1, are extremely small even at high temperatures.

In order to connect the wiring to the lower electrode layer 20, as shown in FIG. 5, the solid electrolyte layer 100 is not present on a part of an upper surface of the lower electrode layer 20, and the part of the upper surface of the lower electrode layer 20 is exposed. When the wiring is connected to the lower electrode layer 20, a wiring connection portion is formed on the insulating film 3 in order to prevent damage to other portions (the porous support material layer 5 and the like) of the fuel cell. In the lower electrode layer connected to the wiring, the lower electrode layer 20 formed on side walls and the bottom portions of the plurality of holes 60 are electrically connected to one another.

An upper electrode layer 10 is formed on an upper side of the solid electrolyte layer 100. The upper electrode layer 10 may be formed of, for example, platinum, or may be formed of a cermet material made of platinum and a metal oxide. Similarly to the lower electrode layer 20, the upper electrode layer 10 also covers the bottom portion of the hole 60, the side wall portion of the hole 60, and the one side surface of the porous support material layer 5.

In order to connect the wiring to the upper electrode layer 10, a region in which the lower electrode layer 20 is not present is formed under the upper electrode layer 10 as in a right side portion on the drawing of a cross-sectional view of FIG. 5. This is to prevent an electrical short circuit between the upper electrode layer 10 and the lower electrode layer 20 when the solid electrolyte layer 100 is damaged due to damage at the time of connecting the wiring. In addition, in order to prevent the damage to other portions (the porous support material layer 5 and the like) of the fuel cell, it is preferable that the wiring connection portion is formed on the insulating film 3. In the upper electrode layer 10 connected to the wiring, the upper electrode layer 10 formed on the side walls and the bottom portions of the plurality of holes 60 are electrically connected to one another.

As described above, the thin-film process type of the fuel cell 1 includes a membrane electrode assembly as a stacked body including the lower electrode layer 20, the solid electrolyte layer 100, and the upper electrode layer 10. The membrane electrode assembly is formed by the film forming process on a surface of the plurality of holes 60 that is not parallel to the main surface of the silicon substrate 2 (that is, the side wall portions of the holes 60). The membrane electrode assembly is also formed at the bottom portions of the plurality of holes 60.

The membrane electrode assembly covers the upper surface of the porous support material layer 5 in which the plurality of holes 60 are formed (that is, the bottom portions of the holes 60, the side wall portions of the holes 60, and a portion in which the holes 60 are not formed). That is, the upper electrode layer 10 is also formed on a surface parallel to the main surface of the silicon substrate 2 in a manner of being continuous (or connected) to the upper electrode layer 10 formed in the plurality of holes 60. In addition, the lower electrode layer 20 is also formed on the surface parallel to the main surface of the silicon substrate 2 in a manner of being continuous (or connected) to the lower electrode layer 20 formed in the plurality of holes 60. The same applies to the solid electrolyte layer 100.

In this example, both the upper electrode layer 10 and the lower electrode layer 20 are formed on the surface parallel to the main surface of the silicon substrate 2. Alternatively, one of them may be formed on the main surface of the silicon substrate 2 alone.

In this manner, since the membrane electrode assembly is formed on the side wall portions of the holes 60, an output power per projected area on the silicon substrate 2 is increased. Further, since the membrane electrode assembly is also formed on the surface parallel to the main surface of the silicon substrate 2, the membrane electrode assembly is formed in a wide region of the silicon substrate 2.

The membrane electrode assembly is supported by the porous support material layer 5 at the entire hole 60 including an upper end portion and a lower end portion.

For a size of the hole 60, a diameter thereof can be, for example, 500 nanometers to 10 micrometers. It is necessary to design the size of the hole 60 and a thickness of the membrane electrode assembly, so that the hole 60 is not completely filled with the membrane electrode assembly formed in the hole 60.

