Hereinbelow the invention will be further elucidated with reference to a number of figures.
FIG. 1 shows the fabrication of a membrane according to the invention in four steps.
FIG. 2 shows two membranes in perspective.
FIG. 3 shows a membrane, which by means of linear openings is divided into cantilevers.
FIG. 4 shows a membrane according to the invention, which is used in a filter.
FIG. 5 shows a preferred embodiment of the method for the fabrication of the membrane in five steps.
FIG. 6 shows a variant of the embodiment according to FIG. 5.
FIG. 7 shows a schematic cross-section through a fibre-positioning means.
FIG. 8 shows a top view of a fibre positioning means.
FIG. 9 shows a perspective, schematic illustration of an application of a cantilever as mirror.
FIG. 10 shows a cascade filter.
In the various figures similar elements are identified with identical reference numerals.
FIG. 1 shows a number of steps for the fabrication of a membrane 2 according to the invention. In a first step, FIG. 1A, a masking layer 3 is applied on two sides of a silicon wafer 1, leaving portions 5 of the silicon surface free. In a second step, FIG. 1B, a portion of the silicon is etched away in a quick-etching step, exposing the so-called (111) planes 8, 9, 10, 11. During this step a membrane 2 having a thickness D is already formed. In a subsequent step, FIG. 1C, a slow-etching step is carried out. As in this stage only the (111) planes 8, 9, 10, 11 are exposed, the etching treatment will be slow. This allows a precise regulation of the thickness of the membrane 2. This treatment is carried out until a desired thickness d is obtained. Finally, as shown in FIG. 1D, the masking layers 3 are removed, providing the membrane 2.
FIG. 2 shows a much simplified perspective view of two membranes 2, 2′, which are obtained in accordance with the embodiment of FIG. 1. The two ends 13 of the membranes 2, 2′ are directed at a mutual point of intersection S, located in a plane below the plane of the wafer 1.
FIG. 3 shows a perspective view of a single membrane 2 that may be obtained by the method shown in FIG. 1. A number of linear openings 12 are formed in the membrane 2. This creates cantilevers 14, all of which are attached at one side Z of the originally formed membrane 2 to the main body of the wafer 1. Such cantilevers may also be fabricated in accordance with the method described by way of the FIGS. 5A to 5E.
FIG. 4 shows a similar embodiment wherein the openings 12, however, are not linear but are substantially round openings 12. Because the lower side of the wafer is provided with a sealing body 15, a fluid can be introduced into the cavity A. The liquid can then only be discharged through the openings 12 in the membrane 2. Any material in the liquid larger than the diameter of the openings 12 will be retained in the cavity A.
FIG. 5 shows a further embodiment of the method according to the invention. Starting point is an already-formed membrane 2, as shown in FIG. 5A.
Subsequently a material layer 16 is applied on one side covering at least a portion of the surface of the silicon wafer 1 and also the surface of the V-shaped recess 6. Such a material will preferably be a material exhibiting a different etching behaviour to that of the silicon used for the wafer.
The material for forming the layer 16 may be any material other than the silicon used for the wafer, such as carbides, oxides and nitrides, in particular silicon carbide, silicon oxide and silicon nitride, but also other pure elements, such as metals including gold, and also synthetic materials and the like.
Subsequently, a masking layer 3 is provided on the material 16 in a predetermined pattern. This is clearly shown in FIG. 5C.
In a following step, an etching treatment is carried out, in which material present under the portions 5 that are not covered by the masking layer 3, is removed. Such a treatment may be carried out for a desired period of time, so as to create through-openings 12. When the etching treatment has been carried out in the desired manner, the masking layer 3 may be removed, as shown in FIG. 5D.
Subsequently, an etching treatment may be carried out for the removal of the remaining silicon portions under the applied material layer 16. This etching treatment will be performed quickly because the etching solution may affect other surfaces than those oriented in the (111) plane. After completion of said etching treatment a product will be obtained as shown in FIG. 5E, of which the exposed silicon surfaces 10′, 11′ will be oriented in the (111) planes.
