New thick-film material for piezoresistive sensors

IrO2-based resistors were prepared with the standard methods of thick-film technology and their electrical properties were studied in order to identify the best composition for piezoresistors suitable for sensors to be operated continuously at temperatures exceeding 150 degreesC. The obvious criterion was to minimise the temperature coefficient of resistance (TCR) and the temperature coefficient of the gauge factor (TCGF), with minimum shift of the resistance in long term high temperature operation, without sacrificing the gauge factor (GF). The results achieved include resistors with sheet resistance lower than 100 k Omega/square; TCR values lower than 250 ppm/degreesC over the temperature range from -40 to 200 degreesC and lower than 100 ppm/degreesC from 25 to 200 degreesC; GF approximate to 7-10; TCGF approximate to -130 ppm/degreesC; relative change of resistance DeltaR/R < 0.1% after ageing at 150 degreesC for 1000 h. Performance characteristics, studied in the temperature range of 25-175 degreesC, of a gauge pressure sensor exploiting IrO2 piezoresistors are reported. (C) 2001 Elsevier Science B.V. All rights reserved.