Rational Design of Semiconductor-Based Chemiresistors and their Libraries for Next-Generation Artificial Olfaction

Artificial olfaction based on gas sensor arrays aims to substitute for, support, and surpass human olfaction. Like mammalian olfaction, a larger number of sensors and more signal processing are crucial for strengthening artificial olfaction. Due to rapid progress in computing capabilities and machine-learning algorithms, on-demand high-performance artificial olfaction that can eclipse human olfaction becomes inevitable once diverse and versatile gas sensing materials are provided. Here, rational strategies to design a myriad of different semiconductor-based chemiresistors and to grow gas sensing libraries enough to identify a wide range of odors and gases are reviewed, discussed, and suggested. Key approaches include the use of p-type oxide semiconductors, multinary perovskite and spinel oxides, carbon-based materials, metal chalcogenides, their heterostructures, as well as heterocomposites as distinctive sensing materials, the utilization of bilayer sensor design, the design of robust sensing materials, and the high-throughput screening of sensing materials. In addition, the state-of-the-art and key issues in the implementation of electronic noses are discussed. Finally, a perspective on chemiresistive sensing materials for next-generation artificial olfaction is provided.     

Detection of organic chemical vapors with a MWNTs-polymer array chemiresistive sensor

Organic chemical hazardous gases pose a significant threat to human life and the environment. An urgent need exists for the development of reliable chemical sensors that would be able to identify these hazardous gases. In a recent study, conductive carbon nanotubes were mixed with six polymers with various chemical adsorption properties to produce a composite thin film for the fabrication of a chemical sensor array. A silicon wafer was used as a microelectrode substrate for a resistance sensor fabricated using a typical semiconductor manufacturing process. This sensor array was then used to identify hazardous chemical gases at various temperatures. Results for two hazardous gases, ammonia (NH₃) and chloroform (CHCl₃), tested with the six polymers at different temperatures, indicated that the variation in sensitivity/resistance increased when the temperature increased. It was found that the MWNTs-PVP and MWNTs-PMVEMA sensing films had high sensitivity, excellent selectivity, and favorable reproducibility in detecting the two chemical agent vapors. In addition, we derived the solubility parameter (Δδ) to demonstrate the sensitivity of the polymers to ammonia (NH₃). The results showed that smaller solubility parameter corresponds to a stronger interaction between NH₃ gas and polymers, and increased sensitivity. Additionally, we used the statistical methods of principal component analysis to identify the interaction of hazardous gases with the MWNTs-polymer sensor.     

Hazardous industrial gases identified using a novel polymer/MWNT composite resistance sensor array

Hazardous industrial chemical gases pose a significant threat to the environment and human life. Therefore, there is an urgent need to develop a reliable sensor for identifying these hazardous gases. In this work, a silicon wafer microelectrode substrate for a resistance sensor was fabricated using the semiconductor manufacturing process. Conductive carbon nanotubes were then mixed with six different polymers with different chemical adsorption properties to produce a composite thin film for the fabrication of a chemical sensor array. This array was then utilized to identify three hazardous gases at different temperatures. Experimental results for six polymers for chemical gases, such as tetrahydrofuran (THF), chloroform (CHCl₃) and methanol (MeOH) at different temperatures, indicate that the variation in sensitivity resistance increased when the sensing temperature increased. The poly(ethylene adipate)/MWNT sensing film had high sensitivity, excellent selectivity, and good reproducibility in detecting all chemical agent vapors. Additionally, this study utilized a bar chart and statistical methods in principal component analysis to identify gases with the polymer/MWNT sensor.     

Array-to-array transfer of an artificial nose classifier.

This paper describes the use of a microsphere sensor technology that allows simple fabrication of vapor sensor arrays with reproducible response patterns. Microsphere sensor fabrication protocols are uncomplicated and yield billions of highly reproducible sensors. Microsphere sensor arrays combined with a generalized Whitney-Mann-Wilcoxen (GWMW) classifier were used to discriminate between the presence and absence of nitroaromatic compounds in high background vapor mixtures. The classifier was trained on one sensor array and then used to obtain 98.2 and 93.7% correct classification rates with data collected using two subsequent arrays made up to six months after the initial training was performed. These results represent an advance in the ability to transfer training data between multiple sensor arrays with a fluorescence-based artificial nose.     

