c t seminar report kgptc

AMOLED DISPLAY SEMINAR REPORT 2015-16

KERALA GOVERNMENT POLYTECHNIC

COLLEGE KOZHIKODE-5

DEPARTMENT OF COMPUTER ENGINEERING

2015-16

Seminar Report

DIPLOMA IN COMPUTER ENGINEERING

OF

THE DEPARTMENT OF TECHNICAL EDUCATION

GOVT OF KERALA


ACKNOWLEDGEMENT

Any mission never concludes cordial co-operation from surroundings. I

take this opportunity to acknowledge all the people who have helped us kind

heartedly in every stages of this seminar. Firstly I thank god for my successful

completion of the paper. It is a matter of great pleasure for you to express our

sincere gratitude and appreciation to our beloved Mr. JAVAHARALI B S Head

of The Department in Computer Engineering.

I am really thankful to our seminar guide Mr. JAVAHARALI B S (Head

of The Department in Computer Engineering) & Ms. ANU MANOHAR

(Lecturer in Computer Engineering) for the sincere co-operation for the success

of this seminar.

I am also express my gratitude all technical staff members in the

department for their promote service and co-operation in the fulfillment of the

repot.

I am also thankful to my fellow classmates for sharing their knowledge

and suggestions. I express my sincere gratitude to the God for giving me health

and all the support in completing the seminar.

NAVANEETH S

Reg No: 13130484


ABSTRACT

Active-matrix OLED (Active-matrix organic light-emitting

diode or AMOLED) is a display technology for use in mobile devices and

televisions. OLED describes a specific type of thin display technology which

doesn't require a backlight, and Active-Matrix refers to the technology behind

the addressing of pixels.

AMOLED technology continues to make progress towards low-power

and low-cost large size (e.g. 40-inch) for applications such as TV.


LIST OF FIGURES


Introduction

What is AMOLED?


CHAPTER 1

INTRODUCTION

An organic light emitting diode (OLED) is a light-emitting diode (LED)

in which the emissive electroluminescent layer is a film of organic

compounds that emits light when an electric current passes through it. This

layer of organic semiconductor material is formed between two electrodes.

Generally, at least one of these electrodes is transparent.

OLEDs are used in television screens, computer monitors, small,

portable system screens such as mobile phones and PDAs, watches,

advertising, information and indication; they can also be used in light sources

for general space illumination and in large-area light-emitting elements.

OLED displays can use either passive-matrix or active-

matrix addressing schemes.


CHAPTER 2

DIFFERENCES BETWEEN AMOLED & PMOLED

There are two types of OLEDs used in displays - PMOLED and AMOLED.

The difference is in the driving electronics - it can be either Passive Matrix

(PM) or Active Matrix (AM).

With Passive-Matrix OLEDs, the display is controlled by switching on

rows and columns. When you turn on row number x and column number y, the

pixel at the intersection is lit - and emits light. Each time you can choose just

one pixel to light. So you have to turn these on and off very quickly. You do so

in a certain sequence, and create the desired image.

PMOLEDs are very easy and cheap to build, but they are limited to small sizes.

The image displaying is a bit complicated. Also the power consumption is not

as good as AMOLEDs.

AMOLEDs have a different driver electronics - each pixel is controlled

directly. AMOLEDs are more expensive, and much more difficult to create, but

can be used for larger displays (current prototypes are up to 40") and are very

power efficient.

The first OLED products in the market used PMOLEDs - these were MP3

players, sub-displays on cellphones and radio decks for automobiles. The

displays were small and usually with just one or two colors. When AMOLED

panels started to emerge in 2007 and 2008 we have seen these larger displays in

mobile video players, digital cameras, mobile phones main displays and

even OLED TVs.


CHAPTER 3

OLED COMPONENTS

Like an LED, an OLED is a solid-state semiconductor device that is 100 to

500 nanometers thick or about 200 times smaller than a human hair. OLEDs

can have either two layers or three layers of organic material; in the latter

design, the third layer helps transport electrons from the cathode to the

emissive layer. In this article, we'll be focusing on the two-layer design.

An OLED consists of the following parts:

Substrate (clear plastic, glass, foil) - The substrate supports

the OLED.

Anode (transparent) - The anode removes electrons when a

current flows through the device.

Organic layers - These layers are made of organic molecules

or polymers.

Conducting layer - This layer is made of organic plastic

molecules that transport "holes" from the anode. One

conducting polymer used in OLEDs is polyaniline.

Emissive layer - This layer is made of organic plastic

molecules (different ones from the conducting layer) that

transport electrons from the cathode; this is where light is

made. One polymer used in the emissive layer is

polyfluorene.

Cathode (may or may not be transparent depending on the

type of OLED) - The cathode injects electrons when a

current flows through the device.


CHAPTER 4

WORKING OF OLED

OLEDs emit light in a similar manner to LEDs, through a process

called electro-phosphorescence.

The process is as follows:

1. The battery or power supply of the device containing the

OLED applies a voltage across the OLED.

2. An electrical current flows from the cathode to the anode

through the organic layers (an electrical current is a flow of

electrons).

The cathode gives electrons to the

emissive layer of organic molecules.

The anode removes electrons from the

conductive layer of organic molecules.

(This is the equivalent to giving electron

holes to the conductive layer.)

