Abstract:
Provided, in one embodiment, is a fuel cell interconnect comprising: a first primary conduit located at the periphery of the interconnect; a second primary conduit located at the periphery of the interconnect; a fuel cell distribution plate located at the top or bottom of the interconnect adapted to interface with a fuel cell and comprising: (i) an internal distribution conduit through the fuel cell distribution plate, and (ii) two or more second distribution conduits through the fuel cell distribution plate located peripheral to the internal distribution conduit but interior to the primary conduits, the internal and second distribution conduits adapted to convey fluid from one to the other along the top or bottom, as relevant, of the interconnect; and one or more manifold plates comprising a conduit from the first primary conduit to the internal distribution conduit and a conduit from the second primary conduit to two or more said second distribution conduits.

Description:
[0001]     The present invention relates to interconnect structures for electrically connecting a fuel cell stack while providing fuel and oxidant flow management.  
         [0002]     A fuel cell is an electrochemical device that generates electricity through the electrode reactions of fuel and oxidants (typically air). As long as fuel and oxidant are supplied, electricity can be generated continuously. The advantages of fuel cells include high efficient, low emission, and high reliability.  
         [0003]     A fuel cell includes a cathode (oxidant electrode), an electrolyte and an anode (fuel electrode). The electrolyte is an ionic conductor/electronic insulator, sandwiched between the cathode and anode as a gas tight membrane. To increase voltage and current, it is desirable to make larger sized fuel cells by using large area fuel cells (to obtain larger current) and connecting single cells in series (to obtain higher voltage). The electrical connections between individual cells are achieved by using of electrical interconnects, which should also provide effective oxidant and fuel passageways.  
         [0004]     Fuel cells using a solid oxide electrolyte (SOFCs) are the promising for power generation. The solid oxide electrolyte is either an oxygen ionic conductive or proton conductive oxide material. Due to the low electrolyte ionic conductivity at low temperature, SOFCs work at elevated temperatures (&gt;400° C., typically &gt;650° C.). The high working temperature brings advantages of high power density and high fuel efficiency. But high temperature create challenges to cell stack and manifold design, including thermal stress in cell structure due to unavoidable temperature gradients, materials compatibility, and stability of cell stack components.  
         [0005]     Among all fuel cell stack designs, a tubular cell stack is among the most advanced. Such a stack can be constructed in large size without a seal requirement, as taught in U.S. Pat. No. 4,876,163. However, the tubular cell design is expensive to fabricate, and has a relative low power density due to the high internal resistance of the supporting cathode tube.  
         [0006]     An alternative to the tubular cell is a planar cell where flat cell disks (trilayer cathode/electrolyte/anode) and interconnect plates (which conducts electrons between cells) are connected in series. The most common structure, as taught in U.S. Pat. No. 5,993,986, is a cross-flow cell stack, as shown in  FIG. 1  (numbering as in cited patent for its FIG. 6). The cells are fabricated as a square plate. Gas passageway channels are built in the interconnect plate. A common interconnector material is a suitable ferric alloy. The stack could be manifolded to supply fuel or oxidant either externally or internally. The planar fuel cell stack has advantages of compact size, and low internal electrical resistance. However, fuel cell stacks using square shaped cell disks have drawbacks of extensive sealing requirements, and asymmetrical temperature distribution that is imposed by the flow field and associated asymmetrical electrode reactions. The asymmetrical temperature distribution results in a high thermal stress across the cell disks, which stress can potentially concentrate at the corners of the cell disk, causing failure of the cell stack during operation.  
         [0007]     An alternative to the cross-flow square cell design is a radial co-flow design. As shown in  FIG. 2  (numbering as in cited patent for its FIG. 2), U.S. Pat. No. 5,399,442 teaches a radial co-flow cell stack design using annular shape cells (cathode/electrolyte/anode tri-layers). Two tubes provide fuel and air flows through the hole in the center of the cell disks. Cathodes are protected from the contact of fuel gas and anode are protected from contacting of air by using tubular gaskets to form seals on the cell disk edges. Several other similar designs have are taught in U.S. Pat. No. 5,549,983, U.S. Pat. No. 4,910,100, U.S. Pat. No. 6,291,089, U.S. Pat. No. 4,770,955 and U.S. Pat. No. 5,589,285. Generally, these designs have disadvantages of extensive sealing requirements, non-symmetrical position of gas tubes resulting in non-uniform flow, and the difficult stack manifolding.  
