Investigation of acoustic properties and Raman scattering of AlN films for biosensor application

In this study, two approach of the molecular-level detection technique, acoustic-based and Raman-scattering-based detection, are adopted. The acoustic resonant signals are sensitive to the loading mass, such as nano particles and bio-molecules, while Raman scattering signals are highly surface sensitive to a wide range of adsorbate molecules. Aluminum nitride (AlN) thin film dominars both of the techniques. In the acoustic device, AlN acts as a piezoelectric layer to excite acoustic wave. In the Raman scattering experiment, the surface morphology of AlN give rise to a surface enhanced Raman signal. Thus, thin film bulk acoustic wave (TFBAW) properties as well as the surface enhanced Raman spectroscopy (SERS) signals of AlN are investigated. To obtain good piezoelectricity, a highly c-axis orientated AlN thin film is prepared by a reactive RF magnetron sputtering system. The c-axis orientated AlN possesses a pebble-like morphology, which is suitable for the SERS. Solidly-mounted resonators (SMR) are adopted to excite high frequency resonant signal, and the 1.5 GHz shear resonance signal is obtained. In the SERS measurement, the aqueous solution of Rhodamine 6G with concentration of 10^-6 M added with 10 mM of sodium chloride was utilized to calibrate the enhancement factors.