Mobile Phones Display's

Properties

You may think that all cell phone screens are the same, but that couldn't be further from the

truth.

Here's an overview of the most common types of screens found on cell phones today.

LCD

OLED

AMOLED

SUPER AMOLED

What is LCD ?

A liquid crystal display (LCD) is a thin, flat panel used for electronically

displaying information such as text, images, and moving pictures.

It is an electronically-modulated optical device made up of any number of

pixels filled with liquid crystals and arrayed in front of a light source(backlight)

or reflector to produce images in color or monochrome.

Its uses include computer monitors ,televisions , instrument panels, and devices

ranging from aircraft cockpit displays, to every-day consumer devices such as

clocks , calculators, and telephones.

LCD Overview

LCDs are a type of light modulating display device. LCD

technology does not directly emit light in order to create

visualizations, it rather modifies the transmission of light to

represent images.

On the other hand Plasma displays, CRT and OLED devices

are all light emitting display devices.

LCDs are rapidly becoming the most popular display device

available.

2006 - Nearly 33% of all TVs sold in North America were

LCDs

2007 - Expected to surpass 50%

LCD

LCD, or Liquid Crystal Display, is a type of screen that is used in many computers,

TVs, and cell phones. LCDs are very thin, but are actually composed of several

layers.

Two types of LCDs are primarily found in cell phones:

1) TFT (Thin-Film Transistor)

2) IPS(In Plane Switching)

Liquid crystal display (LCD) is a flat electronic display panel used as a

visual display aid. It uses liquid crystals to create visual effects on screen.

Liquid crystal is a state of matter between solids and liquids. LCDs do not

generate light on their own but rely on sunlight or room light to generate images

with help of liquid crystal.

TFT-LCDs also consume more power than other types of cell phone displays. In

general, TFT-LCDs are found on more low-end smartphones or feature phones,

and on basic cell phones.

TFT-LCD

TFT stands for Thin Film Transistor, and is a type of technology used to improve

the image quality of LCD.

While TFT-LCDs can deliver sharp images, they also tend to offer relatively poor

viewing angles, meaning they look best when viewed head-on. If you view a TFT-LCD

from the side, it can be difficult to see.

TFT Process

I. Printing the Orientation Layer

II. Rubbing

III. Dispensing Spacers

IV. Injecting the Liquid Crystal

Printing the Orientation Layer

The orientation layer is evenly spread on the pixel area

of the upper and lower plate.

The polyimide is spread on the drum thinly and evenly and is coated on the rubber

plate, which has been patterned in advance.

In turn, the polyimide is printed on the upper color filter or the lower TFT-array

plate.

After printing, the polyimide is hardened through the process of annealing .

Rubbing

Rubbing is the process that forms the straight groove on

the hardened polyimide in a fixed direction in order to make

the liquid crystal orient in a fixed direction.

Dispensing Spacers

The spacers are dispensed evenly in order to secure the fixed cell gap when

assembling the upper and lower plate.

After the spacers are mixed in the liquid with the proper concentration, they are

then transported to the spray nozzle through the pump, and subsequently sprayed

on the surface of the plate from the nozzle with high pressure.

Injecting the Liquid Crystal

The liquid crystal is injected between the upper and lower plate using capillary

action and pressure differences after the upper and lower plate are assembled.

At first, the internal cell vacuum level is maintained at about 10(-3) Torr from the

original vacuum state.

IPS-LCD

IPS stands for in-plane switching. An IPS-LCD is a type of thin display that offers

better viewing angles than TFT-LCDs. IPS-LCDs feature two transistors for each pixel,

where TFT-LCDs use just one.

This requires a more powerful backlight, which delivers more accurate colors, and

allows the screen to be viewed from a wider angle. The downside is that an IPS-

LCD may consume more power than a TFT-LCD.

OLED

OLED, or Organic Light-Emitting Diode, displays are able to deliver sharper and

brighter images than LCDs, while also using less power.

Unlike an LCD, which requires a backlight, OLED screens can emit their own light.

This allows OLED screens to display brighter, sharper images and text, and to

offer better viewing angles.

It also means that OLED screens are thinner and consume less power than their

LCD counterparts.

An OLED is a light emitting diode (LED) which emissive electroluminescent layer is composed of a film of organic compounds.

AMOLED

Architecture of OLED

SUBSTRATE.

ANODE

ORGANIC LAYER:

1-Conductive layer

2-Emmisive layer

CATHODE.

Types of OLED

Passive OLEDs

The organic layer is between cathode & anode run perpendicular.

The intersections form the pixels.

Easy to make.

Use more power.

Best for small screens.

Active OLEDs

Full layers of cathode and anode.

Anode over lays a thin film transistor (TFT).

Requires less power.

Higher refresh rates.

Suitable for large screens

Advantages

Faster response time than LCDs,

Consume significantly less energy,

Can be transparent when off,

Flexible and Conformal Displays,

Thinner display-No backlight required

Better contrast ratio,

Safer for the environment,

Wider viewing angels; up to 170 degrees,

OLEDs refresh almost 1,000 times faster then LCDs,

Low cost materials and fabrication method,

Less Expensive than LCD due to lesser components,

Can be made using plastic screens; LCDs require glass backing,

Disadvantages

OLED seems to be the perfect technology for all types of displays, but it also has some problems:

Lifetime - While red and green OLED films have longer lifetimes (46,000 to 230,000 hours), blue organics currently have much shorter lifetimes (up to around 14,000 hours)

Manufacturing - Currently, manufacturing is more expensive than LCDs,

Water - Water can easily damage OLEDs,

OLED screens are even worse than LCD in direct sunlight,

Overall luminance degradation,

Limited market availability .

Which Organic Compounds Used ?

The applications of organo-metallic compounds are very useful in OLEDs owing

to both transport and emitting properties of compounds. For example, tris-(8-

hydroxyquinoline) aluminum (Alq3), tris-(8-hydroxyquinolinolato) gallium (Gaq3) and

tris-(8-hydroxyquinoline) indium (Inq3) based materials are frequently used as both

electron transport and emissive material in OLEDs.

Other common electron transport materials are bathocuproine (Kijima et al.,

1999) and (bis (2-(4, 6-difluorophenyl) pyridyl-NC2‟) iridium (III) picolinate) or FIrpic

(Adamovich et al., 2003). These materials are used as hole blocking layer.

N, N’-diphenyl-N, N’- bis(3-methyphenly)-(1,1‟-biphenyl)-4,4‟-diamine (TPD) and

N, N’-bis(1-napthalenyl)- N, N’-diphenyl)-(1,1‟-biphenly)-4,4‟-diamine (NPB) are

frequently materials used as HTL in OLEDs.

Thank You