Metal Oxide Semiconductor Sensors Research Articles

Gas Sensing Studies of an n-n Hetero-Junction Array Based on SnO2 and ZnO Composites

A composite metal oxide semiconductor (MOS) sensor array based on tin dioxide (SNO2) and zinc oxide (ZnO) has been fabricated using a straight forward mechanical mixing method. The array was characterized using X-ray photoelectron spectroscopy, scanning electron microscopy, Raman spectroscopy and X-ray diffraction. The array was evaluated against a number of environmentally important reducing and oxidizing gases across a range of operating temperatures (300–500 °C). The highest response achieved was against 100 ppm ethanol by the 50 wt% ZnO–50 wt% SnO2 device, which exhibited a response of 109.1, a 4.5-fold increase with respect to the pure SnO2 counterpart (which displayed a response of 24.4) and a 12.3-fold enhancement with respect to the pure ZnO counterpart (which was associated with a response of 8.9), towards the same concentration of the analyte. Cross sensitivity studies were also carried out against a variety of reducing gases at an operating temperature of 300 °C. The sensors array showed selectivity towards ethanol. The enhanced behaviour of the mixed oxide materials was influenced by junction effects, composition, the packing structure and the device microstructure. The results show that it is possible to tune the sensitivity and selectivity of a composite sensor, through a simple change in the composition of the composite.

Spatially resolved, diffuse reflectance imaging for subsurface pattern visualization toward development of a lensless imaging platform: phantom experiments.

A portable, spatially resolved, diffuse reflectance lensless imaging technique based on the charge-coupled device or complementary metal-oxide semiconductor sensor directly coupled to the fiber optic bundle is proposed for visualization of subsurface structures such as superficial microvasculature in the epithelium. We discuss an experimental method for emulating a lensless imaging setup via raster scanning a single fiber-optic cable over a microfluidic phantom containing periodic hemoglobin absorption contrast. To evaluate the ability of the technique to recover information about the subsurface linear structures, scattering layers formed of the Sylgard® 184 Silicone Elastomer and titanium dioxide were placed atop the microfluidic phantom. Thickness of the layers ranged from 0.2 to 0.7 mm, and the values of the reduced scattering coefficient (μs′) were between 0.85 and 4.25 mm−1. The results demonstrate that fiber-optic, lensless platform can be used for two-dimensional imaging of absorbing inclusions in diffuse reflectance mode. In these experiments, it was shown that diffuse reflectance imaging can provide sufficient spatial sampling of the phantom for differentiation of 30 μm structural features of the embedded absorbing pattern inside the scattering media.

Selective Sensing Using Nanostructured Gas Sensors: A Review

Abstract Fabricating a sensor for a toxic gas like carbon monoxide has been a constant need in many domestic and industrial applications. Although many sensors are commercially available, research is focused on developing a selective sensor with higher sensitivity, selectivity and low operating temperature. This paper reviews the fabrication, comparison and evaluation of different nanostructured titanium dioxide sensors used in detection. After a brief description of the structural properties of, the article presents sensing mechanism in semiconductor metal oxide sensors. For a reducing agent like, the surface reactions result in the reduction of sensor resistance. The parameters associated with sensor performance are discussed. The article presents a summary of main research findings in this field. Nanostructured morphologies offer better sensing performance and selectivity. The improved performance due to nanostructured is highlighted. The review clarifies the specific role of for the future research.

Effect of Precursor Type on Zinc Oxide Formation and Morphology Development during Hydrothermal Synthesis

