier module. Second, the base of the MEMS at least partially delimits the rear expansion volume, the size of the control system is reduced because it is not necessary to provide an additional wall between the rear volume and the MEMS, to close the rear volume. In addition, the base of the MEMS is brought closer to the expansion volume where the heat exchanges take place. The control system therefore has improved energy efficiency.

[0016] Advantageously, the first Stirling micromachine is distinct from the MEMS. In other words, the first deformable membrane is not part of the MEMS. When the regulation system comprises a plurality of Stirling micromachines as described above, these Stirling micromachines are preferably distinct from the MEMS.

[0017] Advantageously, the first deformable membrane and the base of the MEMS completely delimit the rear expansion volume. Thus, the base of the MEMS comes into contact with the first deformable membrane. Initially, the rear expansion volume completely penetrates the base of the MEMS and reduces the height of the regulation system. In addition, the base of the MEMS is in the immediate vicinity of the expansion volume, making it possible to optimize the thermal coupling between the expansion volume and the base.

[0018] Advantageously, the first Stirling micromachine comprises an adaptation layer extending between the first deformable membrane and the base of the MEMS, an opening made in the adaptation layer placing the first deformable membrane and the base of the MEMS opposite each other. This layer thus makes it possible to adapt a base having, for example, a flat surface (or at least without a recess) on the first Stirling micromachine. The adaptation layer is preferably thermally conductive.

[0019] Advantageously, the adaptation layer is electrically insulating. This layer can electrically insulate the first deformable membrane from the base of the MEMS. Thus, an electrical potential can be applied between the first deformable membrane and the base of the MEMS.

[0020] Advantageously, the regulation system comprises a magnetic actuator configured to deform the first deformable membrane, the magnetic actuator comprising a magnetic element and a coil: the magnetic element being fixed on the first deformable membrane; and the coil being fixed to the base of the MEMS; or the magnetic element being fixed on the base of the MEMS; and the coil being fixed to the first deformable membrane.

[0021] Advantageously, the regulation system comprises a piezoelectric actuator configured to deform the first deformable membrane, the piezoelectric actuator comprising a piezoelectric element fixed on the first deformable membrane.

[0022] Advantageously, the base of the MEMS is conductive and the first deformable membrane is conductive.

[0023] Advantageously, the regenerative volume is surrounded by a thermally insulating material. The material, for example, has a sufficiently low thermal conductivity to limit, as much as possible, heat transfers between the hot (compression volume) and cold (expansion volume) sides of the micromachine.

[0024] Advantageously, the rear expansion volume, the expansion volume and the compression volume and the rear compression volume of the first Stirling micromachine are arranged in a direction perpendicular to the first membrane when the latter is at rest. In other words, the first Stirling micromachine is arranged vertically rather than horizontally (the horizon being considered parallel to the first membrane). By "arranged in a direction" is meant, for example, aligned in the direction. This arrangement makes it possible to locate the hot and cold sources on either side of the Stirling machine. Thus, the part corresponding to the compression volume can be easily coupled to a thermal drainage system without disturbing the MEMS. The micromachine can, for example, be placed on a thermal bath and the MEMS can be placed on the micromachine.

[0025] Advantageously, the regulation system comprises at least one second Stirling micromachine comprising a fluid circuit comprising: a first volume, called the “expansion volume”, delimited in part by a first deformable membrane; a second volume, called the “compression volume”, delimited in part by a second deformable membrane; a third volume, called the “rear expansion volume”, separated from the expansion volume by the first deformable membrane; a fourth volume, called the “rear compression volume” separated from the compression volume by the second deformable membrane; a regenerative volume connecting the compression volume to the expansion volume, the base of the MEMS delimiting in part the rear expansion volume of the second Stirling micromachine. In other words, the first and second micromachines are coupled in parallel with the MEMS.

[0026] Advantageously, the rear expansion volume of the first Stirling micromachine and the rear expansion volume of the second Stirling micromachine are common and form a single rear expansion volume.

[0027] Advantageously, the regulation system further comprises at least one additional Stirling micromachine thermally coupled in series with the first Stirling micromachine, the additional Stirling micromachine comprising an expansion volume and a rear expansion volume separated from the expansion volume by a deformable membrane, the rear expansion volume of the second additional Stirling micromachine being coupled to the rear compression volume (340) of the first Stirling micromachine or the rear expansion volume of the additional Stirling micromachine being the compression volume of the first Stirling micromachine.

[0028] Advantageously, the regulation system comprises a plurality of additional Stirling micromachines thermally coupled to each other.

[0029] Advantageously, the regulation system further comprises a controller, configured to control the Stirling micromachine(s) so as to transfer a quantity of heat from the base of the MEMS or to the base of the MEMS.

