Research And Preparation Of High Electromechanical Coupling Coefficient FBAR Using Transfer-bonding Process

In recent years,with the advent of a new generation of mobile communication technology5G,people have more and more demand for radio frequency(RF)filter components.The current development trend of high frequency,wide bandwidth,and high integration of filter components are becoming more and more obvious.Film Bulk Acoustic Resonator(FBAR),as an RF-MEMS device with smaller size and stronger working performance,and can be compatible with the existing CMOS process,is widely used in the current RF filter market.However,the existing zinc oxide(ZnO)and aluminum nitride(Al N)materials of FBAR can no longer meet the requirements of high frequency and wide bandwidth for filter components in the 5G era.The greater the demand for FBAR with a high electromechanical coupling coefficient and high frequency is more and more urgent.Therefore,based on the needs of FBAR devices in terms of performance parameters such as high operating frequency and wide bandwidth,this thesis decided to use lead zirconium titanate(PZT)material with a high electromechanical coupling coefficient as the FBAR piezoelectric layer.Aiming at the difficulty of growing high-quality PZT materials on metal substrates,a transfer-bonding method is proposed to prepare PZT FBAR devices with high operating frequency and wide bandwidth.The specific work content is as follows:1.Through the simulation,the material and thickness of the piezoelectric layer and the electrode layer of the FBAR under high-frequency conditions are studied,and the effect on the resonance characteristics of the device is verified.The absolute advantage of the PZT film in the effective electromechanical coupling coefficient is verified.According to the simulation,the device structure was designed,a pentagon was selected as the shape of the FBAR electrode layer,which laid the foundation for the subsequent process preparation2.Research has explored the complete process of surface-air-gap type FBAR.The preparation process of the air cavity was studied in detail;the high-quality PZT thin-film piezoelectric layer growth process of FABR devices was explored,and the transfer-bonding process was innovatively proposed to prepare PZT FBAR devices,and the growth quality of each layer material was characterized;A cut-away side view description of the device is given,which proves the feasibility of this process flow.3.The S parameter test platform of the FBAR device was built,and the prepared PZT FABR device was tested.The test results show that through the preparation process of the device in this paper,an FBAR device with a resonance frequency of 8.00GHz,a Q value of1467.485 at resonance,and an effective electromechanical coupling coefficient of 17.2%is finally obtained.Through comparison with the simulation results,it is analyzed that the operating frequency becomes lower and the reason for the non-ideal effect and the improvement method are proposed.The comparison with other FBAR devices shows that the performance of the PZT FABR device prepared by the transfer-bonding process has a significant improvement,reaching the research goals of high frequency,high Q value,and high (k_eff²) as envisaged in the early stage of the research.It proved the feasibility of the transfer-bonding process,explored a new path for the FBAR process,and also demonstrated the great potential of PZT materials in the FBAR field.