EP2452174A1

EP2452174A1 - Device for measuring pressure, and method for manufacturing same

Info

Publication number: EP2452174A1
Application number: EP10742200A
Authority: EP
Inventors: Jacques Leclerc
Original assignee: Tronics Microsystems SA
Current assignee: Tronics Microsystems SA
Priority date: 2009-07-06
Filing date: 2010-07-05
Publication date: 2012-05-16
Also published as: FR2947629B1; US20120096944A1; IL217358A0; WO2011004113A1; FR2947629A1

Abstract

The invention relates to a device for measuring pressure through the capacitive effect between two electrodes, including at least one sensitive electrode (11) spaced apart from and opposite a stationary electrode (211) so as to define a cavity (4) in which a reference pressure (Pref) exists. The device according to the invention further includes a protective housing (1) for insulating at least the stationary electrode from the ambient environment in which the pressure (P) to be measured exists, said housing (1) having at least one solid portion, forming a recess (10) for containing at least the stationary electrode (211), and a thinned portion forming the sensitive electrode (11).

Description

PRESSURE MEASURING DEVICE AND METHOD FOR

MANUFACTURING

Technical area

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.

STATE OF THE PRIOR ART Generally, 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, and the fixed membrane forms or supports a fixed electrode. Under the effect of a pressure difference between a pressure to be measured and the reference pressure, 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. In order to protect the sensitive and fixed electrodes, generally made of silicon, from possible attacks from the ambient environment (industrial or biological), 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 obligation not to introduce a gas bubble in the transmission interface during filling and closing of the housing, makes the manufacturing process of this type of sensor particularly difficult and expensive. In addition, leakage of the degassed oil may impair measurement accuracy, but may also be dangerous in applications in the biological environment.

In this context, 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.

Presentation of the invention

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. In other words, the sensitive electrode and the housing form a body (or housing) protection for isolating the fixed electrode from the ambient environment. Thus, unlike the prior art, 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. In this solution, the transmission member present in the pressure sensors of the prior art is no longer necessary.

Advantageously, the housing is made of a metallic material. For example, 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. According to one embodiment, 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.

Preferably, 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.

In other words, 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. According to one embodiment, the profile of the junction has a decreasing thickness in the direction of the sensitive electrode.

According to another embodiment, the profile of the junction has a thinned portion arranged head to tail with the thinned portion forming the sensitive electrode.

Such profiles make it possible to limit the stresses of the sensitive electrode, such as expansion due to the variation of the ambient temperature for example, and thus avoid degradation of the measurement.

Advantageously, 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.

In other words, 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.

Advantageously, 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.

Thus, 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. For example, 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.

Preferably, 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:

- Realization of at least one fixed electrode by etching in a substrate;

- Making at least one thin portion forming a sensitive electrode on a plate of material compatible with the ambient environment in which the pressure to be measured prevails;

- Sealing, under reference pressure, said plate on said substrate by interposition of at least one seal, the sensitive electrode being arranged opposite and at a distance from the fixed electrode so as to define a cavity whose depth is defined by the thickness of said seal;

a sealing of a piece of material compatible with the ambient environment forming a housing, with the plate, to form a protective casing intended to isolate at least the fixed electrode from the ambient environment, said casing having at least a part solid forming said housing, and a thinned portion forming said sensitive electrode.

According to one embodiment, 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. According to another embodiment, 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 .

Advantageously, the substrate consists of a dielectric layer interposed between two semiconductor layers, and the embodiment of the fixed electrode comprises at least steps of:

etching in one of the two semiconductor layers to produce at least one sealing frame, a connecting frame and the fixed electrode, the sealing frame surrounding the fixed electrode and being away from the fixed electrode in a manner delimiting a gap accommodating the connecting frame, said connecting frame flanking the fixed electrode and having at least one projection secured to the sealing frame and another projection secured to the fixed electrode; and

- Elimination of a portion of the dielectric layer facing the fixed electrode, the connecting frame and a portion of the sealing frame.

