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Electric-field-driven dual-functional molecular switches in tunnel junctions

Nature Materials volume 19, pages 843–848 (2020)Cite this article

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Abstract

To avoid crosstalk and suppress leakage currents in resistive random access memories (RRAMs), a resistive switch and a current rectifier (diode) are usually combined in series in a one diode–one resistor (1D–1R) RRAM. However, this complicates the design of next-generation RRAM, increases the footprint of devices and increases the operating voltage as the potential drops over two consecutive junctions1. Here, we report a molecular tunnel junction based on molecules that provide an unprecedented dual functionality of diode and variable resistor, resulting in a molecular-scale 1D–1R RRAM with a current rectification ratio of 2.5 × 104 and resistive on/off ratio of 6.7 × 103, and a low drive voltage of 0.89 V. The switching relies on dimerization of redox units, resulting in hybridization of molecular orbitals accompanied by directional ion migration. This electric-field-driven molecular switch operating in the tunnelling regime enables a class of molecular devices where multiple electronic functions are preprogrammed inside a single molecular layer with a thickness of only 2 nm.

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Fig. 1: Schematic illustrations of the junctions and dimerization.
Fig. 2: Electrical properties of the junctions.
Fig. 3: Operating mechanism of the junctions.

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Data availability

The data used in Figs. 1–3, Extended Data Figs. 1–4 and in the Supplementary Information are available from the Harvard Dataverse (https://dataverse.harvard.edu/dataset.xhtml?persistentId=doi:10.7910/DVN/QUVXXY).

Code availability

The source code used to analyse the raw data from the junctions is available from Harvard Dataverse (https://dataverse.harvard.edu/dataset.xhtml?persistentId=doi:10.7910/DVN/QUVXXY).

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Acknowledgements

We thank the Ministry of Education for supporting this research (award no. MOE2018-T2-1-088), the Prime Minister’s Office, Singapore, under its Medium Sized Centre programme, Science Foundation Ireland (SFI) under awards 15/CDA/3491 and 12/RC/2275 (SSPC), the SFI/Higher Education Authority Irish Center for High-End Computing (ICHEC) for computing resources, the US National Science Foundation (grant no. ECCS#1916874) and the Australian Research Council (grant no. FT160100207). We thank W. Ze for preparing the moulds for the microfluidic PDMS top electrodes, T. Salin for assistance with UPS and XPS measurements, V. Kalathingal for writing the LabView program for endurance measurements and A. Tadich for AR-XPS and NEXAFS measurements conducted at the Australian Synchrotron (under ANSTO).

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Authors and Affiliations

  1. Department of Chemistry, National University of Singapore, Singapore, Singapore

    Yingmei Han, Ziyu Zhang, Hippolyte P. A. G. Astier, Thorin J. Duffin, Zhe Wang & Christian A. Nijhuis

  2. Department of Physics, University of Central Florida, Orlando, FL, USA

    Cameron Nickle & Enrique del Barco

  3. NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore, Singapore

    Thorin J. Duffin & Christian A. Nijhuis

  4. Centre for Materials Science, School of Chemistry and Physics, Queensland University of Technology, Brisbane, Queensland, Australia

    Dongchen Qi

  5. Department of Physics, Bernal Institute, University of Limerick, Limerick, Ireland

    Damien Thompson

  6. Centre for Advanced 2D Materials and Graphene Research Center, National University of Singapore, Singapore, Singapore

    Christian A. Nijhuis

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  1. Yingmei Han
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Contributions

C.A.N. conceived and supervised the project. D.T. conducted all the DFT calculations. E.d.B. and C.N. conducted all the analytical modelling. Y.H. synthesized the compounds and performed the CV, electrical and UV–vis measurements. Z.Z. performed the AR-XPS and NEXAFS measurements and analysed the data with the assistance of D.Q. H.P.A.G.A. and Y.H. performed the switching speed and frequency measurements and H.P.A.G.A. conducted the analysis of all the data. T.J.D. developed the MATLAB code for electrical data analysis. C.A.N. and D.T. wrote the manuscript and all authors commented on it.

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Correspondence to Enrique del Barco, Damien Thompson or Christian A. Nijhuis.

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Extended data

Extended Data Fig. 1 Electrical properties of the junctions.

Heat maps of the log10|J| vs. V (a, b, c and d) and log10(R2/1) vs. V (e, f, g and h) for Ag-S(CH2)11MV2+X-2//GaOx/EGaIn junctions [X- = ClO4- (a, e) and PF6-(b, f)] and Ag-S(CH2)11X//GaOX/EGaIn junctions [X=NH3+Cl- (c, g) and COO-Na+ (d, h)]. Black solid lines are the Gaussian log-averages.

Extended Data Fig. 2 Retention time and endurance measurements.

Current retention of the on and off state of Ag-S(CH2)11MV2+I-2//GaOx/EGaIn junctions (a and b). Read-write-read-erase pulse sequence for Ag-S(CH2)11MV2+X-2//GaOx/EGaIn junction with X=Cl-(c, VW = -1.2 V, VE = +1.2 V, Vr = -0.3 V) and X=I- (e, VW = -1 V, VE = +1 V, Vr = -0.3 V). The corresponding output where red data points indicate R1, blue indicate R2, black indicate W and gray indicate E for junction with X=Cl- (d) and X=I- (f).

Extended Data Fig. 3 Representative J(V) curves.

Individual J(V) curves for Ag-S(CH2)11MV2+X-2//GaOx/EGaIn junctions with X-= I- (a), Br- (b), Cl- (c) and F- (d).

Extended Data Fig. 4 Operating mechanisms.

Experimentally determined maximum R2/1 for Ag-S(CH2)11MV2+X-2//GaOx/EGaIn junctions (X- = I-, Br-, Cl-, F-, ClO4- and PF6-) as a function of the DFT-calculated stability of dimer in on state vs. off state (Δdimer) over experimentally determined energy offset between HOMO and electrode Fermi level (δEHOMO). The error bars represent the 95% confidence intervals. The black dashed line is the linear fit for these six data points with a coefficient of determination R2 = 0.99.

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Supplementary Information

Supplementary Figs. 1–31, Discussion sections 1–14 and Tables 1–6.

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Han, Y., Nickle, C., Zhang, Z. et al. Electric-field-driven dual-functional molecular switches in tunnel junctions. Nat. Mater. 19, 843–848 (2020). https://doi.org/10.1038/s41563-020-0697-5

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