Miniature pressure sensor having a metallic membrane for measuring a pressure of a fluid

Abstract

A pressure sensor to measure the pressure of a fluid comprises: a metallic membrane to be in contact with the fluid and on which are stacked an electrical insulator and at least one gauge for measuring the deformation of the membrane, the whole forming a sensitive measuring element a cap comprising: a cover comprising a cavity and holes; conductors located in the holes, the sensitive element exhibiting a face opposite the cap and located in a plane P; wherein the sensor comprises: at least one metallic zone, located in a plane parallel to said plane P, for hermetic sealing of the cap on the sensitive measuring element; continuous metallic tracks comprising parts for picking up contact with the conductors and parts for picking up contact with at least the gauge. A method for manufacturing the pressure sensor is also provided.

Claims

1. A pressure sensor configured to measure a pressure of a fluid comprising: a metallic membrane having a first surface configured to be in contact with said fluid and a second surface on which are stacked an electrical insulator and at least one gauge configured to measure a deformation of said metallic membrane, the metallic membrane, the electrical insulator, and the at least one gauge forming a sensitive measuring element, a cap comprising: a cover comprising a cavity and holes; and conductors located in said holes, said sensitive measuring element including a face positioned opposite the cap and located in a plane P; wherein said pressure sensor further comprises: at least one metallic zone, located in a plane parallel to said plane P, for hermetic sealing of said cap on said sensitive measuring element; and continuous metallic tracks comprising parts configured to contact said conductors and parts configured to contact at least said gauge.

2. The pressure sensor configured to measure the pressure of a fluid according to claim 1, wherein the parts for picking up contact with said conductors are offset with respect to the parts for picking up contact with at least said gauge, ensuring an electrical link exhibiting a break in transmission axis.

3. The pressure sensor configured to measure the pressure of a fluid according to claim 1, wherein the cover is made of metal and comprises at least one dielectric layer.

4. The pressure sensor configured to measure the pressure of a fluid according to claim 1, wherein said cover is made of ceramic material.

5. The pressure sensor configured to measure the pressure of a fluid according to claim 4, wherein the conductors are vias.

6. The pressure sensor configured to measure the pressure of a fluid according to claim 4, wherein the cover comprises a stack of dielectric layers comprising on their surface metal patterns linked between layers by vias.

7. The pressure sensor configured to measure the pressure of a fluid according to claim 1, wherein said conductors are pins.

8. The pressure sensor configured to measure the pressure of a fluid according to claim 7, wherein said pins are fixed hermetically to said cover with glass elements.

9. The pressure sensor configured to measure the pressure of a fluid according to claim 7, wherein said pins are fixed hermetically to said cover with at least one metallic layer.

10. The pressure sensor configured to measure the pressure of a fluid according to claim 1, wherein the cap comprises at least one opening making it possible to reference the sensitive element to atmospheric pressure.

11. The pressure sensor configured to measure the pressure of a fluid according to claim 1, comprising a connection with which said sensitive element is assembled.

12. The pressure sensor configured to measure the pressure of a fluid according to claim 1, comprising a monolithic component comprising said sensitive element and a connection.

13. A method for manufacturing a pressure sensor according to claim 1, configured to measure the pressure of a fluid, comprising: the production of a sensitive element comprising a metallic membrane, an electrical insulator and at least one gauge for measuring the deformation of said membrane; the production on the surface of said sensitive element of a first metallic sealing zone and the production of metallic contact tracks of at least said gauge; the production on the surface of said cap of a second metallic sealing zone and the production of metallic tracks for picking up contact with the conductors; the assembling of said sensitive element and of said cap by brazing and/or welding in a plane parallel to that of the face of the sensitive element opposite the cap, so as to ensure pickup of contact and sealing.

14. The method for manufacturing a pressure sensor configured to measure the pressure of a fluid according to claim 13, wherein the metallic sealing zones or the metallic tracks are produced by etching of at least a layer made of metal or of at least a material capable of forming an eutectic with a metal or by silk-screen printing of a metal or of a material capable of forming a eutectic with a metal.

15. The method for manufacturing a sensor configured to measure the pressure of a fluid according to claim 13, comprising a sealing operation carried out in the presence of an exterior element as a material necessary for brazing or as an eutectic preform.

