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

Abstract

We investigate the shear-horizontal surface acoustic waves ͑SH-SAWs͒ generated on an AlN/Al 2 O 3 microstructure by laser-micromachined grooves on the AlN film. In the absence of grooves, the AlN/Al 2 O 3 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.

Acoustic plate mode propagation and interaction with ultraviolet light in periodic AIN-on-sapphire structure

“…Since the exact mode number in the experiment could not be identified, the order of one mode ͑m =7͒ was arbitrary selected to fit the frequency values. We were not able to observe the Rayleigh waves, in contrast to earlier observations, 8 where the grating was formed only on the SAW path between the IDTs. Possibly, the presence of the grating structure in the IDT regions in our case might have caused the excitation of the Rayleigh wave to be suppressed by transferring its energy to SH modes.…”

“…Excitation of the acoustic waves faster than the Rayleigh waves has been observed in AlN-onsapphire structure with periodically grooved surface. 8 Similarly, the periodic columnar structure of AlN formed by ELOG technique seems to stimulate the excitation of plate modes in our case. The enhancement of the surface acoustic wave type conversion by periodical gratings was analyzed in Ref.…”

“…AIN due to its high surface acoustic wave velocity ͑ϳ5.76 km/ s͒, wide band gap ͑6.2 eV͒, low temperature coefficient of frequency ͑ϳ−19 ppm/°C͒, 4 low dielectric loss, and high electrical resistance is very suitable for fabricating SAW detectors for solar-blind UV sensing. Up to now, most AlN based acoustic devices, such as bulk wave resonators, 5 leaky, 6 Rayleigh, 7 and shear horizontal 8,9 wave sensors, were used for mass detection. We now report on the response to UV light of acoustic plate modes propagating in a sapphire substrate with AlN overlay with a characteristic periodic structure fabricated by epitaxial lateral overgrowth ͑ELOG͒ technique.…”

Relocation effect and polarization mixing of surface acoustic waves in AlN-GaN bilayers on Al2O3(0001) substrates

“…Shearhorizontal SAWs are attractive, for instance, for biosensing applications, 13 as their damping resulting from the loading of biofluidic materials is negligible. 14 We note that the emergence of the acoustic vibration in the sagittal plane, which enables the excitation of the Love-type mode by IDTs, also leads to a damping when the SAW propagation path is loaded with fluid. It is thus desirable for such applications that the SAW condition be shifted away from the mode proximity region after the launch of the Love-type mode from IDTs, for instance, by adiabatically varying the layer thickness.…”

Collimation of horizontally polarized shear waves by means of ridge grating supported Love modes

“…[13][14][15][16] In particular, shear horizontal ͑SH͒ polarized modes which do exist on substrates or metal samples when ridges are milled, grown or adsorbed onto them are widely used in connection with viscosity, gas, and ͑bio͒chemical sensing such as nondestructive testing. [17][18][19] The wave motion of a nonpiezoelectric, isotropic elastic material is governed by the general lossless equation of motion:…”