Development of low-temperature thick-film materials for piezoresistive sensors
Thick-film materials are very advantageous for piezoresistive pressure and force sensors because of ease of processing, reliability and low cost. However, their applications are restricted because standard thick-film materials require processing temperatures around 850°C, which essentially restricts them to ceramic substrates. In this work, we examine the processing and properties of thick-film dielectric and resistor compositions designed to sinter at lower temperatures, making them compatible with high-strength stainless steel alloys (<700°C). Both dielectric and resistor materials are based on a lead borosilicate glass matrix, with suitable filler materials such as SiO2 (quartz) and Al2O3 for the dielectrics and RuO2 for the resistor. The materials were investigated X-ray diffraction, mechanical and electrical testing. During firing, the thick-film materials undergo liquid-phase sintering through the glass matrix. Glass-filler chemical interactions are significant in the case of SiO2 filler, and very small with Al2O3 or RuO2. By adjusting the fillers, the glass composition and the processing parameters, we can obtain suitable thick-film materials for piezoresistive sensors with low processing temperatures, compatible with high-strength steel substrates.