In the field of nano-fluidics, the generation and manipulation of minuscule droplets with volumes ranging from attoliters (aL) to femtoliters (fL) represents a crucial frontier. Such ultrasmall droplets exhibit immense potential in single-molecule detection, targeted drug delivery, and fundamental research into nanoscale biochemical processes, owing to their unique physicochemical properties, such as low Reynolds number flow and interface-dominated mass transport. Furthermore, ordered liquid-patterned arrays hold promise for applications in optically tunable nano-lenses. However, generation and manipulation of attoliter-scale droplets have long posed significant challenges, particularly for open-interface operations like dispensing, merging, splitting, and patterning into arrays. This study introduces acoustic nano-scissors generated by lateral modes of high-frequency bulk acoustic waves. The induced acoustofluidic effect in thin liquid films forms shear forces between the adjacent wave peaks and wave valleys, thereby successfully cutting the liquid into attoliter-scale droplets at an open interface. This approach could produce droplets with volumes more than three orders of magnitude smaller than those from existing acoustic solutions. Furthermore, the acoustic nano-scissors could generate ordered attoliter droplet arrays with specific patterns, with fast droplet splitting and merging controlled by switching on and off the device. This work provides a novel and flexible solution for various applications requiring attoliter droplet arrays on open interfaces.

Abstract To satisfy the demands of high-speed and high-frequency communication and improve the performance of bulk acoustic wave (BAW) filters, replacing polycrystalline AlN with single-crystalline AlN has become an effective method. However, single-crystalline AlN films grown on silicon (Si) substrates exhibit large tensile stress because of the lattice and thermal mismatch between Si and AlN, resulting in surface cracks; thus, these films cannot be applied to BAWs. A two-step method combining physics vapor deposition (PVD) and metal organic chemical vapor deposition was used to greatly decrease the stress of the AlN piezoelectric layer grown on a 6 inch Si(111) substrate by introducing a PVD AlN buffer layer and fabricating a single-crystalline AlN BAW resonator. The AlN film grown by the two-step method exhibited a lower full width at half maximum of the x-ray-diffraction symmetric (002) curve of 1008 arcsec, a lower surface smoothness of 0.215 nm and a lower stress of 144 MPa. The BAW resonator via single-crystalline AlN had Qmax of 3702 and an effective coefficient ( k eff 2 ) of 5.81%, increased by 88.36% and 11.09%, respectively, compared with poly-crystal AlN BAW resonators.

The ScAlN film has a large electromechanical coupling and low mechanical loss, enabling RF filters with wide bandwidth, low insertion loss, and a steep filter skirt. In order to meet the growing demand for RF filters operating above 5 GHz, the use of polarization inverted multilayers is continuously being proposed. This Perspective discusses the advantages of overtone mode operation in polarization inverted multilayers for high-frequency bulk acoustic wave (BAW) filter applications: high parallel resonance Qp, high series resonance Qs, high electromechanical coupling, high power capability, and better acoustic isolation from the electrode and supporting medium. Three potential approaches for ScAlN polarization inverted multilayers: film transfer technique, unusual N-polar growth, and external DC voltage application are overviewed. This Perspective includes an experimental demonstration of an acoustic isolation of polarization inverted 30-layer resonators as well as frequency switching between the fundamental mode and the third overtone mode in the currently commercial frequency range of 1.3–3.5 GHz. This article provides a metrics of Q and electromechanical coupling coefficient of recently reported BAW and Lamb wave resonators above 5 GHz, along with experimental data on the elastic tensor, dielectric constant, electromechanical coupling coefficient, temperature coefficient of frequency, and relative Q values in ScxAl1−xN films with varying Sc concentration.

Surface acoustic waves (SAWs) offer great potential for quantum information processing, optomechanics, acoustofludics, and acoustic tweezers. However, existing SAW chips lack the ability to control SAWs in a manner similar to current metamaterials, which can achieve versatile subwavelength-resolution manipulation of bulk acoustic waves. This study presents on-chip phased interdigital metamaterials (PIMs) featuring customized interdigital electrodes whose geometries are encoded with deep-subwavelength-resolution phase profiles, enabling versatile transformation of SAWs and manipulation of fluids and micro/nano-objects. Our on-chip PIMs can transform forward SAWs into waves with desired wavefronts and energy patterns, such as SAWs propagating in a specified direction, a SAW jet with energy confined in a wavelength, and twin jets. They also enable “diode-like” SAW transmission, allowing for routing the information carried by SAWs along a forward pathway while blocking backward communication. Additionally, SAWs generated by PIMs exhibit unique energy patterns, allowing for versatile active control of fluid streaming and micro/nano-object distributions.

