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Field Emission Displays (FEDs)
ByByMark Staniford
SS12
18/6/2012 1FED/ Mark Staniford
Content History
Field emission
Field emission displaysField emission displays
Phosphors
Advances
ConclusionConclusion
18/6/2012 FED/Mark Staniford Slide 2
History Field emission was discovered and studied independently from 1880s to 1930s
Fowler‐Nordheim‐equation was developed 1928
A li i d l i f 1930 Application developments ongoing from 1930s
1991 first attempts to develop FEDs were made
2005 Sony started a joint venture with Tex Gate (Field Emission Technologies Inc.))
18/6/2012 FED/Mark Staniford Slide 3
Field emission
Basics
Fowler‐Nordheim‐Tunneling
Field emission from a solid surface into vacuum
Electrons are emitted from an emission tip, by applying electrical currentp y pp y g
Necessary current depends on the Aspect ratio Preferably a long narrow tip with a small curvature radius Preferably a long narrow tip with a small curvature radius
18/6/2012 FED/Mark Staniford Slide 4
Field emission
Applications
Microscopy SEM TEM FIM SEM, TEM, FIM
Electron beam lithographyg p y Field emission lighting Field emission displays
18/6/2012 FED/Mark Staniford Slide 5
Field emission display
Properties
Self emitting display
Direct electron beam
Low voltage device
Emission tips are called “Spind‐tips” when consisting out of metalsp p p g
18/6/2012 FED/Mark Staniford Slide 6
Field emission display
Assembly
Triode assembly
Emission tips werefirstly made out of W or Si (Spind –Tips)
Attempts to use CNTare current
18/6/2012 FED/Mark Staniford Slide 7
Field emission displays
CNT‐FE
Good properties : ‐ low operating voltage ‐ good emission stability‐ long operating life‐ high current density by equal electron distribution
USA & Japan are heavily investigating USA & Japan are heavily investigating
Possible applications: lithography, SEM, TEM, lighting, X‐Ray‐source, microwave generator
Problems are the proccessibility and the costs
18/6/2012 FED/Mark Staniford Slide 8
Cathode
CNT‐FED
Aspect ratio
Chemically and thermally “inert”
Good response time
Energy efficient Energy efficient
18/6/2012 FED/Mark Staniford Slide 9
Comparison
Spindt‐Tips vs. CNT
Requirements Spindt‐FED CNT‐FED
Durability Vanishing on the long term Better in comparisonDurability Vanishing on the long term Better in comparison
Emission density 104‐105 106‐107
Operating voltage “higher” 1 V/µm
Processing CVD or anisotropic etching SWCNT ‐ screen printingMWCNT ‐ CVD
18/6/2012 FED/Mark Staniford Slide 10
Phosphor
Requirements
Fast decay timesPh Phase pure
Thermally stable & low degradation Superior stability against electron bombardmentSuperior stability against electron bombardment Low voltage phosphors Oxides are preferred against sulphides
18/6/2012 FED/Mark Staniford Slide 11
Phosphor
Degradation
Penetration depth depends on the voltage
High surface excitation Leads to a fewer number of excited luminescent centres
Appearance of defects increase on the long termg
18/6/2012 FED/Mark Staniford Slide 12
Phosphor
ExamplesPhosphor Efficacy [lm/W) Colour point [X] Colour point [Y] Colour
SrTiO3:Pr 0.4 0.670 0.329redred
Y2O2S:Eu 0.57 0.616 0.368
Y3(Al,Ga)5O12:Tb 0.7 0.354 0.553green
bg
Y2SiO5:Tb 1.1 0.333 0.582
ZnGa2O4 0.15 0.175 0.186blue
ZnS:Ag Cl 0 75 0 145 0 081
18/6/2012 FED/Mark Staniford Slide 13
ZnS:Ag,Cl 0.75 0.145 0.081
Advances
Four colour system
Usage of NaCaPO4:Mn2+ a yellow phosphor
RGB concept is extended to RGBYSurrounding of a larger colour spaceSurrounding of a larger colour spaceDisplaying of more natural coloursHigher information density (pixel/ area)
18/6/2012 FED/Mark Staniford Slide 14
Advances
NaCaPO4:Mn2+
Fabricated via Pechini sol‐gel method
Ground state [Ar]3d5 6S
O i i f th l i th 4T 6A t iti Origin of the colour is the 4T1 6A1 transition
18/6/2012 FED/Mark Staniford Slide 15
Comparison
OLED (PLED), CNT‐FED & LCD (Pros)OLED (PLED) CNT‐FED LCD
self emitting self emitting backlight
big viewing angle big viewing angle energy efficient
good proccesibility energy efficient good proccesibility
d dgood response time good response time
good colour rendering good colour rendering
good contrast
18/6/2012 FED/Mark Staniford Slide 16
good contrast
Comparison
OLED (PLED), CNT‐FED & LCD (Cons)
OLED (PLED) CNT‐FED LCD
li it d ti ti th d ti li it d i i llimited operating time cathode coating limited viewing angle
organic comp. vulnerable towards O2 and H2
mass production moderate response time
moderate contrast
limited colour rendering
18/6/2012 FED/Mark Staniford Slide 17
Conclusions
FED brings along a variety of advantages
Proccessibility seems to be a hard task
Low voltage phosphors are a prerequisite
Big competing techniques
18/6/2012 FED/Mark Staniford Slide 18
Future aspects
2009 Inventions into Field Emission Technology Inc were cut down
OLED, Plasma, PLED.... are maybe a too big competitor
Four colour technology seems to be promising
18/6/2012 FED/Mark Staniford Slide 19
References http://static.guim.co.uk/sys‐images/Guardian/Pix/pictures/2008/05/20/nanotube.article.jpg
http://kennano.com
T. Jüstel, H. Nikol and C. Ronda, Angew. Chem. Int. Ed. 1998, 37, 3084
G. Li, X. Xu, C. Peng, M. Shang, D. Geng, Z. Cheng, J. Chen and J. Lin, Optics Express, 2011, 19, 16423
L. Brand, M. Gierlings, A. Hoffknecht, V. Wagner and A. Zweck, Kohlenstoff‐Nanoröhren: Potenziale, g , , g , ffeiner neuen Materialklasse für Deutschland, 2009, 79
https://www.fh‐muenster.de/fb1/downloads/personal/kynast/kynast/kynast/VLFM_WS_10_11‐Teil1 Absorption pdfTeil1_Absorption.pdf
18/6/2012 FED/Mark Staniford Slide 20