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This work reports a comparative study of acoustic loss between different Lamb waves at GHz in thin-film lithium niobate (LiNbO3). The propagation loss (PL) of higher-order Lamb waves in thin-film LiNbO3 is studied for the first time using acoustic delay line (ADL) testbeds. The acoustic wave attenuation and quality factors ($Q$) of different Lamb waves are extracted, showing higher $Q\text{s}$ for higher-order Lamb modes than fundamental modes in air and vacuum at room temperature. The extracted $Q\text{s}$ are higher than those reported in thin-film LiNbO3 resonators, implying the electrode and anchor-induced loss as the dominant loss factors. The ADL-based loss analysis framework is readily extendable to acoustic damping study in other microwave acoustic platforms. [2021-0165] [ABSTRACT FROM AUTHOR]

This work reports an experimental study of acoustic loss in thin-film lithium niobate (LiNbO3) using acoustic delay lines (ADLs). Unlike prior resonator-based quality factor (Q) studies, this approach directly extracts the damping in thin-film LiNbO3, avoiding the influence of other intricate loss mechanisms, e.g., anchor loss and electrode-induced loss. Acoustic attenuation of fundamental symmetric (S0) and shear horizontal (SH0) waves are studied in suspended LiNbO3 thin films of different thicknesses. The attenuation is significantly higher in thinner LiNbO3 films, suggesting the LiNbO3 crystal degradation during the microfabrication as the primary loss origin. Nevertheless, the extracted equivalent Q in thin-film LiNbO3 is still higher than reported values, suggesting that anchor design and electrode quality remain the bottlenecks for higher Q. The proposed loss extraction framework is readily extendable to other acoustic thin-film structures. [2021-0107] [ABSTRACT FROM AUTHOR]

In this work, we present the first group of gigahertz low-loss, wideband, and high power handling delay lines (ADLs) using a thin-film lithium niobate (LiNbO3)-on-sapphire platform. The ADLs leverage a single-phase unidirectional transducer (SPUDT) to efficiently excite the shear horizontal surface acoustic wave (SH-SAW) in the film stack. The fabricated miniature SH-SAW ADL at 1.1 GHz shows a low insertion loss (IL) of 2.8 dB, a wide fractional bandwidth (FBW) of 6.14%, and a fast phase velocity of 5127 m/s. The device also features a high 1-dB compression point (P1dB) of 30.4 dBm. The temperature coefficient of frequency is −45 ppm/K. ADLs with delays between 12 and 172 ns have been implemented, with IL between 2.8 and 8.3 dB. SH-SAW propagation characteristics are extracted, showing a group velocity of 4747 m/s and a propagation loss of 6.73 dB/mm or 31.9 dB/ $\mu \text{s}$. The simultaneous low-loss and high power handling illustrate the great potential of LiNbO3-on-sapphire for RF and cross domain applications at gigahertz. [ABSTRACT FROM AUTHOR]

This work presents a class of micro-electro-mechanical system (MEMS)-driven radio frequency filters in the X-band. The X-band center frequencies are achieved by resorting to the third-order antisymmetric Lamb wave mode (A3) in a 650-nm-thick Z-cut lithium niobate thin film. A novel bandwidth (BW) widening technique based on using the self-inductance of the top interdigital transducers and bus lines is proposed to overcome the limitations set by the electromechanical coupling (${k} _{t}^{2}$) and satisfy the demands in miniaturization and wide BW. Four different designs of the filters are designed and fabricated to show the trade-off among BW, insertions loss (IL), out-of-band rejections, and footprint. Due to the spurious-free and high- ${Q}$ performance of the A3 lithium niobate resonators, the fabricated A3 lithium niobate filters have demonstrated small in-band ripples and sharp roll-offs. One of these fabricated has demonstrated a 3-dB BW of 190 MHz, an IL of 1.5 dB, and a compact footprint of 0.56 mm2. Another design is fabricated to demonstrate a 3-dB BW of 170 MHz, an IL of 2.5 dB, an out-of-band rejection of 28 dB, and a compact footprint of 1 mm2. [ABSTRACT FROM AUTHOR]

In this work, we present the low-loss acoustic delay lines (ADLs) at 5 GHz, using the first-order antisymmetric (A1) mode in 128° Y-cut lithium niobate thin films. The ADLs use a single-phase unidirectional transducer (SPUDT) design with a feature size of quarter acoustic wavelength. The design space is analytically explored and experimentally validated. The fabricated miniature A1 ADLs with a feature size of $0.45~\mu \text{m}$ show a high operating frequency at 5.4 GHz, a minimum insertion loss (IL) of 3 dB, a fractional bandwidth (FBW) of 1.6%, and a small footprint of 0.0074 mm2. The low IL and high operating frequency have significantly surpassed the state-of-the-art performance of ADLs. The propagation characteristics of A1 acoustic waves have also been extracted. The demonstrated designs can lead to low-loss and high-frequency transversal filters for future 5G applications in the sub-6-GHz bands. [ABSTRACT FROM AUTHOR]

In this work, we present gigahertz low-loss unidirectional acoustic focusing transducers in thin-film lithium niobate. The design follows the anisotropy of fundamental symmetric (S0) waves in X-cut lithium niobate. The implemented acoustic delay line testbed consisting of a pair of the proposed transducers shows a low insertion loss of 4.2 dB and a wide fractional bandwidth of 7.5% at 1 GHz. The extracted transducer loss is 1.46 dB, and the propagation loss of the S0 waves is 0.0126 dB/ $\mu \text{m}$. The design framework is readily extendable to other acoustic modes, given consideration on the optimal orientation for power flow and electromechanical transduction. [ABSTRACT FROM AUTHOR]

