Research On Broadband Low Loss Bulk Acoustic Wave Resonator

In the current 5G technology,the spectrum resources used are allocated in the two ranges of 3.3GHz-5.0GHz(Sub-6G)and above 24GHz(millimeter wave),and the frequency band N77(3.3GHz-4.2GHz)is A frequency band with a width of 900 MHz,the resonator designed under this condition requires a high frequency and a large electromechanical coupling coefficient,which cannot be achieved by traditional SAW,while the bulk acoustic wave resonator mainly based on Al N-FBAR usually has electromechanical coupling coefficient.smaller.In this thesis,we investigate the piezoelectric behavior in lithium niobate materials,and simultaneously obtain high frequency and large electromechanical coupling coefficient by laterally exciting bulk acoustic waves with interdigitated electrodes mimicking SAW.At the same time,the stray modes in the resonator and the loss in the process of sound propagation are mainly explored through the finite element method and the hierarchical cascade algorithm.The main content of this thesis is divided into four parts.First,the 5G background technology and the role of RF filters in the RF front-end are introduced,and the factors that need to be considered in the design of the resonator,as well as the electromechanical coupling coefficient and quality factor,can be quantitatively reflected in the bandwidth and loss.Then,starting from the most basic piezoelectric effect,the principle of transversely excited bulk acoustic waves,the characteristics of the excited modes,piezoelectric materials,loss methods,and several research methods are introduced,as well as the related theory of phononic crystals.Secondly,a preliminary simulation study of the transverse excitation resonator was carried out,the Euler angle,size and other factors were analyzed,and how to effectively excite the A1 mode and some information on suppressing the stray caused by the acoustic impedance and the high-order modes such as A1-3 were also carried out.topic of.Then,by exploring the behavior of the acoustic wave propagation path in the resonator,such as the lateral leakage,the leakage propagation of the bottom substrate,and the longitudinal finite-length energy non-concentration,phononic crystals,Bragg reflection gratings and other methods were used to make the device.performance improvement.