Aluminum oxide layers as possible components for layered tunnel barriers

Cimpoiasu, E.; Tolpygo, Sergey K.; Liu, X.; Simonian, Nikita; Lukens, J. E.; Klie, Robert F.; Zhu, Yimei; Likharev, K. K.

doi:10.1063/1.1763229

Cited by 50 publications

(40 citation statements)

References 62 publications

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“…Similar kind of changes in junction parameters have also been reported earlier at least for gas annealed Nb/AlAlO x -Nb junctions [13,15]. The change in the absolute values of the barrier parameters are difficult to estimate, as the numerous resonances in the conductance spectrum before the annealing makes fitting to the model unreliable.…”

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confidence: 61%

“…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.…”

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confidence: 99%

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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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confidence: 61%

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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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“…Also interesting to note is that this value is higher compared to the value (0.78 eV) reported for Al 2 O 3 in literature for a thickness range for 100 nm (Mikhaelashvili et al 1998). It is most possible that the PDA at a high temperature has increased the bandgap and band offsets of Al 2 O 3 , resulting in an increase in barrier height, thus reducing the leakage current (Wellekens et al 2007;Cimpoiasu et al 2004). 2.…”

Section: Samplementioning

confidence: 38%

“…5 shows the comparison of the characteristic Schottky plots of both experimental and simulated data at two different temperatures. It has been reported (Cimpoiasu et al 2004) that for a dielectric at room temperature, a barrier height of C1.5 eV is sufficient to suppress the thermionic current, in turn reducing the leakage. The Schottky barrier height, / B obtained from the above fit is 1.35 ± 0.25 eV, which is close to the desired value.…”

Section: Samplementioning

confidence: 99%

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Identification of current transport mechanism in Al2O3 thin films for memory applications

et al. 2014

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The effect of oxygen anneal on the electrical characteristics, especially on the current transport mechanism, of Al 2 O 3 films in the thickness range of 10-30 nm was examined in detail. The analyses were performed at electric fields of B2.5 MV/cm to effectively address the reliability of Al 2 O 3 -based devices operating in the low electric field regime. The general conduction mechanism equations were used to simulate the expected current density (J) values for a given electric field (E) range. The characteristic linear plots of the conduction mechanisms were then used to compare the experimental and simulated data to identify the most probable mechanism occurring in the dielectric. Parameters like barrier height and activation energy were extracted from the fit. It was found that oxygen anneal has profound effects on the electrical properties of Al 2 O 3 films, with annealed films demonstrating a different conduction mechanism than their unannealed counterparts, along with significant improvement in the leakage current and barrier height. This kind of analyses will help optimize the process conditions for Al 2 O 3 deposition and provide an optimal range for device operation, thus improving the reliability of Al 2 O 3 films for applications in CMOS logic and Flash memory.

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