No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Abstract
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.
... Coating the detector with nanomaterials (metal organic frameworks (MOFs)) significantly enhanced the detector response (20 times). Later, we showed that different polymer-coated FBAR sensor arrays could provide quantitative detection and identify overlapping dual mixtures through the PCA method in GC [37]. ...
... SEM image of a film bulk acoustic resonator (left) and structure schematic (right)[36,37]. Reproduced with permission from Ref.[36], Copyright 2018, Elsevier; Reproduced with permission from Ref.[37], Copyright 2016, American Chemical Society. ...
... SEM image of a film bulk acoustic resonator (left) and structure schematic (right)[36,37]. Reproduced with permission from Ref.[36], Copyright 2018, Elsevier; Reproduced with permission from Ref.[37], Copyright 2016, American Chemical Society. ...
Micro gas chromatography (μGC) has been continuously gaining attention since the last century owing to multiple favorable characteristics, such as its small size, low power consumption and minimal production and maintenance costs. μGC has the potential to provide practical solutions to emerging analytical challenges in security, health, and environment. In this review, we summarize recent advances in micro detectors for μGC, including the study of the miniaturization of conventional detectors and the development of novel detectors for μGC chromatography.
... The objective of adding specific coating materials is to functionalize the resonator for it to capture specific volatile organic compounds (VOCs), enabling the development of a new M/NEMS biosensors generation for the biomedical domain due to their increased effective interaction surface. Some strategies arrange several individual nanoelectromechanical sensors in an array configuration [10], while others consider larger surface resonating structures such as cantilevers [11,12], film bulk acoustic wave resonators (FBARs) [13], capacitive micromachined ultrasonic transducers (CMUTs) [14] and membrane resonators [15]. Increasing the sensing element surface improves the sensor-target interaction, and it also eases the functionalization process that requires the deposition of polymer coatings or other materials that must adhere on top of a micromachined surface. ...
... Increasing the sensing element surface improves the sensor-target interaction, and it also eases the functionalization process that requires the deposition of polymer coatings or other materials that must adhere on top of a micromachined surface. Such a deposition is performed through a variety of methods, such as airbrushing [12,16], ink jetting [17] or spin coating [13]. The accommodation of a functionalization phase into commercial technology is not a straightforward technique and, in fact, very few works combining a CMOS-MEMS resonator with a functionalization polymer are available [18]. ...
Based on experimental data, this paper thoroughly investigates the impact of a gas fluid flow on the behavior of a MEMS resonator specifically oriented to gas sensing. It is demonstrated that the gas stream action itself modifies the device resonance frequency in a way that depends on the resonator clamp shape with a corresponding non-negligible impact on the gravimetric sensor resolution. Results indicate that such an effect must be accounted when designing MEMS resonators with potential applications in the detection of volatile organic compounds (VOCs). In addition, the impact of thermal perturbations was also investigated. Two types of four-anchored CMOS-MEMS plate resonators were designed and fabricated: one with straight anchors, while the other was sustained through folded flexure clamps. The mechanical structures were monolithically integrated together with an embedded readout amplifier to operate as a self-sustained fully integrated oscillator on a commercial CMOS technology, featuring low-cost batch production and easy integration. The folded flexure anchor resonator provided a flow impact reduction of 5× compared to the straight anchor resonator, while the temperature sensitivity was enhanced to −115 ppm/°C, an outstanding result compared to the −2403 ppm/°C measured for the straight anchored structure.
... Correspondingly, gaseous samples have consisted of indoor, outdoor, or artificial air, breath, and headspace of liquid or solid samples, such as wastewater, food, and plants [25,[37][38][39][40][41][42][43][44]. Further applications include the use as detector for gas chromatography (GC) instead of mass spectrometry (MS) [45,46] and the use as sensor node in sensor networks [47]. In contrast to that, the use of acoustic sensor arrays as e-tongues or biosensor arrays for liquid samples has been much less common. ...
... An FBAR array with two polymer coatings was successfully applied for quantitative detection of three alkanes and one ketone after GC. Furthermore, binary mixtures of one of the alkanes and the ketone (i.e., pentane and acetone), which could not be separated by the GC column, could be differentiated by the array [46]. ...
