Abstract
Bulk acoustic wave (BAW) resonators exhibit attractive properties in terms of power handling capacity and on-chip integration to realize filters in the GHz range [K. M. Lakin, IEEE Ultrason. Symp. pp. 895–905 (1999)]. In a BAW resonator, a thin piezoelectric layer (a few mm) deposited between two electrodes is driven in its thickness extensional mode of vibration. To get a high quality factor, this structure is decoupled from the substrate by a multilayer Bragg reflector or a back-etched membrane. A current problem in the design of BAW resonators is the existence of spurious resonances close to the thickness extensional mode which generate ripple in the filter passband. In this paper, these spurious modes are analyzed in terms of Lamb waves resonances. Physical modeling of BAW resonators using finite element ATILA code is presented. The influence of lateral dimensions and electrode geometry on spurious resonances is emphasized. With specific electrode design and electrical excitation, it is demonstrated that lateral modes of Lamb waves can be used to realize resonators in the 50–250-MHz range. Experiments on an AlN piezoelectric layer between Pt electrodes on a SiN membrane are presented. [Work supported by a ST Microelectronics grant (CIFRE).]
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