What is TFT LCD? - Definitive Guide

Introduction to TFT LCD Technology

Thin-Film Transistor Liquid Crystal Displays (TFT LCDs) have come a long way since their invention. At the core of this technology is the Thin-Film Transistor, a semiconductor that enhances the image quality of LCDs by improving addressability and contrast. Unlike earlier, simpler LCDs where the display was directly driven by external electronics, TFT LCDs are part of an active matrix system, meaning each pixel is controlled individually through transistors. This ability to control each pixel independently results in better image sharpness and vibrancy, making it ideal for devices like smartphones, televisions, and computers.

TFT LCDs are now ubiquitous across industries, found in a vast array of applications, including industrial automation, medical instrument, consumer electronics. They are dominant in the electronics market, with global shipments of TFT panels expected to surpass 300 million units by 2027. Despite the rise of OLED and other newer technologies, TFT LCDs maintain a significant market share due to their cost-effectiveness and versatility.

The History of TFT LCD

The journey of TFT LCD technology began with the discovery of liquid crystal in 19th century. Here’s an overview of the key milestones:

1. Early Discoveries (1888-1930s)

The first significant discovery related to liquid crystals came in 1888, when German botanist Friedrich Reinitzer observed that a substance he was studying, cholesteryl benzoate, exhibited properties of both solids and liquids. This material was the first identified liquid crystal.

In the 1930s, scientists like George H. Heilmeier began exploring the electro-optical properties of liquid crystals, noting that their orientation changed when exposed to an electric field.

2. The 1960s - The First LCD Prototype

In 1968, the concept of using liquid crystals in displays was advanced by Bernard Lechner of RCA Laboratories. Lechner envisioned using liquid crystals to create a new kind of display technology. His work laid the foundation for the creation of LCDs.

In 1969, Heilmeier developed the first practical liquid crystal display by demonstrating that liquid crystals could be used for displaying visual information when a voltage was applied. His work led to the creation of the first liquid crystal display prototype that used a passive matrix structure (later called Twisted Nematic, TN).

3. The 1970s - Development of TFT LCD

Paul K. Weimer at RCA implemented Bernard Wallmark's ideas and created the TFT in 1962. The concept of using TFTs to drive a liquid-crystal display was conceived by Bernard Lechner of RCA Laboratories in 1968.

Early demonstrations followed, leading to the first CdSe (cadmium selenide) TFT LCD developed by T. Peter Brody, J. A. Asars, and G. D. Dixon at Westinghouse Research Laboratories in 1973. 

4. The 1980s - Breakthroughs and Growth of TFT LCD Technology

In 1982, Sharp Corporation introduced the first commercial LCD panel that could be used for calculators and small digital devices.

1988: TFT LCDs (Thin-Film Transistor LCDs) were introduced for better pixel control. These displays used a matrix of thin-film transistors to individually control each pixel, greatly enhancing performance, and eventually making LCDs popular for larger displays like computer monitors.

5. The 1990s - Widespread Use

By the 1990s, TFT LCD technology had become widespread in computers, TVs, and portable electronics. The development of high-resolution TFT LCDs, along with advances in backlighting technology (e.g., LED backlighting), helped make LCDs the primary display technology for these applications.

6. 2000s - Innovation and Dominance

By the 2000s, TFT LCDs became the dominant display technology for consumer electronics, industrial controls, medical devices. This widespread adoption is not accidental; TFT LCDs offer a compelling combination of performance and cost-effectiveness that has made them a staple in the display industry for many years. 

How TFT LCDs Work: The Basic Principles

The functionality of a TFT LCD relies on the unique properties of liquid crystals. These materials exhibit characteristics of both liquids and solids; they can flow like a liquid but also maintain a certain molecular order like a crystal. In a TFT LCD, the liquid crystal molecules are situated between two polarized glass substrates. When an electric field is applied across these molecules, they realign themselves, altering the polarization of light passing through them. This change in polarization either allows or blocks the light from passing through a color filter, ultimately creating the image seen by the viewer. Imagine tiny blinds that can open or close to control the amount of light passing through; the liquid crystals act in a similar way, but instead of physical slats, they use their molecular alignment to manipulate light.

TFT LCD Basic Structure

A TFT LCD panel consists of multiple layers. The liquid crystal layer is sandwiched between two glass substrates, and a backlight is used to illuminate the display (since liquid crystals do not emit light on their own).

