Research On AlN Based Thin Film Bulk Acoustic Resonator And Filter For Mobile Communication Applications

As the scale of the mobile communication market continues to expand,more and more multi-functional modules are added to wireless terminals,towarding higher communication frequency band.BAW filters have the advantages of low loss,small size,and high quality factor,and are currently one of the best RF filtering solutions for high-frequency mobile communications.In Thin Film Bulk Acoustic Wave Devices(FBAR),there is a large deviation between simulation and actual preparation due to parasitic resonance,film defects,and structural damage during preparation.In this paper,AlN-based thin-film bulk acoustic wave devices are studied in three aspects: reducing parasitic resonance,growing high-quality thin films,and preparing and testing complete devices.The research is carried out in three aspects,and the main contents of the paper include:(1)Simulation analysis of FBAR resonator.Using the finite element two-dimensional simulation model,the effects of film thickness,electrode size,and load layer structure on the frequency characteristics of the FBAR resonator are explored.The simulation results show that when other parameters are fixed,adding a suitable load layer structure can reduce the parasitic effect and improve the fit between the 2D model and the 1D model.(2)Preparation of AlN/Mo thin films for FBAR.First,the AlN piezoelectric thin film with good c-axis orientation and thickness uniformity < 1 % is prepared by magnetron sputtering equipment.Then,combined with magnetron sputtering and dry etching equipment,the preparation of small-angle Mo electrode with thickness uniformity < 1 % and controllable angle(20 ° ～ 5 °)is realized.The prepared film with strong processability and can be applied to subsequent device preparation.(3)Fabrication and test analysis of FBAR resonators and filters.Based on Micro-Electro-Mechanical Systems(MEMS)process,a complete FBAR resonator and filter with a load layer structure are fabricated.The test shows that their frequency is shifted to a certain extent,the Q value is greater than 1000,the effective electromechanical coupling coefficient is 6.4%,and the parasitics are less.The sample passband of the filter is close to 2300-2400 MHz,the out-of-band suppression is greater than 40 dB,the echo performance is good,and the insertion loss is close to 3 dB.After extracting and analyzing the test parameters,the resonator and filter samples with an improved frequency drift are realized by adjusting the thickness of the piezoelectric layer,which provides a certain guidance for the subsequent preparation research.