Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
  • G01L9/0041—Transmitting or indicating the displacement of flexible diaphragms
  • G01L9/0072—Transmitting or indicating the displacement of flexible diaphragms using variations in capacitance
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
  • G01L9/0041—Transmitting or indicating the displacement of flexible diaphragms
  • G01L9/0072—Transmitting or indicating the displacement of flexible diaphragms using variations in capacitance
  • G01L9/0073—Transmitting or indicating the displacement of flexible diaphragms using variations in capacitance using a semiconductive diaphragm

Definitions

• the invention relates to the field of MEMS (acronym for
• Microelectromechanical System in English, or more particularly capacitive type pressure sensors or pressure measuring devices by varying the capacitive effect between two electrodes, and their manufacturing process.
• a capacitive-type pressure sensor comprises a flexible membrane and a fixed membrane, separated from each other by a cavity in which there is a reference pressure, for example a vacuum.
• the flexible membrane forms or supports a deformable sensitive electrode
• the fixed membrane forms or supports a fixed electrode.
• the flexible membrane deforms either towards the fixed membrane or away from the fixed membrane. This variation in the distance between these two membranes results in a variation of the capacitance between these two electrodes, and the measurement of this capacitance variation makes it possible to determine the pressure difference, and therefore the pressure to be measured.
• the sensor described above is particularly intended to be implemented in an industrial or biological environment.
• the assembly formed by the sensitive and fixed electrodes is embedded in a protective casing guaranteeing operation of the electrodes. in a non-aggressive atmosphere.
• This case is generally made of a metal material suitable for the environment, such as titanium for biocompatible applications or stainless steel for industrial applications.
• the pressure to be measured is transmitted from the housing to the sensitive electrode via a transmission interface generally consisting of oil degassed beforehand.
• the present invention aims to provide a pressure sensor free of at least one of the limitations mentioned above.
• An object of the invention is in particular to provide a less expensive industrial or biocompatible pressure sensor.
• Another object of the invention is to eliminate any risk of leakage of the degassed oil.
• the invention thus relates to a device for measuring pressure by capacitive effect between two electrodes comprising at least one sensitive electrode disposed opposite and at a distance from a fixed electrode so as to define a cavity in which there is a reference pressure.
• the device according to the invention further comprises a housing intended to isolate at least the fixed electrode from the ambient environment in which the pressure to be measured prevails, said housing having at least one solid portion forming a housing intended to contain at least one fixed electrode, and a thinned portion forming the sensitive electrode.
• the sensitive electrode and the housing form a body (or housing) protection for isolating the fixed electrode from the ambient environment.
• the sensitive electrode is no longer it is inside a protective casing, but it is an integral part of the casing and is therefore in direct contact with the surrounding environment.
• the capacitance variation representative of a pressure difference between the pressure to be measured and the reference pressure, is measured between the fixed electrode and the sensitive electrode.
• the transmission member present in the pressure sensors of the prior art is no longer necessary.
• the housing is made of a metallic material.
• the housing may be made of a material adapted to the ambient environment, for example of the biocompatible type, such as titanium, or type resistant to stress or aggression in an industrial environment, such as stainless steel.
• the device further comprises a grid or a pierced wall for protecting the sensitive electrode.
• the perforated grid or wall makes it possible in particular to protect the sensitive electrode from certain undesirable effects such as shocks with objects having contending contours liable to damage the surface of the sensitive electrode, while allowing the surrounding environment to be in contact with each other. with the sensitive electrode.
• the protective housing further has an intermediate portion forming a junction between the sensitive electrode and the housing, and having a profile capable of mechanically decoupling the structural variations of the sensitive electrode from those of the housing.
• this junction acts as a means of mechanical decoupling and limits the undesirable effects due in particular to variations in the structure of the housing, such as thermal expansion, on the structure of the sensitive electrode.
• the profile of the junction has a decreasing thickness in the direction of the sensitive electrode.
• the profile of the junction has a thinned portion arranged head to tail with the thinned portion forming the sensitive electrode.
• a sealing frame frames the fixed electrode and is arranged at a distance from the fixed electrode so as to define a gap accommodating a connecting frame, said connecting frame providing a mechanical connection and a mechanical decoupling between the fixed electrode. and the sealing frame.
• the connecting frame serves as a means of mechanical decoupling between the fixed electrode and the sealing frame, and in particular makes it possible to greatly reduce or even eliminate all the constraints on the fixed electrode, related to variations in the structure of the sealing frame, for example thermal expansion.
• the connecting frame frames the fixed electrode and has at least one protrusion secured to the sealing frame, and another projection secured to the fixed electrode.
