Q-Enhanced SH-SAW Ladder Filter in Thin-Film Lithium Tantalate Using Bartlett Apodization

TL;DR

This paper presents a high-performance SH-SAW ladder filter at 4.35 GHz using Bartlett apodization on thin-film lithium tantalate, significantly improving quality factor and filter performance for RF applications.

Contribution

The work demonstrates the application of Bartlett window apodization to enhance quality factor and filter performance in thin-film LiTaO3 SH-SAW filters, enabling compact, low-loss RF filters.

Findings

Quality factor improved from 688 to 1522 using Bartlett apodization.

Achieved a 3.24% fractional bandwidth with over 14 dB out-of-band rejection.

Realized a 4.3 GHz third-order ladder filter with 1.59 dB insertion loss.

Abstract

Shear-horizontal surface acoustic wave (SH-SAW) filters have shown strong potential for low-loss, compact, GHz-frequency RF front ends. In this work, we demonstrate a high-performance SH-SAW filter design at 4.35 GHz utilizing 42{\deg}Y-cut thin-film lithium tantalate (LiTaO3) on a SiO2/Si platform. Despite the limitations of thin aluminum metallization and its associated ohmic losses, we show that implementing a Bartlett window apodization technique, primarily intended for in-band spurious-mode suppression, yields a significantly improved quality factor (Q) of 1,522 from 688 in conventional interdigitated SH-SAW resonators. This enhancement enables a third-order ladder filter at 4.3 GHz with an insertion loss of 1.59 dB, compared with 1.65 dB for a conventional SH-SAW filter. In addition, our filter with apodized resonator designs achieves a 3 dB fractional bandwidth (FBW) of 3.24% and out-of-band rejection exceeding 14 dB, all within a compact footprint of 0.4 mm2. These results suggest that apodized thin-film LiTaO3 designs are highly promising for low-loss, miniaturized, cost-effective radio frequency acoustic solutions in next-generation communication and sensing applications.