Image Edited by Author / Source: rochester.edu

In this article we are going to discuss the latest technology used on digital display industry. Before that lets take a slight look about the earlier technologies used for displays.

1. CRT : Cathode Ray Tube

In this technology, the images generate by focusing high voltage electron beams to a phosphorescent inner flat surface of a pyramid shaped vacuumed tube.

Common disadvantages like Heavy weight, limited screen size, less image quality, high power consumption, more space waste, UV rays and high voltage cautions, Threw this technology away from the use

Image Source: csis.pace.edu

2. LCD : Liquid Crystal Display [with florescent back light]

This is the first generation of LCD and there are two types

I . Passive Matrix LCD -

A passive matrix display applies a voltage to liquid crystals using a simple conductive grid. It has slower response times and limited viewing angles.

This is the oldest LCD technology widely using in monochrome displays, such as calculators, clocks, indicators on machines, meter boards etc.

Image Source: orientdisplay.com

Working principle-

There are no backlights or TFT layers
Two glass substrates with vertical and horizontal conductors and the liquid crystal material placed between this two glass substrates
Two polarizers placed outside of each substrate.
Each conductors made by transparent conductive materials (normally this is indium-tin oxide).
Those vertical and horizontal conductors connected with integrated circuit, and the circuit uses one conductor as anode and the other as cathode.
Electric charge will activate through each horizontal and vertical conductor and the liquid crystals in the point of these horizontal and vertical conductors intersect will turn to untwist.

II . Active matrix LCD -

An active-matrix display uses transistors and capacitors to individually control each pixel. It offers faster response times and better image quality, making it suitable for high-resolution and fast-refresh-rate displays.

This is the most common LCD technology widely used,

The crystal molecules control the light rays emitting from the back fluorescent light, according to electric current that supply by a matrix of Thin Film Transistors (TFT) array.

Generating images on front substrate by focusing back light rays through the RGB colored sub pixels, by the thin film transistor (TFT) controlled crystal molecules.

Image Source: alchetron.com

When electricity OFF stage the crystal molecules are in twisted form.

That means, molecules arranged in a queue from the vertical polarizer end to the horizontal polarizer end by rotating 90 degrees. The vertical light rays (coming through the vertical polarizer) will reflect by 90 degree angle through the crystals and pass through the horizontal polarizer to the colour pixel.

When electricity ON stage the crystal molecules are in untwisted form.

That means, all crystal molecules in a straight queue without any rotation, and the vertical light rays reflects through the crystals in a straight line and blocked at the horizontal polarizer.

There are some variants in this technology based on the way of Crystal molecules arrange when voltage on and off stages

Some of them as follow,

- Twisted Nematic (TN) LCD Panel

- In Plane Switching (IPS) LCD Panel (this technology Invented by LG Electronics)

- Vertical Alignment (VA) LCD Panel

There's no any major changes to the components, the only change has made to Crystal molecule arrangements

This variants introduced by different manufacturers to achieve some improvements like good brightness and contrast, deep black, wide view angle, better image quality, and refresh rate.

However, compare with other LCDs, IPS LCD Panels became famous as most successful LCD model in market.

3. LCD with LED Backlight : Liquid Crystal Display with Light Emitting Diode Backlight

In this Technology, all integrated layers and working principles are similar to the LCD, The only key difference is using LED Matrix backlight layer instead of fluorescent backlight.

4. OLED : Organic Light Emitting Diode

This is the most recent technology broadly used for displays before QLED technology. There are no traditional backlights or Liquid crystals in here

Image Source: viewsonic.com

A layer with thin film transistor (TFT) array, placed In front of the back substrate.
The next layer is emissive layer; consist with cells of light emissive organic compounds,
Cells generate Yellow and blue light rays according to the electric current supply by back TFTs
Colour pixel polarizer placed in front of that emissive layer,
That electroluminescent rays passing through the each sub pixel in colour pixel polarizer and converts into red, green, blue and white, these rays spot in to the final glass or plastic substrate and generates image

In this time, Instead of using all three pixels, an additional white pixel has introduced to generate white colour (This technology has introduced to market by LG electronics).

What is electroluminescent?

In an organic cell, the organic emissive compound layers are placed between a cathode and an anode layer. When an electric current passing from cathode to anode through the organic compounds, it will generate glowing, this retroaction is call as electroluminescent

However as reason of, organic light shelf degradation trend, more potential of screen burn in image retentions this displays not much durable. And also organic materials are usually more expensive.

5. AMOLED : Active Matrix Organic Light Emitting Diode

This is the next generation of OLED Technology,

This also a kind of LED and produced by integrating colour-conversion layers directly to the yellow-blue emissive organic compound cell.

