Browsing by Author "R. Dwivedi"

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Chemical vapor identification by plasma treated thick film tin oxide gas sensor array and pattern recognition
(2011) J.K. Srivastava; Preeti Pandey; Sunil K. Jha; V.N. Mishra; R. Dwivedi
Present study deals the class recognition potential of a four element plasma treated thick film tin oxide gas sensor array exposed with volatile organic compounds (VOCs). Methanol, Ethanol and Acetone are selected as target VOCs and exposed on sensor array at different concentration in range from 100-1000 ppm. Sensor array consist of four tin oxide sensors doped with 1-4 % PbO concentrations were fabricated by thick film technology and then treated with oxygen plasma for 5-10 minute durations. Sensor signal is analyzed by principal component analysis (PCA) for visual classification of VOCs. Further output of PCA is used as input for classification of VOCs by four pattern classification techniques as: linear discriminant analysis (LDA), k-nearest neighbor (KNN), back propagation neural network (BPNN) and support vector machine (SVM). All the four classifier results 100 % correct classification rate of VOCs by response analysis of sensor array treated with plasma for 5 minute. © 2011 IFSA.
Design, fabrication and evaluation of MAGFET
(1990) M. Pant; R. Dwivedi; Pyare Lal; S.K. Srivastava
Design, fabrication and evaluation of a MAGFET (Magnetic Field Effect Transistor) have been described. Aluminium was used as gate material and two additional contacts in the channel were made for Hall voltage measurements. Results of various observations on variation of Hall voltage with drain, gate voltage and also with magnetic current are reported. Sensitivity of such sensors is low due to pre-existence of inversion region. Efforts are being made to improve the sensitivity.
Detection of methanol using temperature gradient sensor array and minimum difference method
(Society of Photo-Optical Instrumentation Engineers, 2000) V.K. Singh; R. Dwivedi; S.K. Srivastava
Gas sensor array in association with a pattern recognition approach can be used for the detection of gases/odors present in an environment. The minimum difference method has been applied successfully to the experimental data set obtained from the temperature gradient sensor array exposed to three different gases/odors. It was observed that, the minimum difference method in association with temperature gradient sensor array, can be used for the detection of gases/odors present in an environment.
Development of a room temperature sensitive tin oxide based CO gas sensor
(Society of Photo-Optical Instrumentation Engineers, 2000) Aparna Chaturvedi; V.N. Mishra; R. Dwivedi; S.K. Srivastava
In the present paper, an effort has been made to develop a highly selective room temperature sensitive CO gas sensor using SnO2 as the base material. To achieve this two sensors were fabricated by thick film technology using tin oxide as the base material doped with Pd as the gas sensing material. The fabricated sensors were annealed in oxygen and hydrogen plasma for 15 minutes. The response of the sensors was studied for different concentrations of CO, LPG, CCl4 and C3H7OH. It was found that though both oxygen and hydrogen plasma treated sensors showed a good room temperature sensitivity, the selectivity was extremely poor in case of oxygen plasma. Hydrogen plasma was found to be highly selective towards CO showing a room temperature sensitivity as high as 74%. Also, hydrogen plasma treated sensor is found to reveal a shorter response as well as recovery time.
Development of high sensitivity tin oxide based sensors for gas/odour detection at room temperature
(Elsevier Science S.A., 1998) R. Srivastava; R. Dwivedi; S.K. Srivastava
An effort has been made to develop thick film tin oxide gas sensors which could detect various gases/odours at room temperature. To achieve this, the fabricated sensors were annealed in oxygen plasma for various durations. It was then found that, the room temperature sensitivity of such sensors was increased to about ten times as compared to the sensitivity of the non-annealed sensors. Further, plasma annealed sensors are found to be practically independent of temperature and the room temperature sensitivity of these sensors are found to be about 1.5 times the sensitivity of the conventional sensors at its operating temperature of 300°C. Studies on the variation of d.c. resistance, sensitivity, temporal response, current-temperature characteristics and impedance spectroscopy with the annealing time have also been made. These studies reveal that, with the increase in annealing time, there is a permanent gradual reduction in the d.c. resistance of annealed sensors. Further, it is also observed that with the increase in annealing time, the response time improves, barrier height reduces, barrier capacitance increases and the dependence of the sensitivity with temperature reduces while the sensitivity itself improves many-fold.