[0030] Advantageously, the controller is configured to measure a temperature-dependent quantity of the MEMS and control the Stirling micromachine(s) as a function of the quantity measured by the probe.

[0031] The quantity is a temperature of the microelectromechanical system or a temperature of the thermal micromachine or a drift in the performance of the microelectromechanical system. It can also be a quantity measured by a sensitive part of the electromechanical system.

[0032] Advantageously, the regulation system comprises a probe for measuring the temperature-dependent quantity of the MEMS.

[0033] Advantageously, the regulation system comprises a detection circuit configured to measure the position of the first membrane and / or the position of the second membrane, the controller being configured to control the first Stirling micromachine as a function of the position of the first membrane and / or the position of the second membrane measured by the detection circuit.

[0034] The invention also relates to an alternative regulation system comprising: a microelectromechanical system called "MEMS", comprising a base; at least one thermoacoustic micromachine comprising a fluidic circuit comprising: a first volume, called "expansion volume"; a second volume, called "compression volume", delimited by a deformable membrane; a third volume, called "rear compression volume", separated from the compression volume by the deformable membrane; a regenerative volume putting the compression volume in relation to the expansion volume, the regulation system being characterized in that the base of the MEMS delimits at least in part the expansion volume of said at least one thermoacoustic micromachine.

[0035] The deformable membrane can be used to compress / expand a gas in the fluid circuit so as to induce an acoustic wave in the fluid circuit propagating between the compression volume and the expansion volume. The fluid circuit then forms a resonant cavity. The passage of the acoustic wave front in the expansion volume allows heat transfer from the MEMS to the expansion volume. The quantity of heat thus captured from the MEMS is then redistributed to the ambient environment, on the compression volume side.

[0036] Similar to the control system comprising a Stirling engine, the implementation of a thermoacoustic micromachine, rather than a Peltier module, allows for good energy efficiency. Firstly, a thermoacoustic micromachine shows better efficiency than a Peltier module. Secondly, the direct contact between the base of the MEMS and the expansion volume of the thermoacoustic micromachine improves the heat transfer between the thermoacoustic micromachine and the MEMS. It therefore further increases energy efficiency. In addition, it reduces the footprint. of the regulation system because it is not necessary to provide an additional wall to close the expansion volume. In an advantageous embodiment, the expansion volume can even penetrate partially, or even completely, into the base of the MEMS, further reducing the size of the system. Bringing the base of the MEMS closer to the regenerative volume also makes it possible to further improve heat exchanges because these mainly take place in the vicinity of the regenerative volume.

[0037] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0038] The figures are presented for information purposes only and in no way limit the invention.

[0039] Figures 1 and 2 schematically show first and second embodiments of a regulation system according to the invention, the regulation system comprising in particular a Stirling micromachine and a MEMS.

[0040] Figures 3 and 4 schematically show third and fourth embodiments of the regulation system according to the invention, the regulation system comprising in particular a controller and a probe.

[0041] Figures 5, 6 and 7 schematically show fifth, sixth and seventh embodiments of the regulation system according to the invention, comprising in particular an assembly of several thermal micromachines.

[0042] Figures 8 and 9 schematically show eighth and ninth embodiments of the regulation system according to the invention, comprising in particular a thermo-acoustic micromachine and a MEMS.

[0043] Figure 10 schematically shows a tenth embodiment of the regulation system according to the invention, the regulation system comprising in particular a Stirling micromachine and a MEMS. DETAILED DESCRIPTION

[0044] Figures 1, 2 and 10 schematically show three embodiments of a regulation system 100 according to the invention. The regulation system 100 aims to thermally regulate a microelectromechanical system 200, called “MEMS”, while offering good energy efficiency (compared to that of a Peltier module) and which remains small in size.

[0045] The MEMS 200 is, for example, a small device, generally millimeter or less, implementing a mechanical element, called a “sensitive part” of very small size, which can be between 1 pm and 500 pm. The sensitive part is, for example, a built-in beam or a deformable membrane.

[0046] The MEMS 200 can be used as an actuator, for example to position an element such as a mirror. The MEMS 200 can be part of a focal plane of a sensor, for example an infrared sensor (focal plane also being called "FPA" or "Focal Plane Array" in English). The MEMS can also be used to switch an electrical circuit, or as a sensor (such as a thermometer), as a scale or as an inertial sensor (for example an accelerometer or a gyroscope).

[0047] The sensitive part of the MEMS 200 (not shown in the figures) is supported by a base 210, also called a “support” or “lower layer” (for example embedded in this base 210). This is an element generally having a larger size than the sensitive part and allowing the MEMS 200 to be fixed on a circuit or against a thermal regulator.

