All about TFT displays
Televisions, computer screens, tablets, notebooks, cell phones. Nowadays all these products are equipped with a TFT display. Not even mentioning industrial, medical, marine and automotive applications.
TFT is an active LCD technology and is revolutionary in the field of full color displays. TFT displays are also called active matrix displays.
Want to find out more? We’ll explain all about TFT displays.
What is a TFT display?
LCD vs. TFT Display
The terms LCD display and TFT display (or active matrix display) are often used interchangeably. But what’s the difference?
An LCD (Liquid Crystal Display) is a flat display with a low power consumption. Liquid crystals are embedded between two layers of polarizing material. Behind the layers, a backlight is placed. By regulating the voltage between the glass plates, the crystals will rotate and the light transmittance can be adjusted. Displaying an image on the LCD.
A TFT display (Thin-Film Transistor) uses thin film transistor technology. Adding this layer to an LCD will provide a better and sharper image. Therefore, a TFT display (or active matrix display) is actually an improved version of an LCD display.
How does a TFT display work?
A TFT is made by combining a thin film of a semi-conductive active layer with a layer that acts as an electrical insulator. They are laid on a supported under layer together with metal contacts.
An LCD pixel is then actively controlled by one to four transistors. By adjusting the voltage, the transistors turn the pixels on and off easily. Red, green and blue color filters are placed on the inside of the top glass to show the color information. The intensity of light transmission is controlled by color filters. As a result, millions of colors can be displayed on one screen.
The embedded TFT layer on the screen reduces crosstalk between pixels. Crosstalk occurs when a signal sent to a pixel, also affects the pixel next to it. This makes TFT display technology the technology that offers the best resolution and image quality. TFT’s are therefore more expensive than regular LCD’s.
TFT displays have become todays standard in producing LCD monitors.
TFT display technologies
TN (Twisted Nematic)
An LCD includes, among other things, liquid crystals. These crystals can be controlled in several ways. Also the structure and the way crystals transmit light, can be influenced. The oldest technology used for this, is the TN technology. TN stands for Twisted Nematic, this technology uses liquid crystals that can twist the polarization of light.
Behind the screen, a polarizing layer causes the light of the backlight to be polarized in one direction. If no voltage is applied to the cells, a TN TFT display will light up. And the crystals are automatically rotated 90 degrees. As a result, the polarization of the incoming light changes 90 degrees. By placing an electrical voltage on the cells, the crystals return to their right position. The polarization remains untouched and retains direction of polarization, provided behind the scenes. A second polarization filter for the crystals causes the non-twisted light to be blocked and the pixels remain black.
If the pixels of a TN display are active, the image will remain dark. Only when the pixels are off, the screen will light up. The TN technology has a fast response time and is therefore ideally suited for fast moving images like movies. One drawback is that the viewing angles of a TN display are limited. In addition, there is a relatively large color gradient when viewing the screen from the side. This occurs because the twisted crystals do not block the same amount of light from every angle.
In particular gamers use TFT displays with TN technology. They especially value the fast response time of a TN display. Since they are often sitting right in front of the screen, the somewhat smaller viewing angle is no problem for gamers.
MVA (Multiple-domain Vertical Alignment)
MVA stands for Multiple-domain Vertical Aligment and is the improved version of VA technology. This technology is the same as the TN technology we’ve discussed earlier.
With MVA technology, the crystals are vertically oriented, just like the TN technology. Because the crystals are always parallel to each other and do not interfere, the MVA technology also has similarities with IPS (see below).
Since TN and IPS technology are combined in the MVA technology, MVA TFT displays switch relatively quickly. TN (or VA) crystals are always active or non-active. With the MVA technology, the crystals can also be slightly active or non-active. This makes the contrast of the display better. In addition, the viewing angles are larger and there is a nicer transition in the crystals and thus colors.
Samsung has produced its own MVA based technology called PVA (Pattern Vertical Alignment). PVA allows excellent color reproduction and a wide color range. It also offers fantastic response times and has viewing angles that approach the great viewing angles of IPS.
IPS (In Plane Switching)
IPS is a TFT display technology and stands for In-Plane Switching. IPS is a variant of an LCD and is used in phones, laptops, tablets, televisions or computer displays.
The base of IPS is similar to TN and MVA. A display has pixels. Each pixel of a display consists of three subpixels. The subpixels are red, green and blue. In an LCD, the pixels are turned on and off by liquid crystals. A transistor in the pixels determines how much color is transmitted from each pixel. This way, millions of colors can be combined.
With IPS, each pixel has a transistor, but each subpixel also has a transistor. This gives IPS a very precise control of the pixels. The special alignment of the pixels also contributes to precise control of the display.
IPS displays are mainly used in the graphics industry, because of their great viewing angles. Its high color brightness makes IPS perfect for the demands of the graphic industry.
IPS was originally developed by LG. Several other brands also developed their own IPS technologies. Among others, Samsung (PLS), AUO (AHVA) and BOE/Hydis (AFFS) have designed IPS solutions for their own TFT lines.
Compare TFT display technologies
TFT display specifications
Take this into account
Custom or standard
Standard, customized or fully custom design. A bespoke TFT display.
Is the display used inside or outside? Consider the environment.
Small (t0 10 inch), medium (to 22 inch) and large (from 22 inch) TFT displays.
What resolution does your application ask for?
Brightness & backlight
The resolution, backlight and ambient light determine the brightness of the TFT display.
What interface does the display need? SPI, I2C, RGB, LVDS or MIPI?
Contrast & viewing angles
The application determines the required contrast and viewing angles.
Does the TFT display need to be able to withstand extreme heat or cold? We take this into consideration.
The active area of the display is the blackened edge where no image can be seen.
How long does the TFT display need to be available? Once? Or long term?