Noise Properties of Single Electron Transistors

We have measured the low frequency (5 mHz<f<30 Hz) noise in current biased aluminium single electron tunneling (SET) transistors. A refined high frequency (HF) shielding allows us to maintain and study a given background charge configuration for many hours at T<100 mK. At frequencies below 10 Hz the noise is mainly due to charge traps, and the noise pattern superimposed on the V(V_g)-curve strongly depends on the particular background charge configuration resulting from the cooling sequence and the applied RF irradiation, including thermal radiation from the 4.2 K environment. The noise spectra, which show both 1/f and 1/f^1/2 dependencies and saturate at f<100 mHz can be fitted by two-level fluctuators (TLF) with Debye–Lorentz spectra and relaxation times on the order of seconds.