[0048] The regulation system 100 may comprise a housing, not shown in the figures, which may be hermetic. The MEMS 200 and its base 210 may be encapsulated in the housing. The housing may make it possible to isolate the MEMS 200 and its base 210 from possible heat flows coming from outside the housing in order to facilitate thermal regulation of the MEMS 200. The housing may also make it possible to maintain the vicinity of the sensitive part under vacuum or in a controlled atmosphere.

[0049] To regulate the temperature of the MEMS 200, the regulation system 100 implements thermal machines using a gas in a closed fluid circuit. Upon receiving mechanical work, the gas undergoes thermodynamic transformations involving a heat exchange between a cold source (the element that is to be heated or cooled) and a hot source (generally the external environment). In order to be suitable for regulating a MEMS, the thermal machines implemented are small in size. Unlike macroscopic Stirling engines that use pistons to compress and expand the gas, these use deformable membranes, which oscillate with an amplitude a few tenths of a millimeter and which also have a thickness of a few tenths of a millimeter. We then speak of "thermal micromachines". The implementation of thermal micromachines makes it possible to obtain better energy efficiency than a Peltier module.

[0050] In common with Figures 1, 2 and 10, the system 100 comprises a MEMS 200, only a portion of which is shown. The MEMS 200 notably comprises a base 210, shown as a portion of the MEMS 200.

[0051] The system 100 also includes a first thermal micromachine 300 configured to operate according to a Stirling cycle. It may also be referred to as a Stirling micromachine 300. The first micromachine 300 includes a closed fluid circuit in which a gas can circulate to undergo thermodynamic transformations.

[0052] The fluid circuit comprises two distinct volumes 310, 320, called "expansion" and "compression", and a medium, or volume, 350 called "regenerator" connecting the expansion and compression volumes 310, 320. The regenerative volume 350 comprises, for example, a porous medium for storing or delivering a quantity of heat to the gas enclosed in the fluid circuit. It may be a metallic material or a synthetic material (for example, nylon or polyester). It could also comprise a large number of non-porous tubes of reduced diameters.

[0053] The first Stirling machine 300 comprises a first deformable membrane 130 partially delimiting the expansion volume 310. As the first Stirling machine 300 is here distinct from the MEMS 200, the first deformable membrane 130 is therefore not part of the MEMS 200.

[0054] This first membrane 130 makes it possible to vary the expansion volume 310 and thus compress or expand the gas in the expansion volume 310. The Stirling engine 300 also comprises a second deformable membrane 150 partially delimiting the compression volume 320. This second deformable membrane 150 makes it possible to vary the compression volume 320.

[0055] The regenerative volume 350 comprises a plurality of channels connecting (in other words putting into relation) the expansion 310 and compression 320 volumes.

[0056] A deflection of the first and second membranes 130, 150 thus makes it possible to compress and expand the gas enclosed in the fluid circuit. Depending on the frequency and phase of the deflections of the deformable membranes 130, 150, the thermodynamic transformations of the gas can follow a Stirling cycle.

[0057] The formation of the fluid circuit can be obtained by a stack of layers. In the examples illustrated, the stack comprises a planar substrate 110 (comprising small diameter channels forming the regenerative volume 350). It can be made of a thermally insulating material. The greater the thickness of the substrate 110, the better the thermal insulation (outside the regenerative volume 350) between the compression volume 310 and the expansion volume 320. The thickness of the substrate 110 therefore results from a compromise between the size of the first micromachine 300 and the insulation between the two volumes 310, 320. The channels of the regenerative volume 350 pass through the substrate 110 from one side to the other, extending for example perpendicularly to the substrate 110. The regenerative medium 350 can also be formed by a porous material.The formation of small diameter channels and / or porous materials in the substrate 110, intended to form a regenerative medium, is known to those skilled in the art.

[0058] A first layer 120 extends against a first face of the substrate 110. The first layer 120 has a first opening delimited by a first flank 121. The first layer 120 is arranged so that this first flank 121 surrounds the channels of the regenerative volume 350 opening onto the first face of the substrate 110.

[0059] The first layer 120 is preferably made of a thermally conductive material. It has a thickness greater than an oscillation amplitude of the first membrane 130 but preferably less than 1 mm.

[0060] The substrate 110 and the first layer 120 can also be made from the same material, for example silicon. The thermal insulation between the expansion and compression volumes is then preferentially adjusted thanks to the thickness of the substrate 110.

[0061] The first opening made in the first layer 120 has an equivalent diameter preferably less than 10 mm. By “equivalent diameter” is meant the diameter of a circle inscribed in the opening.

[0062] The first layer 120 is preferably sealed on the substrate 110 so as to produce a hermetic joint. When the substrate 110 and the first layer 120 are both made of silicon, the sealing of one on the other can be carried out by eutectic sealing (also called “brazing”) or molecular sealing (also called “molecular bonding”) or sealing by molecular fusion (also called “fusion silicon bonding” in English).