FIG. 6 is an enlarged perspective view of a part of the fuel cell 1. The fuel gas is supplied to a lower electrode layer 20 side of the fuel cell 1, and the oxidant gas is supplied to an upper electrode layer 10 side. In this case, the lower electrode layer 20 serves as an anode layer, and the upper electrode layer 10 serves as a cathode layer. The supplied fuel gas diffuses inside the porous support material layer 5 and reaches the lower electrode layer 20. The supplied oxidant gas diffuses to a surface of the upper electrode layer 10 inside the hole 60 so as to be supplied. The oxidant gas and the fuel gas react with each other by ion conduction via the solid electrolyte layer 100, so that the fuel cell 1 operates in the same manner as a known fuel cell. A space between a lower electrode layer 20 side and the upper electrode layer 10 side is sealed, so that the oxidant gas and the fuel gas are not mixed with each other in a gas state.

As for the supply of the fuel gas and the oxidant gas, contrary to FIG. 6, the oxidant gas may be supplied to the lower electrode layer 20 side, and the fuel gas may be supplied to the upper electrode layer 10 side. The lower electrode layer serves as the cathode layer, and the upper electrode layer serves as the anode layer. In this case, the supplied oxidant gas diffuses inside the porous support material layer and reaches the lower electrode layer 20, and the supplied fuel gas diffuses to the surface of the upper electrode layer inside the hole 60 so as to be supplied. Even in this case, the fuel cell 1 operates in the same manner as a known fuel cell.

First Embodiment: Method for Manufacturing Fuel Cell

FIGS. 7 to 16 are diagrams illustrating an example of a method for manufacturing the fuel cell 1 according to the first embodiment. First, the insulating film 3 is formed on the silicon substrate 2 (FIG. 7). Next, the insulating film 3 is removed while remaining an outer edge portion of the insulating film 3 in the X and Y directions (FIG. 8). Therefore, the flat nickel oxide layer 4 (metal-oxide layer) is formed on the exposed surface of the silicon substrate 2, a side wall of the insulating film 3, and an upper surface of the insulating film 3 (FIG. 9). In this manner, the nickel oxide layer 4 is formed on the surface of the silicon substrate 2. Next, a part of the nickel oxide layer 4 is removed to expose the upper surface of the insulating film 3 (FIG. 10).

Next, the plurality of holes 60 extending in a direction perpendicular to the surface of the silicon substrate 2 are formed in an upper surface of the nickel oxide layer 4 as uneven structures (FIG. 11). At this time, the bottom portions of the holes 60 do not penetrate the nickel oxide layer 4. A cross-sectional shape of the hole 60 can be, for example, a circle, but can also be an oval shape, or can be a polygon such as a square, a rectangle, a pentagon, or a hexagon. The cross-sectional shape of the hole 60 may be constant in the upper-lower direction or may change along the upper-lower direction.

A method for forming the uneven structure (the hole 60 in this example) can be appropriately determined by those skilled in the art, and the uneven structure can be formed by, for example, lithography and dry etching. It is preferable that the uneven structures are formed periodically in the X direction and/or the Y direction, but the invention is not limited thereto. In addition, it is preferable that all of the uneven structures are formed in the same shape, but the invention is not limited thereto.

Next, the lower electrode layer 20 is formed on an upper side of the nickel oxide layer 4 and the insulating film 3 (FIG. 12). At this time, the lower electrode layer 20 covers the bottom portions and the side wall portions of the plurality of holes 60 and a region of the upper surface of the nickel oxide layer 4 in which the holes 60 are not formed. Although the lower electrode layer 20 is also formed on the upper side of the insulating film 3, a region in which the lower electrode layer 20 is not formed remains in a part of the upper side of the insulating film 3. This is because a region for connecting the upper electrode layer 10 and the wiring in a later step is prepared.

For example, a chemical vapor deposition (CVD) method or an atomic layer deposition (ALD) method can be used to form the lower electrode layer 20. As a method for providing a region in which the lower electrode layer 20 is not formed, for example, after the lower electrode layer 20 is formed, a part of the lower electrode layer 20 can be removed using the lithography and the dry etching. Alternatively, at the time of forming the lower electrode layer 20, a metal mask or a resist mask is used to cover a part of the region, so that the lower electrode layer can be prevented from being formed in the part of the region.

Next, the solid electrolyte layer 100 is formed (FIG. 13). At this time, similarly to the formation of the lower electrode layer 20, the solid electrolyte layer 100 is formed on the upper side of the lower electrode layer 20 in a manner of covering the bottom portions and the side wall portions of the plurality of holes 60 and the region of the upper surface of the nickel oxide layer 4 in which the holes 60 are not formed. Although the solid electrolyte layer 100 is also formed on the insulating film 3, a region in which the solid electrolyte layer 100 is not formed remains in a part of a region in which the lower electrode layer 20 is formed on the insulating film 3. This is because a region for connecting the lower electrode layer 20 and the wiring in a later step is prepared.