Bulk acoustic wave (BAW) and surface acoustic wave (SAW) sensor devices have successfully been used in a wide variety of gas sensing, liquid sensing, and biosensing applications. Devices include BAW sensors using thickness shear modes and SAW sensors using Rayleigh waves or horizontally polarized shear waves (HPSWs). Analyte specificity and selectivity of the sensors are determined by the sensor coatings. If a group of analytes is to be detected or if only selective coatings (i.e., coatings responding to more than one analyte) are available, the use of multi-sensor arrays is advantageous, as the evaluation of the resulting signal patterns allows qualitative and quantitative characterization of the sample. Virtual sensor arrays utilize only one sensor but combine it with enhanced signal evaluation methods or preceding sample separation, which results in similar results as obtained with multi-sensor arrays. Both array types have shown to be promising with regard to system integration and low costs. This review discusses principles and design considerations for acoustic multi-sensor and virtual sensor arrays and outlines the use of these arrays in multi-analyte detection applications, focusing mainly on developments of the past decade.
... FBAR arrays have also been used as electronic noses to achieve discrimination of VOCs. [22][23][24] A single FBAR can also function as a virtual sensor array with temperature modulation to detect and discriminate VOCs. 25 The surfaces of FBARs are typically functionalized with polymers, 18 supramolecular monolayers, 25 or self-assembled monolayers 23,24 to realize selectivity and improved adsorption. Surface functionalization of the sensors plays a key role in recognition, sensitivity, selectivity, stability, and reversibility. ...
... FBAR arrays have also been used as electronic noses to achieve discrimination of VOCs. [22][23][24] A single FBAR can also function as a virtual sensor array with temperature modulation to detect and discriminate VOCs. 25 The surfaces of FBARs are typically functionalized with polymers, 18 supramolecular monolayers, 25 or self-assembled monolayers 23,24 to realize selectivity and improved adsorption. Surface functionalization of the sensors plays a key role in recognition, sensitivity, selectivity, stability, and reversibility. ...
Film bulk acoustic wave resonators have demonstrated great potential in the detection of volatile organic compounds owing to their high sensitivity, miniature size, low power consumption, capacity for integration, and other beneficial characteristics. However, it is necessary to functionalize the surfaces of these resonators to enhance the adsorption and discrimination of volatile organic compounds. Here, we report a convenient and reliable method for functionalizing the surfaces of film bulk acoustic wave resonators with hydrophobins via self-assembly to enable highly sensitive and polarity sensitive detection of volatile organic compounds. Experiments conducted using various concentrations of five volatile organic compounds possessing different polarities demonstrated that the hydrophobin coating enhanced the responsivity of the proposed sensor. The obtained results were in good agreement with the Brunauer–Emmett–Teller model of multilayer physisorption, which suggests that the hydrophobin coating enhanced the sensitivity by improving the monolayer adsorption capacity. Our work demonstrates that the combination of multifunctional biosurfactants and microelectromechanical devices can permit high-performance gas sensing.
... Hu et al. [184] developed polymer-coated FBAR sensor array for gas chromatographic analysis of different organic vapors. They integrated FBAR sensor array with a commercial gas separating column outlet and from other side connected to network analyzer equipped with a computer for data processing. ...
... Table 5. Comparison of different GC-sensor systems with developed FBAR sensor in terms of limit of detection, dynamic range, linearity, application field and data process method, adapted with permission from [184]. Guo et al. [190] presented a theoretical approach to study VOC sensor based on polymeric layer coated diaphragm integrated with FBAR. ...
Acoustic devices have found wide applications in chemical and biosensing fields owing to their high sensitivity, ruggedness, miniaturized design and integration ability with on-field electronic systems. One of the potential advantages of using these devices are their label-free detection mechanism since mass is the fundamental property of any target analyte which is monitored by these devices. Herein, we provide a concise overview of high frequency acoustic transducers such as quartz crystal microbalance (QCM), surface acoustic wave (SAW) and film bulk acoustic resonators (FBARs) to compare their working principles, resonance frequencies, selection of piezoelectric materials for their fabrication, temperature-frequency dependency and operation in the liquid phase. The selected sensor applications of these high frequency acoustic transducers are discussed primarily focusing on the two main sensing domains, i.e., biosensing for working in liquids and gas/vapor phase sensing. Furthermore, the sensor performance of high frequency acoustic transducers in selected cases is compared with well-established analytical tools such as liquid chromatography mass spectrometry (LC-MS), gas chromatographic (GC) analysis and enzyme-linked immunosorbent assay (ELISA) methods. Finally, a general comparison of these acoustic devices is conducted to discuss their strengths, limitations, and commercial adaptability thus, to select the most suitable transducer for a particular chemical/biochemical sensing domain.
