High performance thick-film pressure sensors on steel

The aim of this work is to examine the possibility of high performance pressure sensors based on piezoresistive thick films deposited on steel membranes, which combine the performance advantage of thin-film sensors (high-strength steel substrates, assembly without elastomer seal) with the low cost of ceramic thick-film sensors. As standard thick-film firing conditions degrade the properties of most high-strength steels, two routes were explored: 1) application of a special steel, which does not undergo mechanical degradation at 850°C, and 2) development and use of thick-film materials firing at a lower temperature. This work presents the development and characterisation of low-firing thick-film systems (dielectrics, resistors and conductors), formulated to achieve chemical and thermal expansion compatibility with a wide range of substrates. Results on electrical properties of these systems: resistance, thermal coefficient of resistance (TCR) and strain response on different steel substrates are compared, together with those of standard thick-film systems on heat resistant special steel.