Xu Huiping, Fu Sulei, Su Rongxuan, Liu Peisen, Zhang Shuai, Lu Zengtian, Xiao Boyuan, Wang Rui, Song Cheng, Zeng Fei, Wang Weibiao, Pan Feng
IEEE Trans Ultrason Ferroelectr Freq Control. 2023 Sep;70(9):1157-1169. doi: 10.1109/TUFFC.2023.3299635. Epub 2023 Aug 29.
The 5G communication system has experienced a substantial expansion of the spectrum, which poses higher requirements to radio frequency (RF) filters in enhancing their operating frequencies and bandwidths. To this end, this work focused on solving the filtering scheme for challenging 5G n77 and n78 bands and successfully implemented the corresponding spurious-free surface acoustic wave (SAW) filters exploiting large-coupling shear horizontal (SH) modes based on X-cut LiNbO3 (LN)/silicon carbide (SiC) heterostructure. Here, we initially investigated the suppression methods for spurious modes theoretically and experimentally and summarized an effective normalized LN thickness ( [Formula: see text] range of 0.15-0.30 for mitigating Rayleigh modes and higher order modes, as well as tilted interdigital transducers (IDT) by about 24° for eliminating transverse modes. Resonators with wavelengths ( λ) from 0.95 to [Formula: see text] were also fabricated, showing a scalable resonance from 2.48 to 4.21 GHz without any in-band ripple. Two filters completely meeting 5G n77 and n78 full bands were finally constructed, showing center frequencies ( f) of 3763 and 3560 MHz, 3-dB fractional bandwidths (FBW) of 24.8% and 15.6%, and out-of-band (OoB) rejections of 18.7 and 28.1 dB, respectively. This work reveals that X-LN/SiC heterostructure is a promising underpinning material for SAW filters in 5G commercial applications.
5G通信系统经历了频谱的大幅扩展，这对射频（RF）滤波器在提高其工作频率和带宽方面提出了更高的要求。为此，这项工作专注于解决具有挑战性的5G n77和n78频段的滤波方案，并成功实现了基于X切铌酸锂（LN）/碳化硅（SiC）异质结构利用大耦合水平剪切（SH）模式的相应无杂散表面声波（SAW）滤波器。在此，我们首先从理论和实验上研究了杂散模式的抑制方法，并总结出有效归一化LN厚度（[公式：见正文]）在0.15 - 0.30范围内以减轻瑞利模式和高阶模式，以及倾斜叉指换能器（IDT）约24°以消除横向模式。还制作了波长（λ）从0.95到[公式：见正文]的谐振器，显示出从2.48到4.21 GHz的可扩展谐振且无任何带内纹波。最终构建了两个完全符合5G n77和n78全频段的滤波器，其中心频率（f）分别为3763和3560 MHz，3分贝分数带宽（FBW）分别为24.8%和15.6%，带外（OoB）抑制分别为18.7和28.1 dB。这项工作表明X-LN/SiC异质结构是5G商业应用中SAW滤波器一种很有前景的基础材料。
