Flexible thin-film acoustic wave devices with off-axis bending characteristics for multisensing applications

Flexible surface acoustic wave (SAW) devices have recently attracted tremendous attention for their widespread applications in sensing and microfluidics. However, for these applications, the SAW devices often need to be bent into off-axis deformations between the acoustic-wave propagation direction and bending direction. Currently there are few studies on this topic, and the bending mechanisms under off-axis bending deformations have remained unexplored for multi-sensing applications. Herein, we fabricated aluminum nitride (AlN) flexible SAW devices by using high quality AlN films deposited on flexible glass substrates and systematically investigated their complex deformation behaviors. A theoretical model was firstly developed using coupling wave equations and boundary condition method to analyze the device’s characteristics with bending and off-axis deformation under elastic strains. The relationships between frequency shifts of the SAW device with bending strain and off-axis angle were obtained which showed the identical results with those from the theoretical calculations. Finally, we performed proof-of-concept demonstrations of multi-sensing applications by monitoring human wrist movements at various off-axis angles and detecting UV light intensities on a curved surface, thus paving the ways for versatile flexible electronics applications