Large tunneling magnetoresistance enhancement by thermal anneal

Sousa, R. C.; Sun, J. J.; Soares, V.; Freitas, P. P.; Kling, A.; Silva, M. F. da; Soares, J. C.

doi:10.1063/1.122747

Cited by 185 publications

(75 citation statements)

References 14 publications

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“…Annealing experiments of magnetic tunnel junctions have shown that above 210°C the junction ͑magneto͒resis-tance drops severely, indicating that irreversible processes take place in or close to the junction barrier at this temperature. 13 Several Co/Al 2 O 3 /Co junctions were inspected with a scanning electron microscope after breakdown, but no visible sign of damage was found, as is expected when breakdown is a very microscopic event. The location of the short was, however, visualized with the use of a thin liquid crystal film deposited on the junction.…”

Section: Resultsmentioning

confidence: 99%

Analysis of breakdown in ferromagnetic tunnel junctions

Oepts

Verhagen

Coehoorn

et al. 1999

Journal of Applied Physics

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Due to their very thin tunnel barrier layer, magnetic tunnel junctions show dielectric breakdown at voltages of the order of 1 V. At the moment of breakdown, a highly conductive short is formed in the barrier and is visible as a hot spot. The breakdown effect is investigated by means of voltage ramp experiments on a series of nominally identical Co/Al 2 O 3 /Co tunnel junctions. The results are described in terms of a voltage dependent breakdown probability, and are further analyzed within the framework of a general model for the breakdown probability in dielectric materials, within which it is assumed that at any time the breakdown probability is independent of the ͑possibly time-dependent͒ voltage that has been previously applied. The experimental data can be described by several specific forms of the voltage breakdown probability function. A comparison with the models commonly used for describing thin film SiO 2 breakdown is given, as well as suggestions for future experiments.

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Section: Resultsmentioning

confidence: 99%

Analysis of breakdown in ferromagnetic tunnel junctions

Oepts

Verhagen

Coehoorn

et al. 1999

Journal of Applied Physics

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“…[12,13,14,15] On the other hand, for magnetic tunnel junctions, improvements in their performance were obtained with vacuum anneals. [16,17] In this letter we discuss how Al-AlO x -Al tunnel junctions can be completely stabilized, and their characteristics improved by thermal annealing in vacuum. The general trend of increase of R T with the annealing is reproduced.…”

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confidence: 99%

Complete stabilization and improvement of the characteristics of tunnel junctions by thermal annealing

Koppinen

Väistö

Maasilta

2007

Applied Physics Letters

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We have observed that submicron sized Al-AlOx-Al tunnel junctions can be stabilized completely by annealing them in vacuum at temperatures between 350 • C and 450 • C. In addition, low temperature characterization of the samples after the annealing treatment showed a marked improvement of the tunneling characteristics due to disappearance of unwanted resonances in the current. Charging energy, tunneling resistance, barrier thickness and height all increase after the treatment. The superconducting gap is not affected, but supercurrent is reduced in accordance with the increase of tunneling resistance.Submicron sized metal-insulator-metal (MIM) tunnel junctions have been used widely in applications such as radiation detectors[1], single electron transistors (SET) [2], and tunnel junction coolers and thermometers [3]. They are also the central element in superconducting quantum bits [4,5,6,7,8], and magnetic junctions [9] are developed for memory applications. However, there are often problems with stability of the junctions in room air conditions, the most noticable being aging, i.e. a slowly creeping increase of the tunneling resistance R T with time. Instability of the junctions is an obvious drawback when considering practical and commercial applications of tunnel junctions.One possible reason for aging is the absorption of unwanted molecules into the barrier. Direct knowledge of these processes is sketchy, although it is known that vacuum conditions can slow down aging significantly. [10] Another possibility is the relaxation of the oxide barrier properties. Typically, tunnel barriers in MIM junctions are fabricated by room temperature thermal oxidation of a disordered base electrode. This procedure results in formation of a polycrystalline or amorphous oxide layer, in which atoms are not in their global equilibrium positions. The relaxation from this "glassy" state could take months at room temperature. Moreover, in AlO x barriers studied here, chemisorbed oxygen ions bound on the barrier surface during fabrication have also been shown to be a source of instabilities. [11] A typical remedy for finding a better energy minimum is thermal annealing, the artificial acceleration of the relaxation processes by heating up the sample for some time and then letting it cool again. For technologically important Nb/Al-AlO x /Nb junctions, annealing treatments in gas atmospheres (He, N 2 , Ar, air) were shown to change the barrier properties, always increasing R T . [12,13,14,15] On the other hand, for magnetic tunnel junctions, improvements in their performance were obtained with vacuum anneals. [16,17] In this letter we discuss how Al-AlO x -Al tunnel junctions can be completely stabilized, and their characteristics improved by thermal annealing in vacuum. The general trend of increase of R T with the annealing is reproduced. The bias voltage dependence of the tunneling conductance reveal that the junction characteristics become more ideal after the anneal. In addition, the charging energy, the effective barrier thickne...

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“…The barriers are known to contain defects, some natural 6 and others of artificial origin. 7,8 Factors such as the barrier roughness 9 and chemical homogeneity 10 have been investigated as well as the specifics of barrier oxidation. 11,12 It is important in the optimization of TMR to understand the oxidation process and in particular how to oxidize the entire Al layer and none of the ferromagnet.…”

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confidence: 99%

Determination of the thickness of Al2O3 barriers in magnetic tunnel junctions

Buchanan

Hase

Tanner

et al. 2002

Applied Physics Letters

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The barrier thickness in magnetic spin-dependent tunnel junctions with Al2O3 barriers has been measured using grazing incidence x-ray reflectivity and by fitting the tunneling current to the Simmons model. We have studied the effect of glow discharge oxidation time on the barrier structure, revealing a substantial increase in Al2O3 thickness with oxidation. The greater thickness of barrier measured using grazing incidence x-ray reflectivity compared with that obtained by fitting current density–voltage to the Simmons electron tunneling model suggests that electron tunneling is localized to specific regions across the barrier, where the thickness is reduced by fluctuations due to nonconformal roughness.

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Large tunneling magnetoresistance enhancement by thermal anneal

Cited by 185 publications

References 14 publications

Analysis of breakdown in ferromagnetic tunnel junctions

Analysis of breakdown in ferromagnetic tunnel junctions

Complete stabilization and improvement of the characteristics of tunnel junctions by thermal annealing

Determination of the thickness of Al2O3 barriers in magnetic tunnel junctions

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