Research On Evaluation Method For Power Handling Capablity Of Bulk Acoustic Wave Resonator

The BAW filter based on bulk acoustic wave(Bulk Acoustic Wave,BAW)technology is a new RF front-end solution that plays a vital role in the development of 5G communication technology.At present,the three industry-recognized technical challenges of BAW filter are high frequency,wideband,and high power.This thesis is aimed at the third technical challenge,and studies the evaluation method for power handling capability of BAW devices(BAW resonator and BAW filter).Specific work includes:(1)An acoustic-electromagnetic-thermal multiphysics simulation method is proposed to accurately simulate the self-heating effect of BAW resonators.The main influencing factor of the power handling capability of high-power BAW devices is the self-heating effect.Firstly,the failure mode and failure mechanism are analyzed,and the important position of performance degradation failure and the influence mechanism of self-heating effect on the resonance frequency are clarified.Then,an acoustic-electromagnetic-thermal multiphysics simulation method is proposed based on the failure mechanism of performance degradation.In this method,a distributed coupled heat source is employed so that the self-heating effect can be accurately simulated.(2)A design modification scheme that can eliminate the resonance frequency offset caused by self-heating is proposed.Starting from the calculation formula of the resonant frequency,the way to eliminate the frequency offset caused by self-heating of the BAW resonator is to adjust the thickness of the piezo-layer.Once the thickness of the piezo-layer is adjusted,the temperature field distribution changes.Therefore,it is necessary to combine the multiphysics simulation method in(1)and eliminate the frequency offset by iterative design.(3)The power handling capability of the BAW resonator is optimized,and the signal feeding rule of “long-side feed-in,long-side feed-out” is proposed.From the point of view of self-heating effect,using the simulation method in(1),the design optimization of power handling capability was carried out.The results show that the signal feeding selection of “long-side feed-in,long-side feed-out” will contribute to the suppression of self-heating effects,which is beneficial to the improvement of power handling capability;Besides,the shape of the active area has little effect on the self-heating effect and thus does not contribute to the design optimization of the power handling capability.(4)Under the premise of comprehensive consideration of self-heating temperature and ambient temperature,the evaluation method for power handling capability of BAW devices is proposed.Taking the specific BAW resonator and BAW filter as examples,the basic flow of the evaluation method is demonstrated.And the evaluation results show that the power handling capability of the BAW resonator case can reach 23 d Bm,but it is less than 35 d Bm;the power handling capability of the BAW filter case can reach 23 d Bm,but it is less than 30 d Bm.In the meantime,thermal simulation of BAW filter with more complex geometry structure(compared with BAW resonator)is realized by adopting the route from thermal coupling to electromagnetic.