Universität Dortmund

Seminar „Moderne Displaytechnik“

Electroluminescence Displays

Fakultät für Elektrotechnik und

Informationstechnik

Lehrstuhl für Kommunikationstechnik

Prof. Dr.-Ing. Rüdiger Kays

Jens Bömerjcbsystems@gmx.de

Seminar „Moderne Displaytechnik“

8. Februar 2002

Folie 2Lehrstuhl fürKommunikationstechnikProf. Dr. Rüdiger Kays

Table of Contents

Introduction Principles of Electroluminescence (EL)

general effect high-field EL

Technological Realization layer structure

Selected Approaches to produce colours make a display

Applications/ Products Pros & Cons

Electroluminescence: Basics & Technology

Seminar „Moderne Displaytechnik“

8. Februar 2002

Folie 3Lehrstuhl fürKommunikationstechnikProf. Dr. Rüdiger Kays

Introduction

tendency to miniaturizement

fast response for video services

low power consumption

Motivating Forces

Seminar „Moderne Displaytechnik“

8. Februar 2002

Folie 4Lehrstuhl fürKommunikationstechnikProf. Dr. Rüdiger Kays

Introduction

phosphorus material

hot-electrons

impact excitation

Electroluminescence

High Field ELLED & OLED

non-thermal conversionof electrical energy into light

pn-junction

electron-hole pair recombination

Seminar „Moderne Displaytechnik“

8. Februar 2002

Folie 5Lehrstuhl fürKommunikationstechnikProf. Dr. Rüdiger Kays

Principles of EL

electrical energy is converted into light energy

operation at low temperatures possible

Requirements

band gap (Eg) higher than 3.0eV

special semiconductor

insulator

Luminescence

Fluorescencet 1s

Phosphorescencet 1min - ...

E

E0

E1

E2

Eg

Seminar „Moderne Displaytechnik“

8. Februar 2002

Folie 6Lehrstuhl fürKommunikationstechnikProf. Dr. Rüdiger Kays

Principles of EL

e-

excited state

impurityground state

topinsulator

bottominsulator

Al

ITO

... insulator/ phosphor interface states

electrons tunnel into phosphor

electrons accelerated by electric field (high energy or “hot” electrons > 2 eV)

Electron transport

Excitation collisions with lattice/ ímpurity atoms (e.g. Mn)

luminescent impurity absorbs electron‘s energy

excited impurity relaxes by emitting a photon

High Field EL

Seminar „Moderne Displaytechnik“

8. Februar 2002

Folie 7Lehrstuhl fürKommunikationstechnikProf. Dr. Rüdiger Kays

Technological Realization

insulator/phosphor/insulator stack

insulators limit short current

electric field strength > 1.5 MV/cm

165 V alternating voltage

thin film EL (TFEL)

AC

electrode

insulator( 250nm)

phosphor( 600nm)

wide viewing angle

luminosity controlled by pulse width modulation

T

Seminar „Moderne Displaytechnik“

8. Februar 2002

Folie 8Lehrstuhl fürKommunikationstechnikProf. Dr. Rüdiger Kays

Colourful Materials

Red

ZnS:Mn

organic red filter

Green

ZnS:TbOF

SrS:Ce

Amber

ZnS:Mn

Blue

SrS:Ce

SrS:Cu,Ag

White

stacked layers

SrS:Ce and ZnS:Mn

rare earth oxidsand oxysulfats

(as in CRT)

Seminar „Moderne Displaytechnik“

8. Februar 2002

Folie 9Lehrstuhl fürKommunikationstechnikProf. Dr. Rüdiger Kays

Facts Concerning Colours

Efficiency

red: 0.8 lm/W

green: 1.0 lm/W

blue: 0.2 lm/W

Luminance (max.)

red: 70 cd/m2

green 160 cd/m2

blue: 100 cd/m2

white: 470 cd/m2

operating temperature-30° C to 65°C

Seminar „Moderne Displaytechnik“

8. Februar 2002

Folie 10Lehrstuhl fürKommunikationstechnikProf. Dr. Rüdiger Kays

Comparison of EL and LCD

18:1-150:1

200 cd/m2

100°(recently up to 170°)

20W

150:1

150 cd/m2

> 160°

3W

LCD:thin film EL

Contrast ratio

Luminance

Viewing angle

Power consumption

Seminar „Moderne Displaytechnik“

8. Februar 2002

Folie 11Lehrstuhl fürKommunikationstechnikProf. Dr. Rüdiger Kays

Selected Approach to Produce Colors

One approach: “Colour by White“

indium-tin oxide (ITO) top electrode

pixel size of 12 or 24 micron

broad band “white“ phosphor

patterned colour filter

simple device fabrication

low-cost production

Seminar „Moderne Displaytechnik“

8. Februar 2002

Folie 12Lehrstuhl fürKommunikationstechnikProf. Dr. Rüdiger Kays

Selected Approach to Make a Display

Active Matrix (AMEL)Display Organization

line drivers column drivers

Technological advantages

EL pixel

ITO

data line

high integration level

low capacity

less current

reduction of control wires

fast response

Seminar „Moderne Displaytechnik“

8. Februar 2002

Folie 13Lehrstuhl fürKommunikationstechnikProf. Dr. Rüdiger Kays

Selected Approach to Make a Display

aging characteristics of the phosphor

inverted structure

brightness controlled by pulse width modulation

high resolution (2000 lpi)

reduced power consumption

higher brightness

expanded grayscal capability

Silicon On Insulator (SOI):

Required isolation between high voltage AC of EL deviceand low voltage digital signals which address each pixel.

Advantages of AMELTechnological features

t

b

Seminar „Moderne Displaytechnik“

8. Februar 2002

Folie 14Lehrstuhl fürKommunikationstechnikProf. Dr. Rüdiger Kays

Applications

What is ACTFEL?

ACTFEL: alternating current thin film electroluminescence

used in cars

high reliability

wide temperature range

luminance:

red: 23 cd/m2

amber: 140 cd/m2

green: 25 cd/m2

transparent

minimize driver‘s eye movement

visibility under sunlight

pixel luminance:

amber: 1200 cd/m2

green: 500 cd/m2

head-up displays (HUD) instrument panels

Seminar „Moderne Displaytechnik“

8. Februar 2002

Folie 15Lehrstuhl fürKommunikationstechnikProf. Dr. Rüdiger Kays

Products

car control panel(ACTFEL)

Products

camcorder

head mounteddisplay

EL foil EL display

Seminar „Moderne Displaytechnik“

8. Februar 2002

Folie 16Lehrstuhl fürKommunikationstechnikProf. Dr. Rüdiger Kays

Pros and Cons

high resolution

fast response

low power consumption

wide viewing angle

ruggedness

low-cost production

use at low temperatures

visibility under sunlight

inadequate brightness and chromaticity

aging characteristics

high voltage

alternating current

PRO CONTRA

Seminar „Moderne Displaytechnik“

8. Februar 2002

Folie 17Lehrstuhl fürKommunikationstechnikProf. Dr. Rüdiger Kays

Summary

HFEL bases on high energy electrons (hot electrons)

Self-emitting technology instead of light through (LCD)

Realization with an insulator/phosphor/insulator stack

Multi-colour displays by “white phosphor“ and colour filters

Various monochrome control panels by variation of dopants

Active matrix integration (AMEL)

Application in cars, laptops, head-mounted-displays, camcorder