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Sensors and Actuators B: Chemical
j o u r n a l ho me p a g e :w w w . e l s e v i e r . c o m /l o c a t e / s n b
Alteration of pore size distribution by sol–gel impregnation for dynamic range and sensitivity adjustment in Kelvin condensation-based humidity sensors
F. Hossein-Babaei
a,∗, S. Rahbarpour
baElectronicMaterialsLaboratory,ElectricalEngineeringDepartment,K.N.ToosiUniversityofTechnology,Tehran,Iran
bElectronicEngineeringDepartment,ShahedUniversity,Tehran159-18155,Iran
a r t i c l e i n f o
Articlehistory:
Received21May2013
Receivedinrevisedform29August2013 Accepted7October2013
Available online xxx
Keywords:
Relativehumidity Humiditysensor Dynamicrange Poresizedistribution Titaniumdioxide Sol–gelimpregnation
a b s t r a c t
Ithasbeentheoreticallyestablishedthatthedynamicrangeofsensitivityinporousdielectricceramic- basedresistiveorcapacitivehumiditysensorsismainlydeterminedbytheopenporesizedistributionin theirsensingpallets.Here,wedirectlyapplytheconceptonceramicresistivehumiditysensorsandutilize theresultsfortheexperimentalverificationofthetheoreticalmodel.Theopenporesizedistributionina numberofidenticaltitaniumdioxidepallets,fabricatedbythesinteringoftheslip-castpowderat1073K, ismodifiedintwodifferentdirections:(a)impregnationwithtitaniumtetraisopropoxide,followedbya heattreatmentat773Kincreasestheproportionofthefinerporesand(b)re-sinteringtheoriginalpallets at1223Kclosesthefinerporesandsubstantiallyshiftsthedistributiontowardslargerporedimensions.
Sensitivitymeasurementresultsareconsistentwiththetheoreticallyestablishedconcept:increasingthe populationoflargerporesheightensthesensitivitytohighrelativehumidity(RH)levelsandshiftsthe dynamicrangeofthepalletsfromtheoriginal20–85%to50–95%RH.Onthecontrary,increasingthe proportionofthefinerporesinthemicrostructureoftheceramicpalletenhancesthesensitivityatthe lowerRHrange,shiftingthedynamicrangeofthesensortothe2–25%RHrange.
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
Thelaboratory,industrial,anddomesticapplicationsofporous solid-basedresistive and capacitive humidity sensorsare wide spread. In the most common type of these sensors, the elec- tric conductivity and/or the dielectric constant of a porous ceramicorpolymerpalletchanges duetotheadsorptionofthe watermoleculestoitseffectivesurface.Thesechangesare,then, translated torelative humidity fluctuations in thesurrounding atmosphere[1].Asaresult,theoperationmechanismandthequal- ityfactorsofthesedevicesarestronglydependentontheprocessof watermoleculesdiffusionintotheopenporesoftheporouspallet andtheirabsorptiontotheporewalls.Therelationshipbetween theporeradiusandwateradsorptionmechanisminaporoussolid hasbeentheoreticallyestablishedmorethanacenturyagobyLord Kelvin:
rk= 2M
RTln(Ps/P) (1)
∗Correspondingauthor.Tel.:+982188734172;fax:+982188768289.
E-mailaddresses:[email protected],[email protected](F.Hossein-Babaei), [email protected](S.Rahbarpour).
wherein,M,andarethemolecularweight,densityandsurface tensionofwater, respectively.Pis thepartialpressureofwater vaporinthesurroundingatmosphereandPsisthesaturationpres- sureof water in thesame ambientconditions. Kelvinequation hasbeenverifiedexperimentallybytwodifferentopticalobserva- tiontechniqueswhichfacilitateddirectobservationofthesurface adsorbedwaterlayers[2,3].
Based onthenatureofthe poroussolidused forpallet fab- rication,humidity sensor elementsaredivided intothree main categories of ceramics, polymer and electrolyte [4,5]. Ceramic palletsareofhigherphysicalandchemicalstabilitiesandareadvan- tagesfromtheviewpointofmanyqualityfactors:theyareoflonger lifetimes[6,7],providemorereproducibleRHmeasurementresults [8],canbeappliedforwatercontentmeasurementsatelevated temperatures[9],andcanberecoveredafterpoisoninginacon- taminatedenvironmentbythermalcleaning[6].Bulk[10,11]and thinfilm[12,13]ceramicelementsarebothutilizedforpalletfab- rication,butinallconfigurationsthesensingmechanismisbased onthemeasurementofthehumidity-sensitiveconductivityand/or dielectricconstantoftheceramicelement.
