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.))

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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

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Field emission

Applications

Microscopy  SEM TEM FIM SEM, TEM, FIM

Electron beam lithographyg p y Field emission lighting Field emission displays

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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

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Field emission display

Assembly

Triode assembly

Emission tips werefirstly made out of W or Si (Spind –Tips)

Attempts to use CNTare current

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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

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Cathode

CNT‐FED

Aspect ratio

Chemically and thermally “inert”

Good response time

Energy efficient Energy efficient

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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

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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

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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

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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

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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)

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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

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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

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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

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Conclusions

FED brings along a variety of advantages

Proccessibility seems to be a hard task

Low voltage phosphors are a prerequisite

Big competing techniques

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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

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http://kennano.com

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