Effect of hydrogen exposure on the interface state density in titanium dioxide based MOS gas sensor
(SPIE, 1998) D. Dwivedi; R. Dwivedi; S.K. Srivastava
Mechanism of the formation of hydrogen induced interface states at the Si/TiO2 interface has been investigated by conductance measurement of metal oxide semiconductor gas sensor. The conductance voltage response of the fabricated MOS capacitor has been studied upon exposure to hydrogen in argon ambient. The fabricated MOS device is sensitive to hydrogen (1-3%) at room temperature. The interface state density (Nit) is determined from the G-V curve, using a bias scan conductance method at fixed frequency. It is observed that, change in conductance is better at lower frequencies, which may be due to the balanced communication of interface traps with valance and conduction band of silicon substrate. Further it has been concluded that, present investigation provides a method for more accurate calculation of hydrogen induced interface traps in such device.
Effect of processing on the particle size of tin oxide nano-powders
(Springer Science and Business Media, LLC, 2013) Meenakshi Choudhary; Nitish Kumar Singh; R. Dwivedi; V.N. Mishra
Nano sized tin oxide powders have been synthesized via two different chemical routes namely solid-state and sol-gel route for the fabrication of tin oxide gas/odors sensor. The synthesized powders have been characterized by simultaneous thermo gravimetric and differential thermal analysis (TG-DTA), powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and Fourier transform infrared (FTIR) spectroscopy. The effect of synthesis routes have been investigated on particle size and morphology of tin oxide powders. Powder XRD patterns show that the synthesized powders have tetragonal (rutile) crystal structure. FESEM of formed thick films reveal that powder prepared by solid-state reaction route is less agglomerated as compared to the powder prepared by sol-gel route. XRD and FESEM indicate that there is the formation of tin oxide nanoparticles in the range of 15-50 nm. FTIR spectrums of synthesized powders show Sn-O or Sn-O-Sn stretching modes and its lattice modes at 615 and 494 cm-1. © 2012 Springer Science+Business Media, LLC.
Fowler-nordheim emission and electron trapping in pure N2O/SiH4 PECVD oxide deposited on N2, H2 and O2 plasma precleaned Si wafers
(1994) H.N. Upadhyay; R.K. Chanana; R. Dwivedi; S.K. Srivastava
[No abstract available]
Open-circuit voltage-decay behavior in p-n junction diode at high injection
(1985) R. Gopal; R. Dwivedi; S.K. Srivastava
The open-circuit voltage-decay of a highly forward biased p-n junction diode switched off abruptly after reaching steady state is studied theoretically for high-level injection. The present theory takes into account the terminal voltage instead of junction voltage as the open-circuit voltage, and is based on ambipolar diffusion phenomenon. The results are in qualitative agreement with the available experimental results for the entire range of decay characteristics.
Performance analysis of a modified solar array under shadow conditions
(1994) A.K. Sharma; R. Dwivedi; S.K. Srivastava; C.M. Pathak
This paper deals with the performance studies of a photovoltaic panel under shadow conditions. The conventional solar array design approach has been modified using a bypass diode across each cell, and the performance of the modified panel has been evaluated experimentally. The observed experimental results have been compared to those obtained theoretically, taking account of the effect of additional series resistance due to the shadowed area. Excellent agreement, both qualitatively and quantitatively, between experiment and theory has been obtained. © 1994.
Performance analysis of a solar array under shadow condition
(1991) A.K. Sharma; R. Dwivedi; S.K. Srivastava
The investigation deals with performance studies of a solar array consisting of two modules, each having 25 cells in series. The load characteristics of the array are studied experimentally and it is observed that, as the shadowed area increases, the overall performance of the array is significantly degraded. Theoretical analysis of such an array has also been carried out to explore the possible mechanisms responsible for array degradation. In the analysis, we consider an additional series resistance for the dark region, whereas earlier workers have overestimated the contribution of the dark region because they have always taken into account identical series resistances for the illuminated, as well as the dark, region. Simulation of the enhanced series resistance of the dark region in the present work has been done by the effective surface resistance of the emitter layer caused by a metallic grid, because of the biasing of the dark region by the illuminated area. Under such biasing, the dark region acts as a load on the illuminated region and causes a loss of current. This is simulated by an additional series resistance (Rsurf). The analysis, which is based on consideration of the enhanced series resistance of the dark region, produces a better match between experimental and theoretical results.
