Selectivity Of Semiconductor Gas Sensors Research Articles

МЕТОД ИЗМЕРЕНИЯ ГАЗОЧУВСТВИТЕЛЬНЫХ ХАРАКТЕРИСТИК ПОЛУПРОВОДНИКОВЫХ СЕНСОРОВ ПО ДИНАМИЧЕСКИМ ПАРАМЕТРАМ ОТКЛИКА

Detection of dangerous gases and vapors is relevant both at work and in everyday life. Sensorelements based on semiconductor structures are highly sensitive to gases of a very differentnature. To increase the accuracy of measurements, calibration and the speed of concentrationdetermination, special methods are required, such as signal processing in various ways. The studyuses gas sensors based on silicon–carbon films that are sensitive to a whole set of gases. In thefirst part of the article, general problems and a method for solving them are considered, whichmakes it possible to increase the selectivity of semiconductor gas sensors. The analysis of dynamicparameters, such as the first and second derivatives of the response curves, as well as the analysisof the Elovich equation is carried out. Such calibration dependences, constructed from the extremesof the derivatives and the slope coefficients of the Elovich equation, show high linearity.As a promising solution, it is proposed to use a set of calibration lines to determine the concentrationof the target gas. The developed method allows, using dynamic response parameters, to determinethe gas type and its concentration using a single sensor, also to increase the accuracy ofmeasurements, along with a reduction in detection time. The experimental results of data processingwith the determination of the gas type and its concentration using the described methodare presented. For a sensor based on silicon-carbon materials, the developed method and algorithmsmade it possible to carry out measurements using a single sensor element for a set of gases(NO2, CO, SO2) with different concentrations. At the same time, the smallest relative error did notexceed 3.6% for SO2, 2.7% for NO2, 2% for CO. The distinctive features of the developed methodare the use of several calibration lines in a multidimensional space, rather than one, as well as anoriginal algorithmic signal processing methods.

Structure and gas sensitivity of WO3–In2O3 and WO3–Co3O4 oxide compositions

Using oxide compositions is a promising method of increasing the sensitivity and selectivity of semiconductor gas sensors on the basis of SnO2, In2O3, WO3and other oxides. We have studied nanocrystalline tungsten oxide (WO3), indium oxide (In2O3), cobalt oxide (Co3O4) and mixed oxide compositions with different WO3/In2O3and WO3/Co3O4ratios synthesized using the sol-gel method after xerogel annealing at 400–600 °C. The morphology, phase composition and structure of the materials have been studied using X-ray diffraction, infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. We showed that stable structures can be produced in WO3–In2O3and WO3–Со3O4nanoheterogeneous compositions. The growth of grain size in WO3and In2O3, WO3and Co3O4during heat treatment of mixed compositions occurs slower than in simple oxides. An increase in the gas sensitivity of the compositions in comparison with simple oxides can be accounted for by smaller grain sizes and hence larger specific surface area, as well as by the dependence of grain surface state on material composition. Both compositions exhibit the greatest nitrogen dioxide response at 130–150 °C and the greatest carbon oxide response at above 230 °C. We have produced low-power nitrogen dioxide sensors with a sensitivity of << 1 ppm and power consumption of ≤ 85 mW.

Increasing the selectivity of semiconductor gas sensors working at sinusoidal-varying temperature for machine industry safety systems

The article considers the possibility of creating a sensor system on the basis of 50%In2O3–50%Ga2O3 thin films, functioning at sinusoidal-varying temperature, with high selectivity to a number of key industrial gases including ethanol, acetone, ammonia, and propane-butane. A study of temperature and time dependencies of resistance at a sinusoidal-varying operating temperature was conducted. The deviation of the dynamic dependencies of the resistance from the harmonic law was detected, the reason of which should be considered to be the non-linearity of the temperature dependencies of the gas-induced response and the response time constants. The complex shape of the obtained dynamic characteristics was analyzed using Fourier transform. It has been shown that the resultant Fourier images can be used as sources of a large number of information parameters, which are suitable for increasing the selectivity of the sensor system operating in the considered mode of operation. It has been demonstrated that the selection of the amplitudes of the first three harmonics of Fourier images as information parameters allows the unambiguous identification of the type of the analyzed gas.

Increase in the Sensitivity and Selectivity of Semiconductor Gas Sensors

Within the limits of a linear model based on processing of data of direct calibration measurements with semiconductor multisensors, a method of their calibration by standard levels of gas concentration is substantiated for its subsequent application for small concentration levels. On an example of data for nitrogen dioxide, the notion of the normalized surface density of the gas is introduced, and its relationship with the volume concentration is established. On this basis, the feasibility of increase in the sensitivity and selectivity of the multisensor system by several orders of magnitude compared with the existing instrumental methods is substantiated by imitational modeling using mathematical methods of modern algebra and regularization theory.

Selective modified SnO2-based materials for gas sensors arrays

An enhancement of selectivity of semiconductor gas sensors, based on nanocrystalline SnO2 is reported. It is shown that modification of the surface of crystallites, forming thick films of conductive sensor materials, with catalytic clusters of gold or oxides of ruthenium, nickel, copper and iron allows selective response of sensors to different gases, such as carbon monoxide, ammonia, hydrogen sulfide, nitrogen dioxide and acetone vapor. These selective sensor responses can be obtained in the ranges of gas concentrations close to or below threshold limit values while the working temperature of sensors can be kept below 300 °C. The described approach for modification of selectivity of sensor materials could be used as perspective route in developingselective gas sensors. These results allow us to propose application of obtained materials in electronic nose sensor systems.

Improving the Selectivity of Semiconductor Gas Sensors Using the Pulse Adsorption Mode

A procedure is proposed for improving the selectivity of semiconductor gas sensors by the pulsed supply of the test gas mixture, with the use of transient spectroscopy for the separation and assessment of component contributions to the response of an electrical conductivity detector. The experimental verification of the procedure showed that the selective determination of several compounds and their mixtures can be performed using the same SnO2 detector. The simulation of the detector response as the sum of simplest relaxations revealed three types of surface sites on SnO2 films, with energy levels of 0.97, 1.38, and 1.50 eV. This means that the number of gas components that can be selectively determined with a single detector is limited to three.

Identification of Organic Solvents by a Virtual Multisensor System With Hierarchical Classification

To improve the selectivity of semiconductor gas sensors, temperature modulation is often used. We present a study showing the potential of this technique with information gained comparable to multisensor systems. A dynamic operating mode coupled with a low-complexity evaluation strategy allows the identification of six organic solvent vapors over a wide concentration range (2-200 ppm) with a single sensor, for example, for leak detection systems. The system features low false alarm rates; in addition, interference by other gases, such as CO or NO/sub 2/, can be suppressed. For even higher identification power, switching on-line between different temperature cycles was studied, which provides better information for critical decisions.

Sensitivity and selectivity enhancement in semiconductor gas sensors

To date numerous efforts have been made to enhance the sensitivity and selectivity of semiconductor gas sensors to a specific gaseous component. Advantages of these modifications will be discussed in terms of the principle factors in physics and chemistry that are associated with the gas-sensing mechanism of semiconductor gas sensors.

Selectivity of semiconductor gas sensors

It is shown that Taguchi Gas sensors Types 812 and 813 exhibit a marked degree of selectivity to carbon monoxide and methane, and curves of their performance in mixtures of these gases are presented.