Single electron transistor fabricated with SOI wafer

The single electron transistor (SET) is the most sensitive device for measuring the charge of electron. It has been proposed by Kane that the SET can be used for readout of calculated results in Si-based quantum computer. We fabricated the SET with SOI substrate utilizing the suspended mask of SiO₂ and Si for the purpose of using it for readout of calculation in Si-Based quantum computer. By using only the above materials for the mask, high temperature processes including ion implantation and activation annealing could be possible and it was never achieved in conventional methods with the suspended mask with photoresist. First, the suspended mask with enough undercut in SOI was made by removing the box oxide of SOI wafer combining with pattern delineation by electron beam lithography, anisotropically reactive ion etching and isotropic wet etching. After forming the suspended mask, Al films were evaporated from two different angles to make an overlap just below the bridge, resulting in completing the SET in the undercut region possible to measure the electron spin. After making the Al/Al₂O₃/Al SET, we measured the I–V characteristic between source and drain at 1.8 K. The Coulomb blockade and the Coulomb oscillation were observed.