Flexible strain sensors fabricated with carbon nano-tube and carbon nano-fiber composite thin films

This paper presents the fabrication of 3 × 3 flexible strain sensor arrays using conductive polymer solutions with fillers including carbon nano-fibers and multi-walled carbon nano-tubes. The strain sensor arrays were made on polyurethane substrates using patterned surface treatment and the tilted-drop process. Atmospheric plasma was used to enhance or reduce the surface energy in specific areas for patterned surface treatment. The performance of fabricated strain sensors made using conductive polymer solutions with different ingredients was investigated. The measured gauge factors were in the 0.34 to 7.98 range for the strain of 3-7%. Under a bending test exceeding 50 times at a 150° angle, sensor damage was not observed. The demonstrated fabrication method is capable of producing conductive polymer sensors with complex designs, high reliability and is suitable for mass production.     

Influence of electrode material on properties of SnO2-based gas sensor

The influence of electrode material on the properties of oxide semiconductor gas sensor was studied. SnO₂ thick films were printed on top of Au and Pt electrodes on alumina substrate using screen-printing technique. The gap between the electrodes was made narrow (approx. 5 μm) to emphasize the effects, which the electrodes might have on the overall conductance and gas-sensing properties of the sensor, at different temperatures. Laser micromachining was used in the fabrication of the electrode structure with the narrow gap. Temperature-stimulated conductance measurements were carried out in different ambient atmosphere conditions in order to have information about the effects that the electrode materials have on the overall sensor conductance. Many different gases at different concentrations in synthetic air were used in the experiments. It is possible to conclude from the results that the interface between the electrode and sensing material has a very important role for the sensing mechanism of tin dioxide gas sensors.     

A DFT study of NO2 and SO2 gas-sensing properties of InX (X = Cl,Br and I) monolayers

Journal of Materials Science - Gas sensors have attracted much attentions due to their applications for alarming dangerous gases. It is important for a gas sensor to find out suitable sensing...     

A novel method for reducing the dimensionality in a sensor array

Specific types of gas sensors are normally produced by adding different dopants to a common substrate. The advancement of technology has made the fabrication of many dopants and consequently various sensors possible. As a result, in each family of gas sensors, one can find tens of different sensors which are only slightly different in the spectrum of response to various volatile compounds. The wide variety of available gas sensors creates a selection problem for any specific application. Sensor selection/reduction becomes even more important when cost and technology limitations are issues of concern. Accordingly, a methodology by which one can tailor a sensor array to a specific need is highly desirable. In this paper, a novel method is introduced to address this task using data from an electronic nose that uses polymer gas sensors. This method has been delineated based on the geometry of eigenvectors in Karhunen-Loeve expansion. The methodology is general and therefore suitable for many other feature selection problems     

Large‐Area Integrated Triboelectric Sensor Array for Wireless Static and Dynamic Pressure Detection and Mapping

Large‐area flexible pressure sensors are of paramount importance for various future applications, such as electronic skin, human–machine interfacing, and health‐monitoring devices. Here, a self‐powered and large‐area integrated triboelectric sensor array (ITSA) based on coupling a triboelectric sensor array and an array chip of CD4066 through a traditional connection is reported. Enabled by a simple and cost‐effective fabrication process, the size of the ITSA can be scaled up to 38 × 38 cm². In addition, unlike previously proposed triboelectric sensors arrays, which can only react to the dynamic interaction, this ITSA is able to detect static and dynamic pressure. Moreover, through integrating the ITSA with a signal processing circuit, a complete wireless sensing system is present. Diverse applications of the system are demonstrated in detail, including detecting pressure, identifying position, tracking trajectory, and recognizing the profile of external contact objects. Thus, the ITSA in this work opens a new route in the direction of large‐area, self‐powered, and wireless triboelectric sensing systems.     