         [0008]     Another example of radial fuel cell stack design uses circular cell disks and interconnects having holes along the peripheries to provide fuel and oxidant inlets and outlets, as taught in U.S. Pat. No. 4,490,445 (see  FIGS. 3A and 3B , numbering as in cited patent for its FIGS. 2 and 3) and U.S. Pat. No. 4,048,385. This design has significant disadvantages of an extensive interface to be sealed, non-uniform gas distribution and weak mechanical strength along the cell edge due to multiple holes for gas transit.  
         [0009]     U.S. Pat. No. 5,851,689 teaches a design that uses plain planar circular cell disks (without hole on the cell disk) to build a cell stack. As shown in  FIG. 4  (numbering as in cited patent for its FIG. 4), the manifolds to provide oxidant and fuel gases to each individual cells are complicated. Because of the narrow thickness of each individual cells (˜2 mm) and the electrical insulating requirement between interconnects, it is very difficult to construct a fuel cell stack with this design.  
         [0010]     In summary, current designs of fuel cell stack have some disadvantages in operation and fabrication process. Specifically, it is desirable to develop a radial flow fuel cell stack that minimizes the sealing interfaces, and obtains a symmetrical flow field. Such a stack can have a more symmetrical electrode reaction and temperature distribution for reliable high performance operation.  
         [0011]     In addition, most fuel cells use hydrogen as the fuel reacting at the anodes, but the fuels most commonly available are hydrocarbon fuels, such as natural gas. Therefore, it can be necessary to convert hydrocarbon fuels to hydrogen. A common method to convert hydrocarbon fuels to hydrogen is by steam reforming reactions. The endothermic steam reforming reactions can take place either outside fuel cell stack (external reforming), or inside the fuel cell stack (internal reforming). Internal reforming has the advantage of high-energy efficiency obtained by directly using waste heat generated from fuel cell reactions to provide heat for reforming. However, most of current designs for internal reforming place the steam reforming reactions inside fuel cell anodes. The highly endothermic steam reforming reactions can further distort temperature symmetry, resulting in higher thermal stress. On-anode internal reforming can require high steam/carbon ratios for the feed gases, which can reduce fuel concentration and result in lower fuel utilization. Therefore it is desirable to design a cell stack that can conduct internal steam reforming away from, but close to, the anodes, such as inside interconnect structures.  
       SUMMARY OF THE INVENTION  
       [0012]     Provided, in one embodiment, is a fuel cell interconnect comprising: a first primary conduit located at the periphery of the interconnect; a second primary conduit located at the periphery of the interconnect; a fuel cell distribution plate located at the top or bottom of the interconnect adapted to interface with a fuel cell and comprising: (i) an internal distribution conduit through the fuel cell distribution plate, and (ii) two or more second distribution conduits through the fuel cell distribution plate located peripheral to the internal distribution conduit but interior to the primary conduits, the internal and second distribution conduits adapted to convey fluid from one to the other along the top or bottom, as relevant, of the interconnect; and one or more manifold plates comprising a conduit from the first primary conduit to the internal distribution conduit and a conduit from the second primary conduit to two or more said second distribution conduits.  
         [0013]     Provided, in another embodiment, is a fuel cell interconnect construct comprising: a first primary conduit located at the periphery of the interconnect; a second primary conduit located at the periphery of the interconnect; a fuel cell layer; a ceramic distribution plate comprising on a top side channels connected to the first primary conduit and the second primary conduit; and sandwiched between the ceramic distribution plate and the fuel cell layer, an perforated metal layer, wherein the perforations convey gas from the channels to an electrode of the fuel cell layer. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIGS. 1, 2 ,  3 A and  4  show structures whose overall design is outside the current invention.  
         [0015]      FIGS. 5A-5D  show a fuel cell stack made up of repeat units, and an exemplary repeat unit.  
         [0016]      FIGS. 6A-6B  show another repeat unit design.  
         [0017]      FIG. 7  shows an interconnect with one distribution layer per reactant gas.  
         [0018]      FIG. 8  shows an interconnect with two distribution layers per reactant gas, which can be used to preheat gas with heat from the fuel cell.  
         [0019]      FIG. 9  shows some alternative structures for a distribution layer.  
         [0020]      FIGS. 10A-10D  show a three layer interconnect with metal outer layers.  
         [0021]      FIGS. 11A-11B  show composite material used to provide CTE matching with the fuel cell disk.  