[0063] The first deformable membrane 130 extends against the first layer 120 so as to close the first opening. It has a thickness of a few tenths of a millimeter. It is for example made of silicon. The first membrane 130 is preferably sealed on the first layer, for example according to one of the aforementioned methods. The first flank 121 of the first layer 120 therefore extends from the substrate 110 to the first deformable membrane 130. The first face of the substrate 110, the first flank 121 delimiting the opening in the first layer 120 and the first deformable membrane 130 thus delimit the expansion volume 310.

[0064] A second layer 140 extends against a second face of the substrate 110, opposite the first face of the substrate 110. It can be made of silicon and, when the substrate 110 is also made of silicon, sealed on the latter according to one of the aforementioned methods. The second layer 140 has a thickness greater than a deformation amplitude of the second membrane 150 and preferably less than 1 mm. The second layer 140 has a second opening delimited by a second flank 141. The second layer 140 is arranged so that the second flank 141 surrounds the channels of the regenerative volume 350, opening onto the second face of the substrate 110. The second opening made in the second layer 140 has an equivalent diameter preferably less than 10 mm.

[0065] The second deformable membrane 150 extends against the second layer 140 so as to close the second opening. It also has a thickness of a few tenths of a millimeter and is for example made of silicon. It can be sealed on the second layer 140 according to one of the aforementioned methods if the latter is made of silicon. The second flank 141 of the second layer 140 therefore extends from the substrate 110 to the second deformable membrane 150. The second face of the substrate 110, the second flank 141 and the second deformable membrane 150 thus delimit the compression volume 320.

[0066] In order for the first membrane 130 to be able to deform freely, a third volume 330, called the “free volume” or “rear expansion volume”, can be left behind the first membrane 130. By “behind”, it is understood on the side opposite the expansion volume 310. Where a Stirling engine according to the prior art can have a cover or an additional layer delimiting the volume 330, the invention provides for delimiting the rear expansion volume 330 in part by means of the base 210 of the MEMS 200. In this way, there is no extra thickness provided by a cover or an additional layer of the prior art and the regulation system 100 can thus have a reduced size.

[0067] In order for the second membrane 150 to be able to deform freely, a fourth volume 340 called the “rear compression volume” is left behind the second membrane 150. By “behind”, it is understood on the side opposite the compression volume 320.

[0068] In the embodiment of Figure 1, the base 210 has a blind recess, also called a “pocket”, for example of cylindrical shape. This recess has a side 212 and a bottom 211. The base 210 is arranged against the first membrane 130 so that the blind recess is arranged opposite the first membrane 130 and in the extension of the expansion volume 310. The base 210 can be sealed on the first membrane 130 according to one of the aforementioned methods. The bottom 211 of the recess is thus arranged opposite the first membrane 130. The recess advantageously has a depth greater than a deformation amplitude of the first membrane 130. It has for example a depth of a few millimeters. The equivalent diameter of the recess (i.e. the diameter of a circle inscribed on the recess) is greater than or equal to the equivalent diameter of the opening made in the first layer 120.It is preferably strictly greater than the equivalent diameter of the opening made in the first layer 120. It is for example 15 mm. The flank 212 of the recess is thus set back from the first flank 121 of the first layer 120, partially delimiting the expansion volume 310.

[0069] It is preferable for the rear expansion volume 330 to be greater than the expansion volume 310 so that the work provided by the first membrane 130 on this rear volume is negligible. In this way, the energy consumption associated with the compression / expansion of the gas in the rear expansion volume 330 remains low. Thus, it is advantageous for the equivalent diameter of the opening made in the first layer 120 and / or the depth of the recess to be adjusted so that the rear expansion volume 330 is greater than the expansion volume 310 and preferably as large as possible.

[0070] In the embodiment of FIG. 1, the base 210 delimits, with the first membrane 130, the entire rear volume 330. The rear volume 330 therefore completely penetrates the base 210 and further reduces the size of the system 100.

[0071] When the base 210 is made of silicon, the recess can be formed using a deep dry etching process, for example reactive ion etching, known as “DRIE” for “Deep Reactive Ion Etching” in English.

[0072] In the embodiments of Figures 2 and 10, the base 210 is planar. It is not modified to form a recess. The first Stirling micromachine 300 comprises an additional layer 160 called the “adaptation layer”. It makes it possible to adapt the base 210 so as to form the rear volume 330 without modification. The adaptation layer 160 extends against the first membrane 130. It also has an opening delimited by a flank 161. For the same reasons as discussed previously, the volume released by the additional layer preferably makes it possible to form a rear expansion volume 330 which is greater than the expansion volume 310. For this, the equivalent diameter (i.e. the diameter of a circle inscribed in the opening) of the opening made in the adaptation layer 160 and / or the thickness of this layer are adjusted so that the rear expansion volume 330 is greater than the expansion volume 310.

