Fuel cell and method for making such a cell with large active surface and reduced volume

TECHNICAL AREA

The present invention relates to a method of manufacturing a fuel cell in high surface area and low volume.

The invention thus relates to the field of fuel cells, particularly fuel cells with solid polymer membrane as the electrolyte, such as PEMFC cells ( "Proton Exchange Membrane Fuel Cell") and DMFC ( "Direct Methanol Fuel Cell ").

Fuel cell type solid polymer electrolyte have applications in particular in land transport, space, sea, particularly in land vehicles, which, at present the subject of numerous development programs, to find alternatives to the use of batteries in electric vehicles.

STATE OF THE ART

Generally, fuel cells consist of a stack of elementary cells. Each cell comprises an anode and a cathode positioned on either side of an electrolyte. At the anode occurs oxidation of the fuel, such as hydrogen H₂For hydrogen fuel cells, producing protons and electrons. Electrons rejoin the external electric circuit, while the protons are directed towards the cathode through the electrolyte, which occurs, generally in the form of an ion-conductive membrane. At the cathode occurs oxidation of oxidant, such as oxygen from the air, accompanied, in the case of hydrogen fuel cells, production of water resulting from the recombination of the ions produced by the reduction and protons.

The power densities obtained at a unit cell are very low and largely inadequate for the operation of electrical equipment. It is therefore essential to assemble a large number of individual cells in order to access a significant power. The assembly is generally performed by a stack of elementary cells, the separation between cells is achieved by means of sealed plates, said bipolar plates.

In the field of fuel cells, many configurations have already been proposed in the prior art.

Thus, at medium power fuel cells, or 10 to 50 kilowatts per cell, are generally prepared by the association "filter press" bipolar plate of graphite or stainless steel and membrane-electrode-electrode assemblies obtained by pressing two electrodes fabric and a proton conductive membrane in NAFION^®.

To the low power fuel cells, or 0.5 to 50 W per cell, known as micro-fuel cells, require for their development the development of architectures and processes, often derived from microelectronics technologies. The difficulty lies in assembling the micro-electrode with the thin film of proton conductive material. In addition, the micro-electrode must have a high electronic conductivity, high gas permeability in particular hydrogen, in the case of a PEMFC architecture for hydrogen / air batteries, a high gas permeability and methanol in the case of a DMFC architecture for methanol / air cells, the ability to be formed into a thin layer on a small surface, good thermomechanical strength. The micro-electrode must also have a surface suitable for deposition of a catalyst in dispersed form.

In the literature, there are porous silicon-based architectures having deposited thereon successively a catalyst and a Nafion membrane^® to form the membrane electrode assembly. However, performance of such a device is limited by the poor cohesion of the different layers, creating a high interface resistance, and by a very low dispersion of the catalyst, the latter being slightly divided, to obtain a deposit strongly electronic conductor.

Different laboratories have developed non-porous silicon based technologies. A team from Lawrence Livermore National Laboratory has developed as a cell micro-fuel cell by depositing, first, a thin metal layer of nickel making electronic collector office on a silicon substrate. The catalyst and the proton conductor are then deposited on nickel. Nickel is then perforated by etching for contacting the catalyst and the reducing agent, namely hydrogen or methanol according to the cell system envisaged fuel. This technique has a number of disadvantages, particularly related to nickel properties. Indeed, the nickel has a sensitivity to corrosion phenomena caused by the strongly acidic nature of the proton conductor. The catalyst is dispersed, more weakly at the perforated nickel layer which has a low capacity to cause a homogeneous dispersion of the reducing agent on the catalyst. Finally, this technology generates a low probability of the presence of triple points.

The patent application <patcit id="pcit0001" dnum="WO9711503A"><text>WO 97/11503</text></patcit> [1] and US Patent <patcit id="pcit0002" dnum="US5759712A"><text>US 5759712</text></patcit> [2] describe a fuel cell architecture based on the use of a micro-porous impregnated with a proton conductor material as the central element of a micro-fuel cell system. The various materials necessary for forming a fuel cell are then deposited on both sides of this substrate by conventional vacuum deposition techniques. This invention has two main disadvantages are, firstly, the fragility of the polymer substrate especially when it is treated with aggressive deposition techniques under vacuum and secondly, poor electrochemical performance including a lack of active surface and also the fragility of the deposited catalyst deposit directly on the proton exchange membrane.

