CO 2 Gas Sensing Properties of Screen-Printed La 2 O 3 /SnO 2 Thick Film

IEEE SENSORS JOURNAL, VOL. 16, NO. 18, SEPTEMBER 15, 2016 6839

CO2 Gas Sensing Properties of Screen-PrintedLa2O3/SnO2 Thick Film

Maryam Ehsani, Mohd Nizar Hamidon, Senior Member, IEEE, Arash Toudeshki,M. H. Shahrokh Abadi, Member, IEEE, and Sarah Rezaeian, Member, IEEE

Abstract— The present investigation deals with the fabricationof CO2 gas sensor based on La2O3/SnO2 metal–oxide material.In this paper, the sensitive material was prepared by La2O3/SnO2nanopowder and the addition of 1 wt.% and 3 wt.% platinum (Pt)using high-speed ball milling method. The sensitive film preparedby sensitive powder was printed on alumina (Al2O3) substrateby screen printing method. This film was characterized byX-Ray powder diffraction spectroscopy, and Field-emission scan-ning electron microscopy. As a result, the prepared 3 wt.%Pt/La2O3/SnO2 thick film sensitive paste exhibits a high sen-sitivity to increasing the CO2 gas concentration at 225 °C in airatmosphere.

Index Terms— La2O3/SnO2 thick film, screen printing,CO2 sensor, gas sensor, Pt.

I. INTRODUCTION

SEMICONDUCTOR based oxide material was used overmany years as sensing materials for fabrication of gas

sensors. The concentration of charges, which are broughton the surface of semiconductor gas sensors, is sensitiveto the composition of surrounding atmosphere. Therefore,these materials were employed for detection of differentgases [1], [2]. SnO2 is one of the most important metal oxidematerials, which is used as the base material for fabrication ofgas sensors [3], [4]. By employing the thick film technologycan manufacture multi layers, over one or both sides of thesubstrate. This is because of many advantages such as itslow-cost, high sensitivity, chemical and mechanical stability.Therefore, this technology can be utilized to achieve low-costmetal oxide gas sensors with good sensing properties in facedwith gaseous ambient [5], [6].

Nowadays, with development of industries, different kindsof air pollutants are emitted from various sources into the

Manuscript received November 2, 2015; revised April 24, 2016 andJune 12, 2016; accepted June 26, 2016. Date of publication July 18, 2016;date of current version August 15, 2016. The associate editor coordinatingthe review of this paper and approving it for publication wasDr. Anupama Kaul.

M. Ehsani is with the Department of Electrical Engineering and InformationTechnology, Faculty of Mess and Sensor Technique, Technical University ofDarmstadt, Darmstadt 64283, Germany (e-mail: [email protected]).

M. N. Hamidon is with the Functional Devices Laboratory, Institute ofAdvanced Technology, Universiti Putra Malaysia, Serdang 43400, Malaysia(e-mail: [email protected]).

A. Toudeshki is with the Citrus Research and Education Center, Universityof Florida, Lake Alfred, FL 33850 USA (e-mail: [email protected]).

M. H. Shahrokh Abadi is with the Faculty of Electrical and ComputerEngineering, Hakim Sabzevari University, Sabzevar 9617976487, Iran (e-mail:[email protected]).

S. Rezaeian was with the Department of Electrical and Electronic Engi-neering, Faculty of Engineering, Universiti Putra Malaysia, Serdang 43400,Malaysia (e-mail: [email protected]).

Digital Object Identifier 10.1109/JSEN.2016.2587779

atmosphere. Carbon dioxide (CO2) gas is one of the color-less and odor-less gases, which is producing by industrialprocesses [7]. High concentration of CO2 gas impacts theearth’s environment this can be harmful for humans and animallife [8]. Therefore, the requirement for CO2 measurement hasincreased with the risk of global warming and environmentalawareness [9].

