High-strain response of piezoresistive thick-film resistors on titanium alloy substrates

We examine, in this work, the integration and high-strain response of piezoresistive thick-film resistors on titanium and titanium alloy, as compared with ferritic stainless steel and the standard alumina substrates. In general, titanium and its alloys are relatively ill suited for use as a thick-film substrate using the standard 850 °C firing process, because of its low oxidation resistance and tendency to dissolve oxygen. This problem can be alleviated by applying suitable thick-film glassy protection layers. Titanium alloys are very elastic, and allow piezoresistive responses well in excess of 4% with little plastic deformation of the substrate, using standard commercial thick-film resistor compositions. In this case, the behaviour of the sensor becomes asymmetric, as failure of the resistor or insulating dielectric under tension––and therefore the mechanical properties of these materials–– becomes the factor limiting the response of the sensor.