Ceramic heater and its manufacturing method, glow plug and ion current detecting device

A ceramic heater comprising:

• an insulating ceramic substrate;
• a resistance heating element made mainly of conductive ceramic and buried in said insulating ceramic substrate;
• and
• an ion current detecting electrode portion made mainly of conductive ceramic and integral with said resistance heating element in said insulating ceramic substrate and having a portion of its own surface exposed as an ion current detecting face to the surface of said insulating ceramic substrate,
• wherein said resistance heating element is made mainly of a first conductive ceramic phase;
• said ion current detecting electrode portion being constructed such that a portion including at least a portion of said ion current detecting face is made of a second conductive ceramic phase having a better oxidation resistance than that of said first conductive ceramic phase.

A method for manufacturing a ceramic heater comprising:

• an insulating ceramic substrate;
• a resistance heating element made mainly of conductive ceramic and buried in said insulating ceramic substrate;
• and
• an ion current detecting electrode portion made mainly of conductive ceramic and integral with said resistance heating element in said insulating ceramic substrate and having a portion of its own surface exposed as an ion current detecting face to the surface of said insulating ceramic substrate;
• said method comprising:
• preparing a composite shaped body, in which an electrode shaped portion for said ion current detecting electrode portion and a heating element shaped portion for said resistance heating element are buried in a substrate shaped portion for said insulating ceramic substrate;
• sintering said composite shaped body;
• and
• forming said ion current detecting electrode portion such that a portion including at least a portion of said ion current detecting face is made of a nonmetallic conductive ceramic having a cation component of at least one nonmetallic element.