Understanding Lcd And Tft Monitors: What's The Difference?

TFT stands for thin-film transistor, and it is a type of LCD (liquid crystal display) that uses thin-film-transistor technology to improve image qualities such as addressability and contrast. In other words, it is a variant of LCD. A TFT display is sharper, brighter, and faster than a regular LCD display. It is also more expensive.

Brightness and speed

TFT LCD screens are known for their brightness and speed. The brightness of a TFT LCD screen is determined by a few factors, including the backlight, colour saturation, and the environment in which it is used. A high-quality high-brightness TFT LCD screen will have a uniform backlight, with some manufacturers offering uniformity of up to 90-95%. The brightness of the screen is also affected by the colour saturation of the finished screen, as well as the brightness, contrast, and backlight illumination.

TFT LCD screens are also known for their speed. The use of thin-film-transistor technology allows for faster response speeds, as each pixel can be directly controlled through point pulses. This means that each node is relatively independent and can be controlled continuously. This results in a faster response speed for the display screen.

In addition to brightness and speed, TFT LCD screens offer several other advantages. They are known for their wide viewing angles, accurate colour reproduction, and high contrast. They are also widely used due to their low cost, which is a result of simpler manufacturing processes and lower-cost raw materials.

However, it is important to note that TFT LCD screens also have some disadvantages. They may have slower response times compared to other technologies, lower contrast ratios, and poorer viewing angles. Despite these limitations, TFT LCD screens remain dominant in the market due to their overall performance, brightness, and speed.

Active-matrix screens

Each pixel is attached to a transistor and capacitor that actively maintain the pixel state while other pixels are being addressed. This is in contrast to passive matrix screens, where each pixel must maintain its state passively without being driven by circuitry. Active-matrix screens do not suffer from the "submarining" effect, where the cursor disappears when moved rapidly.

The concept of active-matrix LCDs was proposed by Bernard J. Lechner at the RCA Laboratories in 1968. The first functional AMLCD with thin-film transistors was made by T. Peter Brody, Fang-Chen Luo and their team at Westinghouse Electric Corporation in 1972. The term "active matrix" was coined by Brody in 1975.

Viewing angles

TFT LCD displays offer a wide viewing angle, which is defined as the angle at which an image on the screen can be seen clearly. This is usually around 160 degrees, but some displays can offer viewing angles of up to 178 degrees.

The wide viewing angle is achieved by the way the liquid crystals in a TFT LCD are aligned. They are aligned horizontally, which means that light can pass through them more easily, resulting in a wider viewing angle and less glare on the screen.

The viewing angle of a TFT LCD display is important because it determines what you can see on your screen and from which direction. This is particularly useful for collaborative work, as more people can easily see what is on the screen at once. It is also beneficial in fast-paced environments such as medical settings, where medical professionals can easily view patient information from different angles.

However, it is important to note that wider viewing angles are not always welcome or needed. For example, if you are working on an airplane, you may not want the person sitting next to you to be able to see your screen. There are more expensive technologies available that narrow the viewing angle to protect privacy.

The viewing angle of a TFT LCD display can be further improved by using wide-angle technology, which can increase the viewing angle to about 150 degrees. There are three popular techniques for a wide display viewing angle: TN+FILM, IPS (in-plane switching), and MVA (multi-domain vertical alignment).

IPS technology, developed by Hitachi in 1996, improves the viewing angle and colour reproduction of TN panels. It does this by moving the crystal molecules parallel to the panel plane instead of perpendicular to it, which reduces the amount of light scattering in the matrix. IPS panels offer a wider viewing angle, more accurate colour reproduction, and faster response times than TN panels.

MVA technology improves viewing angles above 160 degrees and provides shorter response times than IPS and TN+FILM. MVA panels offer wide viewing angles, good black depth, good colour reproduction, and fast response times due to the use of RTC (Response Time Compensation) technologies.