Semiconducting metal oxide sensors have been widely studied due to their small dimensions, low cost and low power consumption. Among semiconductor oxide materials, zinc oxide (ZnO) is a very interesting one due to its chemical and thermal stability, its large exciting binding energy and band gap as n-type semiconductor, and, especially, to its high response to toxic and combustible gases. ZnO is a potential material for gas sensor applications because of its high piezoelectric coefficient, great stability of its hexagonal phase and its pyroelectric property. Hydrothermal synthesis is one of the most useful methods to produce homogeneous, nanosized ZnO powders with high purity, controlled particle size and morphology. Therefore, ZnO with various morphologies can be synthesized via simple hydrothermal reactions. The research objectives of this study were to understand formation and growth process of ZnO particles with various morphologies and to investigate role of starting materials, (i.e., zinc chloride (ZnCl2) and zinc nitrate hexahydrate (Zn(NO3)2.6H2O) on the particle morphology. In the present study, ZnO particles with various morphologies were synthesized via an unstirred hydrothermal method. When the using ZnCl2 as a precursor, the final morphology was rod like with a taped tip (length of the rod 0.5-1um ) after 12 h at 100°C. On the other hand, final morphology of the produced ZnO particles was branch rodlike (5-10um) when using Zn(NO3)2.6H2O as precursor under the same synthesis conditions. Accordingly, a proposed growth mechanism has been suggested. Keywords: ZnO; Hydrothermal synthesis; Phase development; Morphology; Growth mechanism DOI: 10.17350/HJSE19030000034 Full Text:

Using Net Analyte Signal to Estimate the Limit of Detection in Temperature-modulated MOX Sensors

The limit of detection of metal-oxide semiconductor (MOX) sensors degrades due to cross sensitivity to environmental conditions in blank samples. Temperature-modulated MOX sensors are usually calibrated using multivariate methods in which the LOD definition is not well stablished. This work studies the influence of the ambient humidity variations in the LOD for CO detection by extracting the net analyte signal (NAS) of the multivariate response pattern and then applying the IUPAC univariate LOD definition. The calibration range has been optimized to minimize the LOD. LODs below 10 ppm are achieved in intraday calibration using independent test sets. The stability of the LOD in a three-week period is also assessed.

Videolaryngoscopy using an Android smartphone: A direct digital technique.

Sir, Direct laryngoscopy has been the standard of care in securing the airway, in both routine and emergent cases. Videolaryngoscopy, introduced about a decade earlier aims to overcome the limitations of direct laryngoscopy. Some of the disadvantages of direct laryngoscopy include the need for an optimal line of sight for glottic visualisation, greater cervical spine movement during laryngoscopy, a lack of visual feedback for other healthcare providers during resuscitation and for novices undergoing training in laryngoscopy, and lack of image archiving capability.[1,2] Despite the advantages, the high initial cost of investment remains a deterrent for the widespread adoption of videolaryngoscopy over direct laryngoscopy.[3] Videolaryngoscopy may be done inexpensively. The use of complementary metal oxide semiconductor sensors attached to the blade of a conventional Macintosh laryngoscope should suffice. The authors, in an earlier study, demonstrated the use of a low cost universal serial bus (USB) endoscope camera assembled on a Macintosh laryngoscope, to perform videolaryngoscopy.[4] The device used the video processing capabilities of a personal computer to display real time video. The evolution of this technique could then be to utilise the high quality display and graphical processing present in the ubiquitous smartphone, keeping the initial and recurring costs of the technique low. For technical reasons, the use of smartphones for displaying the video stream from an USB endoscope camera is not simple. We chose the Android smartphone operating system (OS) V3.1 or higher (checked using “about device” menu of the OS), that supports the USB on-the-go (OTG) host function. This feature allows direct interfacing of the USB camera with the mobile device using an USB OTG cable. Apple OS devices do not support a similar capability due to restrictions in its use of its host-capable USB port. Initial attempts at obtaining a video stream were unsuccessful, due to lack of inbuilt USB video class drivers in the Android OS kernel of several mobile devices. We attempted to recreate this functionality with open source custom software that processes the USB video stream directly in Google Nexus 2012 Android mobile device.[5] However, a high quality video recording was obtained in most of the mobile devices that we tested, by using “CameraFi” (Vault Micro Inc., Seoul, Korea) app freely downloaded from the online Google Play Store at https://play.google.com/store/apps/details?id=com.vaultmicro. CameraFi. The USB endoscope camera was disinfected prior to use, assembled and upright orientation done as described in our earlier study.[4] The USB camera was fixed about 40 mm from the tip of a Macintosh blade (size 3 or 4) using clean adhesive tape (Durapore, 3M Inc., USA). The application supported capture of high quality images as well as real time video capture Figure 1. The camera required minimal electrical power supplied through the USB port of the mobile device. The electrical safety of the camera was ensured due its completely insulated, waterproof casing. We had successfully tested this assembly for videolaryngoscopy in an adult mannequin. The mouth opening required by the USB camera-blade assembly was the same as that for a conventional Macintosh blade. Figure 1 Real time video capture from universal serial bus endoscope camera using CameraFi app in Android operating system This technique used readily available components with minor modification of a conventional laryngoscope. The technique involves direct digital transmission of the image to a smartphone through its USB port, without the use of cumbersome, optical-based smartphone adapters such as the Airtraq Universal Phone adapter (Prodol Meditec S.A, Vizcaya, Spain) that may affect image quality. Newer USB endoscope cameras of 5.5 mm diameter, 2 m cable length are available from online retailers, which are inexpensive, costing <10$, for example, at http://www.tomtop.com/product?q=endoscope+borescope. Future efforts would involve developing medical grade, 3D-printed laryngoscope conduits that encase the USB camera, conforming to all regulatory standards. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.