Humiditysensitiveceramicpalletsaremostlymadeofoxide- basedceramicdielectricsandwidebandgapsemiconductorssuch asTiO2[14–16],SnO2[17,18],ZnCr2O4[19,20],Al2O3[21,22]and MgCr2O4[23,24].Thephysicalpropertymonitoredinthemajority 0925-4005/$–seefrontmatter© 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.snb.2013.10.032
of these pallets is the electrical conductivity ()of the pallet, whichincreaseswiththeRHlevelinthesurroundingatmosphere.
Inselectingthepalletmaterial,emphasisisonhavinganefficient physical interaction with the water vapor in the atmosphere andalow,buteasilymeasurable,palletconductanceatzeroRH.
Theformercriterionismainlylinkedtothemechanismofwater layerformationontheeffectivesurfaceofthesolid.Theefficacy ofthis mechanism isquantitatively statedby thecontactangle betweenthesolid(metaloxide)andtheliquid(water)phases.A close-to-zerocontactanglemakesthematerialsuitableforpallet fabrication[25].Thelattercriterion,however,placesalimitonthe dryconductivityofthematerial,asahighroomtemperaturedry electricalconductivitycancovertheconductivityincreasedueto thewatervaporadsorption,particularlyatlowRHlevels.Thelower conductivity limit is usually dodged by appropriate electrodes shapeandsize[26]designedtobringthedeviceconductanceinto theeasy-to-measurerange.
Despite their many advantages quality factors, the dynamic rangeofnoceramicpalletaffordsfullRHmeasurementrange.A singlepallet isofacceptablesensitivityonlywithinaportionof the0–100%RHrange;abovethisdynamicrangethesensorissat- uratedandbelowthisrangethesensitivitydecaystounacceptably lowvalues.Inthesesensors,accordingtoKelvinequation,awider dynamicrangeisassociatedwithabroaderporesizedistribution pallet[1,27,28].Sucha palletshouldholdanoptimum blendof poresrangingfromafewnanometerstoseveralmicronsindiam- eter.Indeed,porosity,poresizedistributionandporemorphology ofthe ceramicpallet affectmany other qualityfactors,suchas responseandrecoverytimes,ingasandhumiditysensorsasthey controltheprocessofmoleculardiffusionoftheanalyteintothe palletstructure,aswell[29,30].Researchondesignandfabrica- tionofsolidswithspecifiedporesizedistributionforsensingat predeterminedRHrangesorbroadeningofthedynamicrangeofa particularclassofRHsensorsisstillgoingon[31].Atthepresent stateoftheart,coveringthefullRHrangewithasinglepalletis impractical[32].
TheRHdependenceofconductivityinporoussolidshasbeen thesubjectofnumerousinvestigations[33,34],andquantitative relationshipsbetweentheporesizeand thecapillarycondensa- tionofthewatermoleculeshasbeentheoreticallydevelopedsince asearlyasyear1958[27].ThemodelsuggeststhatastheRHin thesurroundingatmospheregoesdown,thecondensationofwater moleculesonthesolidsurfacerequiresfinerpores.Yamazoeetal.
haveanalyticallypresentedageneralmodelforthisrelationship, whichpredictsaclearrelationshipbetweentheporesizedistri- butionin thepallet structure and thedynamic range of itsRH sensitivity[4].Thepredictionsofthismodelhavebeenverifiedby thefabricationandcharacterizationofdifferentpalletsofdifferent porositylevelsandporesizedistributions[28].Here,forthefirst time,wearereportingthemodificationoftheporesizedistribution ofaspecifichumiditysensorceramicpalletwithdifferentmeansin differentdirectionsandobservethevariationofthedynamicrange ofthesensor.TheexperimentalworkiscarriedoutonTiO2whichis oneofthemostthoroughlyinvestigatedwidebandgapoxidesemi- conductorsutilizedforhumiditysensorpalletfabrication,aswell [35].Acomparisonofthesensorcharacteristicsbeforeandafter poresizemodificationclarifiedthechangesoccurredonthesensor dynamicrange.Weshowthatthesevariationsareconsistentwith thepredictionsofthepreviouslypresentedmodel[4].
