Acoustic Resonator Sensor Research Articles

Analytical Modeling of AIN-Based Film Bulk Acoustic Wave Resonator for Hydrogen sulfide Gas detection Based on PiezoMUMPs

Aluminium nitride (AIN) thin film bulk acoustic resonator (FBAR) sensor for hydrogen sulfide gas detection has been designed and mathematically modelled using CoventorWare and MATLAB software, respectively. The designed FBAR sensor is based on the PiezoMUMPs fabrication technology. The detection principle of the FBAR gas sensor is based on the resonant frequency changes detection due to the mass change on the top electrode of the sensor induced by the absorbed gas molecules by the nanomaterial deposited on the surface of the top electrode device. Reduced graphene oxide hybrid with copper oxide was considered as the sensitive nanomaterials and their mass loaded was evaluated in the theoretically calculation. The resonant frequency of the shear mode of the FBAR sensor has been calculated theoretically and found to be 9.4524 GHz. The effects of the gas molecules on the resonant frequency have been investigated using a mathematical equation and it shown that the increasing of the gas mass on the sensor surface will reduce the sensor resonant frequency. Furthermore, the sensitivity of the sensor was calculated to be 0.22615 Hz/fg.

Label-Free Protein Detection by Micro-Acoustic Biosensor Coupled with Electrical Field Sorting. Theoretical Study in Urine Models

Diagnostic devices for point-of-care (POC) urine analysis (urinalysis) based on microfluidic technology have been actively developing for several decades as an alternative to laboratory based biochemical assays. Urine proteins (albumin, immunoglobulins, uromodulin, haemoglobin etc.) are important biomarkers of various pathological conditions and should be selectively detected by urinalysis sensors. The challenge is a determination of different oligomeric forms of the same protein, e.g., uromodulin, which have similar bio-chemical affinity but different physical properties. For the selective detection of different types of proteins, we propose to use a shear bulk acoustic resonator sensor with an additional electrode on the upper part of the bioliquid-filled channel for protein electric field manipulation. It causes modulation of the protein concentration over time in the near-surface region of the acoustic sensor, that allows to distinguish proteins based on their differences in diffusion coefficients (or sizes) and zeta-potentials. Moreover, in order to improve the sensitivity to density, we propose to use structured sensor interface. A numerical study of this approach for the detection of proteins was carried out using the example of albumin, immunoglobulin, and oligomeric forms of uromodulin in model urine solutions. In this contribution we prove the proposed concept with numerical studies for the detection of albumin, immunoglobulin, and oligomeric forms of uromodulin in urine models.

Miniaturized polymer coated film bulk acoustic wave resonator sensor array for quantitative gas chromatographic analysis

This paper reports a novel miniaturized detector for gas chromatography based on film bulk acoustic resonator (FBAR) sensor array. Polymer coated FBAR demonstrated detection limit of parts per million (ppm) concentrations for several volatile organic vapors. Orthogonal selectivity between n-pentane and acetone is achieved by integrating different polymer coated FBARs as sensor array. A prototype of chromatographic instrument using FBAR sensor array as detector was demonstrated by facile hyphenation of the device with commercial separation column. Such GC system is used to quantitative identification of dual gas mixture by employing principal component analysis (PCA). This MEMS chemical sensor technology offers high sensing performance, miniaturized size, and low power consumption, which are critical for development of portable gas chromatography.

FEM modeling of solidly mounted film bulk acoustic resonator and gas sensor using PIB-sensitive layer

The application of a film bulk acoustic resonator (FBAR) as a gas sensor is presented here. Zinc Oxide is used as a piezoelectric (PZE) material for the resonator and a Bragg reflector is made of Molybdenum and Silicon dioxide in proposed Solidly Mounted FBAR. The structure offers a high quality factor of 1209 at the resonance and shows a coupling coefficient of 7.51% for the 0.7-μm-thick PZE layer. To make it capable of working as a gas sensor, an additional sensitive layer for adsorption is used. A 0.51-μm-thin film of polymer-sensitive layer (polyisobutylene, PIB) is used on the top electrode. The adsorption of CH2Cl2 (dichloromethane, DCM) prompts the change in density of the PIB layer, which causes the change in resonance frequency of the FBAR. The simulation results have shown the sensitivity of 450 Hz/ppm for gas sensing for the above-mentioned structure. The sensitivity of the sensor depends on the characteristic frequencies of the device, which are further the function of the thickness of the resonating structure. No involvement of a harsh etching process in fabrication, in addition to immense sensitivity and quality factor, makes this sensor relevant for DCM sensing.

Kinetic studies of microfabricated biosensors using local adsorption strategy.

