Defect and Temperature Effects on Complex Quantum-Dot Cellular Automata Devices

Abstract

The authors present an analysis of the fault tolerant properties and the effects of temperature on an exclusive OR (XOR) gate and a full adder device implemented using quantum-dot cellular automata (QCA) structures. A Hubbard-type Hamiltonian and the Inter-cellular Hartree approximation have been used for modeling, and a uniform random distribution has been implemented for the simulated dot displacements within cells. We have shown characteristic features of all four possible input configurations for the XOR device. The device performance degrades significantly as the magnitude of defects and the temperature increase. Our results show that the fault-tolerant characteristics of an XOR device are highly dependent on the input configurations. The input signal that travels through the wire crossing (also called a crossover) in the central part of the device weakens the signal significantly. The presence of multiple wire crossings in the full adder design has a major impact on the functionality of the device. Even at absolute zero temperature, the effect of the dot displacement defect is very significant. We have observed that the breakdown characteristic is much more pronounced in the full adder than in any other devices under investigation.

A Scalable Signal Distribution Network for Quantum-Dot Cellular Automata

“…"REVOLVING DOOR" WIRE CROSSING As described earlier, previous research has shown that devices with wire crossings that use second-near-neighbor interactions are highly susceptible to thermal effects and to even the smallest fabrication irregularities, such as displacements in dot location. [13] Thus, it is imperative to find an improved method for handling wire crossings inside QCA devices. One option for implementing an isolated wire crossing in a clocked QCA device is to allow one cell to serve as a "revolving door," conveying information first in one direction and then in the other.…”