1/f Noise in the superconducting transition of a MgB2 thin film

The noise voltage spectral density in the superconducting transition of a MgB2 thin film on a SiN-coated Si thick substrate was measured over the frequency range 1 Hz-to-1 KHz. Using established bolometer noise theory the theoretical noise components due to Johnson, 1/f (excess) and phonon noise are modeled to the measured data. It is shown that for the case of a MgB2 thin film in the vicinity of the mid-point of transition, coupled to a heat sink via a fairly high thermal conductance (≈10−1 W/K) that the measured noise voltage spectrum is 1/f limited and exhibits 1/fa dependence with a varying between 0.3 and 0.5 in the measured frequency range. At a video frame rate frequency of 30 Hz the measured noise voltage density in the film is ≈61nV/Hz, using this value an upper limit of electrical NEP≈0.67pW/Hz is implied for a practical MgB2 bolometer operating at 36.1 K.