CVD of Thin Ruby Films on Si(100) and Stainless Steel for Surface Temperature Sensor Applications

Surface temperature measurements are crucial in many applications; one promising approach is the use of thermographic phosphors. The temperatures of surfaces coated with such a material can easily be detected by measuring and evaluating the luminescence. In the present study, the CVD of chromium‐doped aluminum oxide films (ruby) on Si(100) and stainless steel substrates is investigated with respect to this application. Films are deposited in a cold‐wall reactor from oxygen and the acetylacetonates of aluminum and chromium under pressures between 200 hPa (200 mbar) and 240 hPa, and at temperatures between 1273 K and 1473 K. The growth of aluminum oxide, containing 1 % chromium, is confirmed by X‐ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X‐ray (EDX) spectroscopy. While films grown at 1273 K are mainly γ‐Al 2 O 3 and θ‐Al 2 O 3 , α‐Al 2 O 3 films are grown at higher temperatures. The films are analyzed by laser excitation with regard to the temperature‐dependent luminescence. The films consisting of mainly α‐Al 2 O 3 are promising as temperature sensors, they show the typical phosphorescence of ruby, with phosphorescence lifetimes between 2.3 ms at 298 K and 6 μs at 813 K.