Film Bulk Acoustic Resonator Sensor Research Articles

A prototype portable instrument employing micro-preconcentrator and FBAR sensor for the detection of chemical warfare agents

The presence of chemical warfare agents (CWAs) in the environment is a serious threat to human safety, but there are many problems with the currently available detection methods for CWAs. For example, gas chromatography–mass spectrometry cannot be used for in-field detection owing to the rather large size of the equipment required, while commercial sensors have the disadvantages of low sensitivity and poor selectivity. Here, we develop a portable gas sensing instrument for CWA detection that consists of a MEMS-fabricated micro-preconcentrator (μPC) and a film bulk acoustic resonator (FBAR) gas sensor. The μPC is coated with a nanoporous metal–organic framework material to enrich the target, while the FBAR provides rapid detection without the need for extra carrier gas. Dimethyl methylphosphonate (DMMP), a simulant of the chemical warfare agent sarin, is used to test the performance of the instrument. Experimental results show that the μPC provides effective sample pretreatment, while the FBAR gas sensor has good sensitivity to DMMP vapor. The combination of μPC and FBAR in one instrument gives full play to their respective advantages, reducing the limit of detection of the analyte. Moreover, both the μPC and the FBAR are fabricated using a CMOS-compatible approach, and the prototype instrument is compact in size with high portability and thus has potential for application to in-field detection of CWAs.

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.

Research and Design of High Sensitivity FBAR Micro-mass Sensors

Micro-mass sensors have important application in chemical and biological sensing. Based on the theory of thin film bulk acoustic resonator (FBAR), this paper represents four designs of different micro-mass sensor models. COMSOL Multiphysics™ software is used to simulate the FBAR sensor sensitivity, which with low-impedance acoustic layer and additional electrode frame. In the finate element simulation models, five different values of mass-loading were applied. From the experimental results, the characteristic parameters and the sensitivity of the FBAR sensors were obtained. It is known to us that the FBAR sensor’s frequency quality factor can be improved by using the electrode frame, and its sensitivity can be enhanced by using the low-impedance acoustic layer. To sum up, the above analysis shown that the best sensitivity is 1.351 × 10-12ng/μm2/Hz and the frequency quality factor is 1415, which is the FBAR sensor with a single-step electrode frame and a low-impedance acoustic layer.

The Design of a Frame-Like ZnO FBAR Sensor for Achieving Uniform Mass Sensitivity Distributions.

In this paper, an infinite circular ZnO thin film bulk acoustic resonator (FBAR) with a frame-like electrode operating at the thickness-extensional (TE) mode is studied. Two-dimensional scalar differential equations established for the problem in the Cartesian coordinate system are successfully solved by transforming them into normal Bessel equations and modified Bessel equations in the cylindrical coordinate system. Resonant frequencies and vibration distributions are obtained for this frame-like FBAR sensor. A nearly uniform mass sensitivity distribution in the active area is achieved by designing proper electrode size and mass ratio of the driving electrode to the ZnO film. Numerical results show that compared with the reported ring electrode FBAR sensor, the novel frame-like electrode FBAR can achieve a maximum optimization ratio (up to 97.90%) on the uniformity of the mass sensitivity distribution in the active area under the same structural parameters, which is also higher than the optimization ratio 77.63% obtained by the reported double-ring electrode design. Moreover, the mechanism to achieve a very uniform mass sensitivity distribution in the active area by the frame-like electrode is explained in detail according to dispersion curves. Namely, when the resonant frequency of the FBAR sensor is close to the cut-off frequency of the active region in the dispersion curve, the mass sensitivity distribution is nearly uniform. These conclusions provide a theoretical guidance for the design and optimization of ZnO FBAR mass sensors with high performance.

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.

Dual-Mode Gas Sensor Composed of a Silicon Nanoribbon Field Effect Transistor and a Bulk Acoustic Wave Resonator: A Case Study in Freons.

In this paper, we develop a novel dual-mode gas sensor system which comprises a silicon nanoribbon field effect transistor (Si-NR FET) and a film bulk acoustic resonator (FBAR). We investigate their sensing characteristics using polar and nonpolar organic compounds, and demonstrate that polarity has a significant effect on the response of the Si-NR FET sensor, and only a minor effect on the FBAR sensor. In this dual-mode system, qualitative discrimination can be achieved by analyzing polarity with the Si-NR FET and quantitative concentration information can be obtained using a polymer-coated FBAR with a detection limit at the ppm level. The complementary performance of the sensing elements provides higher analytical efficiency. Additionally, a dual mixture of two types of freons (CFC-113 and HCFC-141b) is further analyzed with the dual-mode gas sensor. Owing to the small size and complementary metal-oxide semiconductor (CMOS)-compatibility of the system, the dual-mode gas sensor shows potential as a portable integrated sensing system for the analysis of gas mixtures in the future.

