Electrical conduction and strain sensitivity in RuO2 thick film resistors

Abstract

We have measured the resistance and strain characteristics of RuO2-based thick film resistors and find that they differ from Ru-based pyrochlore (A2Ru2O7) resistors. The dependence of resistance on RuO2 volume concentration (x), for different (average) particle sizes, obeys a critical conduction expression of the form R=R0/(x−xc)t, with t≊3. The strain dependence of resistance or strain gauge factor (γ) approximately follows the phenomenological expression γ=γ0+Atx/(x−xc), with γ0 between 2 and 3. Pyrochlore resistors obey the same critical conduction behavior, but we had previously found that t≊2. Further, γ is larger for pyrochlore resistors for comparable resistivity and particle size. We account for the differences by postulating that in RuO2 resistors sintered conduction pathways dominate at low resistance, and both sintered interfaces and tunnel junctions contribute to the high resistance behavior. This is in contrast to pyrochlore resistors for which we believe that tunnel junctions always dominate electrical conduction.