3. At the boundary between the emissive and the conductive

layers, electrons find electron holes.

When an electron finds an electron hole,

the electron fills the hole (it falls into an

energy level of the atom that's missing an

electron).

When this happens, the electron gives up

energy in the form of a photon of light.

4. The OLED emits light.

5. The color of the light depends on the type of organic

molecule in the emissive layer. Manufacturers place several


types of organic films on the same OLED to make color

displays.

6. The intensity or brightness of the light depends on the

amount of electrical current applied: the more current, the

brighter the light.

Working of PMOLED

PMOLEDs have strips of cathode, organic layers and strips of anode. The

anode strips are arranged perpendicular to the cathode strips. The intersections

of the cathode and anode make up the pixels where light is emitted. External

circuitry applies current to selected strips of anode and cathode, determining

which pixels get turned on and which pixels remain off. Again, the brightness

of each pixel is proportional to the amount of applied current.

PMOLEDs are easy to make, but they consume more power than other

types of OLED, mainly due to the power needed for the external circuitry.

PMOLEDs are most efficient for text and icons and are best suited for small

screens (2- to 3-inch diagonal) such as those you find in cell

phones, PDAs and MP3 players.

Working of AMOLED

AMOLEDs have full layers of cathode, organic molecules and anode, but

the anode layer overlays a thin film transistor (TFT) array that forms a matrix.

The TFT array itself is the circuitry that determines which pixels get turned on

to form an image.

AMOLEDs consume less power than PMOLEDs because the TFT array

requires less power than external circuitry, so they are efficient for large

displays. AMOLEDs also have faster refresh rates suitable for video. The best

uses for AMOLEDs are computer monitors, large-screen TVs and electronic

signs or billboards.


CHAPTER 5

WORKING PRINCIPLE

A typical OLED is composed of a layer of organic materials situated

between two electrodes, the anode and cathode, all deposited on a substrate.

The organic molecules are electrically conductive as a result of

delocalization of pi electrons caused by conjugation over all or part of the

molecule. These materials have conductivity levels ranging from insulators to

conductors, and therefore are considered organic semiconductors. The highest

occupied and lowest unoccupied molecular orbital (HOMO and LUMO) of

organic semiconductors are analogous to the valence and conduction bands of

inorganic semiconductors.

During operation, a voltage is applied across the OLED such that the anode is

positive with respect to the cathode. A current of electrons flows through the

device from cathode to anode, as electrons are injected into the LUMO of the

organic layer at the cathode and withdrawn from the HOMO at the anode. This

latter process may also be described as the injection of electron holes into the

HOMO. Electrostatic forces bring the electrons and the holes towards each

other and they recombine forming an exciton, a bound state of the electron and

hole. This happens closer to the emissive layer, because in organic

semiconductors holes are generally more mobile than electrons. The decay of

this excited state results in a relaxation of the energy levels of the electron,

accompanied by emission of radiation whose frequency is in the visible region.

The frequency of this radiation depends on the band gap of the material, in this

case the difference in energy between the HOMO and LUMO.

As electrons and holes are fermions with half integer spin, an exciton may

either be in a singlet state or a triplet state depending on how the spins of the

electron and hole have been combined. Statistically three triplet excitons will

be formed for each singlet exciton. Decay from triplet states (phosphorescence)


is spin forbidden, increasing the timescale of the transition and limiting the

internal efficiency of fluorescent devices. Phosphorescent organic light-

emitting diodes make use of spin–orbit interactions to facilitate intersystem

crossing between singlet and triplet states, thus obtaining emission from both

singlet and triplet states and improving the internal efficiency.

Material technologies

Molecules commonly used in OLEDs include organometallic Chelates,

fluorescent and phosphorescent dyes and conjugated dendrimers.

Triphenylamine and derivatives are commonly used as materials for hole

transport layers.

The production of small molecule devices and displays usually involves

thermal evaporation in a vacuum.


Advantages

The different manufacturing process of AMOLEDs lends itself to several

advantages over flat-panel displays made with LCD technology.

+ Low power

+ Low cost

+ Thin, lightweight and rugged

+ Superior image quality

+ Wide-viewing angle

+ Rollable Display


Problems

Lifespan: The biggest technical problem for OLEDs was the limited lifetime of

the organic materials.

Water damage: Water can damage the organic materials of the displays.

Screen burn-in: Unlike displays with a common light source, the brightness of

each OLED pixel fades depending on the content displayed. The varied

lifespan of the organic dyes can cause a discrepancy between red, green, and

blue intensity. This leads to image persistence, also known as burn-in.

Color balance issues: Additionally, as the OLED material used to produce

blue light degrades significantly more rapidly than the materials that produce

other colors, blue light output will decrease relative to the other colors of light.

Manufacturing Cost: Quite high.


CHAPTER

CONCLUSSION

Limited use caused by degradation of organic materials.

AMOLED will replace current LED and LCD technologies

Flexibility and thinness will enable many applications


REFERENCES

http://en.wikipedia.org/wiki/Active-matrix_OLED

www.google.com

http://www.oled-info.com/oled-technology

http://electronics.howstuffworks.com/oled1.htm

http://www.oled-display.net/what-is-amoled

http://en.wikipedia.org/wiki/Organic_LED

http://www.gadgets-reviews.com/store/index.html

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