The solid electrolyte layer 100 can be formed of, for example, the zirconia thin film doped with yttria. A doping amount of yttria can be, for example, 3% or 8%. For example, the chemical vapor deposition (CVD) method or the atomic layer deposition (ALD) method can be used to form the solid electrolyte layer 100. As a method for providing a region in which the solid electrolyte layer 100 is not formed, for example, after the solid electrolyte layer 100 is formed, a part of the solid electrolyte layer 100 can be removed using the lithography and the dry etching. Alternatively, at the time of forming the solid electrolyte layer 100, the metal mask or the resist mask is used to cover a part of the region, so that the solid electrolyte layer 100 can be prevented from being formed in the part of the region.

Next, the upper electrode layer 10 is formed (FIG. 14). At this time, similarly to the formation of the lower electrode layer 20 and the formation of the solid electrolyte layer 100, the upper electrode layer 10 is formed on the upper side of the solid electrolyte layer 100 in a manner of covering the bottom portions and the side wall portions of the plurality of holes 60 and the region of the upper surface of the nickel oxide layer 4 in which the holes 60 are not formed. Although the upper electrode layer 10 is also formed on the insulating film 3, a region in which the upper electrode layer 10 is not formed remains in the part of the region in which the lower electrode layer 20 is formed on the insulating film 3. This is to prevent the upper electrode layer 10 and the lower electrode layer 20 from being electrically directly connected to each other and causing a short circuit failure, and to prepare the region for connecting the lower electrode layer 20 and the wiring in a later step.

The upper electrode layer 10 may be formed of, for example, porous platinum, or may be formed of a cermet material made of platinum and a metal oxide. For example, the chemical vapor deposition (CVD) method or the atomic layer deposition (ALD) method can be used to form the upper electrode layer 10. As a method for providing a region in which the upper electrode layer is not formed, for example, after the upper electrode layer is formed, a part of the upper electrode layer 10 can be removed using the lithography and the dry etching. Alternatively, at the time of forming the upper electrode layer 10, the metal mask or the resist mask is used to cover a part of the region, so that the upper electrode layer 10 can be prevented from being formed in the part of the region.

As described above, the lower electrode layer 20, the solid electrolyte layer 100, and the upper electrode layer 10 are formed in this order in a region including the surface of the holes 60.

Next, a part of the silicon substrate 2 in contact with the nickel oxide layer 4 is partially removed from a lower side to form the opening 50 (FIG. 15). After the opening 50 is formed, the nickel oxide layer 4 is made porous by reduction annealing. For example, a lower side surface of the silicon substrate 2 is exposed to a hydrogen atmosphere, and heat treatment is performed at about 500° C. Accordingly, a part of the nickel oxide layer 4 exposed at the opening 50 is reduced and changed into the porous support material layer 5 (for example, a porous metal nickel layer) (FIG. 16). At this time, a part of a region of the nickel oxide layer 4 covered by the silicon substrate 2 may remain as the nickel oxide layer 4 without being reduced. As a result, the structure in FIG. 5 can be prepared.

By forming the porous support material layer 5 as described above, gas can be diffused via this porous support material layer 5.

First Embodiment: First Modification

FIG. 17 shows a configuration example according to a first modification of the first embodiment. In the first embodiment, the wiring connected to the lower electrode layer 20 is formed on the upper surface of the silicon substrate 2, but in the first modification, the wiring is not provided on the upper surface of the silicon substrate 2.

In the first modification, a conductive silicon substrate doped with impurities is used as the silicon substrate 2. Alternatively, instead of the silicon substrate 2, a conductive metal substrate is used as the first substrate. Accordingly, the lower electrode layer 20 is electrically connected to one side surface (a lower surface in a cross-sectional view of FIG. 17) of the substrate 2 via the porous support material layer 5 and the substrate 2. In the present modification, the porous support material layer 5 is limited to a metal layer, and is, for example, a metal nickel layer.