         [0022]     Definitions  
         [0023]     The following terms shall have, for the purposes of this application, the respective meanings set forth below.  
         [0024]     substantially round  
         [0025]     Certain embodiments are well adapted for use with round fuel cell disks. A substantially round fuel cell is one whose edges stay within or touching two circles with diameters +15% and −15% of a reference circle.  
         [0026]     aligned substantially with the center of the fuel cell  
         [0027]     An internal distribution conduit is aligned substantially with the center of the fuel cell when its center is aligned within or touching a circle originating at fuel cell center and having diameter of 15% the smallest width of the fuel cell.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0000]     Center/Periphery Distributing Embodiments  
         [0028]     In one embodiment, a radial flow planar fuel cell stack is taught. This novel stack uses multi-layer interconnects for gas manifolding, and plain planar cell (cathode/electrolyte/anode tri-layer) structures (e.g., discs  109 ) for the electrical power generation. As illustrated in  FIG. 5A , the planar fuel cell stack  100  can be constructed by a top plate  100 A, a bottom plate  100 B and a number of repeated cell units  100 C. The four vertical primary conduits in the stack are for oxidant inlet  101 , fuel inlet  102 , deplete oxidant outlet  103  and deplete fuel outlet  104 . Flow directions for oxidant Ox, fuel Fl, depleted oxidant dOx, and depleted fuel can be as illustrated in  FIG. 5B .  
         [0029]     An exemplary detailed structure of repeated cell unit  100 C is shown in  FIGS. 5B and 5D  to include interconnect  105 . A break-up view is shown in  FIG. 5C . The fuel cell FC elements of exemplary repeat cell unit  100 C can include a multi-layer interconnect  105 , bonding glass  107 , sealing glass  108  and planar fuel cell disk  109 . It is useful to picture a stack of these fuel cell disks, such that interconnect  105  can be used to deliver, e.g., oxidant Ox to the cathode side of a fuel cell disc  109  in the repeat cell unit  100 C and fuel Fl to a second fuel cell disc  109  in the next repeat cell unit  100 C just below. Space  107 C can be an open space, or can contain a porous material such as glass frit.  
         [0030]     The shape of the cell disk  109  could be square, circular, elliptical and others, although circular is often useful. The cell disk  109  can be bonded on the multi-layer interconnect  105  using, for example, bonding glass  107 . The repeat cell units are assembled to a cell stack using, for example, sealing glass  108 . The feeding gas (such as oxidant gas) comes out of the internal distribution conduit  110  at, for example, the center of the multi-layer interconnect, then flows radially for example along optional radial channels  111 . Radial channels  111  are optional aids to gas flow. In the absence of these channels, flow may be, for example, through space  107 F or in the typically porous electrode. The gas then reacts on the relevant electrode. The gas can of course be pressurized to flow in the opposite direction. Then, the deplete gas flows back into the multi-layer interconnect through second distribution conduits  112 . On the other side of the multi-layer interconnect (the bottom, assuming the illustrated orientation), the complimentary gas (such as fuel) feeds through an internal distribution conduit (separately connected to source gas as described below), flows radially to allow reaction at the complimentary electrode, and flows back into the multi-layer interconnect through other second distribution channels. The feeding and deplete gases are manifolded inside the multi-layer interconnect  105 , and flow in/out of the repeated cell unit through primary conduits  101 ,  102 ,  103 , and  104  illustrated at the corners of the repeated cell unit  105 .  
         [0031]     In another embodiment, gas sealing is accomplished with gaskets  208 . As illustrated in  FIGS. 6A and 6B , the repeated cell unit  200 C is constructed by a multi-layer interconnect  205 , bonding glass  207  and planar fuel cell disk  209 . Then, the repeat cell units  200 C are piled together using gaskets  208  to achieve gas-tight seal between repeat cell units  205 . The gasket material can, for example, be inorganic or metallic.  
