Effect of annealing atmosphere on hydration behavior of MgO thin film in tunneling magnetoresistance sensor

Abstract The magnesium oxide (MgO) thin films are well known as a magnetic shield in read/write sensor head in a hard disk drive (HDDs). The production room regulates the humidity to approximately 50% RH in the HDD manufacturing process, which is initiating the hydration reaction with MgO films. In this work, MgO thin films were heat-treated at 450 °C under different gases (Ar, N2, and air) and stored in controlled humidity to understand and estimate the hydroxide (Mg(OH)2) formation. X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), and focused ion beam scanning electron microscope (FIB-SEM) were employed to estimate the chemical reactions, surface morphology, and thickness of MgO films. It is found that hydration layer formation increased 28%, 42%, and 47%, respectively, for Ar, N2, and air annealed films. Furthermore, the thickness of the MgO films varied differently with different annealing conditions and found that it is proportional to the hydration reaction. The result of this study might be helpful to estimate the better optimization process of read/write sensor head of HDD production.