Wideband Surface Acoustic Wave Filter at 3.7 GHz With Spurious Mode Mitigation

As an essential functional block in radio frequency (RF) front-ends, surface acoustic wave (SAW) filters with large fractional bandwidth (FBW), high center frequency (f(c)), and low loss are highly sought-after in 5G new radio (NR). To address this end, 32 degrees Y-X LiNbO3/SiO2/Si heterostructure with high electro-mechanical coupling coefficient of 23% was constructed, while the propagation characteristics as well as spurious resonance were analyzed through finite element method (FEM) and oneport resonators measurement. It is revealed that by using thin electrodes in the series resonator and thick electrodes in the parallel resonator, spurious modes are successfully eliminated out of the passband. As a result, the SAW filters formed by the above resonators are capable of several superb RF performances: a large bandwidth of 730 MHz (FBWof 19.5%) at f(c) of 3.74 GHz, a small insertion loss (IL) of 3.03 dB, and a flat passband. Furthermore, since our devices were fabricated by standard photolithography process, this work advances commercial implementation of SAW filter in 5G NR.

Automated summary

In this study, a 32-degree Y-X LiNbO3/SiO2/Si heterostructure with high electro-mechanical coupling coefficient was constructed to develop a SAW filter with excellent RF performance for 5G NR. The fabricated filter exhibited a large bandwidth, low insertion loss, and flat passband, demonstrating the potential for commercial implementation of SAW filters in 5G NR.