OXIDATION OF MOLYBDENUM SILICIDE THIN-FILM TEMPERATURE SENSORS

The oxidation characteristics of molybdenum silicide (MoSix) thin films used in resistance-type temperature sensor applications were investigated. In the present study, the electrical resistance variation of sensor films as a function of temperature was measured as an indication of sensor oxidation characteristics. The oxidation resistance of MoSix films was observed to depend significantly on their silicon content. For comparatively molybdenum-rich MoSix (as against stoichiometric MoSi2) sensor films, poor oxidation resistance was observed. Sensors of this category showed linear positive, i.e. metallic, temperature coefficient of resistance (TCR) characteristics up to about 700-degrees-C, followed by sudden disarray of the electrical resistance due to intense oxidation. At the other extremity, relatively silicon-rich MoSix sensor films, e.g. containing 92 at.% Si, exhibited non-linear and negative TCR characteristics, although good oxidation resistance could be obtained by the formation of a protective SiO2 layer. In contrast, a near stoichiometric MoSi2 sensor film showed relatively good oxidation resistance as sell as positive TCR values of (3.1-3.9) x 10(-3) K-1 up to 1450-degrees-C for at least five test cycles. This result indicates that a self-passivating SiO2 layer forms effectively on the top surface of MoSi2 sensors as expected, thus giving the desired sensor performance.