High-frequency and Low-loss SAW Filter Based on Sapphire-based Piezoelectric Heterogeneous Substrate

The 5G radio frequency (RF) front-end puts forward higher requirements for the operating frequency, insertion loss, and out-of-band rejection of the filter. Surface Acoustic Wave (SAW) filters based on piezoelectric heterogeneous substrates are one of the potential solutions. In this paper, a high-frequency and low-loss filter was realized based on the Sapphire-based single-crystalline lithium tantalite thin film heterogeneous integrated substrate (LTOS). Through comparative experiments, it is proved that using Sapphire substrate can effectively avoid RF loss. The filter was designed with a multi-zero, and the tilted electrode was used to suppress the higher-order transverse modes, so as the flat filter passband was achieved. The fabricated resonator achieves a Q value of 1 823 above 3 GHz, while the fabricated filter shows a center frequency of 3.61 GHz, the minimum in-band insertion loss of 1.25 dB, the 3 dB bandwidth of 112 MHz, the out-of-band rejection of about 40 dB and a flat passband.