Noise and switching phenomena in thick-film resistors

Low frequency noise spectroscopy is employed to examine fluctuating phenomena that take place in the material of resistive films and in the film/termination interface of a thick-film resistor. It has been found that the excess low frequency noise apart from the 1/f component contains contributions from thermally activated noise sources with energies in the range 0.015-0.6 eV. These sources are nonuniformly distributed over the whole resistor volume, most probably in the glassy matrix or conductive grain boundaries. All noise sources are subjected to the switching phenomenon which abruptly changes the densities of local currents that describe the coupling of the resistance to noise processes produced in the fluctuators. Redistribution of currents results in switching between different sets of active noise sources that build up the noise spectrum. Extensive experimental studies that consider the influence of various parameters of fabrication process, sample geometry, substrate and operation exposures suggest that the most likely origin of the switching phenomenon is the relaxation of mechanical stress which in thick-film resistors appears due to the mismatch of the thermal expansion coefficients of the materials contained in resistive films, conductive terminations and the substrate.