Visually lossless compression for Bayer color filter array using optimized Vector Quantization

Devices using single sensors to capture colour images are cheaper due to high cost of Charge Couple Device (CCD) sensors or Complementary Metal-Oxide Semiconductor (CMOS) sensors. Single sensor devices use Colour Filter Array (CFA) to sample one colour band at every pixel location. Demosaicking process is applied to interpolate the two missing colours from the surrounding. Typically compression is done on the demosaicked images which may not be efficient due to the individual compression of the different colour space. This work investigated compression of raw data before demosaicking and performs demosaicking to reconstruct the R, G, B bands later. A novel Vector Quantization (VQ) technique for encoding the wavelet decomposed image using Modified Artificial Bee Colony (ABC) optimization algorithm is proposed. The proposed technique is compared with Genetic Algorithm based VQ and ABC based quantization and with standard LBG and Lloyd algorithm. Results show higher Peak Signal-to-Noise Ratio (PSNR) indicating better reconstruction.

Demonstration of a snapshot full-Stokes division-of-aperture imaging polarimeter using Wollaston prism array

A snapshot full-Stokes division-of-aperture imaging polarimeter using a Wollaston prism array (WPA) is theoretically described and experimentally demonstrated. Two-dimensional spatial distributions of six polarization eigenstates, linear (0°, 90°, 45°, 135°), and left and right circular polarization states, are identified and separated by the WPA simultaneously and projected onto the six portions of a single focal-plane array by a lens array. The conditions of the measurement matrix formed by the six polarization modulation channels are naturally superior for immunity to Gaussian and Poisson noise. The unique properties of the WPA, such as its high extinction ratio, optical efficiency and transmittance, can further ensure the achievement of immunity. The snapshot principle and the conditions of the measurement matrix are discussed. A proof-of-concept system using a complementary metal oxide semiconductor (CMOS) sensor for visible light is built and validated using laboratory and outdoor measurements.

Sensor Data Classification for Renal Dysfunction Patients Using Support Vector Machine

Breath analysis is a non-invasive technique used in clinical laboratories for the identification of several morbid conditions. Renal failure patients can be distinguished by observing the degree of ammonia in exhaled breath. Standard treatment for renal failure patients is haemodialysis. Ammonia as a biomarker can also provide the efficiency of dialysis. This study proposes a system that uses metal oxide semiconductor sensors, which is capable of detecting ammonia from exhaled breath and identify whether the patient has been subjected to renal failure. Breath samples are gathered using a specially designed breath collecting tube and the steady-state responses are recorded after the samples have been passed through sensors TGS2444, MQ135, MQ137, and TGS826. From the steady-state response, geometric features are extracted and the support vector machine technique is used for classifying the pre- and post-dialysis groups. The results shown an accuracy of 88 % for the designed classifier for sensor TGS2444.

