Search query: Characteristics of semiconductor gas sensors  state gas response

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abstract: Abstract The steady state gas sensing characteristics of SnO2 gas sensors, as exemplified by the Taguchi Gas Sensor (TGS) are comprehensively studied. Resistance responses to hydrogen, methane, carbon monoxide and water vapor are experimentally characterized, with particular emphasis on multiple gas interactions. We find that the presence of ambient oxygen is essential to the sensor's operation and that the detection of combustible or reducing gas is mediated by reaction with adsorbed oxygen on the sensor surface. A quantitative model of device operation is constructed which unifies the diverse properties of the TGS and other semiconductor sensors. The model supplies the mathematical framework for meaningful comparisons of sensor performances and gas sensitivities. In addition, it provides for the intrinsic power law response of sensor electrical resistance to combustible gas concentrations, the competitive and synergistic interactions of several gases detected simultaneously, and the source of sensor unselectivity. Stoichiometries and activation energies for the pertinent oxidation reactions on the tin oxide sensor surface can be derived from a sensor's resistance response by curve fitting to the mathematical model.
author_names: P K Clifford

David T Tuma
title: Characteristics of semiconductor gas sensors I. Steady state gas response
year: 1982

abstract: The density of oxygen vacancies in semiconductor gas sensors was often assumed to be identical throughout the grain in the numerical discussion of the gas sensing mechanism of the devices. In contrast, the actual devices had grains with inhomogeneous distribution of oxygen vacancy under non ideal conditions. This conflict between reality and discussion drove us to study the formation and migration of the oxygen defects in semiconductor grains. A model of the gradient distributed oxygen vacancy was proposed based on the effects of cooling rate and re annealing on semiconductive thin films. The model established the diffusion equations of oxygen vacancy according to the defect kinetics of diffusion and exclusion. We described that the steady state and transient state oxygen vacancy distributions, which were used to calculate the gas sensing characteristics of the sensor resistance and response to reducing gases under two different conditions. The gradient distributed oxygen vacancy model had the applications in simulating the sensor performances, such as the power law, the grain size effect and the effect of depletion layer width.
author_names: Jianqiao Liu

Yinglin Gao

Xuekui Ed Wu

Guohua Jin

Zhaoxia Zhai

Huan Liu
title: Inhomogeneous Oxygen Vacancy Distribution in Semiconductor Gas Sensors: Formation, Migration and Determination on Gas Sensing Characteristics
venue: Sensors
year: 2017

abstract: The grain size effects on gas sensing characteristics of semiconductor gas sensor are simulated based on the model of gradient distributed oxygen vacancies, which describes the dynamics of oxygen vacancies in an idealized cooling process. Sensor resistance and response to oxidizing gases, as functions of grain size (RC) and depletion layer width (w) are calculated from the steady state vacancy distribution in the depletion layer through Poissons equation. Simulation curves are plotted to fit the experimental data from WO3 and In2O3 sensors in nitrogen oxides detection. The fitting results illustrate the applicability of the model on quantitative interpretation of the grain size effects on oxidizing gas detection. The widths of depletion layer in WO3 and In2O3 nanograins are estimated.
author_names: Jian Qiao Liu

Lin Quan
title: Simulation of Grain Size Effects on Gas Sensing Characteristics of Semiconductor Sensors in Nitrogen Oxides Detection
year: 2014

abstract: The recent advent of integrated gas sensors and advances in pattern recognition techniques have heralded a renewed interest in the electrical characteristics of porous thick semiconductor layers. A linear diffusion reaction model is considered here that may be used to characterise the transient and steady state response of several metal semiconductor metal devices. This approach differs from that of chemical kinematics which is widely adopted and focuses upon the relationship between electrical conductance and the geometrical structure of the device. The theoretical transient response is derived for several MSM device configurations and compared with experimental data on SnO2 gas sensors. There is reasonable agreement with the model predictions at low gas concentrations. Consequently, the electrical conductivity of thick porous tin oxide gas sensors is diffusion limited as the reaction rate is fast compared with the diffusion rate. However, further work is needed to address nonlinear adsorption processes and to consider a diffusion reaction process where the reaction rate is slow compared with physical diffusion.
author_names: Julian William Gardner
title: A diffusion reaction model of electrical conduction in tin oxide gas sensors
year: 1989

