Heating device
A heating device includes an electrode embedded near the heating surface of the ceramic base substantially in parallel to the heating surface. In the rear surface of the ceramic base, a terminal hole extending toward the electrode is formed. Between the bottom surface of the terminal hole and electrode, a conductive ceramic member is embedded and connected to the electrode. The conductive ceramic member has a thermal expansion coefficient equal to that of the ceramic base. The electrode and terminal are electrically connected through the conductive ceramic member.
1. A heating device comprising:
a plate-shaped base mainly composed of an insulating ceramic;
a planar electrode embedded near a first surface of the base;
a terminal hole drilled in an opposed second surface of the base toward the electrode and having a terminus end spaced a distance from the electrode;
an electrical terminal inserted in the terminal hole; and
an electrically conductive ceramic member, having a thermal expansion coefficient equal to that of the insulating ceramic of the base, embedded in the base and located between, and in direct electrical contact with, the terminus end of the terminal hole and the electrode, and connected to the electrode in the base, whereby the electrode and the electrical terminal are electrically connected at least through the conductive ceramic member.
2. The heating device according to claim 1 , wherein the conductive ceramic member has a plate-shape, wherein a part of a main surface of the conductive ceramic member defines at least a portion of the terminus end of the terminal hole, and wherein the main surface of the conductive ceramic member is larger than the terminus end of the terminal hole.
3. The heating device according to claim 1 , wherein the conductive ceramic member has a recess defining the terminus end of the terminal hole, and also defining portions of threaded side surfaces of the terminal hole.
4. The heating device according to claim 1 , wherein the conductive ceramic member has a protruding shape whose surface is exposed to define a portion of the terminus end of the terminal hole, wherein the surface of the protruding shape is smaller than the terminus end of the terminal hole.
5. The heating device according to claim 1 , further comprising a metallic electrode material interposed between the conductive ceramic member and the terminus end of the terminal, wherein a planar part of the metallic electrode material exposed at the terminus end of the terminal hole is smaller than the terminus end of the terminal hole.
6. The heating device according to claim 1 , wherein a volume resistivity of the conductive ceramic member is not more than 10 Ω·cm.
7. The heating device according to claim 6 , wherein the base and the conductive ceramic member are mainly made of aluminum nitride ceramic, and the conductive ceramic member is made of aluminum nitride containing carbon fibers.