2. Experimental 2.1. Samplepreparation
ThematerialusedforceramicpalletfabricationisTiO2powder (MERCK1.00808.1000) usedaspurchased fromthevender.The
Fig.1. TheXRDpatternobtainedfromthetitaniumoxidepowderusedforpallet fabrication;thepatterncontainsanatasepeaksonly.
resultofXRDexamination,giveninFig.1,revealedthatthematerial isofanatasephase.Noadditive,dopantorbinderwasintroducedto thepowderduringthepalletfabricationprocess.Aviscousslipwas preparedbytheadditionof40wt%distilledwatertothepowder.
Theslipwasdroppedas∼12mgdropletsontotheclosestpoint betweentwounparallelfine,d=60m,platinumwires,theendsof whichhadbeensparkweldedtofourrefractorymetalpostssecured inasegmentofalumina(Fig.2(a)).ThedistancebetweenthetwoPt wiresis1mmasmeasuredattheirclosestpoint.Theactualinter- electrodedistanceoccurringwithintheceramicbeadsproduced, measuredafterdryingandsintering,is∼0.5mmasobservedonthe brokenbeads.Thedropletformedasphereofslipsuspendingfrom thePtwires,whichwasdriedatroomtemperatureandformedan approximatelysphericalbead(Fig.2(a)).
ThedriedTiO2ceramicbeadalongwithitsall-refractorysupport structurecanentirelybeplacedinthefiringfurnace.Thismethodof samplefabricationpreventedthelooseninganddeteriorationofthe Pt–TiO2contactsbyunavoidablemovementsduringtheforming, dryingandsinteringprocesses.Drybeadsaresinteredat1073K for30mininaSiC-muffledelectricfurnaceinairandareleftinthe switchedofffurnacetocooldownovernight.Thephotographand aSEMcloseupofthesampleproducedareshowninFig.2(a)and (b),respectively.Thesamplespreparedaccordingtothisprocess arereferredtoasNsamples.
Asecondsetofthesamples,referredtoSsamples,areprepared byimpregnatingtheNsampleswithtitaniumdioxidesolprepared basedontitaniumalcoxide.Thedetailsofthemethodutilizedfor thepreparationofthealcoxidesolutionanditsconversiontoasus- pensionofTiO2nanoparticlesisgiveninRef.[36].Forimpregnation, anNsampleissoakedwithasoldropletofapredeterminedvol- umeproducedatthetipofaliquid sampler.Thevolumeofsol isdeterminedbasedonthevolumeoftheopenporeswhichare intendedtobefilledwiththesolliquid.Theimpregnatedsamples aredriedatroomtemperatureand,subsequently,annealedat773K inair.Theannealingprocessconvertstheresiduesofthedriedsolto TiO2nanoparticleswhichprecipitatewithintheopenporesofthe palletandmodifyitspore-sizedistributionbydividingthelarge micron-sizeporesintoanumberofnanopores.Asaresult,Ssam- ples,comparedtoNsamples,areofloweroverallporosity,buttheir poresizedistributionextendsdeeperintothenanoporeregion(see below).
Athird setof samples,referredtoasL samples,isprepared byre-sinteringanumberoftheNsamplesat1223Kforanother 30min.AlthoughLsamplesareoflowertotalporosity,thegrain growthduringre-sinteringleadstolargergrainsand,evidently, reduce the population of the smaller openpores. Typical SEM
Fig.2. Thephotographofthefabricatedceramicbeadhumiditysensor(a)andthe SEMmicrographofatypicalsamplefiredat1073K(b).
micrographsobtainedfortheTiO2beadsinN,S,andLsamplesare giveninFig.3(a)–(c),respectively,indicatingthattheporosityand themorphologyoftheporeshavesignificantlyalteredbysol–gel impregnationintheSseriesandover-sinteringtheLseries.
2.2. Characterization
Theapparent density ofthe ceramic pallets is measuredby utilizing standard weighing and immersion techniques (ASTM D7263). This parameter is measured on dummybead samples accompanyingN,SandLsamplecategoriespreparedandprocessed via identical fabrication routes. Dummy samples are not con- nectedto wires and these standard tests could becarried out withoutbreaking which can introduce additional errors in the results.Theporosityofeachsamplecategorywasthencalculated bycomparingitsapparentand bulkdensities.Theeffectivesur- facesofthepowdereddummysamplesaredeterminedbynitrogen adsorptionmeasurementsusing Belsorp-miniIIsystemat 77K.