Since the lower electrode layer 20 and the wiring can be connected to each other on the lower surface of the substrate, it is not necessary to form a portion for connecting the lower electrode layer 20 and the wiring on an upper surface side of the substrate. As a result, an entire outer edge portion of the upper surface of the substrate in the X and Y directions can be served as the portion for connecting the upper electrode layer 10 and the wiring.

An outer edge 70 of the lower electrode layer 20 remains on the nickel oxide layer 4, and the lower electrode layer 20 is not formed on the upper surface of the insulating film 3. Therefore, a region in which only the solid electrolyte layer 100 and the upper electrode layer 10 are formed can be formed over an entire outer edge portion of the fuel cell 1 to be served as the portion for connecting the upper electrode layer and the wiring.

First Embodiment: Second Modification

FIG. 18 shows a configuration example according to a second modification of the first embodiment. On the porous support material layer 5, a surface (a lower surface in a cross-sectional view of FIG. 18) opposite to the surface on which the plurality of holes 60 are formed is supported by a mesh-shaped support material layer 6a (second support material layer). The support material layer 6a can be formed of a silicon nitride film, dense metal nickel, a silicon oxide film, or the like.

Since the porous support material layer 5 is supported by the support material layer 6a, sufficient mechanical strength can be secured in the structures of the lower electrode layer 20, the solid electrolyte layer 100, the upper electrode layer 10, and the porous support material layer 5 even when an area of the opening 50 is increased.

First Embodiment: Third Modification

A third modification of the first embodiment will be described with reference to FIGS. 19 and 20. FIG. 19 shows a time point of a manufacturing process, and FIG. 20 shows a configuration after the manufacturing process is completed.

In the first embodiment and each of the above-described modifications, the plurality of holes 60 are formed as the uneven structures in the porous support material layer 5, but in the third modification, as shown in FIGS. 19 and 20, a plurality of columns 40 are formed as the uneven structures in the porous support material layer 5. The column 40 is a protrusion, and may form, for example, a column-shaped pattern.

In particular, in the first embodiment, as shown in FIG. 11, the plurality of holes 60 are formed in the surface of the nickel oxide layer 4, but in the third modification, as shown in FIG. 19, the plurality of columns 40 are formed as the uneven structures on the surface of the nickel oxide layer 4.

The column 40 extends in the upper-lower direction (that is, the direction perpendicular to the main surface of the silicon substrate 2). On the nickel oxide layer 4, the membrane electrode assembly is formed on upper surfaces and side surfaces of the plurality of columns 40 and a portion (bottom portion) of the nickel oxide layer 4 where the columns 40 are not formed in the same manner as in the first embodiment. This membrane electrode assembly is formed by the film forming process on a surface of the plurality of columns 40 that is not parallel to the main surface of the silicon substrate 2. The membrane electrode assembly is also formed at top portions (top surfaces) of the plurality of columns 40.

Further, after the opening 50 (not shown) is formed, the nickel oxide layer 4 is made porous from the lower side by reduction annealing to form the porous support material layer (FIG. 20). A cross-sectional shape of the column 40 in an XY plane can be, for example, a circle, but can also be an ellipse, a square, a rectangle, a pentagon, a hexagon, or the like. The cross-sectional shape of the column 40 may be constant in the upper-lower direction or may change along the upper-lower direction.

The membrane electrode assembly formed on an outer peripheral portion of the column 40 formed on the silicon substrate 2 has the same structure as that of the membrane electrode assembly formed on the side wall portion of the hole 60 in the first embodiment.

The membrane electrode assembly covers the upper surface of the porous support material layer 5 in which the plurality of columns 40 are formed (that is, the top portions of the columns 40, the outer peripheral portions of the columns 40, and the portion in which the columns 40 are not formed). That is, the upper electrode layer 10 is also formed on the surface parallel to the main surface of the silicon substrate 2 in a manner of being continuous (or connected) to the upper electrode layer 10 formed on the plurality of columns 40. In addition, the lower electrode layer 20 is also formed on the surface parallel to the main surface of the silicon substrate 2 in a manner of being continuous (or connected) to the lower electrode layer 20 formed on the plurality of columns 40.

In this example, both the upper electrode layer 10 and the lower electrode layer 20 are formed on the surface parallel to the main surface of the silicon substrate 2. Alternatively, one of them may be formed on the surface parallel to the main surface of the silicon substrate 2 alone.

