The electrical response of thick-film resistors to hydrostatic pressure and uniaxial stress between 77 and 535 K

The longitudinal gauge factor for a thick-film resistor material (Heraeus 8241) printed on an alumina substrate is found to be 12.6 at 295 K. The piezoresistive coefficient G, the unit change in resistivity per unit change in strain is 19.5, with a negative temperature coefficient of - 0.00335 K-1, measured between 77 and 535 K. Thick-film resistors of different geometry were subject to hydrostatic pressure, and by the use of the piezoresistive equation based on elastic theory, and elastic modulus data for Heraeus 8241, G was calculated and found to be 19.7 at 295 K, thus validating the piezoresistive equations and the elastic modulus value for Heraeus 8241. Hydrostatic pressure tests at elevated temperature were believed to be subject to some error, 10% at 500 K, due to adiabatic heating effects. However, it is apparent that resistance change can be predicted with a knowledge of strain in the x, y and z axes. This will prove useful for thick-film strain sensor design, where the thick-film resistor is simultaneously stressed in more than one direction. (C) 1999 Elsevier Science S.A. All rights reserved.