[0073] The adaptation layer 160 may also have a thickness greater than a deformation amplitude of the first membrane 130. For example, it has a thickness of a few millimeters. The equivalent diameter of the opening in the adaptation layer 160 is preferably strictly greater than the equivalent diameter of the opening made in the first layer 120. It is for example 15 mm.

[0074] Due to the larger diameter, the flank 161 is preferably arranged set back from the flank 121 delimiting the first opening of the first layer 120. The base 210 is arranged against the adaptation layer 160 so as to close the opening of the adaptation layer 160. The base 210 then forms the bottom 211 of the rear volume 330.

[0075] The adaptation layer 160 may be made of silicon. It may be sealed to the first membrane 130 according to one of the aforementioned methods. Similarly, the base 210 of the MEMS 200 may be sealed to the adaptation layer according to one of the aforementioned methods. Beyond providing a hermetically delimited volume, this sealing also ensures good quality thermal contact with the first micromachine 300.

[0076] The adaptation layer 160 may be electrically insulating. It thus allows the application of a potential difference between the first membrane 130 and the base 210 (see the case of a capacitive actuator below). It is for example made from a layer of silicon on insulator, also called “SOI” for “Silicon On Insulator” in English. A layer of silicon on insulator comprises two semiconductor layers of silicon separated by an insulating layer (also called “buried layer”). This insulating layer may be made of silicon dioxide or may be gaseous (for example air).

[0077] In the case where the adaptation layer 160 is made from SOI, one of the silicon layers can be soldered to the first membrane 130 and the other silicon layer can be soldered to the base 210 of the MEMS.

[0078] The use of such an adaptation layer 160 is particularly advantageous in the case where the distance between the expansion volume 310 and the element to be cooled does not increase. In this case, if the adaptation layer comprises a material whose conductivity is greater than that of the base 210, the performance of the control system 100, in terms of cooling efficiency, is significantly improved.

[0079] The first Stirling micromachine 300 may comprise actuators for respectively actuating the first and second membranes 130, 150. Only the actuator for the first membrane 130 is described below. However, each type of actuator described below can be implemented to actuate the second membrane 150. The actuators for actuating the first and second membranes 130, 150 respectively can be similar or different.

[0080] In the embodiment of Figure 1, the actuator shown is a piezoelectric actuator. It comprises a piezoelectric element 410 fixed on the first membrane 130. Thus, the deformations of the piezoelectric element 410 can be transferred to the first membrane 130. The piezoelectric element 410 can be arranged in the expansion volume 310 or in the rear volume 330. The actuator can also comprise several elements 410, for example arranged on either side of the first membrane 130.

[0081] In the embodiments shown in Figures 2 and 10, the actuator shown is a magnetic actuator. It comprises on the one hand at least one magnetic element 421, for example several permanent magnets. Each element 421 is fixed on the first membrane 130 and is arranged in the expansion volume 310 (Figure 10) or in the rear expansion volume 330 (Figure 2).

[0082] On the other hand, the magnetic actuator comprises a coil 422 for generating a magnetic field. The coil is arranged on the base 210, in the vicinity of each magnetic element 421. It can be fixed against the base 210 or inserted into a housing provided for this purpose. The housing can be a blind recess which leaves the coil opposite the magnetic elements 421. It can also be an internal housing of the base 210. In the latter case, the material from which the base 210 is made is preferably non-magnetic.

[0083] Alternatively, the coil 422 may be fixed to the first membrane 130 and the magnetic elements 421 may be placed against the base 210 or inserted into a housing provided for this purpose. In this case, the coil 422 may comprise one or more turns deposited on the membrane and acting as a coil.

[0084] Alternatively to these two embodiments (and not shown), the actuator may be capacitive. In this case, the first membrane 130 is conductive (for example metallic) and the base 210 is also conductive (for example metallic or doped semiconductor). Thus, the first membrane 130 can be actuated by applying an electric field between the base 210 and the first membrane 130. In order to ensure electrical insulation between the base 210 and the first membrane 130, the adaptation layer 160 can be electrically insulating. It is for example made from a semiconductor layer of silicon on insulator as described previously.

[0085] Figures 3 and 4 schematically show two embodiments of the regulation system 100 in which the latter comprises a controller 510 and a probe 520.

[0086] The controller 510 is configured to control the first Stirling micromachine 300 (or the plurality of Stirling micromachines if applicable). It is for example configured to power the actuators of the first and second membranes 130, 150. In the case of a magnetic actuator, the controller 510 is for example configured to power the coil 422 with electric current (or the turns on the first membrane 130). In the case of a piezoelectric actuator, the controller 510 is for example configured to apply an electric field to the piezoelectric element 410. In the same way, in the case of a capacitive actuator, the controller 510 is for example configured to apply an electric potential difference between the first membrane 130 and the base 210 of the MEMS 200.

