Thermal equilibrium noise with 1 / f spectrum from frequency independent dielectric losses in barium strontium titanate

We investigated the dielectric losses of doped and undoped BaSrTiO 3 (BST) from thermal noise measurements. The results are compared to impedance measurements. The value for the frequency independent loss angle is about t g δ = 2 × 10 − 2 in the range 100 < f ( Hz ) < 10 5 . The thermal voltage noise of the BST capacitor with losses has a 1 / f spectrum in agreement with 4 k T R ( Z ) and a frequency independent t g δ . The detection limits due to the low noise voltage amplifier are investigated and experimentally verified. The frequency range f high , f low , where the " 1 / f thermal noise" is above the background noise is characterized by the ratio f high / f low = t g 2 δ ( R in / R eqw ) , with R in the input resistance of the low noise voltage amplifier and R eqw the frequency independent part of its equivalent noise resistance at high frequencies.