Search

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 article presents an 8.6-GHz oscillator utilizing the third-order antisymmetric overtone (A3) in a lithium niobate (LiNbO3) radio frequency microelectromechanical systems (RF-MEMS) resonator. The oscillator consists of an acoustic resonator in a closed loop with cascaded RF tuned amplifiers (TAs) built on Taiwan Semiconductor Manufacturing Company (TSMC) RF general purpose (GP) 65-nm complementary metal-oxide semiconductor (CMOS). The TAs bandpass response, set by on-chip inductors, satisfies Barkhausen’s oscillation conditions for A3 while suppressing the fundamental and higher order resonances. Two circuit variations are implemented. The first is an 8.6-GHz standalone oscillator with a source-follower buffer for direct 50-Ω-based measurements. The second is an oscillator-divider chain using an on-chip three-stage divide-by-two frequency divider for a ~1.1-GHz output. The standalone oscillator achieves a measured phase noise of −56, −113, and −135 dBc/Hz at 1 kHz, 100 kHz, and 1 MHz offsets from an 8.6-GHz output while consuming 10.2 mW of dc power. The oscillator also attains a figure-of-merit of 201.6 dB at 100-kHz offset, surpassing the state-of-the-art (SoA) oscillators-based electromagnetic (EM) and RF-MEMS. The oscillator-divider chain produces a phase noise of −69.4 and −147 dBc/Hz at 1 kHz and 1 MHz offsets from a 1075-MHz output while consuming 12 mW of dc power. Its phase noise performance also surpasses the SoA L-band phase-locked loops (PLLs). With further optimization, this work can enable low-power multistandard wireless transceivers featuring high speed, high sensitivity, and high selectivity in small-form factors. [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]

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]

We present the first group of GHz low-loss acoustic radio frequency (RF) couplers using the fundamental symmetric (S0) mode in X-cut lithium niobate thin films. The demonstrated multistrip couplers (MSCs) significantly surpass the insertion loss (IL) and the operating frequency of the previous works in more compact structures, thanks to the large electromechanical coupling and low loss of S0 in lithium niobate. The design space of S0 MSCs is first explored. Devices with different coupling factors are fabricated using different numbers of strips. Based on the S0 testbed with an IL of 4.5 dB at 1 GHz, the hybrid coupler shows an IL of 7.5 dB, while the track changer shows an IL of 5.1 dB, over a 3-dB fractional bandwidth of 8%. Couplers at different frequencies (between 0.75 and 1.55 GHz) are also investigated. Upon further optimizations, the S0 MSC platform can potentially enable low-loss wideband signal processing functions toward an RF acoustic component kit. [ABSTRACT FROM AUTHOR]

In this work, we present first-order antisymmetric (A1) mode resonators in 128° Y-cut lithium niobate (LiNbO3) thin films with electromechanical coupling coefficients ($k^{2}$) as large as 46.4%, exceeding the state-of-the-art. The achievable $k^{2}$ of A1 in LiNbO3 substrates of different orientations is first explored, showing X-axis direction in 128° Y-cut LiNbO3 among the optimal combinations. Subsequently, A1 resonators with spurious mode mitigation are designed and fabricated. In addition to the large $k^{2}$ , the implemented devices show a maximum quality factor ($Q$) of 598 at 3.2 GHz. Upon further optimization, the reported platform can potentially deliver a wideband acoustic-only filtering solution in 5G New Radio. [2020–0003] [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 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 frequencies of the prior art with similar feature sizes because of their simultaneously fast phase velocity, large coupling coefficient, and low loss. In this article, the propagation characteristics of the A1 mode in lithium niobate are 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 7.9 dB, an average insertion loss (IL) of 9.1 dB, and a fractional bandwidth around 4%, with group delays ranging between 15 and 109 ns and the center frequencies between 4.5 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 wideband high-frequency passive signal processing functions for future 5G applications in the sub-6-GHz spectrum bands. [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]