Integration of electronic nose technology with spirometry: validation of a new approach for exhaled breath analysis

New ‘omics’-technologies have the potential to better define airway disease in terms of pathophysiological and clinical phenotyping. The integration of electronic nose (eNose) technology with existing diagnostic tests, such as routine spirometry, can bring this technology to ‘point-of-care’.We aimed to determine and optimize the technical performance and diagnostic accuracy of exhaled breath analysis linked to routine spirometry.Exhaled breath was collected in triplicate in healthy subjects by an eNose (SpiroNose) based on five identical metal oxide semiconductor sensor arrays (three arrays monitoring exhaled breath and two reference arrays monitoring ambient air) at the rear end of a pneumotachograph. First, the influence of flow, volume, humidity, temperature, environment, etc, was assessed. Secondly, a two-centre case-control study was performed using diagnostic and monitoring visits in day-to-day clinical care in patients with a (differential) diagnosis of asthma, chronic obstructive pulmonary disease (COPD) or lung cancer. Breathprint analysis involved signal processing, environment correction based on alveolar gradients and statistics based on principal component (PC) analysis, followed by discriminant analysis (Matlab2014/SPSS20).Expiratory flow showed a significant linear correlation with raw sensor deflections (R2 = 0.84) in 60 healthy subjects (age 43 ± 11 years). No correlation was found between sensor readings and exhaled volume, humidity and temperature. Exhaled data after environment correction were highly reproducible for each sensor array (Cohen’s Kappa 0.81–0.94).Thirty-seven asthmatics (41 ± 14.2 years), 31 COPD patients (66 ± 8.4 years), 31 lung cancer patients (63 ± 10.8 years) and 45 healthy controls (41 ± 12.5 years) entered the cross-sectional study. SpiroNose could adequately distinguish between controls, asthma, COPD and lung cancer patients with cross-validation values ranging between 78–88%.We have developed a standardized way to integrate eNose technology with spirometry. Signal processing techniques and environmental background correction ensured that the multiple sensor arrays within the SpiroNose provided repeatable and interchangeable results. SpiroNose discriminated controls and patients with asthma, COPD and lung cancer with promising accuracy, paving the route towards point-of-care exhaled breath diagnostics.

Sparse Support Regression for Image Super-Resolution

In most optical imaging systems and applications, images with high resolution (HR) are desired and often required. However, charged coupled device (CCD) and complementary metal-oxide semiconductor (CMOS) sensors may be not suitable for some imaging applications due to the current resolution level and consumer price. To transcend these limitations, in this paper, we present a novel single image super-resolution method. To simultaneously improve the resolution and perceptual image quality, we present a practical solution that combines manifold learning and sparse representation theory. The main contributions of this paper are twofold. First, a mapping function from low-resolution (LR) patches to HR patches will be learned by a local regression algorithm called sparse support regression, which can be constructed from the support bases of LR–HR dictionary. Second, we propose to preserve the geometrical structure of image patch dictionary, which is critical for reducing artifacts and obtaining better visual quality. Experimental results demonstrate that the proposed method produces high-quality results, both quantitatively and perceptually.

Onboard Image Processing System for Hyperspectral Sensor.

Onboard image processing systems for a hyperspectral sensor have been developed in order to maximize image data transmission efficiency for large volume and high speed data downlink capacity. Since more than 100 channels are required for hyperspectral sensors on Earth observation satellites, fast and small-footprint lossless image compression capability is essential for reducing the size and weight of a sensor system. A fast lossless image compression algorithm has been developed, and is implemented in the onboard correction circuitry of sensitivity and linearity of Complementary Metal Oxide Semiconductor (CMOS) sensors in order to maximize the compression ratio. The employed image compression method is based on Fast, Efficient, Lossless Image compression System (FELICS), which is a hierarchical predictive coding method with resolution scaling. To improve FELICS’s performance of image decorrelation and entropy coding, we apply a two-dimensional interpolation prediction and adaptive Golomb-Rice coding. It supports progressive decompression using resolution scaling while still maintaining superior performance measured as speed and complexity. Coding efficiency and compression speed enlarge the effective capacity of signal transmission channels, which lead to reducing onboard hardware by multiplexing sensor signals into a reduced number of compression circuits. The circuitry is embedded into the data formatter of the sensor system without adding size, weight, power consumption, and fabrication cost.

