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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]

In this article, near-zero drift and high electromechanical coupling acoustic resonators have been designed and demonstrated. The acoustic resonator is based on Lamb acoustic waves in a bimorph composed of lithium niobate on silicon dioxide. Our approach breaks through a performance boundary in conventional Lamb-wave resonators by introducing the bimorph while operating at higher order resonant modes. This enables the resonator to achieve frequency scalability, a low-temperature coefficient of frequency, and high electromechanical coupling altogether. The electromechanical coupling and temperature coefficient of the resonator were analytically optimized for the A3 mode through adjusting the thicknesses of different materials in the bimorph. Resonators with different dimensions and stack thickness were fabricated and measured, resulting in a temperature coefficient of frequency ranging from −17.6 to −1.1 ppm/°C, high electromechanical coupling ranging from 13.4% to 18%, and quality factors up to 800 at 3.5 GHz. The achieved specifications are adequate for fifth-generation (5G) sub-6-GHz frequency bands n77 and n78. [ABSTRACT FROM AUTHOR]

This article presents the design approach and the first demonstration of a wideband hybrid monolithic acoustic filter in the K-band, which exceeds the limitation of electromechanical coupling on the fractional bandwidth (FBW) of acoustic filters. The hybrid filter utilizes the codesign of electromagnetic (EM) and acoustic to attain wide bandwidth while keeping the advantages of small sizes and high Q in the acoustic domain. The performance trade space and design flow of the hybrid filter are also presented in this article, which allows this technology to be applied for filters with different center frequencies and FBWs. The hybrid filter is simulated by hybridizing the EM and acoustic finite element analysis, which are carried out separately and combined at a system level. The fabricated filter built with resonators having an electromechanical coupling of 0.7% based on the seventh-order antisymmetric Lamb wave mode (A7) has a 3-dB FBW of 2.4% at 19 GHz and a compact footprint of 1.4 mm2. [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]

This work presents an improved design that exploits dispersion matching to suppress the spurious modes in the lithium niobate first-order antisymmetric (A1) Lamb wave mode resonators. The dispersion matching in this work is achieved by micro-machining the lithium niobate thin film to balance the electrical and mechanical loadings of electrodes. In this article, the dispersion matchings of the A1 mode in lithium niobate based on different metals are analytically modeled and validated with finite-element analysis. The fabricated devices exhibit spurious-free responses with a quality factor of 692 and an electromechanical coupling coefficient of 28%. The demonstrated method herein could overcome a significant hurdle that is currently impeding the commercialization of A1 devices. [ABSTRACT FROM AUTHOR]

This work presents a new class of microelectromechanical system (MEMS) resonator toward 60 GHz for the fifth-generation (5G) wireless communications. The wide range of the operating frequencies is achieved by resorting to different orders of the antisymmetric Lamb wave modes in a 400-nm-thick Z-cut lithium niobate thin film. The resonance of 55 GHz demonstrated in this work marks the highest operating frequency for piezoelectric electromechanical devices. The fabricated device shows an extracted mechanical $Q$ of 340 and an $f\times Q$ product of $1.87\times 10^{13}$ in a footprint of $2 \times 10^{-3}$ mm2. The performance has shown the strong potential of LiNbO3 antisymmetric mode devices for front-end applications in 5G high-band. [ABSTRACT FROM AUTHOR]

In this work, we present a new paradigm for enabling gigahertz higher-order Lamb wave acoustic devices using complementarily oriented piezoelectric (COP) thin films. Acoustic characteristics are first theoretically explored with COP lithium niobate (LiNbO3) thin films, showing their excellent frequency scalability, low loss, and high electromechanical coupling ($k^{2}$). Acoustic resonators and delay lines are then designed and implemented, targeting efficient excitation of higher-order Lamb waves with record-breaking low loss. The fabricated resonator shows a $2^{\mathbf {nd}}$ -order symmetric (S2) resonance at 3.05 GHz with a high quality factor ($Q$) of 657, and a large $k^{2}$ of 21.5% and a $6^{\mathbf {th}}$ -order symmetric (S6) resonance at 9.05 GHz with a high $Q$ of 636 and a $k^{2}$ of 3.71%, both among the highest demonstrated for higher-order Lamb wave devices. The delay lines show an average insertion loss (IL) of 7.5 dB and the lowest reported propagation loss of 0.014 dB/ $\mu \text{m}$ at 4.4 GHz for S2. Notable acoustic passbands up to 15.1 GHz are identified. Upon further optimizations, the proposed COP platform can lead to gigahertz low-loss wideband acoustic components. [2020-0127] [ABSTRACT FROM AUTHOR]

This work presents an extensive study on the temperature coefficient of frequency (TCF) for thin-film lithium niobate (LiNbO3) resonators. To capture the temperature-frequency behavior for each vibration mode, a one-dimensional (1D) multi-section TCF model is proposed and verified by both the finite-element method (FEM) and experiments. By partitioning the metallized and non-metallized sections of the interdigitated transducers (IDT) as distinct TCF blocks and properly considering the spatial energy distribution, the TCF of each mode can be accurately predicted. Two higher lateral-order resonators based on the fundamental shear-horizontal mode (SH0) are designed and fabricated on a LiNbO3-on-SiO2 wafer to provide odd- and even-order harmonics. TCFs of the first 6 overtones (from 84 to 515 MHz) are calculated using the material properties given in the literature, exhibiting a maximum TCF difference of 3 ppm/K between the theoretical prediction and measurement results. Although only SH0 resonators are selected for experimental verification, the proposed multi-section TCF model can be applied to other plate wave MEMS resonators. [2019-0112] [ABSTRACT FROM AUTHOR]