All these exposed architectures has the distinction of being all planar and does not, therefore, to obtain a sufficiently high electrode surface to power portable electronic devices.

To this end, several non-planar geometries are proposed in the prior art.

U.S. Patent 6,080,501 [3], 6007932 [4] and 6,001,500 [5] discloses a cylindrical architecture of miniature fuel cell. This architecture is based on winding a membrane-electrode assembly electrode conventionally used in planar geometry around a mandrel of metal foam. However, such an assembly performance is limited mainly for two reasons:<ul><li>assembly electrode-membrane-electrode, initially planar, is not suitable for a cylindrical geometry, which causes it almost impossible to restore the anode contacts the anode, cathode and cathode-membrane-membrane after winding of the electrode assembly -membrane planar electrode; </li><li>the current collectors are not intimately in contact with the anode and the cathode, thereby generating excessively high interface resistance.</li></ul>

Another US team has developed a concept similar miniature tubular fuel cell. A membrane-electrode assembly is wound to form a cylinder. This is then housed in a compact device of the "roll carriers" to ensure the electric current collection. However, this type of architecture is not suitable for portable electronic devices mainly because of congestion generated by using the system of "cylinder holder".

The patent <patcit id="pcit0003" dnum="JP63138667A"><text>JP 63 138667</text></patcit> [6] presents a method for producing a non-planar structure of battery, said process consisting in depositing a stack of film on the inner surface of a part of the holes of a grid support. Also described is the possibility of assembling several of these materials.

However, this device, obtained by the method described has the following drawbacks:<ul><li>due to the configuration of the holes, more precisely from the fact that the holes have a parallelepiped shape very low height, it is difficult to achieve a regular stack of film deposition on the inner surface of said holes;</li><li>due to the geometry and arrangement of the holes in this document, it is necessary to dedicate a portion of the mesh supporting holes for the transport of reactive power of the battery, which causes surface loss to deposit films battery and therefore a power loss of said battery caused by this configuration.</li></ul>

There is therefore a real need for a method of fuel cells, which allows to obtain batteries having a total volume as small as possible while retaining a high active surface electrode, and while enabling the realization of a network of electrical connections and distribution of the reactants.

There is also a need for this type of battery that can develop electric power compatible with use of said cells in the area, including land transport.

PRESENTATION OF THE INVENTION

The object of the present invention is therefore to provide a method of manufacturing a fuel cell, adapted to daily equipment, which satisfies, inter alia, the need referred to above, and which does not have the drawbacks, disadvantages, defects and limitations of the prior art, and which enables in particular to produce a cell having a much higher surface area than its use of the floor surface. In addition, the object of the present invention is to provide a method of making a fuel cell, which allows obtaining a high power cell while providing a large space for the realization of a switching network and electrical connection of reagents of said stack.

The object of the present invention is finally to provide a fuel cell having a reduced volume, while having a large active surface area.

This aim and others are achieved in accordance with the invention, by a method of manufacturing a fuel cell, said cell comprising a set of elementary cells electrically connected together, each unit cell comprising at least three layers, that is to say a membrane layer positioned between a first electrode layer and a second electrode layer, said method successively comprising the following steps:<ul><li>a step of making a plurality of holes on at least two substrates, each hole opening out on either side of two opposite faces of each support by a first orifice section and a second orifice section and each hole having a side surface;</li><li>a step of forming individual cells on the lateral surface of each of said holes;</li><li>a step of forming, on at least one of said opposite faces of each support, a network of electrical connections and a reactant distribution network, said networks connecting the individual cells between them, the group consisting of a support, elementary cells and said networks constituting a base module;</li><li>a step of assembling at least two base modules, so that the elementary cells of each base module are placed facing elementary cells (of) module (s) of adjacent base (s),</li></ul>said method being characterized in that, during the step of producing the plurality of holes, each hole is formed such that at least one of said first and / or second orifice section has a lower surface the surface of at least one section of said hole taken in a plane parallel to said opposite faces and in that, for each hole, the first or second orifice section has a lower surface to the surface of the other orifice section .

It is pointed out that, according to the invention, the terminology "base module" refers to the group consisting of a support, in which are formed elementary cell stack, said cells being electrically interconnected via network of electrical connections and fed by reagent dispensing networks, said networks being performed at at least one side of the support, on which the holes are formed.

