Development of a new single-step process for the production of SnO_1tn2 based gas sensors [Elektronische Ressource] = Entwicklung eines neuartigen einstufigen Herstellungsprozesses für Gassensoren auf SnO_1tn2-Basis / vorgelegt von Thorsten Sahm

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Development of a new single-step process for the production of SnO based gas sensors 2 Entwicklung eines neuartigen einstufigen Herstellungsprozesses für Gassensoren auf SnO Basis 2 D I S S E R T A T I O N der Fakultät für Chemie und Pharmazie der Eberhard-Karls-Universität Tübingen zur Erlangung des Grades eines Doktors der Naturwissenschaften 2007 vorgelegt von Thorsten Sahm Tag der mündlichen Prüfung: 12.07.2007 Dekan: Prof. Dr. Lars Wesemann 1. Berichterstatter: PD Dr. Udo Weimar 2. Berichterstatter: Prof. Dr. Günter Gauglitz Thefirst90%oftheworkneed90%ofthetime.Theresttakestheother90%.Yogi Berra Table of contents 1. Introduction................................................................................................... 1 1.1 Motivation....................................................................................................21.2 Scope of the work ........................................................................................52. MOX sensors: an overview ...........................................................................3 2.1 Sensing materials....................................................................................... 122.1.1SnO ...........................................................................................................................
Publié le : lundi 1 janvier 2007
Lecture(s) : 20
Source : TOBIAS-LIB.UB.UNI-TUEBINGEN.DE/VOLLTEXTE/2007/2938/PDF/DISSERTATION_SAHM_FINAL.PDF
Nombre de pages : 154
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Development of a new
single-step process for the production
of SnO based gas sensors 2

Entwicklung eines neuartigen
einstufigen Herstellungsprozesses
für Gassensoren auf SnO Basis 2


D I S S E R T A T I O N


der Fakultät für Chemie und Pharmazie
der Eberhard-Karls-Universität Tübingen

zur Erlangung des Grades eines Doktors
der Naturwissenschaften

2007

vorgelegt von

Thorsten Sahm




























Tag der mündlichen Prüfung: 12.07.2007
Dekan: Prof. Dr. Lars Wesemann
1. Berichterstatter: PD Dr. Udo Weimar
2. Berichterstatter: Prof. Dr. Günter Gauglitz










Thefirst90%oftheworkneed90%ofthetime.
Theresttakestheother90%.
Yogi Berra





Table of contents

1. Introduction................................................................................................... 1
1.1 Motivation....................................................................................................2
1.2 Scope of the work ........................................................................................5
2. MOX sensors: an overview ...........................................................................3
2.1 Sensing materials....................................................................................... 12
2.1.1SnO ............................................................................................................................132
2.2 SnO – gas interaction............................................................................... 152
2.2.1Oxygen........................................................................................................................18
2.2.2Water...........................................................................................................................20
2.2.3Methane ......................................................................................................................21
2.2.4Carbonmonoxide......................................................................................................21
2.2.5Ethanol .......................................................................................................................22
2.3 Effect of doping......................................................................................... 23
2.4 Synthesis of metal oxides.......................................................................... 24
2.5 Deposition methods.................................................................................. 26
2.5.1Vapourdeposition.....................................................................................................27
2.5.2Sol$gelbasedmethods ..............................................................................................28
2.5.3Classicalmethodsforthickfilms ............................................................................29
2.6 The role of filters ....................................................................................... 30
2.7 The FSP approach..................................................................................... 31
3. Experimental............................................................................................... 35
3.1 Sensor fabrication ...................................................................................... 36
3.1.1Flamespraypyrolysis(FSP).....................................................................................37
3.1.2Screenprinting...........................................................................................................43
3.1.3Spincoating................................................................................................................45
3.2 Sensor characterisation ............................................................................. 46
3.2.1Scanningelectronmicroscopy(SEM) ....................................................................47
3.3 Sensor performance................................................................................... 47
3.3.1Dcelectricalmeasurements .....................................................................................47
3.3.2Catalyticconversionmeasurements........................................................................49
3.3.3Stabilitytests...............................................................................................................50
3.3.4Simultaneousworkfunctionandresistancemeasurements ................................50
4. Material characterisation ............................................................................ 57
4.1 Powder characterisation............................................................................ 58
4.1.1UndopedSnO ..........................................................................................................582