abstract: A mixed potential, electrochemical sensor platform is extended to NH3 sensing by the introduction of a new gold alloy working electrode. A planar, pre commercial NH3 sensor utilized LANL's controlled interface approach, and a Pd Au alloy working electrode was tested in exhaust of a GM 1.9 L diesel engine downstream of a diesel oxidation catalyst through a slipstream arrangement. A fraction of the exhaust was pulled across the sensor with a pump at 20 L/min. In order to simulate NH3 slip inside of a full SCR emissions control system, NH3 was injected immediately upstream of the sensor using a calibrated mass flow controller. The sensor response quantitatively tracked the NH3 as measured via Fourier transform infrared (FTIR) analyzer. A calibration curve was obtained in the exhaust from an ammonia staircase response with the engine running at steady state engine conditions resulting in low background concentrations of NOx and HC <20 ppm) during calibration. Exhaust gas recirculation (EGR) switching and sweeps were used to evaluate the NH3 sensor response under different amounts of total background NOx. The calibration curve was used to directly compare the [NH3] calculated from sensor response to the gas phase composition measured via FTIR. In general, there was excellent quantitative agreement between the sensor response and the actual NH3 in the exhaust gas, and fast response time such that transients <5 ppm) could be easily discerned from baseline. A LANL pre commercial NOx sensor was tested simultaneously with the NH3 sensor and the extent of cross sensitivity between the two sensors will be discussed.
author_names: Eric Lanich Brosha

Vitaly Y Prikhodko

Cortney R Kreller

Josh A Pihl

Scott J Curran

James E Parks

Rangachary Mukundan
title: Response Characteristics of Stable Mixed Potential NH3 Sensors in Diesel Engine Exhaust
venue: Emission Control Science and Technology
year: 2016

abstract: Quantitative analysis of gases, by means of semiconductor sensor arrays and pattern recognition techniques such as artificial neural networks, has been the goal of a great deal of work over the last few years. However, the lack of selectivity, repeatability and drifts of the sensors, have limited the applications of these systems to qualitative or semi quantitative gas analysis. While the steady state response of the sensors is usually the signal to be processed in such analysis systems, our method consists of processing both, transient and steady state information. The sensor transient behaviour is characterised through the measure of its conductance rise time (Tr) when there is a step change in the gas concentration. Tr is characteristic of each gas/sensor pair, concentration independent and shows higher repeatability than the steady state measurements. An array of four thick film tin oxide gas sensors and pattern recognition techniques are used to discriminate and quantify among ethanol, toluene and o xylene [concentration range: 25, 50 and 100 ppm] A principal component analysis is carried out to show qualitatively that selectivity improves when the sensor behaviour is dynamically characterised. The steady state and transient conductance of the array components are processed with artificial neural networks. In a first stage, a feed forward back propagation trained ANN discriminates among the studied compounds. Afterwards, three separate ANN (one for each vapour) are used to quantify the previously identified compound. Processing data from the dynamic characterisation of the sensor array, considerably improves its identification performance, rising the discrimination success rate from a 66% when only steady state signals are used up to 100%
author_names: Eduard Llobet

Jesus Brezmes

Xavier Vilanova

Jesus E Sueiras

Xavier Correig
title: Qualitative and quantitative analysis of volatile organic compounds using transient and steady state responses of a thick film tin oxide gas sensor array
year: 1997

abstract: This paper reports the influence of In2O3 film structure on gas sensing characteristics measured in steady state and transient modes. Films were deposited by spray pyrolysis from InCl3 water solutions. Correlation between gas sensing parameters and structural parameters such as film thickness (20 400 nm) grain size (10 70 nm) refractive index and film texture (I(400)/I(222) were established. It was shown that grain size and porosity are the parameters of In2O3 films that best control gas response to ozone. In the detection of reducing gases, the influence of film structure is less important. Decreases in film thickness, grain size and degree of texture are the best way to decrease time constants of the gas response of In2O3 based gas sensors.
author_names: Ghenadii Korotcenkov

V Brinzari

A Cerneavschi

M Ivanov

V Golovanov

Albert Cornet

Joan Ramon Morante

Andreu Cabot

Jordi Arbiol
title: The influence of film structure on In2O3 gas response
year: 2004

abstract: Abstract A physicochemical model of the behavior of electrochemical gas sensors based in a solid state ion conducting electrolyte is presented and verified. The model focuses on air referenced planar sensors with a porous, diffusive layer covering one of the electrodes. By assuming hypotheses of ergodicity, ordinary diffusion, near equilibrium situation, high catalytic activity and steady state mass conservation in the system layer/electrode/electrolyte/electrode, the model describes the current voltage characteristics both in steady state as in transient conditions. Numerical simulations, including finite element modelling, are used for obtaining the model preditions for I(V) I(t) and V(t) responses in front of binary O2 N2 mixtures and multi component mixtures. The model is validated with our own designed sensors with different diffusion layers.
author_names: Carlos Lopez-Gandara

