Experimental demonstration of quantum-dot cellular automata: Basic cell, binary wire and logic gate.

摘要

An experimental demonstration of Quantum-dot Cellular Automata (QCA) is presented in this dissertation. QCA is a revolutionary computation paradigm that addresses the issues pertaining to device density, interconnect problems and power dissipation. The basic unit in this architecture is an electrostatically coupled quantum-dot cell that consists of four dots at the vertices of a square. The Coulomb repulsion of electrons within a cell, quantum confinement effects, and discreteness of electron charge, combine to produce two ground states of the cell which are used to encode two stable states of digital logic. Two, four, six and eight-dot systems are constructed using aluminum tunnel junction technology to study various elements of QCA paradigm.; QCA switching operation is accomplished by causing an electron to exchange positions in the input set of dots and non-invasively detecting variations in electron populations in the output set of dots. A QCA binary wire is constructed in a similar manner as a QCA cell by connecting three capacitively coupled double-dots. Switching in the first double-dot induces an opposite switching in the adjacent, second double-dot, resulting in a polarization change of the third (output) double-dot. Logic operation of a QCA cell is demonstrated by applying artificial potential swings to the gates of the cell that mimic electron hopping in the neighboring dots. The measured results show correctly performed AND and OR operations by the logic gate. Lower bound of the maximum operating frequency of QCA cells is estimated by considering the thermally averaged conductance reduction during the switching process. The estimated lower bound of the switching frequency is in tens of megahertz for the fabricated devices, the upper bound, which depends on the RC time constant of the circuit, is in hundreds of Gigahertz.; The devices included in this dissertation are the first to show QCA implementations in any system. These experiments mark a key step toward realizing an architecture paradigm that is fundamentally different from existing transistor based digital logic. Advancement in nanotechnology will facilitate molecular implementation of QCA's that will be operable at room temperature.