The research on manufacturability and reliability of XBAR filters

Laterally excited shear mode bulk acoustic wave resonators (XBARs) filters are promising next-generation devices capable of achieving large electromechanical coupling coefficients (K²) [1]-[5]. However, concerns regarding manufacturability, reliability, and power handling remain [6]-[9]. In this study, we propose a novel sandwich structure for piezoelectric single-crystal membrane-type filter devices, in which the piezoelectric layer is encapsulated between dielectric films on both sides. Conventional structures suffer from frequency variations caused by wafer-level thickness nonuniformities of the piezoelectric membrane and instability of K² due to thickness adjustments of the protective dielectric film used for frequency trimming [5]. Our original structure suppresses the frequency variation by compensating thickness nonuniformity through the backside dielectric film and greatly improves K² stability by eliminating structural asymmetry [10]. Furthermore, the introduction of dielectric films on both sides effectively disperses stress, significantly enhancing mechanical shock resistance [11]. Additionally, we developed an Arrhenius-based fracture-mode prediction simulation that incorporates both power dissipation and stress factors, achieving high-accuracy correlation with spurious modes and enabling optimized filter design [12],[13]. These advances enable the development of highly reliable XBAR filters that satisfy market requirements for frequency stability, shock resistance, and power handling.