Effect of annealing atmosphere on MgO thin film for tunneling magnetoresistance sensor

Magnesium oxide (MgO) thin films are the most currently used as magnetic barrier shields in tunneling Magnetoresistance (TMR) sensors. In this work, MgO (50 nm) film on silicon substrates was annealed at different temperatures (250, 350, and 450 degrees C) and atmospheres (Argon, Nitrogen, and air). The structure, morphology, chemical composition, and thickness were investigated by using a focused-ion beam scanning electron micro-scope, atomic force microscopy, and X-ray photoelectron spectroscopy techniques. Increasing annealing tem-perature in a normal air atmosphere increases the film's thickness and roughness due to grain growth induced by Magnesium hydroxide (Mg(OH)2) formation. On the contrary, annealing in Argon does not significantly affect the thickness and roughness of the film. Furthermore, the dielectric breakdown and hardness of the film increase. The mechanism of the change of physical properties of the film due to annealing was elucidated by a qualitative model.