The membrane electrode assembly is supported by the porous support material layer 5 at the entire plurality of columns 40 including upper end portions and lower end portions.

For a size of the column 40, a diameter thereof can be, for example, 100 nanometers to 10 micrometers. It is necessary to design the size of the column 40 and the thickness of the membrane electrode assembly, so that a space between the adjacent columns 40 is not completely filled with the membrane electrode assembly formed on outer peripheries of the columns 40.

As shown in FIG. 20, the fuel gas is supplied to the lower electrode layer 20 side, and the oxidant gas is supplied to the upper electrode layer 10 side. The lower electrode layer 20 serves as the anode layer, and the upper electrode layer 10 serves as the cathode layer. The supplied fuel gas diffuses inside the porous support material layer 5 and reaches the lower electrode layer 20. The supplied oxidant gas diffuses to the surface of the upper electrode layer 10 so as to be supplied. Accordingly, the fuel cell 1 operates in the same manner as in the case in FIG. 6.

As for the supply of the fuel gas and the oxidant gas, contrary to FIG. 20, the oxidant gas may be supplied to the lower electrode layer 20 side, and the fuel gas may be supplied to the upper electrode layer 10 side. The lower electrode layer serves as the cathode layer, and the upper electrode layer serves as the anode layer. In this case, the supplied oxidant gas diffuses inside the porous support material layer and reaches the lower electrode layer 20, and the supplied fuel gas diffuses to the surface of the upper electrode layer inside the hole 60 so as to be supplied. Even in this case, the fuel cell 1 operates in the same manner as a known fuel cell.

Either of the hole 60 according to the first embodiment and the column 40 according to the third modification is the example of the uneven structure that can be easily manufactured. In addition, depending on the configuration of the fuel cell 1, one of the hole 60 and the column 40 may be more easily manufactured. For example, as a characteristic of the nickel oxide layer 4 or a layer corresponding thereto, when it is easy to precisely form the hole, the configuration according to the first embodiment can be more efficiently manufactured. On the other hand, when it is easy to precisely form the column, the configuration according to the third modification can be more efficiently manufactured.

Alternatively, when the membrane electrode assembly is easily formed on the side walls and the bottom portions of the holes 60 at the time of forming the membrane electrode assembly, the configuration according to the first embodiment can be more efficiently manufactured. On the other hand, when the membrane electrode assembly is easily formed on side walls and the top portions of the columns 40, the configuration according to the third modification can be more efficiently manufactured.

First Embodiment: Fourth Modification

FIG. 21 shows a configuration example according to a fourth modification of the first embodiment. In the first embodiment and the first to third modifications, a lower surface of the porous support material layer 5 has a flat shape, but in the fourth modification, unevenness is formed along the side walls of the plurality of holes 60.

A thickness of a part of the porous support material layer in which the plurality of holes 60 are formed is constant. The configuration of the membrane electrode assembly is the same as that according to the first embodiment.

As shown in FIG. 21, the fuel gas is supplied to the lower electrode layer 20 side, and the oxidant gas is supplied to the upper electrode layer 10 side. The lower electrode layer 20 serves as the anode layer, and the upper electrode layer 10 serves as the cathode layer. The supplied fuel gas diffuses inside the porous support material layer 5 and reaches the lower electrode layer 20. As compared with the first embodiment (FIG. 5), the first modification (FIG. 17), the second modification (FIG. 18), and the third modification (FIG. 20), a structure becomes complicated, but since the thickness of the porous support material layer 5 is constant, a diffusion distance is also constant, which is advantageous for the supply of the fuel gas. The supplied oxidant gas diffuses to the surface of the upper electrode layer 10 so as to be supplied. Accordingly, the fuel cell 1 operates in the same manner as in the case in FIG. 6.

As for the supply of the fuel gas and the oxidant gas, contrary to FIG. 21, the oxidant gas may be supplied to the lower electrode layer 20 side, and the fuel gas may be supplied to the upper electrode layer 10 side. The lower electrode layer serves as the cathode layer, and the upper electrode layer serves as the anode layer. In this case, the supplied oxidant gas diffuses inside the porous support material layer and reaches the lower electrode layer 20, and the supplied fuel gas diffuses to the surface of the upper electrode layer inside the hole 60 so as to be supplied. Since the porous support material layer 5 is thin, the diffusion distance is short, which is advantageous for the supply of the oxidant gas. Even in this case, the fuel cell 1 operates in the same manner as a known fuel cell.