It is pointed out that, according to the invention, the side surface denotes the surface of the walls defining the hole.

It states that, according to the invention, the reagent distribution network refers to the network, which will enable power electrodes oxidizing or reducing.

It is specified that, when referring to a section of the outlet hole in a plane parallel to the opposite faces of the support, it refers to all the sections except the above-mentioned orifice sections.

It is specified that by supporting means, preferably, a substantially parallelepiped-shaped carrier.

It is specified that active surface is defined in the above and following, the area occupied by the electrodes, which are the seat of the electrochemical reactions of the cell.

Advantageously, in accordance holes to the present invention may be substantially frustoconical shaped holes, or substantially shaped like a truncated pyramid.

Realizing holes having such geometry has the effect of presenting the following advantages:<ul><li>relative to holes having walls perpendicular to the support as is the case in the embodiment of the aforementioned Japanese document is loaded, to make holes having a walled hole profile substantially inclined relative to the vertical, helps to facilitate the deposit the necessary layers to the constitution of the elementary cells; </li><li>relative to holes having walls perpendicular to the support, the fact of making holes with an orifice sectional area less relative to the surface of the other orifice section provides a space saving in faces which are formed said holes, especially at the face having the aperture sections of the lower surfaces; This saves space can be dedicated to the realization of the electrical connection network and reagents distribution network or to the realization of additional holes, thereby increasing the surface area of ​​the stack;</li><li>relative to holes having walls perpendicular to the support, the side surface (or inner surface of the hole) may be larger, resulting in an increase of the active surface, to the extent that the side surface is the basis for the realization of elementary cells.</li></ul>

It is pointed out that when reference is made above, for comparison, in holes having walls perpendicular to the support, said perpendicular walls with holes have an identical section to the first orifice section or second orifice section mentioned above.

In addition, the advantageous nature of this invention lies in the fact of joining two or more basic modules to further increase the active surface of the resulting battery.

Thus, the interest of the present invention is to be able, in this manner, multiply the lateral surface of the holes, arranging them in vis-a-vis, by assembling at least two base modules.

Thus, thanks to this method of the invention, one can access to fuel cells occupying area reduced ground, while having a high surface area, to the extent that the active surfaces of the stack are in the heart of the material constituting the support.

Moreover, the fact of making of the invention, systems from the assembly of several modules, in addition to the particular geometry of some holes presented the major advantage of facilitating the development of active layers on the walls said holes.

Indeed, if we consider a stack of architecture with a single module, the slope of the walls, for example, holes conical volume, would be fixed by the geometry, in particular the support thickness, section surfaces port holes. In such a system, we should develop steep walls to gain in active area. In contrast, the system based on the assembly of several modules as contemplated by the method according to the invention may consist of modules whose height is lower (that if only one module is used) and therefore the internal walls of the holes may have a less steep profile. Therefore, it is easier from this system to achieve the deposition of layers to form the elementary cells.

According to the invention, the holes made in each support can be produced by etching or by laser ablation.

The support may consist, according to the invention, of a material selected from a group consisting of silicon, such as porous silicon, graphite, ceramics, polymers.

For example, ceramics may be titanium oxide or alumina and polymers Teflon^®, The Peek^® or polysulfones.

Preferably, each hole in each carrier has a first orifice section and a second orifice section of the lower surfaces to the side surface of said hole, which has the advantage to dedicate a large surface side of the support to the setting up networks of electrical connections and reagent distribution networks.

The realization of individual cells, at the holes formed in each carrier according to the invention is carried out by sequential deposition on the side surface of each of said holes at least three layers, for forming the first electrode layer, the membrane layer and the second electrode layer.

This phase embodiment can further comprise, depositing current collectors at each electrode layer According to the invention, assembling of two base modules, when this assembling places two faces without facing networks ( namely electrical connection network and reagents distribution network can successively include the following steps:<ul><li>a step of installation, on at least one of said faces devoid of or said network (s), a bonding layer; and</li><li>a joining step of the base modules at said faces.</li></ul>

According to the invention, the assembly of at least two base modules, placing opposite faces, of which at least one is provided with a network of electrical connections and / or reactants distribution system may successively include the following steps:<ul><li>a step of masking the face or faces provided with the said networks or by a sealed and insulating layer;</li><li>a step of planarizing the face or faces of the feature or of said networks;</li><li>a step of placing a bonding layer on at least one of the faces to be assembled;</li><li>a joining step of said faces to be assembled of the said base modules.</li></ul>

Preferably, the bonding layer is of identical composition to the membrane layer.

