FUEL CELL FORMED IN A SINGLE LAYER OF MONOCRYSTALLINE SILICON AND FABRICATION PROCESS

• US 20060255464A1
• Filed: 05/12/2006
• Published: 11/16/2006
• Est. Priority Date: 05/13/2005
• Status: Active Grant

• Current Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: Coffa, Salvatore, D'Arrigo, Giuseppe
• Granted Patent: US 7,763,372 B2
• Time in Patent Office: Days
• US Class Current: 257/758
• CPC Class Codes: H01M 2008/1095 Fuel cells with polymeric electrolytes
• CPC Class Codes: H01M 8/1004 characterised by membrane-electrode assemblies [MEA] H01M8/12 takes precedence
• CPC Class Codes: H01M 8/1097 Fuel cells applied on a support, e.g. miniature fuel cells deposited on silica supports
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

Fuel cells are formed in a single layer of conductive monocrystalline silicon including a succession of electrically isolated conductive silicon bodies separated by narrow parallel trenches etched through the whole thickness of the silicon layer. Semicells in a back-to-back configuration are formed over etch surfaces of the separation trenches. Each semicell formed on the etch surface of one of the silicon bodies forming an elementary cell in cooperation with an opposite semicell formed on the etch surface of the next silicon body of the succession, is separated by an ion exchange membrane resin filling the separation trench between the opposite semicells forming a solid electrolyte of the elementary cell. Each semicell includes a porous conductive silicon region permeable to fluids, extending for a certain depth from the etch surface of the silicon body, at least partially coated by a non passivable metallic material. Each of the porous and fluid permeable regions communicates with a feed duct of a fuel fluid or of oxygen gas that extends parallel to the etch surface inside the conductive silicon body.

Claims

1-14. -14. (canceled)

15. A fuel cell device including a plurality of fuel cells formed in a conductive monocrystalline silicon layer, the device comprising:

a succession of electrically isolated conductive silicon bodies closely separated by etched parallel trenches in the silicon layer to define etched side surfaces of the silicon bodies;

each fuel cell comprising a pair of semicells including a semicell in the etched side surface of one of the silicon bodies in cooperation with an adjacent semicell in the etched side surface of a next silicon body of the succession, each semicell comprising

a porous conductive silicon region extending into the silicon body from the etched side surface thereof,

a non-passivatable metallic material at least partially coating the porous conductive silicon region, and

a fluid feed duct, for at least one of fuel and oxygen, inside the silicon body and extending parallel to the etched side surface thereof, and in communication with the porous conductive silicon region; and

an ion exchange material filling the trenches between the adjacent semicells and defining a solid electrolyte of the fuel cell.

16. The fuel cell device according to claim 15, further comprising catalytic material particles at least between the porous conductive silicon region and said ion exchange material.

17. The fuel cell device according to claim 16, wherein said catalytic material particles are on a surface of said non-passivatable metallic material.

18. The fuel cell device according to claim 16, wherein said catalytic material particles comprise at least one of platinum black, palladium black, iridium black and ruthenium black.

19. The fuel cell device according to claim 18, further comprising a binder for said catalytic material particles and the non-passivatable metallic material over the surface of said porous conductive silicon region.

20. The fuel cell device according to claim 15, wherein the plurality of fuel cells define an array of monopolar fuel cells.

21. The fuel cell device according to claim 15, wherein the plurality of fuel cells define a battery of bipolar fuel cells.

22. A fuel cell device including a plurality of fuel cells formed in a conductive silicon layer including electrically conductive silicon bodies closely separated by parallel trenches in the silicon layer to define side surfaces of the silicon bodies, each fuel cell comprising:

a pair of semicells including a semicell in the side surface of one of the silicon bodies in cooperation with an adjacent semicell in the side surface of an adjacent silicon body, each semicell comprising

a porous conductive silicon region extending into the silicon body from the side surface thereof,

a metallic material at least partially coating the porous conductive silicon region, and

a fluid feed duct inside the silicon body and extending parallel to the side surface thereof, and in communication with the porous conductive silicon region; and

an electrolyte in the trench between adjacent semicells.

