Improvement of Heating Characteristics of Molybdenum Silicide Thin Film Electric Heaters

Abstract

Molybdenum silicide (MoSi₂) has high electrical conductivity as much as metal, and high chemical stability than such as SiC in various atmospheres. Therefore, many kinds of MoSi₂ bulk-type heaters are practically used for operation up to 1800°C, which is higher than that 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 crucible by RF magnetron sputtering and evaluate their characteristics. MoSi₂ thin film was deposited on outside of the alumina crucible without heating substrate and then Pt wire attached using Pt paste by sintering in vacuum. This MoSi₂ thin film heaters showed almost linear R-T characteristics and uniform heating state. They also showed good controllability of voltage and stability of power-T characteristics to operate up to 1000°C. However, at 1300°C of heating temperature, heating area of MoSi₂ thin film decreased caused by the reaction of 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 linier R-T characteristics up to 1200°C. But, the temperature coefficient of resistance changed as heating operation was repeated. This is due to the diffusion of Mo atoms into MoSi₂. Thus, thin film heater was fabricated with Mo₃Si whose content of Mo is more than that of MoSi₂. This heater showed less diffusion of Mo or Pt atoms into thin film and excellent practical characteristics up to 1000°C.