Obtainingreliableporesize-relatedinformationfromtheobtained gasadsorptiondataishamperedbythetype-IIInitrogenadsorption
Fig.3. TheSEMmicrographsofthefabricatedtitaniumdioxidebeadsof(a)N(a),S (b),andL(c)types.
isotherm[37]observedforallthesamplecategories.Theresultsof density,porosityandeffectivesurfacemeasurementsarepresented inTable1,indicatinghigherbulkdensityandlowertotalporosity valuesfortheSandLsamplescomparedtothoseofNsamples.The magnitudesofbothdensityandporositychangesinSsamplesare consistentwiththeamountsofsolidTiO2introducedintothebulk bythesolimpregnationandsubsequentthermalannealing.Incase
Table1
Physicalspecifications ofthethreesamplecategoriesfabricated.Thelasttwo columnsarebasedontheresultsofnitrogenadsorptionmeasurementsat77K.
Sampleclass Density(g/cm3) Porosity(%) Totalarea (m2g−1)
Totalporevolume (cm3g−1)
N 1.4±0.1 70 7.647 0.51
S 1.7±0.1 60 8.086 0.47
L 2.5±0.1 40 2.676 0.30
Fig.4. TheXRDpatternsobtainedforN(a),S(b)andL(c)samples.
ofLsamples,however,bothchangesareowingtotheextraphysical shrinkageandfinerporeclosurewhichoccurduringre-sinteringat 1223K.
TheXRDpatternsobtainedforN,LandSsamplecategoriesare giveninFig.4(a)–(c),respectively.WhilethestartingpowderTiO2is ofanatasephase,allsamplecategoriesareanatase-rutilemixtures.
ThelatterphaseisthemorestablephaseofTiO2andisproduced fromanataseattemperaturesabove873K;Lsamplescontainmore rutileduetothehigherre-sinteringtemperatureutilized.Poresize distributionswereestimatedbasedoncomparativelineaveraging amongthedummysamplesforsizeandpopulationoftheporeson theSEMmicrographsobtainedfromtheasbrokensurfacesofthe differentdummysamplessimilartothoseshowninFig.3(a)–(c).
TheresultsaregiveninSection3.
Theconductanceofeachsamplesensor,measuredbetweentwo electrodewires,isobtainedatdifferentsurroundingRHlevelsat 298±0.2K.For this measurement,thesample ismounted ona probewhichcanbeinsertedintoachambercontainingairwith apredeterminedRHlevel.Theexperimentalsetupispresentedin Fig.5.Thetemperatureattheouterchamberiscontrolledusing
Fig.5.Theschematicsoftheexperimentalsetup.
(c)
0 50 100 150 200 250 300 350 400 450 500 0
20 40 60 80
Pore size (n m)
Vol (% )
Pore size (n m)
0 50 100 150 200 250 300 350 400 450 500 0
20 40 60 80
Vol (% )
(b) (a)
0 50 100 150 200 250 300 350 400 450 500 0
20 40 60 80
Pore size (n m)
Vol (%)
Fig.6. Theestimatedpore-sizedistributionsofsampleclasses(a)N,(b)S,and(c)L.
asystemcomprisingaPT100temperaturesensor,aPIDcontroller connectedtoadistributedfinewireheatingelementonthecham- berwhichstabilizesthetemperatureinthechamberat298±0.2K.
Tominimizetheelectrode-ceramicconnectiondeteriorationdue totheelectrochemicalcorrosion,conductancemeasurementswere carriedoutat17Hz.Atthisfrequency,thecapacitiveadmittance ofthesampleandparasiticcapacitorsparalleltothesampleare insignificantcomparedtoitsconductance.Closedchambersofdif- ferentRHlevels,intherangeof2–95%,wereobtainedbyinjecting predeterminedvolumesofdistilledwaterintothedryair(RH=2%) chamberusinga micro-sampler.Theinjectedwaterwasevapo- ratedtoobtainthespecifiedhumiditylevelinside thechamber.
