Gas Sensor Characterization Research Articles

Design of an economic, portable, compact, and indigenous instrument setup for measuring sensing characteristics of thin film gas sensors.

Thin film gas sensor characterization is very demanding for various applications because of technical design trade-offs in commercially available gas sensors. For gas sensing characterization, a suitable gas-testing experimental setup is very much needed in this context. Various factors in the experimental setup can affect a thin film gas sensor's response beyond gas exposure. These factors include the test chamber's volume, relative humidity, uniform operating temperature, uniform pressure, uniform gas density, uniform gas distribution, uniform gas concentration in the gas chamber, and uniform relative gas flow velocity over the surface of the sensor. All these environmental parameters, not being so predictive in nature, induce an inherent design trade-off in the experimental setup design. Although all the commercially available gas testing experimental setups are equally good considering the dedicated purpose for which they are made. However, all of them are for generic applications but not for specific applications because of their inherent trade-offs in their usability features. Those trade-offs always provide an opportunity to introduce a new setup with its own unique advantages. Hence, in this article, we have presented a portable, compact, indigenous gas sensing experimental setup for studying the performance of gas sensors. We have characterized and tested the setup using a ZnO based thin film gas sensor when exposed to CO2 gas at concentrations ranging from 1445 to 4631 ppm. The proposed gas sensing setup's compact size offers unique advantages, including portability and compatibility for uniform environmental conditions.

Field Tests of Smart Mos Gas Sensor Systems for Selective Quantification of VOCs

Field Tests of Smart Mos Gas Sensor Systems for Selective Quantification of VOCs

QCM gas sensor characterization of ALD-grown very thin TiO2 films

The paper presents a technology for preparation and characterization of titanium dioxide (TiO2) thin films suitable for gas sensor applications. Applying atomic layer deposition (ALD), very thin TiO2 films were deposited on quartz resonators, and their gas sensing properties were studied using the quartz crystal microbalance (QCM) method. The TiO2 thin films were grown using Ti(iOPr)4 and water as precursors. The surface of the films was observed by scanning electron microscopy (SEM), coupled with energy dispersive X-ray analysis (EDX) used for a composition study. The research was focused on the gas-sensing properties of the films. Films of 10-nm thickness were deposited on quartz resonators with Au electrodes and the QCMs were used to build highly sensitive gas sensors, which were tested for detecting NO2. Although very thin, these ALD-grown TiO2 films were sensitive to NO2 already at room temperature and could register as low concentrations as 50 ppm, while the sorption was fully reversible, and the sensors could be fully recovered. With the technology presented, the manufacturing of gas sensors is simple, fast and cost-effective, and suitable for energy-effective portable equipment for real-time environmental monitoring of NO2.

Enhancement of SO2 gas sensing performance using ZnO nanorod thin films: the role of deposition time

In this study, a sensor with a controllable thin film of zinc oxide (ZnO) nanostructures with different deposition times is successfully synthesized over alumina substrates by chemical bath deposition methods. The seed of ZnO is grown using the dip-coating method, and ZnO thin film is grown by chemical bath deposition (CBD) using the precursor of Zn(NO3)2·4H2O. Chemical bath deposition was done three times to investigate the role of deposition time toward gas sensing properties. Structure, morphology, and composition of the ZnO thin films are characterized using X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy, respectively. From the morphology characterization, the ZnO nanostructure from two-times CBD and three-times CBD process shows different sizes and densities of nanorods compared to the ZnO thin film from one-time CBD process. Increasing thickness of thin film is also observed in two-times CBD of ZnO. The gas sensor characterization test results show that the ZnO thin films from two-times CBD can improve the sensing response to be 93% for SO2 gas at 70 ppm of concentration at working temperature of 300 °C, which is an increase of 15% compared to ZnO thin films from one-time CBD. At different operation temperatures, the response of two-times CBD ZnO nanorod increases 20–40% over one-time CBD ZnO nanorod. The three-times CBD ZnO nanorod showed non-order and high-density nanostructure yielding low resistance value and cause low sensor response.

Highly sensitive CO sensors based on star-like ZnO nanostructures

ZnO with rice-like, stare-like, conical and short rod morphologies have been synthesized by a simple hydrothermal and microwave method using zinc acetate, NaOH and different templates as sucrose, galactose and hexamine. The influence of the type of template and synthesis condition on structural, optical and sensing properties was studied by X-ray diffraction, scanning electron microscopy, UV–Vis spectra, and a gas sensor characterization system. The results show the template and synthesis conditions to have significant effect on morphology, crystallite size, band gap and sensing properties. Star-like ZnO microstructures show the highest response, i.e. 40, to CO gas at 250 °C than the other sensors. Sensing mechanisms are discussed in detail.

Gas mixing apparatus for automated gas sensor characterization

We developed a computer-controlled gas mixing system that provides automated test procedures for the characterization of gas sensors. The focus is the generation of trace gases (e.g. VOCs like benzene or naphthalene) using permeation furnaces and pre-dilution of test gases. With these methods, the sensor reaction can be analyzed at very low gas concentrations in the ppb range (parts per billion) and even lower. The pre-dilution setup enables to cover a high concentration range (1:62 500) within one test procedure. Up to six test gases, humidity, oxygen content, total flow and their variation over time can be controlled via a LabVIEW-based user-interface.

