TFT displays are a widely used and rapidly evolving technology. Knowing about is can help you stay up to date with the latest developments in display technology and understand the types of displays available, their features, and their benefits. This article can help you make a more informed decision and select the device that best fits your needs.
Suppose you are an engineer or a developer, and finding which type of display to use in your product and how to design your product for optimal performance. In that case, this article about about TFT displays can help you make a better decision.
What is a TFT Display?
A TFT display is a type of flat panel display (FPD) that uses thin film transistor (TFT) technology. A TFT combines the thinness of thin film and the activeness of the transistor (switching, amplification). Both Liquid Crystal Display (LCD) and Organic Light Emitting Diode (OLED) displays use this technology. But nowadays, the term “TFT display” generally refers to TFT-LCD. Another type of TFT OLED display is called AMOLED, a TFT-based active-matrix OLED display.
TFT is one of the keys for TFT display technology as a field effect transistor (FET) variant. It can control each pixel by amplifying or switching electronic signals, in contrast to passive matrix mode or simple, direct-driven mode (i.e., a segments LCD).
Over time, the technology has evolved from amorphous silicon TFT to polycrystalline silicon (p-Si TFT), and from high-temperature poly-silicon (HTPS) TFT to low-temperature poly-silicon (LTPS) TFT. The development of TFT technology has also been used in not just LCD, but also OLED and e-ink displays. With the continuous improvement of semiconductor technology, the number of pixels in a display is decreasing, and the resolution is getting higher and higher.
One of the major advantages of TFT displays is that they control each pixel individually and continuously. That can lead to faster response times and accurate color controlling. Early TFT LCD displays were based on Twisted Nematic (TN) technology but suffered from poor viewing angles.
To overcome this problem, engineers and scientists developed in-plane switching (IPS) and multi-area vertical alignment (MVA) technologies. IPS TFT displays can reach wide viewing angles of up to 178 degrees.
The viewing angle of VA TFT displays is not as wide as IPS, but they have the best contrast. Therefore, a VA TFT monitor is the best choice for gamers interested in HDR image content. And the IPS TFT display is the most widely used.
Advantages of TFT LCD Display
Display High Information Content
The early LCDs can only show simple content in segments. These segments were pre-defined and directly connected to the electronics outside of the LCD. These types of displays are commonly used in devices like calculators and digital watches, not smartwatches. They can drive each element directly by applying a voltage across just one segment, without interacting with other segments. It is similar to a 7 segment display.
Segmented LCDs are simple, low cost and have fast response times and high contrast ratio. Therefore they are still widely used in digital calculators and dashboards of various devices, like automobiles and electric appliances.
However, this technology would not be efficient for a large dot matrix display, like a television or computer monitor. Because it would require a large number of pixel elements to connect and control for showing a picture. To avoid this issue, a matrix of row and column electrodes was needed to fabricate a large display. The passive matrix monochrome LCD and the more advanced active matrix TFT LCDs demonstrated this design is valid and useful.
The passive matrix monochrome LCD includes character LCDs and graphic LCDs. They both use a grid of vertical and horizontal transparent conductive Indium Tin Oxide (ITO) wires to control a single pixel at the intersection of each pair of cross conductors. The status of the pixels is the status of the LCD.
Active matrix TFT LCDs add thin film transistors as switches and capacitors at the intersection of every row and column. So, every TFT can activate each pixel in the matrix, unlike PM LCD activating the row and column. That can obtain the maximum contrast and shading.
Achieve Full Color Easily
Passive matrix LCDs cannot accurately reproduce colors because each pixel in a row or column has different color-emitting requirements. Some graphic LCD displays can render graphics in gray scale to enhance UI performance, but this is not a perfect solution. Fortunately, segment VA LCD displays can display colors using color diffusers and silk printing technology. However, they are limited to displaying characters and icons in a few colors, rather than pixel images with 65K+ full colors.
The best solution for full-color LCD displays is an active matrix TFT display, which divides each pixel into three sub-pixels: Red, Blue, and Green. For example, a standard definition color display (800 x 600) has 480,000 pixels, with a total of 1,440,000 RBG sub-pixels. Each sub-pixel needs to be operable on a single panel (glass or plastic) to create a defect-free display. Therefore, it is a significant challenge for arranging millions of TFTs.
The production cost of TFT displays has decreased due to advancements in the semiconductor industry and TFT materials. The circuit layout process of a TFT LCD display is similar to that of semiconductor products. However, TFTs are made from a thin film of amorphous silicon (a-Si), rather than a crystalline silicon wafer used in semiconductors.
For higher-resolution displays, such as viewfinders or projectors, polycrystalline silicon-based (p-Si) TFT is an advanced solution. Nevertheless, it is costly and difficult to produce than silicon-based TFTs. In Go2Display, we mostly use a-Si TFT displays due to their lower production cost.
In 1983, Shinji Morozumi and colleagues in Japan built the world’s first commercial color LCD TV with a 2-inch TN LCD, an active matrix polycrystalline Si TFT LCD. This was a significant milestone in the history of LCDs and led to the development of larger screen displays with high information and full-color content.
Provide Faster Response Time and Better Clarity
An active matrix LCD differs from a passive matrix LCD. It uses a grid of thin-film transistors (TFTs) to apply voltage to each pixel individually, instead of scanning row by column. This method prevents charge from being drained between refreshes, resulting in faster response time and higher image clarity for each pixel.
Today, a 5.5 inch TFT display can produce images with a resolution of 1280 x 720 pixels and a high definition (HD) of 720p. For example, the iPhone 11 has a 6.1 inch Liquid Retina IPS LCD with a resolution of 828 x 1792 pixels, giving it a pixel density of 326ppi. Some TFT displays have a response time of 1ms.