First Embodiment: Effects

FIG. 22 is a graph illustrating an effect according to the first embodiment. Relationships, each between an aspect ratio of the hole or the column and a cell area per projected area on the substrate, in a fuel cell according to the related art and the fuel cell 1 according to the first embodiment are shown. The aspect ratio of the hole is a value obtained by dividing a depth of the hole by the diameter, and the aspect ratio of the column is a value obtained by dividing a height of the column by the diameter.

According to the first embodiment, as the aspect ratio of the hole or the column increases, the cell area per projected area on the substrate can be increased. That is, according to the first embodiment, since the cell area contributing to power generation can be increased with a small substrate area, an output power per substrate area can be increased.

In the first embodiment, a large number of holes 60 can be formed in parallel, and it is not necessary to separately form the holes 60. Therefore, the fuel cell 1 can be manufactured at a cost lower than those in, for example, methods in PTL 1 and PTL 2, and a cost per output power can be reduced.

Second Embodiment

In the first embodiment, as shown in FIGS. 5, 17, 18, 20, and 21, the bottomed holes 60 or the columns 40 are formed, and the membrane electrode assembly is also formed at tip end portions in a depth direction (the bottom portions of the holes 60 or the top portions of the columns 40). In a second embodiment, a through hole is formed instead of the bottomed hole.

FIG. 23 shows a configuration example of a fuel cell according to the second embodiment. A support material layer 6 (first support material layer) is formed on one surface (the upper surface or the lower surface) or both surfaces (that is, the upper surface and the lower surface) of the silicon substrate 2. In addition, a plurality of through holes 61 (first through holes) penetrating the support material layer 6 and the silicon substrate 2 are formed. The through hole 61 extends in the upper-lower direction (that is, the direction perpendicular to the main surface of the silicon substrate 2).

For a size of the through hole 61, a diameter (diameter of the through hole formed in the support material layer 6) of the through hole 61 can be, for example, 10 micrometers. Side walls of the plurality of through holes 61 include the membrane electrode assembly. This membrane electrode assembly is formed by the film forming process on a surface of the plurality of through holes 61 that is not parallel to the main surface of the silicon substrate 2. The membrane electrode assembly is also formed on an upper surface of the support material layer 6 formed on the upper surface of the silicon substrate 2. Hollows 52 are formed on an outer peripheral side of the side walls of the plurality of through holes 61.

Although not shown, as in the right side portion on the drawing of the cross-sectional view of FIG. 5 in the first embodiment, the region in which the lower electrode layer 20 is not present may be formed under the upper electrode layer 10. In this manner, when the solid electrolyte layer 100 is damaged due to damage at the time of connecting the upper electrode layer 10 and the wiring, it is possible to prevent the electrical short circuit from occurring between the upper electrode layer 10 and the lower electrode layer 20.

The upper electrode layer 10 is also formed on the surface parallel to the main surface of the silicon substrate 2 in a manner of being continuous (or connected) to the upper electrode layer 10 formed in the plurality of through holes 61. In addition, the lower electrode layer 20 is also formed on the surface parallel to the main surface of the silicon substrate 2 in a manner of being continuous (or connected) to the lower electrode layer 20 formed in the plurality of through holes 61. The same applies to the solid electrolyte layer 100.

That is, the upper electrode layer 10 connected to the wiring on the upper surface of the silicon substrate 2 is continuous to and electrically connected to the upper electrode layer 10 formed on the side walls of the plurality of through holes 61. The lower electrode layer 20 is formed on a lower surface of the support material layer 6 formed on the lower surface of the silicon substrate 2, and the lower electrode layer 20 is continuous to the lower electrode layer 20 formed on the side walls of the plurality of through holes 61. The lower electrode layer 20 connected to the wiring on a lower surface side of the silicon substrate 2 is continuous to and electrically connected to the lower electrode layer 20 formed on the side walls of the plurality of through holes 61.

