NDLI: Impact of MgO Thickness on the Performance of Spin-Transfer Torque Nano-Oscillators

Content Provider	IEEE Xplore Digital Library
Author	Costa, J.D. Serrano-Guisan, S. Borme, J. Deepak, F.L. Tarequzzaman, M. Paz, E. Ventura, J. Ferreira, R. Freitas, P.P.
Copyright Year	1965
Abstract	A magnetic tunnel junction (MTJ) stack incorporating an MgO wedge was deposited over a 200 mm wafer and nanofabricated into circular nanopillars with a diameter of 200 nm. Due to the variable MgO thickness, we could obtain MTJ nanopillars with resistance x area (RA) ranging from less than 1 Ωμm² up to 15 Ωμm² and tunnel magnetoresistance ratios up to ~100%. It was observed that the ferromagnetic coupling (H_F) displayed by the transfer curves increases for smaller values of RA. This variation is attributed to the orange-peel coupling, which is caused by the MgO roughness, with a larger impact for thinner barriers. The RF output of the nanopillars caused by the spin-transfer torque-induced magnetic precession of the free layer was measured as a function of bias current and external magnetic fields for nanopillars with different RA values. Results concerning typical devices in the thin MgO region (1.3 Ωμm²) and in a thicker MgO region (2.7 Ωμm²) are shown to illustrate the dependence found. It was observed that the higher output power (~300 nW) and the smaller linewidth (~90 MHz) could be obtained with the higher RA region. These results suggest that there must be an optimum RA value for the production of nano-oscillator devices, which depends on the tradeoffs between the need for large breakdown voltages and strong spin polarization of the bias current (favored for larger RA values) and between the need of endurance under large current densities (favored for smaller RA values). Provided the breakdown voltage of the MgO barrrier can be made large enough, nanopillars based on MTJ stacks with an intermediate RA can provide a solution for the production of large output power spin-transfer nano-oscillators.
Sponsorship	IEEE Magnetics Society
Starting Page	1
Ending Page	4
Page Count	4
File Size	530339
File Format	PDF
ISSN	00189464
Volume Number	51
Issue Number	11
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2015-01-01
Publisher Place	U.S.A.
Access Restriction	One Nation One Subscription (ONOS)
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Magnetic tunneling Tunneling magnetoresistance Power generation Torque Junctions Couplings Radio frequency Breakdown Voltage Magnetic Tunnel Junctions Spin Transfer Torque Nano-Oscillators Spin Transfer Torque spin-transfer torque nano-oscillators (STNOs) Breakdown voltage magnetic tunnel junctions (MTJs) spin-transfer torque (STT)
Content Type	Text
Resource Type	Article
Subject	Electronic, Optical and Magnetic Materials Electrical and Electronic Engineering

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4	Project PI / Joint PI	Principal Investigator and Joint Principal Investigators of the project	Dr. B. Sutradhar bsutra@ndl.gov.in Prof. Saswat Chakrabarti will be added soon
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