• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    A system for measuring a tangential force exerted by a fluid, said system comprising: - a conduit (22) in which the fluid flows, the conduit having an inner surface in contact with the fluid, and a cavity (24) disposed in said inner surface of the conduit (22), - a tangential force measuring device MEMS and / or NEMS having a support (4), a movable plate (2) suspended from the support by a pivot connection, said movable plate (2) having a first face (2.1) on which the fluid applies a tangential force, said device being integral with the conduit so that the first face (2.1) of the movable plate (2) is flush with the inner surface (26) of the conduit (22) said device comprising two piezoresistive strain gages suspended between the movable plate (2) and the support, the tangential force applying to the gages a substantially pure compressive or tensile force.
    公开号:FR3027389A1
    申请号:FR1460024
    申请日:2014-10-17
    公开日:2016-04-22
    发明作者:Philippe Robert；Caroline Coutier
    申请人:Commissariat a lEnergie Atomique CEA；Commissariat a lEnergie Atomique et aux Energies Alternatives CEA；
    IPC主号:
    专利说明:

    [0001] TECHNICAL FIELD AND STATE OF THE PRIOR ART The present invention relates to a tangential force measurement system with increased sensitivity, for example intended for the production of flowmeters, of preference microelectromechanical and / or nanoelectromechanical with improved sensitivity. There are several categories of flowmeter whose flowmeters using the measurement of wall stress or shear stress on the wall of the conduit in which the fluid flows, a stress that exists for any fluid having a viscosity. A fluid has zero velocity in the area of contact with the wall of the duct. Moreover, any difference in velocity within a viscous fluid causes shear stresses, the fluid particles moving faster are slowed down by the slower ones.
    [0002] Among the flowmeters, there are the hot-wire flowmeters that operate on the principle of heat transfer, the speed of loss of temperature of the heating wire being a function of the flow rate of the fluid to be measured. There are also the obstacle flow meters, an obstacle is placed in the flow whose flow is to be measured, the pressure is measured on either side of the obstacle, the pressure difference being proportional to the shear stress on the wall. These hot-wire and obstacle flow meters implement an indirect measurement method, since they do not make it possible to directly obtain the value of the flow rate. The use of these flowmeters therefore imposes a good knowledge of the fluid to be measured and a prior calibration according to the different flow conditions. There are also floating element flowmeters. These flow meters include a plate-like element, and operate by measuring the tangential force that is applied to the moving plate by the fluid. The sensor is for example movably mounted in a recess in the wall of the duct in which the flow flows so that the plate is flush with the inner surface of the duct. Under the effect of tangential forces on this element, it moves. The value of the shear stress is deduced directly from the displacement of the movable element. These flow meters therefore use a direct determination method. However, it generally has a low spatial resolution and a low temporal resolution. The implementation of flow meters made from microelectromechanical systems or MEMS (Microelectromechanical systems in English terminology), allows to achieve a good spatial resolution. "A Microfabricated Floating-Element Shear Stress Sensor Using Wafer-Bonding Technology" - Javad Shajii, Kay-Yip Ng, and Martin A. Schmidt - Journal of Microelectromechanical Systems, Vol. I, No. 2, Moon 1992 discloses a piezoresistive sensing flow meter. The flowmeter has a floating element formed of a plate suspended by four arms. The arms are used both as a mechanical support for the plate and as piezoresistive strain gages. The length of the suspension arms is arranged in the flow direction, under the effect of the passage of the fluid, the movement of the plate induces a compressive stress on the two arms placed downstream, and a stress in tension on the other two placed upstream. The measurement is then made by a half bridge Wheatstone. The suspension arms forming the measurement gauges have relatively large dimensions, which makes the flowmeter insensitive. The paper "Design and characterization of microfabricated piezoresistive floating element-based shear stress sensors" A. Alvin Barlian, Sung-Jin Park, Vikram Mukundan, Beth L. Pruitt - Sensors & Actuators, A. 2007; 134: 77-87 also discloses a piezoresistive sensing floating element flowmeter. In this document, the arms are biased in bending and their deformation is measured by piezoresistive strain gauges implanted on the side of the bending arms. Working in bending is detrimental to the sensitivity of the flowmeter.
    [0003] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a tangential force measurement system applied by a fluid to a floating element having increased sensitivity.
    [0004] The purpose stated above is achieved by a system comprising a conduit in which the fluid flows and a tangential force sensor disposed in a cavity of an inner surface of the conduit, the tangential force sensor comprising a suspended mobile plate comprising a face on which the fluid applies the tangential force. The sensor is disposed in the cavity so that the face of the movable plate on which the fluid applies the tangential force is flush with at least the inner surface of the conduit surrounding the cavity. The movable plate is articulated with respect to a support by at least one pivot connection. The system also comprising at least one piezoresistive gauge suspended between the movable plate and the support and distinct from the pivot connection, the gauge being arranged so that the displacement of the movable plate around the pivot connection generates a constraint in the gauge mainly the along the axis of the gauge so that it is subjected to substantially pure compressive stress or a substantially pure tensile stress. In addition, the strain gauge is arranged so that the stress applied to the moving plate by the fluid is amplified by leveraging. The measuring system has an increased sensitivity. According to the invention, the sensor is disposed in a cavity disposed in the inner surface of the conduit so that the movable plate is located in the zone in which the fluid has a velocity gradient between its speed in the duct and its zero velocity at level of the inner surface of the conduit and undergoes shear stress. The sensor is such that it measures the force mainly, or only on the surface of the movable plate which is flush with the inner surface of the duct, and that almost no effort or effort is exerted on the surface of the plate mobile which is opposite the surface flush with the inner surface of the conduit. Furthermore, the mechanical holding function of the movable plate and the piezoresistive measurement of the displacement of the movable plate are separated. Thus the mechanical function and the measuring function can be optimized separately. More particularly, the piezoresistive gauge or gauges can be thinner than the moving plate, a concentration of the stresses is obtained, and a sensor which has a better sensitivity.
