IrO2-based thick-film resistors

IrO2-based thick-film resistors were prepared and their microstructure/electrical property relationship was studied as a function of the firing temperature T-f and composition. The resistor microstructure exhibits a notable change, from a strongly segregated structure for T-f=750 degreesC, to a quasihomogeneous one when the firing temperature increases to T-f=850 degreesC. Likewise, a substantial change is observed in the sheet resistance (R-s) dependence on the volume fraction (v) of the conductive phase. For resistors prepared at T-f=750 degreesC the percolation power law R(s)approximate to(v-v(c))(-t) (where v(c) and t are the critical volume fraction and exponent, respectively) is observed, while samples fired at T(f)greater than or equal to850 degreesC follow the relation ln R(s)approximate toa(v-v(0)) where a and v(0) are proper constants. In addition, the slope of plot a is affected by the firing temperature T-f as well as by the measuring temperature at T<50 K. Very high temperature coefficients of resistance are measured at cryogenic temperatures. The longitudinal gauge factor values are in the range from 3 to 12.4 according to the resistor composition and firing temperature, with the highest values in samples fired at 950 degreesC with sheet resistance in the range from 10(4) to 10(7) Omega/square.