... Along with their large spectrum of chemical constitutions, the polymers also exhibit a large variety of structural properties, ranging from high crystallinity with their respective restrictions to the diffusion into its structure, to an amorphous, high porous, three-dimensional network, through which small molecules can easily access and diffuse [13]. For the sensitization of SAW sensors, besides the variety of possible structural chemical environments, the chemical and mechanical properties of polymers make them an excellent choice for the sensitization of complex surfaces [14], such as those of the SAW sensors elements once they fulfill the necessary requirements for a sensing layer to provide reliable SAW sensors [10,[15][16][17]. ...
The chemical sensitization of surface acoustic wave (SAW) sensors plays a key role for this technology. The analysis of the resulting nanometric sensing layer is crucial for the development of new sensing materials as well as for the quality control of SAW sensors systems for commercial applications. In the previous works, the resulting coating layers using new coating materials based on polyurethane-polymer composites were evaluated considering the ultrasonic analysis, the adhesion, and the sensor responses. In this work, the characterization of the coating process, Bright Field Microscopy (BFM) and Dark Field Microscopy (DFM) were used to evaluate the quality of the material distribution and homogeneity of the obtained sensing layers. The sensing materials analyzed were the four polymers used in the previous works and their respective new composites with polyurethane (PU). The combination of BFM and DFM allows the characterization of the resulting material distribution obtained by the coating process, providing inferences about the interaction of each coating material with the surface of the SAW sensor element as well as about the correlation between the results of the ultrasonic parameters, the real material distribution and the homogeneity of the obtained coating layer of each coating material.
... Eâƒ(Ü, O ˜«Äu /Dan õDa ì>f&,U k Jp>f&éVOCsíN £O Uå.Hu < [17] O ˜«Äu N(Å ì Daì #. .íƒÚÌuÿì,T ‡Å>X ÚzAEDaìäkDa5Up!º€ .z!õÑ $ A:.Meng < [18] JÑ ˜« §ÝN› Ä ÿÁ•{Jp7á zÔDaì ÀJ5,T•{U k Uõ zâDaìÄ •A&Ò ¬Ÿ. ...
... The temporal delay of each analyte peak is called the elution (or retention) time and is a characteristic of the analyte for the particular separation column and test conditions. To enhance the differentiation of analytes with similar retention times, some µGC systems incorporate multiple complementary detectors [4][5][6][7][8][9]. ...
A chemical recognition algorithm is an integral part of any autonomous microscale gas chromatography (µGC) system for automated chemical analysis. For a multi-detector µGC system, the chemical analysis must account for the retention time of each chemical analyte as well as the relative response of each detector to each analyte, i.e., the detector response pattern (DRP). In contrast to the common approaches of heuristically using principal component analysis and machine learning, this paper reports a rule-based automated chemical recognition algorithm for a multi-cell, multi-detector µGC system, in which the DRP is related to theoretical principles; consequently, this algorithm only requires a small amount of calibration data but not extensive training data. For processing both the retention time and the raw DRP, the algorithm applies rules based on expert knowledge to compare the detected peaks; these rules are located in a customized software library. Additionally, the algorithm provides special handling for chromatogram peaks with a small signal-to-noise ratio. It also provides separate special handling for asymmetrical peaks that may result from surface adsorptive analytes. This work also describes an experimental evaluation in which the algorithm used the relative response of two complementary types of capacitive detectors as well as a photoionization detector that were incorporated into the µGC system of interest. In these tests, which were performed on chromatograms with 21–31 peaks for each detector, the true positive rate was 96.3%, the true negative rate was 94.1%, the false positive rate was 5.9%, and the false negative rate was 3.7%. The results demonstrated that the algorithm can support µGC systems for automated chemical screening and early warning applications.
... Furthermore, The FBAR quality factor is a dimensionless quantity that represents the resonator's underdamped performance and expressed the correlation between the resonator bandwidth and its center frequency [279,280]. On other hand, the quality factor is well known and defined as the ratio of the energy stored in the resonator to the energy dissipated for each electromechanical conversion cycle [281,282], as presented in Eq. (8): where the Energy stored is represented the vibration energy stored in the resonator which is divided by the energy of the vibration that dissipated per each cycle. The device with a high-quality factor usually has less energy dissipation per each cycle. ...
Piezoelectric microelectromechanical system (piezo-MEMS)-based mass sensors including the piezoelectric microcantilevers, surface acoustic waves (SAW), quartz crystal microbalance (QCM), piezoelectric micromachined ultrasonic transducer (PMUT), and film bulk acoustic wave resonators (FBAR) are highlighted as suitable candidates for highly sensitive gas detection application. This paper presents the piezo-MEMS gas sensors' characteristics such as their miniaturized structure, the capability of integration with readout circuit, and fabrication feasibility using multiuser technologies. The development of the piezoelectric MEMS gas sensors is investigated for the application of low-level concentration gas molecules detection. In this work, the various types of gas sensors based on piezoelectricity are investigated extensively including their operating principle, besides their material parameters as well as the critical design parameters, the device structures, and their sensing materials including the polymers, carbon, metal-organic framework, and graphene.
