The sensor response of tin oxide thin films to different gas concentration and the modification of the gas diffusion theory (original) (raw)
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Response to oxygen and chemical properties of SnO2 thin-film gas sensors
Vacuum, 2008
The measurements of the response-in terms of the conductance changes-to oxygen adsorption of tin dioxide (SnO 2) thin-film-based gas sensors were performed. The sensing SnO 2 layers were obtained by means of the rheotaxial growth and thermal oxidation (RGTO) method. The sensor responses were measured under a dry gas flow containing oxygen in nitrogen, within the range of temperature from 25 to 540 1C. For comparison, similar studies were performed for a commercial SnO 2 thick-film (TGS 812) gas sensor. The in-depth profiles of the chemical composition of the RGTO SnO 2 layers were determined from the scanning Auger microprobe experiment. The changes in concentration ratios [O]/[Sn] and [C]/[Sn] from the near-surface region towards the grain bulk were shown.
Grain size effect on the electrical response of SnO2 thin and thick film gas sensors
Materials Research-ibero-american Journal of Materials, 2009
Porous nano and micro crystalline tin oxide films were deposited by RF Magnetron Sputtering and doctor blade techniques, respectively. Electrical resistance and impedance spectroscopy measurements, as a function of temperature and atmosphere, were performed in order to determine the influence of the microstructure and working conditions over the electrical response of the sensors. The conductivity of all samples increases with the temperature and decreases in oxygen, as expected for an n-type semiconducting material. The impedance plots indicated the existence of two time constants related to the grains and the grain boundaries. The Nyquist diagrams at low frequencies revealed the changes that took place in the grain boundary region, with the contribution of the grains being indicated by the formation of a second semicircle at high frequencies. The better sensing performance of the doctor bladed samples can be explained by their lower initial resistance values, bigger grain sizes and higher porosity.
Fabrication and Testing of SnO 2 Thin Films as a Gas Sensor
Archives of Applied Science Research, 2012
Tin dioxide ( SnO 2) thin films were prepared using the thermal spray p yrolysis method from SnCl2.2H 2O isopropyl mixing with water solution on the glass substrate h eated at 450 ◦ C. The films were characterized by X-ray diffractio n (XRD), The crystallite size was evaluated to be 4.4 13 nm by using the Scherrer’s equation. Atomic For ce Microscope (AFM) and optical absorption spectra wer e taken to examine the surface morphology and opt ical properties to determine the band gap energy 3.9 eV, increase in band gap energy is revealed that nan ostructure SnO 2 films. These films were tested in butane gas at op erating temperature 470 ◦ C. The response and recovery time is 13 sec, 63 sec respectively. Keyword: SnO 2 Thin films; spray pyrolysis; butane gas sensing; s ensitivity.
SnO 2 films for thin film gas sensor design
Materials Science and Engineering B-advanced Functional Solid-state Materials, 1999
In this report we present the results of the study of the influence of the parameters of SnO2 thin films on their basic gas sensitive characteristics such as kinetics and absolute gas sensitivity. We have particularly investigated the influence of the film thickness, structure, concentration of charge carriers, and presence of uncontrolled impurities in the SnO2 films, which were deposited
Thin film SnO2-based gas sensors: Film thickness influence
Sensors and Actuators B: Chemical, 2009
The influence of the thickness of SnO 2 films deposited by a spray pyrolysis method on the operating characteristics of gas sensors is analyzed in this paper. It outlines how the thickness of metal oxides is an important parameter for gas sensors in determining the main operating parameters, such as the magnitude and rate of the sensor response and the optimal operating temperature. It is also shown that the optimal film thickness of a gas sensing layer depends on the required sensor parameters.
A model for the gas sensing properties of tin oxide thin films with surface catalysts
Sensors and Actuators B-chemical, 1995
The effect of two types of surface additives (Pd and Pt) on the response of reactively sputtered thin films of SnO. gas sensors has been studied, in mixtures of zero grade air and carbon monoxide. The experimental results obtained with surface additives show an abrupt conductance increase around 500 K when carbon monoxide in the ppm range is present, a behaviour which has not been observed with plain SnO, films. A semi-empirical model that explains this behaviour is presented, that is based on the well-established theory for the conductivity of ultrathin discontinuous metal films, i.e. activated charge carrier creation and tunnelling through potential barriers. The proposed model takes into account the dependence of film conductivity both on the thickness of the noble metal deposited on it and on the working temperature. The results of the theoretical analysis are in excellent qualitative agreement with the experimental ones.
