Fabrication and characterization of AlN thin film bulk acoustic wave resonator

摘要

This dissertation presents the fabrication and characterization of the AlN thin film bulk acoustic wave resonator (FBAR). The bulk acoustic wave (BAW) resonators and filters have been considered the most promising devices used in the frequency control and wireless communication field when the performance frequency is up to GHz range. AlN is a piezoelectric material with hexagonal crystal structure. Some of its properties such as high longitudinal acoustic wave velocity (~11000m/s), high thermal conductivity, and high thermal and chemical stability make it a suitable material to fabricate the thin film bulk acoustic wave resonator.In this study, first, the background that includes the concepts of the FBAR resonators and filters, the piezoelectricity, the material properties of some of the piezoelectric materials and the MEMS techniques is introduced. Following the introduction, the fabrication and characterization of the AlN thin film, the composite BAW resonator and membrane type FBAR are presented. AlN thin films deposited under various sputtering deposition conditions have been investigated and characterized. X-ray diffraction (XRD) and scanning electron microscopy (SEM) characterization results show that the highly c-axis oriented AlN thin films have been deposited on the Si and sapphire substrate at the appropriate conditions. The effective piezoelectric coefficient d33eff and the mechanical properties such as the hardness and the reduced elastic constant of the AlN thin film in the four-layer composite resonator have been measured by the single beam laser interferometer and nano-indentation methods, respectively. Then, the transfer matrix method is developed to characterize the impedances and electromechanical properties of the multilayer FBAR and composite BAW resonator. The effects of the type and thickness of the electrodes and support layers on the resonance frequency and effective electromechanical coupling coefficient are discussed. The resonance frequency control and tuning methods including the connection to the external circuits and the incorporation of the support SiO2 layer are also discussed. In addition, the vector network analyzer has been utilized to measure the resonance frequency response of the four-layer composite BAW resonator and the material properties have been characterized from the experimental data. Lastly, the accomplishments of this study are summarized and future perspectives are provided.