4.1.2Pt$dopedSnO ...........................................................................................................622
4.2 Directly deposited layer characterisation ................................................. 65
4.2.1Differentlayerthicknesses .......................................................................................65
4.2.2Multilayerdeposition ...............................................................................................68
4.3 Summary.................................................................................................... 72
5. Results & discussion................................................................................... 73
5.1 Feasibility study of FSP material .............................................................. 74
5.1.1Propanal......................................................................................................................74
5.1.2CO...............................................................................................................................76
5.1.3NO .............................................................................................................................782
5.1.4Summary.....................................................................................................................78
5.2 Simultaneous work function and resistance measurements.................... 79
5.2.1COandhumidity.......................................................................................................80
5.2.2Oxygen........................................................................................................................85
5.2.3Summary.....................................................................................................................89
5.3 Influence of deposition method................................................................ 90
5.3.1Temperaturedependency.........................................................................................90
5.3.2Concentrationdependency ......................................................................................92
5.3.3Summary.....................................................................................................................94
5.4 Effect of platinum doping......................................................................... 95
5.4.1LowCOconcentrationrange..................................................................................96
5.4.2HighCOconcentrationrange .................................................................................97
5.4.3Catalyticconversionmeasurements........................................................................98
5.4.4Stabilitytests.............................................................................................................101
5.4.5Summary...................................................................................................................104
5.5 Grain size effect........................................................................................105
5.5.1InfluenceonCOsensing........................................................................................105
5.5.2Summary...................................................................................................................106
5.6 Layer thickness dependency....................................................................107
5.6.1Reproducibility.........................................................................................................107
5.6.2UndopedSnO ........................................................................................................1082
5.6.3Pt$dopedSnO .........................................................................................................1112
5.6.4Summary...................................................................................................................112
5.7 Multilayer sensors ....................................................................................112
5.7.1Dcelectricalcharacterisation .................................................................................113
5.7.2Catalyticconversionmeasurements......................................................................115
5.7.3Filtereffectonselectivity .......................................................................................117
5.7.4Summary...................................................................................................................118
6. Summary & outlook...................................................................................119
6.1 Summary...................................................................................................120
6.1.1Investigation.............................................................................................................120
6.1.2Benchmarking..........................................................................................................122
6.2 Outlook.....................................................................................................122
7. Bibliography...............................................................................................125
List of abbreviations ......................................................................................140
Acknowledgements........................................................................................143
Curriculum Vitae............................................................................................146





1

Introduction





1.1 Motivation....................................................................................................2
1.2 Scope of the work ........................................................................................5





Introduction


1.1 Motivation

Gas sensing in its very rudimentary meaning is simply about finding a qualitative or
quantitative measure of a certain gaseous atmosphere. This is done subconsciously by
everyhumanbeingintheireverydaylife.Forexample,thehumannoseadvisesagainst
eatingspoiltfood.However,inthecourseofindustrialisationandtechnologicalprogress
the need to control toxic or odourless gases increased tremendously as they are key
measurandsin manyindustrialanddomesticenvironments.Thisneedforced engineers
andscientistsatalltimestodevelopsolutionsfortheactualproblemsinthefieldofgas
thsensing.Accordingly,asearlyasinthe19 centuryagasdetectingdevicewasinventedby
thechemistHumphryDavy[1].In1815,hepresentedasafetylampforcoalminesthat
indicatedthepresenceofmethane,whichtogetherwithoxygencouldformanexplosive
gas mixture leading to many disastrous mine accidents at that time. This is an early
example that scientists and engineers are confronted with the needs of society while
performingtheirresearch.Asincourseoftimetheapplicationsbecamemoreandmore
sophisticated,alsosmartsolutionsforthecorresponding gassensing deviceshadtobe
found.

When in the late 1950ies and early 1960ies scientists discovered that the free charge
carrier concentration of semiconducting metal oxides may be altered due to the
interactionwithreactivegases[2,3,4],anewdirectionofdevelopmentforgassensors
wasinitiated.ItwasTaguchiwhobroughtthefirstsemiconductinggassensorsbasedon
metal oxides toanindustrialapplication[5].Sincethen mucheffort hasbeen madeby
both,academicscientistsandindustrytoimprovethisnewkindofuser$friendly,robust
andcheapgassensingdevices.Today,therearevariouscompaniesindifferentcountries
thatcommerciallyproduceanddistributemetaloxidegassensors,e.g.FigaroandFISin
Japan,UmweltsensortechnikUSTandAppliedSensorinGermany,MICSinSwitzerland
orCityTechnologiesintheUK[6,7,8,9,10,11].Thisdevelopmentisareflectionofthe
socio$economicneedsoftheindustrialisedcivilisationandalwayshastofacetheactual
requirements of potential markets. This is one of the main reasons why research and
developmentarestillanongoingdynamicprocess.


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