Optionally it is possible to cover the portions of the main surface of the silicon wafer that during the silicon etching treatment are not to be removed, with a masking layer. However, this is not further shown in the figures.
An alternative embodiment of the method shown in FIG. 5 is depicted in FIG. 6. The difference between this embodiment and the method according to FIG. 5 is that the lower side of the wafer 1 is now also provided with a material layer 16. This material layer also is provided with a masking layer 3 in a predetermined pattern. This pattern may be substantially aligned with the pattern provided at the upper side. However, this is not obligatory.
By carrying out the same steps described in FIG. 5, a product can be obtained as shown in FIG. 5E.
The steps shown in the FIGS. 5A to 5E may be carried out in a corresponding manner for the fabrication of cantilevers, as shown in a different embodiment in FIG. 3.
It is especially preferred for the etching treatment for the removal of material layers at the places not covered by the masking layer 3, to be carried out such that no through-openings through the silicon membrane layer 2 are formed. The etching treatment must be carried out only far enough to reach the silicon layer. For such a case different masking patterns may be created on both sides. The intermediate layer of silicon may be removed in a subsequent silicon etching treatment, wherein two differently formed layers of material are formed in a desired pattern. This makes it possible, for example, to form two layers of material, each providing a filter pattern whose openings in the one layer of material are larger than the openings in the other layer of material. This makes it possible in particular, to filter out contaminants or other particulate material of a desired size between the two layers of material.
FIG. 7 shows an embodiment for positioning a glass fibre 17. A glass fibre 17 is positioned on two separate membranes. Such membranes may be formed, for example, as cantilevers 14. By providing at least one of these cantilevers 14 with an actuation layer it is possible to position the glass fibre 17 as desired.
A positioning means 18 is further shown in a top view in FIG. 8. A first glass fibre 19 is fixedly positioned in the V-shaped groove 23. Another glass fibre 17 is positioned on two cantilevers 14 of which at least one can be actuated. By positioning the at least one cantilever 14 independently of the other in a suitable manner, the relative positioning of the second glass fibre 17 in relation to the first, fixed glass fibre 19 can be carried out such that it is aligned exactly in the extended direction of the fixed glass fibre 19. After that the second glass fibre 17 can be fixed.
FIG. 9 finally shows an embodiment wherein the cantilever according to the invention functions as mirror. A first cantilever 20 is in rest. A second cantilever 21 is in a bent condition, which may be effected, for example, by activating an actuating layer 22.
Other possibilities consist of cantilevers that are provided with a sensor layer reacting specifically with a certain compound contained, for example, in a fluid. When said sensor-layer bonds with the intended compound a deflection (22) of the cantilever may be produced. A light beam L directed at a surface of the cantilever 21 will therefore deflect at a different angle L′ than when the cantilever 20 is in the starting position. This deflection can be suitably detected by means of known devices.
FIG. 10 shows a cascade filter. Herein covering bodies 15 are provided at two sides of the wafer 1. A liquid to be filtered containing contaminants of different sizes is introduced into the cavity A and via the openings 12 in the first membrane 2 conducted into the cavity B. From there the liquid is conducted through the openings 12′ in the membrane 2′ into the cavity C. Finally, the liquid is conducted through the openings 12″ in the membrane 2″ into the cavity D. The openings 12, 12′ and 12″ have decreasing diameters. Via the cavities A, B, C and D the substances in the liquid retained by the respective membranes 2, 2′, 2″, can be discharged (not shown).
A new concept for the fabrication of a fuel cell element by a significantly simplified production process than in use at present, is shown in FIG. 11. The two compartments 6, 7 are formed in one substrate 1 and are located at both sides of electrodes 25, 26 (anode and cathode). In addition, the present method affords a very large active surface per unit area (high fill factor). Moreover, only one wafer 1 needs to be treated. During assembly, no demands regarding the alignment of the wafers need to be taken into consideration.
The FIGS. 11 and 12 show a cross-section of embodiments of a single fuel cell element according to the present invention. The fuel and the oxidant are conducted through the V-shaped channels 6 and 7 formed by anisotropic etching at the upper and lower side of the wafer 1. The V-shaped channels 6, 7 may optionally also comprise integrated thermal heating elements, for example, in the form of a conductive wire provided on a (111) plane.
