Lu Zengtian, Fu Sulei, Xu Zhibin, Wang Weibiao, Zhang Qiaozhen, Zhang Jianrun, Zhang Hui
School of Mechanical Engineering, Southeast University, Nanjing 211189, China.
Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China.
Micromachines (Basel). 2022 Mar 14;13(3):439. doi: 10.3390/mi13030439.
To cope with ubiquitous wireless connectivity and the increased and faster data delivery in 5G communication, surface acoustic wave (SAW) filters are progressively requiring wider bandwidths. Conventional bulk 15°YX-LiNbO substrates with a large coupling coefficient () are attractive for the low-cost mass production of wideband SAW filters, but these generally suffer from spurious responses, limiting their practical application. In this work, a novel and simple SAW configuration is proposed that uses thickness-modulated interdigital transducer (IDT) structures to overcome the limitations set by spurious responses. Different from the conventional design where the thicknesses of the IDT electrodes in the series and parallel resonators generally kept the same, the proposed configuration adopts IDT electrodes of different thicknesses in the series and shunt resonators to suppress or remove unwanted spurious Rayleigh modes from the filter passband. Two different ultra-wideband SAW filter designs employing thickness-modulated IDTs were designed and fabricated to validate the effective suppression of spurious modes. The SAW filters experimentally featured spurious-free responses in the passband as well as a large 3 dB fractional bandwidth (FBW) in the 18.0% and 24.1% ranges and low insertion losses below 1 dB. This work can significantly broaden the range of applications for SAW devices and can open a pathway to commercialize ultra-wideband SAW filters in 5G communication systems.
为了应对无处不在的无线连接以及5G通信中不断增加且更快的数据传输，表面声波（SAW）滤波器对带宽的要求越来越高。具有大耦合系数（）的传统块状15°YX-LiNbO衬底对于宽带SAW滤波器的低成本大规模生产具有吸引力，但这些衬底通常会受到杂散响应的影响，限制了它们的实际应用。在这项工作中，提出了一种新颖且简单的SAW配置，该配置使用厚度调制叉指换能器（IDT）结构来克服杂散响应带来的限制。与传统设计不同，在传统设计中串联和并联谐振器中IDT电极的厚度通常保持相同，而所提出的配置在串联和并联谐振器中采用不同厚度的IDT电极，以抑制或消除滤波器通带中不需要的杂散瑞利模式。设计并制作了两种采用厚度调制IDT的不同超宽带SAW滤波器设计，以验证对杂散模式的有效抑制。这些SAW滤波器在实验中具有通带内无杂散响应，以及在18.0%和24.1%范围内的大3 dB分数带宽（FBW）和低于1 dB的低插入损耗。这项工作可以显著拓宽SAW器件的应用范围，并为5G通信系统中超宽带SAW滤波器的商业化开辟一条道路。