Mireia Blanes

Josep M Fernandez-Sanjuan

Francisco M Ramos

Albert Cirera
title: Modeling and Optimization of Diffusive Layers in Potentiometric and Amperometric Electrochemical Gas Sensors
year: 2012

abstract: ii Dedication..iv Acknowledgmentsv Vita..vii List of Tables.xii List of Figures..xiii Chapters: 1. Introduction1 1.1 Types of Gas Sensors..2 1.1.1 Potentiometric Gas Sensors.3 1.1.2 Amperometric Gas Sensors..5 1.1.3 Conductometric Gas Sensors..6 1.2 Metal Oxide Semiconductor Gas Sensors..8 1.2.1 Bulk Conductivity Changes.8 1.2.2 Surface Conductivity Changes..10 1.2.3 Conductivity in Polycrystalline Samples..10 1.2.4 Sensing Combustible Gases..11 1.3 Optimizing Metal Oxide Gas Sensors..12 1.3.1 Metal Oxides for Gas Sensing..12 1.3.2 Materials Preparation.13 ix 1.3.2.1 Control of Grain Size..13 1.3.2.2 Sol Gel Preparation.14 1.3.2.3 Other Powder Preparation Procedures..15 1.3.2.4 Reactively Sputtered Metal Oxides..16 1.3.2.5 Control of Film Thickness and Porosity.17 1.3.3 Metal and Metal Oxide Additives..17 1.3.3.1 Additives to Enhance Catalysis..18 1.3.3.2 Additives for Control of Particle Morphology..21 1.3.4 Sensor Arrays.22 1.4 TiO2 as Gas Sensor..24 References..26 2. TiO2 based Sensor Arrays Modeled with Nonlinear Regression Analysis.56 2.1 Experimental.59 2.1.1 Sample Preparation..59 2.1.2 Electrical Measurements and Data Analysis..61 2.2 Basis of the Regression Model.62 2.2.1 Kernel Ridge Regression..63 2.2.2 Determining the Composition of a Gas Mixture64 2.3 Model Development: Sensor Array I..66 2.4 Prediction of Gas Compositions: Sensor Array II69 2.4.1 8% CuO AL Fabrication Method Development69 2.4.2 Implementation of Sensor Array II71 2.5 Factors That Control Orthogonality.73 2.6 Limitations of Predictability75 2.7 Features of the Kernel Regression Model76 2.8 Conclusions..76 References78 x 3. Relationship Between Gas Surface Interactions and Sensor Response for TiO2 based Sensors100 3.1 Experimental..103 3.1.1 Sample Preparation..103 3.1.2 Electrical Measurements..105 3.1.3 Percent Conversion Measurements..105 3.1.4 Materials Characterization..106 3.2 Materials Fabrication and Characterization108 3.2.1 Additive Introduction by Solid State Mixing: La2O3..108 3.2.2 Additive Introduction by Solid State Mixing: La2O3 and CuO..112 3.2.3 Additive Introduction by Deposition Precipitation: Au..113 3.3 Chemical Reactivity..115 3.4 Electrical Response Characteristics..117 3.4.1 Sensor Response and Operating Temperature.119 3.4.2 Recovery Time.122 3.4.3 Sensor Response and Oxygen Concentration..123 3.5 Chemical Reactivity and Electrical Response of ALC with CH4..125 3.5.1 Chemical Reactivity with CH4.125 3.5.2 Electrical Response with CH4: Effect of Temperature and O2 Concentration..126 3.6 Anatase..128 3.6.1 Effect of Operating Temperature.128 3.6.2 Effect of Oxygen Concentration..131 3.7 Role of Additives..132 3.7.1 La2O3132 3.7.2 CuO..134 3.7.3 Au..135 3.8 Possible Additives and Their Effect on Sensor Sensitivity138 3.9 Conclusions.138
author_names: Marla Lea Frank
title: Novel strategies for design of high temperature titania based gas sensors for combustion process monitoring
year: 2003

abstract: Abstract Thin film metal oxide semiconductor (MOX) gas sensors are characterized by high sensitivity and fast response. Those characteristics make them very promising among the several existing technologies for the production of solid state gas sensors. Furthermore, by means of silicon micro machining technology, MOX sensors can be made on micro hotplates, allowing to reach very low power consumption, and the batch production guaranties a high yield. However, reproducibility and reliability are still major issues preventing the use of thin film MOX sensors in mass market applications. In this work, a wafer level fabrication process for micro machined low power consumption thin film MOX sensor arrays is reported. Different solutions for the optimization of the fabrication process are investigated, aiming to increase the reproducibility. The critical technological steps related to signal generation and acquisition, like the thin film definition and positioning and the definition of the sensing layer electrodes, have been optimized. The devices considered are 4 sensor arrays based on thin films of SnO2 deposited by a modified rheotaxial growth and thermal oxidation (M RGTO) technique on micro machined low power hotplates. The different fabrication techniques are described in detail. 45 sensors from 3 wafers, made using the different fabrication techniques, are comparatively characterized. The spread of the main sensor functional parameters values shows an evident decrease when the optimized fabrication process is used.
author_names: Ivan Elmi

Stefano Zampolli

Gian Carlo Cardinali
title: Optimization of a wafer level process for the fabrication of highly reproducible thin film MOX sensors
year: 2008