A Survey of Memristive Threshold Logic Circuits

In this paper, we review different memristive threshold logic (MTL) circuits that are inspired from the synaptic action of the flow of neurotransmitters in the biological brain. The brainlike generalization ability and the area minimization of these threshold logic circuits aim toward crossing Moore's law boundaries at device, circuits, and systems levels. Fast switching memory, signal processing, control systems, programmable logic, image processing, reconfigurable computing, and pattern recognition are identified as some of the potential applications of MTL systems. The physical realization of nanoscale devices with memristive behavior from materials, such as TiO₂, ferroelectrics, silicon, and polymers, has accelerated research effort in these application areas, inspiring the scientific community to pursue the design of high-speed, low-cost, low-power, and high-density neuromorphic architectures.

Negative differential resistance at sequential single-electron tunnelling through atoms and molecules

We have carried out calculations of electron transport in single-electron transistors using single atoms or small molecules as single-electron islands. The theory is based on a combination of (i) the general theory of the sequential single-electron transport through objects with a quantized energy spectrum, developed by Averin and Korotkov, (ii) the ab initio calculation of molecular orbitals and energy spectra within the density functional theory framework (using the NRLMOL software package), and (iii) Bardeen's approximation for the rate of tunnelling due to wavefunction overlap. The results show, in particular, that dc I-V curves of molecular-scale single-electron transistors typically have extended branches with negative differential resistance. This effect is due to the enhancement of one of the two tunnelling barriers of the transistor by the source-drain electric field, and apparently has already been observed experimentally by at least two groups. In conclusion, the possibility of using this effect for increasing the density and performance of hybrid semiconductor/nanodevice integrated circuits is discussed in brief.

Minimal Energy Requirements in Communication

The literature describing the energy needs for a communications channel has been dominated by analyses of linear electromagnetic transmission, often without awareness that this is a special case. This case leads to the conclusion that an amount of energy equal to kTln 2, where kT is the thermal noise per unit bandwidth, is needed to transmit a bit, and more if quantized channels are used with photon energies hnu > kT. Alternative communication methods are proposed to show that there is no unavoidable minimal energy requirement per transmitted bit. These methods are invoked as part of an analysis of ultimate limits and not as practical procedures.