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UNIVERSITI TEKNOLOGI MALAYSIA
BORANG PENGESAHAN STATUS TESIS'
JUDUL: CONDUCTION MECHANISMS OF. MAGNESIUM T.LUORIDE(MsFa) FILMS
SESI PENGAJIAN: 2005/2006
Saya: TANG CHEW YrN6ruRur BESAR)
mengaku membenarkan tesis (PSIW@* ini disimpan di PerpustakaanUniversiti Teknologi Malaysia dengan syaxat-syarat kegunaan seperti berikut:
1. Tesis adalah hakmilik Universiti Teknologi Malaysia.2. Perpustakaan Universiti Teknologi Malaysia dibenarkan membuat salinan untuk
tujuan pengajian sahaja.3. Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran antara
institusi pengaj ian tinggi.4. +*Sila tandakan (r')
I SULIT
TERHAD
TIDAK TERHAD
(TANDATANGAN PENULIS)
Alamat Tetap:
45A. MELUAI\ K._M. C. tr'LAT.JLN BAI\[ HOCK.93100 KUCHING.SARAWAIC
Tarikh: 5 Mav 2006
(Mengandungi maklumat yang berdarjah keselamatan ataukepentingan Malaysia seperti yang termaktub di dalam AKTARAHSTA RASMr 1972)
(Mengandungi maklumat TERHAD yang telah ditentukanoleh organisasi/badan di mana penyelidikan dijalankan)
P.M. DR KARIM DERAMAN(NAMAPENYELIA)
Tarikh: 5 Mav 2006
Disahkan oleh
PSZl9zl6 @nd.1/97)
CATATAN: * Potong yang tidak berkenaan.** Jika tesis ini SULIT atau TERIIAD, sila lampirkan surat daipada pihak berkuasa/organisasi
berkenaan dengan rnenyatakan sekali sebab dan tempoh tesis ini pedu dikelaskan sebagaiSULIT atauTERHAD.
o Tesis dimaksudkan sebagai tesis bagi ljazah Doktor Falsafah dan Sarjana secara penyelidikan,atau disertasi bagi pengajian secara kerja kunus dan penyelidikan, atau Laporan Projek SarjanaMuda (PSM).
CONDUCTION MECHANISMS OF MAGNESIUM FLUORIDE (MgF2)
FILMS
TANG CHEW YIN
A report submitted in partial fulfillment of the
requirements for the award of the degree of
Bachelor of Science and Education
(Physic)
Faculty of Education
Universiti Teknologi Malaysia
May 2006
"I hereby declare that I have read this thesis and in my opinion this thesis is
sufficient in terms of scope and quality for the award of the degree of Bachelor of
Scienoe and Education (Physic)"
Signature
Supervisor
Date 5 Mav 2006
111
I declare that this thesis entitled o'Conduction Mechanisms of Magnesium Fluoride
(MSF) Film" is the result of my own research except as cited in the references. The
thesis has not been accepted for any degree and is not concurrently submitted in
candidature ofany other degree.
Signature
Narne
Date 5 Mav 2006
: TAI.{G CHEW YIN
iv
Especially to
my most respected Supervisor, P.M. Dr. Karim Deraman,
my beloved Father and Mother and all my friends.
Thanks for all the efforts, guidance, tender support and blessings that shower on me.
v
ACKNOWLEDGEMENT
In preparing this project, I was in contact with many people, researchers,
academicians, and practitioners. They have contributed towards my understanding
and thoughts. In particular, I wish to express my sincere appreciation to my project
supervisor, P.M. Dr. Karim Deraman, for encouragement, guidance, critics and
friendship. I am also very thankful to Vacuum Laboratory’s assistants, En. Mohd
Nazari bin Kamiruddin and Pn. Fadzilah binti Lasim for their guidance, advices and
motivation. Without their continued support and interest, this thesis would not have
been the same as presented here.
I am also indebted to Universiti Teknologi Malaysia (UTM) for funding my
project study. Librarians at Universiti Teknologi Malaysia and Multi Media
University also deserve special thanks for their assistance in supplying the relevant
literatures.
My fellow postgraduate students should also be recognized for their support. My
sincere appreciation also extends to my seniors and others who have provided
assistance at various occasions. Their views and tips are useful indeed. Unfortunately,
it is not possible to list all of them in this limited space. I am grateful to all my family
members.
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ABSTRACT
The purpose of this project is to investigate the direct current conduction
mechanisms of Magnesium Fluoride (MgF2) thin film with different thicknesses.
MgF2 thin film is prepared by vapor deposition method at 10-5 to 10-6 torr in Edwards
E306A coating unit. The thickness of the deposited MgF2 thin film is in the range of
200-400 nm. There are five samples with five different thicknesses. The samples are
sandwiched between Aluminum (Al) electrodes which are of thickness 100nm. The
current-voltage (I-V) relationship of the samples is investigated by using regulated
direct current power supply and Keithley programmable electrometer. There are two
slopes in the log J (current density) versus log V (voltage) graph for each thickness.
