Abstract
Mode coupling vibrations in thin-film bulk acoustic wave resonators (FBARs) were systematically analyzed in the series of our work. Previously, the two-dimensional theory of multi-layered FBAR plate has been established and used for the analysis of both free and forced vibrations of a fully electroded plate. In this paper, coupling vibrations in a partially electroded FBAR were taken into account, where the top electrode only covers the central part of the film. The two-dimensional equations were written into matrix form based on the state-vector approach. Transfer matrix functions of the global structure were obtained when continuous and traction-free boundary conditions were satisfied. Aspect ratios of both electroded and unelectroded regions were varied to research the influence of them on the coupling effects. The admittance versus frequency response was also obtained through forced vibration analysis to investigate the coupling effects. Results in this paper show the existence of energy-trapping behavior and the importance of structure size on mode coupling effects, which is important to the design of real FBAR devices.
Highlights
Piezoelectric resonators are key components in almost every communication system
We extend state-vector approach to study the partially electroded film bulk acoustic wave resonators (FBARs) plate
In each frequency spectra figure, we label two representative modes with weak and strong coupling effects, whose mode shapes and admittance response will be analyzed later to show the effects of mode couplings and how they are influenced by structure size
Summary
Piezoelectric resonators are key components in almost every communication system. They are often used for frequency operation, signal generation, etc. The other is exited in-plane, operating with surface acoustic waves (SAWs).5 Comparing these two types of resonators, BAW resonators are more commonly used because of their better performances like higher working frequency and smaller size. FBARs consist of a piezoelectric thin film on an elastic substrate with driving and ground electrodes They are more superior than typical quartz resonators due to their high working frequency, miniature size and the compatibility to the modern developed semiconductor technology.. Most of the existing researches treat FBAR as an infinite plate and/or consider the operating mode only These methods are incapable of dealing with undesired coupling modes and spurious modes, which exist in real devices and highly affect the working performance of resonators.. Admittance versus frequency responses are obtained through forced vibration analysis to show the effects of structure size on mode couplings
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