Reactive Sputter Deposition of Alumina Coatings

Highly ionized pulse plasma processes (HIPP processes) like High Power Impulse Magnetron Sputtering HIPIMS and Modulated Pulse Power MPP have matured in recent years. Current research focuses on the development for industrial processes. HIPP processes offer a tool for tailoring the film properties and to improve hardness, density, refractive index, and further properties beyond state of the art. Alumina coatings are used besides application in cutting tools as insulator for electric and sensor applications. This paper focuses on the process development of an industrial process for deposition of alumina with improved properties regarding the use as insulator. Concerning productivity a high rate deposition process is required for economic production. Therefore, the deposition rate must be increased or the film properties improved in a way that thinner films exceed reference films prepared with state of the art technology. MPP in comparison to a mid-frequency (MF-) process was investigated and the resulting rates are reported. The films were prepared without feedback control in the transition regime close to the threshold of the oxide mode. Regarding the insulating properties the films were characterized by their critical leakage field strength. MPP films with less than 1 μm thickness showed a critical leakage field strength up to 2.9 V/nm. The SEM cross sections of the prepared films showed a dense glassy structure for all the HIPP films.