Toward Band n78 Shear Bulk Acoustic Resonators Using Crystalline Y-Cut Lithium Niobate Films With Spurious Suppression

Abstract

This work presents the study of suspended Y-cut Lithium Niobate shear bulk acoustic resonators for wide band filter applications in the frequency range of 3.5-4.5GHz. The resonator consists of a Lithium Niobate film with Aluminum top interdigitated electrodes (IDE) and floating bottom metal plate. Through vertical electric field excitation, shear bulk acoustic waves are generated in each unit cell of the device functioning as a quasi-independent resonator. Measured devices at 3.7GHz having large relative resonance-antiresonance bandwidth of 16.7% (750MHz) with 2𝛀 impedance at resonance are presented. Suppression of higher order lateral harmonics through etching of trenches in the Lithium Niobate and geometric optimization is discussed. Lastly, the optimized resonators were used in filter synthesis to demonstrate potential use for Band N78 and results are discussed.

Serially connected strip-type acoustic wave resonator using X-40°Y LiNbO3 (XSAR)—feasibility study using macro model

“…3(a) corresponds to the rotated Y cut, which is used in TS mode BAW and YBAR. 12,24,25) The Euler angle in Fig. 3(b) corresponds to the X-cut ψ Y (ψ means the third Euler angle), which is firstly studied in this work.…”

“…Another kind of resonator is so called YBAR, 24,25) which can be regarded as a serially connected strip-type BAW device using Y-cut LN. The reported YBAR realized a BW of 22.6%, which was the same level to the TS mode BAW.…”

“…Following the similar structure as YBAR using X-cut LN, the BW of as large as 29.8% at 4.7 GHz was reported, which was the highest level at this frequency range. 25) However, the slow shear mode spurious response can hardly be removed using X-cut.…”

Lithium Niobate MEMS Antisymmetric Lamb Wave Resonators with Support Structures

“…Remarkably, seminal work by Yang et al has demonstrated A1 mode resonators operating within the 5 GHz range, showcasing a K 2 e f f value of 29% [15], thereby highlighting their considerable potential in the sub-6 GHz domain. Nevertheless, a substantial challenge associated with A1 mode resonators is their vulnerability to spurious modes [16][17][18][19], which constitute a critical barrier to their extensive application. Consequently, the strategic goal of minimizing or eradicating these spurious modes becomes an essential consideration for the advancement of high-performance A1 mode resonators.…”