X-Band Miniature Filters Using Lithium Niobate Acoustic Resonators and Bandwidth Widening Technique

Yansong Yang,Liuqing Gao,Songbin Gong

doi:10.1109/tmtt.2021.3049434

Yansong Yang, Liuqing Gao + Show 1 more

Open Access

https://doi.org/10.1109/tmtt.2021.3049434

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Abstract

This work presents a class of micro-electromechanical system (MEMS)-driven radio frequency filters in the X-band. The X-band center frequencies are achieved by resorting to the third-order antisymmetric Lamb wave mode (A3) in a 650-nm-thick Z-cut lithium niobate thin film. A novel bandwidth (BW) widening technique based on using the self-inductance of the top interdigital transducers and bus lines is proposed to overcome the limitations set by the electromechanical coupling (k 2 t ) and satisfy the demands in miniaturization and wide BW. Four different designs of the filters are designed and fabricated to show the trade-off among BW, insertions loss (IL), out-of-band rejections, and footprint. Due to the spurious-free and highQ performance of the A3 lithium niobate resonators, the fabricated A3 lithium niobate filters have demonstrated small in-band ripples and sharp roll-offs. One of these fabricated has demonstrated a 3-dB BW of 190 MHz, an IL of 1.5 dB, and a compact footprint of 0.56 mm 2 . Another design is fabricated to demonstrate a 3-dB BW of 170 MHz, an IL of 2.5 dB, an outof-band rejection of 28 dB, and a compact footprint of 1 mm 2 .

Highlights

A S MORE radio bands in the sub-6 GHz are licensed for 5G, the spectrum below 6 GHz is getting increasingly crowded
We aim to address these remaining challenges and demonstrate a class of X-band wideband acoustic filters
After a 650-nm-thick Z-cut LiNbO3 thin film is transferred onto a high-resistivity Si wafer, the release windows are defined by etching through LiNbO3

Summary

Introduction

A S MORE radio bands in the sub-6 GHz are licensed for 5G, the spectrum below 6 GHz is getting increasingly crowded. In addition to millimeter-wave frequencies, the systems beyond 5G should explore higher frequencies where the propagation loss is still low, and beamforming can be avoided. One key challenge which lies ahead for the beyond 6-GHz systems is the lack of miniaturized front-end wideband filters [1]. The commercial solutions for the sub-6-GHz miniaturized filters are surface acoustic wave (SAW) filters and bulk acoustic wave (BAW) filters [2], [3]. For SAW devices, Manuscript received October 15, 2020; accepted November 24, 2020. Date of publication January 27, 2021; date of current version March 4, 2021.

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