exploring and exploiting quantum-dot cellular automata

the full adders (fas) constitute the essential elements of digital systems, in a sense that they affect the circuit parameters of such systems. with respect to the mosfet restrictions, its replacement by new devices and technologies is inevitable. qca is one of the accomplishments in nanotechnology nominated as the candidate for mosfet replacement. in this article 4 new layouts are presented for fa; implemented as two at one layer and the other two at three layers; this is performed in a step by step manner and by providing the details and introducing each one’s problems. the layout process continues till an optimized layout is obtained. the layout and correct assessment of the introduced circuit function is accomplished by using qca designer simulation tool. the comparison of the results obtained through simulation confirms that the third design is better than other three designs with respect to cell count and area.