Piezoresistive properties of RuO2-based thick-film resistors: The effect of RuO2 grain size

The piezoresistive properties of thick-film resistors are well documented and widely used in sensors of strain-related quantities. However, the origin of the effect is not well established, and correlations between resistor composition and relevant properties (such as strain sensitivity, temperature coefficient of resistance (TCR) and excess noise) have been not worked out yet. This paper reports a systematic study of these correlations in RuO2-based model resistors prepared with the same glass frit and RuO2 powders covering a range of particle sizes from a few nanometres to micrometres. Gauge factors (GFs) from 2 to 30 have been observed in resistors of sheet resistance R-square in the range 1 k Ohm/square to 3 M Ohm/square. At a selected R-square value, the GF increases linearly with the logarithm of RuO2 grain size, while the TCR and excess noise do not significantly depend on the RuO2 powder size.