Design And Research Of 3400-3600MHz FBAR Filter

The film bulk acoustic resonator(FBAR)filter composed of FBAR have been developed as a new solution for mid-high frequency filters in RF front-end due to its small size,high operating frequency,low insertion loss,low power consumption and easy integration.At present,the most widely used filter in the front-end of 4G communication is also the ideal device in the future wireless high frequency communication system.Although China has already completed the division of 5G communication band,there are few filter products corresponding to 5G communication band in China.Therefore,this paper systematically designed an FBAR filter with 3400-3600MHz in N78 band.The working principle of FBAR and FBAR filters is described in detail,and the Mason model of FBAR is deduced and improved.The FBAR of the first-order edge raised electrode structure is found by finite element analysis software simulation,which can increase the Q value at the shunt resonance frequency by 224,but slightly sacrifice the Q value at the series resonance frequency and the effective electromechanical coupling coefficient.FBAR filters with trapezoidal structure are constructed based on the derived Mason model.The effects of FBAR quality factor and piezoelectric coupling coefficient of piezoelectric materials on the performance of FBAR filters are compared and analyzed.The influence of T-type and PI-type inductance cascade on the performance of the shunt branch of the filter is also analyzed.When the same performance index is reached,the total inductance value of T-type cascade is the smallest and the performance is the best.Using a five-series four-parallel ladder FABR filter circuit structure,the random optimizer and gradient optimizer make the filter circuit structure meet the design requirements of 3400-3600MHz filters.Based on the relevant literature and patent,the layout design rules of this article are formulated.The layout is designed according to the area of each FBAR in the optimized FBAR filter.In this paper,the performance of FBAR filter is further optimized by the results of acoustic electromagnetic co-simulation.The mutual inductance effect,parasitic loss and skin effect in PCB integrated inductance are analyzed.A multi-layer spiral inductor is designed by using PCB integrated inductor.By splitting the resonator,the power dissipation density is reduced,and the final performance of the complete sound-electromagnetic joint simulation is as follows:insertion loss is less than-1.87d B,suppression at N79 band is-64d B,withstanding power greater than 30d Bm;encapsulation size:1.1×0.9mm~2.