Research And Fabrication Of New Film Bulk Acoustic Resonator(FBAR)

In recent years,with the advent of the 5th generation wireless systems and flexible electronic technology,the demands for miniaturization,high frequency,huge frequency bandwidth,and flexibility of electronic components become more and more urgent,and Micro Electro-Mechanical System(MEMS)devices based on semiconductor micronano processing technology are facing new challenges.Thin film bulk acoustic resonator(FBAR),as a rapidly growing product of the MEMS yield,having been widespread applied in the RF front-end due to its small size,the ability to work at high frequency,multi-standard communication,and be integrated with CMOS circuit.Besides,due to the advantage of high sensitivity,good linearity,it can also be applied to biology,medical,physics,and other sensing areas.Based on the basic FBAR technology,new FBAR structures are proposed in this paper,including the high frequency FBAR based on the ultra-thin single crystal lithium niobite(LN)and flexible FBAR based on ?-phase PVDF ploymer.The main research contents and achievements are as follows:1.The design method of single crystal LN as the piezoelectric layer of FBAR was established,and the simulation model of the new FBAR was proposed.Through theoretical analysis and calculation,the acoustic wave transmission and electrical characteristics of single crystal LN at different crystal directions were obtained.And we find that the Z-cut LN is the best choice of FBAR piezoelectric layer.Through mason model simulation carried out by ADS,and finite element simulation conducted by COMSOL,the influence of material structure parameters,the new FBAR vibration mode and the parasitic wave mode were analyzed.And the new FBAR design and optimization structure were obtained.2.We explored the process to fabricate the new ultra-thin single crystal LN FBAR,and finally obtained the new FBAR device with high frequency and high Q value.The ultrathin piezoelectric monocrystalline wafers were obtained by ion implantation and stripping,the through LN via etching process was explored,and the back etch technology was improved,and finally a FBAR device with series resonant frequency of 5.009GHz and parallel resonant frequency of 5.062 GHzwere realized,and the Q value was up to 1800,which is far better than the current research level of single crystal LN FBAR.Moreover,the experimental results are consistent with Mason model and finite element model simulation results.3.We proposed a new flexible FBAR based on ?-phase PVDF polymer,and finally obtained several FBAR sensors with stable performance.The feasibility of ?-phase FBAR were verified by theoretical analysis and finite element simulation.The preparation of the device was realized by a low-temperature photolithography process with twice exposure method,which enables to retain the piezoelectric properties of the ?-phase PVDF film.The resonant frequency of 100 ?m ?-phase PVDF FBAR device is 9.212 MHz,and the electromechanical coupling coefficient(!")is as high as 12.76%.It shows a good stability as a strain sensor with a sensitivity of 80Hz/??.The ?-phase PVDF FBAR also exhibited an exceptionally large temperature coefficient of frequency(TCF)of-4630 ppm/?,with extremely high linearity and no hysteresis.All of these results show that it has a great application prospect in the field of flexible electronics.