Low Frequency Noise Measurements in La 0.7 Sr 0.3 MnO 3 Thin Films on (100) SrTiO 3

We report measurements of the 1/f noise in 75 nm, 100 nm and 200 nm thick La 0.7 Sr 0.3 MnO 3 (LSMO) thin films deposited onto (100) SrTiO 3 substrates by pulsed laser deposition. The samples were patterned using photolithography into bridges with various widths (20 µm to 150 µm) and lengths (50 µm to 300 µm). The voltage noise spectra S V (f) clearly showed two regions: excess noise depending on the bias current with a 1/f behavior at low frequency and Johnson noise (4kTR where R is the resistance of the device) at higher frequency. In the investigated 10 Hz-100 kHz frequency range no deviation from the 1/f behavior was noticed neither as a function of the temperature (300-400 K) nor of the bias current. We particularly investigated the validity of the semi-empirical Hooge relation in the 300-400 K temperature range, which means across the metal-insulator transition. The voltage noise density S V in LSMO bridges was found to be proportional to the square of the bias voltage V in the whole temperature range, indicating that noise arises from resistance fluctuations. Unexpectedly the normalized Hooge parameter α H /n was found not to be volume independent, indicating in a first approach that the noise source localization is not homogeneous. Finally a α H / n value of 8 × 10-31 m-3 have been obtained, which is among the lowest level reported in LSMO thin films and promising for the realization of uncooled bolometers