Near Spurious-Free Thickness Shear Mode Lithium Niobate Resonator for Piezoelectric Power Conversion.

Piezoelectric power converters, where acoustic resonators replace the inductors as energy storage elements, promise much higher power density and higher efficiency compared to conventional circuits. Recently, lithium niobate (LiNbO3) piezoelectric resonators have been integrated within power converter circuits, showing good conversion efficiency, thanks to their high quality factor ( Q ) and electromechanical coupling ( kt 2 ). However, the converter output power range is limited by large spurious modes near resonance. This work reports a near-spurious-free LiNbO3 thickness shear (TS) resonator, demonstrating a high Q of 3500 and kt 2 of 45% at 5.94 MHz, with a fractional suppressed region of 35%. First, we identify the best LiNbO3 crystal orientation for efficient TS resonators. Then, we propose a novel acoustic design without busbars for spurious suppression, which is extensively simulated, fabricated, and characterized. Further analysis is done to identify existing spurious modes in our proposed design, specifically the effect of dicing on our TS resonator design. Upon optimization, LiNbO3 TS resonators could potentially empower a new design space for low-loss and compact power converters.

Nanoscale imaging of super-high-frequency microelectromechanical resonators with femtometer sensitivity.

Implementing microelectromechanical system (MEMS) resonators calls for detailed microscopic understanding of the devices, such as energy dissipation channels, spurious modes, and imperfections from microfabrication. Here, we report the nanoscale imaging of a freestanding super-high-frequency (3 - 30 GHz) lateral overtone bulk acoustic resonator with unprecedented spatial resolution and displacement sensitivity. Using transmission-mode microwave impedance microscopy, we have visualized mode profiles of individual overtones and analyzed higher-order transverse spurious modes and anchor loss. The integrated TMIM signals are in good agreement with the stored mechanical energy in the resonator. Quantitative analysis with finite-element modeling shows that the noise floor is equivalent to an in-plane displacement of 10 fm/√Hz at room temperatures, which can be further improved under cryogenic environments. Our work contributes to the design and characterization of MEMS resonators with better performance for telecommunication, sensing, and quantum information science applications.

Lateral Spurious Mode Suppression in Lithium Niobate A1 Resonators.

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.

Low-Loss Unidirectional Acoustic Focusing Transducer in Thin-Film Lithium Niobate.

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/ [Formula: see text]. The design framework is readily extendable to other acoustic modes, given consideration on the optimal orientation for power flow and electromechanical transduction.

A Wideband Oscillator Exploiting Multiple Resonances in Lithium Niobate MEMS Resonator.

This article presents a comprehensive guide to codesign lithium niobate (LiNbO3) lateral overtone bulk acoustic resonators (LOBARs) and voltage-controlled oscillators (VCOs) using discrete components on a printed circuit board (PCB). The analysis focuses on understanding the oscillator-level tradeoffs between the number of locked tones, frequency stability, tuning range, power consumption, and phase noise. Moreover, this article focuses on understanding the relationship between the abovementioned specifications and the different LOBAR parameters, such as electromechanical coupling ( kt2 ), quality factor ( Q ), transducer design, and the resonator size. As a result of this study, the first voltage-controlled MEMS oscillator (VCMO) based on LiNbO3 LOBAR is demonstrated. Our LOBAR excites over 30 resonant modes in the range of 100-800 MHz with a frequency spacing of 20 MHz. The VCMO consists of an LOBAR in a closed loop with two amplification stages and a varactor-embedded tunable LC tank. By adjusting the bias voltage applied to the varactor, the tank can be tuned to change the closed-loop gain and phase responses of the oscillator so that the Barkhausen conditions are satisfied for a particular resonant mode. The tank is designed to allow the proposed VCMO to lock to any of the ten overtones ranging from 300 to 500 MHz. These ten tones are characterized by average [Formula: see text] of 2100, kt2 of 1.5%, figure of merit ( [Formula: see text]) of 31.5 enabling low phase noise, and low-power oscillators crucial for Internet of Things (IoT). Due to the high [Formula: see text] of the LiNbO3 LOBAR, the measured VCMO shows a close-in phase noise of -100 dBc/Hz at 1-kHz offset from a 300-MHz carrier and a noise floor of -153 dBc/Hz while consuming 9 mW. With further optimization, this VCMO can lead to direct radio frequency (RF) synthesis for ultralow-power transceivers in multimode IoT nodes.

GHz Low-Loss Acoustic RF Couplers in Lithium Niobate Thin Film.

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.

A Unidirectional Transducer Design for Scaling GHz AlN-Based RF Microsystems.

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 [Formula: see text] 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.

A Laterally Vibrating Lithium Niobate MEMS Resonator Array Operating at 500 °C in Air.

