Joining structure between ceramic substrate and power supply connector

A joining structure joining a ceramic substrate having a metal member buried therein and a power supply connector which supplies power to the metal member, the joining structure comprising:

• a counterbore formed in the ceramic substrate having a large-diameter part and a small-diameter part formed at a bottom center portion of the large-diameter part, wherein at least a part of the metal member is exposed from a bottom of the small-diameter part;
• a stress relaxation insert member having a body part and a protrusion extending a distance below a bottom surface of the body part and being provided in the counterbore so that the body part and the protrusion are fitted into the large-diameter part and the small-diameter part, respectively;
• a brazing member connecting the power supply connector to the stress relaxation insert member, and sealing a gap between the counterbore and the stress relaxation insert member;
• and
• an active metal foil containing at least one of titanium, zirconium and hafnium, provided between the brazing member and the metal member;
• wherein the stress relaxation insert member is made of one of Kovar and Permalloy, and the brazing member is made of a metal material containing one of gold and aluminum;
• wherein the stress relaxation insert member is formed so that a ratio b/a has a value in a range of 0.3 to 0.8 and a ratio c/b has a value in a range of 0.05 to 2.0, wherein “a” denotes a horizontal length of a plane of the stress relaxation insert member on which the protrusion is formed, “b” denotes a horizontal length of the protrusion, and “c” denotes a height of the protrusion;
• and
• wherein a side clearance on one side between the counterbore and the stress relaxation insert member is 0.2 mm or less.