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Alumina, Al2O3, is one of the technologically most important ceramic materials. Due to the existence of a variety of different polymorphs, it finds use in a wide range of applications. For example, crystalline alumina phases are commonly utilized in wear-resistant coatings due to their beneficial mechanical and thermal properties. In the present work, crystalline alumina thin films have been deposited using high power impulse magnetron sputtering (HIPIMS) of an Al target in Ar/O2 gas mixtures. HIPIMS is a new, promising technique for ionized physical vapor deposition (I-PVD), in which a high degree of ionization of the deposition flux as well as an inherently high energy of the depositing species can be achieved at relatively low average power, by applying high power pulses with a low duty factor (typically around 1 %) to a conventional sputtering target [See, e.g., Helmersson et al., Thin Solid Films 513, 1 (2006)]. Stoichiometric alumina films could be grown in a stable and essentially arc free process, provided that the total pressure was sufficiently high. The composition of the films was determined by Rutherford backscattering analysis and stoichiometric alumina films could be deposited at rates which are relatively high compared to the deposition rate for pure Al metal and comparable to, or even higher than, what can be achieved with traditional DC or pulsed DC deposition methods. The films were investigated by x-ray diffraction, as well as scanning and transmission electron microscopy. Films deposited directly onto Si substrates at a substrate temperature of 400 °C were found to have a microstructure consisting of small, equiaxed grains with a diameter of the order of 10 nm, and with γ-alumina as the only detectable crystalline polymorph. No evidence for any amorphous content was found. The results demonstrate the potential of depositing dielectric films at relatively high rates using HIPIMS. In addition, HIPIMS deposition of such films opens the possibility of utilizing the ionized deposition flux to improve the film quality and affect the structure of the coatings, also at reduced substrate temperatures. |