16. A pressure sensor configured to measure a pressure of a fluid manufactured according to the method of claim 13.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood and other advantages will become apparent on reading the nonlimiting description which follows and by virtue of the appended figures among which:

(2) FIG. 1 illustrates a first exemplary so-called all-fluid pressure sensor according to the known art comprising a silicon membrane and a separator membrane;

(3) FIG. 2 illustrates a second exemplary so-called all-fluid pressure sensor according to the known art comprising a metallic membrane;

(4) FIG. 3 illustrates a third exemplary so-called all-fluid pressure sensor according to the known art comprising a metallic membrane;

(5) FIG. 4 illustrates a first exemplary miniature pressure sensor according to the known art comprising a metallic membrane;

(6) FIG. 5 illustrates a second exemplary miniature pressure sensor according to the known art comprising a silicon membrane;

(7) FIGS. 6a to 6f represent sectional views and perspective views of a first type of pressure sensor according to the invention comprising conductors opposite the contact pickups for the strain gauges;

(8) FIG. 7 represents an operation of assembling a cap and a sensitive element constituting a step of a method for manufacturing a sensor according to the invention;

(9) FIG. 8a represents a sectional view of the sensitive element in a second type of sensor of the invention comprising conducting elements offset with respect to the contact pickups for the strain gauges;

(10) FIG. 8b represents a view from above of the sensitive element in the second type of sensor of the invention;

(11) FIG. 9a represents a sectional view of the cap in the second type of sensor of the invention;

(12) FIG. 9b represents a view from below of the incorporated cap in the second type of sensor of the invention;

(13) FIG. 10 represents a sectional view of the second type of pressure sensor of the invention;

(14) FIGS. 11a to 11d represent exploded perspective views of the sensitive element part and of the cap of the second type of sensor according to the invention;

(15) FIG. 12 represents a sectional view of a third type of sensor of the invention incorporating a cap produced by the LTCC technique;

(16) FIG. 13 represents a sectional view of a sensor according to the invention assembled with a connection;

(17) FIG. 14 represents a sectional view of a sensor according to the invention comprising a monolithic component incorporating the membrane and a connection;

(18) FIGS. 15a and 15b represent a sectional view and a perspective view of a sensor according to the invention assemblied with a connection.

DETAILED DESCRIPTION OF THE INVENTION

(19) In general, the pressure sensor of the present invention comprises a sensitive element with a membrane equipped with at least one measurement gauge for measuring the deformation of said membrane, under the action of a pressure of interest.

(20) The sensor comprises at least one first metallic zone making it possible to ensure the hermetic fixing of a cap intended to ensure the protection of said membrane and the referencing to a reference pressure, the first metallic zone being located at the interface between the sensitive element and the cap.

(21) The sensitive element comprises a part of the second metallic zones for pickup of contact with the deformation measurement gauge or gauges.

(22) The cap consists of a cover comprising holes in which conductors are positioned. The conductors can typically be pins or vias. The cap also comprises a part of the second metallic zones for pickup of contact with the conductors.

(23) Such a configuration makes it possible to devise sensors of small dimensions, requiring a restricted number of elements.

(24) Advantageously, the sensor can comprise a ceramic cover (made of alumina for example) with expansion coefficient close to that of the metal of the membrane. The benefit of this solution is of having an insulating material which avoids the deposition of an insulating thin layer, a potential source of electrical defects.

(25) When the conductors are metallic pins (Kovar typically) and the cover is produced in a ceramic substrate, the method for sealing the pins at the level of the cover can be a conventional brazing method based on the methods of MoMn metallization, generally in the form of powders. The latter are deposited on the ceramic to be metallized and then the assembly is baked at high temperature. To improve the grip and the wettability of the brazing, an alloy in thin or thick layers is deposited thereafter. The most often used are alloys based on silver (AgCu, AgCuPd, . . . ), copper or alloys based on gold (Au). A metal that is often brazed on alumina is Kovar (Fe-28Ni-18Co alloy), which can therefore constitute an excellent material for the contact pins. Other alloys such as MoMn (so-called active alloys) can also be used.

(26) First Type of Pressure Sensor According to the Invention:

(27) According to this first variant embodiment of pressure sensor, and illustrated in FIGS. 6a, 6b, 6c and 6d, the sensitive element comprises a membrane 20 equipped with measurement gauges on the surface of an insulating layer 20. Conventionally, the sensor can be equipped with an assembly of four gauges mounted as a Wheatstone bridge and positioned in such a way that, under the effect of the deformation, two gauges increase in value and two others decrease. According to this example, the conductors are pins. Thus, the power supply and the output of the bridge can be connected outside the sensor (rendering the signals available/accessible to the outside) by virtue of contact pins 60 previously fixed hermetically by fixing elements 150 to a cover 30 and located in holes.

