Interdiffusion in Exchange Biased NiFe/IrMn/CoFe Electrode in Magnetic Tunnel Junctions
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Interdiffusion in Exchange Biased NiFe/IrMn/CoFe Electrode in Magnetic Tunnel Junctions
Jay H. Lee, Hee D. Jeong, Il C. Rho, Chong S. Yoon, Chang K. Kim Hanyang University, Dept. of Materials Science and Engineering, Seoul, Korea
ABSTRACT Extent of Mn diffusion to the plasma-oxidized AlOx tunnel barrier of magnetic tunnel junction was examined using Auger Electron Spectroscopy (AES) and X-Ray Photoelectron Spectroscopy (XPS). A magnetic film stack consisting of Ta/AlOx/CoFe/IrMn/NiFe/Ta was deposited with the AlOx layer treated under different plasma oxidation durations. AES depth profiles showed that Mn diffusion to the AlOx/CoFe interface increased with increasing oxidation
℃
after annealing at 300 . XPS analysis indicated that Mn found at the CoFe/AlOx interface in the over-oxidized electrode was in the form of MnO2. Our research suggests that Mn diffusion was accelerated by preferential oxidation of Mn at the CoFe/AlOx interface. INTRODUCTION Magnetic Tunneling Junctions (MTJ) are based on the changes in magnotresistance (MR) effect arising from the spin-polarized electrons tunneling across a thin insulating layer. Recently there have been reports of the MR change over 20% at room temperature [1]~[3]. Since then, much interest has been aroused to utilize such large MR ratio in the MRAM (Magnetic Random Access Memory) application as the MTJ offers a potential for non-volatile, fast, high-density memory device. Several researchers have already produced prototype tunnel junctions that are compatible with the current semiconductor technology [1][4]. In spite of the recent progress in the field, there remain a number of problems to be solved in order to incorporate the MTJ with the current semiconductor technology on an industrial scale. The junction must withstand the annealing process of CMOS manufacturing which requires temperatures up to 450
℃ [5].
However, the performance of the annealed junctions has been observed to deteriorate drastically beyond ~270
℃ leading to eventual failure of the junction [6] as shown in figure 1. Loss of spin
polarization at the insulator interfaces, short-circuiting of the electrodes due to the structural change of the FM electrodes, and the inter-diffusion at the ferromagnetic-antiferromagnetic interfaces are believed to be responsible for the degradation of the MTJ upon thermal treatment above 300 [7]. F3.9.1
℃
40
[8] [9] [10] [11] [12] [13] [14] [15]
MR ratio (%)
30
20
10
0 0
100 200 300 400 Annealing Temperature (¡É)
Figure 1. Typical MR ratio of magnetic tunnel junctions after annealing There have been Rutherford Backscattering Spectroscopy (RBS) results which showed that there was a significant amount of Mn diffusion from the CoFe/IrMn pinned layer and possible
℃ junction. XPS analysis of the junction annealed at 375℃ also confirmed the existence of Mn in
structural changes at the insulator interfaces above 300 [7][8]. Both observations have been attributed to the decrease of the spin polarization and the subsequent MR ratio drop of the the AlOx insulation
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