Direct observation of the thickness distribution of ultra thin AlOxbarriers in Al/AlOx/Al Josephson junctions

Zeng, Lunjie; Nik, Samira Mousavi; Greibe, Tine; Krantz, Philip; Wilson, Christopher; Delsing, Per; Olsson, Eva

doi:10.1088/0022-3727/48/39/395308

Cited by 83 publications

(82 citation statements)

References 29 publications

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“…We note that many studies consider the oxygen exposure, i.e. the product of oxidation time and oxygen pressure, as a decisive parameter [28,32]. However, we consider the effect of oxidation time to be negligible as long as the oxidation time is long enough to reach the saturation regime for the AlOx thickness [25,26,29].…”

Section: Methodsmentioning

confidence: 99%

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Structural and nanochemical properties ofAlOxlayers inAl/AlOx/Al-layer systems

Fritz

Radtke

Schneider

et al. 2019

Phys. Rev. Materials

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The structural and nanochemical properties of thin AlOx layers are decisive for the performance of advanced electronic devices. For example, they are frequently used as tunnel barriers in Josephson junction-based superconducting devices. However, systematic studies of the influence of oxidation parameters on structural and nanochemical properties are rare up to now, as most studies focus on the electrical properties of AlOx layers. This study aims to close this gap by applying transmission electron microscopy in combination with electron energy loss spectroscopy to analyze the structural and nanochemical properties of differently fabricated AlOx layers and correlate them with fabrication parameters. With respect to the application of AlOx as tunnel barrier in superconducting Josephson junctions, Al/AlOx/Al-layer systems were deposited on Si substrates. We will show that the oxygen content and structure of amorphous AlOx layers is strongly dependent on the fabrication process and oxidation parameters.Dynamic and static oxidation of Al yields oxygen-deficient amorphous AlOx layers, where the oxygen content ranges from x = 0.5 to x = 1.3 depending on oxygen pressure and substrate temperature. Thicker layers of stoichiometric crystalline -Al2O3 layers were grown by electron-beam evaporation of Al2O3 and reactive sputter deposition.

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Section: Methodsmentioning

confidence: 99%

“…Specifically, the influence of temperature [25] and oxygen pressure during static oxidation [26][27][28] and both combined [29][30][31] were studied. Variations of the critical current are usually attributed to the variation of the AlOx-layer thickness [32,33]. However, AlOx composition variations and changes of the Al-O coordination, i.e.…”

Section: Introductionmentioning

confidence: 99%

Structural and nanochemical properties ofAlOxlayers inAl/AlOx/Al-layer systems

Fritz

Radtke

Schneider

et al. 2019

Phys. Rev. Materials

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“…Although the structure of Al/Al 2 O 3 systems has actively been explored over the decades both theoretically [12][13][14][15][16][17][18][19] and * manana.koberidze@aalto.fi experimentally [4,5,9,[20][21][22][23][24], an in-depth understanding of the interface properties is still an ongoing issue. Experimental observations have provided valuable information, for example, about the most probable crystallographic orientation relationship between Al and Al 2 O 3 at the interface [21,23], Al substrate roughness [4,20], the chemical state of the ions [25], oxide thickness distribution [9], bond lengths and coordinations of the atoms [5] at the interface, Al/O ratios for different oxide thicknesses [24], and different oxidation times and temperatures [25].…”

Section: Introductionmentioning

confidence: 99%

“…Experimental observations have provided valuable information, for example, about the most probable crystallographic orientation relationship between Al and Al 2 O 3 at the interface [21,23], Al substrate roughness [4,20], the chemical state of the ions [25], oxide thickness distribution [9], bond lengths and coordinations of the atoms [5] at the interface, Al/O ratios for different oxide thicknesses [24], and different oxidation times and temperatures [25]. However, experimental determination of the detailed atomic structures of the buried ultrathin interfaces is challenging.…”

Section: Introductionmentioning

confidence: 99%

Structural details of Al/Al2O3 junctions and their role in the formation of electron tunnel barriers

2018

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We present a computational study of the adhesive and structural properties of the Al/Al 2 O 3 interfaces as building blocks of the metal-insulator-metal (MIM) tunnel devices, where electron transport is accomplished via tunneling mechanism through the sandwiched insulating barrier. The main goal of this paper is to understand, on the atomic scale, the role of the geometrical details in the formation of the tunnel barrier profiles. Initially, we concentrate on the adhesive properties of the interfaces. To provide reliable results, we carefully assess the accuracy of the traditional methods used to examine Al/Al 2 O 3 systems. These are the most widely employed exchangecorrelation functionals-local-density approximation and two different generalized gradient approximations; the universal binding-energy relation for predicting equilibrium interfacial distances and adhesion energies; and the ideal work of separation as a measure of junction stability. In addition, we show that the established interpretation of the computed ideal work of separation might be misleading in predicting the optimal interface structures. Finally, we perform a detailed analysis of the atomic and interplanar relaxations in each junction, and identify their contributions to the tunnel barrier parameters. Our results imply that the structural irregularities on the surface of the Al film have a significant contribution to lowering the tunnel barrier height, while atomic relaxations at the interface and interplanar relaxations in Al 2 O 3 may considerably change the width of the barrier and, thus, distort its uniformity. Both the effects may critically influence the performance of the MIM tunnel devices.

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“…This distribution (black bars in Fig. 6) does not follow a Gaussian distribution unlike the results of the two recent studies, 30,31 which performed cross-section HRTEM analysis of thermally grown AlO x tunnel barrier. We believe that the reason for this dissimilarity is that the mentioned studies 30,31 analyzed the thickness distribution of great number of points in their samples, and also, the type of junctions was different (Al/AlO x /Al 30 and Cu/AlO x /Al 31 ) from our junctions.…”

Section: B Hrtem Analysis and The Tunnel Barrier Modelmentioning

confidence: 54%

Dependence of the scatter of the electrical properties on local non-uniformities of the tunnel barrier in Nb/Al-AlOx/Nb junctions

Aghdam

Rashid

Pavolotsky

et al. 2016

Journal of Applied Physics

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In this paper, we study the effect of the tunnel barrier thickness non-uniformity in Nb/Al-AlO x /Nb tunnel junctions using the measurement results of the junction capacitance (C) and the normal resistance (R n ). The local thickness distribution of the AlO x tunnel barrier in Nb/Al-AlO x /Nb trilayer (R n A $ 30 X lm 2 ) was studied by high resolution transmission electron microscopy. The specific resistance (R n A) values of the measured junctions range from 8.8 to 68 X lm 2 . We observed scatter in both the junction specific resistance and capacitance data, which is considerably higher than the measurement uncertainty. We also observed noticeable scatter in the R n C product, which does not stem from junction area estimation uncertainties. We discuss the possible reasons that contribute to this scatter. We suggest that the local thickness non-uniformity of the tunnel barrier significantly contributes to the scatter in the R n C product. We confirm this conclusion through an illustrative model based on the barrier imaging data, which results in the variation of the R n C data consistent with the measurements in this paper. V C 2016 AIP Publishing LLC.

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Direct observation of the thickness distribution of ultra thin AlO_xbarriers in Al/AlO_x/Al Josephson junctions

Cited by 83 publications

References 29 publications

Structural and nanochemical properties ofAlOxlayers inAl/AlOx/Al-layer systems

Structural and nanochemical properties ofAlOxlayers inAl/AlOx/Al-layer systems

Structural details of Al/Al2O3 junctions and their role in the formation of electron tunnel barriers

Dependence of the scatter of the electrical properties on local non-uniformities of the tunnel barrier in Nb/Al-AlOx/Nb junctions

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