There's No Colour pixel polarizers in front of the emissive layer,

A layer with thin film transistor (TFT) array, placed In front of the rear substrate.
The next layer consist with millions of OLEDs in an active matrix (this is why Called a Active Matrix) and each OLED represents sub pixel.
According to the electric current supply by rear TFTs, this OLEDs directly generate red green and blue light rays
That electroluminescent rays spot on to the final glass or plastic substrate and generates image.

The main advantages

Less thickness by less layers
Low production cost
Energy Efficiency

Difference between Photoluminescence and Electroluminescence?

Photoluminescence and electroluminescence differ primarily in their mechanisms for producing light. Photoluminescence involves the re-emission of light subsequent to the absorption of a photon, while electroluminescence generates light by applying an alternating current to a semiconductor.

What is Quantum Dot?

Image Source: samsungdisplay.com

Quantum dots (QDs) are artificially designed Nanoscale crystals in other words artificially synthesized semiconductor nanoparticles with unique optical and electronic properties.

These particles able to transport electrons, enhance light rays and also ability to glow in various colours in different atom densities by exposing into external light sources

Quantum dots can be used on wide range of applications, such as, in composites, solar cells, displays, lightings, fluorescent biological labeling, and medical imagings etc.

Quantum Dot history in brief

A Russian physicist Alexei Ekimov has published his first observation for this quantum nanocrystals in 1980, according to the scientific experiments done by him since the late 1970s.

Then after further study of Alexei Ekimov's observation, an another Russian physicist Alexander Efros published his explanation for the behavior of this nano-crystals in 1982 .

Then a American chemist Louis Brus Inspired by Alexei Ekimov, successfully produced the first colloidal Quantum Dots of Cadmium Sulphide in liquid form, and Brus published his results in 1983.

However, the Sony Corporation has introduced the first TV with a Quantum dot Display in 2013 as 'Triluminos'

The first tablet pc product of this kind was Kindle Fire HDX 7” tablet, launched in 2013.

6. QD–LED : Quantum Dot Light Emitting Diode

There are some earlier versions are available in this QD display technology, Most of them built by including liquid crystal layers and some others by including Organic self-emissive layers (OLED layers)

But in this article we are explain the most latest Quantum dot display technology called QDLED or in other words QDCC (Quantum dot colour conversion), Which has developed by using micro-LEDs and Quantum Dots.

Image Source: viewsonic.com

This technology has recalled LED backlights in to the battle.

Normally LEDs not glowing in white, it convert in to white by covering blue light emitting cell by a phosphorus layer.

because of this matter scientists concerning to use bare blue LEDs as backlight source in this stage.

What are the layers inside a QD-LED display?

Right in front of the rear substrate, there is a layer with thin film transistor (TFT) matrix to control backlight emitting,
Next layer, consist with matrix of micro-LED semiconductors which represent the backlight, and each micro-LED acting as a sub pixel.
Next layer is quantum dot layer, which consist of quantum dot blocks as matrix.
These blocks filled with different density of quantum dots (atoms) to generate required colours and each blocks arranged right in front of each micro-LED sub pixels which on backlight layer.
Front substrate - This is a transparent layer with enhancement for projected images and can be glass or plastic material.

How it works?

The blue light rays generate by led semiconductors on each sub pixels, according to the electric current supply by the TFTs on rear TFT matrix layer

Those rays directly passing through the front quantum dot blocks and it will convert into red or green according to the dots density ( blue rays no need to convert but those will enhance by the quantum dots)

And then quantum dots will spread those colour rays wide-angely into front substrate to generate images.

By this colour spreading technique these displays has wider view angle than others

Advantages of Quantum Dot Technology

Deep black / Peak brightness and contrast
Longer lifespan and No burn-In
Quality natural colors
Wide view angle
Energy efficiency

7. QDEL : Quantum Dot Electroluminescence

Image Source: nanosyshome.squarespace.com

This is the future of Quantum dot. this QDEL™ technology has discovered by a nanotechnology research organization called Nanosys.

Both OLED and QDEL are electroluminescent.

But, QDEL is a Nano-LED produced by artificial Nano crystals, and OLED is produce by Organic Compound materials.

So, Nano-LED is more durable and reliable than degradable organic material integrated OLED.

Working Principle-

Here is a layer consist with millions of QDEL Nano-LEDs as an active matrix and each Nano-LED is represents a sub pixel.
The required electric current for these Nano-LEDs will activate by a layer of thin film transistor (TFT) array, which is in front of the rear Substrate.
According to the electric current supply by rear TFTs, this Nano-LEDs directly generate red green and blue light rays.
That electroluminescent rays spot on to the final glass or plastic substrate and generates image.

QDEL is the most convenient technology for mobile flexible displays, because it can be made using the lowest cost printing techniques like via ink jet, transfer or gravure printing.

And also this has robust advantages like

Ultra thin (limited layers)
Low cost effective
Energy efficiency
Printable
Flexible
Scalable
Less weight
High quality colors
Wider view angle

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