Effect of grain size on nano-indentation property of Co60Fe20B20 thin film

This study investigates the nano-mechanical properties of Co60Fe20B20 thin films and the effect of the size of the grains on them. These films were sputtered onto glass substrates to thicknesses from 1000 Å to 5000 Å under the following conditions: (a) substrate temperature maintained at RT, (b) post-annealing at a treatment temperature of 150 °C for 1 h, (c) post-annealing at a treatment temperature of 250 °C for 1 h, and (d) post-annealing at a treatment temperature of 350 °C for 1 h. A plane-view image was captured under a high-resolution transmission electron microscope (HRTEM) to determine the distribution of grains. The selected-area-diffraction (SAD) pattern was obtained using HRTEM. The electron diffraction pattern revealed that the CoFeB thin film had a nano-crystallization body-centered cubic (BCC) CoFeB structure and strong CoFeB (1 1 0) crystallization. A higher annealing temperature resulted in a larger grain. The average grain size increased with the thickness of the CoFeB thin film. The hardness and Young’s modulus were obtained using nano-indentation. Results concerning the grain size and the nano-indentation measurement an increase in hardness and Young’s modulus are reasonably inferred from a smaller grain size, consistent with the “Hall–Petch” effect. The nano-indentation microstructure was obtained by scanning electron microscopy (SEM). Annealing increased the area of the nano-indentation triangle. This result is consistent with the results concerning hardness and Young’s modulus. The nano-mechanical properties of the post-annealed CoFeB thin film are worse than those of the as-deposited film.

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► A plane-view image was captured under a HRTEM to determine the distribution of grains.
► The increased hardness and Young’s modulus are reasonably inferred from a Hall–Petch effect.
► Annealing increased the area of the nano-indentation triangle by SEM observation.
► The nano-mechanical properties of the post-annealed film are worse than the as-deposited film.