Low temperature AlN thin film growth for layered structure SAW and BAW devices

In this work, c-axis oriented aluminium nitride thin films on silicon substrates were deposited by reactive RF magnetron sputtering method at various substrate temperature (without heating - 400°C) with the same thickness (1.4 μm). The structural, morphological and optical properties of AlN films were investigated by X-ray diffraction, field emission scanning electron microscope, atomic force microscopy and Fourier transform infrared absorbance spectroscopy. It was found that the AlN films showed the same highly [002] preferred orientation with low full width of half maximum of rocking curve, which is about 2° for all the films elaborated in various temperatures. The optical properties of these films analysed by FTIR, exhibit absorption bands attributed to vibrational modes of Al-N bonds, in particular El(TO) at 678 cm^-1 and Al(TO) at 613 cm^-1. The surface roughness of films determined by AFM is less than 0.5 nm for the film grown at low temperature, which is very suitable for SAW device achievement. Elastic properties of deposited AlN films were evaluated by realisation and characterisation of AlN/silicon SAW device. Experimental results show that realised structure exhibits a good frequency response and practical values of electromechanical coupling coefficient and temperature coefficient of frequency.