Letter

1. Division of Chemistry and Chemical Engineering and the Kavli Nanoscience Institute, Caltech, Pasadena, California 91125, USA
   
2. California NanoSystems Institute and the Department of Chemistry and Biochemistry, University of California at Los Angeles, 405 Hilgard Avenue, Los Angeles, California 90095-1569, USA
   
3. Present addresses: Department of Electrical and Computer Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213, USA (Y.L.); Crump Institute for Molecular Imaging, University of California, Los Angeles, California 90095, USA (H.-R.T.); Department of Physics, Ohio State University, 191 W. Woodruff Ave. Columbus, OH 43210-1117 (E. J.-H.)
   
4. These authors contributed equally to this work.

Correspondence to: James R. Heath¹ Correspondence and requests for materials should be addressed to J.R.H. (Email: heath@caltech.edu).

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 m². 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 devices^{5, 6, 7} and small circuits^{8, 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 m²), that is, roughly analogous to the dimensions of a DRAM circuit¹ projected to be available by 2020. A monolayer of bistable, [2]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.