In this example, both the upper electrode layer 10 and the lower electrode layer 20 are formed on the surface parallel to the main surface of the silicon substrate 2. Alternatively, one of them may be formed on the surface parallel to the main surface of the silicon substrate 2 alone.

The membrane electrode assembly is supported by the support material layer 6 at upper end portions and lower end portions of the plurality of through holes 61.

In such a configuration, the fuel gas is supplied to an outer peripheral side of the through holes 61, and the oxidant gas is supplied to an inner peripheral side of the through holes 61. Accordingly, power generation is performed at the side wall portions of the through holes 61, and the output power per projected area on the silicon substrate 2 is increased.

Second Embodiment: Manufacturing Method

FIGS. 24 to 36 are diagrams illustrating an example of a method for manufacturing the fuel cell 1 according to the second embodiment. First, the support material layer 6 is formed on the upper surface and the lower surface of the silicon substrate 2 (FIG. 24). The support material layer 6 is, for example, a silicon nitride film layer. Next, a groove 8 is formed in the support material layer 6 on the upper surface of the silicon substrate 2 (FIG. 25). Next, an electrode material layer 7 is formed such that the groove 8 is completely covered with the electrode material layer (FIG. 26). For the electrode material layer 7, tungsten, silicon doped with impurities, or the like can be used.

Next, the electrode material layer 7 on the support material layer 6 other than that in the groove 8 is removed, so that the electrode material layer 7 remains only in the groove 8 (FIG. 27). For the removal of the electrode material layer, for example, an etch-back method or a chemical mechanical polishing method (CMP method) can be used.

Next, the plurality of through holes 61 perpendicular to the surface of the silicon substrate 2 are formed in a region in which the electrode material layer 7 remains (FIG. 28). A cross-sectional shape of the hole can be, for example, a circle, but can also be an ellipse, or can be a polygon such as a square, a rectangle, a pentagon, or a hexagon.

Next, the lower electrode layer 20 is formed (FIG. 29). The lower electrode layer 20 is formed on the upper surface of the support material layer 6 on the upper surface of the silicon substrate 2, a surface of the electrode material layer 7, the lower surface of the support material layer 6 on the lower surface of the silicon substrate 2, and the side walls of the plurality of through holes 61. The lower electrode layer 20 may be formed of, for example, platinum, or may be formed of a cermet material made of platinum and a metal oxide. For example, the chemical vapor deposition (CVD) method or the atomic layer deposition (ALD) method can be used to form the lower electrode layer 20.

The lower electrode layer 20 formed on each of the side walls of the plurality of through holes 61 is continuous to the lower electrode layer 20 formed on the surface of the electrode material layer 7.

The lower electrode layer 20 is electrically connected to the electrode material layer 7. Although the lower electrode layer 20 is also formed on the upper surface of the support material layer 6, a region in which the lower electrode layer is not formed remains on a part of the upper surface of the support material layer 6 (FIG. 30). This is for bonding to a support substrate in a later step. For removing a part of the lower electrode layer 20, for example, the chemical mechanical polishing method (CMP method) can be used.

Next, a support substrate 102 (second substrate) is prepared (FIG. 31). Silicon, for example, can be used for the support substrate 102. As described above, the fuel cell 1 according to the second embodiment includes the support substrate 102.

Here, in FIGS. 31 to 42, since the silicon substrate 2 is vertically inverted, a positive direction of a Z axis is defined as a lower direction of the drawing. In the following description, the positive direction of the Z axis is referred to as an upper direction, and a negative direction of the Z axis is referred to as the lower direction. Therefore, the upper-lower direction of the drawing in FIGS. 31 to 42 is opposite to the upper-lower direction in the present specification.

Through holes 161 (second through holes) are formed in the support substrate 102. A size of the through hole 161 of the support substrate 102 aligns with the size of the through hole 61 of the silicon substrate 2. The silicon substrate 2 and the support substrate 102 are bonded to each other such that positions of the through holes 61 and the through holes 161 are aligned with and connected to each other.

A through hole 162 (second through hole) and a through hole 163 (second through hole) are formed in the support substrate 102. The through hole 162 is formed at a position corresponding to a part of the silicon substrate 2 in which the electrode material layer 7 is not formed, and the through hole 163 is formed at a position corresponding to a part of the silicon substrate 2 in which the electrode material layer 7 is formed.

