Research On Air-gap Type Film Bulk Acoustic Resonator(FBAR)filter

Bulk acoustic wave device FBAR has the advantages of small size,low loss,integrated,etc.The filter consisting of FBAR has a low insert loss,high Q value,high power capacity and other characteristics in the frequency band above 2.5 GHz,is the best solutions for the expansion of high frequency applications in mobile communication.At present,FBAR technology and the international market are monopolized by a few U.S.and Japanese companies,and their respective product lines are basically spread around three mainstream FBAR structures,back-etching type,air-gap type and SMR.Among them,the air-gap type FBAR has the highest processing difficulty and the most outstanding performance.but the equipment conditions and semiconductor processing level are more demanding.Compared with the international level,there is still a big gap between domestic research on FBAR technology,and there is still a long way to go to realize autonomous design and production.Therefore,this paper presents an in-depth research on the simulation,material growth,structure design and fabrication of air-gap type FBAR devices.The FBAR is simulated using electronic design software and finite element simulation software to analyze the performance characteristics of the resonators and filters.The preparation of Al N piezoelectric films,a key material in FBAR,was analytically investigated.The air-gap type FBAR device structure and process layout were designed,and a complete cavity FBAR chip was prepared and tested on-chip.The main points of innovation and the results of the research achieved are summarized below:First,the MBVD equivalence model was used in the ADS software to study the influence of different total elements and different access methods on the resonant characteristics of FBAR,and the tuning performance of FBAR was summarized;then,the Mason equivalence model was used to study the filter structure,and the results of the tuning performance analysis were combined to design a 7-step ladder type FBAR filter that meets the usage requirements and optimize the structural parameters of each membrane layer.Secondly,to study the Al N film,the core material of FBAR,in the growth process of RF reactive magnetron sputtering,to study the effect of Ar gas flow on the film crystal quality and stress state and the resulting FBAR performance changes.On the premise of the state,the surface migration energy of the deposited particles on the substrate is changed by the flow of Ar gas,which affects the orientation and stress state of the film;Combined with ion beam repairing film to improve the thickness uniformity and surface roughness of the chip,and finally deposited an Al N piezoelectric film with low residual stress,high uniformity and low surface roughness,which improves the processability of the piezoelectric film,and frequency accuracy and working stability of FBAR chip.Based on the high-performance Al N film,the cavity-type FBAR structure and processing method are designed,and the cavity-type FBAR device is prepared.In the actual process,the cavity structure of the FBAR is optimized by the dry method combined with sputtering,results in a flat cavity surface,and improves the accuracy of the exposure pattern for the optimized lithography process.The cavity-type FBAR resonator and filter based on the low-stress Al N piezoelectric film were obtained by the MEMS.Finally,on the test platform built in the laboratory,through the probe station and vector network analyzer,the transmission characteristics of the FBAR chip were measured,and the influence of the material properties on the performance of the FBAR device was analyzed.The overall work provides a new idea for the preparation of air-gap type FBAR.