A NEW HIGH-FREQUENCY HIGH-SENSITIVITY SAW DEVICE FOR NO2 GAS-DETECTION IN THE SUB-PPM RANGE

A high-frequency SAW gas-sensing device has been developed for an operating frequency of 600 MHz. It contains three separate SAW delay lines, which are the frequency-determining elements of oscillator circuits. They can be coated with thin organic films as adsorbents for gas concentration measurement. Due to the adsorption process the mass of the film increases, causing a decrease of surface wave velocity, which will correspondingly cause a downward shift of the oscillation frequency. First measurements are made with two classes of NO2-sensitive films: evaporated lead phthalocyanine layers from 1 to 15 nm thick and Langmuir-Blodgett (L-B) films with molecules consisting of a soluble iron phthalocyanine derivative. The dependence of sensitivity on the thickness of the sublimated films and the type of interaction of NO2 with these coatings are discussed.