    [0005] The suspended gauge or gauges are more stable, especially in temperature, compared to piezoresistive sensors with implanted gauges. In addition, the gauge or gauges work in traction or substantially pure compression, which further increases the sensitivity and linearity.
    [0006] Thanks to this increased sensitivity, it is possible to reduce the size of the moving plate and thus to obtain a better spatial resolution. Very advantageously, the tangential force sensor can be used to form a flowmeter or flow sensor. Indeed, the shear stress applied to an element by a fluid is a force applied tangentially to the surface of this element by the fluid. Thus the measurement of a tangential force applied by the fluid amounts to measuring the shear stress applied to this element by the fluid. The system according to the invention can also be made more reliable in a relatively easy manner, for example with respect to parasitic flows or pollution (dust, debris) in the fluid, for example by adding a film of flexible material of so as to form a fluid barrier between the movable plate and the support. For example, it may be a film encapsulating all or part of the movable plate. The present invention therefore relates to a system for measuring a tangential force exerted by a fluid, said system comprising: a duct in which the fluid is intended to flow, the duct extending over at least a portion in a given direction, said direction of flow, the duct having an inner surface intended to be in contact with the fluid, and at least one cavity disposed in said inner surface of the duct, - at least one MEMS and / or NEMS measuring device tangential force comprising a support having a mean plane and a movable plate, said movable plate being suspended from the support by at least one pivot connection, said pivot connection having an axis perpendicular to the medium plane of the support, said movable plate having a first face on which the fluid applies a tangential force and a second face opposite to the first face, said device being integral with the conduit and being disposed of in the cavity so that the first face of the movable plate is flush with at least one zone of the inner surface of the duct surrounding the cavity, said device also comprising at least one piezoresistive strain gauge suspended and mechanically connected to the movable plate and the support said gauge being disposed in the cavity such that the tangential force applied to the first surface of the moving plate by the fluid in the direction of flow applies a compressive or tensile force to said piezoresistive strain gauge. In the present application, the term "plate" any element having a surface greater than or even greater than its thickness regardless of its geometry The cavity may or may not pass through the wall of the conduit. The distance separating the plane containing the first face of the moving plate and the plane containing at least the area surrounding the cavity is preferably less than or equal to 200 μm and advantageously less than or equal to 100 μm. The gauge is advantageously arranged as closely as possible. of the axis of the pivot connection. The measurement system may advantageously comprise at least two electrically connected differentiated gates connected to a Wheatstone half bridge or at least four differential mounted gates electrically connected to a Wheatstone bridge. In an exemplary embodiment, the movable plate is suspended from the support by two pivot links, said device comprising at least two piezoresistive gauges. At least one rigid force transmission arm can connect the movable plate to each pivot connection, at least one piezoresistive strain gauge being suspended between a force transmission arm and the support Advantageously, each force transmission arm is connected to the movable plate by at least elastically deformable means at least in the direction perpendicular to the flow of the fluid. The strain gauge (s) may have a thickness of between 100 nm and 500 nm and the movable plate may have a thickness of between 3 μm and 40 μm. According to an additional feature, the pivot connection comprises two beams of substantially the same length anchored on the support at two distinct points and anchored to the movable plate at a point through which the axis of the pivot connection.
    [0007] Advantageously, the measuring system comprises means for limiting the flow of fluid between the movable plate and the support. These means may be formed by a structuring of the support and / or the movable plate so as to provide at least one area of reduced flow section between the support and the movable plate. The structuring is for example carried out on the second face of the movable plate and / or on an area of the support facing said face. Advantageously, the measuring system comprises means for preventing the flow of fluid between the movable plate and the support. According to an exemplary embodiment, these means may comprise a flexible element at least partially encapsulating the movable plate and preventing the fluid from flowing between the movable plate and the support. For example, the element is a polymer or a polyimide. According to another embodiment, the means for preventing the flow of fluid between the movable plate and the support comprise a film of flexible material covering the first face of the movable plate and at least a portion of the support. The movable plate may comprise lights, said slots being closed by the flexible element or by the film. The measuring system may advantageously comprise means for reducing the sensitivity to parasitic accelerations and vibrations. These means may comprise a counterweight secured to the movable plate and protected from the fluid so as not to undergo tangential force. The present invention also relates to a system for measuring the flow rate of a fluid flowing in a duct comprising at least one measuring system according to the invention. The present invention also relates to a method for producing a measuring system according to the invention, this method comprising: - the formation of a cavity in the inner surface of a duct, - the realization of a device for tangential force measurement from a stack formed of a substrate, a sacrificial layer and at least a first layer of a conductive or semiconductor material, comprising producing at least one piezoresistive gauge in the first layer, the realization of the movable plate and the at least one pivot connection in said stack and the release of the gauge, the movable plate and the pivot connection.
    [0008] The cavity may be formed so as to be through or not. After formation of the gauge, a protective portion may be formed on said gauge prior to formation of a second layer of a conductive or semiconductor material on the first layer of a conductive or semiconductor material.
