Strategies for Giant Mass-sensitivity using Super-high Frequency Acoustic Waves

Surface acoustic wave (SAW) devices are powerful platforms for mass sensing, chemical vapor or gas detection, and biomolecular identification. Great efforts have been made to achieve high sensitivities by using super-high-frequency SAW devices. Conventional SAW sensing is based on mass-loading effects at the acoustic wave propagation (or delay line) region between two interdigitated transducers (IDTs). However, for many super-high-frequency SAW devices with their small sizes, there is a huge challenge that the sensitivity is difficult to be further increased, simply because there are very limited areas between the IDTs to deposit a sensing layer. Herein, we proposed a novel strategy based on giant mass-sensitivity effects generated on the global area of acoustic wave device (defined as areas of both delay line region and IDTs), which significantly enhances sensitivity and reduces the detection limit of the SAW device. Both theoretical analysis and experimental results proved this new strategy and mechanism, which are mainly attributed to the efficient energy confinement at the IDTs' region for the super-high-frequency SAW devices. The achieved mass sensitivity using this new strategy is as high as 2590 MHz · mm2·μg-1, which is about 500 times higher than that obtained from only using the acoustic wave propagation region with a SAW frequency of 4.43 GHz. Hypersensitive humidity detection has been demonstrated using this newly proposed sensing platform, achieving an extremely high sensitivity of 278 kHz/%RH and the fast response and recovery times of 37 and 35 s, respectively.