Microstructure and exchange coupling parameters of MTJ with CoFeB bottom electrode

In this study, we report the relationship between interface roughness, texture and the exchange bias and the interlayer-Neel coupling fields of the spin-valve magnetic tunnel junction (SV-MTJ). SV-MTJs with the structure: Si(100)/SiO2/buffer/IrMn/CoFeB/AlOx/NiFe/Ta were deposited on two buffers: Cu and Ta/Cu/Ta/Cu, and next the samples were annealed in vacuum and in a magnetic field. XRD analysis reveals that the texture degree of MTJ with Cu buffer is significantly lower than that of the sample with Ta/Cu/Ta/Cu buffer. The enhancement of IrMn and CoFeB texture leads to a higher amplitude of roughness and an increase of exchange bias and Neel coupling fields. The comparison of junctions with CoFe and CoFeB bottom electrodes shows that addition of 5% B in a CoFe layer makes the surface of the pinned layer smoother. This leads to a lower Neel coupling field, which is desirable for application of MTJ in MRAM technology. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.