Characteristics of hydrogenated aluminum nitride films prepared by radio frequency reactive sputtering and their application to surface acoustic wave devices

Abstract

Hydrogenated aluminum nitride (AlN:H) films have been deposited on silicon wafers by the rf reactive magnetron sputtering method with H2 gas addition to Ar-N2 gas mixture. The changes of physical properties of AlN:H films with different H2 gas addition have been examined by x-ray diffraction, scanning electron microscopy, and x-ray photoelectron spectroscopy. The surface acoustic wave (SAW) filters with wavelength of 60 μm using these films have been fabricated and their SAW velocities and electromechanical coupling coefficients have also been measured by a network analyzer. It is found that as the amount of H2 addition increases, the surface of film becomes smooth, the stress is relieved, the concentration of nitrogen atom increases and that of oxygen atom decreases. We also found that AlN/AlN:H/AlN tri-layered films can prevent the blistering phenomena of AlN:H film. By measuring SAW characteristics of AlN/AlN:H/AlN tri-layered films, the SAW velocity is calculated to be 5280 m/s and electromechanical coupling coefficient is 1.35% which is the highest value reported so far.