Novel Quantum Effect Devices for Future Functional Logic Gates

This paper reviews recent progress in quantum effect devices in NTT LSI Laboratories. A novel transistor structure using coupled-quantum-wells (CQW) for the base has succeeded in directly controlling the resonant tunneling collector current. An analysis of the cutoff frequencies of the device makes it possible to evaluate the resonant tunneling time in the quantum well base. A new logic gate, which features the use of the monostable-to-bistable transition of a circuit consisting of two resonant tunneling transistors (RTTs) connected in series, has been proposed. A unique function, "the threshold logic operation for the weighted sum of input signals", has been successfully demonstrated. A quantum interference device using a quantum wire with a stub structure where a stub-tuner gate is introduced has also been studied. Conductance modulation by the input voltage has been accomplished, which is a clear demonstration of the three-terminal operation of a quantum interference transistor based on the electric-field effect.