This has the particular advantage of being able to establish, in a single step, the membranes on the hole walls and the surface bonding layer.

According to the invention embodiment, the bonding layer may also be another adhesive that the membrane layer selected from a group consisting of epoxides, polyimides, silicones, acrylic polymers.

According to another variant of the invention, the bonding layer is of a material selected from silicon oxide and silicon nitride.

Once the link layer implementation, the joining of two basic modules can be achieved, according to the invention, by clamping.

According to another embodiment of the invention, the joining of two basic modules can be done by gluing.

Finally, the attachment may be done by molecular adhesion.

Preferably, the masking step, planarization, and bonding of establishment of the link layer are performed simultaneously by placing a single layer.

According to a particularly advantageous embodiment of the invention, the single layer is an identical constitution of layer to the membrane layer.

Alternatively, the single layer is a bonding layer of a material selected from silicon oxide and silicon nitride.

Another object of the present invention is to provide a fuel cell obtainable by the method described above.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be described in more detail with reference to the accompanying drawings in which:<ul><li>1 shows a sectional view of a hole geometry view according to the present invention, on the surface of which was made by the method of the invention, an elementary cell stack.</li><li>Figure 2 shows an isometric view, showing an assembly of two basic modules (said assembly of two basic modules are called in the terminology of the invention 'level cavities').</li><li>3 shows a sectional view showing an assembly resulting from the joining of two levels of cavities, said assembly being obtainable by a process according to the invention.</li><li>4 shows various assembly modes of four basic modules.</li></ul>

DETAILED FORWARD PRESENTATION OF THE INVENTION.

The method of manufacturing a fuel cell according to the invention comprises, successively, a step of making a plurality of holes in at least two carriers, followed by a step of forming elementary cells at each of the holes, a step of forming, on at least one of the faces of each support, a network of cathode connections, an anode connection network and a distribution network of reagents, the after which the assembly obtained is a base module, a step of assembling at least two base modules, said holes being formed such that at least one of said first and / or second section of port of each hole has a surface smaller than the surface of at least one section of said hole taken in a plane parallel to said opposite faces and in that, for each hole, the first or second orifice section has a lower surface to the surface of the other orifice section.

The step of forming the plurality of holes, at each support, can be effected by any known method, for example by means of etching such as plasma etching or wet etching. Once the holes made, is placed on the side surface of each of these holes, the elementary cell stack, for example, by successive deposition on the side surface of each of said holes of a first electrode layer, a membrane layer and a second electrode layer, and optionally of current collectors at each of the electrode layers. According to the invention, the deposition of the electrode layers can be performed by any known method for accessing deposits in the form of thin layers. This deposition can take place, for example, by physical vapor deposition (PVD Physical Vapor Deposition), chemical vapor deposition (CVD Chemical Vapour Deposition), spin-coated ( "spin-coating"), or by dipping a layer based on, for example, platinized carbon.

According to the invention, the deposition of the membrane layer may be effected, for example, by a liquid. The constituent of the membrane material may be selected, for example, from a group consisting of polyimides, polyethersulfones, polystyrenes and their derivatives, polyether ketones and their derivatives, polybenzoaxoles, polybenzimidazoles and their derivatives, polyarylenes such as paraphénylènes and polyparaxylylènes.

The elementary cells thus formed are intended to be electrically connected in order to add the individual electric powers to each of them. In addition, these cells must be supplied with the reagents. To do this, the method comprises a step of producing an electric connection network and a distribution network reagents on at least one of the faces of the support.

To achieve these stages of electrical connections, photolithography techniques, using photosensitive resin or photosensitive dry film may be used. etching techniques can also be considered, including etching by heavy ion bombardment.

The realization of the reagent distribution system, can be effected by etching channels on at least one side of the support, said channels to ensure proper flow of reagents and said routing being optimized by the introduction of a diffusion layer.

1 shows a hole 1 in geometry according to the present invention, hole on the walls of which are arranged the component layers of an elementary cell, during a step of the inventive method.

