Improvement of heating characteristics of molybdenum silicide thin film electric heaters

Abstract

AbstractMolybdenum silicide (MoSi2) 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 MoSi2 bulk‐type heaters are used in practical operations up to 1800°C, which is higher than the temperature of SiC heaters. However, MoSi2 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 MoSi2 deposited on alumina substrates and crucibles by RF magnetron sputtering and to evaluate their characteristics. MoSi2 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 MoSi2 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 MoSi2 thin film decreased because of the reaction between Pt and MoSi2 in the case of long‐term heating. Thus, Mo thin film was deposited as a buffer layer between Pt and MoSi2 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 MoSi2. Thus, a thin film heater was fabricated with Mo3Si, having a higher Mo content than MoSi2. 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