Hydrogenated aluminum nitride (AlN:H) films have been deposited on silicon wafers by the RF reactive magnetron sputtering method with $H_2$ gas addition to Ar-$N_2$ gas mixture. It is found that as the amount of $H_2$ addition increases, the surface of film becomes smooth and the stress is relieved. It is also found that AlN/AlN:H/AlN tri-layered films can prevent the blistering phenomena of AlN:H film. As the amount of $H_2$ increases, the concentration of nitrogen atom in the film increases and that of oxygen atom decreases. And the stoichiometric AlN films without oxygen impurities can be prepared by adding 10% $H_2$ to reactive gas. The role of H atoms is suggested to facilitate bonding with unbound N atoms in AlN:H films and hinder N-O bonding, thus, reducing oxygen concentration in AlN:H films. Also, the activation energy for the evolution of $H_2$ gas from AlN:H film has been determined to be 0.11 eV/atom and this result implies that the hydrogen atom in film forms the hydrogen bond. In the growth of the AlN:H film, it has been observed that the amorphous phase is formed at the initial stage of deposition and c-axis oriented crystallite nucleates at the amorphous layer. The lattice mismatch between the film and substrate and the stress in the film is reduced and its surface is smooth due to this amorphous phase. The schematic model explaining the growth of AlN and AlN:H films has been proposed and the reason for the easy formation of amorphous phase in AlN:H film has been discussed. By measuring SAW characteristics of AlN/AlN:H/AlN tri-layered films, the SAW velocity is calculated to be 5280m/s and electromechanical coupling coefficient is 1.35% which is the highest value reported so far.
c-axis oriented ZnO/AlN films have been continuously deposited on silicon wafers by RF reactive magnetron sputtering method. The model representing the factors of bottom AlN film determining the preferred orientation of top ZnO film has been proposed and confirmed by experiment. As the summation of surface tilting angle and the FWHM in X-ray rocking curve of AlN film increases, the preferred orientation of ZnO film decreases. By measuring SAW characteristics of the ZnO/AlN bilayered structure, the phase velocity is calculated to be 4300m/s and the electromechanical coupling coefficient is 3.23%, which are high values enough to commercialize. It is also found that the velocity and coefficient follow the better one of two films. The SAW filter fabricated in this work reveals good characteristics as the thickness of ZnO film increases and that of AlN film decreases.