    [0009] Following the formation of the shielding portion, the second layer of a conductive or insulating semiconductor material may be formed on the first layer of a conductive or semiconductor material, and the movable plate and the pivot link being made at least partly in this second layer. In one example, the method may comprise a step of filling at least the lateral air gap between the movable plate and the support, said filling being for example made by liquid phase deposition by centrifugation to form means for preventing flow. of fluid between the movable plate and the support. In another example, the method may comprise a step of forming a film on the movable plate and on at least a portion of the support so as to close the lateral air gap between the movable plate and the support, said film being for example formed by rolling to form means for preventing fluid flow between the movable plate and the support. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be better understood on the basis of the following description and the appended drawings in which: FIG. 1A is a view from above of an embodiment of a force measuring system tangential according to the invention comprising two piezoresistive gages mounted in differential, - Figure 1B is a sectional view along the plane AA of Figure 1A, the cavity is not shown, - Figure 2 is a schematic sectional view FIG. 3 is a top view of an exemplary embodiment of a tangential force sensor comprising four piezoresistive gages mounted in differential, FIG. 4 is a view from above of a FIG. FIG. 5 is a top view of another exemplary embodiment of a tangential force sensor comprising four piezoresistive gauges. FIGS. 6A is a top view of an exemplary embodiment of a tangential force sensor in which the effects of parasitic fluid flow under the plate are reduced; FIG. 6B is a sectional view along the plane BB of the device of FIG. 6A; FIG. 7A is a view from above of another embodiment of a tangential force sensor in which the effects of a parasitic fluid flow under the 7B is a sectional view along the plane CC of the device of FIG. 7A, FIG. 8A is a view from above of an alternative embodiment of a tangential force sensor of FIG. 7A. FIG. 8B is a sectional view along the plane DD of the device of FIG. 8A; FIG. 9A is a view from above of an alternative embodiment of a tangential force sensor of FIG. 7A; FIG. 9B is a sectional view along the plane EE of the device of FIG. 9A, FIG. 10 A is a top view of an alternative embodiment of a tangential force sensor of FIG. 7A; FIG. 10B is a sectional view along the plane FF of the device of FIG. 10A; FIG. 11A is a view. of another embodiment of a tangential force sensor in which the sensitivity to parasitic accelerations and vibrations is limited; FIG. 11B is a sectional view along the plane GG of the sensor of FIG. 11A; FIG. 12A is a view from above of another exemplary embodiment of a tangential force sensor providing an increase in the tangential force exerted on the sensor; FIG. 12B is a sectional view along the plane HH of the sensor; 13A to 13G are diagrammatic views, seen from above and in section, of different steps for producing a tangential force sensor according to the invention according to an exemplary embodiment method; FIG. a representative FIG. 15A to 15C are diagrammatic representations of the mounting of a tangential force sensor in a conduit. DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS The present invention relates to a system for measuring the tangential force applied by a fluid, whether liquid or gaseous. This system makes it possible to very advantageously achieve a flow measurement device. In the remainder of the description, the system is described in an application to measure flow, but it will be understood that this is in no way limiting, all the examples and variants described apply to a force measuring system. tangentially in general. The expressions "shear stress" and "tangential force" are used indiscriminately, the tangential force or shear stress is shown schematically by an arrow designated F. In FIG. 1A, an exemplary embodiment of a designated flow sensor can be seen. C1 mounted in a recess 24 of a conduit 22 in which the fluid flows. More generally, the sensor is mounted in a cavity disposed in the wall of the conduit. The cavity can be through or not. In the case of a through cavity, the seal could be obtained by mounting the sensor as will be explained below. The sensor C1 comprises a mobile part 2 in the form of a plate and a support 4. The plate 2 is movable in the plane of the designated sensor XY. The movable plate 2 is intended to be displaced by the fluid whose flow is to be measured. The fluid flows in a Y direction and is symbolized by the FL arrows. The movable plate 2 is suspended from the support 4. A pivot link 6 Z axis connects the movable plate 2 to the support. The Z axis is orthogonal to the XY plane. In the example shown, the pivot connection 6 is formed by two flexible beams 6.1, 6.2 in the plane fixed by one end to a pad 8 forming integral support 4. The two beams are fixed to the pad 8 at two distinct points and by another end to the movable plate 2 at a common point defining the axis of the pivot Z. This configuration advantageously allows a pure or almost pure rotation of the movable plate 2 about the Z axis. Alternatively, the pivot connection could be formed by a single beam deforming in bending, the axis of the pivot being located substantially in the center of the beam.
    [0010] In the example shown, the sensor also comprises two piezoresistive strain gauges 10, of beam type suspended between the movable plate 2 and second pads 12 forming flush. The gauges extend along the flow Y axis of the flow whose flow is to be measured. They are arranged on either side of the movable plate 2 so as to be biased in tension or pure or almost pure compression. In addition, they are mounted in differential; when the movable plate 2 moves around the Z axis, one is urged in traction the other is urged in traction. The X axis and the Z axis define a plane of symmetry of the pivot link 6. The center of gravity of the movable plate is designated GR and is contained in said plane XZ. In this embodiment, the device is oriented so that the plane containing the Z axis and the center of gravity GR is perpendicular to the Y direction. We will recall below the operation of a piezoresistive strain gage. When the gauge is deformed along its axis, and that its length varies, its electrical resistance also varies, it is by measuring this variation of resistance that one can deduce the tangential stresses applied to the fluid. The variation of the electrical resistance is measured by circulating an electric current in the gauge 10. Due to the arrangement of the gauges relative to the axis of rotation, a lever arm effect appears to amplify the stress applied to the gauges.
    [0011] Very advantageously and as shown, the gauges are connected to the movable plate as close to the pivot axis Z. Thus they benefit from a lever effect the largest possible. Preferably, the distance between the pivot axis Z and the projection on the X axis of their point of attachment to a moving plate is of the order of a few μm, for example 5 μm.
    [0012] Means (not shown) for applying a constant voltage to the gauges 10, and for measuring a variation of current flowing in the gages and for processing the current variation measurements are associated with the device C1. In the example shown, the moving plate 2 has a first parallelepipedal portion 14 of greater width, a second trapezoidal portion 16 whose large base is common to one side of the first portion and a third portion 18 connected to the pivot connection 6. The movable plate 2 has substantially a symmetry relative to the axis X. The third part 18 is also of parallelepiped shape, it has a smaller width coincides with the small base of the second part.
    [0013] The movable plate 2 is generally monolithic, the division into three parts is intended to simplify the description, and is not necessarily representative of the practical embodiment. The gauges 10 are connected to the movable plate at the third portion 18. Advantageously, recesses 20 are made in the third part 18 of the movable plate on either side of the X axis to allow connection gauges 10 to the movable plate at a location on or near the X axis. This configuration has the advantage that all or almost all the intensity of stress applied by the displacement of the movable plate 2 contributes to the deformation along the Y axis of the strain gauges 10. Indeed, when the anchoring of the gauges 10 8 is offset with respect to the axis passing through the pivot connection and the center of gravity GR, a portion of the deformation stress exerts on the gauge a bending force combined with a compressive or tensile force, this bending force not taking part or very little in the variation of the electrical resistance of the piezoresistive gauges 8.