Firstly, the slope of the graph is approximately equal to one, where the current is
proportional to the voltage. This is known as ohmic region. Secondly, the slope of the
graph is approximately equal to two, where the current increase proportionally to
square of voltage. This is known as Space-charge-limited current. The transition
voltage can be gotten from the crossing point of the two slopes. Analysis shows that
the transition voltage increases when the thickness increases. The thermally
generated free carrier density (no), 1.59 ×1022 m-3 was obtained.
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ABSTRAK
Tujuan projek ini ialah mengkaji mekanisma konduksi arus terus bagi saput
tipis Magnesium Fluorida (MgF2) dengan ketebalan yang berbeza. Saput tipis MgF2
ini disediakan dengan menggunakan kaedah penyejatan vakum pada tekanan 10-5
hingga 10-6 torr dalam unit penyejak Edwards E306A. Saput tipis MgF2 disediakan
dalam julat ketebalan 200nm hingga 400nm. Terdapat lima sampel dengan lima
ketebalan yang berlainan. Sampel-sampel ini diapit oleh elektrod Aluminium yang
menpunyai ketebalan 100nm. Hubungan ciri-ciri arus dan voltan dikaji dengan
menggunakan sumber kuasa arus terus dan elektrometer Keithley. Terdapat dua
kecerunan pada graf log J (ketumpatan arus) lawan log V (voltan) bagi setiap
ketebalan. Pada bahagian pertama, kecerunan graf adalah lebih kurang sama dengan
satu, di mana arus adalah berkadar terus dengan voltan. Bahagian ini dipanggil
bahagian ohmic. Pada bahagian kedua, kecerunan graf adalah lebih kurang sama
dengan dua, di mana arus adalah berkadar terus dengan voltan kuasa dua. Bahagian
ini dinamakan sebagai cas-ruang-terhad. Voltan transisi boleh dikira daripada titik
persilangan kedua-dua graf yang berlainan kecerunan tersebut. Analisis ini
menunjukkan voltan transisi meningkat dengan pertambahan ketebalan. Kepekatan
pembawa teruja terma (no), 1.59 ×1022 m-3 telah diperolehi.
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TABLE OF CONTENTS
CAHPTER TITLE
TITLE
DECLARATION
DEDICATION
ACKNOWLEDGEMENTS
ABSTRACT
ABSTRAK
TABLE OF CONTENTS
LIST OF TABLES
LIST OF FIGURES
LIST OF SYMBOLS
PAGE
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1 INTRODUCTION
1.1 Introduction
1.2 Objectives
1.3 Scope of Study
1.4 Scope of Report
1.5 Literature Survey
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2 THEORY
2.1 Introduction
2.2 MgF2
2.3 Deposition Techniques of MgF2 thin film
2.4 Vacuum Evaporation
2.5 Band Theory
2.6 Metal-insulator contacts
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2.6.1 Ohmic Contact
2.6.2 Neutral Contact
2.6.3 Blocking Contact
2.7 Conduction mechanisms
2.7.1 Tunneling
2.7.2 Schottky Emission
2.7.3 Space-Charge-Limited Conduction
2.7.4 Poole-Frenkel Emission
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3 METHODOLOGY
3.1 Introduction
3.2 Preparation of Substrates
3.2.1 Substrate Cutting
3.2.2 Substrate Cleaning
3.3 Preparation Of Masks
3.4 Preparation of evaporation source
3.4.1 Preparation of Aluminum evaporation
source
3.4.2 Preparation of MgF2 evaporation source
3.5 Preparation of MgF2 thin film
3.6 Vacuum system
3.7 Measurement of thin film thickness using FTM5
3.8 Measurement of Current- Voltage (I-V)
Characteristic
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4 RESULTS AND DISCUSSIONS
4.1 Introduction
4.2 Thin MgF2 films preparation
4.3 Current-Voltage characteristics measurement
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5 CONCLUSION AND COMENT
5.1 Conclusion
5.2 Comments
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REFERENCES
APPENDIX A
APPENDIX B
APPENDIX C
APPENDIX D
APPENDIX E
APPENDIX F
APPENDIX G
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LIST OF TABLES
TABLE NO.
2.1
2.2
2.3
3.1
4.1
4.2
TITLE
The physical properties of Magnesium Fluoride (MgF2) thin film The dielectric properties of Magnesium Fluoride (MgF2) thin film The evaporation parameters of Magnesium Fluoride (MgF2) thin film FTM5 parameter for evaporation of Magnesium Fluoride (MgF2) thin film and aluminum The thickness of thin MgF2 films The relationship between thickness and transition voltage.
PAGE 7 7 8
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LIST OF FIGURES
FIGURE NO.
