Ferromagnetic Coupling Field Reduction in CoFeB Tunnel Junctions Deposited by Ion Beam

In this paper, junctions with reduced H/sub f/ coupling were fabricated by ion beam deposition and oxidation, using CoFeB electrodes. The CoFeB layer has a strong (111) texture that can be the origin of lower H/sub f/ and coercivity when compared with CoFe. Junctions processed down to 2/spl times/4 /spl mu/m/sup 2/ with 40-thick CoFeB bottom electrodes have 42% of tunneling magnetoresistance (TMR), (R/spl times/A/spl sim/400 /spl Omega/./spl mu/m/sup 2/), H/sub c/ of /spl sim/10 Oe and H/sub f/ of /spl sim/2 Oe. CoFe-based junctions (R/spl times/A/spl sim/500 /spl Omega/./spl mu/m/sup 2/) have lower TMR (/spl sim/35%) and larger H/sub f/ (/spl sim/5-6 Oe) and H/sub c/ (/spl sim/12-14 Oe). Local chemical composition analysis of the cross section indicated Fe-O segregation with very little Co grown on top of the barrier for CoFe-based junctions and not for CoFeB ones.