Investigation of modified Lamé mode resonator with high coupling coefficient

This paper presents a modified Lame-mode resonator (MLMR) with a high, effective electromechanical coupling coefficient ( K e f f 2 ). With trapezoidal grooves introduced by etching the superficial piezoelectric material between interdigitated electrodes (IDTs), the MLMR can remarkably improve K e f f 2, eliminate spurious modes, and reduce the internal stress of piezoelectric material. The Lame mode resonator (LMR) with four different electrode configurations is investigated by using finite element method simulation first; then, the impact of the groove's vertical ( h ) and horizontal ( θ ) size on K e f f 2 and spurious modes of MLMRs is theoretically analyzed and optimized. It is noted that all the modified structures can improve K e f f 2 except the IDT-Ground structure. This work demonstrates a simulated K e f f 2 as high as 10.47% in the modified IDT-Floating structure, and 10.73% in the modified IDT-IDT structure, which is the highest ever reported in S0 mode AlN LMR. The MLMR shows great prospect for fabricating broad bandwidth filters.