Ratio method for single component gas analysis using doped tin oxide thick film sensors
(IETE, 1994) M.S. Nayak; R. Dwivedi; S.K. Srivastava
In this paper, a novel discrimination technique called Ratio method for the analysis of sensor responses to detect the gas/odour present in an environment is presented. To test the developed method, initially two doped tin oxide (ZnO+Sb2O3 and ZnO) sensors were fabricated using thick film screen printing technique. The responses of these sensors were studied for CCl4, CH2Cl2 and C2HCl3, and the results thus obtained were used to illustrate the ratio method.
Simple approach for the detection and identification of individual gases/odours using an integrated sensor array
(SPIE, 1998) V.K. Singh; R. Dwivedi; S.K. Srivastava
In the present paper, a simple pattern recognition approach for application in the detection and identification of individual gases/odours using the response of an array of eight sensors has been presented. The proposed approach has been validated using experimental data for three different gases.
SIMPLER TECHNIQUE FOR THE FABRICATION OF METAL-INSULATOR-SEMICONDUCTOR (MIS) SILICON SOLAR CELL.
(1985) R.K. Singh; R. Gopal; R. Dwivedi; S.K. Srivastava
A metal-insulator-semiconductor (MIS) solar cell has been fabricated and the technique followed does not require a separate set-up to grow the thin SiO//2 layer used as the insulator. The cell was fabricated on a p-type silicon wafer of resistivity 2-3 OMEGA -cm. The backside of the wafer was metallized by aluminum. The SiO//2 layer was grown on the front surface (polished side) of the wafer when annealing of the backside aluminum metallization takes place in wet nitrogen at 450 degree C. Collecting contacts were obtained by photolithography after deposition of aluminum over SiO//2, Finally, titanium oxide was spread on the front surface to form an anti-reflection coating. The characteristics of the cell, thus formed, have been studied. The observed open-circuit voltage for such a cell is about 0. 3 v.
Study of electrical properties of SiO2 grown over plasma-cleaned silicon surfaces
(1991) R.K. Chanana; R. Dwivedi; S.K. Srivastava
[No abstract available]
Synthesis, characterization and gas sensing properties of tin oxide nanopowder
(2013) Meenakshi Choudhary; V.N. Mishra; R. Dwivedi
In the present work, tin oxide nanopowder has been synthesized by solid-state reaction technique. The as-prepared pure and palladium doped (0.5 and 1%) powders have been used for the fabrication of thick film sensors. The influence of particle size of powders and morphology of the thick films has been studied on the sensing performance of thick film sensor. It is observed that the sensors produced from the SnO2 doped with 1% palladium have an excellent ability for the detection of hydrogen gas. © 2013 AIP Publishing LLC.
The effect of hydrogen-induced interface traps on a titanium dioxide-based palladium gate MOS capacitor (Pd-MOSC): A conductance study
(Elsevier Ltd, 1998) D. Dwivedi; R. Dwivedi; S.K. Srivastava
The conductance versus gate voltage response of a palladium-gate MOS capacitor with 0.5 μm of TiO2 (oxide layer) has been studied as a function of hydrogen gas concentration and signal frequency. The structure of the device was completed by evaporating titanium dioxide over p < 111 > -type silicon wafer (cleaned as per standard silicon technology) having a resistivity of 3-5 Ω cm and subsequent palladium front with aluminium back metallization. The G-V response of the fabricated MOS capacitor was studied on exposure to hydrogen in Ar ambient. The fabricated device is sensitive to hydrogen (1-3%) at room temperature. The interface state density (Dit) was determined at the surface potential corresponding to the peak in the conductance curve, using a bias scan conductance method at fixed frequency. It was found that Dit increases with an increase in hydrogen gas concentration. Further, it has been observed that a change in conductance is better at lower frequencies, which may be due to the balanced communication of interface traps with the valance and conduction bands of silicon substrate. © 1998 Elsevier Science Ltd. All rights reserved.