The primary metric for gauging progress in the various semiconductor integrated circuit technologies is the spacing, or pitch, between the most closely spaced wires within a dynamic random access memory (DRAM) circuit1. Modern DRAM circuits have 140 nm pitch wires and a memory cell size of 0.0408 μm2. Improving integrated circuit technology will require that these dimensions decrease over time. However, at present a large fraction of the patterning and materials requirements that we expect to need for the construction of new integrated circuit technologies in 2013 have ‘no known solution’1. Promising ingredients for advances in integrated circuit technology are nanowires2, molecular electronics3 and defect-tolerant architectures4, as demonstrated by reports of single devices5,6,7 and small circuits8,9. Methods of extending these approaches to large-scale, high-density circuitry are largely undeveloped. Here we describe a 160,000-bit molecular electronic memory circuit, fabricated at a density of 1011 bits cm-2 (pitch 33 nm; memory cell size 0.0011 μm2), that is, roughly analogous to the dimensions of a DRAM circuit1 projected to be available by 2020. A monolayer of bistable, rotaxane molecules10 served as the data storage elements. Although the circuit has large numbers of defects, those defects could be readily identified through electronic testing and isolated using software coding. The working bits were then configured to form a fully functional random access memory circuit for storing and retrieving information.
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This work was supported primarily by the DARPA MolApps Program with additional support from the MARCO Center for Advanced Materials and Devices and the National Science Foundation. J.W.C. and Y.S.S. acknowledge fellowships from the Samsung Corporation. We are grateful to Y. Liu and S. Saha for preparing the rotaxane molecule used in this work. Author Contributions The rotaxane molecular switches were designed and originally synthesized by H.-R.T. and J.F.S. All other authors contributed to the design, fabrication and testing of the memory circuit.
Reprints and permissions information is available at www.nature.com/reprints. The authors declare no competing financial interests.
This file contains Supplementary Methods (including Supplementary Figures 1-4 and Legends); Supplementary Discussion (including Supplementary Figure 5 and Legend) and Supplementary Notes. The Supplementary Methods include a detailed description of the fabrication and testing of the memory circuit. The Supplementary Discussion presents what is known about the current rectification of the individual bits (crosspoint junctions) within the memory, as well as discussion related to the limits of scaling that are possible using our nanofabrication methods. (PDF 812 kb)
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Green, J., Wook Choi, J., Boukai, A. et al. A 160-kilobit molecular electronic memory patterned at 1011 bits per square centimetre. Nature 445, 414–417 (2007). https://doi.org/10.1038/nature05462
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