23. The fuel cell device according to claim 22, further comprising a catalytic material between the porous conductive silicon region and said electrolyte.

24. The fuel cell device according to claim 23, wherein said catalytic material is on a surface of said metallic material.

25. A method of fabricating an array of fuel cells, the method comprising:

providing a conductive silicon layer electrically isolated from a substrate;

depositing a mask on the surface of the silicon layer;

defining parallel pairs of slit apertures in the mask;

removing silicon through the apertures to form parallel pairs of channels;

removing the mask from the surface of the silicon layer;

forming a subsequent conductive silicon layer over the surface of the silicon layer to close top openings of the parallel pairs of channels, to form parallel pairs of buried ducts;

depositing a metal layer over the subsequent conductive silicon layer;

defining parallel apertures through the metal layer parallel to and between the parallel pairs of buried ducts formed in the silicon;

forming trenches by removing silicon through the parallel apertures of the metal layer to define an array of electrically isolated parallel conductive silicon bodies having side surface along the trenches and including the buried ducts therein;

forming porous silicon regions in the side surfaces of the silicon bodies extending to a respective buried duct;

depositing a non-passivatable metal on the porous conductive silicon regions; and

filling the trenches between adjacent silicon bodies with an ion exchange material.

26. The method according to claim 25, wherein removing silicon through the apertures to form parallel pairs of channels comprises:

anisotropically etching the silicon layer through the apertures to a depth of about half a thickness of the silicon layer; and

wet etching anisotropically etched surfaces of the silicon to form the parallel pairs of channels in the silicon layer.

27. The method according to claim 25, wherein forming porous silicon regions comprises chemically eroding the silicon over the side surfaces by biasing each silicon body through the metal layer.

28. The method according to claim 25, wherein depositing the non-passivatable metal comprises activating at least a surface portion of the porous silicon regions by depositing thereon the non-passivatable metal comprising at least one of platinum, iridium, ruthenium, rhodium, palladium, alloys and non-stoichiometric conducting suboxides thereof.

29. The method according to claim 25, wherein the parallel pairs of buried ducts of each silicon body extend alternately from one flank to at least adjacent the other flank of the silicon bodies.

30. The method according to claim 25, wherein one of the buried ducts of each parallel pair of buried ducts extends from one flank of the silicon bodies to adjacent an opposite flank;

and wherein the other buried duct of the pair extends from the opposite flank of the silicon bodies to adjacent the one flank.

31. The method according to claim 29, further comprising forming a ventilation hole on a top surface of alternating silicon bodies to intercept an end of the buried ducts at the other flank of the silicon body.

32. The method of claim 30, further comprising forming a ventilation hole on a top surface of each conductive silicon body to intercept an end of one of the buried ducts of the pair of parallel buried ducts.

33. The method according to claim 25, further comprising depositing catalytic material particles at least between the porous conductive silicon region and the ion exchange resin.

34. The method according to claim 33, wherein the catalytic material particles comprise at least one of platinum black, iridium black, ruthenium black, palladium black, rhodium black, and non-stoichiometric conducting suboxides thereof.

35. A method of making a fuel cell device including a plurality of fuel cells formed in a conductive silicon layer including electrically conductive silicon bodies closely separated by parallel trenches in the silicon layer to define side surfaces of the silicon bodies, the method including each fuel cell being formed by:

forming a pair of semicells including a semicell in the side surface of one of the silicon bodies in cooperation with an adjacent semicell in the side surface of an adjacent silicon body, each semicell comprising

a porous conductive silicon region extending into the silicon body from the side surface thereof,

a metallic material at least partially coating the porous conductive silicon region, and

a fluid feed duct inside the silicon body and extending parallel to the side surface thereof, and in communication with the porous conductive silicon region; and

filling the trench between adjacent semicells with an electrolyte.

36. The method according to claim 35, further comprising providing a catalytic material between the porous conductive silicon region and the electrolyte.

37. The method according to claim 36, wherein the catalytic material is provided on a surface of the metallic material.