Micro/nano scale biosensors integrated with the local adsorption mask have been demonstrated to have a better limit of detection (LOD) and less sample consumptions. However, the molecular diffusions and binding kinetics in such confined droplet have been less studied which limited further development and application of the local adsorption method and imposed restrictions on discovery of new signal amplification strategies. In this work, we studied the kinetic issues via experimental investigations and theoretical analysis on microfabricated biosensors. Mass sensitive film bulk acoustic resonator (FBAR) sensors with hydrophobic Teflon film covering the non-sensing area as the mask were introduced. The fabricated masking sensors were characterized with physical adsorption of bovine serum albumin (BSA) and specific binding of antibody and antigen. Over an order of magnitude improvement on LOD was experimentally monitored. An analytical model was introduced to discuss the target molecule diffusion and binding kinetics in droplet environment, especially the crucial effects of incubation time, which has been less covered in previous local adsorption related literatures. An incubation time accumulated signal amplification effect was theoretically predicted, experimentally monitored and carefully explained. In addition, device optimization was explored based on the analytical model to fully utilize the merits of local adsorption. The discussions on the kinetic issues are believed to have wide implications for other types of micro/nano fabricated biosensors with potentially improved LOD.

Monolithic integrated system with an electrowetting-on-dielectric actuator and a film-bulk-acoustic-resonator sensor

Although digital microfluidics has shown great potential in a wide range of applications, a lab-on-a-chip with integrated digital droplet actuators and powerful biochemical sensors is still lacking. To address the demand, a fully integrated chip with electrowetting-on-dielectric (EWOD) and a film bulk acoustic resonator (FBAR) sensor is introduced, where an EWOD actuator manipulates digital droplets and the FBAR sensor detects the presence of substances in the droplets, respectively. The piezoelectric layer of the FBAR sensor and the dielectric layer of the EWOD share the same aluminum nitride (AlN) thin film, which is a key factor to achieve the full integration of the two completely different devices. The liquid droplets are reliably managed by the EWOD actuator to sit on or move off the FBAR sensor precisely. Sessile drop experiments and limit of detection (LOD) experiments are carried out to characterize the EWOD actuator and the FBAR sensor, respectively. Taking advantage of the digital droplet operation, a ‘dry sensing mode’ of the FBAR sensor in the lab-on-a-chip microsystem is proposed, which has a much higher signal to noise ratio than the conventional ‘wet sensing mode’. Hg2+ droplets with various concentrations are transported and sensed to demonstrate the capability of the integrated system. The EWOD–FBAR chip is expected to play an important role in many complex lab-on-a-chip applications.

Dynamic Changes of Acoustic Load and Complex Impedance as Reporters for the Cytotoxicity of Small Molecule Inhibitors

Cellular motility is the major driving force of numerous biological phenomena including wound healing, immune response, embryogenesis, cancer formation, and metastasis. We studied the response of epithelial FaDu monolayers cultured on gold electrodes of an acoustic resonator (quartz crystal microbalance, QCM) and impedance sensor (electric cell-substrate impedance sensing, ECIS) to externally applied chemical stimuli interfering with cytoskeleton organization. Epithelial cell motility of confluent monolayers is characterized by subtle cell shape changes and variations in the cell-substrate as well as cell-cell distance without net directionality of individual cells. The impact of small molecules such as cytochalasin D, phalloidin, and blebbistatin as well as paclitaxel, nocodazol, and colchicin on actin and microtubules organization was quantified by conventional sensors' readouts and by comparing the noise pattern of the signals which is attributed to cellular dynamics. The responsiveness of noninvasive and label-free techniques relying on cellular dynamics is compared to classical viability assays and changes of the overall impedance of ultrasmall electrodes or acoustic loads of a thickness shear mode resonator. Depending on the agent used, a distinct sensor response was found, which can be used as a fingerprint of the cellular response. Cytoskeletal rearrangements and nuclear integrity were corroborated by fluorescence microscopy and correlated to the readouts of QCM and ECIS.

Review of transducer principles for label-free biomolecular interaction analysis.

Label-free biomolecular interaction analysis is an important technique to study the chemical binding between e.g., protein and protein or protein and small molecule in real-time. The parameters obtained with this technique, such as the affinity, are important for drug development. While the surface plasmon resonance (SPR) instruments are most widely used, new types of sensors are emerging. These developments are generally driven by the need for higher throughput, lower sample consumption or by the need of complimentary information to the SPR data. This review aims to give an overview about a wide range of sensor transducers, the working principles and the peculiarities of each technology, e.g., concerning the set-up, sensitivity, sensor size or required sample volume. Starting from optical technologies like the SPR and waveguide based sensors, acoustic sensors like the quartz crystal microbalance (QCM) and the film bulk acoustic resonator (FBAR), calorimetric and electrochemical sensors are covered. Technologies long established in the market are presented together with those newly commercially available and with technologies in the early development stage. Finally, the commercially available instruments are summarized together with their sensitivity and the number of sensors usable in parallel and an outlook for potential future developments is given.

