Improvement of Saturation Magnetization of Sputtered Fe/Al Multilayer Thin Films Using Taguchi Method Supported by ANOVA, Response Surface Methodology and Regression Analysis

Abstract

Taguchi method has been conducted to improve the saturation magnetisation, M_s, of Fe/Al multilayer thin films deposited using a dual-target magnetron sputtering. The M_s values were obtained from the magnetic hysteresis loops. To evaluate the influence of deposition factors on M_s by using the Taguchi method, L9 orthogonal array with three deposition factors (A — Fe deposition rate, B — Al deposition rate, and C — Fe layer thickness) was carried out with nine experiments at three levels. For the signal-to-noise ratio of the "larger is the better", the improved M_s has been obtained at A3B2C3, where factor A is 0.12 nm/s, factor B is 0.03 nm/s, and factor C is 25 nm. At A3B2C3, a verification experiment was carried out with a 95% confidence level to confirm the prediction of 1597.6 emu/cm³, and in the experimental run,  M_s,exp  was found  to be  1649.0 emu/cm³, which  was  an improvement  from  the highest initial run,  i.e.,  M_s,ini = 1540.2 emu/cm³,  among prescribed runs. Analysis of variance was imposed to obtain the F-ratio and contribution percentage of each deposition factor. Also, the interactions of the deposition factors were determined with response surface methodology. For the structural properties at the best factor combinations, X-ray diffraction experiments revealed that Fe/Al films at A3B2C3 were crystallised with the mixed phase of face-centred cubic and body-centred cubic structures. According to scanning electron microscope images, the film surface is almost uniformly shaped. Furthermore, the model of M_s has also been developed using regression analysis as a function of the deposition factors A, B, and C. Then, from the regression model, high statistical performance was obtained, with values of R² and R²(adj) being 100 and 100%, respectively. It is seen that the Taguchi method supported by response surface methodology, analysis of variance, and regression analysis turned out to be very successful in finding the factors with proper levels in order to improve M_s of Fe/Al multilayer thin fims within the prescribed limit.