Design Of Film Bulk Acoustic Resonator For 5G Applications

Film bulk acoustic wave resonators(FBARs)are extensively used in wireless applications owing to their tremendous performance and compatibility.The announcement of 5th generation(5G)communication has posed an increasing demand for a resonator with high performance.To implement this new standard,an enhanced number of high-performance filters are required for the distribution of different frequency bands,and an extension of existing ones.The occurrences of spurious resonances(or spurious Lateral modes)close to the main resonance degrades the performance of the resonator and quality factor(Q),which results as a ripple in the passband of filters.Different techniques were previously developed and represented by the researchers to suppress the resonances of spurious lateral modes.The use of frame on the edges of the top electrode of FBAR is presented earlier to improve the Q factor and prevents the lateral leakage of energy,potentially providing improved filter performance.The single-step frame,dual-step and double dual-step frame were previously introduced in recent literature,which reflects the lateral leakage of Lamb waves to an active region of the resonator.This work presents the more advanced design of the three-step frame structure that is a competent design with declining steps and reflects the Lamb modes efficiently in the active region of the FBAR.The optimal design proves efficient in order to obtain high Q and better electromechanical coupling(kt2),which is the need for a 5G communication system.The steps of the frame are obtained using a parametric optimization technique.The width and thickness of the steps are arranged so that the displacement involving to the piezoelectrically excited strongest resonance mode is greatly uniform in the center area.Aluminum nitride film-based FBARs have been used enormously for the fabrication of commercial RF front-ends because of CMOS compatibility,high thermal conductivity,and chemical stability.Owning this compatibility,the proposed FBAR is also designed using aluminum nitride film.The simulation of the FBAR is accomplished using OnScale software.2-D finite element method(FEM)analysis is used to determine the effect of three-step and compared the designed with single and dual step FBAR.In which the proposed design shows high Q.The spurious resonances are efficiently suppressed at anti-resonance frequency.The materials used are molybdenum as a top as well as the bottom electrode and silicon nitride as a support layer.Another optimization technique named"apodization" is also implemented on 3-D modeling and compared with the simple FBAR in order to understand its effect on lateral leakage.The equivalent electrical modified Butterworth-Van Dyke(mBVD)model of FBAR admittance response is also presented,which illustrate decent agreement with the designed resonator,paving the way towards its final application in the high-frequency communication system.The optimal design of three-step FBAR is then used to design a high-Q FBAR,which is operating at(4.04-4.14)GHz having a bandwidth of 100 MHz,which is preferable for the "sub-6 GHz" spectrum in 5G applications.The Qs,Qp,and keff2 of the proposed FBAR is 8197,3981,and 5.81%,respectively.The simulation results of the proposed work are then compared with other state-of-the-art FBARs in which the efficient design of three-step FBAR represents better performance electrically as well as mechanically.