Fabrication and DC characterization of single electron transistors at low temperature

Abstract

The metallic single electron transistor (SET) has been shown to provide charge sensitivity on the order of 10-6 e/(Hz)1/2, when operated as a charge amplifier. This makes it an ideal candidate for low-noise measurement schemes, such as monitoring nano-mechanical oscillations, or reading out the charge state of a quantum bit. The SET operates by exploiting quantum tunneling across an ‘island’ between two insulating tunnel junctions, and can be modulated by a capacitively coupled gate electrode. A metallic SET has been fabricated and characterized at low frequencies. The device was fabricated on a silicon substrate coated with a bi-layer resist, using electron beam lithography. The Al-AlOx¬-Al tunnel junctions were created using double angle evaporation. Samples were tested near 300 mK in a custom helium-3 cryostat system. Results which characterize the SET parameters and conductance behaviour were obtained, in both the superconducting and normal states. This thesis contains a discussion of the fabrication procedures and dc measurement techniques required to produce and test a single electron transistor. Relevant background theory relating to SET operation and cryogenic laboratory techniques is presented. A brief discussion of proposed future experiments using a dual gate radio frequency SET as a more sensitive amplifier is introduced.