Metal-core@metal oxide-shell nanomaterials for gas-sensing applications: a review

With an ever-increasing number of applications in many advanced fields, gas sensors are becoming indispensable devices in our daily life. Among different types of gas sensors, conductometric metal oxide semiconductor (MOS) gas sensors are found to be the most appealing for advanced applications in the automotive, biomedical, environmental, and safety sectors because of the their high sensitivity, reduced size, and low cost. To improve their sensing characteristics, new metal oxide-based nanostructures have thus been proposed in recent years as sensing materials. In this review, we extensively review gas-sensing properties of core@ shell nanocomposites in which metals as the core and metal oxides as the shell structure, both of nanometer sizes, are assembled into a single metal@metal oxide core–shell. These nanostructures not only combine the properties of both noble metals and metal oxides, but also bring unique synergetic functions in comparison with single-component materials. Up-dated achievements in the synthesis and characterization of metal@metal oxide core–shell nanostructures as well as their use in MOS sensors are here reported with the main objective of providing an overview about their gas-sensing properties.

Evaluation of the Radiopacities of Bulk-fill Restoratives Using Two Digital Radiography Systems.

This study investigated the radiopacity values of bulk-fill restoratives by using two digital radiography systems. Nine bulk-fill restoratives and a conventional composite were used in the study. Six disc-shaped specimens were prepared from each of these materials, three each at thicknesses of 1 mm and 2 mm, and tooth slices with these same thicknesses were obtained. As a control, an aluminum step wedge varying in thickness from 0.5 to 10 mm in was used. Three specimens of each of the materials, together with the tooth slice and the aluminum step wedge, were placed over a complementary metal oxide semiconductor (CMOS) sensor and a storage photostimulable phosphor (PPS) plate system and exposed using a dental x-ray unit. The images were analyzed using a software program to measure the mean gray values (MGVs). Five measurements were obtained from each of the restorative materials, the enamel, the dentin, and the stepwedge. The MGVs were converted to the equivalent aluminum thicknesses. Three-way analysis of variance (ANOVA) was used to determine the significance of the differences among the groups. A Tukey test was applied for pairwise comparisons (p<0.05). All composite-based restoratives were found to have greater radiopacities than enamel or dentin. Equia Fil had the lowest radiopacity value. Radiopacity increased as the thicknesses of the restorative material increased. The CMOS system showed significantly higher radiopacity values than the PSP system. In conclusion, all investigated bulk-fill restoratives passed the International Organization for Standardization and American National Standard Institute/American Dental Association requirements for radiopacity values when evaluated with the two digital radiography systems.

A customized metal oxide semiconductor-based gas sensor array for onion quality evaluation: system development and characterization.

A gas sensor array, consisting of seven Metal Oxide Semiconductor (MOS) sensors that are sensitive to a wide range of organic volatile compounds was developed to detect rotten onions during storage. These MOS sensors were enclosed in a specially designed Teflon chamber equipped with a gas delivery system to pump volatiles from the onion samples into the chamber. The electronic circuit mainly comprised a microcontroller, non-volatile memory chip, and trickle-charge real time clock chip, serial communication chip, and parallel LCD panel. User preferences are communicated with the on-board microcontroller through a graphical user interface developed using LabVIEW. The developed gas sensor array was characterized and the discrimination potential was tested by exposing it to three different concentrations of acetone (ketone), acetonitrile (nitrile), ethyl acetate (ester), and ethanol (alcohol). The gas sensor array could differentiate the four chemicals of same concentrations and different concentrations within the chemical with significant difference. Experiment results also showed that the system was able to discriminate two concentrations (196 and 1964 ppm) of methlypropyl sulfide and two concentrations (145 and 1452 ppm) of 2-nonanone, two key volatile compounds emitted by rotten onions. As a proof of concept, the gas sensor array was able to achieve 89% correct classification of sour skin infected onions. The customized low-cost gas sensor array could be a useful tool to detect onion postharvest diseases in storage.

Fast response integrated MEMS microheaters for ultra low power gas detection

Semiconducting metal oxide (SMO) gas sensors typically operate at a few hundred degrees Celsius and consume hundreds of milliwatts of power, limiting their application in battery-powered devices. An analytical model is presented for the optimization of the heater dimensions, which suggests the minimal power consumption is achieved when heat loss through air conduction and supporting beam conduction are equal. We demonstrate micromachined SMO sensors with optimized microheaters, which consume only ∼2mW of power when operated continuously at 300°C. We also measure an ultra-fast thermal response time of 33μs via a transient temperature–resistivity response method. The short response time allows the heaters to be operated in ultra-short pulsing mode decreasing the average power consumption to the μW level. These micromachined SMO sensors are used in proof-of-principle experiments as ultralow power hydrogen sulfide SMO gas sensors.

