Production, Characterisation and Optimization of Ni/AL Thin Films

The aim of this study is to production and characterize multilayer Ni/Al thin films on flexible acrylic acetate substrates by the sputtering technique and to determine the fabrication parameter levels that allow achieving the highest saturation magnetization (hMS) for potential applications. Firstly, Ni/Al thin films were produced with different important fabrication parameters such as Ni deposition rate (Ndr), Al layer thickness (Alt) and total film thickness (Tft). Content analysis of the films performed by energy dispersive X-ray spectroscopy showed that the Ni content increased with the increase of Ndr, while the increase of Alt and Tft caused a decrease in the Ni content. It was found that the highest change in Ni content of the films was caused by Alt. Structural analysis by Grazing Incidence X-ray Diffraction showed that all films grew in a face-centered cubic structure proportional to the Ni and Al content amounts. Film surface imaging performed by scanning electron microscopy showed that the film surfaces were severely affected by the Ndr and Alt enhancement, however less affected from the increase in Tft. The film surfaces were found to exhibit homogeneous and smooth morphology with the increase of Ndr and Alt. In the magnetic analyses performed with the vibrating sample magnetometer, it was found that the saturation magnetization (MS) values of the films increased with the increase of Ndr and decreased with the increase of Alt and Tft. The coercive field (HC) values of the films were also determined to slightly decrease with the increase of Ndr and Alt. However, it was found that the HC values of the films changed a little and remained almost constant with the increase of Tft. Afterwards, an experimental series was designed using the Taguchi method, to obtain Ni/Al thin films with the hMS value. Taguchi method was applied for the hMS with the "larger is better" approach. From the responses, signal/noise ratios, mean values, confidence interval, hMS estimate, and quality loss were calculated for the main responses. The production parameter levels that should be achieved with the hMS value of the film were determined. According to the performance estimation, the hMS value of the film was predicted as 532.6 ± 6.2 emu/cm3 with a 95% confidence interval. A validation experiment was also conducted, and the obtained response was compared with the predicted values. The validation experiment showed that the MS value of the film was 528.6 emu/cm3, which is within the confidence interval and slightly below the predicted hMS value. In conclusion, multilayer Ni/Al thin films with the possible hMS value were succesfully fabricated by the sputtering technique for potential applications such as read-write heads, micro-electromechanics systems, magnetic random-access memory, and magnetic sensors.