0 20 40 60 80 100 0.0
0.5 1.5 2.0 2.5 3.0x 10-7
RH (%)
Conductance (S)
S
N L
At 298K
1.0
Fig.7.Theelectricalconductanceofthethreesampleclassesmeasuredinairat differentRHlevels.
ThestableRHlevelsweremonitoredbyacommercialhumidity sensor(HIH4000)priortoeachmeasurement.Theoutputofref- erencesensorwascalibratedinclosedchambersofstandardRH levelsobtainedusingdifferentsaturatedsaltsolutions[38].
3. Resultsanddiscussion
TheporesizedistributionsobtainedforsamplesN,SandLare giveninFig.6(a)–(c),respectively.Theresultsindicatethatcom- paredtoNsamples,Ssamplesareofhigherconcentrationofthe fineopenporeswhilehavingaloweroverallporosity.Thelatteris owingtotheoxideparticlesgrownfromthesolmaterialdriedand decomposedwithinthelargerpores.Thesameprocessincreases thepopulationofthefineporesowingtothepartialfillingofthe largerporesand thefactthatthesolid aggregatesproducedare composedofnanoparticlesandincludenanopores.Thesituation istheotherwayroundintheLsamples:manyofthefinepores havebeeneliminatedorclosedduringtheexcessivegrowthwhich occurredinre-sinteringleadingtoahigherdensityandlowerover- allporositycomparedtoNsamples.Thesameprocessincreasesthe volumepercentageofthelargerporesofthesamplesasdepicted inFig.3(c).Althoughthepopulationoflargerporesincreased,the netporosity in L samplesis lowerthan that in theoriginal N- samplesduetotheoveralldimensionalshrinkageoccurredduring re-sintering.Thesefindingsareconsistentwiththeexperimental datapresentedinTable1.
PalletconductanceinairwithaspecifiedRHlevel,GRH,ismea- suredatdifferentRHlevels;typicalresultsobtainedforthethree samplegroupsarepresentedinFig.7.Theconductanceofallsam- plecategoriesmeasuredinvacuum(10−5Torr)isbelow10−8Sand, hence,theGRHvaluesgiveninFig.7arealmosttotallyowingto thepresenceofhumidair.EachGRHisrecordedafteralongstay inthespecifiedatmosphere.AccordingtoFig.7,G95%inallsam- plesarealmostequal.Thisisdescribedbasedonthefactthatat close-to-saturationRHlevels,almostalltheporesarefilledwith theliquidandtheconductanceisdefinedbythegeometryofthe electrodes.Onthecontrary,thevaluesobtainedforG2%vary∼100 timesamongthethreesamplecategories.Thisstemsfromthefact thatatlowerhumiditylevels,Kelvincondensationoccursinthe nanometricporeswhichareofverydifferentconcentrationsamong differentsamplecategories.
Priortoeachtransientresponsemeasurement,theG2% ofthe samplewasmeasuredbykeepingthesensorfor30minatRH=2%;
thelowesthumiditylevelutilized.Asuddenexposuretoadiffer- entbut constantRHlevelcausestheconductance ofthesensor
Fig.8. Normalizedtransientresponsesandrecoveriesrecordedforthehumidity sensorsfabricatedbasedonthepalletclassesof(a)N,(b)S,and(c)Ldepictingthe limited,butdifferent,dynamicrangesofthethreesampleclasses.
pallet,G(t),tovarywithtime.Thetransientresponseofthesensor isdefinedas:
X(t)=G(t) G2%
(2) inwhich,G(t)isthetransientconductanceofthesensor.Consider- ingthedifferent,butconstant,valueofG2%foreachpallet,theX(t)
0 20 40 60 80 100 0
10 20 30 40 50 60
RH (%)
SensiƟvity (arbitrary unit)
N
L S
At 298K
Fig.9.ComparisonoftheRHsensitivitiesestimatedbasedontheexperimentaldata giveninFig.8andothersimilargraphs,forthestatedsampleclasses.
profilerelatedtoeachsampleis,withachangeofscale,similarto thatoftherespectiveG(t).Thenormalizedtransientresponsesare presentedinFig.8(a)–(c).
ThesensitivityofthesensoraroundaspecifiedRH,SRHisdefined as:
SRH= dGRH
dRH
RH (3)
DuetothenonlinearityoftheGRH(RH),asshowninFig.7,Eq.