An intermediate layer 24, or electrolyte 24, may consist of a solid oxide, a solid polymer, a proton exchange membrane. Alternatively, a catalytic layer 24 may separate the electrodes 25, 26 (anode and cathode).
More specifically, FIG. 11 shows an embodiment of a fuel cell wherein the silicon membrane 1 is completely etched away in order to form two channels 6, 7. The membrane 1 in the (111) orientation is formed by two perforated electrodes 25, 26, one intermediate electrolyte layer 24 and optionally extra layers (not shown the figure).
FIG. 12 shows an embodiment for a fuel cell wherein the perforated silicon membrane 1 is still present (for example to reinforce the electrodes 25, 26 placed on the membrane 1). Part of the silicon membrane is still present, for example, to support the electrodes. For an operating fuel cell, the silicon membrane 1 needs to be perforated.
In practice the elements may be cascaded or in series, as shown in a top view in FIG. 13, in numerous ways. Heating elements may be integrated by depositing conductive electrodes on the (111) sides of the V-shaped channel, for example in a feed groove (top horizontal cavity in FIG. 13) or optionally, next to the reactive surfaces in the reactor compartments, indicated by hatching.
In FIG. 13 the possibility is shown of connecting fuel cell elements in order to increase the capacity or power (the cover plates 27 are not shown). The surfaces 29 are part of the cavities 6 at the upper side, the surfaces 30 are part of the cavities 7 at the lower side of the silicon wafer 1. The active surfaces 31 are indicated with hatching. At the dark surfaces 32, the (111) membranes are completely etched away, creating a passage of a V-groove 6 at the upper side to a V-groove 28 at the lower side. Via the portions 32′ where the (111) membranes are completely etched away, a passage from the groove 35 in the upper side to the groove 7 in the under side is created. Via the passages 32 and in the direction of the arrows 33, fuel or oxidant, respectively, reaches the active surfaces 31 of the membranes. Via the passages 32′ and in the direction of the arrow 34, oxidator or fuel from the groove 35 reaches the grooves 7. In the manner shown, a two-dimensional array may be constructed with serially- and parallel-connected fuel cells. In the manner described above it is also possible to form a cascade with the earlier described filter elements, by connecting the electrodes with one another in the appropriate manner.
The supply of fuel and oxidator will allow a reaction to take place which terminates, for example, when both or one of the two is/are completely used up, or earlier.
With the cantilevers (made of silicon or another material) a probe can be fabricated for example, for a scanning probe microscope (SPM), an AFM, or a friction force microscope. Because of its three-dimensional form, this is especially susceptible to lateral forces in one direction. Moreover, such a probe has other geometric probe properties than conventional probes, which may be advantageous. An example of an embodiment is shown in FIGS. 14 and 15.
FIG. 14 shows the tip of a cantilever provided with a point-like projection, for example, formed in the same manner as the tip of ordinary AFM cantilevers.
The tip of the (111) cantilever may also be formed by a maskless immersion in an etching solution. In that case the geometry is as shown in FIG. 15. The 111 cantilever beam (indicated with dotted lines) may be provided with a sharp tip by short-etching without mask (by dipping). The etched cantilever is shown in the figure with full lines.
There is a need for ways of applying freestanding filaments in a reaction chamber or liquid channel. Freestanding refers to: not deposited on silicon or another heat conductor. An example is a flow sensor based on a heating filament. With the present technique of processing materials deposited on (111) oriented silicon substrates, it is possible to fabricate said freestanding filaments, for example, by depositing a conductor on a (111) membrane, applying a pattern and subsequently selectively etching away the Si membrane.
FIG. 16 finally shows a cross section of two wafers 1, 1′ as illustrated in FIG. 13. Here a continuous flow of fuel and oxidator is possible. Only one continuous flow path 36, indicated with arrow 37, of several flow paths is shown. The grey-shaded portions 31 are the active surfaces.
The invention is not limited to the above specifically described embodiments. It is limited only by the appended claims.
Patent Application
20080020579
