MICROANALYSES FOR PIEZORESISTIVE EFFECT ON ACTUAL AND MODELED INTERFACES OF RuO2-GLASS THICK FILM RESISTORS

The piezoresistive mechanism of composite thick-films based on RuO2 particles in calcium-borosilicate or bismuth-borosilicate glass matrix was investigated by chemical microanalyses. Diffusion pairs of RuO2 and glass were also prepared as model specimens for the composite thick-film resistors. The resistor based on bismuth-borosilicate glass showed higher sensitivity than that based on calcium-borosilicate glass. The diffusion of ruthenium into glass was examined with TEM-EDS and SIMS and the chemical structure was analyzed with EELS. The bismuth-borosilicate glass with higher piezoresistive sensitivity was found to have larger amount of diffused ruthenium, which has trivalent and tetravalent states in the glass. Furthermore, the electron state of oxygen was revealed to be changed by the diffusion of ruthenium and the existence of holes is indicated. The analyses suggest that the conduction mechanism is variable range hopping conduction (VRHC) that carriers (holes) transfer between different sites of the ruthenium. Piezoresistive effect in this type of system is considered to be the result of the change in distance between sites due to the distortion caused by the external force.