Thick film resistors on stainless steel as sensing elements for strain sensor applications

In this paper, thick film resistors (TFRs, R8241, Heraeus) on 430 stainless steel (SS) substrate for strain sensor applications are investigated. TFRs are screen printed and fired on dielectrics-on-430SS substrate by thick film technology. Microstructure analysis shows that no interaction or evidence for new phase can be detected at the interface between TFRs and dielectrics-on-430SS, which indicates the compatibility of the dielectrics and TFRs. Further experiments also show the excellent insulativity and robust bonding between the dielectrics layer and 430SS substrate. Meanwhile, temperature coefficients of resistivity (TCRs), gauge factors (GFs) and noise indices (NI) of TFRs are measured. Finally, thick film technology based steel pressure sensors (SPS) are fabricated by screen printing and firing four TFRs on a machined circular diaphragm and then the TFRs are connected in a Wheatstone bridge configuration. Preliminary tests show that the sensors exhibit a sensitivity of 4.68 mV/V full-scale (FS) with 0.1% FS linearity and 0.15% FS hysteresis and 0.15% FS repeatability. Moreover, the thermal zero drifts and thermal sensitivity drifts of the sensors in the whole temperature range (−40 °C to +125 °C) are less than 2.5% FS.