Integrating acoustic microfluidics with spectroscopic analysis for efficient bacterial lysis and molecular characterisation.

Abstract The purpose of the present work is the investigation of mechanical stress variation in the AlN films deposited by pulsed DC magnetron sputtering under changing of substrate temperature and magnetron power. It has been revealed for the first time that the deposition of AlN films with low mechanical stresses is possible under low values of substrate temperature and magnetron power. A remarkable decrease in mechanical stresses in films from −2.5 GPa to values less than ±300 MPa was found in the case of increasing the film deposition temperature from 60 °C to 300 °C. Comparison of the data obtained by the optical method of measuring the substrate curvature and the XRD method showed that the stress values according to the x-ray diffraction results for films grown at low temperatures (60 °C–100 °C) are significantly higher than those measured by the optical method. This difference can be explained by an increased content of defects for low-temperature films that are shown by results of FTIR spectroscopy, where the absorbance intensity of the E 1 (TO) mode peak increases with temperature. At the same time, with an increase in the deposition temperature to 275 °C–300 °C, the differences between the XRD and optical data vanish, and the mechanical stresses become small enough and satisfactory for the fabrication of multilayer film bulk acoustic wave resonators.

Bulk acoustic wave (BAW) resonators, with their exceptional high-frequency performance and excellent quality factor, have become a key driver of advances in sensing technology. This study reports the fabrication and characterization of a force sensor based on a solid mounted resonator (SMR) structure. This SMR device utilizes a high resonance frequency of 2.257 GHz as its core sensing element. The operational mechanism involves the application of an external load inducing localized downward mechanical deformation in the SMR film at the pin contact region, thereby generating significant in-plane compressive stress within the piezoelectric layer. The applied strain modifies the intrinsic elastic and piezoelectric constants of the film, thereby changing both the acoustic phase velocity and the electromechanical coupling coefficient (Kt2), which ultimately leads to a measurable shift in the resonance frequency. The experimental results reveal a deterministic and robust correlation between the resonance frequency shift and the applied load, which forms a precise function relationship enabling the device to achieve a high sensitivity of 37.79 MHz/N. This indicates that it may possess good application and development potential in various complex industrial fields.

With the emergence and development of 5G, radio frequency (RF) communication systems are increasingly imposing stringent requirements on frequency and power. RF front-end filters are critical components, playing a pivotal role in the stable and efficient operation of RF systems. Currently, acoustic filters, including Surface Acoustic Wave (SAW) filters and Bulk Acoustic Wave (BAW) filters, represent the predominant type of RF front-end filters, with resonators based on piezoelectric materials serving as their fundamental building blocks. However, SAW and BAW resonators exhibit significant nonlinear behaviors in high-power RF applications, primarily manifested as frequency shifts, harmonic distortion, and intermodulation distortion. These nonlinear effects are typically attributed to changes in electromechanical coupling mechanism, device temperature, and the elastic modulus of the materials themselves. Under high-power conditions, frequency offset effects can significantly reduce the bandwidth and in-band insertion loss of SAW/BAW filters. The presence of higher harmonics and intermodulation signals is particularly critical in multi-carrier communication systems, potentially severely impacting the signal-to-interference ratio and thus degrading communication quality. Therefore, in-depth investigations into the nonlinear mechanisms of SAW and BAW devices and their effects on device performance are essential for optimizing the design of acoustic filters and enhancing their applicability. This review summarizes the relevant research on the nonlinear characteristics of SAW/BAW devices, covering the mechanisms of nonlinearity, characterization methods, testing systems, simulation models, and mitigation strategies. It comprehensively reveals the current state of nonlinearity in SAW/BAW while discussing existing studies and presenting potential difficulties, challenges, and future directions in SAW/BAW nonlinearity research.

