Patent ID: 7928347

Claim:
A heating unit comprising: an AlN substrate including a main surface; an elongated heat-generating resistor provided on the main surface of the AlN substrate; and a protection layer for the heat-generating resistor; wherein the protection layer includes a first cover layer covering the heat-generating resistor, a second cover layer covering the first cover layer, and a third cover layer that covers at least part of an exposed region of the main surface where the first cover layer is not provided, wherein the first cover layer is made of crystallized or semi-crystallized glass having a higher crystallization temperature by at least 50° C. than the glass softening point of the crystallized or semi-crystallized glass, the second cover layer being made of non-crystalline glass, wherein the third cover layer is made of non-crystalline glass higher in glass softening point than the non-crystalline glass constituting the second cover layer, and wherein the second cover layer is provided on the first cover layer and at least part of the third cover layer.