Although fabricated gas sensors based on tin oxide materialhas an excellent potential for adsorption of gas molecules, itwas found that fabricated gas sensor by SnO2 are sufferingfrom poor sensitivity to carbon dioxide gas. Impartation ofmetal oxides and noble metals can changes sensor’s sensitivityto the target gas. After launching an amount of La2O3,LiO2 and Na2O (metal oxide), within the optimal operationtemperature of 400 °C, and 4.2 wt. %, it was reported that, thesensitivity to the CO2 was monotonically raised when the gasconcentration was between the range from 0 to 2080 ppm [10].In tin oxide material based sensors, the same effect on sensingthe CO2 gas was also reported for Palladium and Platinum(noble metals) [11]. La2O3 as a rare-earth element has aneffective role to decrease the size of particles and increasethe sensitivity of sensor [12], [13]. However, all presentedresults were reported when sensors working in high operationtemperature, from 350 to 500 °C [10], [14]. In general,operation temperature of electronic components are designedfor significantly lower this temperature [15]. The producedheat with the sensor’s heater which is required to increasethe sensitivity can also be induced on closed-by electroniccomponents. This can change their designed operating pointsto an undesirable point. Therefore, a sensor that can work ina lower operation temperature with better sensitivity is moredesirable.

In this manuscript, it attempts to reduce the operationtemperature of La2O3/SnO2 sensor, and improvement thefabricated sensor’s sensitivity to CO2 gas by adding 1 wt.%and 3 wt.% Pt. The scope of this study has focused on thestructural and morphological properties of sensor’s materials.

II. RELATED WORKS

As it is shown in Table I, two forms ofpowder [10], [16]–[22] and film [23], [24] were typically usedfor producing SnO2 gas sensors. The calcination temperatureof 900 °C were applied for SnO2 with 5% of La samplewhich was produced in powder form at the crystallinesize of 9.6 nm [16]. In another work, the SnO2 with 10%La2O3 was produced in powder form with the crystallinesize of 1.6 nm where the calcination temperature of 400 °C

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6840 IEEE SENSORS JOURNAL, VOL. 16, NO. 18, SEPTEMBER 15, 2016

TABLE I

GENERAL SnO2 SENSOR PRODUCTION METHODS

was applied [10]. The SnO2 sample in powder form wasproduced at the calcination temperature of 550 °C and thecrystalline size of 40 nm [17]. In [23], the SnO2 sample withcombination of Au, Pd and Pt was calcined at the temperatureof 300 °C in form of a film with crystalline sizes between20 and 60 nm. However, the SnO2 sample with combinationof Pt and Pd was also produced in film form by [24] wherethe crystalline size was smaller than [23] at 12 nm and atthe applied calcination temperature of 600 °C which wastwo times higher than the used temperature in [23]. At thecalcination temperature of 800 °C, the SnO2–WO3 material;and the combination of NASICON with Pr6O11-doped SnO2were produced in powder form [19], [20]. In [19], thecrystalline size was reported approximately about 17.1 nm,but it was 10 nm in [20]. The 11 nm crystalline size wasreported for producing the SnO2–Ca sample in a film formwhere the sample was calcined at the applied temperatureof 600 °C [24]. In another related work, the SnO2–Ca withcombination of Pt where the crystalline size was reduced1.85% compared with the size that was reported by [24], butin powder form was produced at the calcination temperatureof 700 °C by [21]. In comparison with [21] and [24], [22]was reported a smaller size of the crystalline (10.7 nmfor SnO2/Ca/Pt and 9.5 nm for SnO2/Ca/Pd sample) andthe lower calcination temperature of 550 °C, which wereproduced in powder form. Recently, the Co–SnO2 samplewith crystalline sizes between 15 and 30 nm was produced inthe form of the powder at the applied calcination temperatureof 600 °C [18]. By the way, there was not any significantcorrelation between the SnO2 sample type or productionform, crystalline size, temperature of calcination and thesensitivity of SnO2 gas sensor to the different concentrationsof the CO2 gas.