According to this particular embodiment, the hole 1 has a truncated pyramidal shape, specifically a square base and opens out on both sides of the opposite faces 9a, 9b of a support 9 by a first orifice section and a second referenced 1a orifice section 1b, the surface of the first orifice section being, in this particular case, all lower than any sections of the hole taken in a plane parallel to the aforementioned opposite sides and said hole having a side surface 1c. This hole has an inner profile slope, which contributes to facilitate the step of performing the elementary cells, with respect to a hole whose walls are perpendicular to the opposite faces of said support.

1c on the side surface of this hole is arranged in succession:<ul><li>an anode current collector 2, said current collector being connected to a surface anodic connection network in the form of tracks 3;</li><li>a first electrode layer 4, filling, according to this embodiment, the anode function;</li><li>a layer of membrane 5;</li><li>a second layer electrode 6, acting as the cathode;</li><li>a cathode current collector 7, the surface connected to a network of cathode connections, in the form of 8 tracks.</li></ul>

In the terminology of the invention, the support, provided with holes, in which are made of elementary cells constitutes a base module, said module being intended to be assembled to at least one other module, so as to form at least one level cavity.

It is noted that the terminology "level cavities" used in the description of the invention, refers to the set resulting from the assembly of two base modules defined above.

Figure 2 provides an understanding, in a particular embodiment of the invention, the manner of which are assembled two core modules, referenced 9 '. Thus, this figure shows two supports 9 substantially identical and parallelepipedal shape, provided with three rows of holes 10, of truncated pyramidal shape with a square base. Each hole 10 forms a unit cell as described previously in Figure 1, the various cells are electrically connected in series by a network of electrical connections 11,12 (anode and cathode respectively) being in the form of tracks, so as to add the active surfaces of each elementary cell. It is understood that, according to a variant of the invention, the electrical connection between the individual cells can be done in parallel. For representation convenience reasons, the reagent distribution network is not shown in this figure.

Prior to assembly, according to this particular embodiment of the invention, the faces without networks of electrical connections and delivery of reagents, two basic modules are covered with a bonding layer 13 impermeable to the reactants. This layer of liaiso n may be, for example; the membrane layer, used in particular for its sealing properties to the reactants but also a layer having adhesive properties, said layer being composed, for example, of a material selected from a group consisting of epoxides, polyimides, silicones , acrylic polymers. Note that the assembling of two base modules must be made so that the holes of a base module to be adjusted opposite the holes of the adjacent base modules, so as to add the active surface a hole of a module with the active surface of the hole of the adjacent modules. To reach this result, the base modules to be assembled are, for example, positioned with the aid of a double positioning machine face with, in each module, a positioning cross system.

Once the positioning carried out, the assembly is completed by a joining step of the two base modules, said step can be performed using various techniques.

Thus, one can consider the securing by clamping, especially when the bonding layer placed on at least one of the faces without networks of the module do not exhibit sufficient adhesive properties to ensure the cohesion of the two base modules.

The attachment can also be made by gluing. Among possible bonding techniques include the molecular bonding, bonding by application of an adhesive or solder nature of polymer materials after treatment at about the glass transition temperature. For example, when the bonding layer is of identical composition to the membrane layer, said membrane being of polymeric material, the fixing may be achieved by heat treating the layer at a temperature greater than or equal to the glass transition temperature of the polymer .

The set resulting from this step of securing two base modules, is, in the terminology of the invention, a level of cavities.

In order to obtain batteries having a ratio of active surface and occupying floor space of said even larger battery, it is conceivable according to the invention, to assemble more than two basic modules, for example, by assembling at least two levels of cavity or at least a cavity level with at least one basic module.

To do this, such an assembly advantageously comprises, where appropriate, a masking step electrical connections and distribution networks reagents faces, intended to be joined together, by a sealed and insulating layer, a planarization step of the or the faces provided with said networks followed by a step of placing a bonding layer on at least one side, intended to be joined together and finally a securing step of the faces in question.

These same steps are applicable in the case of joining two base modules of which at least one side to append is provided with a network of anode connections and / or cathode and / or delivery of reagents.

The masking step is, as the name suggests, to hide the network of electrical connections and reagents distribution networks, in order to avoid the problems of short circuits during the joining of the two sides and problems reagent leakage.

This step is, for example, provided by the establishment of a sealed and insulating layer.

The planarization step is to make the planar faces of the surfaces provided with networks for the joining, for example by introduction of a planarizing layer or by a mechanical process such as polishing. This planarization step is necessary to avoid discontinuity problem surfaces during assembly of the modules.