The precise spatial patterning of living cells represents a foundational capability in bio-systems engineering, enabling the systematic study of collective cellular behaviours and the fabrication of increasingly complex functional tissues. Conventional methods for achieving this control, while numerous, are often constrained by static pattern formation, the need for biochemical labels that can alter cell function, or requirements for non-physiological media. In this context, acoustic-field-based manipulation has emerged as a uniquely powerful and biocompatible alternative. This review synthesizes these advancements under the unifying concept of Acoustic Lithography, a framework that captures the technology’s capacity for rapid, parallel and label-free cellular organization. The discussion covers the core physical principles of acoustic radiation force and streaming before surveying the diverse technological landscape, from bulk and surface acoustic waves to advanced acoustic holography. It further illuminates the impact of these tools across a spectrum of applications, including high-throughput analysis, biomimetic co-culture engineering, advanced biofabrication and clinical sorting. Collectively, these applications demonstrate the field’s trajectory, moving beyond static patterning to encompass the integrated control of structure, environment and function. Viewing the technology through this broader engineering lens underscores its significance as a vital platform, charting a course for the next generation of dynamically engineered living systems.

High overtone bulk acoustic resonators (HBAR) are advantageous for on-chip quantum acoustodynamics (QAD) system as it gives access to stream of phonon modes with high lifetime in the microwave frequency range while retaining low power consumption and microscale footprint. In this paper we present a HBAR based on barium strontium titanate (BST) thin-film mounted on sapphire with modes exhibiting frequency quality factor product (fQ) of 1.72 × 1015 Hz which is the highest reported for a bulk acoustic wave resonator utilizing polycrystalline ferroelectric material as a means for acoustic wave excitation. Unlike other piezoelectric based HBARs, the DC field-induced piezoelectricity utilized in this work offers multiple on-chip tuneability of resonator’s dynamic parameters such as phonon lifetime, frequency modulation and coupling. The higher overtone feature can enable qubit(s) in a hybrid quantum circuit to interact with one or more acoustic modes to form a quantum transducer. Here, the multi-mode resonator exhibits a unique DC bias dependency, and this feature of the ferroelectric thin film adds control variables that efficiently tune static and dynamic material, mechanical and electrical properties of the device. The resonator records a loaded quality factor of 180,000 in X band and 140,000 in the L band when measured at 10 K. A controllable robust resonator with simple fabrication technique offering high fQ can be a strong platform to be used in QAD circuits for applications in metrology, quantum memory and quantum information processing.

ObjectivesA thyrotropin (TSH) assay using bulk acoustic wave technology (TSH-BAW) was recently developed that allows for more accurate differentiation of euthyroid and hyperthyroid cats compared to the currently available TSH chemiluminescent assay (TSH-CLIA). The TSH-BAW is a highly sensitive and specific test for diagnosing hyperthyroidism; however, the effect of nonthyroidal illness (NTI) on this assay aside from cats with chronic kidney disease has not been evaluated. Primary objectives of this study were to compare serum TSH concentrations using both assays in hyperthyroid cats, cats with NTI, and healthy cats, and to evaluate the sensitivity and specificity of the TSH-BAW for diagnosing hyperthyroidism.MethodsProspective cross-sectional study comparing the TSH concentration of hyperthyroid, healthy, and euthyroid sick cats using the TSH-CLIA and TSH-BAW assays. The effect of disease severity was evaluated with hyperthyroidism and NTI.ResultsThe sensitivity and specificity of TSH-BAW for detecting hyperthyroidism were 78% [95% CI 62-90%] and 97% [95% CI 84-100%], respectively. The median serum TSH concentration was significantly different between hyperthyroid cats compared to healthy and NTI cats with both assays (P<0.01), but was not different between the latter euthyroid groups (TSH-CLIA P=0.168, TSH-BAW P=0.673). Eight (8/37; 21.6%) hyperthyroid cats had a detectable TSH-BAW but undetectable TSH-CLIA. The TSH-BAW concentrations were not significantly different between severities of NTI (P=0.565).Conclusions and relevanceThe TSH-BAW has a high specificity for detecting hyperthyroidism and is not significantly affected by NTI. While it is a useful assay for diagnosing hyperthyroidism, a normal TSH-BAW result cannot rule it out.