[0087] The controller 510 therefore makes it possible, via the Stirling micromachine 300, to compress and expand the gas in the fluid circuit so as to subject the gas to thermodynamic transformations. Thus, it makes it possible to heat or cool the MEMS 200. The phase difference between the compressions in the compression volume 320 and the expansion volume 310 makes it possible to cool or heat the MEMS 200. It also makes it possible to adjust the frequency of the compressions / expansions to modify the cooling power (i.e. the quantity of heat removed or supplied per unit of time).

[0088] The controller 510 can be configured to operate the first Stirling micromachine 300 according to a specific operating mode, for example to heat or to cool the MEMS 200, preferably with a predetermined thermal power. To adjust the operating mode or the thermal power, the controller 510 can modify the frequency of the deformations of the members 130, 150 (we then speak of oscillations of the membranes 130, 150) or the phase between the oscillations of the membranes 130, 150. The controller 510 is however preferentially configured to adjust the power of the regulation according to the temperature of the MEMS 200. For this, the controller 510 can take advantage of the probe 520.

[0089] Figure 3 shows an embodiment where the probe 520 is arranged at the MEMS 200, for example at its sensitive part. The probe 520 is configured to measure data relating to the temperature of the MEMS 200. The probe 520 is for example a thermocouple, directly measuring the temperature of the sensitive part. The probe 520 can also measure another quantity, such as a drift in the performance of the sensitive part (for example a shift in a resonance frequency or a decrease in a vibration amplitude). Advantageously, the probe is preferably non-intrusive for the MEMS 200. It can be positioned outside the hermetic housing comprising the MEMS 200.

[0090] The controller 510 can also be configured to measure a quantity detected by the sensitive part of the MEMS 200. In other words, the controller 510 can be configured to estimate the thermal drift of the MEMS 200 by scanning the data measured using the MEMS 200. The controller 510 can, for example, estimate a noise spectral density from the data acquired by the MEMS 200.

[0091] The 510 controller can thus adjust the control parameters of the Stirling 300 micromachine (for example the frequency and amplitude of deformation of the membranes) so as to adjust the temperature regulation of the MEMS 200.

[0092] Figure 4 shows an embodiment where the probe 520 is arranged at the level of the first micromachine 300 and more particularly at the level of the expansion volume 310 (closest to the base 210). Thus the probe 520 can make it possible to determine the temperature of the MEMS 200 from the temperature of the expansion volume 310, so that the controller 510 can adjust the operation of the first micromachine 300.

[0093] Figure 5 schematically shows an embodiment of the control system 100 comprising a plurality of Stirling micromachines 300, 300a, 300b. In this embodiment, the micromachines 300, 300a, 300b are thermally coupled in series. The expansion volume of the first micromachine 300 is thermally coupled to the MEMS 200 according to one of the embodiments described. previously. Two additional micromachines 300a, 300b are thermally coupled in series with each other. By "thermally coupled in series" is meant that a cold source of one of the two additional micromachines 300b is thermally coupled to a hot source of the other additional micromachine 300a, for example by means of a thermal conductor. For example, the rear expansion chamber 330b of one 300b can be thermally coupled to the rear compression chamber 340a of the other 300a. The two rear chambers 330b, 340a are for example hollowed out in the same conductive part while remaining separated from each other. A heat transfer by conduction can then be established between the two micromachines 300a, 300b. Alternatively, the two micromachines 300a, 300b may be nested so that the rear compression chamber 340a of one 300a forms the expansion chamber 310b of the other 310b.

[0094] One of the two additional micromachines, in the example 300a, is thermally coupled in series to the first micromachine 300. In the example illustrated in FIG. 5, its expansion volume 310a is thermally coupled to the compression volume 320 of the first micromachine 300. These two volumes 310a, 320 are then only separated by a deformable membrane, common to the two micromachines 300, 300a. In other words, the rear compression volume 340 of the first micromachine 300 forms the expansion volume 310a of the additional micromachine 300a. Alternatively, these two micromachines 300, 330a could be coupled more simply, without seeking to reduce the size excessively. For example, the two rear volumes 340, 320 can be hollowed out in the same conductive part while remaining separated from each other.

[0095] The additional micromachine 300b at the end of the chain of micromachines 300, 300a, 300b may be coupled to a thermal drainage system or to a heat exchanger such as a radiator. For example, its rear compression volume 340b is thermally coupled to a thermal drainage system or to a radiator. This series assembly of micromachines 300, 300a, 300b makes it possible to increase the thermal power of the regulation system 100 in an environment where the Stirling micromachines must have lateral (or transverse) dimensions close to the lateral (or transverse) dimensions of the base 210 of the MEMS 200, or even of the MEMS 200 as such.