2.1
2.2
2.3
2.4
2.5
2.6
2.7
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
TITLE Energy band for (a) insulator, (b) semiconductor and (c) conductor. Energy diagrams showing the Ohmic contact, ψm<ψi
Energy diagrams showing the neutral contact, ψm=ψi Energy diagrams showing the blocking contact, ψm>ψi Tunneling, (a) the possible tunneling in metal-insulator-metal films, (b) tunnel effect at a thick barrier, (c) tunnel effect at a very thin barrier. The possibility of Schottky emission from the metal at negative potential into the conduction band of the insulator. Poole-Frenkel effect at a donor center Line mark on the glass substrate The ultrasonic agitation in ultrasonic cleaner Brandon 3210 The desiccator The three masks as well as their measurements Aluminum evaporation source Molybdenum Boat Deposition of electrodes and thin film on one portion substrate Vacuum system (Model Edwards E306A) Water Pump
PAGE
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3.10
3.11
3.12
3.13
3.14
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
FTM5 thickness measurement instrument Schematic diagram of current-voltage (I-V) measurement The shield with power supply and Keithley programmable electrometer Regulated Direct Current Power Supply Keithley programmable electrometer Current, I versus Voltage, V graph Current density, J versus Voltage, V graph Log J versus Log V graph for thickness 200nm with the transition voltage is 2.14V. Log J versus Log V graph for thickness 250nm with the transition voltage is 3.36V. Log J versus Log V graph for thickness 300nm with the transition voltage is 4.65V. Log J versus Log V graph for thickness 350nm with the transition voltage is 6.28V. Log J versus Log V graph for thickness 400nm with the transition voltage is 8.47V. Log J versus V1/2 graph Transition Voltage versus Thickness graph with the slope of 3.06×1013 volt m-2
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LIST OF SYMBOLS
A - Richardson constant equal to 120 A/cm2 K2
D - Diffusion coefficient
d - Thickness
e - Electron charge
Ec - Energy of the bottom of conduction band
EF - Energy of Fermi lever
Eg - Energy band gap of the material
Ei - Energy form donor level to conduction band
Et - Energy below the conduction band
h - Planck’s constant
J - Current density
Js - Schottky current density
JT - Tunnel current density
JTE - Thermionic emission current density
k - Bolthzmann’s constant
m - Electron mass
Nc - Effective density of state in the conduction band
no - Thermally generated free carriers density
Nt - Shallow traps carrier density
T - Temperature
V - Applied voltage
Vtr - Transition voltage
εi - Insulator dielectric constant
εo - Dielectric constant
θ - Constant
λo - Extended a distance
µ - Mobility
xv
ψB - Metal-insulator work function
ψi - Insulator work function
ψm - Metal work function
CHAPTER 1
INTRODUCTION
1.1 Introduction
Thin films are material layers of thickness less than 1000 nm. A material can
be classified as metal, semiconductor or insulator depends on its electrical property.
In general, thin film can be defined as a film of material from one to several hundred
molecules thick deposited on a solid substrate such as glass or ceramic or as a layer
on a supporting liquid.
Thin film has been widely studied over the years since the time of Faraday (1838)
whose works on metallic coatings through an electrolysis process was first recorded
(K.L.Chopra and I. Kaur, 1983). In 1907, Badeker used thermal oxidation of
sputtered cadmium (Cd) film to prepare a cadmium oxide (CdO) film. It was the
first semi-transparent thin solid film (J.L. Vossen, 1977). After that, many
researches have involved in development of this technology.
Thin film technology utilizes thin film processes to build passive components
used in data-communication, computer, medical, test equipment, power supplies, and
automotive markets. It greatly makes human’s life easier.
2
In this project, conduction mechanisms in thin transparent films sandwiched
between metal electrodes will be investigated. Furthermore, metal-insulator
contacts such as ohmic contact, neutral contact and blocking contact will also be
investigated due to its different thickness. Magnesium Fluoride (MgF2) will be used
as a transparent film. The processes that have been used to deposit transparent film
are thermal evaporation or vacuum evaporation. 1.2 Objectives
The objectives of this final year project are:
1 Preparing the thin transparent films, MgF2 sandwiched between metal electrodes,
aluminum (Al) by using thermal evaporation system.
2 Preparing different thickness of MgF2 samples.
3 Plotting the graph of current, I versus voltage, V.
4 Investigating the conduction mechanisms of MgF2 films. 1.3 Scopes of Study
The content of this project will be based on the scopes, with particular
emphasize on the material properties, deposition technique and direct current
conduction mechanisms. MgF2 will be used as a transparent film. Thermal
evaporation or vacuum evaporation system are used to deposit aluminum electrode
and MgF2 thin film. There are five samples of MgF2 thin films with five different
thicknesses are prepared which are 200nm, 250nm, 300nm, 350nm and 400nm.
Those samples are sandwiched between aluminum (Al) electrodes which are of