III. METHODOLOGY AND MATERIALS

In order to provide the sensitive powder, in this study, wehave used the same preparation method and similar materials

as [14]. However, the amount of La2O3 and ball-millingdurations were changed. i.g. here just we have used 2wt% ofLa2O3, but this amount was 4.5 mol% (14.6 wt%) in [14].However, in order to cover the ineligible effect of La2O3reduction, we have decided to increase the ball-milling dura-tion to provide the desired nano-particles with a smaller size.Related details for preparing the sensitive material and itsfabrication process are explained in the following.

A. Materials and Fabrication Process

Three different samples were prepared. The first one wasmixing SnO2 powder with purity of 99.9 % with 2 wt. %La2O3 and for other two pastes, amounts of 1 wt. % and3 wt. % Pt were added. Each sample, then, was mixed with10 wt. % glass frit based on SiO2 and B2O3,with additivessuch as PbO, Al2O3, ZnO, BaO, CdO and Bi2O3 in orderto provide appropriate adhesion between substrate and finalprinted sensitive paste which is mixed with m-xylene mediuminside the ultrasonic bath for 24 hours. After that, unlike [14]’sball-milling duration which was 15 hours, in this study, thesamples were subjected to grind using planetary mono-millfor 96 hours, to provide the small particles size. This leadsto increasing the sensitivity of fabricated sensor and thenreducing the operation temperature.

In the next process, samples were dried inside the ovenunder 50 °C for almost 6 hours and calcinated under 700 °C.The organic vehicle made from ethyl cellulose, α-terpineoland m-xylene were added to these mixture to achieve a propersensitive paste. After printing all layers include heater, elec-trodes and sensitive layer were dried at 150 °C for 15 minutes.Moreover, the firing temperatures were applied at 980 °C forheater and electrodes and 750 °C for sensing layer. Thesethermal treatments were applied for drying and stabilizingfilms on the alumina substrate.

Additionally, in order to record the structural properties ofsensitive powder, the X-ray diffraction patterns were used.Moreover, the Field Emission Electron Microscopy (FE-SEM)was employed to characterize the morphology of sensitive filmsurface.

B. Experimental Setup

The Pt/La2O3/SnO2 thick film was used as the sensingelements. The sensing layer was located on electrodes in oneside of substrate. Furthermore, electrodes and heater contactswere fixed about 2 mm apart on the film surface. Therefore,the gas sensing process were carried out by using 4800 mlgas chamber. This chamber was equipped with humidity andtemperature sensors. Finally, the fabricated sensor installedinside the chamber to sense the amount of injected differentconcentration of carbon dioxide.

The experimental set up for measuring the sensor responseis presented in Fig. 1. Three similar fabricated sensorswere tested together, at the same time and under the sameexperimental condition; and each experiment repeated tentimes. During the experiment, the ambient temperature ofabout 27 °C, the humidity of about 50 %, applied voltageof 2.5 V across the sensing electrodes, operation temperatureof 255 °C and the variation of CO2 gas concentration were

EHSANI et al.: CO2 GAS SENSING PROPERTIES OF SCREEN-PRINTED La2O3/SnO2 THICK FILM 6841

Fig. 1. Experimental setup for measuring the sensor response.

similar for all sensors. Data were logged by using Pico� Tech-nology ADC–20 High–Resolution Data Logger when the CO2gas became homogenized inside the chamber, sensors haveworked at the steady–stated operation temperature and thesensing electrodes have shown the stable results. Finally, theaverages of the recorded data for each CO2 gas concentrationwere used to investigate the behavior of the sensor and tocarry out a general approximate mathematical model for thesensitivity as a function of CO2 gas concentration.

C. Calculation

1) Crystalline Size of Particles: The average particle sizesof nano-crystalline achieved by XRD results were calculatedby the Scherer’s equation as follows [25].