Recent advancements in the field of piezoelectric micro-resonators have produced devices, such as lithium niobate laterally vibrating resonators, with very high electromechanical coupling factors ($k_{t}^{2}$) and respectable quality factors (${Q}$). As a result, the records of the figure of merit (FoM) for radio-frequency MEMS resonators have been broken several times in the past five years. As exciting as these high FoMs are, they impose unique caveats in accurately extracting the electromechanical coupling often due to the presence of spurious modes. It is a less noted issue for micro-resonators with moderate ${k} _{t}^{2}$ , as spurious modes either are absent or do not significantly affect the common extraction technique based on identifying resonances and anti-resonances. This paper will first theoretically analyze how disregarding spurious modes can potentially lead to inaccurate extraction of ${k} _{t}^{2}$ of the intended mode and then offer a framework that accounts for spurious modes and accurately extracts electromechanical coupling using a multi-resonance recursive fitting. [2018-0209] [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 paper demonstrates the first nonreciprocal network based on switched low-loss acoustic delay lines. The four-port circulator is built upon a recently reported frequency-independent, programmable, nonreciprocal framework based on switched delay lines. The design space for such a system, including the origins of the insertion loss (IL) and harmonic responses, is theoretically investigated, illustrating that the key to better performance and low-cost modulation signal synthesis lies in a large delay. To implement a large delay, we resort to in-house fabricated low-loss, wideband lithium niobate (LiNbO3)SH0 mode acoustic delay lines employing single-phase unidirectional transducers. The four-port circulator, consisting of two switch modules and one delay line module, has been modularly designed, assembled, and tested. The design process employs time-domain full circuit simulation, and the results match well with measurements. An 18.8-dB nonreciprocal contrast between IL (6.6 dB) and isolation (25.4 dB) has been achieved over a fractional bandwidth of 8.8% at a center frequency 155 MHz, using a record low switching frequency of 877.19 kHz. The circulator also shows 25.9-dB suppression for the intramodulated tone and 30 dBm for IIP3. Upon further development, such a system can potentially lead to future wideband, low-loss chip-scale nonreciprocal radio frequency systems with unprecedented programmability. [ABSTRACT FROM AUTHOR]

In permanent magnet applications, response often scales with volume or dimension in power-conversion and magnetostrictive applications, even in film form. In microelectromechanical devices it is necessary to explore versatile methods of dense film deposition with film thicknesses approaching one micron. In this study, we present a wet chemical route to hard magnetic cobalt ferrite (CoFe2O4) films to produce films with large coercivity, controllable thickness, saturation approaching that of the bulk, and smoother morphology than state-of-the art sputtered or pulsed-laser-deposited films. The development of etching and releasing processes demonstrates how these films are suitable for precise engineering in a variety of form factors and applications. [ABSTRACT FROM AUTHOR]

This paper demonstrates a passive low-insertion-loss (IL) RF filter with periodic passbands and capable of sparsifying the spectrum from 238 to 526 MHz for sparse Fourier transform (SFT)-based spectrum sensing. The demonstrated periodic filter employs LiNbO3 lateral overtone bulk acoustic resonators (LOBARs) with high-quality factors (Qs), large electromechanical coupling ($k_{t}^{2}$), and multiple equally spaced resonances in a ladder topology. To demonstrate the periodic filter, the LOBARs is first modeled to predict $k_{t}^{2}$ of various tones accurately. The fabricated LOBARs show $k_{t}^{2}$ larger than 1.5% and figure of merits ($Q\cdot k_{t}^{2}$) more than 30 for over 10 tones simultaneously, which agree with our modeled response, and are both among the highest demonstrated in overmoded resonators. The multi-band filter centered at 370 MHz has then been obtained with a passband span of 291 MHz, a spectral spacing of 22 MHz, an IL of 2 dB, FBWs around 0.6%, and a sparsification ratio between 7 and 15. An out-of-band rejection around 25 dB has also been achieved for more than 14 bands. The great performance demonstrated by the RF filter with 14 useable periodic passbands will serve to enable future SFT-based spectrum sensing. [2018-0155] [ABSTRACT FROM AUTHOR]

This paper reports the first demonstration of phononic crystals (PnCs) in suspended lithium niobate thin films, which exhibit band gaps for tailoring the performance of laterally vibrating devices. Transmission and reflection properties of lithium niobate PnCs for both shear-horizontal (SH0) and length-extensional (S0) modes have been investigated and subsequently explored in two applications. In the first case, PnC-embedded delay lines were designed for filtering with stopbands, while in the second case, PnC-bounded resonators were implemented for spurious mode suppression. Equivalent circuit models incorporating acoustic scattering parameters of the designed PnCs and Mason’s model of the transducers have been built for each application. Benchmarked to reference devices without PnCs, the measured PnCs embedded in delay lines show 20-dB attenuation in the stopbands and less than 2-dB loss in the passbands for the SH0 mode, and 30-dB attenuation in the stopbands and less than 10-dB loss in the passbands for the S0 mode. The fabricated piezoelectric PnC-bounded resonator has shown a quality factor of 434 at 142.7 MHz with undesired spurious modes significantly suppressed. These demonstrations show that lithium niobate PnCs for laterally vibrating devices can potentially lead to wideband and low-loss acoustic functions for radio frequency signal processing. [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]