Effect of quality factor on frequency stability of filmbulk acoustic resonator oscillator

The loaded quality factor (QL) of the film bulk acoustic resonator(FBAR) oscillator and the quality factor (Q value) of FBAR are related to the frequency stability of FBAR oscillator. In order to study the effect of the two kinds of quality factors on the frequency stability, the multi physical field model of FBAR was established in the COMSOL multiphysics software. The parameters of the modified Butterworth-Van Dyke (MBVD) model were got by frequency domain simulation and model parameter fitting. A model of MBVD circuit was established in the ADS software, and Q value for different loss was obtained by the simulation of S parameters and computing the corresponding Q value with the Bode method. The Pierce-based oscillator was established and simulated with the harmonic balance, thus the phase noise was obtained by changing QL and Q, and the effect of the two factors on frequency stability was got. The results show that the frequency stability increased with the increase of QL and Q, Q decreased with the increase of different losses. If the Q is lower than 338, the effect of increasing QL to improve the frequency stability is poor. Using this kind of FBAR to construct oscillator will not meet the requirements of FBAR wireless communication RF front-end as the reference signal source and the readout circuit of FBAR sensor. This paper provides a reference for FBAR frequency reference design and FBAR sensor readout circuit.

A Sensitivity-Enhanced Film Bulk Acoustic Resonator Gas Sensor with an Oscillator Circuit and Its Detection Application

This paper presents a sensitivity-enhanced gas sensor based on a film bulk acoustic resonator (FBAR). It was designed and fabricated with micro through-holes in its top electrode for sensitivity enhancement. The sensor was driven by a Colpitts oscillator circuit, and the output signal had characteristics of a power of −2.6 dBm@3 V and a phase noise of −90 dBc/Hz@100 kHz. In order to test the performance of the sensor, it was used for the detection of relative humidity (RH) and ethanol. When the relative humidity ranged from 25% to 88%, the frequency shift of the sensor was 733 kHz, which was 3.2 times higher than that of the existing FBAR sensor with a complete top electrode. Fitting results of the frequency shift and the relative humidity indicated that the measurement error was within ±0.8% RH. When the ethanol concentration ranged from 0 to 0.2355 g/L, the frequency shift of the sensor was 365 kHz. The effect of the oscillator circuit on the adsorption reaction and temperature response of the FBAR sensor device was analyzed to optimize its detection application.

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.

A Single FBAR-Based Temperature and Pressure Sensors

A novel temperature and pressure sensor based on a single film bulk acoustic resonator (FBAR) is designed. This FBAR support two resonant modes, which response opposite to the change of temperature. By sealed the back cavity of a back-trench membrane type FBAR with silicon wafer, an on-chip single FBAR sensor suitable for measuring temperature and pressure simultaneously is proposed. For unsealed device, the experimental results show that the first resonant mode has a temperature coefficient of frequency (TCF) of 69.5ppm/K, and the TCF of the second mode is -8.1ppm/K. After sealed the back trench, it can be used as a pressure sensor, the pressure coefficient of frequency (PCF) for the two resonant mode is -17.4ppm/kPa and -6.1 ppm/kPa respectively, both of them being more sensitive than other existing pressure sensors.

Detection of various self-assembled monolayers by AlN-based film bulk acoustic resonator

Various self-assembled monolayers such as carcinoembryonic antigen (CEA), beta actin, and bovine serum albumin (BSA) were detected using an AlN-based film bulk acoustic resonator (FBAR). AlN thin film was deposited by reactive RF magnetron sputtering, on a substrate of Mo (100nm)/Ti (34nm)/SiO2 (480nm)/Si (300μm)/Si3N4 (300nm). The film showed a strongly c-axis preferred orientation with a main (002) peak, as well as a good full width at half maximum (FWHM) of 2.50° in XRD and rocking curve results. The AlN-based FBAR was confirmed to have a resonant frequency of 2.477GHz and a sensitivity of 3514Hzcm2/ng. In beta actin, BSA, and CEA, the frequency properties showed variation values of 472.142, 932.573, and 685.421kHz and mass sensitivities of 3530, 3506, and 3514Hz-cm2/ng, respectively. The FBAR sensor was confirmed to be very useful for detecting target antigens through the binding of an antigen and an anti-body.

Film bulk acoustic resonator pressure sensor with self temperature reference

A novel film bulk acoustic resonator (FBAR) with two resonant frequencies which have opposite reactions to temperature changes has been designed. The two resonant modes respond differently to changes in temperature and pressure, with the frequency shift being linearly correlated with temperature and pressure changes. By utilizing the FBAR's sealed back trench as a cavity, an on-chip single FBAR sensor suitable for measuring pressure and temperature simultaneously is proposed and demonstrated. The experimental results show that the pressure coefficient of frequency for the lower frequency peak of the FBAR sensors is approximately −17.4 ppm kPa−1, while that for the second peak is approximately −6.1 ppm kPa−1, both of them being much more sensitive than other existing pressure sensors. This dual mode on-chip pressure sensor is simple in structure and operation, can be fabricated at very low cost, and yet requires no specific package, therefore has great potential for applications.