    [0014] It will be understood that the shape of the movable plate of Figure lA is not limiting, it may have any parallelepiped shape, for example square or hexagonal or a round or oval shape. In the example shown, two gauges are implemented advantageously allowing a differential mounting, which limits the drifts of the sensor, including temperature drifts. But a flow sensor comprising a single piezoresistive gauge is not beyond the scope of the present invention. In Figure 2, we can see the system of Figure 1A seen in section in another view than that of Figure 1B in which the conduit 22 and the recess 24 are shown. The sensor Cl is mounted in the recess 24 in the wall of the conduit, the support 4 of the sensor being fixed to the bottom of the recess 24 so that the upper face 2.1 of the movable plate 2 is flush with the inner surface 26 of the conduit. The sensor is oriented in the conduit so that the flow direction of the fluid is parallel to the Y axis. It is considered that the upper face 2.1 is flush with the inner surface 26 of the pipe when, preferably, the distance separating the upper surface 2.1 of the movable plate and the inner surface 26 of the duct is less than or equal to 200 μm, preferably less than or equal to 100 μm, the upper surface 2.1 may be recessed or protruding from the inner surface 26 of the duct 22.
    [0015] The distance between the lower face 2.2 of the movable plate and the support is typically less than 10 μm, which makes it possible to limit the appearance of a flow rate under the movable plate. Preferably, the air gap between the lateral edges of the mass which are parallel to the X axis and the support is typically less than 5 μm, which makes it possible to have little and advantageously to have no flow between the lateral edges. and the support on the thickness of the moving mass, which renders parasitic effects negligible The operation of the shear stress measuring system will now be described: The fluid F circulating in the fluidic channel exerts a shear stress on the inner surface of the duct and thus on the movable plate flush with the surface 26, which tends to rotate around the pivot axis Z. The displacement of this movable plate induces a constraint in the suspended piezoresistive gauges 10. This constraint varies the resistance of the gauges. The measurement of this variation of resistance, proportional to the shear stress acting on the movable plate 2, therefore proportional to the flow rate in the channel, can be read via a Wheatstone half-bridge.
    [0016] FIG. 14 illustrates the electrical assembly associated with the sensor C1 making it possible to make measurements using a Wheatstone half-bridge. Wheatstone half-bridge assembly is well known to those skilled in the art and will not be detailed. A voltage source E is used, resistors R of constant value formed for example by fixed gauges and the gauges form resistors with variable value R + dR. The current variation is determined by measuring the voltage variation V on the first anchor pad 8. As will be described below, it is possible to implement a Wheatstone bridge, or even a quarter Wheatstone bridge.
    [0017] According to the invention, the mechanical holding of the movable plate is distinct from the measuring means, these measuring means can then advantageously have a reduced section, which makes it possible to have a concentration of stress and thus a gain in sensitivity while maintaining a sufficient rigidity of the movable plate. In Figure 1B, we can see the section of one of the gauges 10. It has a much lower thickness than the movable plate and that of the beams forming the pivot connection. The gauge or gages has, for example, a thickness of between 100 nm and 500 nm and the moving plate has a thickness of between 3 μm and 40 μm. In addition, the gauge or gages have a reduced width, for example less than 1 μm. According to an example of an embodiment method, the face of the gauge 10 facing the substrate 4 is in the same plane as the face of the movable plate 2 opposite the substrate 4. In FIGS. can see examples of embodiments of flow sensors using two pairs of piezoresistive gauges thus forming a complete Wheatstone bridge.
    [0018] In FIG. 3, the sensor C2 comprises a movable plate 102 having a shape of a rectangle extending along its largest dimension in the direction of the axis X. The movable plate 102 is suspended by two pivot links 106, 106 'disposed on either side of a plane of symmetry of the movable plate 102 containing the X axis and perpendicular to the average plane of the structure.
    [0019] The movable plate is connected to each pivot connection by means of a transmission arm 127 of force extending parallel to the axis X. The arm is connected by a first longitudinal end 127.1 to the support by the pivot connection 206 and by a second longitudinal end 127.2 to the movable plate. The arm forms a rigid connection. Moreover, two gauges 110 are suspended between the first end 127.1 of the arm 127 and the support 104 in order to measure the pivoting of the arm 127 in the plane around the Z axis. The gauges are mounted in differential. Advantageously, the arm 127 is connected to the movable plate 102 by elastically deformable means at least along the axis X so as to transmit the maximum force applied to the movable plate by the fluid to the rigid connection without impede the movement of the movable plate 102. These elastic means 128 give a degree of freedom between the movable plate 102 and the transmission arm 127, forming elastic relaxation means. In the example shown, the elastic means 128 are formed by a flexible blade.
    [0020] The second transmission arm 129 extends along the edge of the movable plate opposite the one along which extends the first transmission arm 127 and is connected to the support by a second pivot connection, this second pivot connection being located at the opposite of the first pivot connection with respect to the Y axis and flow flow. As for the first transmission arm 127, the second transmission arm 129 is advantageously connected to the movable plate 102 by resilient means 130 deformable at least in the direction of the X axis. Two gauges 110 'are suspended between the first end longitudinal 129.1 of the second transmission arm 129 and the support. The gauges are mounted in differential. The four gages 110, 110 'are electrically connected to form a complete Wheatstone bridge. In FIG. 4, another variant embodiment C 3 of the sensor of FIG. 3 can be seen, in which each transmission arm 127 ', 129' is connected to the movable plate at two distinct points, advantageously by two means of transmission 128 ', 130'. This variant offers rigidity in the Z direction and torsional stiffness around the Y axis increased relative to the sensor of FIG. 3.
