Strength of ceramic substrates for piezoresistive thick-film sensor applications

Force and pressure sensors based on the piezoresistive properties of thickfilm resistors are widely used due to their reliability, simplicity and lowcost. Recently, the introduction of low-temperature co-fired ceramic(LTCC) substrates has allowed further increases in miniaturisation and integration, while new high-strength ceramic substrates such as zirconia- toughened alumina (ZTA) has enabled better sensor response.However, the materials' properties are still insufficiently characterised for sensor applications. Properties such as long-term strength, and especiallythe effect on the strength and reliability of thick-film processing, havereceived insufficient attention so far. In this work, the short and long-term strength of these substrates is compared with that of standard 96% alumina,and the effect of various thick-films (resistors, dielectrics, conductors) onthe mechanical behaviour is studied. It is shown that thick-film compositions can have a dramatic effect on the strength of the substrates.