Abstract
The behavior of quantum-dot cellular automata (QCA) networks is typically understood through considering polarization-like interactions with energies arising from the agreement or disagreement of the defined polarization states of neighboring QCA devices. It is known that additional interactions are present in 3-state molecular QCA that alter the required clocking fields needed for a device operation. Recent efforts in implementing logic gates using patterned dangling bonds (SiDBs) on hydrogen passivated silicon reveal significant challenges arising from similar effects. The necessary applied electrical potential needed to increase the population of an SiDB is strongly dependent on the current population of its neighbors, an effect we term congestion. It is unclear whether the strength of these interactions may pose an obstacle for future applications of SiDBs as a nanoscale QCA architecture. In this work, we investigate 3-state QCA in the regime in which congestion is significant and determine the extent to which such effects can be mitigated for SiDB devices. We propose that while SiDB-based QCA wires may be achievable depending on limitations of inter-dot tunneling, higher density devices such as majority gates may need to be replaced by more architecture specific implementations unless net-neutral variants of SiDB QCA devices can be demonstrated.
Highlights
Quantum-dot cellular automata (QCA) is an experimental nanoscale computational architecture that encodes information in the configuration of charges among quantum dots arranged into quantum-dot cellular automata (QCA) devices or cells.[1,2] Each QCA cell is defined by a specific array of quantum dots that can be approximately described in a limited basis of charge states
We propose that while SiDB-based QCA wires may be achievable depending on limitations of inter-dot tunneling, higher density devices such as majority gates may need to be replaced by more architecture specific implementations unless net-neutral variants of SiDB QCA devices can be demonstrated
The observed prominence of congestion interactions in SiDB devices raises questions about the feasibility of certain higher density arrangements such as logic gates or even simple QCA devices. These interactions are relatively overcome for molecular QCA devices such as zwitterionic nido carborane by employing dynamic wave clocking with an increased maximum clocking field
Summary
Quantum-dot cellular automata (QCA) is an experimental nanoscale computational architecture that encodes information in the configuration of charges among quantum dots arranged into QCA devices or cells.[1,2] Each QCA cell is defined by a specific array of quantum dots that can be approximately described in a limited basis of charge states. By excluding the null state configuration, 2-state devices are much simpler to simulate and have become prevalent in the literature They typically rely on some often unspecified mechanism for controlling inter-dot tunneling to achieve clocking. Clocking in 3-state QCA is much simpler, requiring only that the electrostatic potential felt by the charges in the null configuration be controllable relative to the polarized states. This can be done readily with electrodes. SiDB devices pose an additional challenge in that a large applied clocking field can produce too large of a surface population It is unclear whether SiDB based QCA devices could be operated in a regime of clocking parameters for which this congestion is mitigated. V, we discuss the extent to which dynamic wave clocking addresses these challenges for SiDB-based QCA devices
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