(3)resultsinahumidityleveldependentsensitivity,i.e.ataround RH1,thehumiditysensitivityofapallet,SRH1,canbesignificantly differentfromthatofthesamesensoratRH2.Thesensitivitiesof thedifferentsamplepalletsareestimatedbasedontheGRHvs.RH diagramsshowninFig.7.Theresults,presentedinFig.9,depict thedynamicoperationrangesofthethreedifferentsensorclasses, indicatingthatnoneoftheN,S,andLsamplecategoriescancover thecompletehumidityrangewithitsdynamicrange.Theoriginal NsamplespresentamediumRHdynamicrangecoveringfrom20%
to80%.InLsamples,thedynamicrangeshiftstowardshigherRH rangeof60–95%,whiletheS-typepalletsdemonstrateashiftof dynamicrangetolower2–25%RHrange.
Foreachsample,theresponsetime,thetimerequiredforG(t)to ascendfrom5%to95%ofitssteady-stateresponselevel,afterasud- denexposuretoahigherRHsurrounding,andtherecoverytime, measuredinareversefashionatsuddenRHfalls,weremeasured ontherecordedtransientresponses.Typicalnormalizedresponse andrecoverydiagramsrelatedtothethreedifferentsamplecate- goriesaregiveninFig.10.Thelongerresponseandrecoverytimes observedintheS-samplesareconsistentwiththeexpectedlonger diffuse-inanddiffuse-outtimesofthetargetmolecules[30]into thesesamplesofmoreintricateporetopography.
0 20 40 60 80
0 0.2 0.4 0.6 0.8 1.0 1.2
N L
Time (s)
S
Normalized conductance
Fig.10. Normalizedresponseandrecoveryprofilesofthestatedpalletclasses obtainedatthemidstoftheirrespectivehighsensitivityranges.
4. Conclusion
TheporesizedistributioninanumberofTiO2humiditysensing palletswasaltered in twoopposingdirections. Thisresultedin threecategoriesofsamplehumiditysensorsofidenticalnatures butwithdifferentporesizedistributions.Allthesamplesunder- wenttheassessmentsofmajorsensingqualityfactorsin2–95%
humidityrange.Themeasurementresultsareconsistentwiththe predictionsofthemodelswhichdescribethehumiditysensingpro- cessbyconsideringtheadditionalelectricalconductionintroduced bythenetworkofwaterlayersformedbyKelvincondensationon theeffectivesurfaceoftheporousstructureofthedielectricpallets.
Particularly,thepresentedresultsexperimentallyverifiedthepre- dictedrelationshipbetweenthedynamicrangeofthesensorand theporesizedistributioninhumiditysensingpalletsforthefirst time.
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Biographies
FaramarzHossein-BabaeireceivedtheB.S.degreeinelectronicengineeringfrom Amir-KabirIndustrialUniversity,Tehran,Iran,in1971,andtheM.S.degreein materialsscienceandthePh.D.inelectricalengineeringfromtheImperialCollege, London,UK,in1975and1978,respectively.HehasbeenProfessorofElectronic MaterialsattheElectricalEngineeringDepartmentofK.N.ToosiUniversityofTech- nology,Tehran,Iran,since1980,andhasbeenAdjunctProfessorattheDepartment ofMaterialsEngineering,UniversityofBritishColumbia,Vancouver,Canadafrom 2002to2007.Hehasfoundedanumberofhi-techspin-offcompaniesmostlyactive inthefieldofhightemperatureelectronicmaterialsandtechnology.Hispresent researchinterestsincludeelectricheating,electrophoreticdepositionofelectroce- ramicmaterials,microfluidics,metaloxidegassensorsandartificialolfaction.Prof.
Hossein-BabaeireceivedtheKhwarizmiInternationalAwardforhisoutstandingR andDworkonhightemperaturesystemsin2006.
SaeidehRahbarpourreceivedtheB.S.degreefromAmirKabirUniversityofTech- nology(TehranPolytechnic),Tehran,Iranin2003,theM.S.degreeandPh.D.from K.N.ToosiUniversityofTechnology,Tehran,Iranin2005and2011respectively,all inelectronicengineering.SheiscurrentlyassistantprofessorinShahedUniversity.
Herresearchinterestsincludethephysicsofoxidesemiconductorsandthefabri- cationandassessmentofbothSchottkytypeandchemoresistivegasandhumidity sensors.