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X-Ray Diffraction Study of the Optimization of MgO Growth Conditions for Magnetic Tunnel Junctions

Published

Author(s)

O Se Young, C G. Lee, Alexander J. Shapiro, William F. Egelhoff Jr., Mark D. Vaudin, Jennifer L. Klamo, J Mallett, Philip Pong

Abstract

MgO based magnetic tunnel junctions (MTJs) show large tunneling magnetoresistance (TMR) effects and are currently the most promising technology for the applications in magnetoelectronics devices. Conventional MTJs with amorphous AlOx barriers yield TMR ratios ranging from 18 70 %, but there are reports showing MTJs made with (200) oriented MgO exhibiting TMR ratios as high as 400 500 %. Therefore a comprehensive study of MgO growth conditions is essential for making high TMR MTJs. We have carried out a systematic study optimizing the MgO growth via presputter and sputtering conditions and underlayer structures. It was found that to prevent water vapour which is detrimental to MgO (200) growth, the chamber pressure needs to be reduced below 1.3 x 10-6 Pa (10-8 Torr). Pre-deposition ion milling for cleaning the thermal-oxide substrate before depositing metal films does not improve the subsequent MgO crystal growth. Simple underlayers such as 5 nm CoFeB tend to give better MgO, but we have also succeeded in growing MgO on more complicated underlayers such as 1 Ta / 20 Au / 5 Co40Fe40B20 and 1 Ta / 20 Conetic (Ni77Fe14Cu5Mo4) / 1.5 Co40Fe40B20 (units in nm). We accomplished this by reducing the water vapor to the lowest possible level through extensive baking of the deposition chamber and use of Ti-getter films. Short sputtering distance and high sputtering power were found to optimize MgO deposition. We found that both presputter and sputtering conditions have important effects on the MgO growth. X-ray diffraction (XRD) analysis was used as the characterization tool for optimizing the MgO growth conditions.
Citation
Journal of Applied Physics

Keywords

magnetic tunnel junctions, magnetoresistance effects, x-ray diffraction

Citation

O Se Young, O. , Lee, C. , Shapiro, A. , Egelhoff Jr., W. , Vaudin, M. , Klamo, J. , Mallett, J. and Pong, P. (2021), X-Ray Diffraction Study of the Optimization of MgO Growth Conditions for Magnetic Tunnel Junctions, Journal of Applied Physics (Accessed May 26, 2024)

Issues

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Created October 12, 2021