A Low-Loss Wideband SAW Filter With Low Drift Using Multilayered Structure

Abstract

This research aims to overcome the tradeoff between bandwidth, temperature stability of frequency, and loss in surface acoustic wave filters. A novel multilayered structure, SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Cu-grating/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$15^{\circ }~{Y}$ </tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${X}$ </tex-math></inline-formula> LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /sapphire, is proposed. Resonators based on the multilayered structure are studied theoretically and experimentally. The results show that the multilayered structure can sufficiently suppress leaky wave and spurious responses, which significantly degrade the performance of devices based on conventional SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Cu-grating/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$15^{\circ }~{Y}$ </tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${X}$ </tex-math></inline-formula> LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> structure. Fabricated resonators exhibit high performance including low frequency drift, large coupling, and large quality factor. A multilayered structure filter is designed, fabricated, and measured, resulting in a flat and clean passband with a small minimum insertion loss of only 1.01 dB. A large 3-dB fractional bandwidth of 14.74% is achieved, as well as a low temperature coefficient of frequency of approximately −18 ppm/°C. This research proposes a useful solution for high-performance filters in fifth-generation networks.