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.

vii

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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3

4

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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41

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xii

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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xiii

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