... The μPC can significantly improve the sensitivity of the instrument to CWAs through sample enrichment by the adsorption materials that it contains, 18 while the FBAR, as a typical mass-type gas sensor, has greater sensitivity than commercial QCM and SAW sensors. [19][20][21][22] Dimethyl methylphosphonate (DMMP), a simulant of sarin, is used to study the performance of each component and of the integrated instrument. Experimental results show that the proposed instrument has potential for the detection of low concentrations of CWAs in the field. ...
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.
... According to the Sauerbrey equation, a FBAR sensor, resonating at the gigahertz range, offers higher sensitivity than QCM, which has the resonating frequency at several megahertz [29][30][31][32][33]. We are quite interested in applying FBAR gas sensors as GC detectors and have firstly reported the facile hyphenation of the FBARs with GC [34,35]. In this study, we aimed to develop a microfluidic FBAR (mFBAR) gas sensor for in-line detection in GC. ...
A microfluidic film bulk acoustic wave resonator gas sensor (mFBAR) adapted specifically as an in-line detector in gas chromatography was described. This miniaturized vapor sensor was a non-destructive detector with very low dead volume (0.02 μL). It was prepared by enclosing the resonator in a microfluidic channel on a chip with dimensions of only 15 mm × 15 mm × 1 mm. The device with polymer coating showed satisfactory performance in the detection of organophosphorus compound, demonstrating a very low detection limit (a dozen parts per billion) with relatively short response time (about fifteen seconds) toward the simulant of chemical warfare agent, dimethyl methylphosphonate. The in-line detection of the mFBAR sensor with FID was constructed and employed to directly measure the concentration profile on the solid surface by the mFBAR with the controlled concentration profile in the mobile phase at the same time. The difference of peak-maximum position between mobile phase and solid phase could be a convenient indicator to measure mass transfer rate. With the response of the mFBAR and FID obtained in one injection, an injection mass-independent parameter can be calculated and used to identify the analyte of interest.
... Jizhou Hu et al developed a prototype chromatographic system by simple hyphenation of miniaturized sensitive gravimetric gas sensors with a commercial separation column. A 1.21-GHz FBAR (film bulk acoustic resonator) was successfully fabricated through a standard MEMS fabrication process and served as a novel detector for gas chromatography [17]. ...
Traditional algorithms cannot readily address the fact that artificial olfaction in a dynamic ambient environment requires continuous selection and execution of the optimal algorithm to detect different gases. This paper presents a deep learning WCCNN-BiLSTM-many-to-many GRU (wavelet coefficient convolutional neural network–bidirectional long short-term memory–many-to-many-gated recurrent unit) model for qualitative and quantitative artificial olfaction of gas based on the automatic extraction of time-frequency domain dynamic features and time domain steady-state features. The model consists of two submodels. One submodel recognizes a gas by the WCCNN-BiLSTM model, and the experiments based on actual data from our fabricated artificial olfactory system demonstrate that the gas recognition accuracy is nearly 100%. The other submodel quantifies the gas by the many-to-many GRU model with less labeled data; this submodel is comparable to conventional algorithms such as DT (decision tree), SVMs (support vector machines), KNN (k-nearest neighbor), RF (random forest), AdaBoost, GBDT (gradient-boosting decision tree), bagging, and ET (extra tree) according to PCA (principal component analysis) dimensionality reduction. The experimental results of 10-fold cross-validations show that the proposed many-to-many GRU outperforms the aforementioned conventional algorithms with remarkable metrics and can maintain higher concentration estimation accuracy for different unknown gases with less labeled data.
... Polymer-based gas sensors have attracted considerable attention as a result of their many advantages over commercially available metal oxide gas sensors, such as room temperature operation, numerous types of polymers available for sensing materials, and their low manufacturing cost [1][2][3][4][5][6][7]. Despite these advantages, they are not widely applied, because of the serious drawback that most polymers are not conductive. ...
