The insulating substrate (13) has a carrier section (12) at one substrate end, a Pt film circuit (14) at the other end, and a heat generating section. On the substrate carrier section is formed a coating (21), consisting of a material with a low thermal conductivity. The Pt film circuit pref has an end section (15), and a first heat insulating gap (16) is formed between the end section and heat generating section. A second heat insulating gap (22) may be formed between the coating and the end of the Pt film circuit.
