Study On Modification Technology And Process Of AlN Film

The AlN thin films have excellent physical and chemical properties and are widely used in thin film devices and piezoelectric actuators,such as RF filters and resonators for wireless communications,micro-sensors for MEMS,energy collectors,light emitting devices,etc.With the development of wireless communication technology toward high frequency and wide bandwidth,high data transmission rate and extremely fast increase of data volume,higher requirements are put forward for the working frequency and bandwidth of acoustic filters.The high sound velocity of AlN film can meet the requirements of high frequency,but its piezoelectric constant and electromechanical coupling coefficient are low,which is not conducive to wide bandwidth applications.In recent years,doping rare earth elements and transition metals is the main way to improve the piezoelectric response and electromechanical coupling coefficient of AlN thin films.In this paper,the Er/Sc co-doped AlN films with different content ratios were prepared on sapphire substrates by reactive magnetron sputtering.The composition of co-doped thin films were controlled by adjusting the insertion position of metal ingots,and the properties of these thin films are gradually optimized by using uniform design method,orthogonal design method and control variable method.SAW resonators were fabricated by using optimized alloy films.Then,the electromechanical coupling and piezoelectric properties of doped AlN films were studied to provid theoretical guidance for further improve the piezoelectric response of AlN films.The main research contents in this paper include:1.The magnetic field distribution on the target surface is simulated by COMSOL software.According to the proportional relationship between the magnetic field intensity distribution and sputtering efficiency,the number and location of metal ingots in the mosaic target are designed to control the doping content in Er/Sc co-doped AlN films.2.The crystalline quality and orientation of Er/Sc co-doped AlN thin films were successively optimized by uniform method,orthogonal method and control variable method.The effects of process parameters on the properties of Er/Sc co-doped AlN thin films were systematically studied.The empirical formula between process parameters and deposition rate and crystallization quality of Er/Sc co-doped thin films was summarized,and the optimization of Er/Sc co-doped thin films by deposition rate was proposed.3.The effects of Er/Sc ratio on the density,crystal quality,crystal orientation,surface morphology,stress,crystal structure,dielectric properties and optical properties of Er/Sc co-doped AlN films were systematically studied.4.The electroacoustic properties of Er/Sc co-doped AlN film were verified by fabricating Er/Sc co-doped AlN film/sapphire structure SAW resonators.Moreover,the relationship between the electromechanical coupling properties and piezoelectric response of thin films and the occupancy tendency of Er and Sc,covalent bond strength?,stiffness coefficient C33,Bonn effective charge ZB~*and biaxial stress?xx/yy in AlN crystals was discussed.