We present the first group of GHz broadband SH0 mode acoustic delay lines (ADLs). The implemented ADLs adopt unidirectional transducer designs in a suspended X-cut lithium niobate thin film. The design space of the SH0 mode ADLs at GHz is first theoretically investigated, showing that the large coupling and sufficient spectral clearance to adjacent modes collectively enable the broadband performance of SH0 delay lines. The fabricated devices show 3-dB fractional bandwidth ranging from 4% to 34.3% insertion loss between 3.4 and 11.3 dB. Multiple delay lines have been demonstrated with center frequencies from 0.7 to 1.2 GHz, showing great frequency scalability. The propagation characteristics of SH0 in lithium niobate thin film are experimentally extracted. The demonstrated ADLs can potentially facilitate broadband signal processing applications. [ABSTRACT FROM AUTHOR]

We present the first group of gigahertz S0 mode low loss and wideband acoustic delay lines (ADLs). The ADLs use a single-phase unidirectional transducers (SPUDT) design to launch and propagate the S0 mode in an X-cut lithium niobate thin film with large electromechanical coupling and low damping. In this work, the theoretical performance bounds of S0 mode ADLs are first investigated, significantly surpassing those in state-of-the-art. The design tradeoffs of S0 mode ADLs, when scaled to the gigahertz frequency range, are also discussed. The fabricated miniature ADLs show a fractional bandwidth (FBW) of 4% and a minimum insertion loss (IL) of 3.2 dB, outperforming the incumbent surface acoustic wave (SAW) counterparts, and covering a wide range of delays from 20 to 900 ns for digitally addressable delay synthesis. Multiple ADLs with center frequencies from 0.9 to 2 GHz have been demonstrated, underscoring their great frequency scalability. The propagation properties of S0 waves in lithium niobate at the gigahertz range are experimentally extracted. The demonstrated ADLs can potentially enable wide-range and high-resolution delay synthesis that is highly sought after for the self-interference cancellation in full-duplex radios. [ABSTRACT FROM AUTHOR]

This paper demonstrates low-loss acoustic delay lines (ADLs) based on shear-horizontal waves in thin-film LiNbO3 for the first time. Due to its high electromechanical coupling, the shear-horizontal mode is suited for producing devices with large bandwidths. Here, we show that shear-horizontal waves in LiNbO3 thin films are also excellent for implementing low-loss ADLs based on unidirectional transducers. The high acoustic reflections and large transducer unidirectionality induced by the mechanical loading of the electrodes on a LiNbO3 thin film provide a great tradeoff between delay line insertion loss and bandwidth. The directionality for two different types of unidirectional transducers has been characterized. Delay lines with variations in the key design parameters have been designed, fabricated, and measured. One of our fabricated devices has shown a group delay of 75 ns with an IL below 2 dB over a 3-dB bandwidth of 16 MHz centered at 160 MHz (fractional bandwidth = 10%). The measured insertion loss for other devices with longer delays and different numbers of transducer cells are analyzed, and the loss contributing factors and their possible mitigation are discussed. [ABSTRACT FROM AUTHOR]

This letter presents the first piezoelectric micromachined ultrasonic transducer (PMUT) based on thin-film lithium niobate (LiNbO3). The figures of merit (FoMs) of LiNbO3 as ultrasound sensors and transducers are first studied, showing great prospective as a balanced transceiver platform. Efficient flexural mode excitation is achieved using a proposed lateral-field-excitation (LFE) structure. The implemented device shows a flexural mode at 7.6 MHz, with a high electromechanical coupling ($k^{2}$) of 4.2%. Measured quality factor ($Q$) in vacuum is 2605, indicating the low structural loss, while measured $Q$ in air is 264, suggesting the ultrasound radiation. A dynamic displacement sensitivity of 20.2 nm/V is measured. Upon further optimizations, LiNbO3-based PMUTs are promising candidates for miniature ultrasound applications. [2020-0287] [ABSTRACT FROM AUTHOR]

This paper presents the first demonstration of chirp compressors based on laterally vibrating modes in suspended lithium niobate thin films. Both shear-horizontal and length-extensional modes have been explored and demonstrated with the electromechanical coupling coefficients of 30% and 39%, respectively, in a double-dispersive delay line structure. The high electromechanical coupling, along with the low propagation loss in the suspended thin film, produces a low insertion loss of 10 dB over a large fractional bandwidth of 50%. The best fabricated device demonstrates a delay-bandwidth product of 100, and provides a voltage gain of 5 to the corresponding chirp signals. Moreover, significant signal-to-noise ratio enhancements (>100), collectively enabled by the processing gain and filtering characteristics of the chirp compressors, have been demonstrated. The measured devices, in this paper, greatly outperform state-of-the-art chirp compressors based on surface acoustic waves in insertion loss for a comparable TB. As a result, signal-to-noise ratio enhancement and voltage gain have been simultaneously demonstrated for the first time in a passive device and the analog domain. The high performance can be harnessed to greatly enhance the sensitivity of near zero power wake-up radio receivers and enable low-power wireless connectivity for Internet of Things applications. [2017–0126] [ABSTRACT FROM PUBLISHER]