Mass sensitivity of thin film bulk acoustic resonator sensors based on polar c-axis tilted zinc oxide and aluminum nitride thin film

The mass sensitivity of thin film bulk acoustic wave resonator (FBAR) sensors using ZnO and AlN thin films with tilted polar c-axis has been theoretically investigated. The tilted c-axis orientation induces normal plane and in-plane polarizations, which leads to the coexistence of thickness longitudinal mode and thickness shear mode in the resonators. The equation for predicting electric impedance of FBARs with a mass loading layer was derived from the basic piezoelectric constitutive equations. The mass sensitivity of ZnO and AlN dual mode resonators was found by calculating the resonant frequency shifts of the thickness shear mode and thickness longitudinal mode due to thin film mass loading. In the calculation, ZnO and AlN thin film has a c-axis tilt angle from 0°–90°, 2 μm thickness, and 300×300 μm2 electrode area; four different materials (Al, SiO2, Au, and Pt) were considered as the thin film mass loading. It was found that both longitudinal resonance frequency and shear resonance frequency for different c-axis angle have a significant shift due to the mass loading; the mass sensitivities, defined as Δf/(fΔm), of the longitudinal and shear mode for this four mass loading materials are very close, and do not change much with c-axis tilt angle with a value rang around −900 cm2/g for ZnO FBARs and −1550 cm2/g for AlN FBARs. The results can be used in the design and applications of ultrahigh sensitive ZnO or AlN FBAR mass sensors.

Nerve gas sensor using film bulk acoustic resonator modified with a self-assembled Cu 2+/11-mercaptoundecanoic acid bilayer

We present an application of film bulk acoustic resonator for trace nerve gas sensing. The resonator consisted of a piezoelectric Au/AlN/Mo stack and a Bragg reflector has a working resonance near 2.35 GHz and a high performance. A self-assembled composite layer of Cu 2+/11-mercaptoundecanoic acid is modified on the Au electrode as a specific coating to capture organophosphorus compounds. The experimental results show that the chemical modified film bulk acoustic resonator can yield a rapid, sensitive, reversible and reproducible response to dimethyl methyl phosphonate (a stimulant of nerve agent) vapor. When the sensitive layer absorbs organophosphorus compounds, the mass loading increases and the resonance frequency proportionally goes down. The chemical modified film bulk acoustic resonator sensor is able to detect dimethyl methyl phosphonate vapor at the concentration as low as 100 ppb. The advantages of this sensor, including the simple fabrication process, ease of detection method, rapid response and high sensitivity, make this promising in the early alarm of nerve agents.

Influence of process route on membrane profile and Q-factor of an acoustic resonator sensor

Membranes for acoustic resonator sensors can be fabricated using deep reactive ion etching techniques. To produce the pattern a mask is needed. The most common materials used for the mask are photoresist and silicon dioxide. This paper explores what influence the choice of the mask material and etching parameters has on the profile of the membrane and as such on the Q-factor of the resonator. Results are presented for membranes fabricated using photoresist, silicon dioxide, aluminum, alumina, or combinations of these materials as etch masks. Best results were achieved using very thin (∼27 nm) alumina films patterned in a lift-off process as a mask and following the Bosch deep reactive ion etch by an isotropic etch to get a smoother surface.

FBAR Sensor Array for in Liquid Operation

This letter discusses the design of thickness shear mode thin-film bulk acoustic resonator (FBAR) sensor array for in liquid operation with respect to minimizing the observed Q-degradation and crosstalk.

High-temperature battery-free wireless microwave acoustic resonator sensor system

A novel and simple frequency-domain wireless interrogation method for surface acoustic wave (SAW) resonator sensors operating up to 850°C is presented. The method is based on directly measuring the scattering parameter S11 with a frequency-swept interrogating signal and extracting the group delay. Multiple resonators can be simultaneously addressed by frequency multiplexing the resonator responses. A new high-temperature SAW resonator capable of operating up to 1000°C has been used as a temperature sensor. The design uses the newly developed high-temperature Pt/Rh/ZrO2 thin-film electrodes and open-circuit gratings on langasite (LGS, La3Ga5SiO14). Reported is the first successful operation of a wireless SAW resonator at temperatures up to 850°C. The SAW resonator was exposed multiple times to 850°C, providing consistent performance.

