Improvement of heating characteristics of molybdenum silicide thin film electric heaters

Molybdenum silicide (MoSi 2 ) has an electrical conductivity as high as that of a metal, and greater chemical stability than that of, for example, SiC, in various atmospheres. Therefore, many kinds of MoSi 2 bulk‐type heaters are used in practical operations up to 1800 ° C, which is higher than the temperature of SiC heaters. However, MoSi 2 is fragile at room temperature and has low creep resistance at high temperature. The purpose of this study is to fabricate heaters using thin films of MoSi 2 deposited on alumina substrates and crucibles by RF magnetron sputtering and to evaluate their characteristics. MoSi 2 thin film was deposited on the outside of an alumina crucible without heating the substrate and then Pt wire was attached using a Pt paste with sintering in a vacuum. This MoSi 2 thin film heater showed almost linear resistance–temperature ( R – T ) characteristics and a uniform heating state. It also showed good controllability of voltage and stability in the power– T characteristics for operations up to 1000 ° C. However, at a heating temperature of 1300 ° C, the heating area of MoSi 2 thin film decreased because of the reaction between Pt and MoSi 2 in the case of long‐term heating. Thus, Mo thin film was deposited as a buffer layer between Pt and MoSi 2 thin film to prevent such a reaction. This thin film heater showed good linear R – T characteristics up to 1200 ° C. However, the temperature coefficient of resistance changed with repeated heating operation as a result of the diffusion of Mo atoms into MoSi 2 . Thus, a thin film heater was fabricated with Mo 3 Si, having a higher Mo content than MoSi 2 . This heater showed a low degree of diffusion of Mo or Pt atoms into the thin film and had excellent practical characteristics up to 1000 ° C. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 168(2): 11–19, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20806