S1920103 熱可塑CFRP製の超小型深宇宙探査機構造への適用

An ultra-small probe which was named Shinen2 will be launched a H2A rocket with JAXA's asteroid probe the Hayabusa2. The Kyushu Institute of Technology has been developing the Shinen2 system with Kagoshima University. The purpose of this Shinen2 development is the establishment of a deep space communication method and a new structure designing method using a carbon fiber reinforced thermoplastics (CFRTP). Prairie View A&M University and NASA had developed a complementary metal oxide semiconductor (CMOS) sensor which can measure the three-dimensional distribution of the space radiation, was equipped in the Shinen2. This paper describes new deep space communication method and new structure designing method for the Shinen2. Furthermore, the CMOS type space radiation sensor is also described. The Shinen2 is the first small deep-space probe in the world to use an application of Carbon Fiber Reinforced Thermo-Plastics (CFRTP) for structure. A Carbon Fiber Reinforced Plastics (CFRP) is widely used in the aerospace industry. This CFRP has been used for satellite structures, and includes advantages such as high strength, high ductility, welding possibility, reduction of machining time. However, the example that used the CFRTP in structure of an aerospace vehicle is not found, the Shien2 will be the first example that it adapted to structure materials. This paper describes a summary of the Shinen2 structure that applied CFRTP.

Fragrance Measurement of Scented Rice using Electronic Nose

Abstract This article describes about an instrument and method for aroma based quality detection of Basmati and other aromatic rice varieties. It comprises few modules such as odour delivery module, sniffing module, water bath module and computing module. Odour handling module helps to deliver odour to the sensor array; a sniffing unit comprising a sensor array module that includes a eight number of metal oxide semiconductor sensors assembled on a printed circuit board, said printed circuit board fitted into a sensor chamber; a water bath module for preparing rice sample, said water bath module including a heater attachment to facilitate cooking; a computing module to quantify the aroma data acquired by sensors; data acquisition module etc. Principal Component Analysis (PCA) implemented for clustering the data sets acquired from sensor array. Also data generated from sensor array was fed to Probabilistic Neural Network (PNN), Back-propagation Multilayer Perceptron (BPMLP) and Linear Discriminant Analysis (LDA) for identification of different rice varieties. Finally, for aroma quantifying, pure-quadratic response surface methodology model used with mean square error (MSE) 0.0028.

Characterizing integration time and gray-level-related nonlinearities in a NMOS sensor.

We report a nonlinearity effect related to the integration time in a double-beam spectroradiometer equipped with two negative-module metal-oxide semiconductor (NMOS) sensors. This effect can be explained by the addition of photoelectrons produced by the radiant flux on the sensors during the readout phase to the photoelectrons produced during the measurement phase. A new method is proposed to characterize and correct both gray-level and integration-time-related nonlinearities in NMOS sensors. This method is experimentally simple and outperforms other commonly used correction procedures.

Selective detection of hazardous VOCs for indoor air quality applications using a virtual gas sensor array

Abstract. An approach for detecting hazardous volatile organic compounds (VOCs) in ppb and sub-ppb concentrations is presented. Using three types of metal oxide semiconductor (MOS) gas sensors in temperature cycled operation, formaldehyde, benzene and naphthalene in trace concentrations, reflecting threshold limit values as proposed by the WHO and European national health institutions, are successfully identified against a varying ethanol background of up to 2 ppm. For signal processing, linear discriminant analysis is applied to single sensor data and sensor fusion data. Integrated field test sensor systems for monitoring of indoor air quality (IAQ) using the same types of gas sensors were characterized using the same gas measurement setup and data processing. Performance of the systems is reduced due to gas emissions from the hardware components. These contaminations have been investigated using analytical methods. Despite the reduced sensitivity, concentrations of the target VOCs in the ppb range (100 ppb of formaldehyde; 5 ppb of benzene; 20 ppb of naphthalene) are still clearly detectable with the systems, especially when using the sensor fusion method for combining data of the different MOS sensor types.