A particularly advantageous embodiment of the invention is to achieve masking step, planarization and establishment of a binding layer by placing a single layer, that is, for example, an layer of identical composition to the membrane, consisting for example Nafion^®, A layer of inorganic material such as a material selected from silicon oxide, silicon nitride or a multilayer consisting of these different materials.

3 illustrates a sectional view of a cell resulting from the joining of two levels of cavities, obtained according to a particular embodiment of the invention.

The holes 14 performed at these different base modules are of frustoconical shape, which corresponds to a geometry of holes according to the present invention.

Are distinguished, on the side surface 14a of each hole 14 the superposition of layers, namely a first electrode layer 15, a membrane layer 16 and a second electrode layer 17.

A layer 18, corresponding to a tight bonding layer provides the seal between two base modules 19 adjacent component as well, by their assembly a level of cavities 20. In this configuration, obtained according to a particular embodiment of the invention, layer 18 is identical composition to the membrane layer 16. it is noted that according to this particular embodiment, the assembly of two basic modules 19, to reach a level of cavities 20, is to assemble two faces without networks.

A single layer 21, ensuring both adhesion, waterproofing, insulation and planarization ensure the connection between two cavity levels 20. According to this configuration, obtained according to a particular embodiment of the invention, the single layer 21 is of identical composition to the membrane layer 16.

The cells of the two cavities levels are electrically interconnected via electrical connections of networks 22, 23 in series.

The assembling of two base modules, to form a level cavities, as well as two cavities levels can occur in different ways.

Thus Figures 4A, 4B and 4C illustrate various sectional views of different modes of assembly of 4 basic modules. According to these particular embodiments, each of the base modules comprises a plurality of holes, said holes having a frustoconical shape.

According to Figure 4A, each of the two levels of cavities 25 results from the assembly of two base modules 24, in particular by bringing opposite the holes 26 by their bases 27 (shown in solid line in the figure) said levels being then assembled by setting facing the cavities thus formed by their vertices 28 (shown in solid lines in the figure).

According to Figure 4B, each of the levels of cavities 25 results from the assembly of two modules 24 in particular by bringing opposite the holes 26 by their vertices 28, said levels being then assembled condition by means facing the cavities thus formed by their bases 27.

Finally, in Figure 4C, each of the levels of cavities 25 results from the assembly of two base modules 24 by placing opposite the holes 26 against base 27, top 28, said levels being then assembled by placing opposite the cavities thus formed base 27 against top 28. These different assembly variants contribute to create complex cavities, seat unit cells constituting the fuel cell, a large internal surface with respect to the surface of the orifice of the resulting cavities sections. Thus, one obtains a high surface area relative to the exposed surface of the assembly thus formed.

The invention will now be described with reference to the following non-limiting illustration.

<u>Example</u>

The objective is to develop an active area of ​​350 cm² for an apparent area of ​​25 cm² and an energy of 10 Wh.

To do this, the substrate is a monocrystalline silicon wafer of thickness 400 micrometres of apparent surface area 25 cm², Engraved with an array of holes. The holes are made by plasma etching and have a square cross section of 100 microns from the side, an opening area of ​​56%, the opening area corresponding to the ratio between the concave surface and the total surface area and a reduction factor of 80 % between the input surface and output holes. Therefore, the developed surface is 7 times greater than the exposed surface. Are deposited on the sidewalls of the holes in succession the thin layers required for the realization of a fuel cell, namely:<ul><li>an anode including, as part of this example, a current collector and a catalyst layer deposited by spraying an active ink;</li><li>a thin membrane of electrolyte in the form of a thin layer of Nafion^®Filed by dipping; </li><li>a catalyst layer deposited on the membrane to promote the reaction at the cathode, followed by a metal deposition, intended to ensure the collection of electrical current to the cathode.</li></ul>

Networks of anode and cathode connections are made, according to this example, on a side of the support, by techniques of photolithography with the photosensitive resins and photosensitive dry films and the distribution network for reactive etching channel. Is obtained at the end of these steps a basic module.

The assembling of two base modules is achieved by means of layers of NAFION^®Glued after heat treatment at a temperature above the glass transition temperature. Obtained in this way a level of cavities.

The assembly of several levels cavity is provided by a layer of silica and finalized by a step of molecular bonding.

Note that the precise positioning of the modules or cavities levels to be assembled is carried out using a double positioning machine face.