Fabrication of aluminum single-electron transistors with low resistance-capacitance product

The optimum speed and sensitivity of a single-electron transistor (SET) depend crucially on the resistance-capacitance (RC) product of the tunnel junctions. We present a fabrication method of aluminum single-electron transistors with a high percentage of working devices (80%) and record low RC products: SETs with a typical charging energy of 15K and a resistance of 100kΩ. The oxygen pressure during junction oxidation was very low, 8∗10−4mBar, which resulted in devices with a high cut-off frequency (up to 40GHz). The devices were characterized at 4.2K and at 90mK. The noise was typical for an aluminum single-electron transistor (2.5∗10−4e∕Hz), and the gain (dID∕dQg) was high (54.5nA∕e).