         [0032]     A useful component of this invention is a build-in gas manifold in the multi-layer interconnect. A simple manifold structure is illustrated in  FIG. 7  (a break-up view). The primary conduits on the corners of the interconnect  305  are for oxidant inlet  301 , fuel inlet  302 , deplete oxidant outlet  303  and deplete fuel outlet  304 . The interconnect  305  is constructed by five layers  320 A,  320 B,  320 C,  320 D and  320 E. As illustrated with solid arrows, oxidant gas Ox moves, for example, through primary conduit  301 , flows to the center of second layer  320 B (an oxidant gas distribution layer) through channel  313 Ox, and then flows into the top of first layer  320 A through the internal distribution conduit  310 Ox. Then, oxidant gas flows and reacts along the radial channels  311 Ox on the top of first layer  300 A to second distribution conduits  312 Ox and flows back to second layer  320 B, where the deplete gas Dep. Ox is manifolded through space  314 Ox and channel  315 Ox to deplete oxidant outlet  303 . Channel  315 Ox is optional, but it can help increase gas flow uniformity. Similarly, through the corresponding components labeled “Fl” instead of “Ox”, fuel gas flows to the center of fourth layer  320 D (a fuel gas distribution layer) through primary conduit  302  and channel  313 Ox. Then the fuel gas goes into the bottom of fifth layer  320 E through internal conduit  310 Fl, flows and reacts along the radial channels on the bottom of fifth layer  300 E to second distribution conduits  312 Fl and flows back to fourth layer  320 D. The deplete fuel gas flows out of cell unit through open area  314 Fl, optional channel  313 Fl, and primary conduit  304 . Third layer  320 C is a separation layer between oxidant gas distribution layer  300 B and fuel gas distribution layer  320 D.  
         [0033]     The material for the gas distribution layers  320 B and  320 D can be ceramic, which can be conductive, nonconductive with conducting vias or nonconductive ceramic. Since the interconnect needs to convey electrical potential, conductance can be provided though any of many avenues that will be apparent to those of skill. The material for layers  320 A,  320 C and  320 E can be nonconductive ceramic with conducting vias, conductive ceramic, or, conveniently, metal. Layer  320 C can be non-conductive ceramic. If layers  320 A and  320 E use metal, they could be metallically joined (e.g. welded) together along edges to ensure the electrical connection between layers  320 A and  320 E.  
         [0034]     In some contexts, such as where a hydrocarbon fuel is reformed to provide hydrogen, it can be useful to extract heat from the fuel cell reaction into the initial manifold for fuel gas. A structure that provides such heat for both the oxidant gas and the fuel gas is illustrated by the multi-layer interconnect  405  shown in the break-up view of  FIG. 8 . For oxidant gas, the structure can provide pre-heating that helps increase reaction efficiency at the cathode electrode. This illustrated structure integrates oxidant gas pre-heater, hydrocarbon fuel reformer and gas manifold into the multi-layer interconnect. The oxidant gas distribution layer  320 B in multi-layer interconnect  305  is replaced by three layers, including oxidant gas preheating layer  420 B, separation layer  420 C, and deplete oxidant gas layer  420 D. Oxidant gas is heated in layer  420 B due to the layer&#39;s proximity to the fuel cell disk above and the heated deplete gas cycled to fourth layer  420 D below. Gas then goes into the top of first layer  420 A for electrode reactions. The hot depleted oxidant gas flows to fourth layer  420 D and exchanges heat with oxidant gas in second layer  420 B through separation layer  420 C. Similarly, the fuel gas distribution layer  320 D in the multi-layer interconnect  320  is replaced by three layers, including deplete fuel gas layer  420 F, separation layer  420 G and fuel processing layer  420 H. Hydrocarbon fuel gas, mixed with steam, is reformed on reforming catalyst placed in eighth layer  420 H, and then the reforming gases flow to the bottom of ninth layer  420 J for electrode reactions. The hot deplete fuel gases flow to layer  420 F. The heat needed for reforming reactions in layer  420 H is provided from hot deplete fuel gas and electrode reactions in adjacent layers  420 F and  420 J. In this structure, a useful material for top layer  420 A, bottom layer  420 H and separation layers  420 C,  420 E and  420 G is metal or other material that provides good heat transfer. The top layer  420 A and bottom layer  420 J can be metallically joined (e.g. welded) together along the edges to ensure the electrical connection. It will be recognized that the extra layers for one gas handling side of the multilayer interconnect, such as for the oxidant gas or the fuel gas, can be compacted to the structure of  FIG. 7 .  
         [0035]     The structure of oxidant pre-heat layer  420 B and fuel reforming layer  420 H can be optimized for more symmetrical flow and temperature distribution. As shown in  FIG. 9 , fuel reforming layer  420 H can be substituted with alternative layers such as layer  420 H′ or  420 H″. Appropriate baffles in preheat area  416 Fl′ or  416 Fl″ control gases flowing circularly in these layers. The fuel reforming catalyst can be placed in the fuel reforming layer accordingly to have endothermic reforming reactions take place at hot areas of the cell to improve temperature symmetry. Such baffles can be used in conjunction with a single manifold plate (per a given electrode) to position initial entry gas to receive heat from deplete gas.  