Influence of annealing temperature on the photoelectric gas sensing of Fe-doped ZnO under visible light irradiation

Abstract Fe-doped ZnO are fabricated by hydrothermal method. The influence of the annealing temperature on structural and photoelectric property was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–vis diffuse reflectance spectra (UV–vis DRS). Visible light-illumination room-temperature gas sensing to formaldehyde based on Fe-doped ZnO annealed at different temperatures was subsequently investigated by the surface photocurrent spectra and gas sensor characterization system, respectively. Accompanying with increasing annealing temperature from 400 °C to 600 °C, the response to formaldehyde was enhanced due to the increase in crystal quality and active sites on the surface of Fe-doped ZnO. However, when the annealing temperature goes over 700 °C, the phase of ZnFe 2 O 4 was observed from XRD pattern. The existence of ZnFe 2 O 4 hindered the transfer of photo-generated carriers and decreased the amount of surface active sites. As a result, the photoelectric gas response for formaldehyde was weaken to some extent. Our results demonstrated that annealing temperature is a very important parameter in the determination of the sensitivity of photoelectric gas sensing based on Fe-doped ZnO.

A Novel Method for Evaluation of Band Width of MEMS-Based Embedded Gas Sensor

This paper represents a novel method of evaluation of band width of MEMS based embedded gas sensor by using the concept of adding white Noise. In this paper we are providing the details of MEMS based embedded gas sensor and adding a concept to evaluate narrowed bandwidth of MEMS based gas sensor. Novel technique includes the concept of amp litude demodulation and temperature modulation. The gas sensor virtual co mponent encloses the sensor and its associ- ated analog circuitry into a dig ital shell so that all interface connections to the virtual co mponent are digital. The system architecture supports an array of gas sensor elements. System response time is limited by the sensor and is complex. Examp le gas sensor characterization results are presented showing isothermal response to carbon mono xide mo lecules with detection sensitivity better than 100 nanomoles/mo le. In the present scenario all the sensors output is communicated through computer system so evaluation of Centre frequency and bandwidth is important. Bandwidth of MEMS based gas sensor is measured and compared with help of spectral analysis.

The effects of annealing temperature on the CO-sensing property of perovskite La0.8Pb0.2Fe0.8Cu0.2O3 nanoparticles

In this paper, perovskite La0.8Pb0.2Fe0.8Cu0.2O3 nanoparticles were synthesized by a sol–gel method using citric acid as complexing reagent. The thermal stability, grain size and structural properties of La0.8Pb0.2Fe0.8Cu0.2O3 calcined at different temperatures were studied using thermogravimetric analysis and differential scanning calorimeter analysis (TG–DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The results show that the annealing temperature affects only the grain size of the synthesized La0.8Pb0.2Fe0.8Cu0.2O3 nanoparticles but does not change its perovskite structure, confirming the thermal stability of the synthesized material. The electrical and CO gas response properties of La0.8Pb0.2Fe0.8Cu0.2O3-based sensors were investigated by the gas sensor characterization system. Results demonstrate La0.8Pb0.2Fe0.8Cu0.2O3 sample calcined at 800°C exhibits higher response and good selectivity to CO. In addition, the structural and CO-sensing properties of La0.8Pb0.2Fe0.8M0.2O3 (M=Co, Ni and Cu) were discussed. As a result, Co-doping sample shows the highest response and the lowest operating temperature.

The effects of annealing temperature on the sensing properties of low temperature nano-sized SrTiO 3 oxygen gas sensor

A low temperature SrTiO 3 oxygen gas sensor was fabricated by high-energy ball milling and conventional screen-printing techniques. The thermal stability, grain size and lattice constant of the material and the sensing properties of sensor device at different annealing temperatures were studied using DTA/TGA, XRD, TEM and the gas sensor characterization system, respectively. The results show that the annealing temperature affects only the grain size of the synthesized nano-sized SrTiO 3 material but does not change its perovskite structure, confirming the thermal stability of the synthesized material. The sensing properties of sensor device are affected by the annealing temperature due to the change of the grain size of the material. The optimal relative resistance ( R nitrogen/ R 20% oxygen) value of 6.35 is obtained for the synthesized SrTiO 3 sample annealed at 400 °C and operating at 40 °C. The 40 °C optimum operating temperature is much lower than that for the conventional metal oxide semiconducting oxygen gas sensors (300–500 °C).

MEMS-based embedded sensor virtual components for system-on-a-chip (SoC)

The design and implementation of a monolithic micro electro mechanical systems (MEMS)-based gas sensor virtual component is described. The gas sensor virtual component encloses the sensor and its associated analog circuitry into a digital shell so that all interface connections to the virtual component are digital. The system architecture supports an array of gas sensor elements. System response time is limited by the sensor and is complex. Example gas sensor characterization results are presented showing isothermal response to carbon monoxide molecules with detection sensitivity better than 100 nanomoles/mole.

Influence of gaseous species transport on the response of solid state gas sensors within enclosures

The filling of a measurement chamber for gas sensor characterization, with CO diluted in air by the flow-through method is simulated by using a general-purpose CFD code. Numerical data allow to follow the time evolution of CO concentration at any point inside the chamber, thus representing an helpful tool for designing effective test chambers and for interpreting experimental electrical data. In particular, it is shown that CO concentration over the sensor surface increases with time quite slowly, even if the air–CO jet impinges on the device from a short distance. In addition, a comparison of numerical results with experimental data is presented and discussed.

Gas sensor characterization through both contact potential difference and photopotential measurements

Two different electrical measurement methods have been used to study p-Si/SiO 2/SnO 2/Pd structures which could be used in gas sensors. One of the methods is the contact potential difference measurement which characterizes the surface of the structure. A new method using a modulated light beam permits the measurement of the photopotential. These two methods are described. The relation between the surface potential and the photopotential is examined.