Oxidation of molybdenum silicide thin film temperature sensors

Abstract

The oxidation characteristics of molybdenum silicide (MoSi x ) 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 MoSi x films was observed to depend significantly on their silicon content. For comparatively molybdenum-rich MoSi x (as against stoichiometric MoSi 2) 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°C, followed by sudden disarray of the electrical resistance due to intense oxidation. At the other extremity, relatively silicon-rich MoSi x 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 SiO 2 layer. In contrast, a near stoichiometric MoSi 2 sensor film showed relatively good oxidation resistance as sell as positive TCR values of (3.1–3.9) × 10 −3 K −1 up to 1450°C for at least five test cycles. This result indicates that a self-passivating SiO 2 layer forms effectively on the top surface of MoSi 2 sensors as expected, thus giving the desired sensor performance.