We have studied noise in four configurations of un-cooled micro-bolometers: three of them were built in a planar structure with a) a-Six Ge y, y = 0.88, b) a-SixGeyBz:H, y = 0.67 and z = 0.26; c) y = 0.71, z = 0.23 and the fourth d) sandwich structure with y = 0.88. These samples were characterized by SIMS (composition), FTIR (H-bonding and H content), conductivity measurements (σ(T), activation energy, TCR), current-voltage characteristics in dark and under illumination enabling in this way the determination of responsivity. The power noise spectral density (PNSD) versus frequency S(f) was studied in the range of frequency f=1 to f=103 Hz under IR illumination and constant bias. The measurements were performed in a vacuum chamber with pressure P=10 mTorr. In general the S(f) measured on our devices, demonstrated three regions separated by two corner frequencies: fc1 and fc2. The regions are: 1) f ≤ fc1 S1 ~ f β and β = 0.1 to 0.3, 2) fc1 ≤ f ≤ fc2, S2 ~ f-γ and γ = 0.75 to 1.5 and 3) f ≥ fc2 and S3 – const (f). The different samples here studied showed different values of fc1, fc2, β, γ and S3 level. The noise characteristics experimentally observed experimentally are used for determining the detectivity D* of the devices and these data are analyzed and compared with the data reported in literature.