稀疏矢量阵设计的模拟退火算法

对于均匀间隔线列阵,由采样定理可知,当阵元间距超过信号波长的一半时,指向性图会产生与目标等高的栅瓣。为了获得高分辨率,同时避免栅瓣出现,需要大量的传感器。为了减少设备复杂度,可以采用稀疏布阵技术,以较少的阵元获得较高的分辨力。将模拟退火算法应用到稀疏矢量水听器阵的设计中。通过优化阵元位置控制指向性图,可以获得无栅瓣的指向性图。给出了优化后的稀疏矢量阵与均匀间隔矢量阵的指向性图比较。     

Nanoparticle metal-oxide films for micro-hotplate-based gas sensor systems

We report on the use of either reactive magnetron sputtering or screen printing to deposit tin and tungsten-oxide gas-sensitive layers onto integrated micromachined arrays. The procedures allow the deposition of the sensing layers before membranes have been etched, which leads to gas microsensors with an excellent fabrication yield. The microstructure of the sensitive films is analyzed by means of SEM and EDX. The response of the different microarrays to ethanol, acetone, and ammonia vapors and their binary mixtures, and toxic gases such as NO/sub 2/ and CO, is studied at different operating temperatures. The response of the different sensors to ambient humidity is also investigated. Finally, it is shown that by using PCA and fuzzy ARTMAP neural networks, it is possible to simultaneously identify and quantify the toxic gases with a 100% success rate. A 95% success rate is obtained in the semi-quantitative analysis of vapors and vapor mixtures. These results prove the viability and usefulness of the techniques introduced to obtain integrated sensor microarrays that are suitable for battery-powered gas/vapor monitors.     

Quantification of multiple bioagents with wireless, remote-query magnetoelastic microsensors

This paper presents a micromagnetoelastic sensor array for simultaneously monitoring multiple biological agents. Magnetoelastic sensors, made of low-cost amorphous ferromagnetic ribbons, are analogous and complementary to piezoelectric acoustic wave sensors, which track parameters of interest via changes in resonance behavior. Magnetoelastic sensors are excited with magnetic ac fields, and, in turn, they generate magnetic fluxes that can be detected with a sensing coil from a distance. As a result, these sensors are highly attractive, not only due to their small size and low cost, but also because of their passive and wireless nature. Magnetoelastic sensors have been applied for monitoring pressure, temperature, liquid density, and viscosity, fluid How velocity and direction, and with chemical/biological responsive coatings that change mass or elasticity, various biological and chemical agents. In this paper, we report the fabrication and application of a six-sensor array for simultaneous measurement of Escherichia coli O157:H7, staphylococcal enterotoxin B, and ricin. In addition, the sensor array also monitors temperature and pH so the measurements are independent from these two parameters.     

Three-Dimensional Distance-Error-Correction-Based Hop Localization Algorithm for IoT Devices

The Internet of Things (IoT) is envisioned as a network of various wireless sensor nodes communicating with each other to offer state-of-the-art solutions to real-time problems. These networks of wireless sensors monitor the physical environment and report the collected data to the base station, allowing for smarter decisions. Localization in wireless sensor networks is to localize a sensor node in a two-dimensional plane. However, in some application areas, such as various surveillances, underwater monitoring systems, and various environmental monitoring applications, wireless sensors are deployed in a three-dimensional plane. Recently, localization-based applications have emerged as one of the most promising services related to IoT. In this paper, we propose a novel distributed range-free algorithm for node localization in wireless sensor networks. The proposed three-dimensional hop localization algorithm is based on the distance error correction factor. In this algorithm, the error decreases with the localization process. The distance correction factor is used at various stages of the localization process, which ultimately mitigates the error. We simulated the proposed algorithm using MATLAB and verified the accuracy of the algorithm. The simulation results are compared with some of the well-known existing algorithms in the literature. The results show that the proposed three-dimensional error-correction-based algorithm performs better than existing algorithms.     

Evaluation of on-line flue gas measurements by MISiCFET and metal-oxide sensors in boilers

Metal insulator silicon carbide field-effect transistor sensors, metal-oxide sensors, and a linear Lambda sensor in an electronic nose was used to measure on-line in hot flue gases from a boiler. Flue gas from a 100-MW pellets-fuelled boiler has been used to feed the experimental setup. Several reference instruments, which measure the flue gases in parallel to the sensor array, are connected to the electronic nose. Data was collected during six weeks and then evaluated. Using principal component analysis as the data evaluation method, different operating modes for the boiler have been identified in the data set. The different modes could be described in terms of high or low O/sub 2/ and CO concentration. Furthermore, we have shown that it seems possible to use a sensor array to determine the operating mode of the boiler and, by partial least-squares models, measure the CO concentration when the boiler operates in its optimum mode.     

