Evolution of Display Technology

Technology is a part of our everyday lives, with devices like mobile phones, computers, and televisions being the most frequently used. A common feature among these devices is their display, which is crucial for their functionality. These displays differ across devices, and like many technological advancements, they have evolved to become more efficient and user-friendly.

Cathode Ray Tubes (CRT):

One of the earliest electronic displays is the Cathode Ray Tube (CRT), which was first demonstrated in 1897 and made commercial in 1922.The CRT consists of an electron gun that forms images by firing electrons onto a phosphor-coated screen.

The earliest CRTs were monochrome (they could display only blacks and whites) and were used primarily in oscilloscopes and black and white televisions. The first commercial colour CRT was produced in 1954.

CRTs were the single most popular display technology used in television sets and computer monitors for over half a century.

[Source ElectronicDesign]

Liquid Crystal Displays (LCD):

Liquid Crystal Displays or LCD was invented in 1964 at RCA Laboratories in Princeton. These displays use a backlight as a source of illumination to produce the image on a screen.

[Source Sunrom]

DYNAMIC SCATTERING MODE (DSM):

The DSM effect (Dynamic Scattering Mode) was a significant early development in the history of LCD crystals. It is based on the alignment and scattering of light in a liquid crystal when electric field is applied.

Basically when there is no electric field applied , the display is transparent and allows light to pass through it , once the field is applied , the molecules move and scatter the light making the display turn opaque.

These displays were pretty power hungry , which limited their practical application , especially in portable devices.

TWISTED NEMATIC (TN):

Next the Twisted Nematic effect was discovered which helped to produce LCD displays that consume less power thus increasing the efficiency.

How does it work ?:

The liquid crystal molecules are arranged in a helical or twisted manner when there is no electric field passing through it. Once a field has been applied the liquid crystal molecules begin to untwist and the alignment becomes parallel to the applied electric field. This disruption in the structure causes the liquid crystal to block the passage of light.

This kind of displays could produce higher quality images compared to the displays that used the DSM effect that too at a lower power consumption. These also demonstrated much better viewing angles compared to the previous displays.

IPS (IN PLANE SWITCHING)

This was introduced to improve the performance of the displays in the terms of colour accuracy, viewing angles and image clarity.

How does it work ?:

The liquid crystals are aligned parallel to the glass substrates (hence the word in-plane),instead of the vertical alignment used in the previous displays.

When the electric field is applied , the liquid crystals rotate in place adjusting the light passing through them to create images.

These displays produced images with better colour contrast and accuracy , while preserving the detail of the images to a greater extent.

These displays cost more than the ones made using the Twisted Nematic effect

[Source ifan-display]

- Thin Film Transistor (TFT)

TFT is a form of active-matrix technology. Each pixel in a TFT display is controlled by its own transistor, which allows for individual pixel control. This is a significant advancement over passive-matrix displays, where pixels are controlled by a shared grid, leading to slower refresh rates and less control over the image.

This is often used in conjunction with other LCD technologies like TN and IPS to improve the performance of the displays.

The displays we mostly find in our smartphones and monitors are IPS LCD and TFT displays.

Organic Light Emitting Diode (OLED):

An OLED is a type of light-emitting diode that uses organic compounds that emit light when an electric current passes through them. Unlike traditional LEDs that use a solid-state crystalline structure, OLEDs use organic materials for their electroluminescent properties. The organic layer is sandwiched between two electrodes, typically with at least one transparent electrode for light emission.

[Source winstar]

How does it work ?:

The display works by passing electric current through the organic layer causing it to emit light. Each individual pixel in the OLED display is self-illuminating meaning it does not require and backlight like the LCD displays. This leads to a better contrast ratio ( brighter colours appearing brighter and darker colours appearing darker).

AMOLED (Active Matrix OLED):

Active Matrix OLED (AMOLED) displays, each pixel is controlled individually by a thin-film transistor (TFT) matrix, allowing for higher resolution, faster refresh rates, and more control over image quality. AMOLED is widely used in smartphones and other portable devices for its improved performance compared to passive-matrix OLED (PMOLED), where pixels are controlled sequentially, leading to slower refresh rates.

In the devices we use on a daily basis , we find IPS LCD displays and OLED displayed being used the most. Anytime you wish to figure out which display is using OLED technology , display a black image on the screen As there is no backlight involved in OLED displays , the black image appears completely black , whereas on an LCD display it will be showing a slight grey shade as the backlight cannot turned off for certain areas and turned on the for other ones.

Difference between and OLED (left) and LCD (right) in displaying black colour

[Source displaymate]

What have we learnt ?

• We learnt about the first type of displays that have been used

• The progression in display technology to make it display images of higher quality while requiring less energy

• How LCD displays work

• How OLED displays work