A cellulose nanocrystal (CNC)-reinforced polymethylmethacrylate (PMMA) fiber was obtained via electrospinning, and then attached between the two tines of a quartz tuning fork (QTF). The change in the resonance frequency of the CNC/PMMA composite fiber-coated QTF (CP-QTF) was measured upon being exposed to various concentrations of ethanol vapor. The frequency decreased as the ethanol vapor concentration increased, because the modulus of the composite fiber decreased due to the adsorption of the ethanol vapor. The composite fiber obtained at a high relative humidity (RH; 60% RH, CP60 fiber) produced a highly porous structure as a result of the moisture adsorption-induced phase separation of PMMA. The porosity of the CP60 fiber was higher than that of a CNC/PMMA composite fiber obtained at 30% RH (CP30 fiber) or that of a plain PMMA fiber obtained at 60% RH (P60 fiber), because hygroscopic CNCs promote moisture adsorption. The CP60 fiber-coated QTF (CP60-QTF) exhibited a greater frequency change and faster response time than P60-QTF and CP30-QTF upon exposure to ethanol vapor at the same concentration. The enhanced performance of CP60-QTF was attributed to its higher surface area and larger fiber modulus.
... Over the past few years there has been a growing demand for high-throughput separations in numerous fields (e.g., environmental, food, clinical or biological analysis), where either the time response delivery must be reduced, or the productivity enhanced (or in the ideal case both), considering the large number of analyzed samples and diversity of compounds. In order to achieve these goals robust analytical techniques such as liquid chromatography and gas chromatography has been utilized [1][2][3][4] . Although gas chromatography (GC) is in some cases faster, and provides higher separation efficiency, having better properties for combination with a wide range of sensitive and selective detectors, it also has some limitations such the requirement that the molecules to be analyzed must be thermally stable and sufficiently volatile. ...
In this paper, the hazardous effects of various volatile organic compounds (VOCs) on human health and its detection methods have been discussed. This paper also presents the comprehensive study on various VOC sensing mechanisms, their advantages, limitations and key design challenges. It is also reported that acoustic wave sensors are more suitable for VOC detection because of its various advantages as compared to other techniques such as, extended lifetime, miniaturization, high sensitivity, less/zero secondary pollution, low power consumption, lower detection limit and low-cost. The main focus of this paper is on bulk acoustic wave (BAW) devices for VOC detection. The development of film bulk acoustic wave resonators (FBARs) in various aspects such as, structural classification, operating modes, selection criteria of materials (electrode, piezoelectric and sensing layer) and their deposition methods, fabrication process flow and applications have been discussed in this detailed review. Various performance enhancement methods for efficient VOC detection using FBARs have been described in detail to design, model, analyze and optimize a FBAR sensors for the detection of various hazardous VOCs with enriched sensitivity and selectivity.
Small-sized, high-sensitivity, and low-cost sensors are required for gas-sensing applications because of their critical role in environmental monitoring, clinic diagnosis, process control, and anti-terrorism. Given the rapid developments in micro-fabrication and microelectromechanical system (MEMS) technologies, film bulk acoustic resonator (FBAR) gas sensors have received increased research attention because of their improved working frequency and reliability. This chapter discusses the state-of-the-art and recent developments in FBAR gas sensors. The sensing mechanism and limitations of these sensors are summarized. Recent progress in the development of four major aspects of FBAR gas sensors, namely, FBAR gas sensors using different sensing materials, FBAR gas sensors used in electronic noses, system integration of FBAR gas sensors, and FBAR gas sensors used as micro-GC detectors, is reviewed. The potential future of FBAR sensors used in flexible electronics is also discussed.
Microscale gas chromatographs (μGCs) promise in-field analysis of volatile organic compounds (VOCs) in environmental and industrial monitoring, healthcare, and homeland security applications. As a step toward addressing challenges with performance and manufacturability, this study reports a highly integrated monolithic chip implementing a multisensing progressive cellular architecture. This architecture incorporates three μGC cells that are customized for different ranges of analyte volatility; each cell includes a preconcentrator and separation column, two complementary capacitive detectors, and a photoionization detector (PID). An on-chip carrier gas filter scrubs ambient air for the analysis. The monolithic chip, with all 16 components, is 40.3 × 55.7 mm2 in footprint. To accommodate surface adsorptive and low-volatility analytes, the architecture eliminates the commonly used inlet valve, eliminating the need for chemically inactive surfaces in the valves and pumps, allowing the use of standard parts. Representative analysis is demonstrated from a nonpolar 14-analyte mixture, a polar 12-analyte mixture, and a 3-phosphonate ester mixture, covering a wide vapor pressure range (0.005-68.5 kPa) and dielectric constant range (1.8-23.2). The three types of detectors show highly complementary responses. Quantitative analysis is shown in the tens to hundreds ppb range. With 200 mL samples, the projected detection limits reach 0.12-4.7 ppb. Limited tests performed at 80% humidity showed that the analytes with vapor pressures <12 kPa were unaffected. A typical full run takes 28 min and consumes 2.3 kJ energy for the fluidic elements (excluding electronics). By eliminating chip-to-chip fluidic interconnections and requiring just one custom-fabricated element, this work presents a path toward high-performance and highly manufacturable μGCs.