Abstract In this paper, a generalized lowpass filter prototype of a typical ladder-type bulk acoustic wave (BAW) filter is presented, wherein the fully canonical network comprises an Nth-order inline filter and N parallel non-resonant nodes (NRNs). Subsequently, an advanced extracted pole technique is employed to synthesize such low-pass prototype circuits, thereby enhancing the flexibility and efficiency of the synthesis process. Specifically, the direct source-load coupling in the fully canonical network is eliminated, and unit inverters among the resonators are pre-set to simplify the extraction. Besides, a lowpass and corresponding bandpass models of the BAW resonators are proposed, and the mapping relationships between the proposed models and the Mason model are established to facilitate quick access to the elements of the generalized lowpass filter prototype and the initial physical dimensions of the BAW filters, thus simplifying the filter design. To validate the demonstrated lowpass filter prototype and the advanced extracted pole technique, a 7–7 ladder-type BAW filter is designed and fabricated as an example, where the comparison results of the measurement and the simulation agree well.

This paper presents a laterally excited bulk acoustic resonator (XBAR) with reflective arrays, enabling the effective suppression of lateral acoustic leakage and enhanced energy confinement. Building upon previous studies, this work further investigates the critical design parameters of reflective arrays, specifically the optimal distance between the reflective arrays and the interdigital transducers (IDTs) and the selection of the reflective-array metal coverage at this optimal distance. Meanwhile, by systematically analyzing the key parameters of IDTs, including electrode pitch and electrode numbers, their influences on the quality factor (Q value) and spurious modes were also studied. Comparative studies with conventional XBARs and full-release air boundary XBARs further highlight the superior structural stability and performance advantages of the reflective-array design. Both simulations and experimental results confirm that the optimized configuration leverages acoustic impedance mismatch to achieve efficient reflection, effectively improving the Q value. The fabricated devices demonstrate a 2.83× increase in Bode-Q from 279 to 789 while maintaining a high electromechanical coupling coefficient (kt2) of 39.1%. The optimized XBAR further achieves excellent figures of merit FOM1 (=kt2 × Bode-Q) of 308 and FOM2 (=fs × kt2 × Bode-Q) of 10.83 × 1011 Hz, underscoring its strong potential for 5G n77-band applications.

Abstract Thin-film magnetoelectric (ME) coupling heterostructures exhibit significant potential for applications in sensors, mechanical antennas, and filters. However, their optimization based on the underlying coupling mechanisms requires further systematic investigation. This study establishes a finite element model using COMSOL to explore the energy coupling mechanisms in ME heterostructures, considering the effects of coupling mode (magnetization/polarization), device shape (aspect ratio T L /T W ), and thickness (piezomagnetic phase/piezoelectric phase thickness ratio T M /T E ). An optimized design has been achieved with the L-T coupling mode, an aspect ratio of 3:1, and a magnetoelectric thickness ratio of 1:1. Furthermore, the enhanced ME heterostructure was utilized in the bulk acoustic wave (BAW) ME magnetic sensor, demonstrating effective detection of low-frequency magnetic fields. Within a range of 0-63 Oe, the sensor achieved a linearity better than 0.24% and a sensitivity of 0.87 μmV/A. This investigation clarified the internal energy coupling mechanism of thin-film ME heterostructure and provided a viable approach for magnetic sensor design.

Thin films of molybdenum, aluminum, silicon dioxide, and aluminum nitride were deposited by magnetron sputtering for use as the constituent layers of a bulk acoustic wave (BAW) microelectronic resonator. The effect of substrate temperature during sputtering on the mechanical stress in the films was determined. Optimal sputtering conditions were identified that minimize intrinsic stress across the films. Based on these conditions, prototype microelectronic resonators were fabricated, operating at 3.9 GHz with a quality factor of 573.

Developing gas sensors using Film Bulk Acoustic Resonators (FBARs) presents a multifaceted challenge centred around the identification of optimal piezoelectric and electrode materials. The resonance frequency, a critical parameter, must be precisely controlled to ensure efficient vibration, especially in the presence of specific gases that may alter this frequency. Balancing the quality (Q) factor is essential, as a higher Q factor contributes to sharper resonances, enhancing sensitivity. Hence, this work presents the analysis of various design parameters, piezoelectric materials, and electrode materials in enhancing the Q factor, thus improving the performance of FBAR for gas sensors. Comprehensive one-dimensional (1-D) modelling is utilized to optimize the device performance, focusing on variation of parameters such as thickness, width, and length of each layer of FBAR, piezoelectric materials, aluminium nitride (AlN), zinc oxide (ZnO), and electrode material, aluminium (Al). The optimized FBAR using AlN as the piezoelectric material shows better characteristics compared to FBAR using ZnO. The highest Q factor achieved was 8569 at 1 GHz with the area of 30 µm × 30 µm.

