Wiring connection method and functional device

A wiring connection method, comprising:

• forming a metal layer on at least one of a connecting electrode of a first substrate and a connecting electrode of a second substrate;
• placing the first substrate and the second substrate together in order that the connecting electrode of the first substrate and the connecting electrode of the second substrate face each other via the metal layer;
• increasing temperature to an anodic bonding temperature;
• and
• applying DC voltage to the first substrate and the second substrate while maintaining the temperature to anodically bond the first substrate and the second substrate and to melt the metal layer,
• wherein an alloy and/or an intermetallic compound, which does not melt at temperatures the same as or lower than the anodically bonding temperature, is formed between the metal layer and the connecting electrode of the first substrate, and/or, between the metal layer,
• the connecting electrode of the first substrate and the connecting electrode of the second substrate do not contact but form a space when the first substrate and the second substrate are placed together in a stage before the metal layer is formed, and the metal layer protrudes either from the first substrate or from the second substrate, on which the metal layer is formed, and has a size equal to or smaller than the volume of the space;
• and
• the metal layer is made of a metal that forms at least an intermetallic compound or at least an alloy between the connecting electrode of the first substrate and the connecting electrode of the second substrate when melted at the anodic bonding temperature, and the melting temperature of the intermetallic compound or the alloy is higher than the melting temperature of the metal layer as a single body,
• whereby the connecting electrode of the first substrate and the connecting electrode of the second substrate are electrically connected, and
• wherein the combination of materials for at least one of the connecting electrode of the first substrate and the connecting electrode of the second electrode and for the metal layer is one of Sn—Cu, Sn—Ag, In—Ag, Sn—Au, In—Au, Sn—Ni, and Sn—In.