Conference paper

High performance low-firing temperature thick-film pressure sensors on steel

Performance of piezoresistive thick-film pressure sensors on steel substrates is hindered by the high required firing temperatures of the layers, which cause degradation of the substrate mechanical properties. Special steels or alloys that are relatively unaffected by these temperatures are available, but their cost is very high. A much more promising alternative is the reduction of the thick-film firing temperature, in order to allow application of the standard high-strength steels used in thin-film cells. Therefore, a series of thick-film materials systems (dielectrics, resistors and conductors) firing at low temperatures (<700°C) on steel substrates has been developed and electrically characterised (sheet resistance and thermal coefficient of resistance – TCR). It was found that the main issue in these systems lies in mastering the materials interactions during firing, especially at the silver- based resistor terminations. The interaction of silver, resistor and dielectric tends to give rise to highly resistive zones at the terminations, affecting reliability. This can be circumvented by post-firing the resistor terminations at a moderate temperature. Key words: Thick-film materials, steel substrates, low-temperature processing, resistors, termination effects

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