Single-charge transport in coupled nanostructures

Abstract

This thesis research is focussed on the development of strongly coupled single-charge devices. Single-charge devices are sub-micrometer sized electronic circuits that use the fact that charge is quantized. Their main component is the tunnel junction, a resistive element that can be made as small as one nanometer. In the past, many different circuits have been fabricated with the tunnel junction such as ultra-sensitive electrometers. To actually fabricate logical gates and memory, a multi-layer technology is required to couple the circuit elements. We developped a special multi-layer technology, using heavily oxidized aluminum gates. With this new technique it was possible to make a memory cell, where information was coded as the presence or absence of a single electron. Also a logic inverter was fabricated with voltage gain. As another example of the performance of this multilayer technique, an on-chip frequency generator was coupled to a single-electron transistor. By measuring the photo-response of the single-electron transistor, it could be estimated that 75% of the generated signal was coupled through. This is much higher than has been achieved in similar experiments. It can be concluded that the new multi-layer technique performs extremely well. The technique has been used to couple various single-charge devices, demonstrating the feasibility of even more complex single-charge devices.