Search

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]

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 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]

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]

In this work, we present a novel unidirectional transducer design for frequency scaling aluminum nitride (AlN)-based radio frequency (RF) microsystems. The proposed thickness-field-excited single-phase unidirectional transducers (TFE-SPUDT) adopt 5/16 wavelength electrodes and, thus, enable efficient piezoelectric transduction with better frequency scalability. The design space of the TFE-SPUDT is theoretically explored and validated using the acoustic delay line (ADL) testbeds. The ADL testbeds with a large feature size of ${3}~\mu \text{m}$ show a center frequency of 1 GHz, a minimum insertion loss (IL) of 4.9 dB, and a fractional bandwidth (FBW) of 5.3%, significantly surpassing the IL and frequency scalability of the previously reported AlN transducers. The design approach can potentially contribute to various AlN-based RF microsystems for signal processing, physical sensing, optomechanical interaction, and quantum acoustic applications, and are readily extendable to other piezoelectric platforms. [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 reports on the demonstration of wideband spurious-free radio frequency micromechanical systems filters based on one-port shear horizontal (SH0) mode lithium niobate (LiNbO3) laterally vibrating resonators (LVRs). The fabricated filter has been demonstrated with an unprecedented spectral range of spurious-free response (290% of the center frequency), a low insertion loss of 2.1 dB, an excellent 30-dB shape factor of 1.48, and a 3-dB fractional bandwidth of 8.9%. The spurious free response is achieved by optimizing the building blocks of the filters, namely the LVRs, and employing a spurious mitigation design based on arraying single resonators with only two electrodes. The low loss and excellent shape factor are enabled by the demonstrated high electromechanical coupling ( \mathit kt^{2}=16.1 %), high quality factor ( Q =1093 ), and high figure of merit (FoM = 154) of the fabricated resonator arrays. [2016-0250] [ABSTRACT FROM PUBLISHER]

This letter presents wideband spurious-free microelectromechanical systems (MEMSs) filters based on shear horizontal (SH0) mode Lithium Niobate (LiNbO3) laterally vibrating resonators. The filters, monolithically fabricated on the same chip, have center frequencies at 400 and 750 MHz. The measured performance exhibits in-band ripple-free response, a low insertion loss (IL) of 1.7 dB, a 30-dB shape factor of 1.41, and a 3-dB fractional bandwidth (FBW) of 9.6 %-the largest reported for MEMS-resonator-based filters. The high performance was collaboratively enabled by the LiNbO3 material and filter design. The excellent piezoelectric coupling and low acoustic loss in LiNbO3 thin film ensure the low IL and large FBW, while the medium-scale integration of 200 spurious mode-free resonators fully harnesses the potential of LiNbO3 material without introducing spurious response. The filters have a device footprint less than 360 \times 350\,\,\mu \textm^2 , thus suitable for RF frontends in handheld wireless devices. [ABSTRACT FROM PUBLISHER]

We present a group of low-loss Lamb mode acoustic delay lines in an aluminum nitride (AlN) thin film. The low-loss acoustic delay lines are enabled by the thickness-field-excited single-phase unidirectional transducers. The fabricated miniature acoustic delay lines show a fractional bandwidth of 4.5%, a minimum insertion loss of 5.9 dB, outperforming the previously reported aluminum nitride delay platforms. The demonstrated delay ranges from 105 ns to 165 ns with center frequencies from 175 MHz to 255 MHz. The design approach and the significantly lower insertion loss described herein are expected to open new horizons for hybridized signal processing based on AlN and CMOS. [2019-0094] [ABSTRACT FROM AUTHOR]

This paper reports on a spurious mode suppression technique for S0 mode aluminum nitride (AlN) laterally vibrating resonators. The technique utilizes a notch in the resonator body to convert spurious asymmetrical (A0) modes into the intended S0 mode vibration. Finite-element analyses were employed to theoretically investigate the mode conversion from A0 mode to S0 mode, and identify the optimal notch configuration. The technique has been experimentally validated to simultaneously eradicate the A0 spurious mode and enhance the S0 mode electromechanical coupling ( kt^{2} ) for the monolithically integrated resonators over a wide frequency range ( $100\sim 600$ MHz). It is a crucial technology development, because the spurious modes are a major bottleneck obstructing the deployment of single-chip multi-frequency AlN resonators as a commercially viable solution for radio frequency front-end filtering. [2015-0295] [ABSTRACT FROM PUBLISHER]

This paper reports on the analysis and removal of transverse spurious modes in shear horizontal (SH0) mode lithium niobate (LiNbO3) laterally vibrating resonators (LVRs). A length-controlled electrode configuration that employs an optimized overlapping length between the adjacent electrodes has been developed to subdue the spurious modes. The technique modifies the stress and electric field distribution in the resonator body, consequently enabling near zero electromechanical coupling ( kt^{2} ) for the higher order transverse spurious modes. The length-controlled electrode configuration also reduces the loss at the interface between the metal electrodes and the piezoelectric layer, demonstrating a more than 2\times enhancement in quality factors {Q} . The fabricated LiNbO3 LVR with the length-controlled electrode configuration has shown an unprecedented spectral range (100–200 MHz) of spurious-free response, a high \mathit {k}_{t}^{2}$ value of 20.1%, a {Q} value of 1150, and, thereby, a remarkably high figure of merit of 230. [ABSTRACT FROM AUTHOR]

This letter reports on a spurious mode suppression technique for the shear horizontal (SH0) mode lithium niobate laterally vibrating resonators. The concept utilizes triangular and arched edge shapes on the transversal sides of a resonant cavity to effectively distribute and scatter the acoustic waves in the inactive regions, yielding the suppression of transverse spurious modes. 2D models and 3D finite-element analyses were employed to theoretically verify the technique. For devices with the arched-shape edges, complete removal of higher order transverse modes has been experimentally demonstrated with $2\times $ enhancement for quality factor ( Q$ ). The Q$ enhancement arises from the improved concentration of mechanical energy under the inter-digitated transducers. The fabricated device exhibits a Q ) of 17.8%, and a figure of merit of 164. [ABSTRACT FROM PUBLISHER]