• the connecting frame may be disposed at a distance from the fixed electrode and the sealing frame, and may have at least one projection integral with the sealing frame and another projection integral with the fixed electrode.
• the connecting frame may have two projections disposed opposite one another and secured to the fixed electrode, and two other projections arranged opposite one another and secured to the sealing frame.
• the fixed electrode, the connecting frame and the sealing frame form a body having a planar structure disposed in the housing.
• the device may further comprise a reference electrode insensitive to pressure variations.
• the subject of the invention is also a method for manufacturing at least one pressure measuring device as defined above, comprising at least the steps of:
• the method further comprises an embodiment of an intermediate portion forming a junction between the solid portion and the thinned portion, and whose profile has a decreasing thickness in the direction of the sensitive electrode.
• the method further comprises at least one embodiment of an intermediate portion forming a junction between the solid portion and the thinned portion, and whose profile has a thinned portion arranged head-to-tail with the thin portion forming a sensitive electrode .
• the substrate consists of a dielectric layer interposed between two semiconductor layers, and the embodiment of the fixed electrode comprises at least steps of:
• the coefficient of expansion of the material in which the sensitive electrode is made may be 4 to 6 times higher than that of the material in which the electrode is made.
• fixed for example silicon (coefficient of expansion of silicon is of the order of 2.6.10 ⁇ 6 / ° C).
• the seal further comprises steps of:
• the manufacturing method described above applies to an individualized manufacture of pressure measuring device, but also to a collective manufacturing, that is to say a manufacture of several pressure measuring devices presented above.
• a method of manufacturing a plurality of pressure measuring devices as defined above comprises at least the following steps:
• each elementary module comprising at least one of said cavities
• the method further comprises, for each sensitive electrode, an embodiment of an intermediate portion on said plate, intended to form a junction between the housing and the sensitive electrode, and whose profile has a decreasing thickness in the direction of the sensitive electrode.
• the method further comprises at least, for each sensitive electrode, an embodiment of an intermediate portion on said plate, intended to form a junction between the housing and the sensitive electrode, and whose profile has a thinned portion arranged head to tail with the thin portion forming a sensitive electrode.
• the substrate consists of a dielectric layer interposed between two semiconductor layers, and the embodiment of the fixed electrode comprises at least steps of:
• FIG. 1 is a schematic sectional view of a capacitive pressure sensor according to one embodiment of the invention.
• FIG. 2 is a schematic sectional view of a capacitive pressure sensor according to another embodiment
• FIG. 3 is a schematic perspective view of the substrate in which the fixed electrode is made according to one embodiment of the invention.
• FIGS. 4 to 14 show some steps of the manufacturing method of the pressure sensor according to one embodiment of the invention
• FIGS. 15 to 17 show some steps of the method of collective manufacturing of several pressure sensors according to one embodiment of the invention.
• the pressure measuring device comprises a protective casing 1 (only a portion of which has been represented in the figures) which can be made of a metallic material compatible with the ambient environment in which the pressure to be measured P, such as titanium or stainless steel for example.
• This housing 1 has a solid portion forming a housing 10 for receiving a fixed electrode 211, a thinned portion forming a sensitive electrode 11, and an intermediate portion forming a junction 12 between the sensitive electrode 11 and the housing 10.
• the sensitive electrode 11 is therefore directly realized in the material in which the housing 1 of protection is made, and is therefore directly in contact with the ambient environment.
• the housing 10, the sensitive electrode 11 and the junction 12 thus form a structure capable of protecting the fixed electrode 211 from the attacks of the ambient environment.
• a grid 6 or pierced protection wall may be arranged opposite the sensitive electrode 11 to limit undesirable effects, such as shocks with objects having contending contours that may deteriorate the surface of the sensitive electrode 11.
• the junction 12 may have a profile making it possible to mechanically decouple the structural variations of the sensitive electrode 11 of those of the housing 10.
• the profile of this junction 12 may have a thickness e decreasing in the direction of the sensitive electrode 11, as shown in Figure 1.
• the profile of the junction 12 may also have a thinned portion 120 disposed head-bêche with the thinned portion forming the sensitive electrode 11, as illustrated
• the housing 10 contains a substrate 2, for example of the SOI type (acronym for "silicon on insulator”), consisting of a dielectric layer 20, for example oxide, interposed between two semiconductor layers 21, 22, for example silicon.
• a substrate 2 for example of the SOI type (acronym for "silicon on insulator"), consisting of a dielectric layer 20, for example oxide, interposed between two semiconductor layers 21, 22, for example silicon.
• the fixed electrode 211 In one of the two silicon layers 21 are made the fixed electrode 211, a sealing frame 210 and a connecting frame 212 connecting the fixed electrode 211 to the sealing frame 210.
• the sealing frame 210 surrounds the fixed electrode 211 and is arranged at a distance from the fixed electrode 211 so as to delimit a gap 213 accommodating the connecting frame 212, as illustrated in FIG.