(28) The pressure sensor comprises a first metallic zone Z.sub.1, making it possible to ensure the hermetic fixing of said cap on said sensitive measuring element and second metallic contact pickup zones Z.sub.2 for said pins and connected to the deformation measurement gauge or to said deformation measurement gauges. Conducting patterns are defined in a conducting layer 21, and in a conducting layer 31, as illustrated in the assembly of FIGS. 6a to 6d.

(29) The stacking of these conducting patterns produced in the layers 21/31 makes it possible to define locally: the first zone Z.sub.1 resulting from the stacking of the zones Z.sub.1-21 and Z.sub.1-31 arising from the layers respectively 21 and 31 to ensure the fixing of the sensitive element and of the cap; the second zones Z.sub.2 resulting from the stacking of the zones Z.sub.2-21 and Z.sub.2-31 arising from the layers respectively 21 and 31 to ensure the pickup of contact of the gauges via the pins 60.

(30) According to this variant of the invention, the pins are located opposite the second contact pickup zones Z.sub.2-21 and therefore the parts for picking up contact with said conductors are opposite the parts for picking up contact with said strain gauges, as illustrated in FIG. 6b.

(31) To produce the zones Z.sub.1 and Z.sub.2 simultaneously, it is advantageously possible to produce the pressure sensor by assembling the sensitive membrane 20 and the cap 30 comprising pins 60 introduced into the holes, in a single operation, the hermetic sealing and the contact taps between the gauges 100 and the pins 60 being obtained at the same time by refusion (eutectic sealing) of a stack of metallic layers 21+31 in which the metallic patterns are defined. FIGS. 6c and 6d depict the production of metallic patterns making it possible to define at the level of the sensitive element the zones Z.sub.1-21 and Z.sub.2-21 respectively dedicated to the sealing and to the contact pickups for the gauges 100 and at the level of the cap, the zones Z.sub.1-31 and Z.sub.2-31 respectively dedicated to the sealing and to the contact pickups for the pins 60. FIG. 6e represents a variant with a hole T making it possible to produce a so-called gage sensor, having atmospheric pressure as reference pressure. FIG. 6f represents a variant with the addition of a stopper B making it possible to seal the vacuum subsequently.

(32) Preferably, the cover and the membrane are made of materials having the closest possible, very advantageously identical, expansion coefficients. In this case an insulating thin layer, typically of SiO.sub.2 or Al.sub.2O.sub.3 is deposited first on the active faces of the metal, this not being represented in FIGS. 6a and 6b.

(33) To carry out the assembling of the sensitive element and of the cap, it is possible to carry out a brazing operation. In order to ensure an optimum hermetic link, the method of the present invention can advantageously comprise a eutectic metallic sealing operation.

(34) More precisely, the sealing operation can, according to an advantageous embodiment, be performed with the stack of layers illustrated in FIG. 7 with thicknesses of metallic layers of the order of a micrometer (m). The component of the cover 30 comprises a layer made of Au, the sensitive element comprises, stacked on the membrane 20, an insulating layer, a layer in which the gauges are produced, a layer of Au, a layer of Si and a layer of Au, the sealing being a eutectic sealing.

(35) The metallic sealing zone can thus advantageously consist of a layer of eutectic such as Au/Si. Other elements can also be used to form eutectics such as Au/Sn, Al/Ge . . . .

(36) The composition is chosen as a function of the best possible compromise between sealing temperature, leaktightness, bulkiness, solidity, reproducibility. From this point of view a preferred solution can be the composition Au/Si. Eutectic based sealing is obtained by placement in contact, and then thermal treatment at a temperature greater than the melting temperature of the alloy of layers of gold and silicon.

(37) Thus a cap comprising a gold layer and a sensitive element covered with a stack: Au/Si/Au can be fixed between themselves with a sealing temperature of greater than 363 C.

(38) Second Type of Pressure According to the Invention:

(39) According to this variant of the invention, particularly advantageous for miniaturization, as illustrated in FIGS. 8a, 8b, 9a, 9b and 10, the sensitive element part can be the same as in the variant described previously. A component 20 comprises a membrane part, comprising at the surface at least one strain gauge 100 (or indeed preferentially four gauges mounted as a Wheatstone bridge). The production of metallic patterns makes it possible to define at the level of the sensitive element the zones Z.sub.1-21 and Z.sub.2-21 respectively dedicated to the sealing and to the contact pickups for the gauges 100 as shown in FIGS. 8a and 8b.