[0096] The expansion and compression volumes 320, 320a, 320b, 330, 330a, 330b of the different micromachines can be thermally coupled by conduction. A wall can separate the micromachines 300, 300a, 300b from each other but allow heat transfer. It is also possible to consider heat transfer by convection where a heat transfer fluid allows the different micromachines to be thermally coupled to each other.

[0097] In an advantageous development, the compression and expansion volumes of the thermally coupled micromachines 300, 300a, 300b are delimited by the same deformable membrane. In other words, a rear volume of a micromachine forms an expansion or compression volume of another micromachine. This coupling mode makes it possible to reduce the longitudinal size (i.e. in the direction of the thermal coupling of the micromachines 300, 300a, 300b) of the regulation system 100. It also makes it possible to improve the thermal coupling. Thus, according to this development, the compression volume 320 of the first micromachine 300 (the one connected to the MEMS 200) shares the same deformable membrane as the expansion volume 310a of one of the additional micromachines 300'. Conversely, the compression volume 320 of the first machine 300 then plays the role of rear volume 330a of the additional micromachine 300a.In the same way, the expansion volumes 310a, 310b and compression volumes 320a, 320b of the following micromachines 300a, 300b are nested with each other so as to form the rear volumes 330a, 330b, 340a, 340b of these micromachines 300a, 300b.

[0098] Figure 6 schematically shows an embodiment of the control system 100 also comprising a plurality of Stirling micromachines 300, 300', 300”, and in this case first, second and third Stirling micromachines 300, 300', 300”. However, unlike the embodiment of Figure 5, the micromachines 300, 300', 300” are connected in parallel.

[0099] In this embodiment, each micromachine 300, 300', 300” has a rear expansion volume 330, 330', 330” delimited in part by the base 210. The base 210 of the MEMS 200 has, for example, a plurality of recesses forming the rear expansion volumes 330, 330', 330” of the different micromachines 300, 300', 300”. Each compression chamber of the micromachines 300, 300', 300” can be thermally coupled to a thermal bath or to a heat exchanger. such as a radiator. This parallel assembly of micromachines 300, 300', 300” also makes it possible to increase the thermal power of the regulation system 100.

[0100] In a development, the rear relaxation volumes 330, 330', 330” can be connected to each other to form a single rear relaxation volume.

[0101] Figure 7 shows a combination of the assemblies of Figures 5 and 6 where a plurality of micromachines 300, 300a, 300b, 300', 300a', 300b', 300”, 300a”, 300b” form columns of micromachines coupled in series (embodiment of Figure 5) and where the plurality of columns is coupled to the base 210 of the MEMS 200. This assembly of micromachines 300 makes it possible to increase the thermal power of the control system 100 by increasing the number of micromachines 300 without however requiring an excessively wide base 210.

[0102] Figure 8 shows an embodiment of a regulation system 100. Unlike the embodiments shown in Figures 1, 2 and 10, this regulation system 100 comprises a thermo-acoustic micromachine 301 instead of the Stirling machine 300.

[0103] A thermoacoustic micromachine 301 is also based on the Stirling cycle. In a more conventional Stirling machine (micrometric or not), it is the action of one or more pistons or a plurality of deformable membranes that allows the compression / expansion of the gas and its circulation in the regenerative medium to be carried out. In a thermoacoustic machine, it is the action of an acoustic wave that allows the compression / expansion of the gas and its circulation in the regenerator 350 to be carried out. Thus, unlike the Stirling micromachines of figures 1 to 7 and 10, the thermoacoustic machine 301 of figure 8 does not include a first membrane. The thermoacoustic machine 301 includes an expansion volume 310 that extends from the substrate 110 to the base 210 of the MEMS 200. It therefore does not require a rear expansion volume. It only requires a 340 rear compression volume.

[0104] In the embodiment of Figure 8, the flank 212 of the base 210 is aligned in the extension of the flank 122 of the first layer 120. The substrate 110, the flank 122 of the first layer 120, the flank 212 of the base 210 and the bottom 211 of the base 210 therefore entirely delimit the expansion volume 310.

[0105] In a variant, the base 210 can be arranged directly against the first layer 120 in order to delimit the expansion volume 310. This embodiment does not require modification (for example, recessing) of the base 210.

[0106] In the case where the first layer 120 and the base 210 cannot be brought into contact (because their materials do not allow, for example, sealing of one on the other), the adaptation layer 160 can be inserted between the base 210 and the first layer 120 (embodiment of FIG. 9). The flank 161 of the adaptation layer 160 is preferably aligned with the flanks 212, 122 of the base 210 and of the first layer 120. The adaptation layer 160 thus makes it possible to adapt a base 210, for example a flat one, without modification.

