Complementary digital logic based on the ‘‘Coulomb blockade’’

A finite charging energy, e2/2C′, is required in order to place a single electron onto a small isolated electrode lying between two tunnel junctions and having a total capacitance C′ to its external environment. Under suitable conditions, this elemental charging energy can effectively block all tunnel events near zero bias voltage in series arrays of ultrasmall junctions, an effect that has come to be known as the ‘‘Coulomb blockade.’’ This article outlines a new approach to the design of digital logic circuits utilizing the Coulomb blockade in capacitively biased double-junction series arrays. A simple ‘‘on’’/‘‘off ’’ switch is described and complementary versions of this switch are then employed to design individual logic gates in precise correspondence with standard complementary metal–oxide semiconductor architecture. A planar nanofabrication technique is also described that may eventually allow the integration of Coulomb blockade logic onto conventional semiconductor chips, thereby realizing hybrid integrated circuits having device densities and operating speeds far in excess of present technology.