Two glass substrates - a box of liquid crystal in-between; and color filter on top.
Liquid crystal - Positioned between the glass substrates.
Electrodes - Transparent electrodes (often made of Indium Tin Oxide, ITO) are used to control the liquid crystals.
Polarizer - Two perpendicular polarizing filters are used to control the passing of light.

Generating of Image

Backlighting

Since liquid crystals do not produce light by themselves, a backlight is necessary. In early days, CCFLs (Cold Cathode Fluorescent Lamps) were used, but LED backlighting has become the standard in modern LCDs due to better energy efficiency, brightness, and slimmer designs.

How Liquid Crystals Manipulate Light

Liquid crystals are materials that have the properties of both liquids (flowing) and solids (maintaining molecular order). When an electric field is applied to the liquid crystals, their molecules re-align and change their optical properties.

The alignment of the liquid crystals changes the polarization of light passing through them (birefringence). Polarized light can either pass through or be blocked by the liquid crystal depending on its orientation.

Polarizing Filters

Two polarizing filters are used to control the direction of light:
First Polarizer: The first polarizing filter only allows light to pass through in a specific orientation (usually vertical).
Second Polarizer: The second polarizing filter is oriented perpendicular to the first one (usually horizontal).

The liquid crystals manipulate the light’s polarization between these two filters. If the light is properly aligned, it can pass through both filters. If not, it is blocked.

Color Creation

In full-color LCDs, each pixel consists of three sub-pixels—one red, one green, and one blue (RGB). Each sub-pixel is controlled by its own Thin Film Transistor (in active-matrix LCDs).

By adjusting the alignment of liquid crystals in each sub-pixel, varying amounts of light are allowed through each color filter, resulting in different colors being displayed on the screen.

TFT LCD 3 Display Modes

There are three types of TFT LCD, based on how backlight is generated.

Transmissive TFT LCD - The display uses LED backlight as its light source.

Reflective TFT LCD - The LCD has reflective mirror at the back, uses ambient light as its sole light source.

Transflective TFT LCD - It is the combination of transmissive and reflective LCD, having both LED backlight and reflective mirror embedded.

Feature	Transmissive	Reflective	Transflective
Brightness	Hight brightness in indoor and low-light due to backlight.	Excellent in direct sunlight. Poor in low light.	Moderate brightness in both indoor and outdoor. Backlight assists in low light.
Contrast Ratio	Hight contrast ratio achievable. Lower in bright outdoor light.	Lower contrast ratio compare to transmissive. Can be good in direct sunlight.	Moderate contrast ratio, a compromise between transmissive and reflective.
Power Consumption	Higher power consumption.	Very low power consumption in bright ambient light	Moderate consumption, as it uses some reflected light as light source.
Visibility in Sunlight	Needs high power backlight.	Excellent visibility	Good visibility, may not be as bright as reflective in direct sunlight.
Visibility in Low Light	Excellent, due to backlight.	Poor visibility in low light environment	Good visibility due to the backlight
Viewing Angle	Can achieve wide viewing angles with right technology.	Narrower viewing angles compared to transmissive	Moderate viewing angles, often a compromise.
Weight & Size	Generally heavier and thicker, because of backlight unit.	Lighter and thinner	Moderate weight and thickness
Manufacturing Complexity	Relatively simpler	Simple, no backlight is needed	More complex to make
Cost	Moderate cost. Backlight cost is a factor	Generally lower cost, no backlight	Higher cost due to complex design

How to Produce a TFT LCD

TFT-LCD Fabs - Size Matters

TFT-LCD Fabs come in generations - from Gen1 to Gen10.5. The major difference between generations is size of the mother glass.

The larger the mother glass is, the larger the panel can be produced. For example, a Gen10.5 mother glass can produce two 144" panels and achieve 98% efficiency. 

TFT LCD Manufacture Process

Exploring the Different Types of TFT LCD Panels

The term "TFT LCD" encompasses a variety of panel technologies, each with its own unique characteristics and performance trade-offs. While the underlying TFT technology provides the active matrix addressing for precise pixel control, the arrangement and behavior of the liquid crystals differ among these panel types, leading to variations in viewing angles, color accuracy, response times, and contrast ratios. Understanding these differences is crucial for selecting the appropriate display for a specific application.

TN (Twisted Nematic): Known for fast response times, TN panels are often found in gaming monitors where speed is more important than color accuracy. But, their narrow viewing angles and limited color reproduction can make them less desirable for media creation. TN type TFT LCD also tends to be more cost-effective to manufacture compared to other panel types.

