Propagation of a shear-horizontal surface acoustic mode in a periodically grooved AlN/Al2O3 microstructure

We investigate the shear-horizontal surface acoustic waves (SH-SAWs) generated on an AlN/Al2O3 microstructure by laser-micromachined grooves on the AlN film. In the absence of grooves, the AlN/Al2O3 device shows resonance for only a lower velocity SAW mode. However, when grooves of periodicity smaller than half the wavelength of the surface acoustic wave are micromachined, a higher velocity resonance due to a SH-SAW mode is observed in the device. It is found that our SH-SAW mode remains undamped and is able to propagate across the device when loaded with a biofluidic mass. We have also measured the mass sensitivity of the SH-SAW mode under biofludic load in terms of frequency shift. Measurements show that this mode has a very high mass sensitivity of the order 1.35 ng/ml, which suggests that the device can be applied for the detection of a small concentration of antigens in a biofluid. In this article, the fabrication and grooving techniques of the device are also addressed.