In addition, the coefficient of expansion of the material in which the sensitive electrode is made, for example titanium or stainless steel, 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 adhesion by thermo-compression of the housing with the sealing frame proves difficult. Therefore, the realization of a specific seal is then necessary to take into account this difference in expansion, and ensure the adhesion of the sealing frame with the housing.

Preferably, the seal further comprises steps of:

- Making a first metal layer on an inner portion of the solid portion intended to be opposite the sealing frame;

- Making a second metal layer on a portion of the sealing frame; and - Thermo-compression sealing of the first and second metal layers.

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.

For example, a method of manufacturing a plurality of pressure measuring devices as defined above comprises at least the following steps:

- Realization of a plurality of fixed electrodes by etching a substrate;

- Making a plurality of thin portions forming sensitive electrodes on a plate of material compatible with the ambient environment in which the pressure to be measured prevails;

a sealing, under a reference pressure, of said plate on said substrate by interposition of a plurality of sealing joints so as to form a plurality of cavities, each of the cavities being delimited by one of said sensitive electrodes arranged opposite and at a distance one of said fixed electrodes, and having a depth defined by the thickness of the associated sealing joint;

forming a plurality of elementary modules by cutting between two adjacent sealing joints, each elementary module comprising at least one of said cavities;

for each elementary module, a seal with a housing made of material compatible with the ambient environment, to form a protective case intended to isolate at least the fixed electrode of said elementary module from the ambient environment, said case having at least one solid housing portion and a thin portion forming a sensitive electrode. According to one embodiment, 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.

According to another embodiment, 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. Advantageously, the substrate consists of a dielectric layer interposed between two semiconductor layers, and the embodiment of the fixed electrode comprises at least steps of:

etching in one of the two semiconductor layers to produce, for each of the fixed electrodes, a sealing frame bordering at a distance the fixed electrode so as to delimit a gap accommodating a connecting frame having at least one protrusion secured to the frame sealing and another projection secured to the fixed electrode; and

elimination of the portions of the dielectric layer facing at least the fixed electrodes and the connecting frames.

Brief description of the drawings

Other features and advantages of the invention will emerge clearly from the description which is given below, by way of indication and in no way limitative, with reference to the appended figures, in which:

- Figure 1 is a schematic sectional view of a capacitive pressure sensor according to one embodiment of the invention;

- Figure 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; and FIGS. 15 to 17 show some steps of the method of collective manufacturing of several pressure sensors according to one embodiment of the invention. Detailed presentation of a particular embodiment

With reference to FIGS. 1 and 2, 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.

In addition, as illustrated in FIG. 2, 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.

In order to isolate the sensitive electrode 11 from any structural variations of the housing 10, for example a thermal expansion due to a sealing process which can lead to significant temperature variations, 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. For example, 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 These profile examples make it possible in particular to limit the thermal stresses experienced by the housing 10 on the sensitive electrode 11.

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. 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.

Similarly, in order to isolate the fixed electrode 211 from any structural variations of the sealing frame 210, in particular a thermal expansion due to the sealing process, 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. For example, as illustrated in FIG. 3, 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. The sensitive electrode 11 being directly in contact with the ambient environment, no transmission member is therefore necessary, unlike the prior art.

On the free face 220 of the other semiconductor layer 22, it is also possible to have 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:

an embodiment of the fixed electrode 211 (FIGS. 4 to 6);

an embodiment of the reference capacitor 5 and connection means (FIGS. 7 and 8);

an embodiment of the sensitive electrode 11 (FIG. 9);

an embodiment of the seal (FIGS. 10 to 13); and

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. At this stage of the process, it is possible to provide (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. 8) by disposing said other dielectric layer 50 on a part of the free surface 220 of said other semiconductor layer 22, and then disposing a reference electrode 51 on said other dielectric layer 50, so that the reference electrode 51 remains insensitive to any change in pressure. 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). . In addition, 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.

