Abstract
We present the first group of acoustic delay lines (ADLs) at 5 GHz, using the first-order antisymmetric (A1) mode in Z-cut lithium niobate thin films. The demonstrated ADLs significantly surpass the operation frequency of the previous works with similar feature sizes, because of its simultaneously fast phase velocity, large coupling coefficient, and low-loss. In this work, the propagation characteristics of the A1 mode in lithium niobate is analytically modeled and validated with finite element analysis. The design space of A1 ADLs is then investigated, including both the fundamental design parameters and those introduced from the practical implementation. The implemented ADLs at 5 GHz show a minimum insertion loss of 7.94 dB, an average IL of 9.1 dB, and a fractional bandwidth around 4%, with delays ranging between 15 ns to 109 ns and the center frequencies between 4.5 GHz and 5.25 GHz. The propagation characteristics of A1 mode acoustic waves have also been extracted for the first time. The A1 ADL platform can potentially enable wide-band high-frequency passive signal processing functions for future 5G applications in the sub-6 GHz spectrum bands.
Highlights
T HE next-generation radio access technology, namely, the fifth-generation (5G) new radio (NR), requires unprecedented signal processing capabilities [1], [2]
To overcome these outstanding hurdles, we aim to provide a comprehensive framework in this article for analyzing the key parameters and propagation characteristics of A1 waves in LiNbO3 thin films and subsequently implement wideband and high-frequency A1 acoustic delay lines (ADLs)
We have demonstrated A1 ADLs at 5 GHz in LiNbO3 thin films for the first time, significantly surpassing the operation frequencies of the previous reports
Summary
T HE next-generation radio access technology, namely, the fifth-generation (5G) new radio (NR), requires unprecedented signal processing capabilities [1], [2]. The recent demonstrations of low-loss and high electromechanical coupling (k2) piezoelectric platforms [10]–[17] enable devices with lower insertion loss (IL) and wider fractional bandwidth (FBW), potentially overcoming the performance bottlenecks that currently hinder acoustic signal processing from eMBB applications. A1 devices demonstrated so far are analyzed for mostly standing wave structures (e.g., resonators [60]) where the A1 propagation characteristics have not been systematically studied To overcome these outstanding hurdles, we aim to provide a comprehensive framework in this article for analyzing the key parameters and propagation characteristics of A1 waves in LiNbO3 thin films and subsequently implement wideband and high-frequency A1 ADLs. The fabricated ADLs show a minimum IL of 7.9 dB, an average IL of 9.1 dB, and an FBW around 4%, delays ranging between 15 and 109 ns, and the center frequencies between 4.5 and 5.25 GHz. This article is organized as follows.
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