Flow sensor, method of manufacturing the same and fuel cell system

A method of manufacturing a flow sensor, comprising:

• forming an insulation layer as a thin film on a surface of a semiconductor substrate;
• providing a heating element on a surface of the insulation layer;
• providing thermopiles on both sides of the heating element and spaced by a same distance on a surface of the insulation layer;
• forming a gap at the semiconductor substrate under regions of the thermopiles extending bonding portions at ends thereof and to the heating element, and wherein a semiconductor material is used as at least a part of a material that makes up the thermopiles;
• and
• wherein ambient temperature dependence of the thermopiles is kept at a substantially constant ratio to ambient temperature dependence of the flow sensor attributable to factors other than the thermopiles by controlling the dose of an impurity with which the semiconductor material is doped.

A fuel cell system including a flow sensor disposed within a pipe which supplies gas to a fuel reactor and/or a fuel cell main body, said flow sensor comprising;

• a semiconductor substrate;
• an insulation layer formed as a thin film on a surface of the semiconductor substrate;
• a heating element provided on a surface of the insulation layer;
• at least one temperature measuring element provided on at least one side of the heating element on the surface of the insulation layer;
• and
• a gap formed at the semiconductor substrate under at least parts of the heating element and temperature measuring element, the temperature measuring element having ambient temperature dependence which cancels ambient temperature dependence of the flow sensor attributable to factors other than the temperature measuring element.