Piezoresistive effects in thick film resistors: 30 years after

The most successful applications of thick film materials in the sensor area rely on piezoresistive effects exhibited by thick film resistors (TFRs). The earliest evidence of strain sensitivity in TFRs was available in 1973, but its value for thick film strain gauges was not recognized. A few years later attention was drawn on the peculiar set of properties that make TFRs valuable for the implementation of new classes of sensors for strain-related phys. quantities. Since then, piezoresistive properties of TFRs have attracted a great deal of scientific and technological interest and applications have rapidly spread for many diversified areas. Advances in knowledge accumulated in recent years on the properties of thick film piezoresistors are reviewed, in connection with resistive-paste composition, processing and film's micro-structure. Recent theoretical work is also mentioned: taking into account the segregated microstructure of TFRs, this work emphasizes how these piezo-resistive effects are related to this unique type of metal-insulator composites.