Annealing Effect on the Contact Angle, Surface Energy, Electric Property, and Nanomechanical Characteristics of Co40Fe40W20 Thin Films

Wen-Jen Liu,Ko-Wei Lin,Tian-Yi Jhou,Po-Chun Chiu,Yuan-Tsung Chen,Te-Ho Wu,Shih-Hung Lin,Chi-Lon Fern,Yung-Huang Chang

doi:10.3390/coatings11111268

Abstract

This study investigated Co40Fe40W20 single-layer thin films according to their corresponding structure, grain size, contact angle, and surface energy characteristics. Co40Fe40W20 alloy thin films of different thicknesses, ranging from 10 to 50 nm, were sputtered on Si(100) substrates by DC magnetron sputtering. The thin films were annealed under three conditions: as-deposited, 250 °C, and 350 °C temperatures, respectively. The Scherrer equation was applied to calculate the grain size of Co40Fe40W20 thin films. The results show that the grain size of CoFe(110) increased simultaneously with the increase of post-annealing temperature, suggesting that the crystallinity of Co40Fe40W20 thin films increased with the post-annealing temperature. Moreover, the contact angles of all Co40Fe40W20 thin films were all less than 90°, suggesting that Co40Fe40W20 thin films show changes in the direction of higher hydrophilicity. However, we found that their contact angles decreased as the grain size of CoFe increased. Finally, the Young equation was applied to calculate the surface energy of Co40Fe40W20 thin films. After post-annealing, the surface energy of Co40Fe40W20 thin films increased with the rising post-annealing temperature. This is the highest value of surface energy observed for 350 °C. In addition, the surface energy increased as the contact angle of Co40Fe40W20 thin films decreased. The high surface energy means stronger adhesion, allowing the formation of multilayer thin films with magnetic tunneling junctions (MTJs). The sheet resistance of the as-deposited and thinner CoFeW films is larger than annealed and thicker CoFeW films. When the thickness is from 10 nm to 50 nm, the hardness and Young’s modulus of the CoFeW film also show a saturation trend.

Highlights

Magnetic nanofilms have attracted increasing attention in recent years, especially in the CoFeB system
The corresponding X-ray diffraction patterns (XRD) of the CoFeW films have been proved in our previous literature [22]
It was indicated that the CoFe(110) peak and specific Fe2O3(320), WO3(002), Co2O3(422), and Co2O3(511) oxide peaks are displayed in XRD

Summary

Introduction

Magnetic nanofilms have attracted increasing attention in recent years, especially in the CoFeB system. CoFeB magnetic film has been extensively used as a free or pinned layer in MTJs. CoFeB and MgO layers via post-annealing result in a high spin polarization and high tunneling magnetoresistance (TMR) [10,11,12,13,14,15]. Researchers have paid great attention to increasing the PMA and the thermal stability of MTJs structure. The research on the efficacy of CoFeW is noteworthy because it is a promising material It is usually inserted into MTJ as a free layer or pinned layer or is combined with other layers in a multilayer structure. Strong adhesion is a critical property for MTJs. this study measured the contact angle of Co40Fe40W20 thin films with different thicknesses and heat treatment conditions by a measuring analyzer via deionized (DI) water and glycerol. The findings can provide a reference to future research on MTJs

Materials and Methods

Results

Surface Energy