Surface acoustic wave gas phase sensor using self-assembled monolayer film

A surface acoustic wave (SAW) sensor for measuring environment is presented. SAW devices respond to changes in the mass on its surface with a shift in frequency, and offer many attractive features for applications as a gas and liquid phase sensor. In the most gas phase sensor, the device surface is coated with a thin selective film. In this paper a SAW delay line coated with self-assembled (SA) film has been used as environment sensor. A dual delay line was fabricated on a single lithium niobate (128° Y cut X propagating LiNbO₃) substrate and the propagation path was coated with the selective polymer film deposited by SA transfer technique. The polystyrene sulfonic acid sodium was used as a gas sensing material. Due to sorption of molecules, the electrical conductivity of the SA film changes. The effects caused to reduce the velocity of the SAW. Experimental results showed that the SAW velocity change was quite linear in proportion to the concentration of organic gases. Rapid and totally reversible responses were obtained by using a SA monolayer film.