D = κλ

βcosθ(1)

where the shape factor κ is 0.9. Respectively, λ, β and θ areX-ray wavelength, full width of the diffraction line at the halfof maximum intensity (FWHM) and the Bragg angle. Basedon (1), the average crystalline size was yield as 11.8 nm,5.53 nm and 5.3 nm for La2O3/SnO2, 1 wt. % Pt/ La2O3/SnO2,and 3 wt. % Pt/ La2O3/SnO2 sensitive powder , respectivelycalcinated under 750 °C.

2) Sensitivity: The sensitivity of fabricated sensor can becalculated by the following equation [26].

S% = Ra − Rg

Rg× 100 (2)

where Rg is the resistance of sensing layer can be measuredacross electrodes when the CO2 is injected to the chamber andRa is represent this resistance in fresh air. However, it mustbe noted that the electrical resistance of the sensing elementsinfluenced by the heater’s temperature [27], [28].

IV. RESULTS AND DISCUSSIONS

The XRD pattern of La2O3/SnO2 thick film and the atomicpositions of the sample are shown in Fig. 2. This figure

Fig. 2. X-ray diffraction pattern of the La2O3/SnO2 thick film.

indicates that the maximum picks of this sample are locatedat 26.66°, 33.94°, 38°, 39.02°, 42.66°, 48.53°, 51.84°, 54.83°,57.89°, 61.95°, 64.80°, 66.03°, 71.34°, 78.78° which arematched with the Joint Committee on Powder DiffractionStandards (JCPDS) files of 98-000-8285, and 98-010-456.Analyzing the XRD pattern has shown that the main phasecorresponds to SnO2 crystal structure. This is caused by thepriority issue of SnO2 percentage (98wt.%) to La2O3 (2wt.%).

This result were analyzed for other two samples withaddition of platinum.By increasing the Pt percentage, peakposition became lower and line breeding at half maximumvalue of intensity became wider. Comparing the size of thepure SnO2 sensitive powder, which was used in the formerstudies [26] with the crystalline size of SnO2 mixed withLa2O3 and Pt in this work, indicates that adding lanthanumoxide (La2O3) and platinum material leads to reduce thesize of tin oxide (SnO2) crystals. The gas sensor’s electricalproperties were significantly improved by minimizing thecrystalline size of the sensitive powders, as it was expected.This improvement has happened due to the enlargement ofthe cubic surface area of the sensitive materials. Therefore,more ions have the chance of combination with the small–sized crystalline as the connection surface is increased.

The surface morphologies of the three thick film sensitivepastes, sintered at 750 °C were observed by field emis-sion electron microscopy (FESEM) operated at a voltageof 16.5 KV.

Fig. 3(a) shows the granular structure with a hexagonalfeature for La2O3/SnO2 thick film, on the surface of fabri-cated sensor. Based on this exhibited result, the dimensionaldistribution of printed sensitive paste on the alumina substrateis almost uniform. Moreover, the composition of sensitivepowder is also homogeneous. This can assist to make amore reliable data analysis by minimizing uncertainties andundesirable errors during the sensitivity calculation.

Fig. 3(b) and 3(c) show the morphologies of 1 wt. %and 3 wt. % Pt-doped La2O3/SnO2 thick films respectively.As indicated in these figures, in both samples the distrib-utions of Pt dopant were almost uniform. Furthermore, thecomposition of sensitive powders at the surface of gas sensor


Fig. 3. (a) FE-SEM image of the screen printed La2O3/SnO2 thick film on the alumina substrate. (b) FE-SEM micrograph of the La2O3/SnO2 thick filmdoped with 1wt. % Pt. (c) FE-SEM micrograph of the La2O3/SnO2 thick film doped with 3wt. % Pt. (d) EDX image of the screen printed La2O3/SnO2,La2O3/SnO2/ 1 wt. % Pt, La2O3/SnO2/ 3 wt. % Pt thick film on alumina substrate

were homogeneous. The shapes of samples for 1 wt. % and3 wt. % Pt/ La2O3/SnO2 thick films on the surface of fabri-cated sensor can be observed in these figure. It can be seenthat, increasing of Pt percentage would affect the sizes ofparticles and make them smaller. Moreover, with high level ofPt, shapes of samples tend to elongated and hexagonal shape.

