Allowing Electronics to Face the TSI Era—Molecular Electronics and Beyond

If single atoms at solid surfaces are used for storing the information, the chemical composition of the surface is fixed, and the information is coded as a conformation or an electronic state (between two possible ones) of any given surface atom (the Feynman dream), then the maximum bit density would be of the order 10¹⁵ cm⁻²—the peta scale integration (PSI). The manipulation of atoms, however, requires the use of macroscopic-scale apparatuses that may be operated at a negligible rate. Information coded by electrons, that can be lodged with densities on the order of 10¹² bit cm⁻² (the tera scale integration, TSI) at most, can instead be managed and felt by already existing mesoscopic-scale apparatuses in the giga scale integration (GSI). Even though there is no idea for the full exploitation of the performances of TSI devices, this density is within reach of present technology. Rather than scaling down conventional CMOS (complementary metal-oxide-semiconductor) circuits, the TSI may almost be achieved via a hybrid 11-2architecture where a silicon-based CMOS circuitry controls a nanoscopic crossbar structure hosting in each cross-point a collection of reprogrammable molecules able to mimic by themselves the behavior of a nonvolatile memory cell. Solutions to the severe problems posed by this hybrid architecture are proposed.