Volatile organic compounds (VOCs) have gained the biomedical community attention given their relevance in exhaled human breath analysis for non-invasive disease diagnosis. Today, only bulky, expensive and high-skill bench-top equipment is commercially available to reach the outstanding resolution and selectivity required for their detection. However, these solutions fail to meet the society demands of portable and low-cost devices required for point-of-care diagnosis and e-health. In this line, resonant inertial mass sensing has emerged as a promising technique to achieve high-resolution VOCs identification, fulfilling the portability requirements. Their excellent distributed mass sensitivity and integration capabilities within standard CMOS microfabrication techniques constitute excellent candidates for building Lab-on-Chip applications in line with current technological trends. The capability of operating as self-sustained oscillators provides an inherent real-time tracking system with quasi-digital output. Resonator coating using novel sensing films for specific analyte caption is required to boost the mass loading effect and improve sensing selectivity. This paper reviews and analyzes resonator topologies proposed in the literature together with the techniques used for the electromechanical transduction, as well as coating materials and procedures. The ultimate goal is to discuss the advantages achieved for CMOS fully integrated solutions, analyzing the state-of-the-art in the field, providing specific design guidelines while foreseeing upcoming trends.
This paper demonstrates an optical-thermally actuated multi-layer graphene resonator for humidity sensing. A ∼10-layered graphene resonator with a diameter of 125 µm peripherally clamped on the fiber ferrule end face was actuated to vibrate using the intensity-modulated laser, and the vibration was detected based on the optical fiber Fabry-Perot interference method. The humidity sensing experiment exhibited an up to 350 Hz/%RH humidity sensitivity in the range of 0–100 % RH at 25 °C, which was 10 times higher than those of the previously reported Quartz Crystal Microbalance (QCM)-based humidity sensors. Also, a good repeatability of the frequency-humidity response was observed for the presented graphene resonator. Moreover, in view of the coupling effect of temperature on the graphene resonator, the temperature drift of 0.942 kHz/°C was measured in the range of 25–50 °C, thereby inducing an absolute humidity error of about 0.6 g/(m³·°C).
Carbon nanotube (CNT)-based chemiresistors are promising gas detectors for gas chromatography (GC) due to their intrinsic nanoscale porosity and excellent electrical conductivity. However, fabrication reproducibility, long desorption time, limited sensitivity, and low dynamic range limit their usage in real applications. This paper reports a novel on-chip monolithic integrated multimode CNT sensor, where a micro-electro-mechanical system-based bulk acoustic wave (BAW) resonator is embedded underneath a CNT chemiresistor. The device fabrication repeatability was improved by on-site monitoring of CNT deposition using BAW. We found that the acoustic stimulation can accelerate the gas desorption rate from the CNT surface, which solves the slow desorption issue. Due to the different sensing mechanisms, the multimode CNT sensor provides complementary responses to targets with improved sensitivity and dynamic range compared to a single mode detector. A prototype of a chromatographic system using the multimode CNT sensor was prepared by dedicated design of the connection between the device and the separation column. Such a GC system is used for the quantitative identification of a gas mixture at different GC conditions, which proves the feasibility of the multimode CNT detector for chromatographic analysis. The as-developed CMOS compatible multimode CNT sensor offers high sensing performance, miniaturized size, and low power consumption, which are critical for developing portable GC.
Reliable and long-term operation of thin film bulk acoustic resonators (FBARs) under high power relies on the optimization of thermal resistance. In this work, thermal design strategies for high power FBARs are explored theoretically. For accurate estimation of the thermal characteristics of FBARs, the thermal conductivity of the AlN epilayer with temperature and thickness dependence is included in the finite element simulation model, of which AlN thermal conductivity is calculated through normal-process, Umklapp, and boundary scattering. To further reduce thermal resistance and improve power capacity, the effects of aspect ratio, AlN thickness, the number of resonators, and pitch distance on thermal resistance are investigated. Compared with FBARs with a square electrode, the thermal resistance of the FBAR-on-diamond device is decreased by 43% at an aspect ratio of three. Meanwhile, the optimal AlN thickness is 2 µm, which maintains the balance between thermal resistance and electric performance. The power capacity is increased by 1.93 dB by substituting six resonators for four resonators. The improvement in power handling ability is attributed to the reduced thermal spreading resistance and lower power density. Our study can provide detailed thermal design strategies for high power FBARs toward high throughput data transmission.