This paper reports the high-temperature characteristics of a laterally vibrating piezoelectric lithium niobate (LiNbO3; LN) MEMS resonator array up to 500 °C in air. After a high-temperature burn-in treatment, device quality factor (Q) was enhanced to 508 and the resonance shifted to a lower frequency and remained stable up to 500 °C. During subsequent in situ high-temperature testing, the resonant frequencies of two coupled shear horizontal (SH0) modes in the array were 87.36 MHz and 87.21 MHz at 25 °C and 84.56 MHz and 84.39 MHz at 500 °C, correspondingly, representing a -3% shift in frequency over the temperature range. Upon cooling to room temperature, the resonant frequency returned to 87.36 MHz, demonstrating the recoverability of device performance. The first- and second-order temperature coefficient of frequency (TCF) were found to be -95.27 ppm/°C and 57.5 ppb/°C2 for resonant mode A, and -95.43 ppm/°C and 55.8 ppb/°C2 for resonant mode B, respectively. The temperature-dependent quality factor and electromechanical coupling coefficient (kt2) were extracted and are reported. Device Q decreased to 334 and total kt2 increased to 12.40% after high-temperature exposure. This work supports the use of piezoelectric LN as a material platform for harsh environment radio-frequency (RF) resonant sensors (e.g., temperature and infrared) incorporated with high coupling acoustic readout.

GHz Broadband SH0 Mode Lithium Niobate Acoustic Delay Lines.

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.

Gigahertz Low-Loss and Wideband S0 Mode Lithium Niobate Acoustic Delay Lines.

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.

Using Functionalized Graphene Oxide as Carrier for Immobilization of Glutaryl-7-Aminocephalosporanic Acid Acylase.

Graphene oxide has been widely used in biological applications because of good biocompatibility. In the present work, graphene oxide was synthesized successfully and was employed to immobilize glutaryl-7-aminocephalosporanic acid acylase (GLA). The immobilization conditions like pH, temperature, immobilization time, and enzyme/carrier ratio were investigated. Under the optimal immobilization conditions, the immobilization yield and efficiency were 86% and 52%, respectively. The characterization of the immobilized GLA was performed and compared with the free enzyme. The results indicated that the stability of the immobilized GLA was 1.7-folds than that of the free enzyme, and the kinetic parameters were also calculated. All these results show the potential industrial applications of the immobilized GLA in the production of 7-aminocephalosporinal acid (7-ACA).

A Frequency Independent Framework for Synthesis of Programmable Non-reciprocal Networks.

Passive and linear nonreciprocal networks at microwave frequencies hold great promises in enabling new front-end architectures for wireless communication systems. Their non-reciprocity has been achieved by disrupting the time-reversal symmetry using various forms of biasing schemes, but only over a limited frequency range. Here we demonstrate a framework for synthesizing theoretically frequency-independent multi-port nonreciprocal networks. The framework is highly expandable and can have an arbitrary number of ports while simultaneously sustaining balanced performance and providing unprecedented programmability of non-reciprocity. A 4-port circulator based on such a framework is implemented and tested to produce a broadband nonreciprocal performance from 10 MHz to 900 MHz with a temporal switching effort at 23.8 MHz. With the combination of broad bandwidth, low temporal effort, and high programmability, the framework could inspire new ways of implementing multiple input multiple output (MIMO) communication systems for 5G.

Lithium Niobate Phononic Crystals for Tailoring Performance of RF Laterally Vibrating Devices.

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.

Study of cross-resistance mediated by antibiotics, chlorhexidine and Rhizoma coptidis in Staphylococcus aureus.

This study aimed to determine whether selection by antibiotics, chlorhexidine (CHX) and Rhizoma coptidis extract (RCE) would lead to cross-resistance or decreased susceptibility in Staphylococcus aureus. The S. aureus reference strain ATCC 25923 as well as 14 clinical isolates were exposed to antibiotics, CHX and RCE at sublethal doses for up to 14 days. Changes in susceptibility were determined by analysis of minimum inhibitory concentrations (MICs). All isolates were cross-resistant to more than one other antibiotic following tetracycline exposure, and increased resistance (≥4-fold MIC increase) to RCE and CHX was observed in six and three isolates, respectively. Following selection by CHX, most of the treated strains showed no significant change in sensitivity to CHX. However, all strains developed cross-resistance to at least one antibiotic, and decreased susceptibility (≥4-fold MIC increase) to RCE appeared in seven strains. Following exposure to RCE, 11 isolates showed cross-resistance to at least one antibiotic. In addition, three RCE-exposed strains showed reduced susceptibility to CHX (4- or 8-fold MIC increase). The results obtained in this study imply that antibiotics, biocides and antimicrobial Chinese herbs might employ some of the same mechanisms of action against bacteria, triggering mutual cross-resistance to further foster the development of bacterial resistance.