Non-contact liquid level measurement with electromagnetic–acoustic resonator sensors

Electromagnetic–acoustic transduction represents an alternative to piezoelectric transduction with unique properties and advantages for resonator sensors. We have shown that such devices are suitable as mass microbalances similar to quartz crystal resonators, and as liquid density and viscosity sensors by exciting a suitable in-plane mode featuring dominant shear vibration. Generating out-of-plane vibrations we have applied these devices also as liquid level sensors. In contrast to classic time-of-flight ultrasonic liquid level sensors, the resolution is not limited by the wavelength, since small frequency changes due to interference effects with a standing acoustic wave are evaluated. For this contribution we have extensively evaluated this liquid level sensing and will present and compare new measurement and modeling results. The model comprises electromagnetic–acoustic interaction with a lossy transmission line representing the acoustic wave in the liquid. In impedance measurements with standard lab equipment a resolution as low as 3 µm at a liquid level of 10 mm and an operating frequency of 275 kHz has been achieved.

Novel magnetic–acoustic resonator sensors for remote liquid phase measurement and mass detection

Electromagnetic excitation of miniaturized acoustic resonator sensors is a novel approach with distinct advantages over piezoelectric resonators. A much wider range of transducer materials can be utilized, and remote excitation of resonant vibrations in a wide variety of different mode shapes is possible. These resonant modes display similar quality factors and characteristics as those in piezoelectric transducers and can be applied for mass detection as well as liquid phase sensing. In this contribution, we focus on the electromagnetic excitation of acoustic face shear mode (FSM) resonators for liquid property sensing. A variety of non-piezoelectric transducer materials has been investigated. For liquid phase sensing, we have found circular face shear mode resonators to be most sensitive to fluid properties, e.g., density and viscosity, while radial flexural plate modes excite compressional waves and are thus most sensitive to fluid volume, or rather the distance to the liquid surface, i.e. liquid level. Experimental results have been compared with an FEM eigenmode analysis and equivalent circuit models providing a better understanding of the generation and detection mechanisms.

Magnetic acoustic resonance immunoassay (MARIA): a multifrequency acoustic approach for the non‐labelled detection of biomolecular interactions

A unique sensing platform, comprising an electromagnetic field detector and an acoustic resonator, has been used as a wireless system for remote sensing of biorecognition events. The MARS (Magnetic Acoustic Resonator Sensor) technique has proven useful for detecting the formation of protein multilayers derived from specific binding phenomena. The technique enables multifrequency analysis, without the need of electrodes attached to the sensing element, and also facilitates the in situ surface modification of the substrate for antibody attachment. The MARS sensor was utilized as the platform on which a standard immunoassay was carried out. Two different conditions for the attachment of the first antibody to the quartz surface were tested: (i) Adsorption of the antibody onto the surface of a bare quartz disc; (ii) covalent immobilization of the antibody to a chemically modified quartz surface. Both methods can be successfully utilized for the 'label-less' detection of the biorecognition event between goat IgG and anti-goat IgG by analysis of the multifrequency spectrum. Covalent attachment of the primary antibody results in a more efficient immobilization, with higher surface density, and a consistently enhanced response for the binding of the secondary antibody. This approach will be of interest to life scientists and biochemists that require high performance assay methodologies that do not use chemical labels.

Surface energy and the response of transverse acoustic wave devices in liquids

A magnetic acoustic resonator sensor was silanized with octadecyltrichlorosilane in order to produce a hydrophobic surface. Confirmation of the presence of the silane film was obtained from quantitative X-ray photoelectron spectroscopy and from measurement of advancing water contact angle. Frequency shifts for operation of the device in water, compared with air, were much smaller than for bare, untreated sensors. This result is consistent with analogous experiments conducted with the thickness-shear mode acoustic wave sensor. Atomic force microscopy showed that the cavities (depth, 2.9 nm; width, 11 nm) present on the bare surface numbered about 2860 per square micrometer. The calculated frequency shift associated with cavity-trapped water for the hydrophilic sensor was about half the value found by experimental measurement, assuming all similar-sized cavities on the hydrophobic device are filled with gas. Furthermore, since the cavities on the latter surface were largely filled by silane the level of supposed trapped gas was much reduced, leading to a gross overestimate of the possible air to water shift in frequency. The results of this work confirm that an alternative explanation for surface free energy effects connected to acoustic device responses is required.

Magnetic–acoustic–resonator sensors (MARS): a new sensing methodology

A new type of acoustic shear wave sensor fabricated from inexpensive glass and metal plates, in which the acoustic plate is remotely excited and detected with a radio frequency signal and a strong magnetic field, is described. This new acoustic plate resonance requires neither piezoelectric materials nor wire contacts, and is referred to as a magnetic–acoustic–resonator sensor or MARS device. This paper reports the concept of the MARS device and describes how shear wave resonances in aluminium and aluminium–glass composites are detected and verified. The effect of mass loading an aluminised glass plate demonstrates that MARS has Sauerbrey-like characteristics similar to the Quartz Crystal Microbalance (QCM). Prospects for liquid phase measurements are also indicated.