Clocked Quantum-dot Cellular Automata Circuits Tolerate Unwanted External Electric Fields

TL;DR

This study demonstrates that molecular quantum-dot cellular automata circuits can withstand strong external electric fields, with immunity influenced by molecular orientation, supporting their potential for robust low-power computing.

Contribution

It provides the first analysis of the robustness of various molecular QCA circuits against external electric fields, highlighting the importance of molecular orientation for immunity.

Findings

QCA circuits can tolerate strong external electric fields.

Molecular orientation affects circuit immunity.

Robustness is achievable despite strong unwanted fields.

Abstract

Quantum-dot cellular automata (QCA) may provide low-power, general-purpose computing in the post-CMOS era. A molecular implementation of QCA features nanometer-scale devices and may support THz switching speeds at room-temperature. Here, we explore the ability of molecular QCA circuits to tolerate unwanted applied electric fields, which may come from a variety of sources. One likely source of strong unwanted electric fields may be electrodes recently proposed for the write-in of classical bits to molecular QCA input circuits. Previous models have shown that the input circuits are sensitive to the applied field, and a coupled QCA wire can successfully transfer the input bit to downstream circuits despite strong applied fields. However, the ability of other QCA circuits to tolerate an applied field has not yet been demonstrated. Here we study the robustness of various QCA circuits by calculating their ground state responses in the presence an applied field. To do this, a circuit is built from several QCA molecules, each described as a two-state system. A circuit Hamiltonian is formed and diagonalized. All pairwise interactions between cells are considered, along with all correlations. An examination of the ground state shows that these QCA circuits may indeed tolerate strong unwanted electric fields. We also show that circuit immunity to the dominant unwanted field component may be obtained by choosing the orientation of constituent molecules. This suggests that relatively large electrodes used for bit write-in to molecular QCA need not disrupt the operation of nearby QCA circuits. The circuits may tolerate significant electric fields from other sources, as well.