IPS (In-Plane Switching): Offering superior color accuracy and wide viewing angles, IPS panels are favored in devices that demand high image quality, like smartphones and professional monitors. The cost is higher than TN panels, but the image quality makes it worthwhile for most users.  The evolution of IPS technology has led to variations like Super-IPS (S-IPS) and Advanced Super-IPS (AS-IPS), which offer further improvements in refresh timing and contrast ratio.

VA (Vertical Alignment): A hybrid between TN and IPS, VA panel's liquid crystal molecules are aligned vertically to the glass substrates when no voltage is applied. VA panels provide excellent contrast ratios, black levels and decent viewing angles. They are typically used in TVs and multimedia devices where good contrast is more important than the ultimate color accuracy. Sub-types of VA panels include Multi-Domain Vertical Alignment (MVA) and Patterned Vertical Alignment (PVA), which further refine viewing angles and response times. 

Other less common but still relevant TFT LCD types include Super Twisted Nematic (STN) panels, an advanced version of TN offering improved contrast and viewing angles, though still generally inferior to IPS and VA. Advanced Fringe Field Switching (AFFS) panels are a variant of IPS technology that provides even wider viewing angles and improved outdoor visibility by enhancing light transmission and reducing reflections. These are often used in outdoor signage and automotive displays where readability in bright conditions is crucial.   

To better understand the trade-offs between these common TFT LCD panel types, the following table provides a comparative overview:

Feature	TN	IPS	VA
Viewing Angles	Narrow	Wide	Good (wider than TN)
Color Accuracy	Fair	Excellent	Good
Response Time	Fast	Moderate	Moderate
Contrast Ratio	Fair	Good	Excellent
Cost	Lowest	Higher	Moderate
Application	Budget gaming monitor, Basic displays	Professional monitors, Medical devices, Smartphones	TVs, Monitors, Car Console

Advantages and Disadvantages of TFT LCDs

Advantages

TFT LCD technology offers numerous benefits that have contributed to its widespread adoption. One of the primary advantages is the sharpness and high image quality they provide. TFT LCDs can produce high-definition images with excellent clarity and detail. Compared to older display technologies like Cathode Ray Tubes (CRTs), TFT LCDs are also known for their lower energy consumption. Their energy-efficient operation allows devices to be used for longer periods on battery power. Furthermore, TFT LCDs offer fast refreshing rates, resulting in smooth image transitions, which is particularly beneficial for applications involving fast-moving visuals such as gaming and video playback. The versatility of TFT LCD technology is evident in the wide range of sizes in which they can be manufactured, making them suitable for everything from small wearable devices to large television screens.

The integration of touchscreen capabilities, both resistive and capacitive, further enhances their utility in interactive devices. Additionally, TFT displays offer excellent aspect ratio control, preventing image distortion and ensuring that content is displayed correctly. Their improved visibility and the reduction of eye fatigue compared to older technologies are also significant benefits. The sleek and lightweight physical design of TFT LCDs contributes to the portability and aesthetic appeal of modern electronic devices. In specific industrial and automotive applications, certain TFT LCDs are designed to withstand harsh environmental conditions, offering enhanced durability. For example, automotive-grade TFT LCDs are built to endure vibrations and temperature fluctuations within a vehicle. 

Disadvantages

Despite their numerous advantages, TFT LCDs also have certain drawbacks. One common disadvantage, particularly for some types of TFT panels like TN (Twisted Nematic), is the limitation in viewing angles. The image quality and color accuracy can degrade when viewed from off-center angles. While IPS (In-Plane Switching) panels offer much wider viewing angles, they may come at a higher cost. Another inherent limitation of TFT LCDs is their reliance on backlighting, as they cannot emit light on their own. This necessity adds to the complexity of the display and can potentially increase power consumption in some cases, although LED backlighting has mitigated this to some extent. Compared to OLED (Organic Light-Emitting Diode) displays, TFT LCDs typically have shallower black levels and lower contrast ratios, as OLED pixels can be completely turned off to achieve true black.

Another potential issue is backlight bleed, where light from the backlight is visible in dark areas of the screen, which can detract from the viewing experience. In some older TFT panels, color saturation might also be lower compared to newer technologies like IPS or AMOLED. While generally robust, TFT LCDs can be susceptible to physical damage, such as cracking or scratching of the glass substrate. It is important to note that the severity of these disadvantages can vary depending on the specific type of TFT LCD panel being used.

