Thermal, magnetic, electric, and adhesive properties of amorphous Co60Fe20B20 thin films

Abstract

In this experiment, a Co60Fe20B20 target is used to deposit a monolayered Co60Fe20B20 thin film on glass substrate by dc magnetron sputtering to a thickness of 1000–5000Å under the following conditions; (a) the substrate temperature (Ts) is maintained at room temperature (RT), (b) post-annealing at TA=150°C for 1h, (c) post-annealing at TA=250°C for 1h, and (d) post-annealing at TA=350°C for 1h. This study analyzes the thermal, magnetic, electric, and adhesive properties of amorphous Co60Fe20B20 thin films with thicknesses from 1000 to 5000Å using the sputtering method. X-ray diffraction (XRD) reveals that each Co60Fe20B20 thin film had an amorphous structure at room temperature. XRD demonstrates that post-annealing treatment made the CoFeB films more crystalline or nanocrystalline. To elucidate the transformation of an amorphous CoFeB film to a crystalline structure, Kissinger’s formula is used to calculate the activation energy (Q) of crystallization. The results indicate that activation energy has a concave-up feature and the critical thickness of activation energy is 3000Å in the amorphous state. The 3000Å-thick of as-deposited CoFeB film forms a crystalline state more easily than any other film. The plots of the magnetic properties, including low-frequency alternative-current magnetic susceptibility (χac), saturation magnetization (Ms), and remanence magnetization (Mr), are concave-down feature. The results concerning the χac properties of CoFeB films indicate that post-annealing at 150 and 250°C increases because of magneto nanocrystalline anisotropy. And the 3000Å-thick of each condition is a critical point. However, post-annealing at TA=350°C for 1h reduces χac by disturbance, weakening magnetic spin coupling. In addition, the Ms and Mr results of each condition show the similar trend to χac. The electrical resistivity (ρ) of the as-deposited film exceeds that of the post-annealed films because the grain boundaries and the surface scatter the electrons, so the as-deposited film has a higher ρ than the post-annealed films. Thinner films also have a higher ρ. The surface energy and adhesion of the CoFeB films follow the same trend as the fitter Kissinger plot. This result suggests that stronger crystallization is associated with a lower surface energy and weaker adhesion. The surface energy plot exhibits a concave-up feature and the critical thickness is 3000Å in all cases. Based on the above properties, CoFeB films can be utilized in magnetic recording media, semiconductors, and seed layer applications.