Due to a significant difference between the expansion coefficients of silicon and titanium or stainless steel, the realization of the sealing joint 3 (FIGS. 10 to 13) can notably consist in:

depositing an intermediate layer of oxide on a portion of the sealing frame 210 (FIG. 10);

depositing 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);

depositing a metallic intermediate layer 31 of titanium type (FIG. 1 Ib) on the intermediate oxide layer 30, then a second gold-type metal layer 32 on said metal intermediate layer 31; or directly depositing the second metal layer 32 (Figure 11a) on said intermediate layer of oxide 30; and

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. Of course, other types of sealing at lower temperatures are possible. However, in the particular case of titanium, 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. 15) so as to obtain several sensitive electrodes 11a, 11b and several junctions 12a, 12b as defined above. 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. Finally, for each elementary module 8a, 8b, there is provided a protective housing (FIG. 17) having a solid portion forming a housing 10a, 10b, an intermediate portion forming a junction 12a, 12b and a thinned portion forming a sensitive electrode 11a, 11b. A plurality of pressure sensors is thus obtained, the particularity of which is to present a sensitive electrode integrated in the protective case in contact with the ambient environment. Good understood, for each elementary module, it is possible to provide a protective grid and a reference electrode as defined above.

It follows from the above that 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. For example, 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.

Claims

1. Device for measuring pressure by capacitive effect between two electrodes comprising at least one sensitive electrode (11) disposed facing and away from a fixed electrode (211) so as to delimit a cavity (4) in which there is pressure reference (P _ref ),

characterized in that it further comprises a protective housing (1) for isolating at least the fixed electrode from the ambient environment in which the pressure to be measured (P) prevails, said housing (1) having at least one solid housing portion (10) for containing at least the fixed electrode (211), and a thinned portion forming the sensitive electrode (1 1).

2. Device according to claim 1, characterized in that the housing (1) is made of a metallic material.

3. Device according to one of claims 1 or 2, characterized in that it further comprises a grid (6) or perforated wall for protecting the sensitive electrode (11).

4. Device according to one of claims 1 to 3, characterized in that the housing (1) of protection further has an intermediate portion forming a junction (12) between the sensitive electrode (11) and the housing (10), and having a profile capable of mechanically decoupling the structural variations of the sensitive electrode from those of the housing.

5. Device according to claim 4, characterized in that the profile of the junction (12) has a decreasing thickness in the direction of the sensitive electrode (11).

6. Device according to claim 4, characterized in that the profile of the junction (12) has a thinned portion (120) arranged head to tail with the thinned portion forming the sensitive electrode (11).

7. Device according to one of claims 1 to 6, characterized in that a sealing frame (210) surrounds the fixed electrode (211) and is disposed at a distance from the fixed electrode (211) so as to delimit a gap (213) accommodating a connecting frame (212), said connecting frame (212) providing a mechanical connection and mechanical decoupling between the fixed electrode (21 1) and the sealing frame (210).

8. Device according to claim 7, characterized in that the connecting frame (212) surrounds the fixed electrode (211) and has at least one projection (212c,

212d) secured to the sealing frame (210), and another projection (212a, 212b) secured to the fixed electrode (211).

9. Device according to one of claims 1 to 8, characterized in that it further comprises a reference electrode (51) insensitive to pressure variations.

10. A method of manufacturing at least one pressure measuring device according to one of claims 1 to 9, characterized in that it comprises at least:

an embodiment of at least one fixed electrode (211) by etching in a substrate (2);

- An embodiment of at least one thin portion forming a sensitive electrode (11) on a plate of material compatible with the ambient environment in which the pressure to be measured (P) prevails;

- Sealing, under reference pressure (P _ref ), said plate on said substrate (2) by interposition of at least one seal (3), the sensitive electrode (11) being disposed opposite and at a distance of the fixed electrode (211) so as to delimit a cavity (4) whose depth is defined by the thickness of said seal (3);

- a sealing with the plate, a piece of material compatible with the ambient environment forming housing (10), to form a housing (1) of protection for isolating at least the fixed electrode (211) of the environment ambient, said housing (1) having at least one solid portion forming said housing (10), and a thinned portion forming said sensitive electrode (11).

11. The method of claim 10, characterized in that it further comprises an embodiment of an intermediate portion forming a junction (12) between the solid portion and the thinned portion, and whose profile has a thickness (e) decreasing towards the sensitive electrode (11).

