Effect of Annealing on the Characteristics of CoFeBY Thin Films

Wen-Jen Liu,Po-Wei Chi,Yuan-Tsung Chen,Ding-Yang Tsai,Yi-Chen Chiang,Te-Ho Wu,Yung-Huang Chang

doi:10.3390/coatings11020250

Abstract

In this study, the addition of Y to CoFeB alloy can refine the grain size to study the magnetic, adhesion and optical properties of as-deposited and annealed CoFeB alloy. XRD analysis shows that CoFeB(110) has a BCC CoFeB (110) nanocrystalline structure with a thickness of 10–50 nm under four heat-treatment conditions, and a CoFeB(110) peak at 44° (2θ). The measurements of saturation magnetization (MS) and low frequency alternate-current magnetic susceptibility (χac) revealed a thickness effect owed to exchange coupling. The maximum MS of the 300 °C annealed CoFeBY film with a thickness of 50 nm was 925 emu/cm3 (9.25 × 105 A/m). The maximum χac value of the 300 °C annealed CoFeBY nanofilms with a thickness of 50 nm was 0.165 at 50 Hz. After annealing at 300 °C, CoFeBY nanofilms exhibited the highest surface energy of 31.07 mJ/mm2, where the thickness of the nanofilms was 40 nm. Compared with the as-deposited CoFeBY nanofilms, due to the smaller average grain size after annealing, the transmittance of the annealed nanofilms increased. Importantly, when a CoFeB seed or buffer layer was replaced by a CoFeBY nanofilm, the thermal stability of the CoFeBY nanofilms was improved, promoting themselves on the practical MTJ applications.

Highlights

Since the discovery of Co50Fe50 in CoFe systems by Ellis in 1927 and Elmen in 1929, it has shown good soft magnetic properties [1]
The purpose of this study is to investigate the changes of the structure and magnetic properties of CoFeBY films with the thickness of the films, and to study the CoFeBY films after heat treatment, so as to determine whether they will change due to the high temperature environment, changing their magnetic efficiency
When the annealing temperature is 250 ◦C, the CoFeB layer is amorphous, but when the annealing temperature is increased to 300 ◦C, the amorphous phase becomes nanocrystalline, which leads to the tunneling magnetoresistance (TMR) change of magnetic tunnel junctions (MTJ) [25]

Summary

Introduction

Since the discovery of Co50Fe50 in CoFe systems by Ellis in 1927 and Elmen in 1929, it has shown good soft magnetic properties [1]. Due to the unique properties of rare earth elements, the high temperature resistance, mechanical strength, ductility and other physical properties of magnetic films can be improved. They can form compounds with transition metals such as iron, nickel and cobalt, some of which have Curie temperatures much higher than room temperature. Perhaps its properties can be used to improve the thermal stability of magnetic films at high temperature. There are few studies on the addition of rare earth elements in soft magnetic CoFe alloys. To improve the magneto-thermal stability of CoFeB alloy, it is very important to study the effect of Y addition on the structure and magnetic properties of CoFeB alloy. The main purpose of this study is to investigate the structure and magnetic properties of CoFeBY thin films with different thicknesses, and to discuss the structure, magnetic properties, adhesion and optical properties of CoFeBY films after heat treatment

Objectives

Methods

Results