LOW-FREQUENCY NOISE IN SINGLE-ELECTRON TUNNELING TRANSISTOR

The noise in current biased aluminium single electron tunneling (SET) transistors has been investigated in the frequency range of 5 mHz < f < 30 Hz. A refined high frequency (HF) shielding including resistive c oaxial lines, that prevents spurious electromagnetic radiation and esp ecially high energy photons emitted by the 4.2 K environment from reac hing the sample, allows us to study a given background charge configur ation for many hours below approximate to 100 mK. The noise at relativ ely high frequencies originates from internal (presumably thermal equi librium) charge fluctuations. For f greater than or equal to 10 Hz, we find the same input charge noise, typically Q(N) = 5 x 10(-4) e/Hz(1/ 2) at 10 Hz, with and without the HF shielding. At lower frequencies, the noise is due to charge trapping, and the voltage noise pattern sup erimposed on the V(V-g) curve (voltage across transistor versus gate v oltage) strongly depends on the background charge configuration result ing from the cooling sequence and eventual radio frequency (rf) irradi ation. The measured noise spectra which show both 1/f and 1/f(1/2) dep endencies and saturation for f < 100 mHz can be fitted by two-level fl uctuators with Debye-Lorentzian spectra and relaxation times of order seconds. In some cases, the positive and negative slopes of the V(V-g) curve have different overlaid noise patterns. For fixed bias on both slopes, we measure the same noise spectrum, and believe that the asymm etric noise is due to dynamic charge trapping near or inside one of th e junctions induced when ramping the junction voltage. Dynamic trappin g may Limit the high frequency applications of the SET transistor. Als o reported on are the effects of rf irradiation and the dependence of the SET transistor noise on bias voltage. (C) 1998 American Institute of Physics.