Filter Synthesis using Shear Wave Piezoelectric Layer Resonators
Résumé
CONTEXT Acoustic waves in elastic solids are used in numerous applications in signal processing, including frequency generation, control and filtering in modern wireless communication systems. With the growing demand for multimedia and mobile applications, the new generations of telecommunication satellites require higher performances, higher functionalities and still stronger cost and size constraints.[1][2][3] In that context, BAW devices have many potentialities for the development of smart RF subsystems. For instance this technology is now used as alternative to Surface Acoustic Waves (SAW) filters in handset duplexers for UMTS and DCS standards around 2 GHz with Aluminum Nitride piezoelectric layers[12]. However, Aluminum Nitride is not suitable for large band applications, due to its electromechanical coupling coefficient. Its relative percentage, which represents the difference between resonant and antiresonant frequencies is 7%. This material is mainly processed for local oscillators or narrowband filtering operations (<5%) [4] [5]. That is why Lithium Niobate layers are studied to reach large band pass specifications for satellites requirements. It is essential to maximize the values of electromechanical coupling coefficient in Lithium Niobate, and to use wisely crystallographic cuts in order to perform the best results for longitudinal or transverse waves coupling larger difference between resonant and antiresonant frequencies. Thanks to Lithium Niobate shear wave propagation behavior, the goal will become synthesizing large bandpass frequency response of simple filters structures.