Comparison Between In-situ Annealing and External Annealing For Barium Ferrite Thin Films Made by RF Magnetron Sputtering

Due to their large magnetic anisotropy perpendicular to the film plane, barium ferrite thick films (BaFe12O19, or BaM) with c-axis orientation are attractive candidates for microwave applications [1,2]. Barium ferrite thin films on silicon substrates without under layer have been deposited under various conditions by RF magnetron sputtering. The structure of the as-grown films is amorphous. External annealing in air has been done at 950°C for ten minutes to crystallize the films. C-axis oriented thin films with squareness of about 0.87 and coercivity of about 3.8KOe are obtained.Thick BaM films with c-axis orientation are difficult to achieve with one single deposition. Multilayer technique looks promising to grow thick films [3]. The external annealing process is difficult to incorporate with the multilayer procedure. An in-situ annealing procedure has been developed to obtain films, which can be used as the basic component for future multilayer deposition. Barium ferrites are first magnetron sputtered on bare silicon substrates in Ar + O2 atmosphere at substrate temperature of 500-600°C, the deposition pressure was kept about 0.008 torr. After the deposition, the temperature of the substrate is immediately increased to about 860°C for ten minutes in 140 torr of argon (80%) and oxygen (20%) mixture of gas, which was introduced into the chamber without breaking the vacuum. With the in-situ process, c-axis oriented thin films of 0.88 squareness and coercivity value of about 4.3KOe are obtained.Both annealing methods seem to have the similar effect on the perpendicular squareness and coercivity at various film thicknesses. The average value of the saturation magnetization Ms obtained from the in-situ annealing using multilayer technique is higher than that of the external one. We have grown films up to 1.0 micron thickness using the multilayer technique, in which three layers of 0.3 μm thickness each are deposited until the final thickness is reached. After the deposition of each layer, it was in-situ annealed before starting the deposition of the next layer. With the multilayer technique, coercivity of about 3.5 KOe and average value of the saturation magnetization Ms of about 4.0 K Gauss is obtained.