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Design and fabrication of memory devices based on nanoscale polyoxometalate clusters


Flash memory devices—that is, non-volatile computer storage media that can be electrically erased and reprogrammed—are vital for portable electronics, but the scaling down of metal–oxide–semiconductor (MOS) flash memory to sizes of below ten nanometres per data cell presents challenges. Molecules have been proposed to replace MOS flash memory1, but they suffer from low electrical conductivity, high resistance, low device yield, and finite thermal stability, limiting their integration into current MOS technologies. Although great advances have been made in the pursuit of molecule-based flash memory2, there are a number of significant barriers to the realization of devices using conventional MOS technologies3,4,5,6,7. Here we show that core–shell polyoxometalate (POM) molecules8 can act as candidate storage nodes for MOS flash memory. Realistic, industry-standard device simulations validate our approach at the nanometre scale, where the device performance is determined mainly by the number of molecules in the storage media and not by their position. To exploit the nature of the core–shell POM clusters, we show, at both the molecular and device level, that embedding [(Se(iv)O3)2]4− as an oxidizable dopant in the cluster core allows the oxidation of the molecule to a [Se(v)2O6]2− moiety containing a {Se(v)–Se(v)} bond (where curly brackets indicate a moiety, not a molecule) and reveals a new 5+ oxidation state for selenium. This new oxidation state can be observed at the device level, resulting in a new type of memory, which we call ‘write-once-erase’. Taken together, these results show that POMs have the potential to be used as a realistic nanoscale flash memory. Also, the configuration of the doped POM core may lead to new types of electrical behaviour9,10,11. This work suggests a route to the practical integration of configurable molecules in MOS technologies as the lithographic scales approach the molecular limit12.

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Figure 1: Structure and electrochemical properties of compound 1a.
Figure 2: Image of the flash memory device and the drain current behaviour with an applied voltage to the control gate.
Figure 3: Scheme depicting the formation of the Se(v)–Se(v) bond within the cluster cage.
Figure 4: The write-once-erase device.
Figure 5: Device modelling simulations of compounds 1a and 2.

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Atomic coordinates for the reported crystal structures have been deposited with the Cambridge Structural Database under the accession codes 997534 (compound precursor), 997535 (compound 1a), 997536 (compound 1c) and 997537 (compound 1d), and full synthetic, electrochemical, device theory, device modelling and electronic device data is given in the Supplementary Information.


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We gratefully acknowledge financial support from the EPSRC for funding (grants EP/H024107/1, EP/I033459/1 and EP/J015156/1), the COST Action CM1203 (PoCheMoN), the Royal Society Wolfson Foundation for a Merit Award, and the University of Glasgow. V.P.G. and A.A. thank S. Markov and S. M. Amoroso for discussions.

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L.C. conceived the idea, designed the project and coordinated the efforts of the research team. J.Y. synthesised the clusters and conducted the first electrochemistry experiments and structural characterization with D.-L.L. H.N.M., C.B., L.V.-N., and L.C. helped to characterize the physical properties of the clusters. C.B. did the electron paramagnetic resonance, electrochemistry and spectroscopic measurements. L.V.-N., L.C., V.P.G. and A.A. designed the theory-to-modelling strategy. L.V.-N., with J.M.P., did the DFT calculations. V.P.G. and A.A. did the device simulation. R.H.P. and N.G. fabricated and characterized the electrode arrays, produced the devices, made the measurements and characterized the data. M.M.M. and D.J.P. designed the nanowire arrays and M.M.M. fabricated the electrodes and optimized the data with D.J.P., who helped analyse the results. C.B., L.V.-N. and L.C. co-wrote the paper with input from all the authors.

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Correspondence to Leroy Cronin.

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The authors declare no competing financial interests.

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Supplementary Information

This file contains Supplementary Text and Data, Supplementary Figures 1-14, Supplementary Tables 1-8 and Supplementary References. (PDF 3238 kb)

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Busche, C., Vilà-Nadal, L., Yan, J. et al. Design and fabrication of memory devices based on nanoscale polyoxometalate clusters. Nature 515, 545–549 (2014).

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