12. The method of claim 10, characterized in that it further comprises an embodiment of an intermediate portion forming a junction (12) between the solid portion and the thinned portion, and whose profile has at least one thinned portion ( 120) disposed head-to-tail with the thinned portion forming a sensitive electrode (11).

13. Method according to one of claims 10 to 12, characterized in that the substrate (2) consists of a dielectric layer (20) interposed between two semiconductor layers (21, 22), and in that that the realization of the fixed electrode (211) comprises at least steps of:

etching in one of the two semiconductor layers (21) to provide at least one sealing frame (210), a connecting frame (211) and the fixed electrode (211), the sealing frame (210) flanking the fixed electrode (211) and being away from the fixed electrode (21 1) so as to delimit a gap (213) accommodating the connecting frame (212), said connecting frame (212) flanking the electrode fixed (211) and having at least one projection (212c, 212d) secured to the sealing frame and another projection (212a, 212b) secured to the fixed electrode (211); and

- Elimination of a portion of the dielectric layer (20) facing the fixed electrode (211), the connecting frame (211) and a portion of the sealing frame (210).

The method of claim 13, characterized in that the sealing further comprises steps of: - Making a first metal layer (33) on an inner portion of the solid housing portion (10) intended to be opposite the sealing frame (210);

- Realizing a second metal layer (32) on a portion of the sealing frame (210); and

- Thermo-compression sealing of the first and second metal layers (33, 32).

15. The manufacturing method according to claim 10, characterized in that it comprises at least:

- an embodiment of a plurality of fixed electrodes (211a, 211b), by etching a substrate (2);

an embodiment of a plurality of thinned portions forming sensitive electrodes (11a, 11b), on a plate of material compatible with the ambient environment in which the pressure to be measured (P) prevails;

- sealing, under reference pressure (P _ref ), said plate on said substrate by interposition of a plurality of sealing joints (3a, 2b) so as to form a plurality of cavities (4a, 4b), each of cavities (4a, 4b) being delimited by one of said sensitive electrodes (l ia, Hb) arranged opposite and at a distance from one of said fixed electrodes (211a, 211b), and having a depth defined by the thickness of the sealing joint (3a, 3b) associated;

- forming a plurality of elementary modules (8a, 8b) by cutting between two adjacent sealing joints (3a, 3b), each elementary module (8a, 7b) comprising at least one of said cavities (4a, 4b);

- for each elementary module (8a, 8b), a seal with a housing (10a, 10b) of material compatible with the ambient environment, to form a protective housing for isolating at least the fixed electrode (211a, 211b) said elementary module (8a, 8b) of the ambient environment, said housing having at least one solid housing portion (10a, 10b) and a thinned portion forming a sensitive electrode (11a, 11b).

16. The method of claim 15, characterized in that it further comprises, for each sensitive electrode (l ia, Hb), an embodiment of an intermediate portion on said plate, intended to form junction (12a, 12b) between the housing (10a, 10b) and the sensitive electrode (11a, Hb), and whose profile has a thickness (e) decreasing in the direction of the sensitive electrode (l ia, 1 Ib).

17. The method of claim 15, characterized in that it further comprises, for each sensitive electrode (l ia, Hb), an embodiment of an intermediate portion on said plate, intended to form junction (12a, 12b) between the housing (10a, 10b) and the sensitive electrode (l ia, 1 Ib), and whose profile has at least one thinned portion arranged head-bêche with the thin portion forming sensitive electrode.

18. Method according to one of claims 15 to 17, characterized in that the substrate (2) consists of a dielectric layer (20) interposed between two semiconductor layers (21, 22), and in that the realization of the fixed electrode (21a, 21b1) comprises at least steps of:

etching in one of the two semiconductor layers (21) for producing, for each of the fixed electrodes (211a, 211b), a sealing frame (210a, 210b) remotely framing the fixed electrode (211a, 21b) to define a gap accommodating a connecting frame (212a, 212b) having at least one projection secured to the sealing frame and another projection secured to the fixed electrode; and

- Elimination of the portions of the dielectric layer (20) facing at least the fixed electrodes (21a, 21b1) and connecting frames (212a, 212b).