    [0021] In FIG. 5, another variant C4 of the sensor of FIG. 3 can be seen, in which the transmission arms 227, 229 are connected to the movable plate 202 at its longitudinal ends along the X axis. arm then have the shape of L, a branch 227.1 of L along a longer side of the movable plate and a branch 227.2 of the L partly along a shorter edge length. The transmission arms being connected to the movable plate at their longitudinal ends opposite those to which the gauges are suspended, the amplification of the lever arm stress is increased. Advantageously, the arms 227, 229 are connected to the movable plate 202 by resilient means 228, 230 elastically deformable in the direction of the axis X. In this variant, the elastic means are formed by cutting two lights of rectangular shape in the movable plates 202 in the direction of the X axis so as to define two narrow strips in the movable plate 202 extending along the shorter edge of the plate 202. They then provide elasticity in the direction X. Fluid flowing in the duct and whose flow rate is to be measured, flows along the X axis on the upper surface of the movable plate and due to shear stresses displaces the movable plate along the axis Y. Or the movable plate is suspended above the support, a space is present between the lateral edges of the movable plate and the support and between the lower face of the movable plate and the support. Or the fluid can flow between the movable plate and the support, and applied a parasitic force on the movable plate and thus distort the measurements. The examples shown in FIGS. 6A to 11B comprise means for reducing or even eliminating these parasitic forces.
    [0022] FIGS. 6A and 6B show an exemplary embodiment of a flow sensor C5 in which the movable plate and the support are structured so as to limit the parasitic flow. The movable plate and the support are structured so as to delimit at least one zone a reduced passage section for the fluid. In the example shown and preferably, the lower face of the movable plate 2 comprises a recess 34 and the support 4 comprises opposite a corresponding recess 36 opposite which delimit between them a reduced passage section relative to the delimited section normally between the movable plate 2 and the support 4. The flow of fluid flowing under the plate is thus reduced. By structuring the lower face of the movable plate, the lateral air gap between the movable plate and the support may not be reduced. Alternatively only the support or only the face 2.2 of the movable plate can be structured. Moreover, preferably the electrical connections 38 are formed on the rear face, avoiding the presence of projections in the front face in the flow in order to limit the disturbances of the flow. This applies to all the devices according to the invention. The connections are made for example by vias type TSV (through silicon via English terminology). In FIGS. 7A and 7B, an exemplary embodiment of a sensor C6 in which the parasitic throughput is suppressed can be seen. The device comprises an element 40 filling the air gap between the lower face 2.2 of the movable plate 2 and the support 4 and between the lateral edges of the movable plate 2 and the support 4 and covering the upper face 2.1 of the movable plate. The element 40 has a sufficient flexibility not to hinder the movement of the movable plate under the effect of the flow on the upper face of the movable plate. The element is for example polymer or polyimide. The stiffness of the polymeric material under the plate and on the sidewalls of the plate is advantageously at least 10 times less than the stiffness of the MEMS mechanical structure. The element 40 ensures complete encapsulation of the movable plate 2. The element 40 is for example deposited by spin-coating in the liquid phase at the level of the support, or simply by dispensing with the Using a syringe on each of the structures, for example after release of the movable plate 2. In this example, since no fluid can flow between the movable plate and the support, no parasitic flow is present.
    [0023] It could be provided that the space between the sensor and the side edges of the recess in the channel wall is filled with a material, advantageously avoiding the occurrence of turbulence. In Figures 8A and 8B, there can be seen a variant C7 of the sensor of Figures 7A and 7B, wherein the element 40 'fills only the air gap surrounding the movable plate and covers the face 2.1 of the movable plate. It then forms a barrier to the flow of fluid between the movable plate and the support and under the movable plate. The element 40 'is for example put in place before release of the movable plate which is released by openings made in the rear face. The element is for example polymer or polyimide. In FIGS. 9A and 9B, there can be seen an embodiment variant C8 of the sensor of FIGS. 7A and 7B, in which the movable plate 302 comprises slots 342 and an element 340 filling both the lateral gap between the movable plate 302. and the support 304, the gap between the lower face of the movable plate and the support, filling the slots and covering the upper surface of the movable plate. This variant has the advantage of limiting the effect of the pressure of the fluid on the device. The tangential forces applied by the fluid on the movable plate are then partly transmitted by the flexible material. In FIGS. 10A and 10B, another variant C9 of the sensor of FIGS. 7A and 7B can be seen, in which the passage of the fluid is prevented by means of a dry film 44 deposited on the upper surface of the mobile plate, of the support and overlapping the lateral gap between the movable plate 2 and the support 4. The movable plate 2 is then partially encapsulated. The film 44 then forms a barrier for the fluid, parasitic flow rates are then removed. The film is for example of polymer or polyimide. The dry film is for example glued or deposited by rolling before or after releasing the movable plate. In FIGS. 11A and 11B, an exemplary embodiment C10 of a sensor according to the invention can be seen having a reduced sensitivity to parasitic accelerations and vibrations. For example, the duct in which it is desired to measure the flow rate may be subjected to vibrations which may distort the measurements by displacement of the moving plate under the effect of shear stresses. The sensor C10 comprises a counterweight element 46 rigidly connected to the movable plate. This counterweight 46 is attached to the movable plate so that the pivot connection is located between the movable plate and the counterweight. In addition, the device comprises means 50 for protecting the counterweight 46 of the fluid to be measured so that it does not interfere in the measurement. The means 50 are for example formed by a cover covering the counterweight 46, so the fluid does not come into contact with the upper surface of the counterweight and does not exert on it shear stresses. This counterweight makes it possible to make the moving plate 2 less sensitive to parasitic accelerations and vibrations. Thus only the shear stresses applied by the fluid move the movable plate 2 and are seen by the gauges. In the example shown, the movable plate 2 and the counterweight 46 are connected by two beams 51 extending along the X axis on either side of the pivot connection. This embodiment is not limiting and any other embodiment is within the scope of the present invention. In FIGS. 12A and 12B, another exemplary embodiment C11 can be seen in which the tangential force applied by the flow on the movable plate is increased. . For this, the movable plate 2 has projecting elements 52 on its upper face.
