We present a comparative study of three configurations of un-cooled micro-bolometers based on amorphous silicon–germanium thin films deposited by plasma at low temperature and compatible with the IC technology. The temperature dependence of conductivity δ(T), current–voltage characteristics I(U) and current noise spectral density (NSD) have been measured in order to characterize and compare the performance characteristics, such as responsivity and detectivity in three configurations of micro-bolometers: (a) planar structure with a silicon–germanium intrinsic (a-SixGey:H) thermo-sensing film; (b) planar structure with a silicon–germanium–boron alloy (a-Six-GeyBz:H) thermo-sensing film and (c) sandwich structure with an intrinsic (a-SixGey:H) thermo-sensing film. The samples studied demonstrated different cell resistance Rc = 105–108 X and responsivities R1 = 101–10-3 A/W, while the values of detectivity D* were quite similar D* = (4–7) X 109 cm Hz1/2 W-1.