Rapid determination of liquid properties is essential for various fields of human endeavor, such as medicine, pharmacology, and various chemical industries. To this end, we have developed an acoustoelectronic liquid sensor based on a High overtone Bulk Acoustic Resonator using microwave longitudinal bulk acoustic waves. Sensor is designed to measure the acoustic impedance of liquids. The sensor is built on a multilayer piezoelectric structure composed of "Al/Al0.72Sc0.28N/Mo/(100) diamond". To protect the sensitive element from potential chemical damage from the analytes being tested, a metal housing is used, with the thin-film piezoelectric transducer "Al/Al0.72Sc0.28N" located within the housing. The analytes are placed on the opposite free side of the diamond substrate, and the sensor has been tested on aqueous solutions of NaCl, glycerol, and isopropyl alcohol at various concentrations. The samples weighed several milligrams. The relationship between the electrical reflection coefficients of the sensor and the acoustic impedance of liquids and solutions was found to be linear. Thanks to the high chemical tolerance and abrasion resistance of a diamond substrate, this sensor can be reused for studying a wide range of substances, including aggressive liquids, without any loss of performance.

Single cell manipulation and analysis are crucial for understanding cellular heterogeneity, yet conventional microfluidic approaches suffer from poor selectivity, structural complexity, and low throughput. Here, we present an acoustofluidic-microstructure integrated platform combining a right triangle-shaped bulk acoustic wave (RTBAW) resonator with a serpentine microchannel. The platform enables selective capture (efficiency >90%) and addressable release (efficiency >90%) of single cells by leveraging acoustic streaming-induced hydrodynamic forces. Unlike existing methods relying on optical or electrical fields, our design eliminates thermal damage and ionic interference while achieving submillisecond response time and parallel processing of 4 cells per array unit. This simplified architecture reduces fabrication complexity and enhances throughput by directing untargeted cells through curved bypass channels. We validated the platform's utility in live/dead cell sorting, demonstrating its potential for high-precision single-cell diagnostics, drug screening, and rare cell isolation.

Nanoelectromechanical systems based on (Al,Ga)As/GaAs heterostructures with a two-dimensional electron gas can rely on both piezoelectric and electrostatic driving and detection. While this multifunctionality may be beneficial, disentanglement of these two physical mechanisms is important. In a multi-mode nanoelectromechanical system, we experimentally discern the electrostatic and piezoelectric effects in various configurations. A well-controlled system relying entirely on the electrostatic effect is demonstrated, where a field-effect transistor reads out the oscillations of its cantilevered side gate. We show that, apart from the two mentioned mechanisms, an additional time-delayed driving force arises due to the generation of bulk acoustic waves in the entire chip.

Abstract Piezoelectric thin films are playing an increasingly important role in micro‐electromechanical systems (MEMS) as the expansion of 5G networks and the rise of Internet of Things (IoT) technologies fuel the need for smaller, more reliable, and energy‐efficient sensors and actuators. Alloying Aluminum Nitride (AlN) with Scandium (Sc) is a promising approach to enhance piezoelectric properties in wurtzite semiconductors. However, investigations on ScAlN piezo‐on‐Silicon (Si) have been largely focused on sputtered materials, which often limit resonators to operate in the out‐of‐plane mode, resulting in limited Q. In this study, the piezoelectric properties of ScAlN thin films are reported, which are epitaxially grown on AlN‐buffered Si (111) with enhanced in‐plane crystallinity and a high piezoelectric modulus d33 up to 25.7 pC/N for Sc composition of 30%. This enables us to demonstrate extensional mode ScAlN‐on‐Si bulk acoustic wave (BAW) resonators with an ultra‐high Q of ≈97k at 70.28 MHz, resulting in a frequency‐Q product of ≈6.86 × 1012, indicating low energy loss and high frequency precision, making it ideal for emerging wireless technologies with extremely low latency demands.