    [0024] In the example shown, these are square section studs distributed over the entire upper surface of the movable plate. The projections are distributed here in parallel lines to the X axis and arranged in staggered rows. These projections have a limited height so that they do not exceed the area where the shear stresses apply. Preferably the height of the projections is less than or equal to 100 μm. The shape of these projections is not limiting, other shapes may be suitable ... Thanks to the invention, a tangential force measuring system is realized whose sensor sensitivity is greatly increased compared to what is done in the state of the art by separating the mechanical part of the detection part. In addition, the sensor according to the invention implements a lever arm between the movable plate and the gauge or gauges, which amplifies the constraints finally seen by the gauges, the sensitivity is further increased. It is also possible to use a gauge or suspended gauges thinned with respect to the mechanical part of the movable element to increase the concentration of stress, which makes it possible to further increase the sensitivity. As a result, by increasing the sensitivity of the sensor it is possible to reduce the surface of the moving plate, thus to further miniaturize the sensor and thus increase its spatial resolution. The system according to the invention is particularly suitable for the realization of differential measurements, and the realization of a Wheatstone half-bridge or an entire Wheatstone bridge.
    [0025] In addition, the invention uses suspended gauges, which prevents the appearance of high temperature leakage currents as in the case of gauges implanted or diffused piezoresistive flowmeters of the state of the art. The invention then makes it possible to produce flow meters which do not have this limitation in temperature of use.
    [0026] An example of a method for producing a sensor implemented in the system according to the invention. In Figures 13A to 13G, we can see the different steps of an example of a method of producing a sensor. Each figure represents the element obtained during the various steps in plan view in section along the designated planes 1-1 in the top view. For example, a SOI (silicon on insulator) substrate comprising, for example, a silicon layer 54, a buried oxide layer 56 having for example a thickness of 2 μm, and a silicon layer 58 , for example of thickness between a few tens of nm and a few μm on the layer 56. The layer 56 forms the sacrificial layer. The stack could also be carried out by transferring the layer 58 of Si onto the stack of layers 54 and 56, or deposit this layer 58 on layer 56. Preferably, layer 58 is made of monocrystalline silicon.
    [0027] Photolithography is then performed, followed by etching of the silicon layer 58 to define the piezoresistive gauge 10 and define the zone of contact with the substrate. Etching is stopped on the SiO 2 layer. The element thus obtained is shown in FIGS. 13A.
    [0028] In a subsequent step, an oxide layer is formed, for example by deposition, for example SiO 2, for example with a thickness of between 1 μm and 2 μm, intended to form a barrier layer. The oxide layer is for example deposited by plasma-assisted chemical vapor deposition (or PECVD for Plasma-Enhanced Chemical Vapor Deposition in English terminology).
    [0029] Next, a photolithography is made to delimit portions of oxide 60 covering the piezoresistive gauges. An etching of the oxide layer is then performed with a stop on the layer 58, eliminating the latter except at the portion 60. The oxide in the area of contact with the substrate is also etched. Stripping can be done to remove the etch residue and mask. The element thus obtained is shown in FIGS. 13B. In a subsequent step, a layer 62, for example silicon, is formed on the layer 58. The layer 62 is preferably formed by epitaxial growth on the layer 58 of Si and on the portions 60 of oxide. This layer has, for example, a thickness of between 1 μm and a few tens of μm. A chemical mechanical polishing can then take place. The element thus obtained is shown in FIGS. 13C. In a subsequent step, a photolithography is performed to delimit the moving part, the anchoring studs and to remove the portion 60 above the piezoresistive gauges by selective etching of the layer 62. Vertical etchings are then performed 64 in the thickness of the layer 62 with stopping on the oxide layer 56 and the oxide portion 60.1 for example by deep reactive ion etching or DRIE (Deep Reactive Ion Etching). The element thus obtained is shown in FIGS. 13D.
    [0030] In a next step, the rear face of the substrate is metallized to make the electrical connections. For example, a layer of AlSi 66 is deposited on the entire rear face of the substrate. Next, lithography and etching of the layer 66 are carried out, thereby defining the contact pads. The element thus obtained is shown in FIG. 13E. In a subsequent step, the contact pads are traced by etching the substrate by the rear face with a stop on the SiO 2 layer 56. The etching is for example a DRIE etching.
    [0031] The element thus obtained is shown in FIGS. 13F. In a next step, the movable plate 2 and the pivot connection are released, partially removing the oxide layer 56 and the piezoresistive gauges 10 are released by removing the portion 60.1, for example by means of sulfuric acid vapor. This is a time engraving. The sulfuric acid is left in contact with the oxide layer 56 and the oxide 60.1 the time necessary to release the movable plate and the gauges while leaving the sacrificial layer under the fixed parts of the system. The element thus obtained is shown in FIG. 13G. The sensor is for example made on a card or on a housing 67 for outputting the contacts 69 (Figure 15A). Then, a bore 68 is made in the side wall of the duct 22 in which the sensor is to be disposed (FIG. 15B) and the sensor is sealingly mounted in the bore 68 via the card or the casing 67 and FIG. a seal 70 disposed between the housing 67 and the outer surface of the conduit 22 so that the movable plate sees the flow of fluid in the conduit 22 (Fig. 15C). The sensor can then be connected to an external system.
    [0032] We can consider implementing a network of sensors. The device according to the invention makes it possible to measure a tangential force applied by a fluid whether it is liquid or gaseous. It can then make it possible to produce flow sensors offering a high sensitivity, it can be used to measure flow rates of liquid or gas.
    [0033] Several sensors may be integrated in the wall of a conduit in one or more recesses or one or more bushings. For example it can be installed in a pipeline of gas or water, for example equipping individual houses to measure the consumption of subscribers. It can also make it possible to determine the viscosity of a fluid from the measurement of a known flow rate.