Comparing TFT LCD with other Display Technologies

While TFT LCDs represent a significant improvement over earlier display technologies, it's important to understand how they compare to other contemporary options like OLED and e-paper.   

Compared to traditional passive matrix LCDs, TFT LCDs offer vastly superior image quality and response times. In passive matrix displays, pixels are addressed row by row, which can lead to slower refresh rates and a lack of sharpness, especially in fast-moving content. TFT LCDs, with their active matrix technology where each pixel is individually controlled, overcome these limitations, providing much clearer and more responsive displays. This fundamental difference cemented TFT LCDs as the dominant form of LCD technology for applications requiring decent to high performance.

OLED (Organic Light-Emitting Diode) technology is a major competitor to TFT LCDs, particularly in the high-end display market. OLED displays differ fundamentally from LCDs in that each pixel in an OLED display emits its own light when an electric current is passed through the organic material. This self-emissive nature allows OLEDs to achieve perfect black levels (by completely turning off pixels) and incredibly high contrast ratios, which are generally superior to those of TFT LCDs. OLEDs also tend to offer wider viewing angles and faster response times than many TFT LCDs. However, TFT LCDs often have an advantage in brightness and can be more cost-effective to manufacture, especially in larger sizes. OLED technology can also be susceptible to screen burn-in over long periods, although advancements are being made to mitigate this issue.

AMOLED (Active-Matrix Organic Light-Emitting Diode) is a specific type of OLED display that uses a TFT backplane to control the individual organic light-emitting diodes. The "active-matrix" part refers to the TFT layer that actively switches each pixel on and off. AMOLED displays are known for their vibrant colors, deep blacks, and energy efficiency, especially when displaying dark content as black pixels consume no power. They are widely used in high-end smartphones and wearable devices due to their excellent image quality and power-saving capabilities. While AMOLED offers many advantages, the underlying control mechanism still relies on TFT technology, highlighting the foundational role of TFTs in advanced display systems.

E-paper (electronic paper) technology presents a different set of strengths compared to TFT LCDs. E-paper displays are designed to mimic the appearance of ink on paper, offering excellent readability, especially in bright sunlight, and extremely low power consumption, as they only require power to change the display, not to maintain it. However, e-paper typically has a much slower refresh rate than TFT LCDs and traditionally has been limited to grayscale displays, although color e-paper is becoming more available. Due to these characteristics, e-paper is primarily used in e-readers and some signage applications where low power consumption and high readability are prioritized over vibrant colors and fast motion. TFT LCDs, on the other hand, excel in displaying dynamic color content and are therefore better suited for general-purpose displays in devices like smartphones, tablets, and monitors.

Table below summarizes the key differences between these display technologies:

Feature	TFT LCD	OLED	AMOLED	E-paper
Image Quality	Good to Excellent	Excellent	Excellent	Good
Contrast	Good to High	Very High	Very High	High
Black Levels	Moderate	Perfect	Perfect	Good
Color Accuracy	Fair to Excellent	Excellent	Excellent	Limited
Power Consumption	Moderate	Low	Low	Very Low
Viewing Angles	Narrow to Wide	Very Wide	Very Wide	Very Wide
Response Time	Fast to Moderate	Very Fast	Very Fast	Slow
Brightness	Good to Very High	Good	Good	Low
Cost	Moderate	High	High	Moderate
Application	TV, Monitor, Smartphone	High-end TV, Smartphone, Wearable	Smartphone, Wearable	E-readers, Signage

The Growing Demand for TFT LCDs

The versatility and performance characteristics of TFT LCDs have made them indispensable across a wide range of industries.

Consumer Electronics

TFT LCDs are the backbone of numerous devices. Smartphones and tablets overwhelmingly use TFT LCDs due to their ability to display vibrant colors and high resolutions, coupled with their support for touch-sensitive capabilities.

Televisions and computer monitors still widely utilize TFT LCD screens, particularly in budget-friendly and mid-range models, thanks to their ability to display vivid images with fast refresh rates and their cost-effectiveness compared to newer technologies like OLED.

Even home appliances now incorporate TFT LCDs in their control panels for user interfaces. Information kiosks and Point of Sale (POS) terminals use TFT LCDs for displaying information and facilitating transactions. The suitability of TFT LCDs for these diverse applications stems from their ability to provide a good balance of image quality, cost, and power efficiency.

