TMR film and head technologies

We have developed Al-O barrier magnetic tunnel junctions (MTJs) and obtained a magneto-resistance (MR) ratio of 27% with a resistance-area product RA of about 3 Ωμm 2 . We have also studied Ti-O and Mg-O as new low barrier energy materials for MTJs. Ti-O barrier MTJs showed a very small RA of less than 2 Ωμm 2 . We can obtain a high MR ratio of about 100% for Mg-O barrier MTJs with an RA of 2 to 3 Ωμm 2 using a CoFeB magnetic layer for the pinned and free layers. The coercivity of the free layer can be reduced using a Co 74 Fe 26 /NiFe free layer, which is suitable for head applications. An MR ratio of 40 to 50% was obtained with an RA of 2 to 3 Ωμm 2 . Mg-O barrier MTJs are the most promising for future TMR heads for recording densities over 200 Gbit/in 2 . We fabricated Al-O barrier TMR heads whose target areal recording density is around 100 Gbit/in 2 . These heads have a 25% MR ratio with an RA of 4 Ωμm 2 , and the width and height of the TMR head element are 110 nm and 100 nm, respectively. We can obtain an average output signal of about 5000 μVpp at a 150 mV bias voltage (V b ) using a synthetic ferrimagnetic medium. We have also investigated the characteristics of head noise and found that thermal magnetic noise is the dominant noise in our TMR heads. We also investigated the thermal magnetic noise as a function of the exchange coupling field H ex between the pinned and antiferromagnetic layers of TMR heads by using micromagnetic simulations. We clarified the importance of increasing not only the MR ratio but also H ex to realize ultra high density magnetic recording.