Papers by Keyword: Chemical Sensor

Abstract: In this paper, a suitable process technology is employed to fabricate a new open gate silicon carbide-based junction field-effect transistor (OG-4H-SiC-JFET) intended to be used for all types of biochemical sensing applications. The main focus is dedicated to the fabrication steps and specifically the plasma etching of the SiC as it is the key step to pattern the device components. All necessary I-V characteristics (I_DS-V_DS and I_DS-V_GS) have been derived and show acceptable electrical performance. Furthermore, the electrical characteristics of the OG-4H-SiC JFET were simulated using 3D Silvaco ATLAS and are in line with the experimental electrical characteristics. The efficacity and simplicity of the process described in this paper is the first step for future development of biochemical sensors based on SiC-FETs.

Abstract: A “smart” molecular imprinted photonic crystal (MIPC) sensor has been developed based on the combination of photonic crystal (PC) and molecular imprinting technique (MIT). It can give rise to readable optical signals and color changes upon sensing benzocaine with detection limit of 16.5 μg/ml. In fish sample detection, the developed MIPC sensor shows satisfied result accuracy with HPLC. With the advantage of satisfactory specificity, rapid responsiveness and excellent recoverability, this MIPC material shows great potential towards on-site screening and visual detection of trace benzocaine in real sample.

Abstract: The 2, 4, 6-trinitrotoluene (TNT) vapor detection by quartz crystal microbalance (QCM) coated with 18-crown-6 ether film is introduced. The film acts as selective or sensitive layer for detecting TNT molecule. The frequency shift response is depend on the amount of mass of molecule adhere on the coated film surface. In this study, the concentrations of TNT vapor which is related to responses are studied. It shows that the TNT vapor concentration is related to the time for steady state condition and the frequency shift response. The high concentration vapor will increase the frequency shift response but increase the steady state time.

Abstract: Sensors had gained importance in all fields of science and technology and development of real time small devices with high sensitivity for in situ measurements at low cost has gained momentum. Micromachined cantilever provides a solution to this hunt. MEMS cantilever are the simplest of all the other mechanical structures and hence is considered for the ease of fabrication. Here a chemical CO₂ sensor is considered with the metal oxide layer as receptor to adsorb the CO₂ molecules leading to an increase in mass and microcantilever as the transducer part converting the change in mass to change in natural frequency. The sensitive SnO₂ layer increases the mass and hence decreases the resonant frequency. The inherent natural frequency of the cantilever is altered by the sensitive coating on top of the beam and the residual stresses present on the structure. In this paper, we investigate the SiO₂ cantilever with SnO₂ deposited on the top surface. Initially the microcantilever is analytically modelled and then is fabricated and characterized experimentally. Finally the error % is analysed between the analytical model and experimental results.

Abstract: Gas sensor array based on polymer/multi-walled carbon nanotubes (polymer/MWCNTs) composites prepared by screen printing technique was examined for rice aroma detection. The sensor array consists of two sets of three different sensors, i.e., MWCNTs dispersed in the matrix of poly (2-Acrylamido-2-methyl-1-propanesulfonic acid-co-acrylonitrile (S1-S2), polyvinyl alcohol (S3-S4) and poly (styreneco-maleic acid) partial isobutyl/methyl mixed ester (S5-S6). Sample temperature, which is one of the important parameters, has been found to influence the releasing rate of the volatiles from rice grain when needed to operate on the electronic nose system. In this case, the fabricated sensor array installed within a lab-made electronic nose system with optimum sample temperature at 70°C could provide rapid and best responses to the volatiles released from the milled rice sample. Moreover, the responsive signals could be recovered to original state as well within four minutes by only purging with fresh air at room temperature. Based on the principal component analysis (PCA) pattern recognition, it was shown that the electronic nose can discriminate six rice samples based on the content of aroma.

Abstract: In this work, we present the development of MEMS switch array and ZnO nanowire-based sensor technology to detect multiple analytes in a sensitive manner. A novel approach that incorporates the advantages of MEMS technology with highly sensitive ZnO nanowire sensor technology has been described. We demonstrate the fabrication of MEMS switch arrays and ZnO nanowire sensing chip that has been appropriately developed. Our integrated approach is believed to enhance the sensitivity of the entire sensor system in addition to increasing the capability of the system to detect multiple analytes with high degree of selectivity.

Abstract: Four types of tungsten trioxide (WO₃) particles (spherical, disk, cuboid, and hexagonal) were prepared and WO₃ thick film sensors were fabricated by dropping suspensions containing the obtained various WO₃ powders on Au comb-type microelectrodes. The sensing properties to 0.05-ppm NO₂ revealed that a cuboid WO₃ film sensor had the best response-recovery characteristics with the 90 % response and 90 % recovery times of 1.3 and 0.9 min at 200 °C, respectively. On the other hand, a hexagonal WO₃ film sensor showed extremely high sensor response even to 0.01-ppm NO2 at 200 °C, but the sensor response fluctuated greatly over the operating temperature range from 80 to 300 °C. Practical evaluation of the cuboid WO₃ thick film sensor in a roadside atmosphere was carried out and it was demonstrated that the evaluated values for the sensor unit had accuracy and resolution equivalent to CLD (Chemical Luminescence Detection) without any maintenance and calibration for 10 weeks.

Abstract: In order to improve the sensing-properties of carbon nanotube based composite for potential applications in chemical sensors, CNTs/PANi core/shell-structured nanowires were prepared with in-situ polymerization approach. A series of characterizations was carried out by TEM (transmission electron microscopy), the Fourier-Transform Infrared (FTIR) spectra, and so on. A chemical prototype sensor was constructed based on CNTs/PANi core/shell-structured nanowires and interdigital-structured electrodes on flexible polymer substrate. The gas-sensing behaviors of the sensor to some gases operating at room temperature were examined. Results showed that the sensitivity of CNTs/PANi core/shell-structured nanowires was increased dramaticly compared with pure carbon nanotube materials. This provides a carbon nanotube based composite materials with enhanced gas-sensitivity, which would have potential applications in some chemical sensors.

Abstract: Microring resonator based on Si₃N₄ waveguides was fabricated by using CMOS compatible processes with 1 µm wide waveguides and 200 µm in radius. The optical characteristic of the resonator was measured with a Q factor up to 20,000 and a free spectrum range (FSR) of 1 nm. The structure was further packaged to be a sensor for liquid sensing. Finally, the sensor was applied to detect concentrations of glucose solutions with sensitivity of 1.78×10^-5 refractive index unit (RIU), which proves its functionality and feasible application as high sensitivity chemical sensor.

Abstract: Distributed Bragg reflector (DBR) porous silicons exhibiting unique reflectivity were successfully obtained by an electrochemical etching of silicon wafer using square wave currents. Optically encoded smart dust which retained optical reflectivity was obtained from DBR porous silicon film in organic solution by using ultra-sono method. The size of optically encoded smart dust was measured by field emission scanning electron micrograph (FESEM) and was about 500 nm to few microns depending on the duration of sonication. Investigation for the optical characteristics of smart dust revealed that smart dust could be useful for application such as chemical sensor for detecting organic vapors.