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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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).
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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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).
The authors declare no competing interests.
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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.
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).
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).
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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Han, Y., Nickle, C., Zhang, Z. et al. Electric-field-driven dual-functional molecular switches in tunnel junctions. Nat. Mater. (2020). https://doi.org/10.1038/s41563-020-0697-5