The energy–dispersive X–ray spectroscopy (EDX) gives anidentification, weight and atomic percentage of La, Sn, O, Ptelements. The elemental composition result of all thick film

sensitive paste are shown in Fig. 3(d). Analysis of EDX indi-cates that the matrix contains Sn, O, and La with the atomicpercentages of 22.81, 76.84, and 0.35%. Respectively, theweight percentages are 67.95, 30.85, 1.21%. This infers thatthe screen printed La2O3 thick film is a non–stoichiometriccompound. Stoichiometry has an important influence onfilm morphology. In fact, non–stoichiometry of particles canchange the position of equilibrium. This leads to make thedynamic exsolution particles easily, which became feasible


Fig. 4. Parts of the fabricated thick film La2O3/SnO2 gas sensor. (a) Heater.(b) Electrodes. (c) Sensing layer.

by adding oxides and metallic nano particles or a mixture ofboth [27].

The EDX spectrum for La2O3/SnO2/ 1 wt, and 3 wt. % Ptshows a homogeneous distribution of La and Pt in to SnO2. Forthe sample with 1 wt . % Pt first peak of La and Pt observedin 1.1 and 1.7 keV, respectively. While the highest peak ofLa and Pt are located at 4.3 and 1.6 keV, subsequently. Themost significant peak of Sn identified around 3.6 keV. For thesample with 3 wt . % Pt,first peak of La and Pt were locatedat 4.1 and 2 keV, and the significant peak of Sn are identifiedat 3.5 keV.

A. Gas Sensor Structure

The sensor with dimensional size of 8.75 × 5.5 mm wasequipped which is including a platinum (Pt) heater. This heatercan control the working temperature of the sensor. Control-ling the operational temperature can provide a desirable heatfor activation of sensitive material. This activated sensitivematerial is always facing with gas molecules. Electrodes asa part of sensing element of the sensor were made as twocomp–shaped forms, which are placed claw–to–claw, in frontof each other. This proposed configuration can minimize thesensitive material resistance of fabricated sensor by increasingthe contact area of electrodes with the sensitive material. Firstof all, the heater element was printed on the alumina substrate.Next, the electrodes were aligned on other side of the aluminasubstrate. Finally, the sensitive layer was covered electrodeswith the local feature size of 5.5 × 5.5 mm. Fig. 4 showsall parts of the fabricated sensor that includes the heater,electrodes, and the sensing layer.

B. Sensitivity to CO2

While the sensitive layer was heated at the operationtemperature of about 225◦C, based on the amount of theCO2 gas concentration which was existing inside the testchamber, the voltage across the sensing electrodes was sig-nificantly changed. As a result, depend on sensing the amountof CO2 gas, the resistance of the sensing layer was decreased,and the sensitivity increased.

The relation between the sensitivity and concentrationof CO2 gas when the concentration was changed from0 to 1000 ppm in operation temperature of about 250 °Cis shown in Fig. 5. It is observed that the sensitivity of the

Fig. 5. Relation between CO2 gas concentration (ppm) and the sensitivityof thick film La2O3/SnO2 thick film sensitive layer at operation temperatureof 225 °C.

La2O3/SnO2 thick film to CO2 gas exhibits a positive correla-tion with increasing the ppm value of CO2 gas. The optimal fitto data points which were extracted from testing results of thesensor’s sensitivity, in different CO2 concentration, has showna linear behavior with the coefficient of determination (R2)of 0.9468. Therefore, we are suggesting the linear equation asan approximate mathematical model with the slope of 0.002and the offset of 0.225 % for modeling the behavior of thefabricated CO2 gas sensor as follows.

