In this paper we analyze for the first time quantitatively the acoustic losses in a film bulk acoustic wave resonator (FBAR), which are expected to deteriorate the device performance. To this end, we regard the effective acoustic admittance, conduct laser probing measurements and finite element modeling (FEM). For our device under test (DUT) at the anti-resonance frequency, we compare the relative power of observable modes in the active and passive area and point out the relevant energy loss mechanism in terms of a single mode. By scattering analysis of the resonator's border region, we can identify the respective excitation mechanism within the active area and therefore can consider specific countermeasures to improve the device performance. Practically applied for the first time, the utilized methods and the overall procedure are explained in detail and are applicable to investigate acoustic energy loss as well at other frequencies as in other devices.

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This paper demonstrates a novel frequency domain analysis (FDA) to evaluate the scattering behavior of a waveguide mode at arbitrary scattering geometries by a time harmonic simulation based on the finite element method (FEM). To this end, we add an injection-damping mechanism (IDM) to avoid interference at the acoustic input port. The IDM can be easily constructed by a numerical operation. Our approach offers improved time consumption and calculation power necessary over the established method in the time domain. After checking the validity of the proposed method, we discuss the importance of considering wave scattering phenomena in film bulk acoustic wave resonator (FBAR) devices by applying the proposed method to two simplified models of an FBAR device.

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This paper proposes a method to estimate power carried by a propagating Lamb mode in an arbitrary multilayer waveguide from calculated or measured surface displacements. To this end, we calculate the so-called mode power coefficient relating the surface amplitude of the mode to the total power flow toward the lateral direction. The coefficient is given by the gradient of the effective acoustic admittance with respect to the lateral wavenumber, and can be readily calculated by slightly modifying software codes developed for calculating the dispersion relation of Lamb waves. This calculation procedure is simpler and more efficient than the conventional technique based on the estimation of total power flow passing through the waveguide cross section. We apply this technique to the quantitative evaluation of acoustic losses in a thin-film bulk acoustic wave resonator (FBAR), and the effectiveness of this technique is demonstrated.