Automotive Industry

Dashboard displays utilize TFT LCDs to present drivers with clear and easily readable information. Infotainment systems in modern vehicles often feature touch-enabled TFT LCD screens for controlling navigation, media, and other vehicle functions. Some vehicles even incorporate TFT LCDs into rearview mirrors to display camera feeds and other information.

In fact, the automotive sector alone is expected to account for a 25% share of the TFT display market by 2027, with applications ranging from vehicle dashboards to advanced driver assistance systems (ADAS).

Healthcare Sector

TFT LCD displays play a critical role in various medical equipment. Medical imaging equipment such as MRI machines, CT scanners, and ultrasound devices rely on high-resolution TFT LCDs to allow healthcare professionals to visualize and analyze diagnostic images with precision, which is essential for accurate diagnosis and treatment planning. 

Patient monitoring systems also utilize TFT LCDs to display vital signs and other critical data. The clarity and reliability of TFT LCDs are paramount in these applications, where accurate visual information can directly impact patient care.

Industrial Applications

Industrial control systems utilize robust and reliable TFT LCDs for monitoring and controlling various processes. Human-Machine Interface (HMI) panels in manufacturing facilities employ TFT LCDs to display production processes, performance metrics, and facilitate operator input. Testing and measurement equipment often incorporates TFT LCDs for displaying results and providing user interfaces. TFT LCDs used in industrial environments are often designed to withstand harsh conditions, including dust, moisture, and extreme temperatures, ensuring their functionality in demanding settings. 

Future Trends and Emerging Display Technologies

Emerging trends in display technologies are rapidly evolving, driven by advancements in materials science, energy efficiency, and consumer demand for better image quality, thinner panels, and more immersive experiences. Here are some of the key trends currently shaping the future of displays.

OLED and AMOLED Displays

OLED (Organic Light Emitting Diode) and AMOLED (Active Matrix Organic Light Emitting Diode) are already widely used in smartphones, high-end TVs, and wearables, but they are becoming more prominent due to their ability to deliver better contrast ratios, deeper blacks, and wider viewing angles than traditional LCDs.

Flexible and Foldable Displays: One of the most exciting trends in OLED technology is the rise of flexible and foldable displays. Devices like foldable smartphones, are leading the way. Flexible OLED panels are thinner, lighter, and can be bent without losing functionality, paving the way for entirely new form factors.

Improved Lifespan: Advances in material science, especially with OLED longevity, aim to reduce burn-in and enhance color stability, making OLED a more durable option for long-term usage.

Quantum Dots (QLED Technology)

QLED display is still an LCD, but incorporates a layer of quantum dots between the backlight and the liquid crystal display. When the backlight shines through the quantum dots, they emit very pure and precise colors that make the display much more vibrant and color-accurate compared to traditional LCDs. 

The key benefit is that quantum dots improve the brightness and color range of displays, providing wider color gamut and more accurate colors for a better viewing experience.

MiniLED

MiniLED is a breakthrough in LED backlighting, using significantly smaller LEDs for better dimming control and greater contrast than traditional LED-backlit displays. MiniLED display is still a TFT LCD, but packing more LEDs into backlight space.

MiniLED displays provide better local dimming, brighter highlights, and deeper blacks. are making their way into high-end TVs, monitors, and laptops, competing with OLED displays but offering the advantage of not having the burn-in issue.

MicroLED

MicroLED is an emerging display technology that competes with both OLED and LCD displays. Each pixel in a MicroLED display is a tiny LED that generates its own light, meaning it offers perfect black levels and superior contrast without the drawbacks of OLED (e.g., burn-in).

Scalability: MicroLED technology allows for modular displays, where multiple small panels can be combined to create large, customizable screens without sacrificing resolution or quality.

Energy Efficiency: MicroLEDs are more energy-efficient than traditional LCDs and OLEDs, making them ideal for large-scale, high-brightness displays used in digital signage, stadiums, and TVs.

Summary

In conclusion, the history of LCD technology spans over a century of research, from the discovery of liquid crystals to their widespread use in consumer electronics and industrial controls.

The technology has evolved from passive matrix to active matrix displays, with TFT technology enhancing pixel control and enabling high-resolution displays. 
The basic working principle of an LCD involves polarized light passing through liquid crystals that manipulate the light’s polarization to create images, with a backlight illuminating the display.

This technology continues to be refined, with quantum dots and miniLED technologies pushing the boundaries of color accuracy, brightness, and energy efficiency in modern LCD displays.