TFT Display Panel Types: TN vs IPS vs VA
Scientists and engineers have solved 3 major problems with LCD technology, including wide viewing angle, color saturation, and brightness. As a result, TFT-addressed LCD has become the leading technology not only for LCDs but for the entire FPD industry. TFT displays are available in three main LCD panel technologies, namely TN (Twisted Nematic), IPS (In-Plane Switching), and VA (Vertical Alignment), each with its own advantages and disadvantages.
TN TFT Display
TN panel is an LCD technology that is both simple and old, and it is frequently used in PM LCDs. A TN-based TFT display controls the image by arranging liquid crystal molecules. While it has a quicker response time, its viewing angle is restricted to 90 degrees.
To overcome this issue, a layer of film is applied to the upper surface. That can help it widen the viewing angle up to 140 degrees. Nevertheless, this still does not fulfill market requirements. As a result, the IPS panel was developed to solve this problem and enhance low-quality color reproduction at the same time.
IPS TFT Display
The IPS display, also known as a super TFT display, is an advanced TFT display solution. Unlike the TN panel, the IPS panel arranges the liquid crystal molecules in parallel on the substrate when voltage is applied. This enables an IPS display to achieve a wide viewing angle of up to 178 degrees and prevent the water ripple effect when being pressed.
However, this technology has difficulty displaying black due to the arrangement of the liquid crystal molecules. Furthermore, that will create a problem with the contrast. To balance this problem, TFT display manufacturers developed the Super-IPS (S-IPS) panel to improve the contrast ratio. But that will increase the response time at the same time.
As a result, color production is superior to the other panel types, ensuring color accuracy even at sharp angles. Furthermore, some advanced VA technologies, such as Multi-domain Vertical Alignment (MVA), Patterned Vertical Alignment (PVA), and others, were developed to overcome these issues and improve low-quality color contrast.
VA TFT Display
Manufacturers are trying to find a technology combining the advantages of TN and IPS. MVA and PVA panels offer wider viewing angles and better contrast than either TN or IPS panels. VA panels arrange the liquid crystal molecules in vertical on the substrate when voltage is applied. This arrangement can speed up the response time from white to black, but slows down that between two dark tones. This will lead to ghosting effects.
In real products, the color reproduction of MVA and PVA is better than TN but not as good as S-IPS or even IPS. Their response time is also not as good as TN or IPS. Furthermore, PVA panels have a greater contrast ratio than MVA panels. VA panels have impressive contrast ratios, making them ideal for HDR (High Dynamic Range) video TVs.
At Go2display, TN and IPS TFT displays are the major products in small to medium sizes, while VA TFT displays are more suitable for large sizes such as TVs.
TFT Display vs AMOLED Display
An OLED display is a type of FPD with self-emission ability, unlike an LCD with LED backlights. It sets a film of organic compounds as the electroluminescent layer to emit light when applied an electric current.
Similar to LCD, OLED (Organic Light-Emitting Diode) has two main variants, PMOLED and AMOLED, according to their way of addressing the pixels. PMOLEDs are commonly used in mini to small displays. And it is obviously unable to meet the requirement of high color, large size, and fast responsive displays. Therefore, AMOLED is the best option to compete with IPS TFT display.
TFT Display better than AMOLED
Compared to AMOLED, a TFT LCD display is still better in some aspects.
Lower Price
All the technologies used in TFT displays have become mature, including liquid crystal materials, TFT materials, deposited techniques, color filter film, backlight, and more. Even when manufactured at a large scale, the quality is still guaranteed. The most significant advantage of a TFT display is its cost-effectiveness.
Longer Lifetime
On the other hand, the self-emissive organic compound of an AMOLED display has a significantly shorter lifetime than the led backlight of TFT LCDs. In an OLED, the lifespan of different pixels varies, and the blue pixel usually has the shortest. This will result in a screen-burning phenomenon after 2-3 years of use. Generally speaking, the lifetime of a TFT display is about 8 times of an AMOLED.
All Size Displays Available
TFT LCD displays are available in a variety of sizes, from 1 inch to 80 inches, making it a comprehensive display terminal solution. Additionally, simple segment, character, and graphics monochrome LCD displays are still widely used in fields such as industry, commerce, medicine, and automobiles.
Lower Power Consumption in some use cases
AMOLED displays theoretically consume less power because they only supply current for light-on pixels. In contrast, TFT displays always illuminate their LED backlights. However, when producing content on white backgrounds, such as a desktop monitor or notebook, TFT displays consume less power than AMOLED displays. This is because most websites and office software have white backgrounds.
Easier Sunlight Readable Solutions
Increasing the screen’s brightness is a simple and cost-effective way to create a sunlight-readable display. To accomplish this, an AMOLED display would need to use high-end organic compound materials. In contrast, a TFT display only replaces the backlight. Obviously, the solution of TFT display is simpler and lower cost than AMOLED..
Both TFT displays and AMOLED displays have their own advantages. AMOLED has inborn gifts in a slim design, curved design, color saturation, contrast, and viewing angle. However, TFT displays are still the best choice for many applications due to their 5 advantages mentioned above.
Summary
TFT displays are still the best choice for many applications, including desktop monitors, notebooks, medical equipment, car stereos, cheap mobile phones, and more. In addition, TFT displays can easily add a resistive or capacitive touchscreen to enable more versatile use cases. Additionally, the technologies of IC controller, LED backlight, and communicating interface for TFT LCD display modules are highly developing. Therefore, you can easily customize an LCD display module and integrate them into devices for specific requirements. Meanwhile, engineers can freely develop applications with Raspberry Pi and Arduino TFT displays.