NOVELTY - A solid oxide fuel cell device (10) comprises elongate substrate having reaction zone along first portion of a length to be heated to an operating reaction temperature, and cold zone along second portion of the length to remain at low temperature below the operating reaction temperature when the reaction zone is heated; first multi-layer anode-cathode structure having anodes in opposing relation with cathodes within the substrate in the reaction zone and electrolyte between each of the opposing anodes and cathodes; and external contact pads.    USE - For solid oxide fuel cell system.    ADVANTAGE - The device is a multi-layer structure and may be made using a multi-layer co-fired approach. It is monolithic, which helps to make it structurally sound, and lends itself to traditional high volume manufacturing techniques such as those used in multi-layer co-fired ceramic (MLCC) production of capacitor chips. Thin electrolyte layers can be achieved within the structure at no additional cost or complexity.    DETAILED DESCRIPTION - The solid oxide fuel cell device comprises elongate substrate having length that is the greatest dimension, coefficient of thermal expansion having only one dominant axis that is coextensive with the length, opposing first and second sides along the length, reaction zone along a first portion of the length to be heated to an operating reaction temperature, and cold zone along a second portion of the length to remain at low temperature below the operating reaction temperature when the reaction zone is heated; first multi-layer anode-cathode structure having anodes in opposing relation with cathodes within the substrate in the reaction zone and electrolyte between each of the opposing anodes and cathodes, each of the anodes and cathodes having tab portions extending from within the substrate to the opposing first or second side to form electrical pathways to a respective exposed anode and cathode surfaces; and external contact pads on the opposing first and second sides over the exposed anode and cathode surfaces to electrically connect the anodes and cathodes in series and/or parallel. INDEPENDENT CLAIMS are included for:    (1) a solid oxide fuel cell system;    (2) a method of using the solid oxide fuel cell device; and    (3) a method of using the solid oxide fuel cell system.    DESCRIPTION OF DRAWING(S) - The figure is a side cross-sectional view of the solid oxide fuel cell device.    Solid oxide fuel cell device (10)    Ends (11ab)    Fuel inlet (12)    Fuel passage (14)    Fuel outlet (16)    Air inlet (18)    Air passage (20)