S%(C O2) = 0.002 C O2 + 0.225% (3)

where S is the percentage of the sensing layer’s sensitivity, andC O2 represents the amount of CO2 concentration in ppm.

In this experiment, the CO2 sensing mechanism,which is based on the electrical conductivity variationof Pt/La2O3/SnO2 thick film, is controlled by the CO2 gasspecies and the amount of the chemisorption of oxygen onthe surface, at the operation temperature of 225 °C. As thescreen printed sensitive paste on the alumina substrate wasporous and non-stoichiometric. Therefore, on the surface ofthe thick film, the oxygen is chemisorbed and electrons aretransferred from the conduction band to chemisorbed oxygenatoms.

This results into the formation of oxygen species(O2−, O−, 1

2 O2), the potential barrier at grain boundaries andthen formation of depletion layer. Moreover, when the thickfilm sensitive layer is exposed to the CO2 gas, the chemisorbedoxygen is removed by oxidizing because of the CO2 andcaptured electrons from the bulk, when they are injected intothe conduction band again. Therefore, in this case, the heightof barrier can decrease and as a result the conductivity willbe increased.

According to received result from many different studies,the stability and sensitivity, and the electrical conductivity ofmetal oxide based gas sensors increase with the addition of asmall amount of Pt to sensing material. The Table II shows thecomparison between the performance of all fabricated sensorsin this work with the existing sensors which are reported inother researches. The results from this research show that thesensitivity of sensor based on La2O3/SnO2 increased with the


TABLE II

COMPARISON BETWEEN SENSITIVITY OF FABRICATEDSENSORS WITH THE EXISTING SENSORS

addition of Pt percentage at the same operation temperatureof 225 °C.. The results illustrates the minimum value ofPt percentage which leads to maximum sensitivity wasattributed to 3 wt.

V. CONCLUSION

In this work, Pt/La2O3/SnO2 thick films were preparedby using screen printing method. These thick films werecharacterized by using XRD and FE-SEM coupled with EDX.The FE-SEM result for each sample, after the ball–millingprocess, has shown a granular structure with the hexagonalfeature and the uniform dimensional distribution.

The CO2 gas sensing properties were investigated at dif-ferent gas concentrations form 0 to 1000 ppm under the sameoperation temperature of about 225 °C. The La2O3/SnO2 with3 wt. % Pt film exhibits an excellent CO2 gas sensing proper-ties, even the applied operation temperature was approximatelyabout two times lower than the employed temperature inconventional sensors. Moreover, it was shown that the screenprinted 3 wt. % Pt /La2O3/SnO2 thick film can be reliablyused to monitor the concentration of CO2 over the range of100 ppm. A positive correlation was observed between thesensor’s sensitivity and increasing the CO2 concentration from100 up to 1000 ppm. Finally, in order to model the behaviorof the fabricated sensor, an approximate mathematical modelwas suggested.

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Maryam Ehsani was born in Isfahan, Iran, in 1982.She received the B.Sc. degree in telecommunica-tion engineering from Islamic Azad University, Iran,in 2006, and the M.Sc. degree from Univeristi PutraMalaysia in 2014. In 2009, she joined the Depart-ment of Electrical and Computer, Foulad Instituteof Technology, as a Lecturer. Since 2012, she hasbeen a member of the IEEE Advancing Technologyfor the Institute of Electrical and Electronic Engi-neering. She was a Researcher with the Departmentof Electrical and Information Technology, Technical

University of Darmstadt, in 2015. Her area of research interest includesnanotechnology, microelectronics and semiconductor engineering, sensors,sensing, and bioelectronics.

Mohd Nizar Hamidon received the B.Sc. degree inphysics from Univesiti Malaya, Malaysia, in 1995,the M.Sc. degree in microlelectronics from Univer-siti Kebangsaan, Malaysia, in 2001, and the Ph.D.degree in electronics and electrical engineering fromthe University of Southampton, U.K., in 2005.Hejoined Universiti Putra Malaysia (UPM) after hisB.Sc. study with the Matriculation Center for fiveyears before became an UPM Engineering FacultyMember in 2000 until now, where he was in chargeof research program at the department and faculty.