A silicon nitride film 103 is formed on the upper surface and the lower surface of the support substrate 102 and side walls of the through holes 161, 162, 163. The silicon nitride film 103 is an insulating film and is formed as a protective film against etching. A plurality of through holes 162 are formed, and one or more through holes 163 are formed. After the support substrate 102 is processed as described above, the silicon substrate 2 in FIG. 30 is vertically inverted and bonded to the support substrate 102 as shown in FIG. 31. Therefore, the plurality of through holes 61 (or at least a part thereof) and the plurality of through holes 161 (or at least a part thereof) are connected to each other.

Next, the solid electrolyte layer 100 and the upper electrode layer 10 are formed (FIG. 32). At this time, the solid electrolyte layer 100 and the upper electrode layer 10 cover the side wall portions of the plurality of through holes 61, side wall portions of the through holes 161, and the lower surface of the support material layer 6 on the lower surface side of the silicon substrate 2. In this example, both the upper electrode layer 10 and the lower electrode layer 20 are formed on the surface parallel to the main surface of the silicon substrate 2. Alternatively, one of the upper electrode layer 10 and the lower electrode layer 20 may be formed on the surface parallel to the main surface of the silicon substrate 2 alone.

The solid electrolyte layer 100 can be formed of, for example, the zirconia thin film doped with yttria. A doping amount of yttria can be, for example, 3% or 8%. For example, the chemical vapor deposition (CVD) method or the atomic layer deposition (ALD) method can be used to form the solid electrolyte layer 100. The solid electrolyte layer 100 is not formed on an exposed surface side (that is, an upper surface side) of the support substrate 102. The film thickness of the solid electrolyte layer 100 can be, for example, 100 nanometers to 1 micrometer.

The upper electrode layer 10 may be formed of, for example, porous platinum, or may be formed of a cermet material made of platinum and a metal oxide. For example, the chemical vapor deposition (CVD) method or the atomic layer deposition (ALD) method can be used to form the upper electrode layer 10. The upper electrode layer 10 is not formed on the exposed surface side (that is, the upper surface side) of the support substrate 102.

In this manner, the membrane electrode assembly is formed on inner peripheral surfaces of the plurality of through holes 61 and at least one side surface (lower surface in the present embodiment) of the support material layer 6. As described above, the membrane electrode assembly is a stacked body including the lower electrode layer 20, the solid electrolyte layer 100, and the upper electrode layer 10.

Next, an electrode material layer 107 is formed in the through hole 163 of the support substrate 102 (FIG. 33). The electrode material layer 107 is electrically connected to the lower electrode layer 20. The electrode material layer 107 is used to connect the lower electrode layer 20 to the wiring.

Next, a part of the support material layer 6 on the silicon substrate 2 that is in the through hole 162 of the support substrate 102 is removed to expose the surface of the silicon substrate 2 (FIG. 34).

Next, a part of the silicon substrate 2 that is exposed via the through hole 162 is removed. For example, a portion in contact with the membrane electrode assembly formed in the plurality of through holes 61 is removed. The removal is performed by partially etching using, for example, a potassium hydroxide (KOH) aqueous solution. Accordingly, the hollow 52 is formed in the silicon substrate 2 (FIG. 35).

Accordingly, a flow path of the fuel gas is formed inside the silicon substrate 2, and the output power per projected area on the silicon substrate 2 is increased. In addition, by particularly removing the portion exposed via the through hole 162, the through hole 162 can be used as the flow path of the fuel gas, so that the manufacturing process is simplified.

The through hole 162 serves as a hollow opening 51 through which the hollow 52 communicates with the outside. As described above, a plurality of through holes (through holes 161, 162 in the present example) are formed, and a part (through hole 161 in the present example) of the plurality of through holes is connected to any one of the through holes 61, and a remaining part (through hole 162 in the present example) of the plurality of through holes is connected to the hollow 52 to be served as the hollow opening 51. With such a configuration, it is possible to form the flow paths for both the fuel gas and the oxidant gas.

The membrane electrode assembly is formed on the side walls of the plurality of through holes 61, and is supported by the support material layer 6 at the upper end portion (that is, an end connected to the through hole 161) and a lower end of the through hole