Fabrication and measurement of metallic single electron transistors

Using the so-called self-aligned in-line technique, we have fabricated single electron transistors based on the metals aluminum, tantalum and chromium. The material deposition was carried out without exception by sputtering. The samples were electrically characterized both in a dilution refrigerator and in a helium-3 cryostat. In case of transistors made completely of (superconducting) aluminum we observed in the modulation characteristics deviations from the predictions of the orthodox theory of sequential quasiparticle tunneling. They are caused by additional current contributions due to Josephson-quasiparticle cycles. Furthermore, we report on the low-temperature behavior of mixed single electron transistors made of tantalum and chromium islands, respectively, between aluminum oxide barriers and external aluminum electrodes.