Gas separation and detection technology is closely related to people’s daily production and life. With the emergence of various detection equipment, it has made remarkable progress in recent decades. Gas sensing materials play an important role in the process of gas separation and detection. Compared with traditional gas sensing materials, metal-organic frameworks (MOFs), as a new type of porous materials, has ultra-large surface area, extremely high porosity, regular pore structure and adjustable pore size. These unique advantages make MOFs particularly suitable as promising candidates for the gas pre-concentration, pre-separation and detection, so as to realize the collection and enhancement of low concentration gas, the separation of complex gas mixtures, and the reliable detection of trace target gases. The detection ability and separation efficiency are greatly improved eventually. Therefore, MOFs are expected to surpass the traditional materials, and their application in gas separation and detection deserves the attention of both academia and industry. © 2022 Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences.
Here we present a critical review related to the important acoustic device technologies being used for the gas sensing applications. Acoustic devices find wide applications in chemical and biological sensing due to miniaturized size, high sensitivity, integration with on-field electronics, ruggedness and wireless sensing ability. An overview on the acoustic devices such as quartz crystal microbalance (QCM), Film bulk acoustic wave resonators (FBAR), and surface acoustic wave resonators (SAW) is discussed with their working principle, selection of piezoelectric, electrode material for fabrication, resonance frequencies, operation of the respective acoustic device-based gas sensors, temperature dependency and sensing layers for different gases. Recent advancements made in acoustic devices based on gas sensing technology, their structures and working mechanism along with their fabrication method, as well as the recent advances made in the design are reviewed and discussed.
Printed electronics employing flexible substrate offers prospective features for various applications such as, tactile sensing, energy harvesting, wearable electronics and acoustic wave sensors. In this work, an acoustic FPW (flexural plate wave) sensor is printed on thin and flexible PZT-PDMS (lead zirconate titanate-poly dimethyl siloxane) composite film with silver ink. The prototype FPW resonator has a resonant frequency of 22.65 MHz with an attenuation of −1.552 dBm. Gravimetric mass sensitivity of the sensor was measured by applying PDMS layers in between the input and output interdigital transducers (IDTs). The mass sensitivity was measured to be −7.8 cm
2
/g. The sensor is highly responsive to VOCs (volatile organic compounds) with PDMS as a sensing layer. Gas sensitivities with acetic acid and toluene concentrations were measured to be 0.66 and 160.63 kHz/ppm, respectively. The limit of detection for acetic acid and toluene were 10.9 and 0.03 ppm, respectively. Further, the sensor shows good repeatability and response time with both the VOCs. The thermal stability and high piezoelectric charge coefficient of PZT-PDMS composite compared to other piezoelectric composite and polymer substrates are advantageous for the flexible printed sensor. The reported FPW gas sensor shows potential for low concentration measurement of VOCs.
A nano-gravimetric detector (NGD) for gas chromatography is based on a nanoelectromechanical array of adsorbent-coated resonating double clamped beams. NGD is a concentration-sensitive detector and its sensitivity is analyte-dependent based on the affinity of the analyte with the porous layer coated on the NEMS surface. This affinity is also strongly related to the NGD temperature (NGD working temperature can be dynamically set up from 40 to 220 °C), so the sensitivity can be tuned through temperature detector control. An adsorption-desorption model was set up to characterize the NGD response on a large set of n-alkanes from C10 to C22 at different NGD temperatures. For fast identification of petroleum mixture based on chromatogram fingerprint, a general strategy for NGD temperature program design was developed leading to a constant relative response factor between 0.96 and 1.03 for all the alkanes, and then chromatograms are very similar to those obtained with a flame ionization detector (FID). The analysis of a real petroleum fluid was also performed and compared to FID results: quantitative results obtained for all the analytes were satisfactory according to precision (<5%) and accuracy (average relative error = 4.3%). Based on such temperature control strategy, NGD sensitivity and the dynamic linear range can be adjusted and detection limits at a picogram level can be easily achieved for all n-alkanes.