Film bulk acoustic resonator nanosensors for multi-task sensing

This paper shows that film bulk acoustic resonator (FBAR) arrays can be very useful sensors either to detect physical parameters such as temperature and pressure directly or to detect bio-chemicals with extremely high sensitivities by incorporating a chemisorption layer or bio-probe molecules. Furthermore, it also shows that surface acoustic wave devices can be integrated with a FBAR sensor array on the same piezoelectric substrate as the microfluidics systems to perform transportation and mixing of biosamples etc. demonstrating the possibility to fabricate integrated lab-on-a-chip detection systems, in which all the actuators and sensors are operated by acoustic wave devices. This makes the detection system simple, low cost and easy to operate and hence has great commercial potential.

Room Temperature Ozone Detection using ZnO based Film Bulk Acoustic Resonator (FBAR)

This study describes room temperature ozone sensing with a ZnO based film bulk acoustic resonator (FBAR). The resonant frequency of FBAR decreased upon ozone exposure. For 1400 ppb ozone, the frequency downshift was 131 kHz with a response time of 12 s. The frequency decrease of the FBAR sensor was proposed to be due to the density increase of the ZnO film. Ozone can be adsorbed on the ZnO surface by capturing free electrons from the film, which increases the film density. An analytical model was developed to predict the relationship between resonant frequency and ozone concentration. In agreement with the experiment, a hyperbolic function was obtained.

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.

AlN-based sputter-deposited shear mode thin film bulk acoustic resonator (FBAR) for biosensor applications — A review

A new type of biosensor device is here presented which is fabricated using the same processes used for the fabrication of integrated electrical circuits to enable tighter integration and further sensor/biosensor miniaturization. The device is a so-called thin film bulk acoustic resonator (FBAR) operating in shear mode. Here specifically AlN-based shear mode FBAR is addressed but also an overview of the shear mode FBAR development in general is presented. Developments are reported of a low temperature reactive sputtering process for growing wurtzite–AlN thin films with a close to homogenous c-axis inclination over a 4″ substrate wafer. This process enabled fabrication of shear mode FBAR sensors. The sensor operation is described along with how the design parameters influence its performance. Specifically, sensitivity amplification utilizing low acoustic impedance layers in the FBAR structure is demonstrated and explained. The resolution of the AlN shear mode FBAR sensor is demonstrated to already be comparable with the conventional quartz crystal microbalance (QCM) sensor, suggesting that shear mode FBAR may be a competitive and low cost alternative to QCM.

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.

Fully integrated FBAR sensor matrix for mass detection

A fully integrated Film Bulk Acoustic Resonator (FBAR) based mass detection sensor matrix was developed for label-free in-vitro DNA and protein diagnostics. A 64 pixels sensor matrix was post-processed on top of a CMOS readout circuitry at wafer level. A novel and patented resonance frequency detection method was developed. To our knowledge this is the first realized full integrated FBAR matrix sensor.

On the applicability of high frequency acoustic shear mode biosensing in view of thickness limitations set by the film resonance

The IC-compatible thin film bulk acoustic resonator (FBAR) technology has made it possible to move the thickness excited shear mode sensing of biological layers into a new sensing regime using substantially higher operation frequencies than the conventionally used quartz crystal microbalance (QCM). The limitations of the linear range set by the film resonance using viscoelastic protein films are here for the first time addressed specifically for FBARs operating at 700 MHz up to 1.5 GHz. Two types of protein multilayer sensing were employed; one utilizing alternating layers of streptavidin and biotinated BSA and the other using stepwise cross-linking of fibrinogen with EDC/NHS activation of its carboxyl groups. In both cases the number of protein layers within the linear regime is well above the number of protein layers usually used in biosensor applications, further verifying the applicability of the FBAR as a biosensor. Theoretical calculations are also presented using well established physical models to illustrate the expected behavior of the FBAR sensor, in view of both the frequency and the dissipation shifts.

Mercuric Ion Sensing by a Film Bulk Acoustic Resonator

This paper describes a film bulk acoustic resonator (FBAR) mass sensor for detecting Hg2+ ion in water with excellent sensitivity and selectivity. When a thin Au film was deposited on the surface of an FBAR, the resonant frequency shifted to a lower value when the film was exposed to Hg2+ in aqueous solution. The FBAR sensor detected as low as 10(-9) M Hg2+ (0.2 ppb Hg2+) in water. Other ions such as K+, Ca2+, Mg2+, Zn2+, and Ni2+ had little or no effect on the resonant frequency of the FBAR. Coating of the FBAR Au surface with a self-assembled monolayer (SAM) of 4-mercaptobenzoic acid decreased the Hg2+ response.