A 200 MHz surface acoustic wave resonator mass microbalance

Abstract

Surface acoustic wave (SAW) piezoelectric sensors typically used by researchers in analytical applications are based on SAW delay lines. We report here the development of a 200 MHz SAW instrument based on a SAW resonator instead of a conventional delay line. The instrument is small, compact and uses two separate 200 MHz resonator crystals which operate in the dual difference mode. The difference frequency stability is better than 55× 10⁻⁹ (±1 Hz) which is comparable to a 10 MHz bulk crystal (on an absolute frequency basis) and at least an order of magnitude better than other commercially available SAW delay lines that operate at comparable frequencies. The mass sensitivity is about 9 × 10¹⁰ Hz cm²/g. Response to temperature change is found to be about 20 Hz/°C from −30 °C to 30 °C. Response to pressure is found to be linear from 760 to 415 Torr at 3 Hz/Torr. Detection limits for HCl vapors were determined to be in the low ppb range using a SAW resonator coated with triethanolamine.