Synthesis and microstructural characterisation of reactive RF magnetrorr sputtering A1N films for surface acoustic wave filters

摘要

Wurtzite aluminium nitride (A1N)thin films were deposited by RF reactive magnetron sputtering technique on (1 00)silicon substrates at low temperature (400 deg C).The microstructural properties of sputtered A1N films were investigated using X-ray diffraction (XRD),scanning electron microscopy,transmission electron microscopy and atomic force microscopy (AFM),to aim improvement of piezoelectric coupling for surface acoustic wave (SAW)devices.It was found that the A1N films deposited in the optimum experimental conditions,as revealed by XRD and selected area electron diffraction,exhibit a high (0 0 2)preferred orientation,where columnar crystals are grown in a non-epitaxial pattern and aligned almost perpendicular to silicon substrate.The omega rocking curve,shows that the standard deviation of columns of thin A1N films is less than 1deg,which exhibit a high quality of these films.Furthermore,the AFM found a very low surface roughness less than 7 A,which is very crucial to decrease a loss propagation in A1N films.The films synthesised with optimum conditions were used to perform SAW devices by developing inter-digital transducer on AIN/Si structure.Frequency characteristics show that the realised SAW devices exhibit good filtering performances and a good compromise between phase velocity,electromechanical coupling coefficient and temperature coefficient of frequency.