Metallic single-electron transistor without traditional tunnel barriers

We report a new type of single-electron transistor (SET) comprising two highly resistive Cr thin-film strips (~ 1 µm long) connecting a 1 µm-long Al island to two Al outer electrodes. These resistors replace small-area oxide tunnel junctions of traditional SETs. Our transistor with a total asymptotic resistance of 110 kΩ showed a very sharp Coulomb blockade and reproducible, deep and strictly e-periodic gate modulation in wide ranges of bias currents I and gate voltages Vg. In the Coulomb blockade region (|V| ≤ about 0.5 mV), we observed a strong suppression of the co-tunneling current allowing appreciable modulation curves V(Vg) to be measured at currents I as low as 100 fA. The noise figure of our SET was found to be similar to that of typical Al/AlOx/Al single-electron transistors, viz. δQ ≈ 5 × 10-4e/√Hz at 10 Hz.