Dielectric Characteristics of Magnetic Tunnel Junctions Using Amorphous CoNbZr Layers

Abstract

Magnetic tunnel junctions (MTJs) consisting of amorphous CoNbZr layers have been investigated and compared with traditional MTJs using Ta layers. The amorphous CoNbZr layer was employed as a buffer layer under the pinning layer IrMn in TiN/CoNbZr/IrMn/CoFe/Ru/CoFe for better uniformity of barrier. To investigate the dependence of the reliability of the MTJs on the bottom electrode, we carried out time-dependent dielectric breakdown (TDDB) measurements under constant voltage stress. The Weibull fit of our data clearly shows that tBD scales with the thickness uniformity of MTJ’s tunnel barrier. Assuming a linear dependence of log(tBD) on stress voltages, we obtained a lifetime of 104 years at an operating voltage of 0.4 V for MTJs with CoNbZr layers. This study shows that the reliability of the new MTJ structure was improved due to the ultrasmooth barrier because the surface roughness of the bottom electrode influenced the uniformity of the tunnel barrier.