Flat Panel Technologies
Written October 16, 2019
Flat Panel Technologies
Flat panel technologies for dynamic digital displays continue to develop, with refinements and innovations taking place constantly. There are, however, a number of established technologies for dynamic display.
Thin Film Transistor- Liquid Crystal Displays
TFT-LCDs consist of a lower glass plate on which the TFT is formed, an upper glass plate on which the color filter is formed, and injected liquid crystal between both glass plates. The TFT plays a critical role in the transmission and control of electric signals, which in turn determines the voltage directed to the liquid crystal. The liquid crystal controls light by using molecular structures that change transmission properties when voltage is applied.
This strategy allows the color and image to be displayed as the light passes through the color filter. TFT-LCDs are more energy efficient than traditional cathode-ray tubes (CRT), and do not emit electromagnetic waves as CRT technology does. Unlike conventional CRT monitors that are able to display many different input resolutions, liquid crystal displays are pixilated, i.e., they have fixed resolution. In the case of active matrix (TFT) LCD’s, each pixel corresponds with individual transistors that are ‘hard-wired’.
The plasma display panel is the latest iteration in display technology for televisions and computers. Developed at the dawn of the computer age, it has now been developed enough to commercialize profitably. The plasma display panel is a very high quality display device, which was developed with common physics principals applied in a very novel way. In its simplest form, an AC plasma cell consists of two plates of glass separated by a gas-filled gap. On the inner faces of the plates are two sets (horizontal and vertical) of transparent electrodes, covered by a thin glass insulating layer. This creates a monochrome clear display, which tends to give off an orange to blue glow once the enclosed gas is excited; color is dependent on the mixture of the gas. To create color, phosphors are laid down in each cell, which emit the desired color once hit by ultraviolet light. Small ridges separate the phosphors, so that when voltage is applied to one phosphor, then the other phosphors won't be excited unless desired.
The main advantage of plasma display technology is that one can produce a very wide screen using extremely thin materials. And because each pixel is lit individually, the image is very bright and looks good from almost every angle. The image quality isn't quite up to the standards of the best cathode ray tube sets, but it certainly meets most people's expectations.
Luminescence results from the characteristics of certain substances emitting absorbed energy. The stimulation of luminescence by electricity is called electroluminescence (EL). EL commonly uses fluorescent compounds, luminophores, and phosphor compounds as light-emitting substances. EL structures tend to be very simple, using layers of materials that are quite thick by LCD and semiconductor standards. The displays have quick response times, and have a wide viewing angle. Their coarse construction makes it difficult to create fine resolution devices, so the technology is being applied mostly to segmented displays and television screens. The most likely application for electroluminescent displays for the near future will be limited to televisions. This technology should be able to compete well against large LCDs and plasma displays.
Organic light-emitting devices (OLEDs) operate on the principle of converting electrical energy into light, a phenomenon known as electroluminescence. They exploit the properties of certain organic materials, which emit light when an electric current passes through them. In its simplest form, an OLED consists of a layer of this luminescent material sandwiched between two electrodes.
When OLEDs are used as pixels in flat panel displays, they have some advantages over backlit active-matrix LCD displays - greater viewing angle, lighter weight, and quicker response. Since only the part of the display that is actually lit up consumes power, the most efficient OLEDs available today use less power.
Based on these advantages, OLEDs have been proposed for a wide range of display applications including magnified micro displays, wearable, head-mounted computers, digital cameras, personal digital assistants, smart pagers, virtual reality games, and mobile phones as well as medical, automotive, and other industrial applications. With careful selection of materials, an OLED structure can be incredibly thin, with organic layers less than one tenth of a mm thick.
In Polymer OLEDs (Poly-OLEDS), the organic material is a special polymer, which can be quickly and easily applied to an appropriate substrate. This allows a simple manufacturing process that could eventually lead to high volume mass production of these innovative displays.
LED Television (Outdoor)
Depending on the manufacturer, LEDs are arranged in clusters, with each cluster containing red, green, and blue LEDs. One such cluster forms a pixel. Thousands of these pixels are then joined in strips to build a huge electronic display. If you stand far enough away from this aggregation of LEDs, and you see a smooth image with little of the pixel elements evident.
Because the pixel pitch (physical size of an RGB LED array) is fairly large compared to flat-matrix displays, the viewing distances must be greater to minimize the apparent structure. Typical LED pixel pitches can range from as small as 10mm to as large as 20mm, which is quite coarse for close-up viewing. By contrast, even the largest plasma display panels have a dot pitch of just over 1mm, while a typical 27" TV set has a dot pitch of .8mm on center.
LED displays are always constructed from blocks of LED pixels, so there's no limit to how large they can be, or what shape they may take. LED walls have been constructed in conventional squares and rectangles, and even long and narrow shapes. LED walls are staking their own place in the permanent install and staging/rental markets.