IOP Conference Series: Materials Science and Engineering, 2016
This research is focused on structural and electrical characterisation of tin oxide (SnO2) applied as a thick film and investigation of its properties as gas sensitive material. Micron sized SnO2 powder was milled in an agate mill for six hours to fabricate SnO2 nanopowder, which was afterwards sieved by 325 mesh sieve and characterized by XRD and SEM. This powder was used as functional part in the production of thick film tin oxide paste containing a resin vehicle with 4 wt. % nanosize glass frits acting as permanent binder. The glass frits where additionally milled for twelve hours in the agate mills to nanosized powder and sieved by a 325 mesh sieve as well. The achieved thick film paste was screen printed on alumina and fired at 850 o C peak temperature for 10 minutes in air. After the sintering process, thick film samples where characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The reflectivity was measured on the same samples by UV-VIS spectrophotometer: the band gap was determined from the slope of reflectance. After that a matrix of different interdigitated electrode structure of PdAg paste was printed and sintered using the mentioned sintering conditions. The tin oxide thick film was printed over the interdigitated electrodes as a top layer and sintered again under the same conditions. The total electrical resistance was measured as a function of the electrode spacing and temperature. A negative temperature coefficient (NTC) was identified and measured in the range from room temperature (27°C) to 180°C in a climate chamber. Finally the samples were placed into a gas reactor with NOx and CO gas and the resistance was measured in the same temperature range (27°C-200°C).
Microstructure and morphology of tin dioxide multilayer thin film gas sensors
Sensors and Actuators B-chemical, 1997
Structural, morphological, and electrical measurements have been carried out on SnO 2 multilayer thin film grown by the rheotaxial growth and thermal oxidation method on Al 2 O 3 substrates. The analysis of X-ray and electron diffraction patterns shows that, in addition to the SnO 2 cassiterite phase, a contribution from another SnO 2 phase is present, which can be related to cassiterite by introducing microtwinning effects. The electrical measurements show that these thin films have a higher sensitivity towards CO with respect to the conventional single layer SnO 2 sensors. © 1997 Elsevier Science S.A. 0925-4005/97/$17.00 © 1997 Elsevier Science S.A. All rights reserved. PII S 0 9 2 5 -4 0 0 5 ( 9 7 ) 0 0 2 1 8 -9
Thickness Dependence of Sensitivity in Thin Film Tin Oxide Gas Sensors Deposited by Vapor Pyrolysis
International Journal of Engineering, Transactions B: Applications, 2003
Transparent SnO 2 thin films were deposited on porcelain substrates using a chemical vapor deposition technique based on the hydrolysis of SnCl4 at elevated temperatures. A reduced pressure self-contained evaporation chamber was designed for the process where the pyrolysis of SnCl4 at the presence of water vapor was carried out. Resistive gas sensors were fabricated by providing ohmic contacts on the layers obtained and the installation of a custom made micro-heater beneath the substrate. The sensitivity (S = Ra/Rg) of the fabricated sensors to acetone vapor contamination was measured at 270 ºC. S increased linearly with contamination level up to 8000 PPM, and saturation was observed at higher concentrations. The experimental relationship between S and thickness of the sensitive film was investigated in films obtained by CVD for the first time. It was shown that S was inversely related to the film thickness, and higher S values were recorded for thinner sensors. The upper limit for S was imposed by the conduction instabilities observed in the thinnest films deposited.
Sensitivity of Tin Oxide Thin Film Synthesized by Sol Gel Method
The present paper concerns about the synthesis of Tin Oxide(SnO 2 ) thin film on glass substrate by sol-gel dip coating method and annealed at 500 0 C for one and half hour. The grain size which plays a vital role in gas sensing was measured from XRD data and found to be 48.54nm by using Debye Scherrer formula. Carbon monoxide gas sensing of the film was measured at different temperature and was found to be highly sensitive at 220 0 C at concentration 50ppm. The prepared film was investigated for response time and was found that the sensor responded quickly to carbon monoxide gas at about 20 sec. The Optical characteristics were studied by using ELCO UV/VIS spectrophotometer Model-SL 159 in the wavelength range 300nm to 1000nm. The result of change in conductivity of the sensor in presence of CO gas was reported.