    权利要求:
    Claims (25)
    [0001]
    REVENDICATIONS1. A system for measuring a tangential force exerted by a fluid, said system comprising: a duct in which the fluid is intended to flow, the duct extending over at least a portion in a given direction (Y), said direction of flow, the conduit having an inner surface for contact with the fluid, and at least one cavity (24) disposed in said inner surface of the conduit (22), - at least one MEMS and / or NEMS measuring device tangential force device comprising a support (4, 104, 204, 304) having a middle plane and a movable plate (2, 102, 202, 302), said movable plate being suspended from the support by at least one pivot connection (6), said pivot connection (6) having an axis perpendicular to the median plane of the support (4), said movable plate (2) having a first face (2.1) on which the fluid applies a tangential force and a second face (2.2) opposite to the first face (2.1), said device being integral with the duct and being arranged in the cavity so that the first face (2.1) of the movable plate is flush with at least one zone of the inner surface of the duct (22) surrounding the cavity (24), said device also comprising at least one piezoresistive strain gauge (10) suspended and mechanically connected to the movable plate (2, 102, 202) and to the support, said gauge (10) being disposed in the cavity so that the tangential force applied to the first surface (2.1) of the moving plate by the fluid in the direction of flow (Y) applies a compressive or tensile force to said piezoresistive strain gauge.
    [0002]
    2. Measuring system according to claim 1, wherein the distance separating the plane containing the first face (2.1) of the movable plate (2) and the plane containing at least the area surrounding the cavity (24) is less than or equal to 200 μm and advantageously less than or equal to 100 μm.
    [0003]
    3. Measuring system according to claim 1 or 2, wherein the gauge (10) is disposed closer to the axis of the pivot connection (6).
    [0004]
    4. Measuring system according to one of claims 1 to 3, comprising at least two electrically connected differential gages (10) electrically connected to a Wheatstone half-bridge or at least four differentially mounted gates electrically connected to a Wheatstone bridge.
    [0005]
    5. Measuring system according to one of claims 1 to 4, wherein the movable plate (102, 202) is suspended from the support by two pivot connections (106, 106 ') said device comprising at least two piezoresistive gauges (110, 110 ').
    [0006]
    6. Measuring system according to the preceding claim, wherein at least one rigid force transmission arm (127, 129, 127 ', 227', 227, 229) connects the movable plate (102, 202) to each pivotal connection. (106, 106 '), at least one piezoresistive strain gauge (110, 110') being suspended between a force transmission arm and the support.
    [0007]
    7. Measuring system according to the preceding claim, wherein each force transmission arm (127, 129, 127 ', 227', 227, 229) is connected to the movable plate (102, 202) by at least deformable means resiliently (128, 130, 128 ', 130', 228, 230) at least in the direction perpendicular to the fluid flow.
    [0008]
    8. Measuring system according to one of claims 1 to 7, wherein the strain gauge has a thickness between 100 nm and 500 nm and the movable plate has a thickness between 3 um and 40 um.
    [0009]
    9. Measuring system according to one of claims 1 to 8, wherein the pivot connection (6) comprises two beams (6.1, 6.2) of substantially the same length anchored on the support at two distinct points and anchored to the movable plate ( 2) at a point through which the axis (Z) of the pivot connection (6) passes.
    [0010]
    10. Measuring system according to one of claims 1 to 9, comprising means for limiting the flow of fluid between the movable plate and the support.
    [0011]
    11. Measuring system according to the preceding claim, comprising a structuring (34, 36) of the support (4) and / or the movable plate (2) so as to provide at least one area of reduced flow section between the support (4) and the movable plate (2).
    [0012]
    12. Measuring system according to the preceding claim, wherein the structuring (34, 36) is performed on the second face (2.1) of the movable plate (2) and / or on an area of the support (4) facing said face.
    [0013]
    13. Measuring system according to one of claims 1 to 12, comprising means for preventing the flow of fluid between the movable plate and the support.
    [0014]
    14. Measuring system according to the preceding claim, comprising a flexible element (40, 40 ') at least partially encapsulating the movable plate (2) and preventing the fluid from flowing between the movable plate (2) and the support (4). ).
    [0015]
    15. Measuring system according to the preceding claim, wherein the element (40, 40 ', 44) is a polymer or a polyimide.
    [0016]
    16. Measuring system according to claim 13, wherein the means for preventing the flow of fluid between the movable plate and the support comprise a film (44) of flexible material covering the first face (2.1) of the movable plate (2). ) and at least a part of the support (4).
    [0017]
    17. Measuring system according to one of claims 14, 15 or 16, wherein the movable plate comprises lights, said lights being closed by the flexible element or by the film.
    [0018]
    18. Measuring system according to one of claims 1 to 17, comprising means for reducing the sensitivity to parasitic accelerations and vibrations.
    [0019]
    19. Measuring system according to the preceding claim, wherein said means (46, 50) for reducing the sensitivity to parasitic accelerations and vibrations comprise a counterweight (46) integral with the movable plate (2) and protected from the fluid so that not undergo tangential force.
    [0020]
    20. System for measuring the flow rate of a fluid flowing in a duct comprising at least one measuring system according to one of claims 1 to 19.
    [0021]
    21. A method of producing a measuring system according to one of claims 1 to 19, this method comprising: - the formation of a cavity in the inner surface of a duct, - the realization of a measuring device of tangential force from a stack formed of a substrate, a sacrificial layer and at least a first layer (58) of a conductive or semiconductor material, comprising producing at least one gauge piezoresistive in the first layer, the realization of the movable plate and the at least one pivot connection in said stack and the release of the gauge, the movable plate and the pivot connection.
    [0022]
    22. A method of producing a measuring system according to claim 21, wherein after forming the gauge, a protective portion is formed on said gauge prior to forming a second layer of a conductive or semi-conductive material. conductor on the first layer of a conductive or semiconductor material.
    [0023]
    23. A method of producing a measuring system according to claim 22, wherein following the formation of the protective portion, the second layer of a semiconductor, conductive or insulating material is formed on the first layer of a conductive or semi-conductive material, and wherein the movable plate and the pivot connection are made at least in part.
