Research Of New Film Bulk Acoustic Resonator (FBAR) Technology

In recent years,the huge demand for emerging consumer electronics led to the vigorous development of Micro-electromechanical System(MEMS)industry which is based on the semiconductor Micro-nano processing technology.Thin film bulk acoustic resonator(FBAR),as a rapidly growing product of the MEMS yield,is getting widespread concern and research.FBAR has the excellent characteristics of small size(um class),high resonant frequency(GHz),high quality factor(1000),large power capacity and excellent roll-off effect.Filters based on FBAR are gradually replacing the traditional SAW and ceramic filters,playing a huge role in RF wireless communications field.Besides,due to the advantage of high sensitivity,it can also be applied to biology,physics,medical and other sensing areas.Based on the basic structure of FBAR,the back-trench FBAR process is optimized,and a novel FBAR is fabricated by using graphene as the electrode whose resonant performance is good.We also fabricated FBAR magnetic sensor based on the polyimide(PI)substrate and made the device flexible and transparent by using willow glass.The main research contents and achievements are as follows:1.The technology and different device structures of back-trench FBAR are studied.The high c-axis growth of ZnO thin films on Si substrate was deposited and the film quality was characterized.By optimizing the etching process we improved the yield of FBAR back-trench devices.We fabricated FBAR on thin silicon oxide wafer with Au electrodes and improved the performance by optimizing the electrode shape.The resonant frequency of this kind of FBAR device is 1.672GHz with a super high Q value of 1672.With the same process,FBAR devices with aluminum electrodes were fabricated on the thick silicon oxide wafer.Compared with the thin oxide device,two resonant peaks with good resonant performance were obtained.2.FBAR based on graphene electrode was prepared.The advantages of graphene electrode were analyzed by theoretical simulation.On the basis of the back etched device,the upper electrode was replaced by graphene since the transfer process and the fabrication process were optimized.We successfully made the new device whose structure contained multilayer graphene and graphite sheet respectively.The resonant frequency of the multilayers graphene device is 1.277GHz with a Q value of 650 which is higher than the Al-based device.And the device with graphite sheet resonates at 1.398GHz with a Q value of 350 which is comparable with the performance of the devcice based on ITO electrode.3.A PI-type magnetic FBAR sensor was obtained.The theoretical feasibility of PI-type FBAR is verified by COMSOL finite element simulation.The FBAR magnetic sensor is fabricated using nickel as electrodes and the resonant frequency will increase by about 7 kHz in the magnetic field.The mechanism of magnetostrictive sensing is proposed and ADS circuit simulation based on Mason model is made to verify it.4.A flexible transparent FBAR was fabricated on willow glass substrate.The device works after bending,whose resonant frequency is 1.77GHz and the Q value is 443,which is superior to the flexible FBAR performance on PET and paper.There will be 1MHz frequency migration under the applied pressure.