Preparation Of Er-Modified AlN Film And Basic Research Of SAW Device

AlN film has extremely excellent physical properties and chemical stability.With the electronic equipment developing to high frequency and ultra high frequency,AlN film becomes a popular piezoelectric material for high-frequency devices because of its high velocity of sound.It is widely used in RF high-frequency filters,surface acoustic wave sensors,transducers,and piezoelectric actuators.However,pure AlN thin films have poor piezoelectric properties,which are very difficult to meet the fabrication requirements of corresponding wide-band devices.Therefore,in this paper,Er element is used to improve the piezoelectric response of AlN thin film,thereby improving the electromechanical coupling effect and working bandwidth of the corresponding device.In this paper,Er-doped AlN films with different sputtering process parameters were deposited on sapphire substrates by RF magnetron sputtering reaction.The crystal quality and surface topography of ErAlN films under different sputtering process parameters were studied.At the same time,SAW resonators were prepared based on ErAlN films with different doping amount of Er and nitrogen/argon flow ratios.The effects of Er content and nitrogen/argon flow ratio on the sound veolicty and piezoelectric response of AlN films were studied by analyzing the electroacoustic properties of SAW resonators.The main research work of this paper are as follows:1.The ErAlN films are deposited by RF-magnetron sputtering.The control variable method was used for the experimental design.The effects of sputtering power,sputtering temperature,nitrogen to argon flow rate,and sputtering gas pressure on the deposition rate,crystal quality,and surface morphology of Er-modified AlN films were studied respectively by XRD,SEM,AFM methods,obtaining the best parameters of ErAlN film under this preparation method;2.To study the effect of Er content on the electroacoustic properties of AlN films,the SAW resonators were prepared based on a set of high c-axis oriented AlN films with different Er contents(0~10%).The change trend of device center frequency and electromechanical coupling coefficient with Er content was studied.The results show that the increase amount of Er leads to an increase in the degree of softening of the AlN film,so that the center frequency decreases and the piezoelectric response increases;3.To study the effect of nitrogen/argon ratios on the electroacoustic properties of AlN films,the SAW resonators were fabricated based on a set of Er-doped AlN films with different nitrogen/argon flow ratios.The change trend of device center frequency and electromechanical coupling coefficient with nitrogen/argon flow ratio was studied.The results show that when the degree of c-axis orientation of ErAlN films is better,the greater the electromechanical coupling coefficient of the corresponding SAW resonator,the better the piezoelectric response.