In summary, TFT LCD displays offer wide viewing angles that can be further improved by using techniques such as TN+FILM, IPS, and MVA. The viewing angle is an important consideration when choosing a display, as it determines what can be seen on the screen and from which direction.

Manufacturing process

The manufacturing process of TFT LCDs can be divided into three main parts: array, cell, and module. The first two steps are about the production of the light and colour control system, which contains the thin-film transistor (TFT), colour filter (CF), and liquid crystal (LC). The last step is the assembly of the cell, circuit, and light system.

The manufacturing process can be simplified into the following steps:

Array Process

• Deposit semiconductor material and ITO (Indium Tin Oxide) in a designed order on a glass substrate. ITO is crucial here as it has the characteristic of electrical conductivity and optical transparency, and can be easily deposited as a thin film.
• Photoresist coating.
• Partial exposure, then clean the exposed photoresist.
• Tear off the semiconductor and ITO without the cover of photoresist to form part of the circuit.
• Clean the remaining photoresist.
• Repeat the above steps around five times to build the whole circuit.
• Create a black matrix on the glass substrate as a boundary using the PR (photoresist) method.
• Coat red, green, and blue material within the black matrix separately using the PR method.
• Coat an overcover on the RGB layer.
• Deposit the ITO circuit.

Cell Process

• Assemble the TFT and CF glass and fill in the LC at the same time.
• Coat polyimide film on the ITO side of both TFT and CF glass. This is used to constrain the initial direction of LC molecules.
• Use glue to build a boundary for the LC on both glasses. On the CF glass, apply one more layer of conductive adhesive to enable LC molecules to link to the control circuit.
• Fill LC within the boundary.
• Stick the two glasses together, then cut the large glass into smaller pieces.
• Attach a polarizer film to both sides of the incised glass.

Module Assembly Process

• Link the cell to the circuit system.
• Link the cell to the driver IC.
• Link the driver IC to the FPC (flexible printed circuit).
• Link the FPC to the outer PCBA (printed circuit board assembly).
• Attach the light source, usually an LED or CCFL, to the light guide plate. Underneath there should be a reflector film.
• Put the diffuser film and prism film on the light source. Together with the reflector film, these films turn the point light from the light source into area light and enhance light intensity.
• Link the light source to the light control circuit, which is usually another type of PCBA.
• Assemble all the components together with the screen frame, and do an ageing test.

Cost

The cost of LCD and TFT monitors varies depending on several factors, including brand, size, features, and display technology. Here is a detailed breakdown of the cost considerations for these monitors:

LCD Monitors:

LCD monitors are available in a wide range of prices, catering to different budgets and requirements. Here are some examples of LCD monitor prices:

• Budget-friendly options: LCD monitors can be found for less than $200, making them an affordable option for basic everyday tasks.
• Mid-range options: Many LCD monitors fall in the $200 to $500 range, offering features such as fast refresh rates, response times, and high resolutions like 4K Ultra HD.
• Premium options: High-end LCD monitors can cost upwards of $500 and offer advanced features such as curved screens, ultra-wide displays, and gaming-specific enhancements.

TFT Monitors:

TFT monitors, or Thin-Film Transistor LCDs, also vary in price depending on their specifications. Here are some factors influencing the cost of TFT monitors:

• Simpler manufacturing and raw material costs: TFT monitors are often considered more affordable than other display technologies due to their simpler manufacturing process and lower-cost raw materials.
• Display size: The price of TFT monitors can range from a few hundred dollars to over a thousand, depending on the screen size. For example, a 2.8-inch TFT LCD screen module costs around $500, while a 10.1-inch display can exceed $10,000.
• Display features: The cost of TFT monitors also depends on their features. For instance, a basic 7-inch TFT monitor may cost around $3,000, while a 7-inch capacitive touch screen LCD can be priced at over $5,000.
• Display technology: Within the TFT category, different technologies impact the cost. For example, amorphous silicon-based TFTs are typically more affordable due to lower production costs, while polycrystalline silicon TFTs are more expensive and challenging to produce.

Frequently asked questions