The influence of sintering additives on the lifetime of the heater for sensor application with Al2O3 substrate

A micro-heater was fabricated by co-firing the laminates of Al2O3 green sheets with Pt heater pattern and its lifetime characteristics were studied in relation to the substrate conditions by varying the sintering temperatures and the sintering additives such as MgO, CaO, and SiO2. The MgO-doped heater showed the longer lifetime than undoped, CaO-doped or SiO2-doped ones, and the heater lifetime increased with the sintering temperature. This arose from the improvement of connectivity and homogeneity of the Pt pattern by the densification of Pt particles or Al2O3 substrate. The migration of the Mg2+ ion toward the negative electrode was observed as a darkened phase and analyzed by micro-compositional analysis in the heater operated at high temperature. Its tendency was proportional to increasing the MgO doping into high purity Al2O3. The desirable amount of MgO doping was 7 mol% both for prevention of Mg2+ ion migration and for increasing heater lifetime. (C) 1998 Elsevier Science B.V. All rights reserved.