The proposed nanometre-sized electronic devices are generally expected to show an increased probability of errors both in manufacturing and in service. Hence, there is a need to use fault-tolerant techniques in order to make reliable information processing systems out of those devices. Here we examine and compare four fault-tolerant techniques: R-fold multiple redundancy; cascaded triple modular redundancy; von Neumann's multiplexing method; and a reconfigurable computer technique. It is shown that the reconfiguration technique is the most effective technique, able to cope with manufacturing defect rates of the order of 0.01-0.1, but the technique requires enormous amounts of redundancy, of the order of 103-105. However, in the case of transient errors, multiple modular redundancy and multiplexing are the only feasible options.

In Stadler et al (2003 Nanotechnology 14 138), a scheme for a molecular memory was presented. It was based on the influence of the positions of chemical side-groups attached to aromatic molecules on the paths for electrons propagating through these molecules in the ballistic and tunnelling transport regimes. Here we extend this concept in the following ways. (i) A graphical method is derived from an electron scattering formalism based on a topological Hückel description, which allows us to estimate whether the electron transport between two electrodes attached to specific atomic sites in an arbitrary molecule is finite or zero at the Fermi level. (ii) The same scheme that was used for the implementation of the molecular memory is extended to logic functions, in particular a half-adder. (iii) A more realistic description of the chemical nature of the proposed intra-molecular circuits is achieved by using the elastic scattering quantum chemistry (ESQC) technique in an extended Hückel implementation and by specifying the side-groups as nitro-groups, which are rotated in order to feed the signal inputs into the computational circuit.

We present a scheme for a molecular memory, which is based on the influence of the positions of chemical side-groups attached to aromatic molecules on the paths for electrons propagating through these molecules in the ballistic and tunnelling transport regimes. Using the elastic scattering quantum chemistry technique in a topological Hückel implementation, we show how it is possible to represent four different output states with a benzene molecule attached to one input and three output electrodes. To achieve this we choose single atomic orbitals as side-groups and by varying their number and positions the desired output pattern is met, at least in the ballistic regime. This case is also compared to the situation where only two electrodes are attached; the differences with respect to the tunnelling regime are analysed in detail. Since our scheme is based on path and therefore phase differences in electronic wave propagation, we also compare its properties with those of other interference-based concepts for information processing, such as quantum computing or photonics.

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Nanoelectronic devices are anticipated to become exceedingly noisy as they are scaled towards thermodynamic limits. Hence the development of nanoscale classical information systems will require optimal schemes for reliable information processing in the presence of noise. We present a novel, highly noise-tolerant computer architecture based on the work of von Neumann that may enable the construction of reliable nanocomputers comprised of noisy gates. The fundamental principles of this technique of parallel restitution are parallel processing by redundant logic gates, parallelism in the interconnects between gate resources and intermittent signal restitution performed in parallel. The results of our mathematical model, verified by Monte Carlo simulations, show that nanoprocessors consisting of gates incorporating this technique can be made 90% reliable over 10 years of continuous operation with a gate error probability per actuation of and a redundancy of . This compares very favourably with corresponding results utilizing modular redundant architectures of with , and with no noise tolerance. Arbitrary reliability is possible within a noise limit of , with massive redundancy. We show parallel restitution to be a general paradigm applicable to different kinds of information processing, including neural communication. Significantly, we show how our treatment of para-restituted computation as a statistical ensemble coupled to a heat bath allows consideration of the computation entropy of logic gates, and tentatively sketch a thermodynamic theory of noisy computation that might set fundamental physical limits on scaling classical computation to the nanoscale. Our preliminary work indicates that classical computation may be confined to the macroscale by noise, quantum computation possibly being the only information processing possible at the extreme nanoscale.