Structure and Optical, Electrical, and Adhesive Characteristics of CoFeB Thin Films.

This study investigated the structure and thermal, electrical, optical, and adhesive properties of two magnetic CoFeB thin films with compositions of Co40Fe40B20 and Co60Fe20B20.The thin films were deposited on a glass substrate by using direct current (DC) magnetron sputtering at room temperature (RT) and ranged in thicknesses from 25 to 200 Å. X-ray diffraction (XRD) patterns indicated that the thin films were amorphous. The activation energy (Q) of the Co40Fe40B20 and Co60Fe20B20 thin films exhibited concave up and concave down trends, respectively. The critical thickness of the films was 75 Å. The 75-Å-thick Co60Fe20B20 thin film exhibited the highest Q value, indicating that transforming the amorphous structure into a crystalline structure is difficult. When the Co concentration ratio was increased, the stability of the amorphous state of CoFeB increased apparently. The 75-Å-thick Co60Fe20B20 thin film exhibited the highest resistivity, whereas the 75-Å-thick Co40Fe40B20 thin film exhibited the lowest resistivity. As the thickness of the Co40Fe40B20 and Co60Fe20B20 thin films was increased, the transmittance decreased and absorbance increased. The Co60Fe20B20 thin film exhibited a higher surface energy and stronger adhesion than did the Co40Fe40B20 thin film.

Susceptibility of CoFeB/AlOx/Co Magnetic Tunnel Junctions to Low-Frequency Alternating Current.

This investigation studies CoFeB/AlOx/Co magnetic tunneling junction (MTJ) in the magnetic field of a low-frequency alternating current, for various thicknesses of the barrier layer AlOx. The low-frequency alternate-current magnetic susceptibility (χac) and phase angle (θ) of the CoFeB/AlOx/Co MTJ are determined using an cac analyzer. The driving frequency ranges from 10 to 25,000 Hz. These multilayered MTJs are deposited on a silicon substrate using a DC and RF magnetron sputtering system. Barrier layer thicknesses are 22, 26, and 30 Å. The X-ray diffraction patterns (XRD) include a main peak at 2θ = 44.7° from hexagonal close-packed (HCP) Co with a highly (0002) textured structure, with AlOx and CoFeB as amorphous phases. The full width at half maximum (FWHM) of the Co(0002) peak, decreases as the AlOx thickness increases; revealing that the Co layer becomes more crystalline with increasing thickness. χac result demonstrates that the optimal resonance frequency (fres) that maximizes the χac value is 500 Hz. As the frequency increases to 1000 Hz, the susceptibility decreases rapidly. However, when the frequency increases over 1000 Hz, the susceptibility sharply declines, and almost closes to zero. The experimental results reveal that the mean optimal susceptibility is 1.87 at an AlOx barrier layer thickness of 30 Å because the Co(0002) texture induces magneto-anisotropy, which improves the indirect CoFeB and Co spin exchange-coupling strength and the χac value. The results concerning magnetism indicate that the magnetic characteristics are related to the crystallinity of Co.