Patent ID: 7488543

Claim:
An aluminum nitride joined body comprising two pieces of aluminum nitride sintered body plates joined together without using adhesive, and a metal layer formed on a portion of the junction interface thereof, wherein, as viewed on a side section passing through the center of the joined body, a plurality of voids are existing in the directly joined region where the sintered body plates are directly facing each other on the junction interface, the voids having an average length L of 0.5 to 4 μm along the junction interface, thereby forming non-joined portions due to the voids, and a non-joined ratio Q on the side section as calculated by the following formula (1), Non-joined ratio Q=(X/Y)×100 (1) where X is a length of the non-joined portion in the direction of junction interface expressed by the sum of lengths L of the voids existing in the directly joined region, and Y is a length of the directly joined region where the voids are existing, is in a range of from 0.1 to 0.5% on average.