Device variability and circuit redundancy in signal processing based on nanoswitches

Abstract

Signal processing based on molecular switches whose conductance can be tuned by an external stimulus between two (on and off) states has been proposed recently (Cervera et al 2008 J. Appl. Phys. 104 084317). The basic building block is a metal nanoparticle linked to two electrodes by an organic ligand and a nanoswitch. The net charge delivered by this nanostructure exhibits a sharp resonance when the alternating potential applied between the electrodes has the same frequency as the periodic variation between the on and off conductance states induced on the nanoswitch. This resonance can be used to process an external signal by selectively extracting the weight of the different harmonics. However, because of the fabrication process at the nanoscale, the nanostructures will show a significant variability in the physical characteristics. By using a phenomenological model that includes this variability, the stochastic nature of electron transference, and the thermal noise, we demonstrate that reliable signal processing can still be achieved by adapting the number of nanoswitches per bit of information (circuit redundancy) to the nanostructure tolerance (device variability). Extensive kinetic Monte Carlo simulations show that a moderate level of redundancy can compensate for significant nanostructure variability. This result gives support to the concept of ensembles of redundant switches as reliable components for signal processing at the nanoscale.

Information Processing Schemes Based on Monolayer Protected Metallic Nanoclusters

“…The values of in Figure 14 correspond to the tolerances assumed in the values of the individual electrical parameters (conductances and capacitances) of the nanostructures in the array of Figure 13(c). 36 The comparison Fig. 13.…”

“…35 36 We assume that the switch conductance can be modulated periodically between two on and off states by an external stimulus (an applied potential or a light pulse; 4 Fig. 13(a)).…”

Nanoscale switch based on interacting molecular dipoles: Cooperativity can improve the device characteristics

“…14,15 On the contrary, small domains of moderately defective nanoscale units could still be used as reliable switches due tothe averaging effect of many nanostructures interacting cooperatively. The control of single molecules and the connection to the external environment is difficult.…”

Reliable signal processing using parallel arrays of non-identical nanostructures and stochastic resonance

“…This variability acts as a static noise to be added to the dynamic noise caused by thermal fluctuations. [7][8][9][10] Logical and signal processing nanodevices based on the transport of a small number of electrons have attracted great interest due to the continuous miniaturisation of electronics. [11][12][13] For instance, the tunnelling current through a gold colloid quantum dot between two electrodes could be modulated by the attached ligands, forming a nanoparticle (NP)-based single electron transistor whose tunnelling barriers are defined by monolayers of thiols.…”

“…It has been reported that the high parameter variability influences the conductance of molecular memories, 17 the threshold potential of voltage-driven molecular switches, 18 and the tunnelling junction characteristics of disordered arrays. 19 Fault-tolerant approaches [8][9][10]20,21 are needed to perform reliable information processing from inherently unreliable nanostructures. Recently, we have explored theoretically the application of nanoscale switches to implement a signal processing scheme and a frequency-dependent associative memory, 22 paying attention to the effects of the nanostructure tolerance and the thermal fluctuations.…”