The influence of the texture on properties of IrMn spin valve magnetic tunnel junctions with MgO barrier and CoFeB electrodes

The influence of seed-buffer layers on the texture and tunneling parameters was investigated. The spin valve magnetic tunnel junctions (SV-MTJs) were deposited onto thermally oxidized Si wafers by magnetron sputtering in the following sequence of layers: substrate Si(100)/SiO2 47 nm/buffer layers/Ir17Mn83 10 nm/CoFeB 3 nm/MgO 2 nm/CoFeB 4 nm/top layers. The following buffer systems have been used in order to induce different degree of the texture: (A) low textured buffer Cu 25 nm and (B) high textured buffer Ta 5 nm/Cu 25 nm. The type of buffer layers strongly influences the texture of IrMn anti-ferromagnetic layer and induces roughness of magnetic layers and MgO barrier. The highest TMR ratio 141 % was obtained for sample with small roughness annealed in vacuum at 350 degrees C. A strong influence of the roughness, due to the barrier thickness fluctuations, on the resistance-area product (RA) of the junctions is discussed. The Neel coupling field increases in case of high textured and rough layers and it becomes small for smooth interfaces. The proper design of the composition of the buffer layers allows to improve the magnetic and tunneling properties of MTJs. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.