A current-driven single-atom memory

Journal name:
Nature Nanotechnology
Volume:
8,
Pages:
645–648
Year published:
DOI:
doi:10.1038/nnano.2013.170
Received
Accepted
Published online

Abstract

The possibility of fabricating electronic devices with functional building blocks of atomic size is a major driving force of nanotechnology1. The key elements in electronic circuits are switches, usually realized by transistors, which can be configured to perform memory operations. Electronic switches have been miniaturized all the way down to the atomic scale2, 3, 4, 5, 6, 7, 8, 9. However, at such scales, three-terminal devices are technically challenging to implement. Here we show that a metallic atomic-scale contact can be operated as a reliable and fatigue-resistant two-terminal switch. We apply a careful electromigration protocol to toggle the conductance of an aluminium atomic contact between two well-defined values in the range of a few conductance quanta. Using the nonlinearities of the current–voltage characteristics caused by superconductivity10 in combination with molecular dynamics and quantum transport calculations, we provide evidence that the switching process is caused by the reversible rearrangement of single atoms. Owing to its hysteretic behaviour with two distinct states, this two-terminal switch can be used as a non-volatile information storage element.

At a glance

Figures

  1. Creation of a bistable atomic switch.
    Figure 1: Creation of a bistable atomic switch.

    a, Representative scanning electron microscope image (in false colours) of a break-junction sample. b, Principle of the break-junction set-up. A lithographically defined suspended nanobridge on a flexible substrate is elongated by bending the substrate in a three-point bending mechanism. The magnification represents an artist's view of the atomic arrangement when the nanobridge is stretched such that it forms a single-atom contact. c, Conductance of a break-junction structure made from aluminium as a function of time when applying the control current given in d. Inset: conductance versus control current for the bistable part. d, Control current applied for creating atomic rearrangements as a function of time. e, Examples of several bistable junctions plotted as a function of control current.

  2. Density plot of the counts for measuring a switch with low conductance GL and high conductance GH.
    Figure 2: Density plot of the counts for measuring a switch with low conductance GL and high conductance GH.

    Lines are guides to the eye, showing the diagonal (solid) and parallel (dashed) lines with offsets of 0.3G0 and 1.0G0. The bin size for GL and GH is 0.1G0.

  3. Transmission channel analysis of a bistable switch.
    Figure 3: Transmission channel analysis of a bistable switch.

    a, Conductance versus time and its decomposition into transmission eigenchannels. The black trace is the conductance measured continuously as a function of time. Dots show the results of the superconducting I–V curve-fitting procedure for τi in the low conductance state with GL = 1.12G0 (blue) and in the high conductance state with GH = 1.84G0 (red). Red and blue triangles indicate the sum of the τi and correspond well to the conductance measured directly. b. I–V characteristics for two atomic contacts of the bistable situation shown in a, measured (symbols) at a temperature of T = 270 mK and fit (solid lines) with the theory of multiple Andreev reflections from which we deduce channels with transmissions τ1 = 0.77, τ2 = 0.24, τ3 = 0.07 (blue) and τ1 = 0.86, τ2 = 0.75, τ3 = 0.20 (red).

  4. Scenario for the switching process of Fig. 3.
    Figure 4: Scenario for the switching process of Fig. 3.

    a, Theoretically determined conductance versus electrode displacement, the transmission probabilities τi of the eigenchannels (left axis) and the number of open channels (right axis), a channel being counted when τi >0.05. b,c, Configuration of the wire at displacements of 1.50 nm (b) and 1.61 nm (c). At these points, indicated in a by the vertical red dashed lines, the conductance and channel transmissions in b are  =  1.83G0, τ1 = 0.99, τ2 = 0.69, τ3 = 0.14 and in c are  =  1.09G0, τ1 = 0.85, τ2 = 0.16, τ3 = 0.09, similar to the experimentally observed switch in Fig. 3. The change of the positions of the atoms during the stretching process can be traced as exemplified by the atoms indicated by arrows and labelled as 1 and 2. The two red dashed lines in b indicate the bonds that have to be broken to cross over to the configuration shown in c.

  5. Atomic switch operated as a memory device through a stepwise variation of the current.
    Figure 5: Atomic switch operated as a memory device through a stepwise variation of the current.

    a,b, Conductance (a) and control current (b) as a function of time. At high bias currents of negative and positive sign, the switch is written into the low-conductance (0) or high-conductance (1) states, respectively. At low currents the information can be read without erasing it.

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Author information

Affiliations

  1. Department of Physics, University of Konstanz, D-78457 Konstanz, Germany

    • C. Schirm,
    • M. Matt,
    • F. Pauly,
    • P. Nielaba &
    • E. Scheer
  2. Departamento de Física Teórica de la Materia Condensada and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain

    • J. C. Cuevas
  3. Present address: Astrium GmbH, 81663 Munich, Germany

    • C. Schirm

Contributions

C.S. performed the experiments. M.M. conducted the calculations and theoretical modelling. F.P., J.C.C., P.N. and E.S. planned the project and advised the students. All authors discussed the results and prepared the manuscript.

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The authors declare no competing financial interests.

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