QCA Devices Research Articles

Edge effects in quantum cellular automata binary wire

The molecular quantum cellular automata approach provides a paradigm for molecular electronics, where the charge configurations at reduction–oxidation centers of molecules represent binary information. The QCA cells are coupled by electrostatic fields and enable implementing devices for digital data transmission and logic operation at the molecular scale. Designing inputs for the desired operation of molecular QCA devices has been a challenging task, where the edge effects of electrodes may reduce the reliability of the QCA devices. We calculate the fringing fields of a pair of electrodes implemented on a model platform for the operation of a molecular QCA binary wire. The calculated nanogap and fringing fields are used in a simple quantum mechanical model to analyze the edge effects on the polarization propagation and polarization loss throughout the wire. Discussions on the stability of the wire in the presence of the fringing fields using the excited state of the wire and polarization uncertainties are presented.

Effect of a Clock System on Bis-Ferrocene Molecular QCA

Molecular quantum-dot cellular automata (mQCA) is found to be the most promising among all emerging technologies. It is expected to show remarkable operating frequencies (THz), high device densities, noncryogenic working temperature, and reduced power consumption. The computation relies on a new paradigm based on the interaction between nearby molecular QCA cells. This computation requires the aid of an external signal normally referred to as clock that enables/inhibits the molecular activity. The influence of clock on realistic molecules has never been deeply studied. In this paper, we performed a thorough analysis of the clock signal added to the molecular QCA cell based on an ad hoc synthesized bisferrocene molecule. Ab-initio simulations and further postprocessing of data have been used for characterizing the performance of bisferrocene molecule under the influence of a clock signal. Quantitative results on the molecule in terms of newly defined figures of merits, i.e., aggregated charge , equivalent voltage, and Vin-Vout trans-characteristic have been shown. Meanwhile, we demonstrate when and how much the presence of clock signal enhances or hinders the interactions between QCA molecules. These unprecedented data give a fundamental improvement to the knowledge on how information can be propagated through QCA devices. The results suggest directions to chemists, technologists, and engineers on how to proceed in the next steps for this promising technology.

Radius of effect in molecular quantum-dot cellular automata

Molecular quantum-dot cellular automata (mQCA) is a promising technology for building molecular computers, where binary information is represented by the charge configuration within molecular redox centres. Molecular QCA devices are coupled by electric fields and no current flows in the circuits, in theory. The Coulomb forces, which cause electrons to move from one redox centre to another within a cell, may result in faults in neighbouring cells as well. A simple electrostatic model is presented that describes the interactions of double-dot molecules within an effective radius-of-effect (RoE). The proposed model can be applied to approximate the RoE in device simulation, as well as determining a reliable cell-spacing in mQCA circuits as to avoid faults. Compared with full quantum chemistry calculations, which are of high computational cost, this simple model provides a rapid and straightforward tool for application in reliable mQCA device and circuit design.

A model for computing and energy dissipation of molecular QCA devices and circuits

Quantum-dot Cellular Automata is an emerging technology that offers significant improvements over CMOS. Recently QCA has been advocated as a technology for implementing reversible computing. However, existing tools for QCA design and evaluation have limited capabilities. This paper presents a new mechanical-based model for computing in QCA. By avoiding a full quantum-thermodynamical calculation, it offers a classical view of the principles of QCA operation and can be used in evaluating energy dissipation for reversible computing. The proposed model is mechanically based and is applicable to six-dot (neutrally charged) QCA cells for molecular implementation. The mechanical model consists of a sleeve of changing shape; four electrically charged balls are connected by a stick that rotates around an axle in the sleeve. The sleeve acts as a clocking unit, while the angular position of the stick within the changing shape of the sleeve, identifies the phase for quasi-adiabatic switching. A thermodynamic analysis of the proposed model is presented. The behaviors of various QCA basic devices and circuits are analyzed using the proposed model. It is shown that the proposed model is capable of evaluating the energy consumption for reversible computing at device and circuit levels for molecular QCA implementation. As applicable to QCA, two clocking schemes are also analyzed for energy dissipation and performance (in terms of number of clocking zones).