Claims

CLAIMS

1. A control system (100) comprising: - a microelectromechanical system (200) called “MEMS”, comprising a base (210); - at least one first thermal micromachine (300) configured to operate according to a Stirling cycle, called a “Stirling micromachine”, the first Stirling micromachine comprising a fluidic circuit comprising: - a first volume (310), called “expansion volume”, delimited in part by a first deformable membrane (130), the first Stirling micromachine (300) comprising the first deformable membrane (130); - a second volume (320), called “compression volume”, delimited in part by a second deformable membrane (150); - a third volume (330), called the “rear expansion volume”, separated from the expansion volume (310) by the first deformable membrane (130); - a fourth volume, called the “rear compression volume” separated from the compression volume by the second deformable membrane; - a regenerative volume (350) connecting the compression volume (320) to the second expansion volume (320); the regulation system (100) being characterized in that the base (210) of the MEMS (200) partly delimits the rear expansion volume (330) of the first Stirling micromachine (3).

2. Regulation system (100) according to the preceding claim, in which the first deformable membrane (130) and the base (210) of the MEMS (200) entirely delimit the rear expansion volume (330). [Claim s] Regulation system (100) according to one of the preceding claims, in which the first Stirling micromachine (300) comprises an adaptation layer (160) extending between the first deformable membrane (130) and the base (210) of the MEMS (200), an opening being made in the adaptation layer (160) placing the first deformable membrane (130) and the base (210) of the MEMS (200) opposite each other.

4. Regulation system (100) according to the preceding claim, wherein the adaptation layer (160) is electrically insulating.

5. A control system (100) according to one of claims 1 to 4, comprising a magnetic actuator configured to deform the first deformable membrane (130), the magnetic actuator comprising a magnetic element (421) and a coil (422); the magnetic element (421) being fixed on the first deformable membrane (130); and the coil (422) being fixed to the base (210) of the MEMS (200); or the magnetic element (421) being fixed on the base (210) of the MEMS (200); and the coil (422) being fixed to the first deformable membrane (130).

6. A control system (100) according to one of claims 1 to 4, comprising a piezoelectric actuator configured to deform the first deformable membrane (130), the piezoelectric actuator comprising a piezoelectric element fixed (410) on the first deformable membrane (130).

7. Regulation system (100) according to one of claims 1 to 4, in which the base (210) of the MEMS (200) is conductive and the first deformable membrane (130) is conductive.

8. Regulation system (100) according to one of claims 1 to 7, in which the rear expansion volume (330), the expansion volume (310), the compression volume (320) and the rear compression volume (340) of the first Stirling micromachine (300) are arranged in a direction perpendicular to the first membrane (130), when the latter is at rest.

9. Regulation system (100) according to one of claims 1 to 8, comprising at least one second Stirling micromachine (300') comprising a fluidic circuit comprising: a first volume (310'), called "expansion volume", delimited in part by a first deformable membrane; a second volume (320'), called "compression volume", delimited in part by a second deformable membrane; a third volume (330'), called "rear expansion volume", separated from the expansion volume by the first deformable membrane; a fourth volume (340'), called "rear compression volume" separated from the compression volume by the second deformable membrane; a regenerative volume (350') putting the compression volume in relation to the expansion volume, the base (210) of the MEMS (200) partially delimiting the rear expansion volume (330') of the second Stirling micromachine (300').

10. Regulation system (100) according to the preceding claim, in which the rear expansion volume (330) of the first Stirling micromachine (300) and the rear expansion volume (330') of the second Stirling micromachine (300') are common and form a single rear expansion volume.

11. A control system (100) according to one of the preceding claims, further comprising at least one additional Stirling micromachine (300a) thermally coupled in series with the first Stirling micromachine (300), the additional Stirling micromachine comprising an expansion volume (310a) and a rear expansion volume (330a) separated from the expansion volume by a deformable membrane, the rear expansion volume of the second additional Stirling micromachine being coupled to the rear compression volume (340) of the first Stirling micromachine or the rear expansion volume of the second additional Stirling micromachine (300a) being the compression volume (320) of the first Stirling micromachine.

12. Regulation system (100) according to the preceding claim, comprising a plurality of additional Stirling micromachines (300a, 300b) thermally coupled to each other.

13. A control system (100) according to one of the preceding claims, further comprising a controller (510), configured to control the one or more Stirling micromachines (300) so as to transfer an amount of heat from the base (210) of the MEMS (200) or to the base (210) of the MEMS (200).

14. The control system (100) of claim 13, wherein the controller (510) is configured to measure a temperature-dependent quantity of the MEMS (200) and control the Stirling micromachine(s) (300) as a function of the quantity measured by the probe (520).

15. A control system (100) according to claim 13, comprising a detection circuit configured to measure a position of the first membrane (130) and / or the position of the second membrane (150), the controller (510) being configured to control the first Stirling micromachine (300) as a function of the position of the first membrane and / or the position of the second membrane measured by the detection circuit.

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