Nanoscopic processes of current-induced switching in thin tunnel junctions

Ventura, J.; Araújo, João P.; Sousa, J.B.; Liu, Yaowen; Zhang, Zongzhi; Freitas, P. P.

doi:10.1109/tnano.2006.869658

Cited by 10 publications

(15 citation statements)

References 30 publications

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“…Temperature dependent measurements were performed in a closed cycle cryostat down to 20 K. 19,20 Let us define here the relative MTJ-resistance change ͑for parallel and antiparallel states͒ between 300 and 20 K as ␣ P,AP = ͑R 300 K P,AP − R 20 K P,AP ͒ / R 300 K P,AP , so that ␣ Ͻ 0 ͑Ͼ0͒ indicates tunnel-͑metallic-͒ like transport. Temperature dependent measurements were performed in a closed cycle cryostat down to 20 K. 19,20 Let us define here the relative MTJ-resistance change ͑for parallel and antiparallel states͒ between 300 and 20 K as ␣ P,AP = ͑R 300 K P,AP − R 20 K P,AP ͒ / R 300 K P,AP , so that ␣ Ͻ 0 ͑Ͼ0͒ indicates tunnel-͑metallic-͒ like transport.…”

Section: Methodsmentioning

confidence: 99%

Pinholes in thin low resistance MgO-based magnetic tunnel junctions probed by temperature dependent transport measurements

Ventura

Teixeira

Araújo

et al. 2008

Journal of Applied Physics

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Magnetic tunnel junctions (MTJs) with thin crystalline MgO(001) barriers displaying large tunnel magnetoresistance (TMR) and low resistance-area product (R×A) will likely be used as the next generation sensors in read heads of ultrahigh density hard drives. However, the thin insulting barrier may result in the unwanted presence of metallic pinholes joining the two electrodes. Here we study the transport properties of thin MgO-based low resistance MTJs (barrier thickness, t=0.6nm), deposited by physical vapor deposition, with R×A values as low as 8Ωμm2 and TMR as high as 70% at room temperature. We performed temperature dependent (300–20K) resistance and magnetoresistance measurements on different samples of the same series and observed different behaviors for different samples and magnetic states. All samples showed positive dR∕dT for the parallel state due to the presence of pinholes in the barrier. However, in the antiparallel state the R(T) curves always exhibit a mixed character, with dR∕dT changing from negative to positive with decreasing temperature. Our results then show an interesting competition between tunnel and metallic transport in the studied samples.

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Section: Methodsmentioning

confidence: 99%

Pinholes in thin low resistance MgO-based magnetic tunnel junctions probed by temperature dependent transport measurements

Ventura

Teixeira

Araújo

et al. 2008

Journal of Applied Physics

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“…In this case breakdown (at |I| ≈ 35 mA), leads to a slight and gradual R (and TMR; not shown) decrease. This behavior is related with defect-driven extrinsic breakdown of the barrier reflecting the growth of existing pinholes [5], [6] likely through thermally assisted electromigration of metallic ions from the electrodes into the barrier [14], [15]. Three more breakdown events are visible at higher currents (|I| ≈ 50 mA, ≈ 65 mA and ≈ 80 mA), further reducing R and bringing TMR to zero.…”

mentioning

confidence: 96%

Dielectric Breakdown in Underoxidized Magnetic Tunnel Junctions: Dependence on Oxidation Time and Area

Ventura¹,

Ferreira

Sousa³

et al. 2006

IEEE Trans. Magn.

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Abstract-Magnetic tunnel junctions (MTJs) with partially oxidized 9 Å AlOx-barriers were recently shown to have the necessary characteristics to be used as magnetoresistive sensors in high-density storage devices. Here we study dielectric breakdown in such underoxidized magnetic tunnel junctions, focusing on its dependence on tunnel junction area and oxidation time. A clear relation between breakdown mechanism and junction area is observed for the MTJs with the highest studied oxidation time: samples with large areas fail usually due to extrinsic causes (characterized by a smooth resistance decrease at dielectric breakdown). Small area junctions fail mainly through an intrinsic mechanism (sharp resistance decrease at breakdown). However, this dependence changes for lower oxidation times, with extrinsic breakdown becoming dominant. In fact, in the extremely underoxidized magnetic tunnel junctions, failure is exclusively related with extrinsic causes, independently of MTJ-area. These results are related with the presence of defects in the barrier (weak spots that lead to intrinsic breakdown) and of metallic unoxidized Al nanoconstrictions (leading to extrinsic breakdown).

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“…Returning to the CIS(I p ) cycle of figure 1(b), high positive current pulses induce ionic EM in the reverse direction, switching the tunnel junction resistance [35] into the previous intermediate resistance state (B). This shows virtual reversibility of the EM effects induced by comparable magnitude positive and negative current pulses.…”

Section: Resultsmentioning

confidence: 99%

Three-state memory combining resistive and magnetic switching using tunnel junctions

Ventura¹,

Pereira²,

Araújo³

et al. 2007

J. Phys. D: Appl. Phys.

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Magnetic fields generated by current lines are the standard way of switching between resistance (R) states in magnetic random access memories. A less common but technologically more interesting alternative to achieve R-switching is to use an electrical current crossing the tunnel barrier. Such current induced magnetization switching (CIMS) or current induced switching (CIS) effects were recently observed in thin magnetic tunnel junctions, and attributed to spin transfer (CIMS) or electromigration of atoms into the insulator (CIS). In this work, electromigration-driven resistance changes (resistive switching) are superimposed with thermally induced pinned layer reversal (magnetic switching), producing a reproducible, three-state memory device. The tunnel junctions under study show a tunnel magnetoresistance of 14% with a RA product of 50 µm 2. The reversible electromigration-driven resistance changes amount to 7-8% of the full resistance change and more than 10 4 R-switching events can be current induced without significant damage to the tunnel junction. Typical critical current densities are of the order of 2 × 10 6 A cm −2 .

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Nanoscopic processes of current-induced switching in thin tunnel junctions

Cited by 10 publications

References 30 publications

Pinholes in thin low resistance MgO-based magnetic tunnel junctions probed by temperature dependent transport measurements

Pinholes in thin low resistance MgO-based magnetic tunnel junctions probed by temperature dependent transport measurements

Dielectric Breakdown in Underoxidized Magnetic Tunnel Junctions: Dependence on Oxidation Time and Area

Three-state memory combining resistive and magnetic switching using tunnel junctions

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