(40) According to this variant of the invention, the output pins 60 are located in a central, hollowed out part of the cover. FIGS. 9a and 9b thus illustrate the cover 30 equipped with contact pickup pins 60, and the zones Z.sub.1-31 and Z.sub.2-31 respectively dedicated to the sealing and to the contact pickups for the pins 60, positioned in emergent holes 63.

(41) The assembling operation can be identical to that developed in the previous variant. FIG. 10 illustrates the sensor and its cavity 32 after assembling of the parts 20 and 30. The placement in contact of the zones Z.sub.1-21 and Z.sub.1-31 arising from the layers respectively 21 and 31 makes it possible to define the zone Z.sub.1 to ensure the fixing of the sensitive element and of the cap. The placement in contact of the zones Z.sub.2-21 and Z.sub.2-31 arising from the layers respectively 21 and 31 makes it possible to define the zone Z.sub.2 and to ensure the pickup of contact of the gauges via the pins 60. This figure depicts the offsetting of the pins 60 and of the contact pickup zones Z.sub.2-31 with respect to the metallic contact pickup zones Z.sub.2-21. This figure also depicts that the hermetic sealing and the contact pickups for the gauges are ensured at the level of the plane P corresponding to the plane of the face of the sensitive element opposite the cap.

(42) The benefit of this variant is that the width of the sealing bead, corresponding to the zone Z.sub.1, can be reduced independently of the diameter of the output pins, which pins cannot be miniaturized to the extreme. By virtue of this solution it thus becomes possible to go a very long way in miniaturization.

(43) FIGS. 11a and 11b illustrate perspective views of this variant of the invention, depicting respectively on the one hand the zones Z.sub.1-21 and Z.sub.2-21 defining metallic patterns that may result from the etching of the metallic layer 21 produced on the surface of the sensitive element and on the other hand the pins 60, referenced 60+31, clad at their end with the metallization layer 31 and making it possible to ensure the definition of the zones Z.sub.2-31. The end of the pins 60 can equally well emerge from the bottom of the cover cavity holes (FIG. 11b), as be aligned with the cavity bottom (FIG. 11c), or else be located inside the emergent holes of the cover (FIG. 11d), the layer 31 nonetheless infiltrating the emergent holes and also cladding their end so as to ensure pickup of contact.

(44) Third Type of Pressure Sensor According to the Invention:

(45) An alternative to the cover comprising a ceramic substrate can be to use a stack of ceramic layers. Accordingly it is possible to use LTCC (Low Temperature Co-fired Ceramics) techniques to produce the cap comprising incorporated conductors. FIG. 12 illustrates an exemplary cap comprising a stack of dielectric layers 30a, 30b on the surface of which are produced metallic patterns 60.sub.b-a linked together by metallic vias 60a, 60b. The circuit is then produced from flexible sheets of ceramics (30a and 30b). These sheets are then cut, drilled with vias and the metallic patterns silk-screen-printed with conducting ink. The manufacture of the cap is then finalized by baking the stack in an oven.

(46) In general, the sensor of the present invention is a compact and miniaturizable pressure sensor, which can be easily attached to client connection. To ensure this attachment function, the sensor comprises a connection.

(47) First Exemplary Pressure Sensor According to the Invention Comprising a Connection Intended to Cooperate with a Client Connection:

(48) According to this example, the metallic component 20 is tied to a connection 40 itself exhibiting a threaded part as represented in FIG. 13, to ensure leaktight fixing with a client connection.

(49) Second Exemplary Pressure Sensor According to the Invention Comprising a Connection Intended to Cooperate with a Client Connection:

(50) According to this example, the membrane 20 and the connection are produced in a monolithic metallic component, the connection part itself exhibiting a threaded part as represented in FIG. 14, to ensure leaktight fixing with a client connection.

(51) Third Exemplary Pressure Sensor According to the Invention Comprising a Connection Intended to Cooperate with a Client Connection:

(52) The setup of a solution with the membrane flush with the fluid to be measured makes it possible to optimize the miniaturization while offering a response to the dynamic measurement requirements. According to this example, the metallic component 20 is assembled with a connection 40 itself exhibiting a threaded part as represented in FIGS. 15a and 15b, to ensure leaktight fixing with a client connection.