Binary adders of multigate single-electron transistors: specific design using pass-transistor logic

We describe how to construct area-efficient adders using single-electron transistors (SETs). The design is based on pass-transistor logic and multigate SETs are used as pass transistors. The proposed design enables us to construct a full adder using only six SETs. We also show that multibit binary adders can be built using cascaded SET structures without any long wires. The small number of transistors and no-metal-interconnection configuration significantly reduces the circuit area and capacitance to be charged. A Monte Carlo simulation shows that even when the inter-SET-node capacitances are reduced and consequently the carry signal level terribly fluctuates in its path due to single-electron charging effects, the carry can correctly propagate as long as the final output node capacitance is sufficiently large. This proves that the area reduction and speed improvement are compatible in our design. We also discuss the possibility of large-scale integration, touching on the random-offset-charge issue.