• the connecting frame 212 is made in such a way as to have a profile making it possible to mechanically decouple the structural variations of the fixed electrode 211 from those of the sealing frame 210.
• the connecting frame 212 surrounds the fixed electrode 211, and is disposed at a distance from the fixed electrode 211 and sealing frame 210.
• the connecting frame has two projections 212a, 212b disposed facing one another and secured to the fixed electrode 211, and two further projections 212c, 212d disposed facing one of the and other secured to the sealing frame 210.
• This profile has the particular advantage of securing the fixed electrode 211 to the sealing frame 210, while limiting the thermal stresses to the sealing frame 210 on the fixed electrode 211.
• the fixed electrode 211, the connecting frame 212 and the sealing frame 211 thus form a body having a flat structure.
• the substrate 2 is secured to the housing 1 by means of a sealing gasket 3, so as to dispose the sensitive electrode 11 opposite and away from the fixed electrode 211, to delimit a cavity 4 whose depth is defined by the thickness of said sealing joint 3.
• the cavity 4 is under a reference pressure P ref , for example a vacuum, and the variation in capacity, representative of a pressure difference between the pressure to be measured and the reference pressure, is measured between sensitive electrode 11 and the fixed electrode 211.
• P ref for example a vacuum
• a reference electrode 51 by means of another dielectric layer 50, for example oxide, to produce a reference capacity 5 insensitive to any variation in pressure. It is also possible to have on this same free face 220 electrical contact zones as well as means for processing the sensor signals.
• the method of manufacturing such a pressure sensor according to an embodiment comprises in particular:
• FIG. 14 An embodiment of the protective case (FIG. 14).
• the embodiment of the fixed electrode 211 consists in particular in performing an etching (FIGS. 4 and 5) on one of the two semiconductor layers 21 of the wafer so as to form the fixed electrode 211, the connecting frame 212 and the sealing frame 210 as defined above.
• the fixed electrode 211 is released by elimination (FIG. 6) of a portion of the dielectric layer 20 facing the fixed electrode 211, the connecting frame 212 and a portion of the sealing frame 210.
• FIG. 7 access through the other semiconductor layer 22 and the dielectric layer 20 in anticipation of an electrical contact 7 for the fixed electrode 211. It is it is also possible to realize the reference capacitor 5 (FIG.
• a material compatible with the ambient environment for example titanium or stainless steel, is shaped to provide the housing 210, the sensitive electrode 211 and the junction 212 as defined above, and thus to form the protective housing 1 (FIG. 9).
• the protection of the sensitive electrode 11, such as grid or pierced wall disposed opposite the sensitive electrode can also be performed at this stage.
• the realization of the sealing joint 3 can notably consist in:
• a first metal layer 33 for example of the gold type, on a portion of the housing 1 designed to face the sealing frame 21 (FIG. 12);
• thermo-compression sealing (FIG. 13) of the first and second metallic layers 33, 32, under reference pressure P ref , so that the sensitive electrode 11 is opposite and at a distance from the fixed electrode 211 to delimit the cavity 4 whose depth is defined by the thickness of the seal 3 made.
• P ref reference pressure
• other types of sealing at lower temperatures are possible.
• a direct titanium seal on silicon oxide can be advantageously used as a replacement for thermocompression.
• a housing 10 is then welded to the plate to form the housing 1 of protection ( Figure 14) in which is disposed the fixed electrode 211 which is thus isolated from the ambient environment.
• the manufacturing process described above is also applicable to a collective fabrication (FIGS. 15 to 17) of several pressure measuring devices, which may comprise the production of a structure 8 of several elementary modules 8a, 8b, each elementary module. 8a, 8b including a cavity 4a, 4b delimited by a sensitive electrode 11a, 11b, a fixed electrode 211a, 211b and a seal 3a, 3b whose thickness defines the depth of the cavity 4a, 4b.
• the structure 8 can be made from a plate of material compatible with the ambient environment and a substrate as defined above.
• the plate is shaped (FIG.
• the substrate is also etched (FIG. 15) according to the principle for producing a fixed electrode exposed above, to obtain several sealing frames 210a, 210b, connecting frames 212a, 212b and fixed electrodes 211a, 211b.
• the plate is sealed (FIG. 16) to the substrate by the interposition of several sealing joints 3a, 3b in order to make several cavities 4a, 4b as defined above and thus to obtain a plurality of elementary modules 8a, 8b.
• the structure is then cut to separate the elementary modules 8a, 8b between them.
• a protective housing for each elementary module 8a, 8b, there is provided a protective housing (FIG.
• the pressure sensor of the invention is free of transmission interface, including degassed oil, and can in particular be implemented for applications requiring inexpensive biocompatible pressure sensors.
• the pressure sensor of the invention can in particular be easily integrated into a catheter, but can also be implemented for industrial applications and in particular those of the aeronautics.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Measuring Fluid Pressure (AREA)

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• 2009
  • 2009-07-06 FR FR0954667A patent/FR2947629B1/fr not_active Expired - Fee Related
• 2010
  • 2010-07-05 US US13/379,399 patent/US20120096944A1/en not_active Abandoned
  • 2010-07-05 WO PCT/FR2010/051415 patent/WO2011004113A1/fr active Application Filing
  • 2010-07-05 EP EP10742200A patent/EP2452174A1/de not_active Withdrawn
• 2012
  • 2012-01-04 IL IL217358A patent/IL217358A0/en unknown

Non-Patent Citations (1)

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