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Surface Acoustic Wave (SAW) Filters on Piezo-On-Insulator (POI) Substrates: Effective Figures of Merit and Design Considerations
The current 5G telecommunication standard is paving the way of academic and industrial research to the development of innovative electronic components and more specifically of passive filters particularly based on surface acoustic waves (SAW). Following pioneer works in the early 2000s, the rise of engineered substrates based on sub-micron single-crystal piezoelectric layers bonded on silicon combining various technologies, among which are molecular bonding and Smart-Cut, yielding the so-called Piezo-On-Insulator (POI) substrates, represents an effective breakthrough for the development of modern SAW filters. The latters today are exhibiting remarkable features such as insertion losses smaller than 1dB, rejection in excess of 40dB together with unrivaled power dissipation capabilities and thermal stability. A significant effort has been dedicated by the men-of-the-art and particularly by our group to characterize SAW properties on various POI configurations for frequencies ranging from 600MHz to 3.5GHz, generating a substantial database of Figures-of-Merit providing material constants and experimentally-supported rules for SAW filter design. In this presentation, we report on these FoM and propose a critical analysis of their nature and effective interest in that purpose. We are particularly focusing on de-embedded characteristics such as quality and coupling factors and most of the usual design parameters to provide a clear understanding of the mode behavior and the corresponding impact on various filter structures. Illustrations of the proposed approach are reported for some of these structures, combining acoustic and electromagnetic models particularly applied to SAW-on-POI filters based on impedance element combination and Surface Cavity Acoustic Waves (SCAW) filters in the so-called mid-high band spectral region. The use of the above mentioned FoM to qualify the filter characteristics and performances is particularly emphasized through the selected examples. The relation with the selected POI substrates is also highlighted.