Population congestion in 3-state quantum-dot cellular automata

Retallick, Jacob; Walus, Konrad

doi:10.1063/5.0007289

Cited by 5 publications

(2 citation statements)

References 26 publications

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“…In this case, the repulsion by the driver cell's mobile charge and the attraction to the driver cell's neutralizing charge further bias the target cell toward the null state so that a stronger clock than before is required to activate the target cell. This effect has been termed "population congestion," and has been studied in detail [22]. Fig.…”

Section: A Molecular Device Descriptionmentioning

confidence: 99%

Robust Electric-field Input Circuits for Clocked Molecular Quantum-dot Cellular Automata

Cong,

Blair

2021

Preprint

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Quantum-dot cellular automata (QCA) is a paradigm for low-power, general-purpose, classical computing designed to overcome the challenges facing CMOS in the extreme limits of scaling. A molecular implementation of QCA offers nanometer-scale devices with device densities and operating speeds which may surpass CMOS device densities and speeds by several orders of magnitude, all at room temperature. Here, a proposal for electric field bit write-in to molecular QCA circuits is extended to synchronous QCA circuits clocked using an applied electric field, E. Input electrodes, which may be much larger than the cells themselves, immerse an input circuit in an input field Ey ŷ, in addition to the applied clocking field Ez ẑ. The input field selects the input bit on a field-sensitive portion of the circuit. Another portion of the circuit with reduced Eysensitivity functions as a shift register, transmitting the input bit to downstream QCA logic for processing. It is shown that a simple rotation of the molecules comprising the shift register makes them immune to unwanted effects from the input field or fringing fields in the direction of the input field. Furthermore, the circuits also tolerate a significant unwanted field component Ex x in the third direction, which is neither the clocking nor input direction. The write-in of classical bits to molecular QCA circuits is a road-block that must be cleared in order to realize energy-efficient molecular computation using QCA. The results presented here show that interconnecting shift registers may be designed to function in the presence of significant unwanted fringing fields from large input electrodes. Furthermore, the techniques devloped here may also enable molecular QCA logic to tolerate these same unwanted fringing fields.

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Section: A Molecular Device Descriptionmentioning

confidence: 99%

Robust Electric-field Input Circuits for Clocked Molecular Quantum-dot Cellular Automata

Cong,

Blair

2021

Preprint

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“…The separation between cell pairs in a circuit may be chosen to optimize desirable device interactions and to minimize an undesirable device interaction known as population congestion. 27 Here, Coulomb repulsion between mobile charges in the plane of the active dots z = h increases the strength of the clock E z required to active cells.…”

Section: Introductionmentioning

confidence: 99%

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

Cong,

Blair

2022

Preprint

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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.

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Clocked molecular quantum-dot cellular automata circuits tolerate unwanted external electric fields

Cong

Blair

2022

Journal of Applied Physics

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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 [Formula: see text]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 of 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.

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Population congestion in 3-state quantum-dot cellular automata

Cited by 5 publications

References 26 publications

Robust Electric-field Input Circuits for Clocked Molecular Quantum-dot Cellular Automata

Robust Electric-field Input Circuits for Clocked Molecular Quantum-dot Cellular Automata

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

Clocked molecular quantum-dot cellular automata circuits tolerate unwanted external electric fields

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