SU8 protective layers in liquid operating SAWs

In some applications, the medium can be aggressive with sensing devices. In this work, an epoxy based resist is proposed as protective layer for a SAW-type viscosity sensor in liquid media, in order to provide the sensor with durability and stability. Love-type devices are developed on ST-quartz substrates. Ti/Ag bilayer and SiO2 are used as IDTs and waveguide materials respectively. SU8-50 is chosen as protective coating. Several configurations are developed. For 20, 30 and 40 μm wavelengths, transmission signal spectra are obtained and the influence of different device parameters is analyzed. Propagation wave damping is determined for the SAW devices when different viscosity samples are dropped on the sweet spot.