Dans ce travail, nous avons réalisé et caractérisé des couches minces de AZO pour des applications capteurs ultrasensibles fonctionnant à la température ambiante. La méthode de détection des gaz choisie est la méthode de mesure du bruit basse fréquence (BF). L'élaboration du matériau est réalisée au moyen d'un bâti de pulvérisation cathodique RF à magnétron. Nous avons investigué l’effet de différents paramètres de dépôt sur la résistivité électrique afin de trouver un compromis entre eux et nous conduire à une faible résistivité. Pour cela, nous avons étudié l’influence de l’épaisseur des couches minces de AZO (50 nm à 450 nm) sur les propriétés structurales, morphologiques, électriques (en continu et bruit BF). Puis une étude de l’effet de la puissance RF de dépôt et du recuit post-dépôt sur les différentes propriétés est présentée. Les propriétés de détection de la série AZO à épaisseurs variables à la température ambiante en présence d’argon ou d’oxygène à différentes pressions par la méthode du bruit BF sont exposées. Une plateforme d'analyse des gaz contenant l'ensemble de l'instrumentation associée à notre capteur a été développée et présentée. Nous avons étudié en détail la réponse de la série de AZO en fonction de l’épaisseur sous différentes pressions l’oxygène injectées, et évalué les performances des différents capteurs. Les résultats obtenus ont montré que la détection de l’oxygène par la mesure de bruit BF est plus sensible que par la méthode en continue. Nous avons conclu de cette étude que : i) le niveau du bruit en 1/f mesuré pour un courant continu donné en présence de l’oxygène diminué par rapport à son niveau atteint à l’air ambiant, ii) la sensibilité Gₙₒᵢₛₑ augmente avec l’augmentation de l’épaisseur de la couche active de AZO du capteur, iii) la sensibilité Gₙₒᵢₛₑ augmente avec la pression d’oxygène puis sature, iv) le temps de réponse (temps d'attente pour atteindre l'état stationnaire pour le bruit) augmente avec l’augmentation de l’épaisseur de la couche active.
Volatile organic compounds (VOCs) are pervasive in the environment. Since the early 1980s, substantial work has examined the detection of these materials as they can indicate environmental changes that can affect human health. VOCs and similar compounds present a very specific sensing problem in that they are not reactive and often nonpolar, so it is difficult to find materials that selectively bind or adsorb them. A number of techniques are applied to vapor sensing. High resolution molecular separation approaches such as gas chromatography and mass spectrometry are well-characterized and offer high sensitivity, but are difficult to implement in portable, real-time monitors, whereas approaches such as chemiresistors are promising, but still in development. Gravimetric approaches, in which the mass of an adsorbed vapor is directly measured, have several potential advantages over other techniques but have so far lagged behind other approaches in performance and market penetration. This review aims to offer a comprehensive background on gravimetric sensing including underlying resonators and sensitizers, as well as a picture of applications and commercialization in the field.
Gravimetric resonators based on Micro/Nanoelectromechanical System (M/NEMS) are potential candidates in developing smaller, less expensive, and higher performance gas sensors. Metal organic frameworks (MOFs), with high surface areas, recently come into focus as advanced nano-porous sensitive materials in micro gravimetric gas sensors. The surface of MOFs on those sensors is critical in offering water stability and varying absorption behaviors. However, the influences of surface on sensing performance are less explored and the strategy to tune surface properties of MOFs mounted on gravimetric resonators is still rare. In this paper, a straightforward strategy to engineer surface properties of MOFs, specifically Cu3(benzenetricarboxylate)2 (known as HKUST-1), is reported and the surface hydrophilicity/hydrophobicity of HKUST-1 is tuned by chemical vapor deposition combined with monolayer self-assembly. It is found out that the hybrid inorganic and organic surface engineering strategy not only preserves the absorption capacity of inner MOFs but also significantly enhances sensor stability toward water.
This paper reports a complete micro gas chromatography (μGC) system in which all the components are lithographically microfabricated and electronically interfaced. The components include a bi-directional Knudsen pump, a preconcentrator, separation columns and a pair of capacitive gas detectors; together, these form the iGC3.c2 system. All the fluidic components of the system are fabricated by a common three-mask lithographic process. The Knudsen pump is a thermomolecular pump that provides air flow to the μGC without any moving parts. The film heaters embedded in the separation columns permit temperature programming. The capacitive detectors provide complementary response patterns, enhancing vapor recognition and resolving co-eluting peaks. With the components assembled on printed circuit boards, the system has a footprint of 8×10 cm2. Using room air as the carrier gas, the system is used to experimentally demonstrate the analysis of 19 chemicals with concentration levels on the order of parts per million (p.p.m.) and parts per billion (p.p.b.). The tested chemicals include alkanes, aromatic hydrocarbons, aldehydes, halogenated hydrocarbons and terpenes. This set of chemicals represents a variety of common indoor air pollutants, among which benzene, toluene and xylenes (BTX) are of particular interest.