Dependence of magnetic tunnel junction's reliability on oxidation condition

Abstract

Time-dependent dielectric breakdown measurements under constant voltage stress were carried out for magnetic tunnel junctions (MTJs), prepared by different oxidation techniques. Insulating barriers in MTJs were fabricated by oxidation of a predeposited Al layer with different oxidation techniques, such as conventional O-2 plasma, off-axis O-2 plasma, Ar-mixed O-2 plasma, and off-axis Ar-mixed O-2 plasma oxidations. The time to breakdown (T-BD) of the MTJs was estimated from Weibull failure distribution plot. The estimated T-BD when 63% of the junctions formed by conventional O-2 plasma oxidation failed was estimated to be about 55 s. The T-BD increased up to about 250, 750, and 2,500 s for the junctions of off-axis, Ar-mixed, and off-axis Ar-mixed O-2 plasma oxidation, respectively. We believe that the enhanced reliability of MTJs is due to the reduction of plasma damage during oxidation process, resulting in low electron trap density in the Al2O3 tunneling barrier. Low-frequency 1/f noise power density was measured to estimate the relative electron trap density as a function of the oxidation method, which supports our conjecture about the enhanced reliability of MTJs. (C) 2004 American Institute of Physics.