| A proposal for a new computing architecture called Quantum-dot Cellular Automata (QCA) is examined by investigating the practical requirements for realization. In the proposal, two stable electron configurations are predicted for a 'cell', defined as a particular charge island configuration, when two extra electrons are confined within the configuration. Because of the bistable nature of the cell, cell configurations can be designed such that primitive logic functions are realized. Two fundamental requirements for stable cell operation are inter-cellular electrostatic coupling and intra-cellular electron sharing. The nature of the coupling and sharing is dependent on the materials, fabrication processes and the island and cell configurations. Two other requirements exist: the ability to write information into the cell (to locally change the electron configuration) and to read information from the cell (to locally detect the electron configuration). Given the requirements for QCA operation, we have identified and evaluated tooling, materials, processing, characterization requirements and devices working towards the realization of III-V semiconductor QCA operation.;From this investigation, a robust process sequence was developed to produce devices exhibiting single-electron confinement. Within this effort, an electron beam lithography system capable of producing device critical dimensions less than 50 nm with level alignment tolerance less than 50 nm was realized. A comprehensive characterization strategy, apparatus and control system was implemented to provide the required feedback for process control, device characterization. With these tools, we produced and demonstrated devices exhibiting two-dimensional confinement as well as devices exhibiting three-dimensional confinement. Moreover, we were able to realize a non-invasive single electron detection scheme and develop design criteria for non-invasive probing of single electron structures. |
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