         [0036]     The thickness of individual layer in the multi-layer interconnect is, for example, between 20 μm (20 micron) and 2000 μm, such as between 50 μm and 500 μm. In certain embodiments, the thickness is from greater than or equal to one of the following lower values to less than or equal to one of the following upper values. The lower values are 20, 25, 30, 35, 40, 45, 50, 100 and 200 micron. The upper values are 100, 200, 300, 400, 500, 750, 1000, 1500 and 2000 micron.  
         [0037]     Certain fuel cell used in the invention can have edges that stay within or touching two circles with diameters +Value A and −Value B of a reference circle. Value A in certain embodiments can be 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2% or 1% of the reference diameter.  
         [0038]     In certain embodiments, the internal distribution conduit can be aligned with a point off the center of the fuel cell when the conduit&#39;s center is aligned within or touching a circle originating at fuel cell center and having diameter of B of the smallest width of the fuel cell. Value B in certain embodiments can be 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2% or 1% of the smallest width.  
         [0039]     This invention provides advantages for the fuel cell stack including: 
        1. Minimized internal thermal stress for reliable operation—the symmetrical flow passageway of oxidant and fuel gases will ensure a symmetrical gas flow and electrode reaction, and result in a symmetrical temperature distribution across the cell disk.     2. High fabrication yield for low cost fabrication—by using plain (no holes) planar tri-layer (cathode/electrolyte/anode) cell disk, the possible stress accumulation on the corners of cell disk can be reduced or eliminated, which will result in a high cell disk fabrication yield. The modular repeated cell unit structure can improve stack assembly yield. The stack sealing mechanism can increase the flatness tolerance, which will increase fabrication yield as well.     3. Integrating gas pre-heater and fuel reformer into fuel cell stack can provide high energy efficiency—The heat generated form electrode reactions could be consumed directly in stack by fuel reforming reactions and gas pre-heating. In addition, this integrated structure has advantage of easy stack heat management to avoid over-heating during operation. 
 
 Corrugated Embodiments 
       
 
         [0043]     In addition to use flat metal foil (or plate) in the multi-layer interconnect, the interconnect can also use corrugated metal foil (or plate). The corrugated metal layer can increase the bonding area of ceramic with metal, facilitate metal stress releasing through the corrugated shape, thereby making it more practical to use metallic materials that have larger CTE mismatch with ceramic components in the multi-layer interconnect structure.  
         [0000]     Metal-Sandwiched Embodiments  
         [0044]     In addition to the radial flow stack structure, a multi-layer interconnect can have internal gas manifold structure with co flow and crossing-flow in square plate. As shown in  FIG. 10A  (perspective view, three separated layers) and  FIG. 10C  (side view, all three layers), an illustrative interconnect  505  can have four primary conduits (oxidant and fuel inlets and outlets) ( 501 ,  502 ,  503 ,  504 ) located in the corners or the side of the plate. Two separated sets of gas manifold conduits/channels are embedded on the opposite surfaces of the ceramic core layer  520 B. On the illustrated side, these include first manifold conduit  517 Ox, multiple second manifold conduits  518 Ox, and third manifold conduit  519 Ox. A pair of primary conduits (e.g.,  501  and  503 ) is connected with one set of manifold conduits. Small distribution holes  532  are stamped in the surface metal layer  520 A (e.g., a foil) above the manifold conduits to deliver gas for electrode reactions, and release reaction products. Therefore, in the proposed manifold, gases flow through the triangular (for illustration) primary conduit to the manifold conduits, then to electrodes through the small distribution holes  532 . Depleted gases flow back to gas distribution channels, and then to the outlet triangular holes. This manifold structure can provide either co-flow (such as illustrated in  FIG. 10B ) or cross-flow (gas ingresses any given distribution hole  532  and may egress the same hole) of air or fuel gases at the opposite side of the interconnects. In many geometries of the fuel cell, cross flow is believed to provide greater thermal balance.  
         [0045]     One exemplary pattern of flow is illustrated in  FIG. 10B , where barriers to flow (not shown) provide that two of the primary conduits are isolated from the illustrated manifold channels, and that half of the second manifold channels serve to delivery gas, while the other half serve to collect depleted gas.  
