Experimental demonstration of radio frequency quantum-dot cellular automata devices.

Over the past four decades the transistor-based microelectronics industry has developed dramatically. As transistor size approaches nanometer range, many problems such as device interconnection, power dissipation and short-channel effects become increasingly hard to overcome and degrade device performance. A new computation paradigm named Quantum-dot Cellular Automata (QCA) provides a possible solution for transistor-less circuitry design and computation at the nanometer scale. In a QCA structure, binary information is encoded by the bi-stable charge configuration within quantum-dot cells, and neighboring cells are coupled by the Coulomb interaction. No current flows within the cells. Functional QCA logic devices such as binary wires, majority gates, shift registers and fan-outs have been demonstrated in metal-dot systems at dilution refrigerator temperatures (<100 mK). However, the switching speed was on the order of seconds. This dissertation is focusing on investigating the time evolution of the binary state in QCA logic devices, as well as experimentally verification of the high-speed capabilities of clocked QCA devices. In order to detect the switching activity within the QCA devices, the QCA dots are capacitively coupled to the island of a radio frequency single-electron transistor (RF-SET), which provides sub-electron charge sensitivity and radio frequency response. We investigate two kinds of RF-SETs, whose islands are featured by single-walled carbon nanotube (SWNT) and aluminum dot. The reflectometry measurement setup is explained. The performance and issues are discussed. In this work, experimental demonstration of real-time electron switching is realized in a clocked aluminum-based electronic QCA device. The measurement is done in a 3He cryogenic system at elevated (compared to dilution refrigerator) temperatures. The operation speed has been improved up to micro-seconds. With the switching speed becoming faster, decrease in the error rate is demonstrated in the short-term QCA memory device. The technique presented here can serve as a prototype to explore an experimental solution for studying the intrinsic switching speed in a QCA.