Realization of Nanolene: A Planar Array of Perfectly Aligned,Air‐Suspended Nanowires

Air suspension and alignment are fundamental requirements to make the best use of nanowires' unique properties; however, satisfying both requirements is very challenging due to the mechanical instability of air‐suspended nanowires. Here, a perfectly aligned air‐suspended nanowire array called “nanolene” is demonstrated, which has a high mechanical stability owing to a C‐channel‐shaped cross‐section of the nanowires. The excellent mechanical stability is provided through geometrical modeling and finite element method simulations. The C‐channel cross‐section can be realized by top‐down fabrication procedures, resulting in reliable demonstrations of the nanolenes with various materials and geometric parameters. The fabrication process provides large‐area uniformity; therefore, nanolene can be considered as a 2D planar platform for 1D nanowire arrays. Thanks to the high mechanical stability of the proposed nanolene, perfectly aligned air‐suspended nanowire arrays with an unprecedented length of 1 mm (aspect ratio ≈5100) are demonstrated. Since the nanolene can be used in an energy‐efficient nanoheater, two energy‐stringent sensors, namely, an air‐flow sensor and a carbon monoxide gas sensor, are demonstrated. In particular, the gas sensor achieves sub‐10 mW operations, which is a requirement for application in mobile phones. The proposed nanolene will pave the way to accelerate nanowire research and industrialization by providing reliable, high‐performance nanowire devices.     

Gamma radiation nose system based on In/sub 2/O/sub 3//SiO thick-film sensors

A prototype gamma radiation monitoring system based on In/sub 2/O/sub 3//SiO thick-film sensors array was designed. Four sensors had an identical pn-heterojunction structure with different material compositions. These sensors were subjected to gamma radiation emitted by /sup 137/Cs source with an activity of 370 kBq. Changes in their current-voltage characteristics were recorded and compared. The performance parameters of the devices, such as sensitivity to /spl gamma/ radiation exposure and working dose region, were found to be highly dependent on the composition of the materials used. To cover a wider range of radiation and improve the overall sensitivity, an approach of using sensor arrays was utilized. A dynamic selection of the multiple sensors of various sensitivities and working dose ranges was implemented by applying a pattern recognition analysis.     

Conducting polymer 1-dimensional nanostructures for FET sensors

In this review we have highlighted advantages of 1-dimensional nanostructures for field effect transistor (FET)/chemiresistor based sensors and advantages of conducting polymer as material of construction over other nanomaterials. Here we have ensembled different techniques used for the fabrication, assembly/alignment, functionalization and sensing applications of conducting polymer nanowire/tube/junction based FET sensors for gas and biomolecule detection. The advantages and disadvantages of various fabrication, functionalization, and assembling techniques are discussed. We evaluate how such devices have enabled the achievement of improved sensor performance in terms of high sensitivity, selectivity and low detection limits. Finally, we conclude by highlighting overall merits of different techniques and challenges researchers face in the field of conducting polymer 1-dimensional nanostructures-based sensors and also predict the future direction in which research efforts are likely to flourish.     

碳纳米管传感器的研究进展

综述了不同功能碳纳米管传感器(微型碳纳米管气体离子传感器、无线被动碳纳米管气体传感器、碳纳米管化学和力学传感器、碳纳米管阵列生物传感器、碳纳米管温度和风速传感器、碳纳米管神经毒气传感器)的制备、结构特点、性能和发展方向.     

纳米ZnO气敏传感器研究进展

半导体金属氧化物气敏传感器被广泛应用于有毒性气体、可燃性气体等的检测.ZnO是一种重要的半导体气敏材料,特别是纳米ZnO,由于其粒子尺寸小,比表面积大,成为被广泛研究的气敏响应材料之一.简要介绍了纳米ZnO气敏传感器的气敏机理、主要特性,综述了通过新型纳米形貌、结构制备以及元素掺杂改性提升纳米ZnO气敏性能等方面的研究进展,并进一步指出了纳米ZnO气敏传感器研究中存在的问题和未来的研究方向.     

气敏传感器的近期进展

综合介绍了气敏传感器材料及元件的最新进展,侧重于气敏材料研究工作的概述,并分析了气敏传感器的发展趋势