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

• Type: Article in International Scientific Journal
• Date: 2015

Authors

Costa, JD (Author) Other; Serrano Guisan, S (Author) Other; Borme, J (Author) Other; Deepak, FL (Author) Other; Tarequzzaman, M (Author) Other; Paz, E (Author) Other; ventura, j. (Author) FCUP; Ferreira, R (Author) Other; Freitas, PP (Author) Other

Journal

Title: IEEE Transactions on Magnetics

Vol. 51

Pages: 1-4

ISSN: 0018-9464

Publisher: IEEE

Indexing

ISI Web of Knowledge - 5 Citations

Scopus - 6 Citations

Other information

Authenticus ID: P-00G-T8B

DOI: 10.1109/tmag.2015.2441141

Abstract (EN): 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 Omega mu m(2) up to 15 Omega mu m(2) and tunnel magnetoresistance ratios up to similar 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 Omega mu m(2)) and in a thicker MgO region (2.7 Omega mu m(2)) are shown to illustrate the dependence found. It was observed that the higher output power (similar to 300 nW) and the smaller linewidth (similar to 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.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 4