| AVS 65th International Symposium & Exhibition | |
| Materials and Processes for Quantum Computing Focus Topic | Tuesday Sessions |
| Session MP+EM+NS-TuM |
| Session: | High Coherence Qubits for Quantum Computing |
| Presenter: | Eva Olsson, Chalmers University of Technology, Gothenburg, Sweden |
| Correspondent: | Click to Email |
The atomic structure of tunnel barriers in Josephson junctions for quantum devices and the corresponding interfaces determine the properties of the junction. The thinnest region in the barrier of a junction will be the preferential tunneling channel for charge carriers and the highest current. The current increases exponentially with decreasing barrier thickness. As a consequence, a variation on the individual atom plane length scale results in inhomogeneity of the tunnel current across the barrier. There are several earlier experimental indirect indications that only a small fraction of the junction area is active.
We are using high resolution annular dark field (ADF) scanning transmission electron microscopy (STEM) imaging to obtain high resolution (better than 1 Å) and high precision (better than 1 pm) information about the local atomic structure [1]. We use ADF STEM imaging to directly determine the thickness distribution along the oxide barrier in Al/AlOx/Al Josephson junctions [2]. The barrier thickness is about 1-2 nm. The thickness distribution shows that less than 10% of the junction area dominates the electron tunneling. We also study the influence of oxygen pressure and oxidation time on the thickness distribution. In addition, we determine the atomic structure and coordination of Al atoms within the oxide barrier layer using electron energy loss spectroscopy and nanobeam electron diffraction [3]. A lower Al coordination is observed at the metal/oxide interface compared to the interior of the oxide barrier. We also study the structure of the interfaces between the Al contact and the substrate [4,5].
[1] A.B. Yankovich, R. Verre, E. Olsen, A.E.O. Persson, V. Trinh, G. Dovner, M. Käll and E. Olsson, ACS Nano 11 (2017) 4265.
[2] L.J. Zeng, S. Nik, T. Greibe, P. Krantz, P. Delsing and E. Olsson, J. Phys. D: Appl. Phys.48 (2015) 395308
[3] L.J. Zeng, D.T. Tran, C.-W- Tai, G. Svensson and E. Olsson, Sci. Rep. 6 (2016) 29679.
[4] L.J. Zeng, T. Greibe, S. Nik, C.M. Wilson, P. Delsing and E. Olsson, J. Appl. Phys. 113 (2013) 143905
[5] L.J. Zeng, P. Krantz, S. Nik, P. Delsing and E. Olsson, J. Appl. Phys. 117 (2015) 163915.