Film Bulk Acoustic Resonator Structure Analysis And Simulation

With the development of wireless terminal's multi-functions, frequency components are required to be smaller size, low-power dissipation, high-performance. The traditional solution approaches for RF components are mostly microwave dielectric ceramics and surface acoustic wave technologies. The former have good performance, but too big in size, and the latter's small in size, but it's with such drawbacks as low work frequency, high power loss, and low power capacity. A Film Bulk Acoustic Resonator (FBAR) has excellent properties as with dielectric ceramics resonators and the small size as with surface acoustic wave resonators. Meanwhile, it overcomes the drawbacks of the both, and has advantages such as high work frequency, big power handling capacity, low power loss, and small size. It is the only one promising for integration RF filter technology, and thus becoming a hot research issue.The principles of a FBAR and a FBAR–based filter were described systematically in this dissertation, and three mostly used FBAR structures and their processing were then analyzed by comparison. A novel structured FBAR with a porous substrate was introduced. Meanwhile, the materials used in a FBAR and their properties were also described in details, in which piezoelectric thin films are most important. The suitability in order is following, AlN, ZnO, and then PZT.On the basis of the fundamentals of acoustics, piezoelectrics, electromagnetics and elastic mechanics, impedance resolution models for an ideal FBAR and then the composite were developed, resulting in impedance functions with regards of mechanic and electric losses. The electricity impedance characteristics of a FBAR were simulated using Matlab software, and FBAR's structure parameters affecting frequency response behaviors were evaluated in details. It was found that the resonance frequency of a composite FBAR is lower than a deal FBAR based on the same piezoelectric thin film. It is due to the sound path of the electrode layer, which leads to an increase of the length of the equivalent sound path, and consequently causes a decrease of the resonance frequency. A prediction software for FBAR's resonance frequency was accordingly developed using VB interface, which is easily operated, and of significance for FBAR designs. The principle of the BVD model of equivalent circuit for FBAR was described in details in this dissertation, along with the approaches for the BVD parameters. The equivalent circuit for a FBAR filter was thus developed, which is simulated by ADS application software. It was found that the attenuation of outer band-pass in the FBAR filter increases sharply with the filter series, but with slow increase in the band-pass loss. Consequently, the FBAR filter series should be eclectically considered for a design.