    [0024]
    24. A method of producing a measurement system according to one of claims 21 to 23, comprising a step of filling at least the lateral gap between the movable plate and the support, said filling being for example made by deposit in the liquid phase by centrifugation to form means for preventing the flow of fluid between the movable plate and the support.
    [0025]
    25. A method of producing a measuring system according to one of claims 21 to 23, comprising a step of forming a film on the movable plate and on at least a portion of the support so as to close the air gap laterally between the movable plate and the support, said film being for example formed by rolling to form means for preventing the flow of fluid between the movable plate and the support.
    类似技术:
    公开号 | 公开日 | 专利标题
    EP3009819A1|2016-04-20|System for measuring tangential force applied by a fluid with increased sensitivity
    EP2921836A1|2015-09-23|Sensor for measuring microelectromechanical and/or nanoelectromechanical differential pressure
    EP2541222B1|2018-02-21|Pressure-measurement device with optimised sensitivity
    EP0626572B1|2000-02-02|Diaphragm pressure transducer comprising a shock protective system, and gradiomanometer incorporating such a transducer
    EP2491406B1|2016-09-21|Sensor for in-plane piezoresistive detection
    EP2211143B1|2018-08-08|Micromachined planar gyrometer with an out-of-plane detection by strain gauge
    EP2771661B1|2019-02-20|Micromechanical structure having a deformable membrane and a protection against strong deformations
    FR2983844A1|2013-06-14|PIVOT MECHANICAL BONDING FOR MEMS AND NEMS MECHANICAL STRUCTURES
    FR2872281A1|2005-12-30|Pressure sensor for detecting fuel pressure in vehicle, has diaphragm inserted into recess portion in substrate, corresponding to area where strain gauges are formed so that substrate insulation layer is bonded to diaphragm
    WO2012146756A1|2012-11-01|Micro flow meter and method for producing same
    EP3234535B1|2020-01-08|Pressure sensor suited to measuring pressure in an aggressive environment
    EP3538479A1|2019-09-18|Device for transmitting a movement and a force between two zones that are insulated from one another
    EP3498661A1|2019-06-19|Microelectromechanical and/or nanoelectromechanical device providing increased sturdiness
    EP3667309A1|2020-06-17|Thermal flow sensor with heating wire
    EP3217181A1|2017-09-13|Damped linear accelerometer
    EP0931250B1|2004-07-14|Cell for converting differential pressure into an electric signal
    EP3388808B1|2019-10-02|Device for detecting pressure with mechanical uncoupling
    EP3663752A1|2020-06-10|Thermal flux sensor with heating filaments
    FR2950692A1|2011-04-01|SENSOR DEVICE AND METHOD FOR MANUFACTURING SUCH A SENSOR DEVICE
    FR2703781A1|1994-10-14|High precision pressure sensor, gradiomanometer incorporating such a sensor and method of manufacturing this sensor.
    FR3105415A1|2021-06-25|Autonomous membrane sensor
    同族专利:
    公开号 | 公开日
    FR3027389B1|2016-11-25|
    US20160109348A1|2016-04-21|
    EP3009819A1|2016-04-20|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    US6408698B1|1998-09-03|2002-06-25|Board Of Trustees Operating - Michigan State University|Sensors and method for measurement of flow rates and cumulative flow in ducts|
    US20040025598A1|2000-09-21|2004-02-12|Festo Ag & Co.|Integrated fluid sensing device|
    FR2983844A1|2011-12-12|2013-06-14|Commissariat Energie Atomique|PIVOT MECHANICAL BONDING FOR MEMS AND NEMS MECHANICAL STRUCTURES|
    US7024945B2|2002-02-22|2006-04-11|Compumedics Limited|Flow sensing apparatus|
    US9021855B2|2011-11-14|2015-05-05|Leroy C. Delatorre|Torsional flow sensor|CN109059837B|2018-08-14|2019-08-30|北京航空航天大学|Measurement method and device suitable for nearly wall distance|
    CN109489870A|2018-11-02|2019-03-19|河海大学|A kind of ball-type bed-sit starting shearing stress measuring device|
    CN109489869A|2018-11-02|2019-03-19|河海大学|A kind of air-cushion type bed-sit starting shearing stress measuring device and measuring method|
    US10591395B1|2019-07-12|2020-03-17|Halliburton Energy Services, Inc.|Lubricity testing with shear stress sensors|
    US10920571B2|2019-07-12|2021-02-16|Halliburton Energy Services, Inc.|Measurement of torque with shear stress sensors|
    US10920570B2|2019-07-12|2021-02-16|Halliburton Energy Services, Inc.|Measurement of torque with shear stress sensors|
    US10697876B1|2019-07-12|2020-06-30|Halliburton Energy Services, Inc.|Fluid analysis devices with shear stress sensors|
    CN111307352B|2020-03-30|2021-03-12|天津大学|Flexible sensor capable of measuring friction force between fluid and solid|
    法律状态:
    2015-11-02| PLFP| Fee payment|Year of fee payment: 2 |
    2016-04-22| PLSC| Search report ready|Effective date: 20160422 |
    2016-10-28| PLFP| Fee payment|Year of fee payment: 3 |
    2018-07-27| ST| Notification of lapse|Effective date: 20180629 |
    优先权:
    申请号 | 申请日 | 专利标题
    FR1460024A|FR3027389B1|2014-10-17|2014-10-17|TANGENTIAL FORCE MEASUREMENT SYSTEM APPLIED BY AN INCREASED SENSITIVITY FLUID|FR1460024A| FR3027389B1|2014-10-17|2014-10-17|TANGENTIAL FORCE MEASUREMENT SYSTEM APPLIED BY AN INCREASED SENSITIVITY FLUID|
    US14/885,433| US20160109348A1|2014-10-17|2015-10-16|System for measuring shear stress of a fluid with enhanced sensitivity|
    EP15190237.6A| EP3009819A1|2014-10-17|2015-10-16|System for measuring tangential force applied by a fluid with increased sensitivity|
    [返回顶部]