**1. Introduction**

Magnetic nanofilms have attracted increasing attention in recent years, especially in the CoFeB system. CoFeB is a soft ferromagnetic material, which has been extensively applied in spintronic devices. When a CoFeB film is thinner than 1.7 nm, it shows a perpendicular magnetic anisotropy (PMA), implying its easy axis is obviously out-ofplane [1,2]. The PMA in Ta/CoFeB/MgO stack, first identified by Ikeda et al., has promising applications in spin-transfer torque devices [3]. Moreover, magnetic tunnel junctions

**Citation:** Liu, W.-J.; Chang, Y.-H.; Fern, C.-L.; Chen, Y.-T.; Jhou, T.-Y.; Chiu, P.-C.; Lin, S.-H.; Lin, K.-W.; Wu, T.-H. Annealing Effect on the Contact Angle, Surface Energy, Electric Property, and Nanomechanical Characteristics of Co40Fe40W20 Thin Films. *Coatings* **2021**, *11*, 1268. https://doi.org/10.3390/ coatings11111268

Academic Editor: Angela De Bonis

Received: 7 October 2021 Accepted: 18 October 2021 Published: 20 October 2021

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(MTJs) have been widely investigated because of their wide applications in spintronic magnetic devices, such as reading heads of hard disks and magnetoresistance random access memories (MRAM) [4–7]. The CoFeB film was combined with the MgO layer to form MTJs. A PMA in magnetic films is an essential characteristic for MTJs [8,9]. On the other hand, 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) [10–15]. Meng et al. reported that post-annealing at 250 ◦C could effectively increase TMR about nine times [16]. The CoFeB-MgO-based MTJs are considered as a potential candidate for MRAM with high PMA, lower critical switching current density (Jc), and high TMR [17,18]. Researchers have paid great attention to increasing the PMA and the thermal stability of MTJs structure. Inserting other metal spacer layers in the MTJs system was common and effective in improving its various properties [19–21]. Tungsten (W) has a high melting point, high mechanical strength, and high-temperature thermal conductivity. In recent years, people have paid more and more attention to adding new elements to material in magnetic fields. Especially, the study of adding other elements to the CoFe matrix has also increased. However, few researchers have paid attention to adding W to CoFe alloy. 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. It can be widely used in magnetic and semiconductor applications. In our previous studies, the relationship between magnetism and structure of CoFeW films, as deposited and annealed, has been studied [22]. This study is an extension of our previous research to investigate contact angle and surface energy. However, few research studies have focused on the adhesive properties of CoFeW films. In addition, the effectiveness of CoFeW-based multilayer structure is sensitive to the temperature environment. It is of great significance to study the characteristics of CoFeW films deposited by direct-current (DC) magnetron sputtering in as-deposited and annealing conditions. The strong adhesion is a critical property for MTJ. Strong adhesion is a critical property for MTJs. Therefore, 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 Young equation was used to calculate the surface energy. Finally, this study discussed the correlation between grain size, contact angle, surface energy, and adhesion. The findings can provide a reference to future research on MTJs.
