There has been considerable interest in the development of hybrid electronics devices and chips that utilize one or more organic molecules to store or manipulate information in discrete oxidation states of the molecule(s) (see, e.g., U.S. Pat. Nos. 6,208,553, 6,212,093, 6,272,038, 6,324,091, 6,381,169, and 6,451,942, and PCT Publication WO 01/03126, etc.).
In certain embodiments, an electroactive (redox-active) molecule such as a porphyrin and/or metallocene is covalently attached (directly or through a linker) to a conductive surface such as gold or silicon. The electroactive molecule(s) can be oxidized, e.g., to a cationic state upon application of an applied potential. When the potential is removed, the molecules store charge for extended periods. This forms the basis of the memory storage device.
General challenges in fabricating a hybrid chip containing molecular materials for information storage include, but are not limited to the efficient and effective attachment (electrical coupling) of the charge-storage molecule to an electroactive surface, controlling placement of the charge storage molecule(s) and/or associated electrolyte(s), and controlled deposition/location nof counterelectrodes. Particularly pressing problems are that often the methods for attachment of molecules to surfaces often require very high concentrations, high temperature, and/or the use of reactive intermediates (see, e.g. Cleland et al. (1995) J. Chem. Soc. Faraday Trans. 91: 4001-4003; Buriak (1999) Chem. Commun. 1051-1060; Linford et al. (1995) J. Am. Chem. Soc. 117: 3145-3155; Hamers et al. (2000) Acc. Chem. Res. 33: 617-624; Haber et al. (2000) J. Phys. Chem. B, 104: 9947-9950). Such conditions are readily applicable to small robust molecules but become less satisfactory and often fail altogether as the molecules become larger and/or more elaborate.
Another problem is associated with increased miniaturization of the electroactive memory elements. As the feature size of a memory cell shrinks to nanoscale dimensions, fewer and fewer molecules occupy the cell feature. Consequently, it becomes increasingly difficult to detect the stored charge.