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Tunable spin-tunnel contacts to silicon using low-work-function ferromagnets

Nature Materials volume 5, pages 817–822 (2006)Cite this article

Abstract

Magnetic tunnel junctions have become ubiquitous components appearing in magnetic random-access memory, read heads of magnetic disk drives and semiconductor-based spin devices. Inserting a tunnel barrier has been key to achieving spin injection from ferromagnetic (FM) metals into GaAs, but spin injection into Si has remained elusive. We show that Schottky barrier formation leads to a huge conductivity mismatch of the FM tunnel contact and Si, which cannot be solved by the well-known method of adjusting the tunnel barrier thickness. We present a radically different approach for spin-tunnelling resistance control using low-work-function ferromagnets, inserted at the FM/tunnel barrier interface. We demonstrate that in this way the resistance–area (RA) product of FM/Al2O3/Si contacts can be tuned over eight orders of magnitude, while simultaneously maintaining a reasonable tunnel spin polarization. This raises prospects for Si-based spintronics and presents a new category of ferromagnetic materials for spin-tunnel contacts in low-RA-product applications.

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Figure 1: Schottky barrier and required resistance–area product of ferromagnet/insulator/silicon spin-tunnel contact.
Figure 2: Structural and electrical characteristics of tunable ferromagnet/insulator/silicon spin-tunnel contacts.
Figure 3: Tunnel magnetoresistance and TSP of MTJs with low-work-function ferromagnet.
Figure 4: Optimum resistance–area product of tunnel contacts for a Si spin MOSFET.

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Acknowledgements

The authors thank R. Keim for the transmission electron microscopy analysis. We acknowledge financial support from NanoImpuls and NanoNed, the nanotechnology network in the Netherlands, the Dutch Technology Foundation (STW) and Sony corporation.

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Authors and Affiliations

  1. MESA + Institute for Nanotechnology, University of Twente, Enschede, 7500 AE, The Netherlands

    Byoung-Chul Min, Kazunari Motohashi, Cock Lodder & Ron Jansen

  2. Sendai Technology Center, Sony Corporation, 3-4-1 Sakuragi, Tagajo-shi, Miyagi-ken, 985-0842, Japan

    Kazunari Motohashi

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Correspondence to Ron Jansen.

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Min, BC., Motohashi, K., Lodder, C. et al. Tunable spin-tunnel contacts to silicon using low-work-function ferromagnets. Nature Mater 5, 817–822 (2006). https://doi.org/10.1038/nmat1736

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