He is currently an Associate Professor with the Electrical and ElectronicEngineering Department and the Deputy Director of the Institute of AdvancedTechnology with UPM. Due to his outstanding research activities, UPMhave appointed him as the Head of the Functional Devices Laboratory,Institute of Advanced Technology in early 2012, where he was the DeputyDirector. His research is primarily concerned with the study of electronic andmicroelectronic devices, including the materials and the systems. Specifically,he has contributed significantly to the development of gas sensor systemand sensor system for wireless applications. His research has been primarilyfunded by the Ministry of Science, Technology and Innovation Malaysia,the Ministry of High Education Malaysia, and university internal funding.He is also involved in consultancy work for the Ministry of Information,Communication, and Culture Malaysia to the implementation of WSN-basedstructure and infrastructure monitoring system and also e-halal monitoringsystem. He has authored over 100 technical papers and a few book chaptersrelated to his research area. He has given many lectures, seminars, and invitedtalks at universities, research institutions, and international conferences, andhas served as a reviewer for several international conferences and journals.He has been the Organizing Chair and Technical Member for several IEEEconferences and at the moment as a Chapter Chair for the IEEE ElectronDevice Malaysia Chapter.

Arash Toudeshki received the Diploma degree inelectronics from Isfahan Polytechnics School, Iran,in 1994, the B.Sc. degree in electrical engineer-ing from Islamic Azad University, Iran, in 2000,and the M.Sc. and Ph.D. degrees from UniveristiPutra Malaysia, in 2010 and 2013, respectively.Since 2012, he has been a member with the Centrefor Advanced Power and Energy Research, Uni-veristi Putra Malaysia. Since 2015, he has beena Post-Doctoral Research Associate with the Cit-rus Research and Education Center, Department of

Agricultural and Biological Engineering, University of Florida, USA. Hehas also developed or collaborated in several projects for many countriesaround the world. His area of research interest includes study on the energyand plasma, ignition systems, voltage multipliers, electrostatic, electron gun,vacuum and cathode ray tubes, particle accelerators, X-ray, ultraviolet lightsensing, laser, sensors, radio frequency-based wireless charging and energyharvesting, effects of high frequency and high-voltage on human body, ohmicheating, microwave and induction heating, design of high-voltage pulse-generators, power supplies, vibration, acceleration analysis, image processing,and spectrophotometry.

M. H. Shahrokh Abadi received the ElectronicEngineering degree in 1993, and the M.Sc. and Ph.D.degrees in electronics engineering from the Univer-sity of Putra Malaysia, in 2007 and 2010, respec-tively. Three years later, he was hired by the NationalIranian Copper Industries Company (NICICo) as anExpert and soon after became the Supervisor ofthe Electrical and Instrumentation Division with theConcentration Department, NICICo, for five years,and then he resigned from his job in 2005 to continuepost-graduate education. He joined Hakim Sabzevari

University, Sabzevar, Iran, as an Assistant Professor, in 2012. He is interestedin semiconductor materials and devices: analysis, design, and fabrication. Heis an expert in MOS-chemical sensors. He is currently working on lab-on-tagfor detection of food spoilage based-on RFID, high-k properties of La(1-x)Hf(x)O3: Raman and IR spectroscopy, and piezoelectricity properties ofSiO2 extracted from rice husk ash.

Sarah Rezaeian (M’14) was born in Tehran, Iran,in 1984. She received the B.Sc. degree in computerscience software engineering from Allame MohadesNoori University, Iran, in 2007, and the M.Sc. degreein smart technology and robotics engineering fromUniversiti Putra Malaysia in 2015. Her focus ison electronic nose, autonomous robots, and neuralnetworks.

Documents

CO 2 Gas Sensing Properties of Screen-Printed La 2 O 3 /SnO 2 Thick Film