         [0046]     Electrical connection can be, for example, through the metal layers  520 A and  520 B, and conductive vias  531 . Or, connectivity can be at the sides of the construct, such as by welded connections.  
         [0047]      FIG. 10D  shows a cut-away view oriented as shown in  FIG. 10C . In the illustration, the second manifold channels  518 Ox are parallel to second manifold channels  518 Fl. Of course, these channels can be offset by 90 degrees. As illustrated, electrical connectivity can be by, or supplemented by, a welded end plate  540 .  
         [0048]     The sandwiched interconnect has useful strength, while minimizing the use of metal, providing weight reduction. The bulk of the interconnect can be made with a good CTE match in the x-y plane with the fuel cell disk, while the metal layers are kept compliant due to their strong binding to the ceramic center layer. Thus, this structure can be used in a device adapted to start fast (providing shifting thermal gradients), and excellent thermal cycling stability. The metal layers also serve to increase the conductance of electrons into or out of the adjacent electrode. In certain embodiments, electron flow is into or from the electrode, into or from a such metal layer, and into or from lateral conductors (such as welds),  
         [0049]     The metallic layers (e.g., foil or plate)  520 A and  520 C can be flat as shown in  FIG. 10D , or corrugated structure for a better CTE adjustment with ceramic layer to match the CTE with fuel cell components.  
         [0000]     Composite Materials for CTE Matching  
         [0050]     Comparing with ceramic interconnect materials, metallic interconnects are cheaper and a favorite for commercial applications. Due to the high operating temperature of solid oxide fuel cells (SOFC), the oxidation resistant properties of metallic interconnects are important for fuel cell stack performance. The sustained oxidation of metallic interconnect will result in a high stack internal resistance and reduce fuel cell stack performance. On the other hand, the thermal expansion coefficients (CTE) of metal components must be matched with other components of cell stack.  
         [0051]     Zirconia based solid oxide fuel cells are the most common commercial fuel cells. The CTE of a zirconia based fuel cell disk is relatively small, such as about 11×10 −6  1/° C. Among high temperature alloys, only low Cr content stainless steel (such as  400  series stainless steel) has a roughly matched CTE. However, the oxidization resistant of this kind of alloy is not satisfactory at temperature higher than 650° C., which is the typical operation temperature of SOFCs. Although the high temperature oxidization resistance of some other alloys, such as  300  series stainless and Ni based high temperature alloys, is higher, these alloys are not satisfactory for use in zirconia based SOFCs due to their high CTE.  
         [0052]     In this invention, a new structure is taught to modify CTE of high temperature alloy for fuel cell application. As shown in  FIG. 11A , two thin layers of high temperature alloy ( 101 ,  103 ) are bonded on two sides of a glass ceramic core layer ( 102 ). Typically, CTE of alloy layer is much higher, and CTE of the ceramic core layer is lower than the CTE of the fuel cell disk (such as higher and lower than 11×10 −6  1/° C.). The thickness and the CTE of the ceramic core layer ( 102 ) are carefully selected. The final CTE of the multi-layer structure will be tailored to that of the fuel cell disks. Two alloy layers can be welded together along the edges to ensure the electrical connections.  
         [0053]     If the CTEs difference of alloy layer and ceramic layer is too high, intermediate layers could be used in the structure. As shown in  FIG. 11B , the CTE of the intermediate layers ( 202 ,  204 ) is between CTE of core layer ( 203 ) and alloy surface layer ( 201  and  205 ). This structure will reduce the bonding tension between core layer and alloy layers.  
         [0054]     The metal/ceramic/metal composite is particularly suited for top and bottom layers in multi-layer interconnects. For example, these can be used to form first layer  320 A, fifth layer  320 E, first layer  420 A and ninth layer  420 J. Similarly, the corrugated structure described above can be useful in these top and bottom layers.  
         [0055]     Publications and references, including but not limited to patents and patent applications, cited in this specification are herein incorporated by reference in their entirety in the entire portion cited as if each individual publication or reference were specifically and individually indicated to be incorporated by reference herein as being fully set forth. Any patent application to which this application claims priority is also incorporated by reference herein in the manner described above for publications and references.  
         [0056]     While this invention has been described with an emphasis upon preferred embodiments, it will be obvious to those of ordinary skill in the art that variations in the preferred devices and methods may be used and that it is intended that the invention may be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications encompassed within the spirit and scope of the invention as defined by the claims that follow.